Analysis of Complex Natural Products by GC/MS(MS) with Column Backflushing

Abstract

The GC/MS analysis of natural products is complicated by the fact that extracts usually contain compounds of low volatility that are difficult to elute from a GC column. These compounds may decompose in a hot GC inlet or accumulate in the GC column, resulting in retention time shifts, carryover, loss of sensitivity, and MS source contamination. Traditionally, the answer to these issues was to clean up the sample extract prior to analysis. However, extensive cleanup takes extra time, increases the cost of analysis, and may result in analyte loss. Backflushing is a technique that reverses the flow through all (or a portion of) the GC column after the analytes of interest pass a pneumatic junction. Highly retained compounds that have not passed this junction are eluted backwards through the column and pass through the inlet's split vent. This technique reduces or eliminates retention time shifts, carryover and source contamination, making the method much more rugged. This technique has been applied to the analysis of botanicals for pesticide residues, fish oils for PCB contamination and olive oil for authentication. The oil samples were simply diluted in solvent before injection. Without backflushing, all three sample types caused serious chromatographic problems, even after only one injection. With backflushing, all three methods proved to be very rugged.