Evaluation of uncertainty of measurement from method validation data: an application to the simultaneous determination of retinol and alpha-tocopherol in human serum by HPLC.

An isocratic RP-HPLC method for the determination of retinol and alpha-tocopherol in serum, with fluorescence and UV/VIS detection, respectively, was developed and validated according to international guidelines. Detection (retinol 0.015 mg/L, alpha-tocopherol 0.29 mg/L) and quantification (retinol 0.05 mg/L, alpha-tocopherol 0.95 mg/L) limits were determined. Repeatability was <3.3% and <2.9% and intermediate precision was <4.6% and <3.2%, for retinol and alpha-tocopherol, respectively. Certified reference materials were utilised to assess bias and guarantee traceability to SI units. Expanded uncertainties (retinol 8.9%; alpha-tocopherol 7.9%), estimated according to the EURACHEM/CITAC guide from method validation data, satisfied fit-for-purpose requirements based on biological variability.

Quality specifications for the determination of copper, zinc, and selenium in human serum or plasma: evaluation of an approach based on biological and analytical variation.

BACKGROUND: Trace element external quality assessment schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. However, monitoring of participant performance varies according to the scheme and can lead to conflicting conclusions. METHODS: Quality specifications based on biological intra- and interindividual variability were calculated and compared to those currently used by various trace element external quality assessment schemes for plasma or serum copper, zinc, and selenium concentrations. For this purpose, we evaluated results reported by participating laboratories in different schemes, at key concentrations, using z scores. RESULTS: Minimal quality specifications developed from the biological intra- and interindividual variability were, for Cu, +/-0.84 micromol/L or 12% of the assigned target concentration, whichever is greater; for Zn, +/-1.20 micromol/L or 15% of the assigned target concentration, whichever is greater; and for Se, +/-0.072 micromol/L or 12% of the assigned target concentration, whichever is greater. Reported performance of the participating laboratories depended on analyte, concentration, and the selected quality specification. In addition, the most commonly used methods for the determination of Cu, Zn, and Se may give different results. CONCLUSIONS: The proposed minimal quality specifications based on biological variation are generally slightly less stringent than those currently in use, although they do not drastically change the performance evaluation in the different schemes. These specifications are a first step in the harmonization of practices among the schemes and remain to be evaluated.

Differences in national legislation for the implementation of lead regulations included in the European directive for the protection of the health and safety of workers with occupational exposure to chemical agents (98/24/EC).

BACKGROUND: The European Council Directive 98/24 on the protection of the health and safety of workers exposed to chemical agents sets out provisions for environmental and biological monitoring, making specific reference to binding limit values and health surveillance measures for those with exposure to lead OBJECTIVES: To compare how the Directive has been implemented at a national level in EU countries and to determine whether workers receive equivalent protection. METHODS: Information on selected key issues was collected from 14 EU countries by means of a structured questionnaire. RESULTS: National occupational exposure limit values generally reflect that set by the Directive (0.15 mg/m(3)), but in five cases lower limits are set. National binding biological limit values range from 20 microg/100 ml blood in one country up to 80 microg/100 ml blood in others. The risk to the unborn child is generally recognised with specific measures for women of child-bearing potential or those that are pregnant or breast feeding. In only three countries are special arrangements included for young workers. Limits at which medical surveillance is put into effect are more consistent at 40 microg/100 ml in most countries. The Directive also refers to guidelines for health surveillance but none have been issued with respect to lead. Thus monitoring strategies and requirements for analytical performance vary considerably. CONCLUSIONS: The results of this survey suggest that protection of workers against the risk of exposure to lead at work is far from uniform across the European Union. Such disparity may also have implications on the requirements set at national level for laboratories measuring lead in blood and/or air. In the interest of harmonisation within the EU, further consideration should be given to the Annex II of the EC Directive 98/24, taking into account the suggestions for lower binding limit values for lead; this should include full guidelines for medical surveillance and requirements for laboratories should be issued.

Salivary uric acid at the acidic pH of the stomach is the principal defense against nitrite-derived reactive species: sparing effects of chlorogenic acid and serum albumin.

