High-performance liquid chromatography for determination of α-tocopherol in vegetables

A simple method for the determination of α-tocopherol in vegetables is described. The procedure consists of the following steps: saponification, extraction, silica-column clean-up, and high-performance liquid chromatography. Elution time for D, L-α-tocopherol was 9.0 min using a Zorbax Sil (250 x 4.6 mm) column and an isocratic mobile phase of hexane-methanol (99.3 + 0.7), with a flow rate of 1 ml/min, and detection at 292 nm using a variable UV detector. The average recovery of α-tocopherol was 91.2%, and the minimum detectable amount was 0.1 mg/100 g of fresh vegetable tissue. This method is comparable to gas-chromatographic determination of α-tocopherol, but has fewer analytical steps and gives more reproducible results.

Determination of the Residues of Eleven Organophosphorus Insecticides in Job's-tears by Gas Chromatography with a Nitrogen-Phosphorus Detector

A simplified method for determining 11 organophosphorus insecticides (dichlorvos, methamidophos, acephate, diazinon, dimethoate, chlorpyrifos, malathion, parathion, quinalphos, methidathion, and ethion) in the Chinese herbal medicine Job's-tears is described. Standards were fortified into Job's-tears (5 g) at 4 levels. The organophosphorus insecticides were extracted with dichloromethane and cleaned up with a mixture of Celite 545–activated carbon (4 + 1). The extracts were analyzed by gas chromatography using a nitrogen-phosphorus detector. Analysis of fortified Job's-tears shows average recoveries ranged from 73.90–98.70%, 86.31–93.15%, 84.92–96.22%, and 83.29–104.23% at 0.05, 0.1, 0.5, and 1.0 mg/kg levels, respectively. The minimum detectable amount ranged from 1.0 × 10−10 to 5.0 × 10−10 g, and the limit of quantitation for the method was 0.05 mg/kg. The method is rapid, simple, sensitive, reproducible, and applicable to the determination of these 11 organophosphorus insecticides in Job's-tears.

Determination of Fumonisin B1 and B2 in Corn and Corn-Based Products in Turkey by High-Performance Liquid Chromatography

The purpose of this study was to investigate fumonisin B1 (FB1)- and B2 (FB2)-contaminated corn and corn-based products consumed especially by the Turkish population. FB1 and FB2 were detected using high-performance liquid chromatography with fluorescence detection. The total number of commercially available corn and corn-based product samples analyzed in this research was 82. The recoveries were found to be 94.4 ± 4.62% and 86.5 ± 4.86% for cornmeal spiked with known amounts of FB1 and FB2 (1 ppm), respectively. The minimum detectable amount for the o-phthaldialdehyde derivatives of FB1 and FB2 were 1 ng and 5 ng, respectively. Detected levels of FB1 were between 0.25 ppm and 2.66 ppm in 25.6% of the samples, and detected level of FB2 in a single cornmeal sample was 0.55 ppm.

Elimination of caffeine interference in HPLC determination of urinary nicotine and cotinine.

We report an analytical reversed-phase liquid-chromatographic procedure for quantifying nicotine and cotinine in urine, taking into account the presence of interfering caffeine frequently encountered in such specimens. These analytes are extracted from the alkalinized urine with chloroform. After evaporation of the chloroform, the residue is dissolved in methanol and injected into a chromatographic C18 column. Extraction recoveries averaged 80% to 97%. Chromatographic conditions were investigated to obviate caffeine interference. The proposed eluent mobile phase is a polar mixture of water, acetonitrile, methanol, and a pH 4 acetoacetate buffer (65/2/29/4 by vol) adjusted to pH 4.30 +/- 0.02 with triethylamine. High resolution and linearity were obtained for each analyte up to a concentration of 200 mg/L. The minimum detectable amount of each compound was 20 ng per injection, corresponding to 10 micrograms per liter of urine. Correlation with results of gas-liquid chromatography was excellent (r = 0.99). This simple, rapid procedure allows routine screening of tobacco exposure with acceptable precision: within- and between-run coefficients of variation were less than 2% and less than 5%, respectively.

Rapid, simplified radioimmunoassay of arginine-vasopressin and atrial natriuretic peptide in plasma.

We have improved a radioimmunoassay for arginine-vasopressin (AVP) and atrial natriuretic peptide (ANP) by using Sep-Pak C18 cartridges to extract AVP and ANP from acidified plasma. The analytes are co-eluted by use of a mobile phase consisting of 1,2-dimethoxyethane and 40 g/L aqueous trifluoroacetic acid (95/5, by vol). After rapid evaporation of the solvents, AVP and ANP are assayed by a nonequilibrium radioimmunoassay method in which commercially available antibodies and radiolabeled antigens are used. The bound fractions are separated from the free by use of polyethylene glycol with human gamma globulin and rabbit anti-human IgG as the second antibody. This results in very low nonspecific binding: 0.44% for the ANP assay, 0.70% for AVP. The minimum detectable amount of ANP is 0.39 pg per tube; for AVP, it is 0.13 pg per tube. Compared with other published methods, this method is substantially more reliable, economical, and easily established in a clinical chemistry laboratory.