Two crops, lettuce and kale, were treated with a maneb formulation at a rate of 2.4 lb active/acre. Samples were harvested at various times after application for residue analysis. The residues determined were maneb and ethylene thiourea (ETU). On lettuce, residues of maneb decreased from 45 to 5 ppm in 15 days. On kale, the decrease was from 90 to 15 ppm in 7 days. With both crops, ETU which was already present in the formulation did not accumulate, but quickly decreased from 0.6 ppm to undetectable amounts after 7 days.

Chopped kale samples were fortified with maneb, zineb, or Dithane M-22, a maneb formulation. Samples were stored in a freezer or refrigerator and analyzed daily for 3 days. Using the carbon disulfide evolution procedure, the dithiocarbamate content in the samples was determined. Zineb was more stable than maneb or Dithane M-22 in both the frozen and refrigerated state. Immediately upon mixing, there was a loss of about 10% Dithane M-22 and 25% maneb. Freezing the samples prevented further losses.

A gas chromatographic method for the simultaneous determination of four dinitrophenolic herbicides [dinitrocresol (DNOC), dinitrobutylphenol (DNBP), dinitroamylphenol (DNAP), and dinitrocyclohexylphenol (DNOCHP)] in crops has been developed. After a 50 g sample was extracted with chloroform, a 10 g aliquot was concentrated and reacted with diazomethane to form the methyl ether derivatives. The sample was subjected to a two column cleanup step. acid-Celite and Florisil, and the residue was analyzed by GLC with an electron capture detector. Recoveries of fortification levels of 0.1 ppm DNOC and 0.2 ppm DNBP, DNAP, and DNOCHP exceeded 80%. The crops studied included green beans, pole beans, lima beans, peas, apples, and oranges.

Three different methylation procedures using diazomethane were evaluated on 2,4-D, 2,4,5-T, 2,4,5-TP, 2,4-DB, 2,3,6-TBA, DNOC, DNBP, and DNOCHP: (I) diazomethane alone, (II) diazomethane and methanol, (III) diazomethane, methanol, and HC1. Evaluations were made by comparing electron capture GLC peak heights or peak areas of reacted products with those of standards. Volatility losses were observed with method I. Completeness of dinitrophenol methylation varied with the lot of methanol used with methods II and III. From the results of this study, method I was modified by the addition of isooctane to the reaction vessel to prevent the sample from evaporating to dryness and the use of a 70°C water bath to speed up the reaction. Conversion of all pesticides by the modified procedure was over 90%.

Four dinitrophenol pesticides, DNOC, DNBP, DNAP, and DNOCHP, can be separated on cellulose thin layer plates, either as the phenols or their methyl ethers. Methyl ethers are prepared by reaction with diazomethane. Partition chromatography between an immobile phase of mineral oil and a mobile aqueous phase gives complete resolution. The compounds are revealed by spraying first with stannous chloride, then with p-dimethylaminobenzaldehyde to yield yellow-orange spots which fluoresce under UV light. The lower limit of detection in the phenolic form varies with the compound, ranging from 0.05 μg for DNOC to 0.3 μg for DNOCHP. The lower limit for the ethers is the same for all compounds, 0.1 pg.