To protect consumers' health, most countries have maximum legal limits for pesticide residues in foods. Trade difficulties can arise when limits differ between countries. The Codex Alimentarius Commission was established in 1962 to implement the Joint FAO/WHO Food Standards Programme, the purpose of which is to protect consumer health and ensure fair practices in international food trade. The Codex Committee on Pesticide Residues (CCPR), an intergovernmental body which advises the Commission on matters related to pesticide residues, is responsible for establishing maximum residue limits (MRLs) for pesticides in foods and feeds that move in international trade. Codex MRLs are based on residue data obtained mainly from supervised trials that reflect approved pesticide use in accordance with "good agricultural practice." MRLs must be toxicologically acceptable in terms of estimated pesticide intake by consumers. CCPR Working Groups examine problems related to establishing and implementing MRLs, including sampling and methods of analysis. Despite time and effort expended, acceptance and application of Codex MRLs face many problems in international trade.
A rapid procedure that involves treatment with sodium methoxide (NaOMe) solution is described for the qualitative confirmation of lindane (and other BHC isomers) residues in cereal, animal feed, meat, and fat samples. Losses encountered in the evaporation and partition steps are discussed. Optimum GLC conditions, both programmed and isothermal, for the separation of the 1,3,5-, 1,2,4-, and 1,2,3-trichlorobenzene products are given. Comparison of the NaOMe solution reaction with an alkaline pre-column technique revealed that the latter saved time in the analysis of cereal, animal feed, and cheese extracts. The alkaline pre-column method did not eliminate interferences in some meat and fat samples; the NaOMe solution reaction does eliminate these interferences. A lower level of 0.01 ppm lindane in a 10 g sample can be confirmed by the procedures described.
A study was undertaken to compare and evaluate the different types of 63Ni and 3H electron capture (ECD) and flame photometric detectors (FPD) as part of the Canadian Check Sample Program on Pesticide Residue Analysis. Twenty-seven laboratories were supplied with chlorpyrifos standard solutions for the determination of linear range and minimum detectable amounts (MDA). Each laboratory selected its own operating conditions except for the FPD study. Results for the FPD were compared with standardized flame conditions designed to optimize the exponential factor i, the S-mode. The MDA of the ECDs (pulsed and direct-current) ranged from 0.09 to 0.17 pg/sec for 63Ni and 3H sources respectively. The corresponding MDA for the linearized ECDs (pulse modulated or constant current) was 0.04 pg/sec and a linear range of 10(4) or greater with nitrogen as the carried gas. Use of argon/methane and a pulse width of 0.1 usec extended this range to 10(5) but the sensitivity was not as great as with nitrogen carrier gas. The practical limit of detector sensitivity was found to be instrument dependent depending primarily on the noise level. In the FPD study, operating in the P-mode gave an average MDA of 5.97 pg/sec and a linear range of 2 x 10(3). Similarly, the S-mode parameters were 81.1 pg/sec and 8 x 10(2) respectively with an average exponential factor of n 1.8. Attempts to apply optimized detector gas-flow conditions improved sensitivity and linearity in the S-mode only.
An interlaboratory investigation of technical chlordane residues in food crops was carried out to determine the most practical and consistent method of reporting results. Using a technical chlordane reference standard, 8 gas chromatographic stationary phases were studied for their resolution capabilities. The best separations were obtained with SE-30 and its OV-1 equivalent. Using these columns and electron capture detection, potatoes and carrots from supervised field experiments were analyzed in duplicate and quantitated by using 4 methods of calculation. The data were statistically treated to determine the precision and bias for each method. Also, 1 sample was analyzed in duplicate on 2 different occasions by 6 laboratories to substantiate the initial conclusions. Based on the criterion of high precision it is suggested that a comparison of total area under the chromatogram of the sample with total area of a standard technical chlordane be the method of quantitation. Only peaks which are common to both standard and sample have any significance in this type of calculation.
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