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The CHROMacademy Essential Guide to
Troubleshooting GC Separation Part II – Selectivity, Resolution and Baseline Issues

On Demand Webcast | Registration is required see below.

The Essential Guide from LCGC’s CHROMacademy presents the fourth and last in our series of webcasts on Practical GC Troubleshooting.  In this session, Dr. John Hinshaw (Senior Scientist , BPL Global Ltd) and Tony Taylor (Technical Director, Crawford Scientific), present practical troubleshooting tips for GC separations, with special emphasis on selectivity changes, loss of resolution and baseline problems.  The session includes a wealth of practical information on GC separation issues and all our real world problems are related to both separation chemistry and hardware issues.   We consider the common problems and highlight causes and remedial actions in a very practically relevant way.  A must see for everyone working with GC instruments.

Topics Include

  • What causes selectivity changes in GC – both sudden and over time
  • What are the main causes of loss of resolution within a separation and what are the signs and symptoms to look out for
  • Typical problematic baselines and their causes
  • Learn how to quickly identify problems and investigate the root cause
  • Build up a portfolio of preventative and corrective maintenance operations

Find out more about this Month's Essential Guide Webcast »

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Troubleshooting GC Separations Part II
Selectivity, Resolution and Baseline Issues

This session examines the common causes of loss of chromatographic selectivity and resolution as well as baseline issues typically encountered with common GC detectors. Strategies for problem identification, corrective chromatographic and / or GC system actions will be described for the major causes of the symptoms observed. Strategies for identifying the causes of problems with current methods and best practice for future method development are also included.

 


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GC Troubleshooting made easy

Try the CHROMacademy Interactive GC Troubleshooter

We developed the CHROMacademy GC Troubleshooter with busy chromatographers in mind. In 3 simple steps we can help you overcome your instrument, separation and quantitation issues.

Step 1. Select your chromatographic symptoms.

Step 2. Select your instrument symptoms.

Step 3. We return a list of possible causes ranked by our industry experts.

The troubleshooter provides a concise summary of the problem and recommends solutions - supported by over 1000 references, feature articles and CHROMacademy content written by experts in GC.

  CHROMacademy Interactive GC Troubleshooter
 
 
 


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The most important thing in HPLC is to obtain the 'optimum resolution in the minimum time'. [1, 2, 3]

A resolution value of at least 1.8 between two peaks will ensure that the sample components are well ('baseline') separated - to a degree at which the area or height of each peak may be accurately measured.

Resolution is a function of three other parameters, the retention factor (k), the selectivity (α) (separation of the peak apexes) and the efficiency (N) (width) of the peaks. The width at the base of each peak is the segment of the peak base intercepted by the tangents drawn to the inflection points on either side of the peak as shown below.

 

Figure 1.  Resolution between two peaks.

 
 

The peak width as well as the retention time is measured in time units, because of that resolution is a dimensionless parameter.

So how are we able to control the resolution obtained from a chromatographic separation? The fundamental resolution equation, shown below, indicates that resolution is affected by three important parameters:

  • Selectivity (separation factor)
  • Efficiency
  • Retention (capacity factor)
 
Resolution equation
 

Figure 2.  Graphical representation of selected chromatographic parameters.

 
 

So how do each of these factors contribute to the resolution of the separation and are there target values to aim for or limits beyond which a change in the parameter will have no meaningful effect? The answer to these questions is yes and it is important to understand the way in which each parameter affects resolution.

The resolution equation reveals an explicit interdependence between resolution, selectivity, retention factor and efficiency.  So it is not surprising that any factors such as column chemistry, temperature and flow rate will have a major impact in chromatographic resolution.  A decrease in resolution is usually associated with at least one of the following conditions: [4-8]

  • Incorrect temperature or program
  • Incorrect column type
  • Column contamination and/or degradation
  • Incorrect flow rate

Perhaps the first thing to do when noticing a reduction in resolution is to check if column length has been drastically reduced so efficiency has been seriously decreased.  In addition, shorter columns require lower pressures to achieve the correct carrier gas flow rate.

Once it is confirmed that the correct column dimensions have been used, try to determine the nature of the resolution problem by looking at your chromatogram.  In order to troubleshoot resolution problems, consider the following two scenarios:

  • Decrease in selectivity
  • Peak widening and distortion
 
 
 


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Overview

When a change in selectivity has taken place, then the logical troubleshooting approach include the following steps:

  1. Check column dimensions
  2. Look for differences in column phase
  3. Check the correct column temperature has been used
  4. Look for additional peaks and get rid of them
 
Loss of resolution

Figure 3.  Loss of resolution due to a change in selectivity.

 
 

Column Dimensions

Column Length

Column length affects three important parameters:

  • Efficiency
  • Retention (analysis time)
  • Pressure

It is a common practice to trim the capillary GC column to get rid of contamination to bring the column back to a usable condition; however, by so doing, the actual column length is reduced a few centimeters each time.

 

Column Internal Diameter

Column diameter affects the following important parameters:

  • Efficiency
  • Retention
  • Carrier flow rate
  • Capacity
  • Pressure drop
  • Resolution
The column internal diameter is inversely proportional to column efficiency. Therefore, halving the column internal diameter doubles the efficiency and improves resolution by a theoretical factor of 1.41. Increases in efficiency arise due to the increase in analyte / stationary phase interactions in the smaller diameter tubes.
 
 

Column Stationary Phase

Overview

Using the wrong stationary phase could lead to a situation where whatever the efforts, the required separation cannot be achieved.  You also need to make sure the correct stationary phase film thickness being used.

Column stationary phase film thickness (df) affects five critical GC parameters – these being: retention, inertness, capacity, resolution and bleed.

With the advent of time and use, the GC column will deteriorate, predominantly through loss of bonded phase (phase bleed).

Most phases used in the production of fused silica columns are bonded phases. There are many different types available. These are made by the reaction of a suitable silane group to the Si-OH (silanol group) on the base silica. [2-5]

The siloxane bridge is not available for ligand binding without chemical intervention. As can be seen in the upper diagram these groups tend to be randomly distributed on the silica surface.

 
Silanol functional groups

Figure 4.  Different types of silanol functional groups.

 
 

Column selection is crucial to achieve optimum chromatographic results.  Make sure you are using the correct column for your application otherwise selectivity will be compromised.  A classification of GC columns based on stationary phase is provided next. [6-13]

 

Figure 5.  Polysiloxane Classifications.

 
 

In choosing an appropriate GC stationary phase it is generally accepted that the principle of ‘like dissolves like’ holds well, and that to separate polar analytes a polar stationary phase is required, and vice versa. The skill of stationary phase selection lies in knowing (or empirically discovering), the degree of polarity required to avoid overly long retention times whilst still obtaining a satisfactory separation.

 
Like dissolves like

Figure 6.  Like dissolves like.

