Optimizing the balance between false positive and false negative error probabilities of confirmatory methods for the detection of veterinary drug residues.

GC-MS data on veterinary drug residues in bovine urine are used for controlling the illegal practice of fattening cattle. According to current detection criteria, peak patterns of preferably four ions should agree within 10 or 20% from a corresponding standard pattern. These criteria are rigid, rather arbitrary and do not match daily practice. A new model, based on multivariate modeling of log peak abundance ratios, provides a theoretical basis for the identification of analytes and optimizes the balance between the avoidance of false positives and false negatives. The performance of the model is demonstrated on data provided by five laboratories, each supplying GC-MS measurements on the detection of clenbuterol, dienestrol and 19 beta-nortestosterone in urine. The proposed model shows a better performance than confirmation by using the current criteria and provides a statistical basis for inspection criteria in terms of error probabilities.

Statistical model for assessing the quality and cost of inspection procedures in forensic and environmental analysis.

Legal regulations on the composition and safety of food products require inspection programmes to maintain the standards required or to obtain an insight in the real situation. Such programmes consist of a sampling procedure followed by analysis of the samples. When monitoring environmental contamination similar programmes are required. When large numbers of samples have to be analysed in order to monitor contaminants in either environmental or food-chain samples, and the majority fulfil the legal requirements, a two-stage control system is desirable. Firstly, samples are analysed by a simple 'screening method', to sift out the large number of samples that fulfil the requirements (negative results). The minority not fulfilling the requirements (positive results) are investigated further by a more sophisticated confirmatory method, specific for the analyte(s) of interest, for an ultimate judgement. For this type of inspection a simple model is used in this study, in order to calculate the fraction of false negative results in the final decision. It is assumed, that, when the quality criteria for the confirmatory method are appropriate, the fraction of false positive results is negligibly small. The quality of the inspection is expressed in terms of the fraction f of false negative results with respect to the real positive samples and is related to labour and costs. In an example given, the costs of analysing 40,000 samples with f = 6.6% are ecu 7,800,000. Improving f down to 3.2% creates additional costs of ecu 16,000,000. The proposed model might not be sufficiently realistic, but more realistic models can be implemented.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioactive contamination of food sampled in the areas of the USSR affected by the Chernobyl disaster.

In October 1990 a Netherlands humanitarian fact finding mission on aid to people affected by the Chernobyl disaster visited contaminated regions in Russia, Byelorussia and the Ukraine. The mission consisted of medical, socio-psychological and agricultural experts. The results of radioactivity measurements on food products sampled in the contaminated areas are reported here and the radiation burden for the Soviet citizens due to these products is discussed. The radiocaesium contamination measured in 19 food products ranged between 0 and 170 Bq kg-1 and 40K from 25 to 200 Bq kg-1 in the fresh product. Strontium-90, measured in a few samples, was found to be between 1.8 and 30 Bq kg-1. Mushrooms and reindeer moss were very highly contaminated: from 103,000 to 284,000 Bq kg-1 of radiocaesium in the fresh product. Strontium-90 in these samples was 7.8-1550 Bq kg-1. The contamination of all food products was far below the stated limits, except for mushrooms. Extrapolation of the results to the total food consumption gave the radioactive burden due to this food as an estimated 0.2 mSv per year. All of the food products investigated, except mushrooms, can be regarded as safe with respect to radioactive contamination. In addition to sampling agricultural produce, field exposure measurements were also carried out. The measured values, expressed in equivalent doses, ranged from 1.8 to 14 mSv per year at a height of 1 m, with a median value of about 4 mSv per year.

Quality criteria for the detection of analytes in test samples with special reference to anabolic agents and related compounds.

In order to create a system for qualitative analysis, in which well defined limits of ambiguity can be set, criteria have been formulated for application to the identification method(s) used. Criteria are presented for separation techniques (thin-layer chromatography, gas chromatography, high-performance liquid chromatography) and for spectrometric methods (ultraviolet-visible spectroscopy via diode array, mass spectrometry, infrared spectroscopy), as well as general considerations for the whole procedure.

Application of diethylstilbestrol dipropionate in bulls. I. Excretion of residues in urine and faeces and histological and immunohistochemical changes in the prostate.

In this experiment 20 one year old bulls received a single intramuscular injection of the anabolic preparation diethylstilbestrol dipropionate (DES-DP) (an oil preparation or an emulsion). Four animals received a corresponding placebo. The application of DES-DP to bulls caused characteristic histological alterations in the peripheral glandular epithelium of the prostate, which could be observed until four weeks after treatment. The value of histological investigation as a screening method was, however, limited by the occurrence of only few metaplastic lesions and a rapid recovery. By contrast, immunohistochemistry using a polyclonal cytokeratin antiserum K40 appeared to be a specific and very sensitive method to detect oestrogen-induced lesions in the prostate. In only two animals, six weeks after injection with the DES-emulsion, false-negative results were obtained, demonstrating the potential value of this screening method. The excretion of DES in the urine and faeces was monitored using radioimmunoassay following chromatographic purification of the urine and faeces extracts. The excretion of DES in urine was faster for animals of the oil group. The DES content in urine decreased to the 1 microgram/l level after 42 days (emulsion group) or 70 days (oil group). The excretion in faeces was comparable to that in urine. After day 21 the excretion patterns of the two excreta were indistinguishable.

Spectrometric and liquid chromatographic determination of natamycin in cheese and cheese rind.

Methods for determining natamycin content of cheese rind and cheese are presented. Cheese and rind samples are extracted with methanol and the fat precipitated by cooling the sample solution in methanol-water at -15 to -20 degrees C for ca 1 h. Natamycin levels are measured by UV spectrometric detection at absorbance minimum 311 nm, maximum 317 nm, and at exactly 329 nm, or by LC separation over Lichrosorb RP-8 column with detection at 303 nm. For measuring low levels, a concentration step is provided. The method is applicable to natamycin in cheese rind and in the interior of the cheese. Detection limit is 0.5 mg/kg. The method is suitable for controlling a maximum tolerance of natamycin on the cheese rind, at a level of 1 mg/dm2, and for detecting migration of natamycin into the cheese.

Determination of natamycin in cheese and cheese rind: interlaboratory collaborative study.

A collaborative test on the determination of natamycin in cheese and cheese rind was conducted. Participants were from 37 laboratories in 13 countries. Eight samples, consisting of 4 duplicates, were investigated by a spectrometric method and a liquid chromatographic (LC) method. The spectrometric method gave good results (coefficient of variation [CV] = 12%) and the LC method with ultraviolet detection gave reasonable results (CV = 25%) for levels down to 15 mg/kg (0.9 mg/dm2). For very low levels, a preconcentration step is necessary, but even then quantitation is poor (CV = 35-37%) for both methods at 1.7 mg/kg, although the presence of natamycin can be detected qualitatively. For a level of 0.3 mg/kg, quantitation is poor (CV = 39%) for the LC method and impossible (CV = 60%) for the spectrometric method.