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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.8, #5)
Scientist vs the law by D. Brynn Hibbert (pp. 179-183).
An Australian case study is presented in which defendants convicted of manufacturing a drug of abuse were acquitted on appeal because of shortcomings in the prosecution's case that established the identity of the material seized. The need to have proper standard operating procedures that can be followed routinely and correctly is highlighted.Education is needed for forensic analysts and the legal profession to try and produce systems in which the proper outcome is achieved.
Keywords: Forensic science Courts Uncertainty Accreditation
Achieving traceability in chemical measurement—a metrological approach to proficiency testing by Paul Armishaw; Bernard King; Roderick G. Millar (pp. 184-190).
ISO/IEC 17025 requires that testing laboratories establish the traceability of their measurements, preferably to the SI units of measurement. The responsibility for establishing traceability lies with each individual laboratory and must be achieved by following a metrological approach.The results of measurements made in such a way are traceable to the standards used in method validation and to the calibration standards used during the measurement process. If these standards are traceable to SI then the measurements will also be traceable to SI.Participation in appropriate proficiency studies (an ISO/IEC 17025 requirement) enables laboratories to demonstrate the comparability of their measurements. If the materials used for the studies have traceable assigned values, then proficiency testing also provides information about measurement accuracy and confirms, or otherwise, that appropriate traceability has been established. This paper will report on a new approach for the establishment of traceable assigned values for chemical testing proficiency studies. The work is conducted at a "fit for purpose" level of measurement uncertainty, with costs contained at a level similar to previous "consensus" based proficiency studies. By establishing traceable assigned values in a cost effective way, NARL aims to demonstrate the added value of the metrological approach to participant laboratories.
Keywords: Traceability Metrological Chemical Proficiency Testing
High accuracy analysis by isotope dilution mass spectrometry using an iterative exact matching technique by Lindsey Gillian Mackay; C. Peter Taylor; Richard Bruce Myors; Ruth Hearn; Bernard King (pp. 191-194).
The selection of an appropriate isotope dilution mass spectrometry technique for the practical application of this potentially primary method of analysis is highly important. The NARL approach for the application of the exact matching double isotope dilution mass spectrometry technique developed by Henrion is presented. NARL's approach utilises exact matching to minimise the effect of measurement biases within the method but also includes the thorough examination of all other biasing factors. The approach has been successfully tested in international CCQM intercomparisons with other national metrology institutes.
Keywords: Isotope dilution mass spectrometry (IDMS) Exact matching Primary method
The measurement uncertainty of ratios which share uncertainty components in numerator and denominator by D. Brynn Hibbert (pp. 195-199).
When calculations are made of ratios of values of the same kind of quantity, correlations often arise from the use of the same instrument to make the measurement. The combined uncertainty in this case is usually much smaller than that from a treatment in which the numerator and denominator are assumed to be independent. For a simple ratio % MathType!MTEF!2!1!+- % feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOuamaala % aabaGaamyyaaqaaiaadkgaaaaaaa!389F! $$ R{a over b} $$ , with a and b having the identical uncertainty u, the relative uncertainty in R is given by % MathType!MTEF!2!1!+- % feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaada % WcaaqaaiaadwhaaeaacaWGHbaaamaabmaabaGaaGymaiabgkHiTiaa % dkfaaiaawIcacaGLPaaaaiaawEa7caGLiWoaaaa!3F05! $$ left| {{u over a}left( {1 - R}
ight)}
ight| $$ . This type of positive correlation usually reduces uncertainty and may cancel when the ratio is unity. An example from the EURACHEM guide, Quantification of Uncertainty in Analytical Measurement, overestimates the combined uncertainty of a titration by assuming complete independence of terms in a ratio.
Keywords: Measurement uncertainty Correlation Standard addition Propagation of uncertainty
Measuring atmospheric carbon dioxide—the calibration challenge by Roger James Francey; Lloyd Paul Steele (pp. 200-204).
The measurement of CO2 in the atmosphere presents a significant metrology and quality assurance challenge. While global trends can be well determined with just a few sampling sites, the plethora of natural processes involved in exchange of CO2 with the atmosphere makes the identification of those most effective in regulating the long–term atmospheric levels elusive. To unambiguously link particular processes with significant global trends requires continuous monitoring of small spatial and temporal differences in the atmospheric mixing ratio of CO2 (and related tracers) over the major global CO2–exchanging regions. Such differences are often comparable in magnitude to the precision of conventional non–dispersive infrared or gas chromatograph analysers, and much smaller than the uncertainty in the link to a primary standard. In general, laboratories cannot currently merge data at high precision and thus achieve adequate global coverage. We describe an improvement in precision (and operating cost) of the conventional infrared analyser technique. Apart from immediate biogeochemical applications, the new system has demonstrated outstanding diagnostic capabilities and revealed a number of unsuspected sources of bias affecting conventional measurement and calibration methods. In addressing these biases, opportunities are created to improve the link between CO2 measurement and fundamental constants, and to improve the propagation of CO2 standards to field measurement systems.
