Fenitrothion [HRP]

A method for determining eight pesticide (cyhalothrin, flufenoxuron, fenitrothion, EPN, bifenthrin, difenoconazole, triflumizole, and azoxystrobin) residues in made green tea as well as a tea infusion (under various brewing water temperatures; 60, 80, and 100 degrees C) using gas chromatography (GC) micro-electron capture detector (mu ECD) was developed and validated. The extraction method adopted the relatively commonly used approach of solid sample hydration, with the green tea hydrated before being extracted through salting out with acetonitrile followed by a cleanup procedure. The analytes were confirmed using GC-coupled to tandem mass spectrometry (GC/MS/MS) with a triple quadrupole. The linearity of the calibration curves yielded determination coefficients (R-2) >0.995. Recoveries were carried out using blank samples spiked with all analytes at two levels. The results demonstrated that all pesticides were recovered within the range of 77-116% with a relative standard deviation (RSD) <= 14%. The quantification limits of 0.015-0.03 mg/kg were lower than the maximum residue limits (MRLs) set by the Korea Food and Drug Administration (KFDA) for all analytes (0.05-10 mg/kg). The infusion study indicated that cyhalothrin, flufenoxuron, and bifenthrin did not infuse into the tea brew from the made tea. Increases in brewing time resulted in increased transfer of azoxystrobin, fenitrothion, and difenoconazole from the made tea to the brew; however, this was not the case with triflumizole or EPN. We conclude that transfer of pesticides appeared to be dependent on their water solubilities and drinking a cup of tea is recommended to be at a water temperature of 60 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.

The second-order rate constants (k(OH)-) for the reactions of Y-substituted-phenyl diphenylphosphinates (4a-4i) with OH- in H2O at 25.0 +/- 0.1 degrees C have been measured spectrophotometrically. Comparison of k(OH)- with k(EtO)- (the second-order rate constants for the corresponding reactions with EtO- in ethanol) has revealed that EtO- is less reactive than OH- although the former is ca. 3.4 pK(a) units more basic than the latter, indicating that the reactivity of these nucleophiles is not governed by their basicity alone. The Bronsted-type plot for the reactions of 4a-4i with OH- is linear with beta(lg) = -0.36. The Hammett plot correlated with sigma(-) constants results in a slightly better correlation than that correlated with sigma(o) constants but exhibits many scattered points. In contrast, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation with rho = 0.95 and r = 0.55. The r value of 0.55 implies that a negative charge develops partially on the 0 atom of the leaving group. Thus, the reactions of 4a-4i with OH- have been concluded to proceed through a concerted mechanism.