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Chlorophyll is one of the most problematic matrix co-extractives in pesticide residue analysis because of its non-volatile characteristics. When samples containing chlorophyll are injected into a gas chromatography (GC) system, chlorophyll accumulates in the GC inlet and GC column, causing active sites and affecting GC performance. Graphitized carbon black (GCB) is widely used to remove chlorophyll from fruit and vegetable samples. However, GCB will strongly adsorb planar pesticides, such as carbendazim and thiabendazole, resulting in low recoveries. To resolve this issue, UCT has invented a novel sorbent, ChloroFiltr®, to remove chlorophyll from QuEChERS extracts without sacrificing the recovery of planar pesticides. ChloroFiltr® should not be used for mycotoxin analysis.
1. Weigh 10 g of homogenized spinach sample into a 50-mL centrifuge tube (ECPAHFR50CT).
2. Spike with 100 μL of 50 ppm triphenyl phosphate internal standard.
3. Vortex for 30 s and equilibrate for 15 min.
4. Add 10 mL of acetonitrile, shake for 1 min.
5. Add salts in Mylar pouch (ECQUUS2-MP), shake vigorously for 1 min.
6. Centrifuge at 5000 rpm for 5 min. The supernatant is ready for cleanup.
Extraction and Clean-up Materials
1. Transfer 1 mL supernatant into a 2-mL dSPE tube (with ChloroFiltr® or GCB), shake for 30 s.
2. Centrifuge at 10,000 rpm for 5 min.
3. Transfer 0.4 mL of the cleaned extract into a 2-mL autosampler vial.
4. The sample is ready for liquid chromatography tandem mass spectrometry (LC–MS–MS) analysis.
Figure 1: Crude spinach extract (a) cleaned with ChloroFiltrÂ® (b) is less green than that cleaned with graphitized carbon black (GCB) (c), indicating that ChloroFiltrÂ® is more efficient in chlorophyll clean-up.
LC–MS–MS parameters and multiple reaction monitoring (MRM) transitions are available upon request.
The recoveries of carbendazim, thiabendazole, pyrimethanil and cyprodinil were adversely affected by GCB, especially thiabendazole with a much lower recovery of 55.9% compared to 93.2% obtained by ChloroFiltr®. Diazinon, pyrazophos and chlorpyrifos were less or not affected by GCB because of the non-planar side chains in their structures.
Table 1: Comparison of pesticide recoveries and RSDs obtained by dSPE clean-up of spinach sample using ChloroFiltrÂ® and GCB (n = 4).
ChloroFiltr®, a novel sorbent, is found capable of removing chlorophyll efficiently without affecting the recoveries of planar pesticides. ChloroFiltr® offers a successful substitute for GCB in chlorophyll removal.
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