A complex antioxidant system is present in human saliva, with uric acid being the most concentrated component. Ascorbic acid, present at low concentrations in saliva, is actively secreted into the gastric lumen. We report that ascorbic acid added to human saliva at pH 2 was consumed within a few minutes, regenerating HNO(2), whereas uric acid was consumed relatively slowly in a nitrite-dependent manner. The consumption of uric acid was (i) rapid under normoxic conditions and slower at low oxygen tensions, (ii) coupled to *NO release, (iii) linked to the decrease in nitrite consumption and in nitrate formation, and (iv) unaffected by the nitrosation catalyst thiocyanate. Both chlorogenic acid and bovine serum albumin, representative of a phenol- and a protein-rich meal, respectively, were able to spare uric acid, although chlorogenic acid increased, whereas bovine serum albumin inhibited, *NO release. We hypothesize that the major role of uric acid in saliva at pH 2 could be to preserve the stomach from the formation of toxic nitrogen species and that low levels of uric acid, together with ascorbic acid consumption, may contribute to the high occurrence of tumors at the gastroesophageal junction and cardia. The sparing effects of dietary compounds may therefore be an important not fully appreciated effect.

Estimate of uncertainty of measurement from a single-laboratory validation study: application to the determination of lead in blood.

BACKGROUND: Lead is an environmental pollutant, and human exposure is assessed by monitoring lead concentrations in blood. Because the main source of environmental exposure has been the use of leaded gasoline, its phase-out has led to decreased lead concentrations in the general population. Therefore, validated analytical methods for the determination of lower lead concentrations in blood (<150 microg/L) are needed. In addition, new ISO standards require that laboratories determine and specify the uncertainty of their results. METHODS: We validated a method to determine lead in blood at concentrations up to 150 microg/L by electrothermal atomic absorption spectrometry with Zeeman background correction according to EURACHEM guidelines. Blood samples were diluted (1:1 by volume) with 2 mL/L Triton X-100. NH4H2PO4 (5 g/L) and Mg(NO3)2 (0.5 g/L) were used as modifiers. Matrix-matched standards were used for calibration. RESULTS: We determined the limits of detection (3.1 microg/L) and quantification (9.4 microg/L). Repeatability and intermediate imprecision within the range 35-150 microg/L were <5.5% and <6.0%, respectively. We assessed trueness by use of certified reference materials, by recovery tests, and by comparison with target values of other reference materials (candidate external quality assessment samples). The expanded uncertainty ranged from 20% to 16% (with a confidence level of 95%) depending on concentration. CONCLUSIONS: This study provides a working example of the estimate of uncertainty from method performance data according to the EURACHEM/CITAC guidelines. The estimated uncertainty is compatible with quality specifications for the analysis of lead in blood adopted in the US and the European Union.

Comparison of procedures for evaluating laboratory performance in external quality assessment schemes for lead in blood and aluminum in serum demonstrates the need for common quality specifications.

BACKGROUND: The different scoring methods used by eight European External Quality Assessment Schemes (EQASs) for occupational and environmental laboratory medicine were compared to develop suitable quality specifications as a step toward harmonization. METHODS: Real results for blood lead and serum aluminum assays, reported by participants in Italian and United Kingdom EQASs, were evaluated according to individual scheme scoring criteria. The same results were then used to produce z scores using scheme-based between-laboratory SDs as the estimate of variability to determine whether simple performance-derived quality specifications produced better agreement among schemes. RESULTS: The schemes gave conflicting assessments of participants' performance, and participants judged to be successful by one scheme could be defined as performing inadequately by another. An approach proposed by Kenny et al. (Scand J Clin Lab Invest 1999;59:585), which uses clinical inputs to set targets for analytical imprecision, bias, and total error allowable, was then used to elaborate quality specifications. CONCLUSIONS: We suggest that the CLIA '88 recommendations for blood lead (+/- 40 micro g/L or +/- 10% of the target concentration, whichever is the greater) could be used as a quality specification, although a revision to +/- 30 micro g/L or +/- 10% is recommended. For serum aluminum, a suitable quality specification of +/- 5 micro g/L or +/- 20% of the target concentration, whichever is the greater, is suggested. These specifications may be used to compare laboratory performance across schemes.

[Chemical compound safety: typology of competency accreditation for assay centers and analytical laboratories]. / La sicurezza dei composti chimici: tipologie di riconoscimento della competenza per i Centri di saggio e i laboratori di analisi.

The use of chemicals warrants many benefits on which modern society is entirely dependent. On the other hand, the lack of reliable information about the impact of the use of chemicals raises increasing concern. In order to guarantee the safety of chemicals it is mandatory to proceed to risk assessment, which in turn consists of hazard evaluation and exposure estimation. These activities are strictly dependent upon the availability of reliable data and information, produced by, e.g., test facilities, test laboratories and clinical laboratories, the specific competence of which has been properly recognised. All this applies in the pre-marketing phase as well as during the use of chemical substances. In this latter phase it is necessary to carry out an appropriate monitoring of environment, food and, in specific situations, human beings (biological monitoring). In the field of chemical safety, standards, legal instruments and operative instruments are nowadays available. These tools make it possible to assess both the quality of data and the competence of the entities involved in the production of the data themselves.