Alachlor residues were determined in pepper and pepper leaf, after 49 days of manufacturer-recommended single- and double-dose application to the soil and plant. The samples were extracted with acetonitrile, partitioned with n-hexane, and purified through solid-phase extraction, and finally detected with a gas chromatography-microelectron capture detector. The linearity of the analytical response across the studied range of concentrations (0.05-4.0 µg/mL) was excellent, obtaining coefficients of determination (r(2) ) of 0.999. Recovery studies were carried out on spiked pepper and pepper leaf samples, at two concentrations levels (0.2 and 1.0 mg/kg), with three replicates performed at each level. Mean recoveries of 73.1-109.0% with relative standard deviations of 1.3-2.3% were obtained. The method was successfully applied to field samples, and alachlor residue was found in pepper (0.02 mg/kg) and pepper leaf (0.03 mg/kg), at levels lower than the maximum residue limits (0.2 mg/kg) set by the Korea Food and Drug Administration. The field-detected residues were further confirmed with gas chromatography-mass spectrometry with the help of pepper leaf matrix protection.

Fenvalerate, a non-systematic insecticide is extensively used for protection of tea leaves in Bangladesh. Excessive use of insecticides with improper pre-harvest intervals may cause the tea unsuitable for consumption and trade. The study was designed to determine the safe perharvest interval after the application of fenvalerate on tea trees at two different doses. Fenvalerate was applied on tea plants in experimental plots at the full and half of the recommended doses (0.1 kg a.i /ha and 0.05 kg a.i /ha, respectively). Tea leaves were collected at 0 (2 h after application), 1, 3, 5, 7, 10 and 14 days after application of the insecticide and made into black tea which was infused with hot water. Both brew and brew free residue were extracted, cleaned up and analyzed by GC-ECD. The residue levels in the brew were 0.189, 0.033 and 0.007 mg/kg at zero, 7 and 10 days, respectively, when it was applied at half of the recommended dose. In case of the recommended dose, residue levels were 0.644 and 0.010 mg/kg at 0 and 10 day, respectively. Residues were below the maximum residue level (MRL: 0.1 mg/kg) on 5 day at half of the recommended dose and on 7 day at recommended dose. Dissipation of fenvalerate followed first order kinetics at both doses with half lives of 2.6 days in brew part and 4.6 days in brew free part. Recoveries were 6.56±0.003% and 90.6±0.033% in brew part and brew free residue part, respectively, giving a total recovery of 96.6±0.036%. LOD and LOQ were 0.002 and 0.006 mg/kg, respectively.