 
 

The selection of the correct stationary phase is one of the most critical parameters in the success of any GC method. As the interaction of the analyte molecules with the mobile phase is almost negligible, the column temperature and the interaction of the analyte with the stationary phase will govern the selectivity of the separation.

 
Reduced selectivity and peak shape distortion

Figure 7.  Reduced selectivity and peak shape distortion as consequence of incorrect column selection.

 
 

Silanol groups responsible for classical mixed mode effects with polar analytes due to dipole-dipole and hydrogen bonding interactions.  Can result in many unwanted conditions, including:

  • Selectivity issues
  • Peak shape issues (distortion, splitting, etc)
  • Retention time issues (short, long or irreproducible retention times)

When things go wrong, the best approach is to start by checking the obvious.  So, if you notice an abrupt change in selectivity, then suspect the use of an incorrect stationary phase column.  Even if the correct column was used, still you need to make sure the stationary phase is in good working order (see below).

 
 

Column Degradation

The following guidelines will help ensure longer column lifetime:

  • Remember to seal the column ends when they are not in use to exclude atmospheric oxygen and moisture. The easiest way is to seal the column using silicone septa
  • Don‘t leave the column out on the bench where it can be damaged. Store the column so it will not be scratched. If scratched, the stress to the column may cause it to crack
  • Store the column boxed with the test chromatogram in a dark place. Exposure to high levels of ultra-violet light can initiate oxidization of the stationary phase
 
Oxidization of the stationary phase

Figure 8.  Exposure to high levels of ultra-violet light can initiate oxidization of the stationary phase.

 
 

Oxygen rapidly degrades the stationary phase by cleaving bonds along the back-bone of the column. This is known as a “cyclic back biting reaction” where the siloxane chain breaks into more thermodynamically stable cyclic siloxanes. This damage is irreversible.  An increase in the number of secondary Si-OH interactions and peak tailing may be observed. This effect is most noticeable with polar compounds.

 
Siloxane bleed – O2 catalysed back biting reaction

Figure 9.  Siloxane bleed – O2 catalysed back biting reaction.

 
 
Reduction in selectivity

Figure 10.  Column deterioration could lead to a reduction in selectivity.

 
 

Column Contamination

Column contamination should be avoided by implementing best sample preparation practices (using high quality reactants, implementing sample filtration, etc.) and implementing column protection (guard columns, gas traps, etc.).

Peaks due to column contamination, tend to be broader than the other peaks in the chromatogram.  However, the presence of such broad peaks does not confirm column contamination.

 
Protect your column by using a guard column

Figure 11.  Protect your column by using a guard column.

 
 

Temperature

Temperature plays an important role in GC; as both the kinetics and thermodynamics of the chromatographic process are temperature dependent. [2-4]

Under isothermal conditions, the column is held at a constant temperature during the analysis.  In simple terms, the lower the oven temperature, the longer the analytes remain on the column.  As a rule of thumb, retention factor times decrease by a factor of two for every 20oC increase in column temperature.  Unfortunately, the prediction of changes in selectivity are not as straight forward (note that selectivity is defined as the ratio of retention factors).

When performing temperature programmed operation, the column is subjected to an increasing temperature throughout the analysis.[5]  Broadly speaking, selectivity increases with decreasing temperature but so does analysis time and band broadening.

Incorrect temperature (isothermal operation) or temperature program, as well as lack of proper temperature control are root causes for a number of problems in GC.  In particular, whenever retention time variation or reduction in selectivity are experienced, then check temperature settings and make sure the GC oven is in good working order.

The oven temperature control system in a modern gas chromatograph will consist of a box containing resistive heating elements through which air is forced to rapidly heat the enclosed column to a pre-set temperature.  This arrangement allows the column temperature to be accurately maintained and quickly changed to meet the desired temperature profile for the analysis.

 
The GC oven

Figure 12.  The GC oven.

 
 

From a practical point of view, no oven can guarantee instantaneous isothermal conditions along the whole column.  However, differences up to 1oC across the column will not affect retention time drastically, as long as the gradient program is stable and reproducible.  Given that no electrical problems are occurring, heating problems will be minimized by making sure the oven fan, heater and temperature sensor are all in good working order.  Likewise, make sure the oven temperature (or temperature profile) was set correctly.

Note that ovens and columns require an equilibration period after cooling down before a new analysis can commence.  The column temperature could be higher than the temperature sensor due to its inherent thermal mass.  An equilibration time is required for the column, and most importantly the carrier gas travelling through it, to reach thermal equilibrium with the oven  - 1 to 5 minutes is usually adequate for most situations. [6]

It should be noted that each GC will have a maximum temperature (reproducible) programming rate, effectively dictated by the instrument and power source design.  One should take care not to exceed this limit or irreproducible temperature programs may be encountered. [7-9]

To ensure the accuracy of the oven temperature during temperature programming, it is possible to use accurate thermocouples attached to the column to confirm instrument readout data; note that such devices require periodic calibration.  In most laboratories, a check of the validity of and repeatability of the oven temperature profile would be part of the Operational Qualification / Performance Verification (OQ / PV) testing.

 
 

Additional Peaks

Additional peaks in the chromatogram can be regarded as a resolution problem, as long as peak co-elution is happening.  The obvious solution is to get rid of the additional peaks, so you need to track them down before removing them.
 
Additional peaks

Figure 13.  Additional peaks.

 
 

Table 1 helps you to identify the origin and propose remedial actions when additional signals occur.

 
Potential Cause Potential Remedial Action
Contaminated sample
  • Improve sample clean up
Contaminated vials / syringe
  • Clean vials
  • Use only glass vials
  • Clean or replace syringe
Contaminated septa
  • Use correct septa
  • Install laminated septa, Teflon side down
Septum bleed
  • Reduce injector temperature
  • Replace for a high temperature septa
Column contamination
  • Flush column
  • Trim column
  • Replace column
Adsorption in transfer line
  • Use glass-lined or passivated stainless steel for transfer lines
Carrier gas contamination
  • Install or replace carrier gas purifiers
Sample decomposition
  • Reduce temperature

Table 1.  Additional signals.

 
 
 


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When a decrease peak distortion occurs, then the logical troubleshooting approach include the following steps:

  1. Check column dimensions
  2. Check carrier gas flow rate and velocity
  3. Look for column contamination
  4. Check sample concentration
  5. Check injector settings (flows, temperatures, etc.)
  6. Improper solvent effect or lack of focusing
  7. Reinstall the column (especially after inlet maintenance)
 
Loss of resolution due to a reduction in peak separation

Figure 14.  Loss of resolution due to a reduction in peak separation.

 
 

Topics 1 and 3 were already covered in the previous section, so the other five topics will be further explained.

 

Carrier Gas Flow Rate and Velocity

Overview

The practical implications of setting an incorrect flow rate are tremendous, of course, and not only retention time but significant changes in resolution and peak distortion can occur.

