Restek® Technical Posters
WEDNESDAY, APRIL 13
Be a GC Pro: Free-and-Easy Dry Lab Method Development and Method Improvement Tools
Rebecca Stevens (presenter)
Sign up at the SS AOAC registration desk on Tuesday or Wednesday morning!
For more information, e-mail Rebecca Stevens.
Gas chromatography (GC) method development can be a tedious and resource-intensive process. Time spent in the lab perfecting a method by making small changes to oven temperature and carrier gas flow could be better spent preparing and analyzing samples. Additional concerns about choosing an appropriate stationary phase and column dimension makes GC method development from scratch a complex problem. In this workshop, we will discuss some free online tools provided by Restek that can help streamline GC method development.
The Pro EZGC® chromatogram modeler is an application capable of producing model GC chromatograms under user-defined instrument conditions for hundreds of common target compounds including volatiles, semivolatiles, pesticides, and PCBs. Optimization of instrument conditions for any particular separation is simple and will be thoroughly demonstrated.
The EZGC® method translator and flow calculator is a convenient tool for translating existing GC methods between columns of different dimension or different carrier gases, as well as between standard detectors and mass spectrometry.
The difference between method development and method translation will also be explored because this distinction is critical when choosing the correct tool for a situation. The utility and accuracy of both tools will be demonstrated through worked examples and real world anecdotes from users.
Shoot-and-Dilute Gas Chromatography-Mass Spectrometry: Polycyclic Aromatic Hydrocarbons Quantification in Tea using Modified QuEChERS Extraction and No Sample Cleanup
Julie Kowalski (presenter), Amanda Rigdon, Jack Cochran
For more information, e-mail Julie Kowalski.
Food contamination with toxic polycyclic aromatic hydrocarbons (PAHs) occurs by exposure to environmental contamination and during food preparation, especially heat processing like smoking, grilling, and roasting. Consequently, foods must be tested to determine if they contain toxic PAHs. While classic sample extraction methods such as Soxhlet and pressurized fluid extraction (PFE) yield excellent recoveries for PAHs, they require expensive equipment/glassware, are solvent- and resource-intensive, and are relatively slow. The QuEChERS sample preparation method avoids these problems but produces a comparatively dirty sample. There are notorious problems associated with splitless injection of dirty samples, most notably for PAHs is decreasing response. This can occur very quickly with real samples, especially without exhaustive sample cleanup.
Methods to address these problems explored here included streamlined sample preparation and shoot-and-dilute gas chromatography-mass spectrometry (GC-MS). A modified QuEChERS extraction was paired with a simple silica solid-phase extraction (SPE) cleanup. This sample preparation method is much less resource intensive and provided satisfactory recovery of all PAHs tested. In addition, sample extracts without cleanup were also analyzed in order to determine if sample cleanup was necessary when combined with shoot-and-dilute GC-MS/MS. Shoot-and-dilute GC-MS/MS methods used split injection, which can alleviate matrix-related issues occurring at the GC inlet and column. Increased flow through the inlet during split injection minimizes poor response for involatile compounds (e.g., high molecular weight PAHs) and maintains acceptable data quality longer.
This work demonstrates that the ruggedness and sensitivity of shoot-and-dilute GC-MS/MS allows quantitation of the EU 15+1 PAHs in extracted tea samples without the need for sample cleanup. Incurred values at sub 10 ng/g levels were determined and proved similar to values determined via splitless injection GC-TOFMS. Ruggedness was evaluated by tracking PAH relative response factors for over 100 injections of tea extracts with no cleanup. Even with no inlet or column maintenance, response factors were consistent (less than 20% RSD) even for the highly nonvolatile dibenzopyrenes. The combination of split injection and highly sensitive GC-MS/MS allowed samples with low PAH levels to be quantified without sample cleanup and, at the same time, with prolonged system performance.