Keywords: Carbon dioxide Infrared analyser Measurement bias Metrology
An uncertainty evaluation for multiple measurements by GUM, II by JongOh Choi; Dal-ho Kim; Euijin Hwang; Hun-Young So (pp. 205-207).
The former approach is extended to determine the overall uncertainty by combining the uncertainties of the individual results of n measurements where the difference in the individual results is statistically significant. The difference, defined as an unrecognized uncertainty arising from a random effect, is considered as an additional uncertainty. Now, it is possible to determine the overall uncertainty by combining the uncertainties of the individual results whether the individual results are statistically different or not.
Keywords: Uncertainty Multiple measurements Covariance Uncertainty propagation GUM
A comparison of the complimentary and different issues in ISO/IEC 17025 and OECD GLP by Tina Engelhard; Etty Feller; Zahava Nizri (pp. 208-212).
Laboratories with a quality system accredited to ISO/IEC 17025 have a definite advantage, compared to non-accredited laboratories, when preparing their facilities for the Organization for Economic Cooperation and Development good laboratory practice (OECD GLP) recognition. Accredited laboratories have an established quality system covering the administrative and technical issues specified in the standard. These issues include: internal audits, job descriptions and responsibilities, procedures for equipment/instrument maintenance and calibration, document control, handling of reagents, chemicals and reference materials, sample reception and sampling, validation of test methods, traceability and uncertainty of the test results, training of personnel, client complaints, corrective and preventive actions. Several of these issues are also required for OECD GLP recognition either with a different emphasis and/or with additional requirements. This article describes the complimentary and additional issues of ISO/IEC 17025 and the OECD GLP series of principles.
Keywords: GLP ISO/IEC 17025 Quality system
Basic calculations about the limit of detection and its optimal determination by Walter Huber (pp. 213-217).
The limit of detection (LOD) is based strictly on an accepted probability for a false positive decision (type 1 error). For the needed standard deviation of the blank, a basic value for the calculation, three experimental different methods are described, which should be applicable in every case. Table values for simple but exact calculation, not only for single, but also for mean values, and with probabilities for the type 1 error of 1% and 5% are presented. Demands for an acceptable uncertainty of the LOD and for the validation of the result are specified.
Keywords: Limit of detection Table values Uncertainty Validation
Estimating measurement uncertainty in an afternoon. A case study in the practical application of measurement uncertainty by Paul Armishaw (pp. 218-224).
The ISO/IEC 17025:1999 standard requires chemical testing laboratories to have an estimate of the uncertainty of their measurements. This is a new requirement for many laboratories and there is confusion as to how to estimate uncertainty. Concerns have been raised about the time and effort required to obtain uncertainty estimates.Uncertainty budgets were prepared for the measurement of benzene, toluene, ethyl benzene and xylenes (BTEX) in water using purge and trap coupled with GC/MS. A time limit of one working afternoon (2 pm–5.30 pm) was imposed for preparing the uncertainty estimate. Details of the uncertainty estimate for toluene are described.The method in question had been in routine use for several years and the laboratory held third party (NATA) accreditation for the test. Consequently a considerable amount of performance data was readily available. Relevant information was extracted from the documented test method, validation data, instrument calibration and from routine quality control. This data was combined according to the principles of the ISO Guide to the Expression of Uncertainty, as promulgated in the Eurachem document "Quantifying Uncertainty in Analytical Measurement."The uncertainty estimates were compared to estimates obtained from generalised empirical models (the Horwitz and Lowthian equations), and from interlaboratory studies of this analysis.A traceability chain from routine measurements to the SI units of metre, kilogram and mole is described.Realistic and useful uncertainty estimates were obtained with a few hours work using data extant in the laboratory.
Keywords: Measurement uncertainty Traceability Toluene in water
Uncertainty budget for final assay of a pharmaceutical product based on RP–HPLC by Thomas Anglov; Kirsten Byrialsen; Jan Karkov Carstensen; Finn Christensen; Steen Christensen; Birger Stjernholm Madsen; Else Sørensen; Jeanett Norrbohm Sørensen; Karin Toftegård; Henrik Winther; Kaj Heydorn (pp. 225-230).