The carrier gas flow rate is temperature dependent.  At moderate conditions of temperature and pressure, the so called “ideal gas” law holds:

 

Pressure Management Issues

In constant pressure mode the flow rate of 0.92 mL/min at 50oC falls to 0.38 mL/min. at the end of the analysis according to the flow decay curve shown above – the carrier gas pressure is 5 psi.

In constant flow mode the carrier gas flow rate is 0.92 mL/min. throughout the analysis, the pressure being ramped from 5psi to a final value of 11.5psi at 300oC according to the pressure ramp curve shown above.

 
Constant pressure GC

Figure 15.  Constant pressure GC separation of acrylic acid impurities using FID detection.

 
 
Constant flow GC

Figure 16.  Constant flow GC separation of acrylic acid impurities using FID detection.

 
 

In figure 16 we can see that the chromatography has been improved in several respects when using constant carrier flow in Temperature Programmed GC.  There has been an overall gain in sensitivity (the peaks areas have increased), mainly due to a decrease in peak width.

The rising baseline has been eliminated due to the constant flow into the mass flow sensitive detector – allowing more reproducible integration and quantitation of peaks 4 and 5.  The retention time has decreased by a factor of three.
 
 

Leaks

Leaks are a major root cause of retention time variability.  In this case, the flow rate is decreased unless electronic pressure controllers are used.

GC detectors are prone to developing leaks, especially when installing the GC column.  When installing your GC column, please bear in mind the following pointers:

  • Column cutters are needed for a clean square cut at column end
  • Look for crushed column remnants
  • Ensure that guidelines for column insertion distances are followed closely

If the GC system lacks pressure controllers, then a leak in the injector will cause an increase in retention time.

The situation with pressure controllers is a slightly more complicated, as flow will be changed (usually increased) to compensate for the leak.  Here, a fraction of the flow will leak while the rest would go to the column.  If the amount of carrier gas to the column is large enough, then a reduction in retention time is possible, otherwise retention time will increase as the limits of the pressure control system are exceeded.

 
electronic leak detector

Figure 17.  Always check for leaks (use an electronic leak detector whenever possible).

 
 

Carrier Gas Velocity

One of the primary parameters to investigate when retention time issues occur is the carrier gas flow rate.  The practical implications of setting an incorrect flow rate are tremendous, of course, and not only retention time but significant changes in resolution and peak distortion can occur.  Clean carrier gas is essential to prolong the lifetime of GC columns, and is required to achieve low levels of noise and good peak shape. [14-17]

The carrier gas flow rate (mL/min) can be expressed as an average linear velocity (cm/s) at which a non retained compound travels through the column.  This velocity can be found by injecting a highly volatile analyte that is not retained by the column, and using the following expression:

Where:

 is the average carrier gas linear velocity (cm/s)
L is the total column length (cm)
tm is the retention time of the non-retained compound (seconds, minutes)

 
 

In a similar way, the flow rate (F) is given by:

Where rc is the column’s internal radius (usually expressed in mm) and j is can be calculated as follows:

 

Where pi is the inlet pressure and po the outlet pressure.

From the previous equations it follows that the GC instrument actually measures pressure and then calculates flow rate.  The algorithm includes the geometric column dimensions, so you must make sure the correct column dimensions were used, otherwise incorrect velocities would be calculated.

 
 

Every time the column is shortened, which is the case when performing column installation or maintenance, the retention time is decreased.  Note that other parameters such as separation efficiency and resolution are changed when the column length is altered.  Selected non-retained analytes currently used to measure carrier gas flow rate are listed in the table below.

 
GC Detector Compound
FID Methane, butane
TCD Methane, butane
ECD Methylene chloride*, halogenated methanes*
PID Ethylene, acetylene
NPD Acetonitrile*
MS Butane, air, halogenated methanes*

Table 2.  Selected compounds used to measure carrier gas linear velocity.

* Liquid at room temperature

 
 

The effective column length is key to understanding retention time decrease when shortening the column.  Count the number of full turns of the column on the hanger and multiply by the average length of a single turn, add the remaining length of column connected to the inlet and detector.  The correct linear velocity for your shorter column can be estimated by:

Where  and L denote velocity and column length respectively.

 
 

From the previous equations it should be clear that in order to get the correct flow rate, you must use the correct column dimensions. .

For more information in GC flow rate, please visit the links below:

Developing Fast Capillary GC Separations

GC troubleshooting gas supply and inlet issues

 
 

Measuring Gas Flow

As temperature and air pressure may vary from place to place, standard reference conditions for testing, reporting and calibration should be used.  Selected standard reference conditions for gases are listed in the table below:

 
Reference Pressure (kPa)* Temperature (oC)
STP 100.000 0
NTP 100.325 20
SATP 101.000 25
ICAO 100.325 15

Table 3.  Selected gas reference conditions (approximated).

* Approximately 1 atmosphere (1atm ≈ 101325 Pa ≈ 760 torr ≈ 14.7 psi)

 
 

Many GC systems express their readings on a standard 25oC and 1 atmosphere basis.  Therefore, a flow measured with an external device (such as a bubble meter) may not agree with your instrument reading.  Given that flow was measured at local rather than standard conditions.  Make sure you know and use the same reference conditions than your GC system uses.  In case of doubt, consult your GC manufacturer’s handbook.

When measured and instrument display flows are not equal:

  • Use calibrated electronic flow meter to compare with instrument readings
  • Check column dimensions entered into software
  • Check correct gas was selected in the instrument firmware
  • Check the split line and split trap is free of restrictions
Check for leaks at the septum nut and column inlet connection
 
Leak testing

Figure 18.  Leak testing.

 
 

Sample Concentration

Peaks will become broader as the concentration is increased.  Please consider the following pointers when performing sample preparation: [13-18]

  • Use certified volumetric laboratory glassware
  • When preparing a solution, bear in mind that volumes are not additive
  • When measuring low volumes use micro-pipettes
  • Precipitation could change sample concentration.  If mixing an organic solution with an aqueous buffer, add the organic component to the aqueous buffer (do it gradually)

Overloading the column will lead to problems including peak distortion and inconsistent retention times.  There are two ways of overloading your column:

  • Concentration Overloading: sample concentration is increased while the injected sample volume remains constant
    (injecting a more concentrated sample)
  • Volume Overloading: sample concentration is kept constant while the injected sample volume is increased
    (injecting a larger sample volume)
 
peak fronting

Figure 19.  Typical peak fronting and loss of efficiency associated with column overloading.

 
 

Column capacity is defined as the maximum amount of sample that can be loaded onto a column without separation efficiency and peak integrity being compromised – usually determined using peak asymmetry measurements.  As a rule of thumb, column capacity will increase with the amount of stationary phase.

The table below reports approximate sample capacity for selected GC columns.  For more accurate data, please consult your column manufacturer.
 
