Use of a centrifuge in solid-phase extraction is a valid platform for cleanup in the high-throughput analysis of chemical contaminants in nonfatty and fatty foods

Abstract

In recent years, the “quick, easy, cheap, effective, rugged, safe, efficient, and robust” (QuEChERSER) mega-method was developed for sample preparation and analysis of pesticides, environmental contaminants, veterinary drugs, and other residues in a wide variety of foods. In addition to wider analytical scope, QuEChERSER has many other advantages over the previous QuEChERS method, such as better cleanup for improved quality of results. For example, automated robotic mini-cartridge solid-phase extraction (µ-SPE) has been shown to provide excellent cleanup prior to gas chromatography - tandem mass spectrometry (GC-MS/MS) analysis. However, not all laboratories have the resources and expertise needed to adopt the robotic method. To address this limitation, a new approach is herein introduced using centrifugal µ-SPE as a simpler and lower-cost alternative using the same commercial mini-cartridges as the robotic version. In this study, both robotic and centrifugal µ-SPE were compared for the cleanup of QuEChERS and QuEChERSER extracts of 10 commodities (avocado, blueberry, egg, mixed grains, honey, bovine kidney/liver, whole milk, black olive, spinach, and tilapia) in the low-pressure GC-MS/MS analysis of 245 pesticides and environmental contaminants. QuEChERS extracts overwhelmed the sorbents in the mini-cartridges in most cases, leading to less cleanup and worse performance in the most complex matrices, but the 4-fold more dilute QuEChERSER extracts avoided that problem while still meeting detection limit needs. This study demonstrated that graphitized carbon black (GCB) was not needed for cleanup of samples that did not contain chlorophyll, and inclusion of more than 1 mg of GCB in the mini-cartridges led to <3 % recovery of certain structurally planar analytes. In QuEChERSER, analyte recoveries averaged 99 % in all matrices using both robotic and centrifugal µ-SPE, but robotic liquid handling demonstrated better precision of 4 % RSD compared to 6 % using the centrifugal option. Cleanup was also slightly better using robotic automation. Laboratories may choose either option in QuEChERSER (or QuEChERS) to achieve better cleanup, analytical performance, and greater ruggedness than the dispersive-SPE format commonly employed in this application for the past 20 years.