The Number One Reason GC-MS Sensitivity Matters
Posted on October 30th, 2015
It determines the complexity, cost and efficiency of your sample preparation.
When you design an analytical process for trace analysis, detector sensitivity is a critical parameter. In fact, if you are smart, it’s where you start.
To achieve the limit of detection required, your method must deliver enough molecules to the mass spectrometer for the resulting signal to be at least 3 times greater than the noise. The better the signal to noise ratio that you end up with – the more robust your method will be.
Over the years GC-MS performance has improved dramatically. You can see how big the changes have been by comparing the installation specifications for Agilent GC-MSDs shown here:
1980’s GC/MSD installation spec in EI ng level
1990’s high pg level
2000’s mid pg level
2010’s low pg level
For the Agilent 7000C QQQ we’re at low fg and for the 7010 QQQ sub-fg levels.
When mass specs were less sensitive, we all had to work harder.
To compensate for a lack of sensitivity, we had to do all or some of the following:
- Extract a large volume of samples
- Concentrate the extracts
- Inject large volumes of extract into the GC-MS
This held true for gas, liquid and solid phase samples.
Working with large volumes of sample is always slow, inconvenient and expensive. It is also difficult and very expensive to automate – so you were usually stuck with a largely manual process.
Sample concentration will involve an evaporative process, solid phase extraction or, in the case of volatiles, trapping and desorption.
Large volume injection is less taxing than the others, but developing a robust sample preparation method required skill, many didn’t have.
Every additional step in your sample preparation represents an opportunity for things to go wrong:
- Analytes losses always occur to some extent
- Contaminants will be introduced
- Mistakes will be made and errors will arise
As Mass Spectrometers have got more sensitive, it has becomes possible to greatly simplify sample preparation and simpler is always better.
If you continue to prep your samples by hand, increased sensitivity is a huge benefit . You will do less work on each sample and get better quality results into the bargain.
There is a further large benefit that flows from this; it opens up the use of automated sample preparation for more analytical processes.
Automated sample preparation reduces the amount of work needed to prepare each sample by as much as 90%, data quality improves with less human intervention and you can get a lot more done at lower cost.
As the performance of mass spec improves, clearly, our thinking about sample preparation should change. Often, this doesn’t happen.
This results in an awful lot of unnecessary work and an awful lot of waste.
If you have a method that might benefit from being automated, our lab team can look at this for you, carry out an assessment and advise upon its suitability for automation. We will do this for free.
If you want to discuss your application, just give us a call on +44 (0)1223 279210 or email email@example.com.
Thanks to Chris Sandy of Agilent Technologies for the information on MSD sensitivities.