Column ID (mm) Film Thickness (μm)
0.1 0.25 0.5 1.0
0.10 10 ng 30-40 ng 50-70 ng 100-200 ng
0.18 20-30 ng 60-80 ng 100-150 ng 250-350 ng
0.25 30-40 ng 125-175 ng 175-250 ng 400-500 ng
0.32 50-70 ng 200-250 ng 250-350 ng 600-800 ng
0.45 80-100 ng 300-400 ng 400-500 ng 800-1000 ng
0.53 100-120 ng 400-500 ng 500-700 ng 1000-1500 ng

Table 4.  Approximate GC sample capacity as a function of column diameter and film thickness (note that amounts are PER ANALYTE not per sample).

* Where 1 ng = 10-9 g

One might use Table 4 to calculate the sample mass injected on a per analyte basis.  If a sample contains an analyte of interest at approximately 1% and a 0.32mm x 0.5mm i.d. column is being used then the maximum sample load would be 250 – 350μg

 
 

Split/Splitless Injection Volume

The nature and volume of the sample solvent injected into the split/splitless inlet will have a major effect on the accuracy and reproducibility of quantitative analysis and the chromatographic peak shape. As the injection is made, the sample solvent rapidly volatilises and expands into the gas phase. To avoid quantitative problems, the total volume of the gas should be able to be constrained within the volume of the inlet liner. If this is not the case, then the excess gas will spill over into the inlet gas supply and septum purge lines. The temperature in these lines rapidly decreases, and it is possible for the sample solvent vapour (containing the analyte), to recondense, ultimately depositing analyte onto the inner walls of the tubing.

When the next ‘overloaded’ injection is made, the sample solvent from this injection will again ‘backflash’ into the gas lines. In this instance analyte deposited during the previous injection will be ‘lapped’ back into the inlet – ultimately finding its way onto the column. This will cause ‘carry-over’ and will reduce quantitative accuracy and reproducibility.
 

Figure 20.  Backflash.

 
 
 
Ghost peaks

Figure 21.  Ghost peaks.

 
 

The expansion volume of the sample solvent is governed by the inlet pressure and temperature, as well as the natural expansion coefficient of the solvent. It is possible to predict the expansion volume and hence the volume of solvent that may be safely injected into an inlet liner of known volume, under set temperature and pressure conditions.

A technique known as ‘pressure pulsed’ injection may be used, in which the inlet pressure is raised during the sample injection cycle. This constrains the expansion of the solvent within the inlet liner and allows for larger injection volumes. [2-3]

 

Figure 22 is a useful calculator which allows you to assess the possibility of backflash with your current hardware and operating conditions.

 

Figure 22.  Optimizing injection volume using a simple backlash calculator.

 
 

Injector Settings

The correct selection of injector settings is critical not only in terms of sensitivity and repeatability but to achieve high resolution and good chromatographic peak shape.

Consider:

  • Sample Solvent (sample solubility / compatibility with stationary phase)
  • Injection Mode (split, splitless)
  • Injector settings (splitless time / pressure pulsed injection)
  • Injection Volume (backflash and column overload)
  • Inlet Temperature
  • Initial Oven Temperature (Focussing in splitless / de-focussing in split!)
 
 

Solvent Effect and Analyte Focussing

Sample Solvent

Small changes in retention time (and retention factor) for peaks eluting near the solvent front might occur if there is a change in the sample solvent.  In general the larger the difference in polarity between the sample solvent and analytes, the larger the extent of this problem.

Changes in solvent polarity will lead to retention factor variability.  Basically, the retention factor, a measurement of the tendency of an analyte to remain in the stationary phase over the mobile phase, will be more affected for early eluting peaks (or while the injection solvent is part of the mobile phase).

Amount of Sample Entering the Column

A large change in the amount of a sample entering the column (usually hundred times or even more) will compromise retention time.  Good sample preparation and injection technique are crucial to avoid this problem.

During split injection, the amount of sample entering the column will be dependent upon the split ratio, so a carefully controlled split ratio must be set.

So it is not possible to assign a unique retention time representative of the eluting analyte band.  As an illustration, consider splitless injection with cold trapping (low temperature).  If your sample was injected in a solvent whose polarity is very different to that of the stationary phase; then condensation at different positions would occur and sample will be unevenly infused into the column.  Please refer to figure 23.
 
Sample focussing

Figure 23.  Large difference in polarity between injection solvent and stationary phase will lead to inefficient focusing and sample being unevenly infused into the column.

 
 

Analyte Focussing

The lack of solvent effect or cold trapping, when performing splitless or on-column injection can result in peak shape abnormalities, such as peak tailing and broadening.

The analyte is slowly introduced from the inlet during the whole of the splitless time (the inlet volume may be exchanged as few as two times during this whole splitless period).

This slow sample vapour transfer can result in the analyte band entering the column over a period of 30 – 60 seconds or so, depending upon the exact analytical conditions. Without proper focussing these effects can entirely negate any efficiency gained through the use of capillary columns and the resulting chromatographic peaks would be unacceptably broad.

Figure 24 illustrates the principles of focussing in splitless injection.  The general rules of thumb are:

  • Initial column oven temperature at least 10oC below the sample solvent boiling point
  • Match the polarity of the sample solvent with that of the stationary phase chemistry
 

Figure 24.  Sample focusing.

 
 

Inlet Considerations and Purge Time

During splitless injection, it is of vital importance that the inlet is purged of residual vapours once the analyte has been transferred to the capillary column. If this is not done, the solvent peak will show a high degree of tailing and the GC baseline signal may be noisy and rise markedly as the analysis progresses. This is due to the slow bleed of excess solvent and sample (not analyte) components from the inlet into the capillary column. An example showing a splitless injection in which the inlet is not purged is shown below.

 

Figure 25.  Split/splitless injection (inlet is not purged).

The inlet purge is achieved by actuating the split (purge) valve that allows a high split flow through the liner, which quickly purges the residual solvent vapours from the inlet. The split flow is high as the aim is to quickly purge the inlet – split flows of 100-200 mL/min. are typical. The time from the beginning of the injection to the time at which the split line is turned on is known as the splitless or purge time.

 
 

What Happens if the ‘Split on’ or ‘Purge’ Time is Too Short?

It is vital that the splitless time is optimised for each application. Too short a splitless time will mean that analyte still resident in the liner will be discarded via the split line. This may lead to poor analytical sensitivity and reproducibility.
 
Splitless time too SHORT

Figure 26.  Splitless time too SHORT –loss of higher boiling analytes.

 
 

What Happens if the ‘Split on’ or ‘Purge’ Time is Too Long?

Too long a splitless time will lead to badly tailing solvent peaks, extraneous peaks and a rising baseline – making reproducible integration difficult.

 
Splitless time too LONG

Figure 27.  Splitless time too LONG –broad solvent peak and rising baseline.

