Determining pesticides in dietary supplements with QuEChERS extraction, cartridge SPE, and GCxGC-TOFMS

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Courtesy of Restek Corporation

Regulatory requirements are driving the development of new multiresidue pesticide methods for dietary supplements. Minimizing matrix interference is critical for data accuracy. The novel approach employed here combines QuEChERS extraction, cartridge SPE cleanup, and GCxGC-TOFMS analysis, and results in good recoveries across a range of compounds found in these complex matrices.

Introduction
Dietary supplement manufacturers must now comply with the current Good Manufacturing Practice (cGMP) regulations that also guide the manufacture of pharmaceuticals. cGMPs require testing that ensures product safety, and, since many dietary supplements are botanically based, pesticide residue methods are among the new analyses being developed. Methods that minimize matrix interference are especially important, as plant-based dietary supplements are extremely complex and data integrity can depend on removing or reducing matrix contributions.

Existing procedures for agricultural commodities are a good starting point for multiresidue pesticide methods. For example, the QuEChERS approach to sample extraction and cleanup was first developed as a fast, easy way to prepare fruit and vegetable samples for pesticide analysis, but it can also be applied to other areas. In recent work [1], we used a QuEChERS extraction method [2] with cartridge solid phase extraction (cSPE) cleanup to prepare dietary supplement samples for pesticide residue analysis by GC/MS. For dandelion root samples, matrix interferences were substantially reduced by using the higher capacity cSPE cleanup, and recoveries for a wide range of pesticides reported in dietary supplements [3] were very good.However, in more complex samples, quantification bias appeared for some pesticides, leading us to consider a relatively new technique, comprehensive two-dimensional gas chromatography (GCxGC) with time-of-flight MS.

GCxGC offers greater potential for accurate pesticide determinations than single dimension GC, because resolution is enhanced by applying two independent separations to a sample in one analysis. GCxGC involves a serial column configuration (differing phases) separated by a thermal modulator. A separation is performed on the first column, and then effluent from the first column is continually (and quickly) focused and injected onto the second column. By keeping the second column short, a series of high speed chromatograms are generated, and the first column separation can be maintained. Separation results are plotted as a retention plane (column 1 time x column 2 time). Use of orthogonal stationary phases optimizes peak resolution.

This work shows the application of QuEChERS, cSPE, and GCxGC-TOFMS with an Rxi®-5Sil MS x Rtx®-200 column combination to quantify pesticides in dietary supplements. The approach used here reduces matrix interferences and improves accuracy relative to one dimensional GC-TOFMS.

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