Compliance with specified limits for the content of active substance in a pharmaceutical drug requires knowledge of the uncertainty of the final assay. The uncertainty of measurement is based on the ISO recommendation as expressed in the Guide to the Expression of Uncertainty in Measurement (GUM). The reported example illustrates the estimation of uncertainty for the final determination of a protein concentration by HPLC using UV detection, using the approach described by EURACHEM/CITAC. The combined standard uncertainty for a protein concentration of 2400 µmol/L was estimated to be 14 µmol/L.. All known and potential uncertainty components are presented in Ishikawa diagrams and were carefully evaluated using Type A or Type B estimates. Special efforts were made to avoid duplication or omission of significant contributions to the combined uncertainty. Hence, before accepting the uncertainty budget, the estimated combined standard uncertainty was verified using the variation observed in a number of quality control samples.
Keywords: Uncertainty budget HPLC Drug assay Validation data Verification
Determination of the expiration date of chemical solutions by J. M. F. Nogueira; P. Serôdio (pp. 231-234).
Thirty-five chemical solutions, acids, bases, complexing, argentometric, reducing, oxidising, salts and eluent mixtures, were studied continuously over a 7.5-month period. Twenty-seven remained reasonably stable and had acceptable expiration dates, which were equal to or more than 2 months longer than the established average deviation of ±2% relative to the initial value. Exceptions were made for potassium permanganate (0.1 M), perchloric acid (0.1 M) and disodium hydrogen phosphate (10%) solutions, as well as for HPLC eluent mixtures, which showed stability with expiration dates equal to stated values or shorter by 1 month. The eight chemical solutions presenting expiration dating higher than 6 months were hydrochloric acid (0.1 and 1 M), sulphuric acid (0.5 and 1.5 M), ethylenediamine tetraacetic acid (EDTA) (0.1 M), silver nitrate (0.1 M), ammonium thiocyanate (0.1 M) and iodine (0.1 M). The present data is a suitable guideline for the date of several chemical solutions routinely used in the analytical laboratories.
Keywords: Date Chemical solutions Stability Shelf-life Chemical analysis
Validation of salt spray corrosion test by Eugenija Ramoškienė; Mykolas Gladkovas; Mudis Šalkauskas (pp. 235-241).
Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment.Corrosion tests have been conducted for a long time but there are only a few cases of corrosion data quality assessment or interlaboratory comparisons for such measurements. Each test method when used in different laboratories gives different results, as it is impossible to perform the whole procedure exactly in the same manner. Therefore, a very essential parameter of the method is its robustness. A proper validation of the corrosion test method means the evaluation of the impact of various environmental features and performance variations on the uncertainty of the test result.Our aim was to present an experimental evaluation of the corrosivity of the salt spray corrosion test cabinet, to indicate the gaps in the description of the corrosion test method according to ISO 9227 and to estimate the main components of the uncertainty of the corrosivity measurement.The validation results require changes in the salt spray test method description and maybe in the performance.
Keywords: Validation of method Corrosivity Measurement uncertainty
Validated reference standards to support the identification of asbestos fibers by Ivančica Trošić (pp. 242-246).
National Institute for Occupational Health and Safety stated: "all levels of asbestos exposure demonstrated asbestos-related diseases and there is no level of exposure below which clinical effects do not occur". New legislation in European Community and the United Nations Environment Program states that all forms of asbestos should be banned and added to an international list of chemicals submitted to trade controls. The asbestos reference standards have been prepared and validated by Institute of Occupational Medicine under contact to the Health and Safety Executive, UK. The identification of commonly encountered asbestos fibers is performed with a dispersion staining objective using well matched high dispersion liquids. The certainty of the method is analyst dependent, since the subjective nature of asbestos analysis is involved. Appropriate training is of fundamental importance to both sampling and analysts. Microscopic determination of asbestos requires the analyst to make repeated assessments of a number of physical properties and maintain consistent diligence in the search for fibers. Analysts should be thoroughly familiar with the appearance and characteristic of asbestos. Misidentification occurs not only when other kinds of fibrous material are incorporated into a bulk material, but also when more than one kind of asbestos are present in such a material. For routine purposes the examinations by means of polarized light microscopy (PLM) are usually sufficient to identify positively whether asbestos is present and its type.
Keywords: Asbestos Identification Polarized light microscopy Reference asbestos samples High dispersion liquids Interpretation
The role of reference materials in analytical chemistry by A. Zschunke (pp. 247-251).
The paper demonstrates a concept and possible models for an international infrastructure of chemical measurements by using reference materials.The function of reference materials to establish traceability and means of quality assurance is emphasized.
Keywords: Amount of substance standards Chemical composition standards Traceability Third party assessment Primary reference materials
BERM-9—9th International Symposium on Biological and Environmental Reference Materials
by Jean Pauwels (pp. 255-255).