 
 

The splitless time is usually empirically optimised by monitoring the peak area of a mid-eluting peak in the chromatogram. The peak area is plotted against the splitless time and a plot of the form shown below should be produced.

 
Determining optimum splitless time

Figure 28.  Determining optimum splitless time.

For reproducible analysis the splitless time should be chosen just onto the plateau of the area response curve as indicated. Typical splitless times lie in the region – 20 – 90 seconds.

 
 

Oven Temperature in Split/Splitless Injection

During split injection, a small amount of sample is transferred to the column during a very short period of time.  In general terms, the oven temperature is kept beyond the boiling point of the sample solvent.

During splitless injection, the whole sample is transferred to the column during a long period of time.  In general terms, the oven temperature is kept below the boiling point of the sample solvent, so sample focusing takes place at the head of the column.

From the previous paragraphs it follows that although, temperature should be kept at a reasonably low value with both interfaces (split and splitless), it is more critical with splitless injection.

For more information in split/splitless injection in GC please visit the links below:

CHROMacademy, GC, Theory and Instrumentation of GC, Sample Introduction

Split Splitless Injection

 
 

Column Installation

Incorrect column cutting and installation leads to a multitude problems (peak shape distortion, reduced efficiency, loss of resolution, etc.).
[10-12]

Important considerations when performing column installation include:

  • Column is cut at 90o to the column wall with no jagged edges or burrs
  • The column is positioned correctly within the inlet and detector to avoid dead volume and ensure optimum sampling efficiency
  • There should be no leaks at the inlet or detector fittings during the whole temperature program cycle Use a scribe (ceramic wafer, diamond tipped pen) to score the polyamide coating of the column and, holding firmly just below the score, flick the column above the score away from you.  The wafer has two edges, the rough edge should be used to score the polyimide coating
 
Cutting the column

Figure 29.  Cutting the column.

 
 
Inspect the cut edge with a 10-20X magnifier.  The cut end should be at a 90o angle relative to the tubing wall.  There should be no burrs or large, jagged areas.  If necessary, re-cut the column until a proper end is obtained.  If a good column cut is not made, then significant activity (resulting in poor quantitative precision) and split or tailing peaks may be observed in the chromatogram.
 
Examples of good and bad column cuts.  Courtesy of Agilent Technologies

Figure 30.  Examples of good and bad column cuts.  Courtesy of Agilent Technologies.

 
 

Poorly cut columns expose excess silanol groups and subject the analytes entering the column to turbulent eddy currents. Secondary retention mechanisms and turbulent eddies cause peak tailing and splitting problems.

Some workers prefer to use fused silica column cutters of the type shown in figure 31.

  1. Insert capillary column (A) in the column cutter as indicated
  2. Fix the capillary column by turning the securing disk (B)
  3. Cut the column by turning the cutting disk (C), one full rotation is usually sufficient
  4. Use the magnifier (D) to verify the cut
 
Fused silica column cutter

Figure 31.  Fused silica column cutter.  Courtesy of Hewlett-Packard.

 
 

Wipe the column with acetone to remove finger grease and other residues from the exterior surface of the column.

For more on column contamination please visit this link : Troubleshooting Column and Detector Issues

 
 
 


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The appearance or profile of the baseline can aid in the identification of many problems that are associated with the GC system components.
[3, 5, 17-18]

Typical baseline problems include:

  • Drifting baselines
  • Cycling Baseline
  • Wandering Baseline
  • Noisy baselines
  • Spikes in the baseline
  • Off-scale baselines
 
 

Flow Rate Considerations

Ideally GC detectors should be insensitive to changes in flow rate.  Unfortunately, this doesn’t hold with all GC detectors.  For example, the FID detector is virtually insensitive to changes in column flow, however, the FID response is highly dependent on the hydrogen:air ratio which must be carefully controlled.  Likewise, signal response can be affectd by the flow rate with some of the most common GC detectors (ECD, TCD and NPD).

There are many reasons why a GC instrument would not reach the required flow rate (and pressure) or a constant carrier gas flow rate would not be achieved.  These include:

  • Leaks at the column fitting or inlet septum fitting
  • Insufficient gas supply
  • Wrong system configuration (typically low flows with large internal diameter capillary columns)
  • Problems with the proportioning valves of the electronic pressure control system

In the constant flow operating mode, the carrier pressure is ramped to attain a constant flow through the temperature program (as temperature is increased carrier gas viscosity also increases and therefore a higher pressure is required to keep the required flow at a constant value).  With mass-flow or flow sensitive detectors, this phenomenon can manifest itself as either a gradually increasing or decreasing baseline signal depending upon the response characteristics of the detector.

For more information in carrier gas flow rate, flow controllers and leaks, please visit the link below:

GC troubleshooting gas supply and inlet issues essential guide

One needs to ensure that the gas supply pressure and inlet pressure (if applicable) set-points are high enough to sustain the required gas pressures at the upper temperature of the program.  This can be particularly important when using columns of certain length and internal diameter.

If the carrier supply is intermittent or inconsistent, then this will typically result in wandering or noisy baselines accompanied by reduced sensitivity.

 
 

Column Conditioning

It is well known that capillary GC columns have a small amount of volatile contaminants coming from their manufacturing, installation and storage.  The heating of a GC column to remove such contaminants is known as conditioning and it is required whenever a column is installed.  The lack of conditioning will result not only in baseline rising/falling problems but in a number of additional problems such as additional peaks, blobs, and humps.

Figure 32 illustrates a typical GC baseline obtained without column conditioning.  This type of baseline drift can be seen even with a poorly conditioned column in temperature program mode or with a mass flow sensitive detector if operating in temperature programming mode using ‘constant pressure’ rather than ‘constant flow’ carrier gas modes.  Note that after certain period of time, the baseline should begin to fall rapidly.  One should eliminate these potential causes of the symptom prior to troubleshooting the detector.
 
Upward baseline drift

Figure 32.  Upward baseline drift encountered with an FID detector.

 
 

Typically, FID detectors may give rise to baseline drift when the gas stoichiomtery is incorrect.  One should pay particular attention, in this case, to the hydrogen flow rate, as a non-optimal setting can give rise to pronounced baseline drift.

If the drift is cyclical in nature, one should check the pressure stability of the in-coming gases – especially when using gas generator devices.

The following is only one of many suggested schemes for column conditioning

  1. Connect the column
  2. Allow carrier gas to flow through the column for 10 minutes at room temperature
  3. Rapidly increase the column temperature to 20-25oC above the top oven temperature desired for analysis (do not exceed the gradient upper temperature limit)
  4. Hold at this temperature
  5. The baseline position should rise, possibly to an off-scale value, after a short while
  6. 5 to 15 minutes after the oven reaches its maximum temperature, the baseline should begin to fall rapidly
  7. After 30 – 90 minutes at the upper conditioning temperature the baseline will have recovered to lower, steady value
  8. As soon as the baseline has been stable for more than three minutes, conditioning should be stopped
  9. The more polar the stationary phase and the thicker the film, the longer will be required for conditioning
  10. If the baseline position has not lowered or is not stable after 60-90 minutes of conditioning, one should suspect a leak which is introducing oxygen into the column and causing excess column bleed through oxidative degradation
  11. The VAST MAJORITY of capillary columns do not contain enough degradation material to foul the detector and so the column can be connected to the detector during conditioning. This gives extra information as to the extent of conditioning as the baseline position can be monitored.

