Estimation of measurement uncertainty in pesticide residue analysis.

Proficiency test results from 5 countries involving 61 separate interlaboratory proficiency tests for pesticide residues were examined in this study. A total of 24 different matrixes and 869 relative standard deviations of the mean (or median) pesticide residue concentration were statistically evaluated in relation to the Horwitz function. The aim was to determine whether or not the concentration-dependent relationship described by Horwitz would hold for the much narrower range of chemicals and concentrations covered in routine pesticide residue analysis. Although for fatty (animal-derived) matrixes the variability increased as the concentration decreased in line with the Horwitz equation, the between-laboratories relative standard deviations for nonfatty matrixes (fruit, vegetables, and grain) remained at 25% over the entire concentration range of 1 microg/kg to 10 mg/kg for the pesticides studied. Given these findings, the Horwitz equation remains valid for calculating uncertainties involving pesticide residues in fatty matrixes. However, for pesticide residue analyses involving nonfatty matrixes, a constant relative standard deviation of 25% is more appropriate for calculating uncertainties, particularly when a reported result is assessed against a regulatory limit.

International proficiency testing of analytical laboratories for foods and feeds from 1990 to 1996: the experiences of the United Kingdom Food Analysis Performance Assessment Scheme.

The Food Analysis Performance Assessment Scheme (FAPAS) organized by a Secretariat of the UK Ministry of Agriculture, Fisheries, and Food has checked the proficiency of analytical laboratories for foods and feeds from 1990 to 1996. FAPAS was started for UK laboratories but was expanded worldwide at the request of analysts in other countries who did not have a home-based scheme. Thirteen thousand homogeneity-checked test materials were issued, covering a very wide range of analytes, including pesticides, toxins, veterinary drug residues, trace and nutritional elements, food colors, preservatives, sweeteners, alcohol congeners, fatty acids, nitrate, and proximate analysis. Participants returned 85% of requested data, and 47,000 z-score proficiency assessments were made, of which 81% were satisfactory. Evidence is presented of improvements in overall analytical ability with increased participation in proficiency testing in the areas of proximate analysis; organochlorine pesticide analysis; and lead, mercury, and acesulfame-K analyses. Little improvement was shown in other analytical areas such as calcium analysis. Overall accuracies for analysis of specific pesticides and specific trace elements in the circulated test materials were compared.

Analytical quality assurance for the WHO GEMS/Food-EURO programme--results of 1993/94 laboratory proficiency testing.

As a means of assessing the performance of European laboratories who contribute analytical data on food contamination to the World Health Organization (WHO) Global Environmental Monitoring Scheme (GEMS), a series of five proficiency testing exercises were carried out during 1993 and 1994. In total 136 laboratories from 21 different countries took part in one or more of the exercises which covered the analysis of trace elements (lead, cadmium and mercury) in milk powder, pesticides (organochlorine, organophosphorus and pyrethroid) in spinach powder, nitrate in spinach powder, aflatoxins in nut-based animal feed and patulin in apple juices. The proficiency testing was carried out according to the ISO/IUPAC/AOAC INTERNATIONAL Harmonized Protocol and laboratories were awarded z-scores signifying their analytical capability based on their reported results for each of the respective exercises. Overall 60% of laboratories were satisfactory for accuracy for trace element analysis, 41% for pesticides, 43% for nitrate, 88% for aflatoxins and 53% for patulin. These results gave an overall poorer performance (68%) than the average for other similar schemes (79%), indicating the need for care in collating data for such programmes as GEMS and the need for remedial measures to assist in improving performance.

Surveillance and control of aflatoxin contamination of dried figs and fig paste imported into the United Kingdom.

Samples of dried figs and fig pastes from Turkey supplied voluntarily by UK importers and retailers during the period November 1988 to January 1989 showed both a high incidence and high levels of contamination with aflatoxins. In the samples tested, 24% had total aflatoxin concentrations above 10 micrograms/kg, with the highest level being 165 micrograms/kg. More rigorous monitoring of the 1989 fig harvest was undertaken on bulk consignments for all figs from Turkey entering the UK. For whole dried figs 20 kg samples were taken (as 20 sub-samples), and for fig paste 5 kg samples were taken (again as 20 sub-samples). Figs were minced, blended with water and mixed prior to sub-sampling for analysis. Analysis was by immunoaffinity column clean-up with HPLC determination of aflatoxins with fluorescence detection. Examination showed that 11% of 112 consignments of fig paste and 9% of 93 consignments of whole dried figs were contaminated with total alfatoxin concentrations above 10 micrograms/kg, with the highest level of contamination being 40 micrograms/kg. As a result of this surveillance programme 14 consignments of figs were refused entry into the United Kingdom.

Liquid chromatographic determination of aflatoxin levels in peanut butters using an immunoaffinity column cleanup method: international collaborative trial.

