Simultaneous Determination of Chlorothalonil and Hexachlorobenzene in Technical and Formulated Materials by Capillary Gas Chromatography: Collaborative Study

A collaborative study was conducted for the capillary gas chromatographic (GC) method for the simultaneous determination of the fungicide chlorothalonil (CTL) and the accompanying impurity, hexachlorobenzene (HCB), in technical and formulated materials. The method calls for the dissolution of technical and dry formulations of CTL and HCB from the aqueous flowable formulation. The 10 participating laboratories were asked to analyze the samples by adhering to the method as closely as their instrumentation and data systems allowed, and to note any deviations from the method. Collaborators were asked to prepare the standards and samples, set up the capillary GC systems, analyze the samples, and calculate the results. CTL produced reproducibility relative standard deviations (RSDR) of 0.4–2.5 (active ingredient concentrations ranged from approximately 52 to 98% by weight). HCB produced RSDR values of 5.2–22% (HCB concentrations were 0.02–0.04% by weight). The method was adopted First Action by AOAC INTERNATIONAL.

Simultaneous determination of chlorothalonil and hexachlorobenzene in technical and formulated materials by capillary gas chromatography: collaborative study

A collaborative study was conducted for the capillary gas chromatographic (GC) method for the simultaneous determination of the fungicide chlorothalonil (CTL) and the accompanying impurity, hexachlorobenzene (HCB), in technical and formulated materials. The method calls for the dissolution of technical and dry formulations of CTL and HCB from the aqueous flowable formulation. The 10 participating laboratories were asked to analyze the samples by adhering to the method as closely as their instrumentation and data systems allowed, and to note any deviations from the method. Collaborators were asked to prepare the standards and samples, set up the capillary GC systems, analyze the samples, and calculate the results. CTL produced reproducibility relative standard deviations (RSDR) of 0.4-2.5 (active ingredient concentrations ranged from approximately 52 to 98% by weight). HCB produced RSDR values of 5.2-22% (HCB concentrations were 0.02-0.04% by weight). The method was adopted First Action by AOAC INTERNATIONAL.

Simultaneous Determination of Chlorothalonil and Hexachlorobenzene in Technical and Formulated Materials by Capillary Gas Chromatography

A capillary gas chromatographic method using flame ionization detection was developed for simultaneous assay of chlorothalonil and hexachlorobenzene in technical material and formulated products. Method precision is excellent, and the method allows simultaneous determination of one chemical impurity. The method uses an internal normalization reagent (n-butyl phthalate). Modification and extension of the method to formulated products, including wettable powders, water-based flowables, and dispersible (or dry flowable) granular formulations, are discussed. Preliminary statistical analysis of intra- and interlaboratory comparisons was performed to evaluate method ruggedness. Average relative standard deviations for technical materials were 0.34 and 0.17% from 2 laboratories. Additional method validation studies were conducted to examine the influence of pH, solvent systems, gas chromatographic systems, and temperature conditions on different formulations.

Some characteristics of nitrate reductase from higher plants

With respect to cofactor requirements, NADH, and FMNH(2) were equally effective as electron donors for nitrate reductase obtained from leaves of maize, marrow, and spinach, when the cofactors were supplied in optimal concentrations. The concentration of FMNH(2) required to obtain half-maximal activity was from 40- to 100-fold higher than for NADH. For maximal activity with the corn enzyme, 0.8 millimolar FMNH(2) was required. In contrast, NADPH was functional only when supplied with NADP:reductase and exogenous FMN (enzymatic generation of FMNH(2)).All attempts to separate the NADH(2)- and FMNH(2)-dependent nitrate reductase activities were unsuccessful and regardless of cofactor used equal activities were obtained, if cofactor concentration was optimal. Unity of NADH to FMNH(2) activities were obtained during: A) purification procedures (4 step, 30-fold); B) induction of nitrate reductase in corn seedlings with nitrate; and C) inactivation of nitrate reductase in intact or excised corn seedlings. The NADH- and FMNH(2)-dependent activities were not additive.A half-life for nitrate reductase of approximately 4 hours was estimated from the inactivation studies with excised corn seedlings. Similar half-life values were obtained when seedlings were incubated at 35 degrees in a medium containing nitrate and cycloheximide (to inhibit protein synthesis), or when both nitrate and cycloheximide were omitted.In those instances where NADH activity but not FMNH(2) activity was lost due to treatment (temperature, removal of sulfhydryl agents, addition of p-chloromercuribenzoate), the loss could be explained by inactivation of the sulfhydryl group (s) required for NADH activity. This was verified by reactivation with exogenous cysteine.Based on these current findings, and previous work, it is concluded that nitrate reductase is a single moiety with the ability to utilize either NADH or FMNH(2) as cofactor. However the high concentration of FMNH(2) required for optimal activity suggests that in vivo NADH is the electron donor and that nitrate reductase in higher plants should be designated NADH:nitrate reductase (E.C. 1.6.6.1).