No thanks! I would like to know more about CHROMacademy

 Over 3000 E-Learning topics / 5000 Articles & Applications
 

New to LC-MS? 10 practical tips that will make a real difference


1.   Contamination, contamination, contamination! LC-MS is hugely affected by contamination. Sensitivity drops rapidly and can only be restored by a vent and clean. Make sure your samples are clean – particularly for dissolved contamination. This often means using SPE.
   
2.   Use a divert valve between the HPLC and the MS. Only introduce the mobile phase stream to the ms for the retention areas of interest. Divert everything else (particularly t0 and high organic portion of the gradient) to waste. Everything you inject into the HPLC will enter the mass spectrometer to build contamination.
   
3.   Vent the instrument as seldom as you can. Mass spectrometers are at their most reliable when left running. The more you vent the instrument, the more likely you are to cause other problems. The need to vent is caused by the need to clean, which is caused by contamination, which brings us back nicely to points 1 and 2.
   
4.  
Clean it all – not just one bit.

If you’ve gone to all the trouble of venting the instrument, take an extra few minutes to remove and clean everything up to the mass analyser.

There’s nothing more frustrating than venting, cleaning just the front items, then re-establishing vacuum to find sensitivity hasn’t improved and having to repeat the whole process to now clean the pre-filter.

 

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

   
5.  

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

  Although there are some general rules, you have to assume LC-MS is compound dependant.

This means you should, where practical, perform an infusion of your compounds of interest and optimise all parameters.

Have an individual tune file for each group of compounds.

No infusion pump? No excuse. If you’re using LC-MS you need one.

   
6.   Tune by mixing your infused sample into a representative mobile phase stream through a tee piece. This allows you to optimise source temperatures and gas flows to the proposed mobile phase flowrate and composition. Bear in mind that temperatures take time to stabilise.
   
7.  
Control of pH is critical to so many aspects of LC-MS.

It is essential that your mobile phase contains components that control pH.

At the very least a volatile acid (0.1% formic acid) or base
(0.1% ammonium hydroxide – if the column is rated to high pH), but ideally a buffer (10mM ammonium formate),
adjusted to a specified pH (2.8 or 8.2).

 

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

   
8.   During tune, evaluate your compound by mixing it through a tee piece with acidic then basic pH mobile phases. It’s usually worth evaluating both positive and negative ion mode at each pH.
   
9.   Find a suitable test compound, test conditions and expected results which you know work reliably (i.e. a benchmark). Go back to this anytime you have problems with the ms to evaluate quickly if this is related to an instrument fault.
   
10.   LC-MS still relies on a good chromatographic separation before the ms. When using SIM or SRM many quantitative problems are caused co-eluting substances entering the ion source with the analyte of interest, causing ionisation efficiency issues.
It’s a good idea to run full scan acquisition on a representative sample to visualise potential co-elution problems. Don’t just blame the ms for quantitation issues, many of these problems are due to ineffective sample prep or chromatographic separation.
loading data
loading data
loading data
loading data
loading data
 
 


Colin Towers
(BSc.(Hons), MRSC, C.Chem, GPhc)
 

This article was written by Colin Towers.

After graduating with a degree in pharmacy, Colin went straight into private industry to work as an analytical chemist. He did several years of high throughput routine QC testing using primarily HPLC, with several further years as an instrument troubleshooting and maintenance specialist on a variety of instrumental analytical techniques. The next roles led to a further 11 years on the bench in contract analytical testing as a method development / validation specialist, primarily in LC-MS/MS, GC-MS, HPLC, GC, AAS and SPE on a huge variety of applications. This was supplemented by a 3 year lecturing contract teaching the analysis of controlled drugs and analytical toxicology as part of a forensics degree course, then 2.5 years working as a community pharmacist in the East End of Glasgow.

Colin joined Crawford 3.5 years ago to work as a technical specialist, trainer and consultant.

'Initially self taught in LC-MS I learned the hard way, so if there's a mistake to be made or something to break, I've probably done it in my early stages. Years of practical, hands-on experience in operating singles, traps, triples, Q-TOFs and currently an Orbitrap. Coming from a contract background it's been drummed into me from an early age that everything has to be done as practically, quickly, accurately, reliably and compliantly as possible.'


 

group  subsCHROMacademy can deliver to corporate clients on a multi-user subscription basis.
Served up from secure servers to the corporate intranet or individual desktops.

  • Microsite - your own learning site powered by CHROMacademy
  • Your Landing Pages -with your logo and branding
  • Customized Assessments - Based on content agreed upon Certificate of Completion
  • Certification Programs - Offer your learners a goal to strive towards
  • LMS : Connect - Our Learning Management System is S.C.O.R.M. compliant and will connect to your system
  • Engagement Package - E-newsletter stimulation program derived from your content and ours
  • Full archive of Essential Guide webcasts & tutorials
  • 1000’s of eLearning topics - HPLC / GC / Sample Prep / Mass Spec
  • Ask the Expert - our experts will answer your chromatography questions within 24 hrs.
  • Assessments - test your knowledge
  • Application notes & LCGC articles
  • Troubleshooting and virtual lab tools

Request a quote

 

 
 Home | About UsContact Us | SubscribeTerms and Conditions | Advertise | Privacy Policy 

loading data

loading data

loading data

 

loading data


loading data