Measurement uncertainty interval in case of a known relationship between precision and mean

Background: Measurement uncertainty is typically expressed in terms of a symmetric interval y±U, where y denotes the measurement result and U the expanded uncertainty. However, in the case of heteroscedasticity, symmetric uncertainty intervals can be misleading. In this paper, a different approach for the calculation of uncertainty intervals is introduced. Methods: This approach is applicable when a validation study has been conducted with samples with known concentrations. In a first step, test results are obtained at the different known concentration levels. Then, on the basis of precision estimates, a prediction range is calculated. The measurement uncertainty for a given test result can then be obtained by projecting the intersection of the test result with the limits of the prediction range back onto the axis of the known values, now interpreted as representing the measurand. Results: It will be shown how, under certain circumstances, asymmetric uncertainty intervals arise quite naturally and lead to more reliable uncertainty intervals. Conclusions: This article establishes a conceptual framework in which measurement uncertainty can be derived from precision whenever the relationship between the latter and concentration has been characterized. This approach is applicable for different types of distributions. Closed expressions for the limits of the uncertainty interval are provided for the simple case of normally distributed test results and constant relative standard deviation.

Essential terminology and considerations for validation of non-targeted methods

Through their suggestive name, non-targeted methods (NTMs) do not aim at a predefined "needle in the haystack." Instead, they exploit all the constituents of the haystack. This new type of analytical method is increasingly finding applications in food and feed testing. However, the concepts, terms, and considerations related to this burgeoning field of analytical testing need to be propagated for the benefit of those associated with academic research, commercial development, or official control. This paper addresses frequently asked questions regarding terminology in connection with NTMs. The widespread development and adoption of these methods also necessitate the need to develop innovative approaches for NTM validation, i.e., evaluating the performance characteristics of a method to determine if it is fit-for-purpose. This work aims to provide a roadmap for approaching NTM validation. In doing so, the paper deliberates on the different considerations that influence the approach to validation and provides suggestions therefor.

European Analytical Criteria: Past, Present, and Future

In this paper, the past, present, and (possible) future of the European analytical criteria for residues are described. The elaboration of the revision of Commission Decision 93/256/EC was a long process starting in 1996 and ending with the formation of a European Commission (EC) working group in 1998. This working group took account of developments in scientific and technical knowledge at that time and produced a draft version of the revision within 6 months. The revision, finally published in 2002 (2002/657/EC), includes new ideas on the identification of analytes and the criteria for performance assessment as well as validation procedures. Currently (2009), the evolution in analytical equipment and progress in scientific research, accompanied by recent European regulatory changes, demands an update or revision of the 2002/657/EC.

Validated Determination of Eight Antibiotic Substance Groups in Cattle and Pig Muscle by HPLC/MS/MS

The described multimethod is suited for the determination of 53 substances of eight antibiotic groupstetracyclines, quinolones, macrolides, sulfonamides, diphenylsulfones, diamino-pyrimidine derivatives, pleuromutilines, and lincosamidesin cattle and pig muscle. All substances were analyzed simultaneously with the same sample preparation and in one HPLC/MS/MS run. The validation of the multimethod was successfully accomplished with the help of an alternative in-house validation concept requiring only 48 experiments. The substances were validated at concentrations of 0.25, 0.5, 1.0, 1.5, and 2.0 MRL (maximum residue limit) or 5, 10, 20, 30, and 40 g/kg for substances without an MRL. The calculated relevant validation parameters were based on and comply with the requirements of Commission Decision 2002/657/EC, i.e., the decision limit, detection capability, repeatability, within-laboratory reproducibility, and recovery. The robustness of the method was demonstrated by varying seven factors of the analytical procedure. Several proficiency tests were carried out successfully to provide evidence for the applicability of the method.

Methylbis(2,6-dichIorthiophenoIato)bismut(III) — Synthese, fungizide und bakterizide Aktivität/ Methylbis(2,6-dichlorothiophenolato)bism uth(III) — Synthesis, Fungicidal and Bactericidal Activity

The methylbis(thiophenolato)bismuth(III) derivative CH3Bi(SCAH3Cl2-2.6)2 was prepared by reaction of CH3BiBr2 with equivalent amounts of the appropriate lithium thiolate. The new Bi organyl was characterized by elemental analysis, 1H NMR. IR . and mass spectroscopy. The biological activity against bacteria, yeasts, and moulds was investigated.

