Collaborative study of the gravimetric method for the determination of mercury in chlorinated pesticide formulations.

The official first action AOAC gravimetric method for mercury, 6.C01-6.C03, and the official CIPAC titrimetric method, M2.3, were collaboratively studied by 4 CIPAC laboratories, using the same 4 samples analyzed by AOAC collaboration in 1972. Averages at the 3.7 and 3.4% level were the same by both methods whereas the CIPAC method produced, on the average, 4% higher results, all levels included. The AOAC method performs well in the presence of copper and chlorinated pesticides and is less complex to use than the present CIPAC method for mercury in these mixtures. The method has been adopted as official final action.     

State programs for pesticide residues in foods

Two U.S. data collection and dissemination programs, FEEDCON and FOODCONTAM, are described. FEEDCON provides information on contamination levels in animal feeds of toxic chemical residues (pesticides, industrial chemicals, heavy metals, mycotoxins, natural plant toxins, salmonella, and therapeutic drug cross-contaminations). FEEDCON data are collected from approximately 40 state feed regulatory agencies, feed manufacturers, and related groups who subscribe ($100-$200 per year) to the program, which is sponsored by the Association of American Feed Control Officials. FOODCONTAM provides similar information, but is limited to pesticides, heavy metals and industrial chemicals (polychlorinated and polybrominated biphenyls, etc.) in human foods. Both programs have been developed and initiated under U.S. Food and Drug Administration contracts with the Mississippi State Chemical Laboratory. Program structures of both are outlined conceptually, and FOODCONTAM is described in detail. FOODCONTAM data-sharing program development is essentially complete, but expansion by incorporating FDA data with State Laboratory data is nearing reality.     

Collaborative study of an improved method for the enumeration and confirmation of Clostridium perfringens in foods.

A collaborative study was conducted in 10 laboratories to evaluate the performance of a new method for the enumeration of vegetative cells of Clostridium perfringens in foods. Results obtained by the new method were compared with results from the official first action method, 46.049-46.053. Per cent recoveries of 4 C. perfringens strains from inoculated roast beef samples were higher and more consistent in tryptose-sulfite-cycloserine (TSC) agar with or without added egg yolk than in sulfite-polymyxin-sulfadiazine (SPS) agar, specified in the official first action method. The confirmatory technique utilized in the new method was also found to be more reliable than the technique described in the official first action method. Based on the collaborative results, the new method with TSC agar for enumeration and a modified motility-nitrate medium together with a lactose-gelatin medium for confirmation of C. perfringens has been adopted as official first action to replace 46.049-46.053.     

The Luke et al. method for determining multipesticide residues in fruits and vegetables: collaborative study

Ten laboratories analyzed unfortified and fortified samples of lettuce, tomatoes, and strawberries for organochlorine and organophosphorus pesticides by applicable portions of the comprehensive multipesticide method of Luke et al. The 3 crops were fortified with 6 pesticides, alpha-BHC, dieldrin, chlorpyrifos, acephate, omethoate, and monocrotophos, each at 3 levels per crop. Included in the 54 fortifications were 16 pairs of blind duplicates: same pesticide, crop, and level. Recoveries were calculated by area comparisons with known reference materials, using the responses obtained from 2 separate element-specific gas chromatographic (GC) systems. The organochlorine pesticides were chromatographed on a methyl silicone column and detected with a Hall 700A electrolytic conductivity detector, and the organophosphorus pesticides were determined with a flame photometric detector after being chromatographed on a specified DEGS column material. Chlorpyrifos was quantitated on both GC systems. Mean recoveries ranged from 82.6% for acephate fortified at 0.5000 ppm in strawberries to 118.1% for 0.0636 ppm fortification of chlorpyrifos in lettuce. Interlaboratory coefficients of variation ranged from 4.0% for 0.6360 ppm fortification of chlorpyrifos in tomatoes to 17.8% for the 0.0636 ppm chlorpyrifos level in lettuce. The procedure features essentially no cleanup before GC and proved comparable to existing multiresidue methods for pesticides of the class types studied, as evidenced by the intra- and interlaboratory measurements of precision and recoveries obtained. The method with the 2 GC systems has been adopted official first action.     

Determination of chlorinated pesticide residues in foods. I. Rapid screening method for chlorinated pesticides in milk.

A rapid analytical method for determining chlorinated pesticide residues in milk was developed. Thirteen pesticides were almost completely extracted. Ten mL samples of fortified milk were extracted 3 times with 20 mL portions of n-hexane as follows: (A) in the absence of water-soluble solvent; in the presence of (B) 1 mL acetonitrile; (C) 3 mL acetonitrile; (D) 5 mL acetonitrile; (E) 5 mL ethanol; (F) 5 mL acetonitrile and 1 mL ethanol. System F produced the highest pesticide recoveries but the lowest fat extraction, thus eliminating the necessity for liquid-liquid partitioning and minimizing Florisil column cleanup. Pesticide recoveries throughout the procedure were 94--103%. It was noticed, however, that the fat in high fat-containing raw milk is more readily extracted than that in commercial milk.     

