Determination of methomyl insecticide residues in tomato and cucumber fruits by high performance liquid chromatography: kinetic study

A sensitive high performance liquid chromatographic method using ultraviolet detector has been developed for the determination of methomyl insecticide residues on tomato and cucumber fruits. The developed method consisted of extraction with ethyl acetate, adsorption clean up [by adsorbing mixture consisting of charcoal/celite in ratio 2: 1], followed by high performance liquid chromatographic determination using methanol: water [1: 1] as a mobile phase and UV detection at 233 nm. The range of percentage recovery was between 88.2% and 90.4% for both plant samples. [These recoveries are good for those types of extraction of pesticides traces from plant materials, refer to [1] to compare recoveries]. The method was applied to determine residues and rate of decline of methomyl from fruits of tomatoes and cucumber [open field and greenhouse treatment, with methomyl formulation [Lannate 90% SP] for 100 liter water]. The insecticide incorporated into the plants decreased rapidly with a half-life around 1 day in winter and 0.5 day in summer

Simultaneous determination of bisoprolol Fumarate and hydrochlorothiazide in tablets by derivative spectrophotometry and densitometry

Derivative spectrophotometry [second and fourth] and densitometry were used to determine bisoprolol fumarate [I] and hydrochlorothiazide [II] simultaneously in combined pharmaceutical dosage form. Using second derivative spectrophotometry, the amplitudes in the second derivative spectra at 272.6nm and 284.8nm were selected for simultaneous determination of [I] and [II], respectively, in the mixture. Where, the HZ concentration was calculated from the amplitude at 284.8 nm [where BSF showed no absorbance] and BSF concentration was calculated from the amplitude at 272.6 nm after subtraction of the amplitude due to HZ. While, applying fourth-derivative spectrophotometry technique, the peak amplitudes at 289.8 nm and 272.8 nm were selected to determine [I] and [II], respectively. The calibration graphs were linear in the range of 30-280 microg/ml for [I] and 3-24 microg/ml for [II] in both methods. Furthermore, a densitometric procedure with ultraviolet detection at 223nm was applied using chloroform: ethanol: Glacial acetic acid [7:3:2 by volume] as a developing system. The plot of peak area of [I] and [II] to the respective concentrations of each drug was found to be linear in the range of 2.5-30micro g/spot and 1-7 micro g/spot, respectively. The suggested methods were used to determine both compounds in synthetic mixtures and in commerical tablets. The validity of the proposed methods was further assessed by applying standard addition technique. The obtained results were statistically compared with compandial HPLC method, showing no significant difference with respect to accuracy and precision