Proficiency test for antibiotics in beef

The aim of this proficiency study was to give laboratories the possibility to evaluate or demonstrate their competence for the analysis of antibiotics in bovine tissues, including the screening analysis. This study also provided an evaluation of the methods applied for screening and quantitative and confirmatory analysis of antibiotics in beef

Proficiency test for antibiotics in bovine muscle

The aim of this proficiency study was to give laboratories the possibility to evaluate or demonstrate their competence for the analysis of antibiotics in bovine muscle, including the screening analysis. This study also provided an evaluation of the methods applied for screening and quantitative confirmatory analysis of antibiotics in bovine muscle

Generic sample preparation combined with high-resolution liquid chromatography- time-of-flight mass spectrometry for unification of urine screening in doping-control laboratories

A unification of doping-control screening procedures of prohibited small molecule substances—including stimulants, narcotics, steroids, ß2-agonists and diuretics—is highly urgent in order to free resources for new classes such as banned proteins. Conceptually this may be achieved by the use of a combination of one gas chromatography–time-of-flight mass spectrometry method and one liquid chromatography–time-of-flight mass spectrometry method. In this work a quantitative screening method using high-resolution liquid chromatography in combination with accurate-mass time-of-flight mass spectrometry was developed and validated for determination of glucocorticosteroids, ß2-agonists, thiazide diuretics, and narcotics and stimulants in urine. To enable the simultaneous isolation of all the compounds of interest and the necessary purification of the resulting extracts, a generic extraction and hydrolysis procedure was combined with a solid-phase extraction modified for these groups of compounds. All 56 compounds are determined using positive electrospray ionisation with the exception of the thiazide diuretics for which the best sensitivity was obtained by using negative electrospray ionisation. The results show that, with the exception of clenhexyl, procaterol, and reproterol, all compounds can be detected below the respective minimum required performance level and the results for linearity, repeatability, within-lab reproducibility, and accuracy show that the method can be used for quantitative screening. If qualitative screening is sufficient the instrumental analysis may be limited to positive ionisation, because all analytes including the thiazides can be detected at the respective minimum required levels in the positive mode. The results show that the application of accurate-mass time-of-flight mass spectrometry in combination with generic extraction and purification procedures is suitable for unification and expansion of the window of screening methods of doping laboratories. Moreover, the full-scan accurate-mass data sets obtained still allow retrospective examination for emerging doping agents, without re-analyzing the samples

Practical estimation of the uncertainty of analytical measurement standards

Nowadays, a lot of time and resources are used to determine the quality of goods and services. As a consequence, the quality of measurements themselves, e.g., the metrological traceability of the measured quantity values is essential to allow a proper evaluation of the results with regard to specifications and regulatory limits. This requires knowledge of the measurement uncertainties of all quantity values involved in the measurement procedure, including measurement standards. This study shows how the uncertainties due to the preparation, as well as the chemical and compositional stability of a chemical measurement standard, or calibrator, can be estimated. The results show that the relative standard uncertainty of the concentration value of a typical analytical measurement standard runs up to 2.8% after 1 year. Of this, 1.9% originates from the preparation of the measurement standard, while 2.0 and 0.53% originate from the chemical and compositional stability during storage at -20 A degrees C. The monthly preparation of working calibrators stored at 4 A degrees C and used on a weekly basis, results in an additional standard uncertainty of the analyte concentration value of 0.35% per month due to compositional stability. While the preparation procedure is the major contributor to the total measurement uncertainty, the uncertainties introduced by the stability measurements are another important contributor, and therefore, the measurement procedure to evaluate stability is important to minimize the total measurement uncertainty

Application of EU guidelines for the validation of screening methods for veterinary drugs

Commission Decision (CD) 2002/657/EC describes detailed rules for method validation within the framework of residue monitoring programmes. The approach described in this CD is based on criteria. For (qualitative) screening methods, the most important criteria is that the CCß has to be below any regulatory limit. Especially when microbiological or immunochemical methods are involved, the approach described in the CD is not easily applied. For example, by those methods, a large number of analytes (all antibiotics) within several different matrices (meat, milk, fish, eggs, etc.) are detected. It is not completely clear whether all those analytes and all matrices have to be taken into account during method validation. To clarify this, a working group - from EU Reference Laboratories - came up with a practical approach to validate multi-analyte multi-matrix screening methods. It describes how many analyte/matrix combinations have to be tested and how these combinations are selected. Furthermore it describes how to determine CCß for screening methods in relation to a large list of compounds and maximum residue limits (MRLs). First for each analyte/matrix combination the 'cut-off' level - i.e. the level at which the method separates blanks from contaminated samples - is established. The validation is preferably at the concentration of 50% of the regulatory limit. A minimum set of 20 different samples has to be tested. From the experiences with applying these guidelines it was concluded that the validation approach is very 'practical'; however, there are some remarks. One has to be careful with selecting 'representative' analytes and matrices and it is strongly recommended to collect additional validation data during the routine application of the method