A mass spectrometer is likely to be the most expensive investment you make in an analytical lab. If you are making this investment then the last thing you want is your mass spectrometer procrastinating and sitting there idle while it waits for the next sample to elute from your (U)HPLC. You want your mass spectrometer analysing to be almost continuous to ensure you are getting maximum value and return-on-investment (ROI) on your outlay. In conventional LC-MS, the mass spectrometer is typically procrastinating about 30% of the time. In fact this goes for any liquid chromatography detector, not just a mass spectrometer. So how do you stop the mass spectrometer from procrastinating and make sure it pays you back?
Stopping Procrastination
The easiest way to stop your mass spectrometer from procrastinating is to perform Tandem LC-MS. In this approach you simply use two pumps in your HPLC set-up, two identical columns and column switching valves in your column compartment. On the first column you perform your analytical separation, whilst in parallel you re-equilibrate the second column. Then at the end of the analytical separation you simply switch the two columns (the analytical separation now occurring on the second column and the first column re-equilibrates). This ensures a sample is always presented to the mass spectrometer and you have removed the time the mass spectrometer sits idle whilst the column re-equilibrates. As an added bonus, you can also perform more stringent and extended column washes as most analytical gradients give the time to achieve this.
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Tandem LC-MS Is Not New
Now, Tandem LC-MS is not completely novel. It has been possible to do in the past, but it has not become commonplace as it was complex to set up and implement. This has changed with the recent introduction of the Thermo Scientific™ Vanquish™ Duo UHPLC system. This system contains two pumps -- either individual modules or the unique dual pump --and most importantly, initiative and wizard-driven software control with Thermo Scientific Chromeleon™ CDS software to make operation as simple as a standard HPLC system. This is demonstrated in this application note which uses the Tandem LC-MS approach to increase peptide mapping throughput and productivity. The application note also shows the use of two binary pumps rather than a dual pump if high-pressure gradient (HPG) pumps are preferred to low-pressure gradient (LPG) pumps.
What’s the downside?
This all sounds too good to be true, there must be some downside to this? Well, there is one small downside in that a dual gradient pump costs slightly more than a standard single gradient pump, but then I think that is a small price to pay to stop your mass spectrometer procrastinating. Can you really afford for your mass spectrometer to be sitting idle 30% of the time? Now, it’s time for me to start procrastinating about going for that run….
Additional Information
- More information on the Vanquish Duo UHPLC and its workflows (Dual LC, Tandem LC or LC-MS and Inverse Gradient) can be viewed in these on-demand webinars in English, French, German, Italian and Spanish
- Which HPLC system is the best fit for your application? Compare your options in the HPLC System Selection Guide
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