Short Chain Fatty Acids (SCFA's) may be best known for their unpleasant odors, but they are also key indicators of serious human digestive disorders such as colorectal cancer and celiac disease. Unfortunately, the SCFA's are not easy to measure and the matrix is...poop! Current methods involve extensive sample preparation: pH adjustments, water / ether extractions, filtering, etc. The excessive sample manipulation leads to a sacrifice in precision and sensitivity. Fortunately, this can all be mittigated by applying modern chromatography technology to legacy methods. The first method improvement involved reducing sample preparation from 6 steps to just one: water extraction. Historically, water is not injected into GC’s due to its excessive expansion coefficient (1200x). However, modern GC's can handle direct water injections by using a pressure-pulsed injection to dramatically reduce the volume of water vapor. The next method simplification employs headspace GC to eliminate the one remaining step of sample preparation: dissolving the sample. Headspace is best suited for the determination of volatile compounds in a complex matrix. There is no question as to the volatility of the analytes (they smell!) and the complexity of the sample “matrix”. The raw sample is placed into a headspace vial, and just the volatile compounds (SCFA) are injected into the GC. This approach leaves behind all of the non-volatile extractables and keeps the GC inlet much cleaner. The latest method improvement takes advantage of Solid Phase Micro Extraction (SPME). In this case, a fiber coated with an adsorbent is introduced to the vapor surrounding the sample: the volatile analytes stick to the fiber and release when inserted into the hot injection port. Imagine a method where the analyst simply waves their “magic wand” (SPME fiber) around the sample and then inserts it into the hot GC. These method improvements will allow medical researchers to analyze more samples on simpler equipment with greater sensitivity and precision…while reducing the amount of time the analyst has to spend with the malodorous samples!

GC saves lives! Determination of short chain fatty acids (SCFA) in human fecal samples

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