Determination of low-level agricultural residues in soft drinks and sports drinks by gas chromatography with mass-selective detection: single-laboratory validation

In this study, sponsored by PepsiCo Inc., a method was validated for measurement of 19 pesticide residues in soft drinks and sports drinks by gas chromatography/mass spectrometry (GC/MS) with mass selective detection The pesticide residues determined in this validation were alpha-benzenehexachloride (BHC); beta-BHC; gamma-BHC; delta-BHC; methyl parathion; malathion; chlorpyrifos; aldrin; 2,4-dichlorodiphenyldichloroethylene (DDE); alpha-endosulfan; 4,4-DDE; 2,4-dichlorodiphenyldichloroethane (DDD); dieldrin; ethion; 4,4-DDD; 2,4-dichlorodiphenyltrichloroethylene (DDT); beta-endosulfan; 4,4-DDT; and endosulfan sulfate when spiked into a 200 mL matrix sample at 0.50 microg/L. The samples were diluted with acetonitrile and water, then liquid-liquid phase extracted into petroleum ether. The resulting extract was concentrated to near dryness and diluted with hexane:dichloromethane (50:50). The concentrated samples were purified by gel permeation chromatography. The resulting solution was concentrated and separated on a Florisil substrate. The eluent was concentrated to near dryness, reconstituted to produce a 200-fold concentration, and analyzed using a GC/MS instrument operated in the selective ion monitoring mode. The GC/MS instrument was equipped with a large volume injector capable of injecting 25 microL. External standards prepared in dichloromethane were used for quantification without the need for matrix-matched calibration because the extraction step minimized the matrix effects. The calibration curves for all agricultural residues had coefficients of determination (r2) of greater than or equal to 0.9900, with the exception of one value that was 0.988. Fortification spikes at 0.50 microg/L in 3 matrixes (7UP, Gatorade, and Diet Pepsi) over the course of 2 days (4 days for Gatorade), where n=8 each day, yielded average percent recoveries (and percent relative standard deviations) as follows (n=64): 95.6 (24.8) for alpha-BHC; 91.9 (23.6) for beta-BHC; 89.1 (21.3) for gamma-BHC; 91.7 (19.0) for delta-BHC; 96.2 (20.1) for methylparathion; 99.8 (26.5) for malathion; 120 (27.3) for chlorpyrifos; 103 (31.4) for aldrin; 111 (25.8) for 2,4-DDE; 116 (21.1) for alpha-endosulfan; 132 (34.6) for 4,4-DDE; 123 (34.4) for 2,4-DDD; 104 (20.8) for dieldrin; 141 (31.4) for ethion; 107 (24.5) for 4,4-DDD; 142 (29.2) for 2,4-DDT; 130 (35.9) for beta-endosulfan; 146 (25.3) for 4,4-DDT; and 91.5 (21.6) for endosulfansulfate.