For more in GC column conditioning, please follow the link below:

GC troubleshooting column detector issues Essential Guide
 
 

Column Bleed

Column bleed is the elution of degradation products of the stationary phase causing a background signal in the GC detector.  All columns produce bleed products and the most common degradation reaction is the 6 member so-called ‘back biting’ reaction shown in Figure 33.  It should be noted that a rising baseline during a GC temperature program is often attributed solely to ‘column bleed’ whereas this may also be caused by septum bleed products, sample matrix bleed, changes in the carrier flow rate when using mass flow sensitive detectors and operating in ‘constant pressure’ mode etc. [14, 16]

 
Siloxane bleed – O2 catalysed back biting reaction

Figure 33.  Siloxane bleed – O2 catalysed back biting reaction.

 
 

Bleed is best characterized using a ‘bleed profile’ – a temperature program that ramps to the column top operating temperature and holds for 10-15mins. A typical profile is shown in Figure 34 –any major deviations from this type of profile are not due to column bleed.  Bleed is a continuous process - any peaks in a blank run are not from column bleed, but most likely originate from contaminants in the GC system.

Column bleed increases with stationary phase polarity, film thickness and column age.  Exposing the column to oxygen (air) or consistently using the column at its upper temperature limit accelerates the onset of higher column bleed.  A sudden or rapid increase in column bleed is usually an indicator of column damage or a problem in the GC system.  Prolonged heating of a column above its upper temperature limit, constant exposure of the column to oxygen (usually via a leak), or repeated injection of damaging compounds (water, acetonitrile etc.) are the most common root causes of column bleed.

Important Column Bleed Characteristics

  1. The baseline is relatively flat during the lower temperature region of the blank run
  2. A sharp rise in the baseline begins at 30-40oC below the upper limit of the column and continues until the upper temperature limit is reached
  3. Upon holding at the upper temperature limit, a fairly flat baseline is obtained.  Several minutes may elapse before the baseline becomes completely flat.  Major deviations from this profile are not due to column bleed
Column bleed is an abnormal elevated baseline at high temperature –it is not an elevated baseline at low temperature, a wandering or drifting baseline or (most typically) discrete peaks.
 
Column bleed

Figure 34.  Important characteristics of column bleed.

 
 

Excessive column bleed appears as a larger rise in the baseline at the higher temperature regions.  There is no absolute measurement to indicate when column bleed is excessive.

Column bleed is best measured as the difference or change in the background signal at two temperatures –Relative Bleed.

Usually the column’s upper temperature limit and a lower value around 100oC are used.  The absolute background signal is a composite of the background generated by the entire GC system.  It is not possible to determine the contribution of column bleed to this total background signal.  By measuring the relative amount of column bleed, the other contributors to the background signal are subtracted out.

Most columns are tested using an FID detector.  The output signal for an FID is in picoamps (pA).  Bleed levels are usually reported as the difference (DpA) in the FID signal at two temperatures.
 
Measuring relative column bleed

Figure 35.  Measuring relative column bleed.

 

As columns age they may also exhibit unacceptably high levels of column bleed.  One should always measure the bleed profile of a new GC column against which to compare at regular intervals to assess column aging / degradation.

 
 

Septum Problems

The materials used to plasticise the septum, bleed continuously (phthalates etc.). In capillary GC the bleed products may give rise to discrete noise peaks and may also result in a rising baseline as shown below. The septum purge flow of the inlet helps to reduce these effects; however, correct septum choice with regards to inlet temperature is important.  Septa eventually wear through continuous piercing, and will ‘core’ to deposit fragments into the liner.

Eventually the liner will split or core so badly that a pressure seal is no longer maintained during the injection phase. Peak shape will suffer when this occurs and the baseline shifts are diagnostic of a worn septum.
 
Care is required with the torque on the septum nut to ensure extended operating lifetime

Figure 36.  Care is required with the torque on the septum nut to ensure extended operating lifetime.

 
 
The figure below shows a typical chromatographic symptom created by a leak at the septum during injection. The baseline position changes after the elution of a large (usually solvent), peak. This indicates that the septum is not sealing correctly around the needle, and will therefore leak during injection and for a short time afterwards. This symptom is exacerbated if the diameter of the needle used is too large.
 
Septum bleeding profiles

Figure 37.  Septum bleeding profiles.

 
 

Septum fragments in the column can also lead to drifting baselines.  In this case, remove 1-2 coils from contaminated end.  Make sure the tip of the needle would always easily penetrate the septum.

A very badly cored or split septum will leak and fail to maintain system (head) pressure. Without a proper maintenance regime, this may be the first thing you realise when the septum is causing problems! [17]

Septa eventually wear through continuous piercing, and will ‘core’ to deposit fragments into the liner.  Eventually the liner will split or core so badly that a pressure seal is no longer maintained during the injection phase. Peak shape will suffer when this occurs and the baseline shifts are diagnostic of a worn septum.
 
Septa integrity versus injection number

Figure 38.  Septa integrity versus injection number (N).

 
 

There are many types of septa available. Care should be taken to use the correct septum and syringe combination for optimum performance.

 

Figure 39.  Septum selection tool.

 
 
There are many types of septa available. The most successful designs include a septum core (made of one or more different materials) which can be coated or sandwiched between different layers.  Care should be taken to use the correct septum and syringe combination for optimum performance.
 

Figure 40.  Selected types of septum currently used in GC/GC-MS applications.

 
 

Detector General Considerations

Most GC Detectors require a period of equilibration to reach a stable response whenever they are switched on or when temperature or gas supply changes are made. During this time, it is not unusual to experience baseline drift or wander, sometimes accompanied by higher noise levels than usual. Some detectors, such as the Nitrogen Phosphorus Detector (NPD), may require longer periods of equilibration. [12, 18]

To reduce gas contamination, high purity gases are used in conjunction with gas purifiers (‘traps’). The traps are fitted as close as possible to the GC instrument to reduce contamination between the trap and the instrument.

Detector contamination can also lead to drifting baselines. Ensure your detection system is fully functional.  Follow the instructions given by your system manufacturer.

Drifting baselines related to the temperature program are not uncommon for concentration dependent detectors. As was explained, when the temperature goes up, the carrier gas flow rate goes down. If during the temperature program the volumetric flow rate of carrier gas has changed, then a change in background signal would follow.
 