Reliability of precision data obtained from interlaboratory studies

Precision data, such as laboratory-to-laboratory SD (SL) and repeatability SD, obtained from interlaboratory tests are needed to assess analytical test methods. These precision data describing random error are subject to random variation. In order to avoid distorted assessments of test methods, interlaboratory tests must fulfill minimal requirements for achieving, e.g., a desired reliability in S(L). In 2009, McClure and Lee considered reliability of S(L) as a characteristic of an interlaboratory study. They developed an approach to approximate that reliability to make it possible to adapt the study design of an interlaboratory study to a desired reliability in S(L). The McClure and Lee approach introduces the "margin of relative error" to arrive at the magnitude of the uncertainty in S(L). This article discusses their approach and presents a generalized approach. The limitations of McClure and Lee's approximation are shown to result in underestimation of the actual variability of S(L) due to the disregard of the inherent negative bias of S(L). This bias corresponds to the fact that the expected value of the obtained S(L) lies below the true value sigmaL one would obtain in an interlaboratory study with an infinite number of laboratories and replicates. In order to achieve the reported level of reliability in S(L), the actual number of laboratories required is typically approximately 25% higher than that calculated by McClure and Lee. We present a generalized approach using "margins of relative random error," which takes the impact of the bias of the S(L) into account, resulting in a more realistic estimation of the variability of the precision parameter S(L).

Validated determination of eight antibiotic substance groups in cattle and pig muscle by HPLC/MS/MS

The described multimethod is suited for the determination of 53 substances of eight antibiotic groups-tetracyclines, quinolones, macrolides, sulfonamides, diphenylsulfones, diamino-pyrimidine derivatives, pleuromutilines, and lincosamides-in cattle and pig muscle. All substances were analyzed simultaneously with the same sample preparation and in one HPLC/MS/MS run. The validation of the multimethod was successfully accomplished with the help of an alternative in-house validation concept requiring only 48 experiments. The substances were validated at concentrations of 0.25, 0.5, 1.0, 1.5, and 2.0 x MRL (maximum residue limit) or 5, 10, 20, 30, and 40 microg/kg for substances without an MRL. The calculated relevant validation parameters were based on and comply with the requirements of Commission Decision 2002/657/EC, i.e., the decision limit, detection capability, repeatability, within-laboratory reproducibility, and recovery. The robustness of the method was demonstrated by varying seven factors of the analytical procedure. Several proficiency tests were carried out successfully to provide evidence for the applicability of the method.

Matrix-comprehensive in-house validation and robustness check of a confirmatory method for the determination of four nitrofuran metabolites in poultry muscle and shrimp by LC–MS/MS

An already well-described method for the determination of nitrofuran metabolites 3-amino-5-methyl-morpholino-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM) and 1-aminohydantoin (AHD) was adapted to the needs of our laboratory and checked for its robustness regarding sample conditions and the processing step. Using the same data, the method was validated and the measurement uncertainty was estimated. All criteria and requirements of Commission Decision 2002/657/EC were fulfilled. The CC(alpha) determined lies between 0.1 and 0.7 microg/kg, the CC(beta) lies between 0.1 and 0.9 microg/kg, the measurement uncertainty was estimated as being between 7 and 17% taking into account matrix, time and sample preparation influences.

Validation of a confirmatory method for the determination of residues of four nitrofurans in egg by liquid chromatography–tandem mass spectrometry with the software InterVal

A method for the detection and determination of nitrofuran derivatives in egg by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was validated with the software InterVal and can be applied for the confirmation of nitrofuran metabolites in fresh or lyophilised eggs. The validation study comprises variations in operator, storage condition, breeding, equipment and duration of sample preparation. A comprehensive overview of the robustness of the method is obtained by analysing eight samples at six concentration levels. First results of short- and medium-term investigations for stability of analytes in solution show that standard solutions of nitrofuran metabolites are stable for at least 1 year when stored at +4 degrees C in the dark. The decision limit CCalpha expressed for the underivatised metabolite is 0.05 microg kg(-1) for 3-amino-5-methyl-morpholino-2-oxazolidinone, 0.03 microg kg(-1) for 3-amino-2-oxazolidinone, 0.20 microg kg(-1) for semicarbazide and 0.22 microg kg(-1) for 1-amino-hydantoin.