Thirteen laboratories in 7 different countries participated in a collaborative trial to evaluate the immunoaffinity column cleanup procedure with quantitation by fluorescence liquid chromatography (post-column derivatization) for the determination of aflatoxins in peanut butters. Participants were sent 10 randomly numbered samples of roasted peanut butter for analysis (5 pairs of undisclosed duplicates). Two of the pairs were "blank" peanut butters to which aflatoxin standards had been added; these "spiked" samples were used for recovery purposes. The other 3 pairs of samples were a nominal "blank" and 2 naturally contaminated peanut butters. A full statistical presentation of the results is given. Coefficients of variation (CVs) for the total aflatoxin determinations for mean levels of 4, 15, and 38 microns/kg were between 32 and 44% for the blank and 2 trial samples. Recovery levels for the 2 spiked samples were 51-67%, with aflatoxin B1 recovery of 60%. Relative standard deviations for method repeatability (RSDr) and reproductibility (RSDR) for the 3 trial samples were 15-26% and 33-45%, respectively.

A survey of the occurrence of agaritine in U.K. cultivated mushrooms and processed mushroom products.

The naturally occurring compound agaritine (beta-N-[gamma-L(+)glutamyl]-4-hydroxy-methylphenyl-hydrazine) has been determined in fresh, dried and processed mushrooms. A method was developed involving extraction of the toxin into methanol, clean-up where appropriate (for processed products) by high-performance size exclusion liquid chromatography and determination by reverse-phase HPLC with electrochemical detection. Diode array UV monitoring was used for confirmation. The method had a recovery of 90-98%, a relative standard deviation of 3-5% and a limit of detection of agaritine of 5 mg/kg on a dry-weight basis. Fresh cultivated mushrooms showed agaritine levels of 100-250 mg/kg and 80-190 mg/kg for two different commercial strains. There were slight differences in levels of agaritine between mushrooms of different sizes, and between those of the same size but harvested at different times (different breaks). Retail processed mushrooms products had low agaritine levels in the range 6-33 mg/kg, with the exception of one dried sliced mushroom product found to contain 6520 mg/kg.

Determination of aflatoxin B1 levels in peanut butter using an immunoaffinity column clean-up procedure: inter-laboratory study.

Ten United Kingdom laboratories participated in an evaluation of an immunoaffinity column sample preparation procedure used to prepare aflatoxin B1 containing extracts obtained from peanut butters contaminated by aflatoxins. Each laboratory was sent seven randomly numbered samples of roasted peanut butter which included two sets of undisclosed triplicates. These two peanut butters were naturally contaminated with aflatoxin B1 at levels of about 12 and 35 micrograms/kg. The other sample was a nominal blank peanut butter containing approximately 2 micrograms/kg of aflatoxin B1 which was also employed by participants for recovery experiments. Participating laboratories were instructed to follow a protocol regarding the use of the immunoaffinity columns for extract preparation, but were allowed a free choice of instrumental technique for quantification of aflatoxin levels. Mean recovery for spikes was 72%. Coefficients of variation for the results from the 10 participants for the two contaminated roasted peanut butters were, respectively, 45% (on a mean of 13.6 micrograms/kg) and 36% (on a mean of 37.2 micrograms/kg).

Determination of aflatoxin concentrations in peanut butter by enzyme-linked immunosorbent assay (ELISA): study of three commercial ELISA kits.

Sixteen United Kingdom analytical laboratories participated in an evaluation of 3 commercially available enzyme-linked immunosorbent assay (ELISA) kits for analysis of aflatoxin in peanut butter. Each laboratory was sent 3 sets of 10 randomly numbered samples of peanut butter. Each set consisted of 5 pairs of undisclosed duplicates. Four of the sets of duplicates were naturally contaminated butters with "target" aflatoxin values (estimated by liquid chromatography) between 8 and 81 micrograms/kg. The fifth pair was a blank peanut butter containing approximately 3 micrograms/kg of total aflatoxins. A statistical treatment of the results of the study is presented, together with discussion of the relative merits of the different kits.

A method for the analysis of lincomycin in porcine and bovine kidney.

A method of analysis has been developed for the estimation of lincomycin in porcine and bovine kidney. The method employed high performance liquid chromatography and Sep-Pak clean-up of methanolic tissue extracts and nitrogen specific gas chromatographic detection. Using spiked (0.1 mg kg-1) extracts recoveries in the range 40-50% were obtained. Analysis at the 0.05 mg kg-1 level is possible. Fifty four samples of kidney destined for UK sale were analysed for the presence of this drug. No samples were found to contain lincomycin.

Ammonia caramels: specifications and analysis.

Twenty three UK commercially produced ammonia caramels and eight experimentally produced ammonia caramels have been analysed by a range of physical and chemical tests, which include solids content, nitrogen levels, colour intensity and pH. A statistical treatment of the results is reported.