 

Drifting Baselines

Drifting baselines show discernible pattern.  The main reasons for baseline drifting are gas flow related or un-equilibrated detector. Poor temperature and flow control as well as gas contamination (carrier, detector, etc) are amongst the most common reasons for wandering baselines.

 
Drifting baselines

Figure 41.  Drifting baselines – note this behavior may be considered normal with some mass flow sensitive detectors in constant pressure mode OR when running in Temperature Programming mode.

 
 

Table 5 helps you to identify the origin and propose remedial actions when baseline drifting occur.

 
Potential Cause Potential Solution(s)
Un-equilibrated detector
  • Increase equilibration time
Improperly conditioned column /
column bleed
  • Use gas traps
  • Condition the column as per manufacturer’s instructions
FID:  Poor gas flow control
(hydrogen and air mainly)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller
NPD:  Poor gas flow control
(hydrogen and air mainly)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller
ECD: Detector contamination
(for compounds of high electron affinity, such as halogenated compounds)
  • Clean the detector as indicated by the manufacturer
  • Given that the ECD detector contains a radioactive source, cleaning may need to be carried out by the manufacturer

Table 5.  Drifting baseline.

 
 

Cycling Baseline

Cycling baselines show discernible pattern.  The main reasons for cycling baselines are lack of gas flow or temperature control.

 
Cycling baseline

Figure 42.  Cycling baseline.

 
 

Table 6 helps you to identify the origin and propose remedial actions when cycling baselies occur.

 
Potential Cause Potential Solution(s)
Poor temperature control
  • Check if the temperature sensor is broken and replace if appropriate
Poor make-up gas flow control
  • Replace controllers
  • Replace cylinder before pressure falls below 300 psig
FID:  Poor gas flow control (hydrogen and air mainly)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller
FID: Hydrogen flow variation (using generator)
  • Increase output pressure from generator / check generator supply continuity
FID: Hydrogen flow variation (using generator)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller
NPD: Hydrogen flow variation (using generator)
  • Increase output pressure from generator / check generator supply continuity

Table 6.  Cycling baseline.

 
 

Wandering Baselines

Wandering baselines show no discernible pattern.  The main reasons for wandering baselines in GC are gas related or un-equilibrated detector. Poor temperature and flow control as well as gas contamination (carrier, detector, etc) are amongst the most common reasons for wandering baselines.
 
Wandering baseline

Figure 43.  Wandering baseline –baseline position varies with no discernible pattern.

 
 

Most GC Detectors require a period of equilibration to reach a stable response whenever they are switched on or when temperature or gas supply changes are made. During this time, drifting or wandering baselines may happen (sometimes accompanied by higher noise levels than usual). Some detectors, such as the Nitrogen Phosphorus detector (NPD), may require longer periods of equilibration.

If equilibration is taking an unusually long time or if more than two hours are required for detector equilibration, please consult with your manufacturer or service provider.  Table 7 helps you to identify the origin and propose remedial actions when wandering baselies occur.

 
Potential Cause Potential Solution(s)
Poor temperature control
  • Check if the temperature sensor is broken and replace if appropriate
Poor make-up gas flow control
  • Replace controllers
  • Replace cylinder before pressure falls below 300 psig
Un-equilibrated detector
  • Most GC Detectors require a period of equilibration to reach a stable response whenever they are switched on or when temperature or gas supply changes are made
  • Increase equilibration time
Poor oven temperature control
  • Check and replace sensor
  • Consult the detector’s instruction manual
  • Look for expert advice
FID:  Poor gas flow control (hydrogen and air mainly)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller
NPD:  Poor gas flow control (hydrogen and air mainly)
  • Adjust flows to within instrument specifications
  • Replace regulator or flow controller

Table 7.  Wandering baseline.

 
 

Noisy Baselines

Baseline noise is not always visible but always present in the GC chromatogram.  All it takes is a closer look (more sensitive settings) to confirm the noisy nature of the signal.

All GC detector systems are in some way susceptible to interference from external electronic sources.  This might include a poorly smoothed electrical supply to nearby electrical equipment.  Noisy baselines usually present themselves as high frequency baseline noise or disturbances or ‘spikes’ on the baseline.

Noisy baselines can usually be overcome by fitting a power scrubber to the supply and isolating any equipment giving rise to the problem and removing to a different area of the laboratory or placing on a different ring circuit.  Defective electronics, cables or detector are common causes of noisy baselines.  Likewise, high external electromagnetic fields in the vicinity of the GC detector could also lead to noisy baselines.

Column or detector contamination can render irregular baseline noise.  The noise pattern usually changes with time and it is usually accompanied by a drifting baseline.  So contamination should be avoided or reduced the best you can.  You should:

  • Use guard columns
  • Trim the GC column
  • Provide periodic maintenance to your GC system
  • Follow the instructions given by your system and column manufacturer
Table 8 helps to identify the origin and propose remedial actions when noisy baselines occur.
 
Potential Cause Potential Solution(s)
Defective electrometer
  • Consult with your service provider
Incorrect column-detector installation
  • Reinstall column.  Consult with your service provider
Incorrect air and hydrogen flow rate ratios
  • Find the optimum settings for your detector to operate (application dependent)
Incorrect detector attenuation / sensitivity setting
  • Check and adjust as necessary the attenuation / sensitivity settings within the instrument and/or acquisition software
Insufficient hydrogen flow
  • Increase flow rate
Air leak in the vicinity of the detector (EDC, TCD, NPD)
  • Investigate and repair if possible – otherwise consult service provider

Table 8.  Noisy baselines.

 
 

Spiky Baselines

In essence, spikes are narrow lines that usually appear irregularly separated.  Broadly speaking, spikes are due to fast increases or decreases in signal detector.

Defective electronics, cables or wires are common causes of spikes.  Likewise, high external electromagnetic fields in the vicinity of the GC detector could also lead to spikes.

The passage of a large solvent band through the detector, especially where the solvent is water, can extinguish the flame momentarily.  Most modern FID detector systems have measures which prevent this occurring or which can re-ignite the flame.

One may try to divert the solvent using a switching device or simply reduce the injection volume to avoid the problem.

Check the detector gas stoichiometry to ensure the gas ratios are correctly set, as poorly adjusted gases can contribute to the flame being more easily extinguished.
 
Noisy and spiking baselines

Figure 44.  Noisy and spiking baselines.

 
 

Table 9 helps to identify the origin and propose remedial actions when spiky baselines occur.

 
Potential Cause Potential Solution(s)
Contamination
  • Use gas traps
  • Replace carrier gas cylinder
Particulate matter passing through the detector
  • Clean the detector per the instruction manual
  • Check column ends
Loose connections
  • Reconnect as needed
Electrical surges
  • Fit surge protector  / power smoother on supply
  • Check oven motor is drawing regular current
Column Positioning – Flame Based Detectors
  • Re-position the column in the detector so tip is below flame

Table 9.  Spiky baselines.

