Methods have been developed for the analysis of residues of a new soil insecticide, diethyl 1-(2,4-dichlorophenyl)-2-chlorovinyI phosphate (SD 7859, Birlane*) in a range of crops and soils. Enzyme inhibition procedures using plasma and fly-head cholinesterases and gas-liquid chromatography (GLC) can be used for the measurement of Birlane in crop and soil extracts down to a level of 0.01 pg/ml which corresponds to 0.02 ppm in the original sample at the normal sample/solvent ratios that are used.Treated soils may be stored for at least one month at -10" without decomposition of the Birlane residues and Birlane in solvent extracts is stable for at least one month at 0". Extraction procedures have been investigated using chloroform and acetone-hexane mixtures with different extraction times.Recoveries of Birlane average 95 "/, from soils at the 0.2-1 .O ppm level and average 100% from a range of crops at the 0.05-0.10 ppm level. Without clean-up, blank values of soil extracts can approach 0 . 2 ppm (using GLC) but are generally 0.05 ppm or less in crops apart from carrots. The interference, however, can readily be removed using column chromatography.
Crops and soils from a large number of field trials have been analysed for residues of 2,6dichlorothiobenzamide (chlorthiamid) and for residues of 2,6‐dichlorobenzonitrile (dichlobenil).
The thiobenzamide is converted to the benzonitrile after application to the soil and only a small percentage of the material applied initially remains unchanged after 4 weeks. However, both the benzonitrile and the thiobenzamide are of similar low mammalian toxicity.
The initial half‐life of the ‘total nitrile’ residues (the thiobenzarnide + the benzonitrile) is, on average, near 4 weeks but varies from 1 to 12 weeks depending on the locality, soil type, climate, dosage level and formulation.
The penetration of the herbicide into soils of different types is considered and it is shown that in sand, loam, and clay, residues in the 4–12 in. layer are less than 10% of the residue at the same time in the 0–4 in. layer.
Residues of the thiobenzamide and the benzonitrile could not be detected in a very wide range of crops (other than rice) harvested at 2–6 months after soil applications of the thiobenzamide at 1–16 lb/acre. In rice grains, where the plants can be in intimate contact with the herbicide, the ‘total nitrile’ residues did not exceed 0·05 ppm.
The use of lasers for the detection of fingermarks is widespread in the forensic field. Despite this, and the fact that many studies have been conducted into the composition of fingermark residue, the components responsible for the inherent visible fluorescence remain unidentified.
Traditionally compositional studies have been performed on sweat, sebum, or skin surface washes, none of which are truly representative of the situation when a fingerprint is deposited on a surface. In this paper thin-layer chromatography (TLC) has been performed on sebum-rich fingermarks laid directly onto TLC plates and an argon ion laser used to visualize the separated components. It has been found to be a robust and reproducible method for studying the fluorescent components in fingermark residue and is considered to be more realistic than other methods of sample preparation as it eliminates the chances of extraneous matter being extracted from the skin surface. Investigations into the nature of the separated compounds have also been made and the results are reported.
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