How do you use GC-MS in combination with other analytical techniques and tools?

One technique I have found to be very valuable to GC-MS users is Thermal Desorption. This pre-concentration technique enables users to take samples from the Air or Emitted from Materials and characterize Volatile and Semi-volatile organic compounds down to sub-ppt level. It is used in standardised methods for Air monitoring around the globe, but also for more niche applications like identifying the VOC profiles in Breath for disease diagnostics.

It is very important to know the context of the sample in preparation. For example, in the case of the development of an aroma in the flavoring industry, volatile compounds coexist and others are thermolabile. If distillation is chosen as sample preparation, it is possible that when the distillate is injected, then the fresh profile of the fruit is not obtained as expected but rather a cooked profile due to heating during sample preparation. That is why the idea must be developed that extraction methods are complementary and therefore none of them are infallible and they don't compete with each other. In that sense, opening your mind is essential.

In my experience SPME (Solid Phase Micro Extraction) is a useful tool for the fragrance industry as well as determining potential containments when exploring leachables and extractables. Combing GC-FID with MS via two columns using a dual inlet ferrule is a common method for obtaining comparative analysis from a single sample injection. If the original data was obtained using the same GC-FID setup the subsequent GC-FID and GC-MS separation run data analysis and correlation power are increased. For some targets GC-FID is also not the best ancillary detector in which case a method or laboratory can standardize on a different detector.

In my experience depending on the nature of the analysis sample preparation can also selectively enhance the final GC separation. In certain cases, SPME, super critical fluid extraction or even a preparative HPLC separation can be used manually or in an automated fashion to ensure separation of target compounds. These adjunct applications are combatable with standard GC analysis (1-column) or multidimensional system(s).

This is where the problem is going to become serious. It is necessary that there are chromatographer-spectrometrist users and not GCMS analyst users. Because the responsibility of creating correct mass spectral libraries is essential in the comparison. Many errors are already being noticed in the creation of structures and that depends solely on the user.

NIST hybrid search can be a powerful new technique for unknown identification. See my free course on using all the NIST mass spectral tools. https://littlemsandsailing.wordpress.com/2020/08/17/ms-master-class/ Also use accurate mass GC-MS and LC-MS data to identify unknowns using large "spectraless" databases accessed by SciFinder-n and ChemSpider. https://littlemsandsailing.wordpress.com/2011/05/01/unknown-identification-known-unknowns-with-accurate-mass-mass-spectrometry/ https://littlemsandsailing.wordpress.com/2011/05/22/accurate-mass-measurements-identifying-known-unknowns-using-chemspider/

Libraries should be used in addition to in line sample set standards, as well as a system suitability check in quantitative analysis. If possible, a analyst or at least instrument specific reference library using standards. The library can be augmented cumulatively with each successful run. Some acquisition systems accomplish a similar end point by using a blank or background subtraction automatically. Bracketing standards around each run maximizes data integrity. This is more common in HPLC-MS however applying the same approach and rigor to GC-MS serves to further reduce the level of uncertainty from the system as well as any independent or dependent analyst uncertainty (such as human error).

It is important to use orthogonal techniques or data points when assigning a structure to an unknown. Advances in this area include multi-technique searching which allow you to query reference datasets for multiple analytical techniques at once while providing you with the most confident match between all techniques. Common instrumentation that is used along with MS is FTIR, Raman, and NMR. For more advanced analyses, chemometrics or machine learning can be deployed for multivariate calibration and pattern recognition. As with any experimental technique, it's important to use appropriate DOE methodology to obtain statistically significant results.

The Griffin G510 portable GC/MS is a great compliment to anyone who uses FTIR and Raman instruments. The GC/MS can confirm the presence of compounds that the FTIR and Raman can identify, but it can also identify other components in the sample due to the separation using a GC column.