Troubleshooting analytical instrumentation can be a cumbersome process. If we remember a few rules, the task can be simplified. First, take a moment to review the manuals for the instrumentation. Second, examine the facts and use valid reasoning to identify the root cause of the problem. Concentrate on anything that may have changed, like a column, trap, etc. Avoid “quick fixes” as they may cause more problems down the road. The most important thing is to be patient.
Finding the root cause of the problem might be easier said than done due to the multiple components employed for the analysis (MS, GC, Concentrator, and Autosampler). Here, we can use common problem solving techniques, to help simplify the process. If we can break down the system into simpler components and ensure that the most basic parts are functioning properly, we can build upon them to isolate the problem.
As an example, we’re having a problem with a Purge and Trap-GC/MS analysis. Let’s split the system into four separate entities (Figure 1).
Figure 1: Splitting the system into four separate entities.
First, we need to eliminate the GC/MS. To do this, it is not necessary to disconnect the Purge &Trap from the inlet of the GC. Confirm normal operation of the MS by ensuring the MS is tuned correctly and the vacuum is holding stable. If there is an issue in this step, simply cleaning the source might help correct it. Once the MS is ruled out, the next step is to confirm normal operation of the GC. This is done by direct injecting a standard used in the P&T on to the GC. If you observe poor chromatography, poor resolution, or reduced response, there could be an active site within the GC. To eliminate this active site, perform injector maintenance or a simple clip of the column to correct this problem.
Once the GC/MS is eliminated as a source of any issues, proceed to the concentrator and the autosampler. To confirm normal operation of the P&T concentrator, leak check the system to make sure the PTC is leak tight. From diagnostics, run a benchmark test to ensure all the components are operating properly. One way to eliminate the autosampler is by manually loading a sample using a Luer lock syringe and run the analysis. Are the analytes getting to the GC/MS? If not, then check the gas flow and make sure you can see the sample being purged. You can also check the sample log in our Teklink software for historical purge pressures.
Once the P&T and GC/MS are ruled out, the last component to check is the autosampler. Confirm normal operation of the autosampler. If no sample is being transferred to the P&T, check to see if the sample is being pulled from the vial and that the valves are working correctly.
By breaking the instrumentation down into separate components, troubleshooting becomes a much more manageable task. Check the manuals and be methodical in your approach. Concentrate on anything that has changed since the last time the instrument was run. Always remember: avoid the quick fix and be patient.