 
 

Off-Scale Baselines

There is a number of reasons for which the baseline is off-scale.  The most important include detector malfunctioning, contamination and incorrect gas flow or analysis temperature.

The position of the column within the detector housing relative to the flame is vitally important.  If the column is positioned too low (away from the flame) then the dead volume created between the column end and the flame will cause sample diffusion and hence loss of efficiency in the analyte bands as they elute from the column.

Follow the recommendations given by your system manufacturer when installing the column into the detector.
 
Typical off-scale response

Figure 45.  Typical off-scale response.

 
 

Table 10 helps you to identify the origin and propose remedial actions when off-scale baselines occur.

 
Potential Cause Potential Solution(s)
Wrong instrument/detector gases or flow rates
  • Verify gases are suitable for instrument and detector
  • Consult with system manufacturer
Detector electrical short
  • Disassemble and reassemble the detector ensuring insulators are correctly positioned
  • Clean detector as necessary
  • Consult with system manufacturer
TCD.  Imbalance in column reference and sample flows
  • Measures flows and adjust as necessary
Column bleed / conditioning
  • Condition column as per manufacturers instructions
  • Trim or replace column
Incorrect attenuation / sensitivity settings
  • Adjust to obtain a lower detector output

Table 10.  Off-scale baselines.

 
 
 


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  1. “Chromatographic Parameters” from CHROMacademy’s “Theory and Instrumentation of GC”
  2. “GC Method Development” Chapter 5. Crawford Scientific 2010
  3. “Fundamental Gas Chromatography” Chapters 1-3. Crawford Scientific 2009
  4. Practical GC Troubleshooting and Maintenance. Crawford Scientific 2007
  5. Fundamental Gas Chromatography. Crawford Scientific 2009
  6. GC Method Development. Crawford Scientific 2010
  7. “GC Temperature Programming” from “Theory and Instrumentation of GC”. CHROMacademy
  8. John V. Hinshaw. “GC Ovens - A Hot Topic” GC Connections. LC-GC Europe - July 2001
  9. “Chromatographic Parameters” from “Theory and Instrumentation of GC”. CHROMacademy
  10. “GC Columns” from CHROMacademy’s “Theory and Instrumentation of GC”
  11. CHROMacademy Resolver Issue 3: Column Choice for Capillary GC
  12. The CHROMacademy Essential Guide to GC Troubleshooting - Column & Detector Issues
  13. “GC Temperature Programming” from CHROMacademy’s “Theory and Instrumentation of GC”
  14. The CHROMacademy Essential Guide to Troubleshooting GC Separations
  15. The CHROMacademy Essential Guide to Developing Fast Capillary GC Separations
  16. “Sample Introduction” from CHROMacademy’s “Theory and Instrumentation of GC”
  17. The CHROMacademy Essential Guide to Gas Cylinder, Regulator and Tubing - Maintenance and Good Practice Cylinders
  18. “GC Detectors” from CHROMacademy’s “Theory and Instrumentation of GC”
 
 

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The following subjects are covered in CHROMacademy.com

The Theory Of HPLC
Introduction (1.5hrs)
Chromatographic Parameters (3hrs)
Band Broadening (3hrs)
Column chemistry (4hrs)
Reverse phase (partition) chromatography (6hrs)
Ion-Pair Chromatography (3hrs)
Normal phase (absorption) chromatography (3hrs)
Gradient HPLC (3hrs)
Quantitative and Qualitative HPLC (3hrs)
FAST HPLC (4.5hrs)
HILIC (3hrs)
SFC (3hrs)
Ion Chromatography(3hrs)

Theory and Instrumentation of GC
Introduction (1.5hrs)
Chromatographic Parameters (3hrs)
Band Broadening (3hrs)
Gas Supply and Pressure Control (2hrs)
Sampling Techniques (4.5hrs)
Sample Introduction (5hrs)
GC Columns (5.5hrs)
GC Temperature Programming (3hrs)
GC Detectors (2.5hrs)
SFC (3hrs)

Instrumentation of HPLC
Mobile Phase Considerations (3.5hrs)
Solvent Pumping Systems (4hrs)
Autosamplers (4.5hrs)
Detectors (4.5hrs)

Solid Phase Extraction
Molecular Properties (4hrs)
SPE Overview (3.5hrs)
SPE Mechanisms (4.5hrs)
Method Development (5.0hrs)
Primary Sample Preparation Techniques (2hrs)
Liquid / Liquid Extraction Techniques (1.5hrs) Approaches to Automation for SPE (1.5hrs)

Fundamental GC-MS
Introduction (1.5hrs)
GC Considerations (4.5hrs)
GC -MS Interfaces (2.5hrs)

Fundamental LC-MS
Introduction (1.5hrs)
Electrospray Ionisation Theory (6hrs)
Electrospray Ionisation Instrumentation (4hrs)
Mass Analyzers (9.5hrs)
Atmospheric Pressure Chemical Ionisation (3.5hrs)
Atmospheric Pressure Photoionisation (3hrs)
Solvents, Buffers and Additives (3.5hrs)
Vacuum Systems (3hrs)
Flow Rates and Flow Splitting (3hrs)
Orbitrap Mass Analyzers (3hrs)

MS Interpretation
General Interpretation Strategies (11hrs)
Intro to MS Proteomics Research (3.5hrs)

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The Essential Guide from LCGC’s CHROMacademy presents the fourth and last in our series of webcasts on Practical GC Troubleshooting.  In this session, Dr. John Hinshaw (Senior Scientist , BPL Global Ltd) and Tony Taylor (Technical Director, Crawford Scientific), present practical troubleshooting tips for GC separations, with special emphasis on selectivity changes, loss of resolution and baseline problems.  The session includes a wealth of practical information on GC separation issues and all our real world problems are related to both separation chemistry and hardware issues.   We consider the common problems and highlight causes and remedial actions in a very practically relevant way.  A must see for everyone working with GC instruments.

Tony Taylor
Technical Director
Crawford Scientific
John V Hinshaw
Senior Scientist
BPL Global Ltd.

Who Should Attend:

  • Anyone who uses GC equipment and who wants to improve their separation troubleshooting and problem solving skills

Key Learning Objectives:

  • Learn how to quickly identify separation problems in GC
  • Identify strategies to confirm the problem and investigate the causes
  • Investigate the major causes of selectivity change in GC separations and how to fix / prevent these issues including problems with stationary phase chemistry, temperature programs and methodological problems
  • Highlight the interrelationship between resolution and selectivity, efficiency and retention.
  • Identify common causes for loss of resolution including efficiency problems and stationary phase / column issues
  • Discuss the common baseline issues in GC and highlight useful tests to pinpoint the issues
  • Develop tests and rememdies for all the ills’ highlighted above!
  • Develop curative and preventative maintenance operations to optimize the quality of your GC data