translocated into the terminal buds and subtending internodes in amounts that inhibited terminal bud growth and induced internodal abscission. During the development of these responses, the lateral buds apparently did not absorb sufficient A'-(3-nitro-l -naphthyl)phthalamic and Ar-(5 -acenaphthenyl) phthalamic acids at the dosage levels used to inhibit their subsequent growth. It is probable that any residual amounts of these compounds became inactive during this period as far as growth inhibition was concerned, since there was no evi-DEFOLIANT RESIDUES dence of inhibitory or formative effects on axillary buds that developed subsequently.

Residues of both dimethoate and dimethoxon are extracted from finely chopped plant or animal tissues with methylene chloride. The resulting extract is concentrated and cleaned up by silica gel chromatography, if necessary. The concentrate is injected into a gas chromatograph equipped with either a flame photometric or an alkali flame ionization detector and a column containing 11% DC-200 on 60–80 mesh Gas-Chrom Q/0.01% Versamid 900. Recovery values for dimethoate and dimethoxon added a t 0.002–1.0 p pm ranged from 56 to 112% with an overall average of 89.2% for dimethoate and from 60 to 127% with an overall average of 81.9% for dimethoxon. The lower limit at which recovery values were obtained for both compounds was 0.05 p pm for plant tissues, 0.02 for animal tissues and eggs, and 0.002 for milk. Residue values obtained for animal tissues involving both exposure and feeding studies a n d for field-treated plant samples are also presented.

A gas-liquid chromatographic (GLC) method is described for determining sulfonamide residues in animal tissues, with specificity for 7 sulfonamides. Residues are extracted from tissues with acetonechloroform, fatty substances are removed, and the sulfonamide residue is methylated with diazomethane in acetone-ether to render it amenable to determination by gas-liquid chromatography on an all-glass column suitable for direct on-column injection and a Ni electron-capture detector. Quantitation is achieved by external standardization. The method has a validated limit of sensitivity of 0.10 ppm with the corresponding control values for all tissues being less than 0.01 ppm. Satisfactory recoveries have been obtained for sulfamethazine in swine and cattle tissues. Specificity for sulfamethazine in the presence of sulfathiazole, sulfaquinoxaline, sulfadimethoxine, sulfabromomethazine, sulfaethoxypyridazine, and sulfachloropyrazine is attained by resolution of the respective methyl derivatives on the GLC column.

A total phosphorus method incorporating thin-layer chromatographic isolation is described for the determination of Cygon Insecticide (generic name, dimethoate) and its oxygen analog. Residues of the insecticides are extracted from macerated plant tissue, and the extract, after solvent partitioning and concentration, is spotted on a thin-layer chromatographic plate. After development of the plate, the areas corresponding to the two compounds are scraped and eluted. The phosphorus content of the respective eluates is determined by an improved molybdenum blue method, and concentrations of dimethoate and its oxygen analog in the original samples are calculated.

A gas chromatographic (GC) method has been reported for the determination of sulfamethazine residues in cattle and swine tissues. The extracts from this procedure were found to be directly amenable to examination by gas chromatography–mass spectrometry (GC-MS), allowing positive confirmation of an apparent residue of sulfamethazine. Chemical ionization mass spectrometry (CIMS) was chosen as the MS technique because it generated an ion indicative of intact sulfamethazine and fragment ions indicative of the amine functionality and sulfanil moiety. Positive ion (PI) chemical ionization mass spectrometry was adequate by itself for a confirmatory technique. Negative ion (NI) chemical ionization mass spectrometry alone could not be used for the confirmatory analysis of sulfamethazine, but it did offer a means to check the quantitative data from the positive ion analyses and provided complementary confirmatory data. Satisfactory recoveries were obtained for sulfamethazine in swine and cattle tissues at the tolerance level of 0.1 ppm. Apparent sulfamethazine residues in control tissues were less than 0.01 ppm.