Determination of chloramphenicol residues in crustaceans: Preparation and evaluation of a proficiency test in Germany

Chloramphenicol (CAP) is banned for use in food-producing animals and is, thus, controlled on the basis of the National Residue Control Plans in the European Union. Due to current problems with residues of CAP in shrimp, crayfish and prawns, a sensitive GC/NCI/MS method was optimised and in-house validated. The validation study resulted in a decision limit (CCalpha) of 0.07 microg kg-1, a recovery of 95% and a within-laboratory reproducibility of 9%. The method was used for preparing a proficiency test to assess the quality of residue control in Germany. The proficiency test involved analysis of five samples and the results were very satisfactory. The reproducibility standard deviation for five samples ranged from 17 to 24%, and the median concentrations lay between 0.43 and 0.51 microg kg-1 CAP. These values are clearly below the corresponding Horwitz standard deviation of about 50%. From the study, it can be concluded that there are, irrespective of the method applied, well-established and proper working analytical procedures for the control of CAP around the minimum required performance limit (MRPL) of 0.3 microg kg-1.

Validation of a method for the detection and confirmation of nitroimidazoles and corresponding hydroxy metabolites in turkey and swine muscle by means of gas chromatography-negative ion chemical ionization mass spectrometry

The results of a validation study of a GC-NCI-MS method for the quantitative determination of 5-nitroimidazoles [1,2-Dimethyl-5-nitroimidazole (dimetridazole, DMZ), 1-methyl-2-[(carbamoyloxy)methyl]-5-nitroimidazole (ronidazole, RNZ), 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole (metronidazole, MNZ) and 2-isopropyl-1-methyl-5-nitroimidazole (ipronidazole, IPZ)] including the hydroxy metabolites of these agents [2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI), 1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole (MNZOH), and 1-methyl-2-(2'-hydroxyisopropyl)-5-nitroimidazole (IPZOH)] in turkey and swine muscle are presented. The validation was carried out according to the requirements of the draft for the revision of Commission Decision 93/256/EC, which is expected to be adopted by the European Commission in due course. The determination of the method's performance parameters revealed decision limits (CCalpha) between 0.65 and 2.8 microg/kg for DMZ, RNZ/HMMNI, MNZ and MNZOH. Confirmatory analyses according to the requirements of the forthcoming EC decision are possible for all analytes except for IPZ and IPZOH where already the decision limits (CCalpha) were higher (5.2 microg/kg) than for the above-mentioned nitroimidazoles. The within-laboratory reproducibility and the mean recovery were in an acceptable range for all analytes.

Measurement of beta-agonist residues in retinal tissue of food producing animals

This report presents the results of an investigation on the accumulation of beta-agonist residues in the retinal tissue of food producing animals. Three different species, calf, pig and turkey, were treated with six different beta-agonists and analysed for beta-agonist residues in retinal tissue applying a newly developed retina preparation procedure which provides sufficient sample material for multiple analyses. The results show that all selected beta-agonists accumulate in the retina, though in varying concentrations. The results are discussed on the basis of existing binding theories and with regard to their impact on the existing residue control strategy for beta-agonists.

Multi-residue method for non-steroidal anti-inflammatory drugs in plasma using high-performance liquid chromatography-photodiode-array detection. Method description and comprehensive in-house validation

A multi-residue high-performance liquid chromatography (HPLC) method with photodiode-array detection is presented for the determination of 12 non-steroidal anti-inflammatory drugs (NSAIDs) in plasma. This method has been validated under the consideration of actual alpha- and beta-errors according to an in-house validation concept based on a fractional factorial experiment. A wide range of matrices and other influencing factors have been included in the validation experiment. In order to assess the method's performance the power curve, which demonstrates the detection power of the analytical method, was computed and CCalpha and CCbeta values were calculated.