Colorimetry and High Performance Liquid Chromatography of Atrazine Residues in Soil: Comparison of Methods

The colorimetric method for determining residual atrazine levels in soil is compared with reverse phase high performance liquid chromatography (HPLC). The soil samples are extracted with water-acetonitrile (10 + 90) and the filtrate is partitioned with methylene chloride. For the colorimetric analysis the organic phase is filtered through activity V alumina, collected, and evaporated to dryness. The residue is dissolved first in ethyl ether, and then in water as the ether is removed. The atrazine solution is buffered (citric acid, pH 7.0) and heated with added pyridine. When the reaction is complete, the product is complexed with ethylcyanoacetate, and the solution absorbance is measured at 550 nm. The complex obeys Beer’s law and has a sensitivity of 230 ng for a 1% full scale deflection at 1 AUFS. For the HPLC method, the methylene chloride extract is dried, the chromatographic solvent is quantitatively added (either chloroform or methanol), and the solution is analyzed with a UV detector at 254 nm. Minimum amount detectable for a 1% full scale deflection is 5 ng at 0.01 AUFS. Soil background interferences were investigated for both methods, and buffering the pyridine-triazine reaction solution was the most efficient method for removing the background for colorimetry. The recovery efficiencies for the colorimetric and HPLC methods were 45.5 ± 3.8% and 94.4 ± 3.4%, respectively.

Gas-Liquid Chromatographic Analysis of N-(4-Chlorophenyl-N′-2,6-difluorobenzoyl)urea Insecticide After Chemical Derivatization

The gas-liquid chromatographic analysis of TH 6040 (N-(4-chlorophenyl)-N′-(2,6-difluorobenzoyl)urea) was carried out after the insecticide was converted to its N,N′-dimethyl analog (N-methyl-N-(4-chlorophenyl)-N′-methyl-N′-(2, 6-difluorobenzoyl)urea). The methylation was accomplished in DMSO with sodium hydride and methyl iodide. The derivative was thermally stable and chromatographed as a single peak on 3% OV-1 at 235°C. Support for the structure of the product was given by mass spectrometry. The sensitivity of the product to electrolytic conductivity detection was approximately 50 ng for 50% full-scale deflection in the nitrogen mode and 70 ng for the same response in the chloride (reductive) mode. About 0.25 ng was required for 50% full-scale deflection by electron capture (at 1 × 10−9 amp standing current). Foliage samples were analyzed for TH 6040, using the proposed method.

Simple Automated Spectrophotometric Method for Assay of Trypsin and Chymotrypsin in Duodenal Juice

Trypsin and chymotrypsin were automatically assayed by a simple spectrophotometric method, with specific ester derivatives as substrates. Samples containing 0.25 to 2.5 enzyme units in 0.5 ml were analyzed at a rate of 40 to 60 assays per hour, each sample being incubated for 6 min. The acidity developed during esterolysis was measured, with phenol red as the acid—base indicator. The full-scale deflection of the recorder, corresponding to 0.5 absorbance at 420 nm, was obtained with a sample containing 5 U of enzyme per milliliter, incubated in Tris-HCl buffer (25 mmol/liter, pH 8.0), in the presence of phenol red (124 µmol/liter). This variation corresponded to a decrease of 0.4 pH unit.

DESIGN AND OPERATION OF A 'MEAN DEVIATION METER'

An instrument was constructed and calibrated to measure the mean deviation of the counting rate from a series of pulses that are not uniformly spaced. Two resistance–capacitance 'memory' circuits measure the instantaneous and the average counting rates. A rectifier bridge circuit is used to compute the relative deviation. Over a large part of the range the response is linear and reproducible within 5% for full scale deflection. The instrument is used in conjunction with the counting of radioactive radiations; other uses are discussed.