Collaborative study of an automated method for the determination of crude protein in animal feeds.

An automated macro Kjeldahl instrument determines per cent protein at the rate of 20 samples/hr. The methodology involved is similar to the present official final action Kjeldahl method, sec. 7.016. The 2 methods were compared in a collaborative study. Sixteen animal feeds, 4 meats, tryptophan, ammonium dihydrogen phosphate NBS standard, and ammonium sulfate primary standard were analyzed by the participating laboratories. The data were agreement between the 2 methods. The automated method has been adopted as official first action for the determination of crude protein in feeds, plants, and cereal foods.     

Collaborative study for the comparison of two methods for the determination of total cholesterol in multicomponent foods.

The gas chromatographic method for determining total cholesterol in multicomponent foods, collaboratively studied by the AOAC in 1974 (Method 1), has been evaluated by 9 collaborating laboratories and compared with the Interim Methodology Instructions No. 2 modified method (Method 2). The 5 samples selected for collaboration were deviled ham sandwich spread, vegetable beef stew, frozen chicken pot pie, frozen fish sticks, and mayonnaise. The recovery data were obtained from a sample of wheat germ oil spiked with 0.297% cholesterol as cholesteryl palmitate. Collaborators performed 2 replicate analyses on all samples by both methods. The statistical evaluation of the results showed that Method 1 is superior to Method 2. Average recoveries from the spiked wheat germ oil samples were 91.4% (9 laboratories) and 85.8% (7 laboratories) with coefficients of variation of 12.5 and 14.4%, respectively. Based on the collaborative results and statistical evaluation, Method 1 has been adopted as official first action.     

Collaborative study of an on-column periodate reaction method for the determination of ephedrine sulfate in sirups.

Fifteen laboratories collaboratively studied a method for the quantitative ultraviolet determination of ephedrine sulfate in sirups. Ephedrine is separated from water-soluble impurities and strong acids by elution from a weakly basic Celite column. Further cleanup is accomplished by retention of the ephedrine on a weakly acidic column while the weak acids, weak bases, and organic-soluble neutral compounds are eluted. Ephedrine is eluted from the column after neutralization with NH3 and is converted to benzaldehyde via an on-column periodate reaction. The samples collaboratively studied consisted of 2 commericial ephedrine-containing sirups and 2 commercial non-ephedrine-containing sirups to which ephedrine was added. Recoveries for the spiked sirups averaged 100.7 and 100.3% for mixtures containing 2.5 and 5.0 mg ephedrine sulfate/ml, respectively. The means and standard deviations for the commercial preparations were 4.088 plus or minus 0.068 and 2.375 plus or minus 0.053 mg/ml. The method has been adopted as official first action and has been incorporated into the official method for phenylpropanolamine hydrochloride, 38.199-38.203.     

Collisionally activated decomposition mass spectrometry/mass spectrometry determination of organophosphorus pesticide residues in foods

Representative collisionally activated decomposition mass spectrometry/mass spectrometry spectra of omethoate, parathion, and azinphos-methyl pesticides are described. Crude and cleaned up extracts of strawberries or lettuce fortified at the 0.2 ppm level with omethoate, parathion, and azinphos-methyl were examined using the direct exposure probe. Cleaned up extracts produced better data because the large overburden of interfering coextractives was removed.     

Collaborative study of a method for the detection of Clostridium botulinum and its toxins in foods.

The mouse toxicity and protection technique for the detection and identification of Clostridium botulinum and its toxins in foods was collaboratively studied by 11 laboratories. Each laboratory received 4 samples of cream of mushroom soup; 2 contained spores and toxin of C. botulinum type A, 1 contained spores and toxin of C. botulinum type E, and 1 contained spores of C. sporogenes. The media used were cooked meat medium (beef heart or chopped liver broth) and trypticase peptone glucose yeast extract broth with trypsin. The results indicate that this method has a high degree of repeatability and reproducibility. All 11 laboratories correctly identified the toxins and the nontoxic sample in the food and detected and identified the viable spores in the samples by means of the subsequent cultures. This method has been adopted as official first action.     

Collaborative study of a method for the determination of ochratoxin A in green coffee.

A method for the semiquantitative determination of ochratoxin A in green coffee has been studied collaboratively by 11 laboratories. The average recovery for the 7 samples spiked at 3 levels of ochratoxin A was 69.1%, ranging from 60.5 to 85.6%. This is comparable to other visual thin layer chromatographic methods of mycotoxin detection. The method has been adopted as official first action for the determination of ochratoxin A in green coffee beans.