Control charts in multi-element analysis of human urine

A plan for internal quality control (IQC) was designed to monitor the quality of analytical results obtained from the simultaneous determination by ICP-MS of nine trace elements (As, Cd, Mo, Ni, Pb, U, V, W and Zr) in 1350 samples of human urine collected as part of an epidemiological study. Analytical performances, assessed during the method validation, were as follows: limit of quantification ranging from 0.002 μg/L (U) to 0.9 μg/L (Ni); recovery rates varying between 82 % (As) and 110 % (W); intermediate precision as relative standard deviation ranging from 2.5 % (Mo) to 14.2 % (V). Only for Zr, a significantly higher relative standard deviation was obtained. Initially, two commercially certified reference materials (CRMs) based on freeze-dried human urine and containing the elements of interest at suitable levels of concentration were used as control materials. However, due to considerations of reliability, convenience and cost, a control material based on fresh human urine was prepared in-house, evaluated by comparison with the CRMs and implemented for the IQC. The IQC strategy was as follows: at least one control material was analysed in each analytical session and one more control material was analysed after every ten urine samples. The central lines of the control charts were based on the assigned concentration values; the warning and action limits were set on a statistical basis, as two-times and three-times the value of the uncertainty of certified values or the observed standard deviation. At the end of the study, the data collected for the in-house control material were re-evaluated and confirmed its suitability for the purpose. The use of an in-house control material had important advantages: it was more representative of the test samples; its preparation did not involve additional steps, therefore, reducing the risk of contamination; the cost of implementing the IQC was also reduced. Some issues concerning the control charts for As and Mo were addressed and will be discussed.     

Preparation of liquid milk for proficiency test and internal quality control for chemical elements in food

Laboratories dealing with the analysis of food of animal origin have to face the shortage of both appropriate certified reference materials and pertinent proficiency tests (PTs). Therefore, internal quality control (IQC) materials have to be prepared in-house. The combination matrix/analytes/concentration, as well as the physical state, is a key issue. The European Union Reference Laboratory for Chemical Elements in Food of Animal Origin (EURL-CEFAO), within its activity as PT provider, has set a procedure to prepare test items of liquid milk spiked with arsenic, cadmium and lead at adequate values of concentration. This work describes in detail the steps of this procedure. Homogeneity and stability of the PT test items thus prepared were evaluated by the EURL-CEFAO using a sensitive and accurate method accredited according to ISO/IEC 17025. The analyte concentrations in spiked milk were found stable up to 18 months which is of particular interest for cadmium due to the low value of spiking (roughly 5 μg/kg). The outcome proves that the procedure used to prepare liquid milk spiked with chemical elements is suitable to produce in-house reference materials stable enough for analytical purposes. Furthermore, this procedure is easy to perform and can be applied by routine laboratories to produce samples for their IQC.     

Internal quality controls applied in inductively coupled plasma mass spectrometry multi-elemental analysis in the second French Total Diet Study

In 2006, the French Food Safety Agency (AFSSA) started the second French Total Diet Study to assess exposure to essential and non-essential elements through dietary intake by analysing 1352 food samples. A total of 21 elements were analysed to date by Inductively Coupled Plasma Mass Spectrometry after closed vessel microwave digestion, in 660 samples corresponding to at half of the study. This work presents and discusses the results of the various internal quality controls (IQC) applied to ensure that the analytical procedure is correctly carried out, from digestion to analysis, and to enable analytical chemists to validate the results obtained. The whole IQC allows to estimate uncertainties according to elements and to select those that should be discarded from the study or only given as indicative values for elements that were not within defined quality limits.     

Clinical quality vs analytical performance: what are the right targets and target values?

For optimal performance of laboratory tests, testing processes should be designed to provide clinically useful quality and QC procedures should be selected to assure that the necessary clinical quality is achieved in routine production. One important issue is how to define clinical quality. Today’s practice guidelines, quality regulations, and quality standards provide some targets for analytical quality, but they fail to adequately address clinical quality. Target values for precision and accuracy are not the same as clinical quality, though analytical performance certainly contributes to the clinical quality of test results. How can we proceed in our quest to improve quality when there are inconsistencies and inadequacies in the specifications found in practice guidelines, regulations, and standards? Today target values are often being set for the wrong targets. A better approach is possible if we focus on test interpretation guidelines to define clinical quality, then derive specifications for the accuracy and precision that are appropriate for the method, as well the QC rules and numbers of control measurements that are necessary to guarantee the desired quality will be achieved in routine operation of the testing process.     

Strategies for internal quality control in antidoping analyses

Internal quality control (IQC) is one of the most important elements contributing to quality assurance in the laboratory. In this study, the strategy for the implementation of an IQC program to monitor performance of the analytical procedures used in an antidoping control laboratory is presented. Different IQC parameters have been defined according to the aim of the method (qualitative or quantitative, screening or confirmation). They are based on the analysis of control and calibration samples in each analytical batch and on the use of an internal standard in chromatographic methods. IQC parameters for chromatographic and immunological methods and the acceptance criteria used to check the quality control data obtained are described and discussed. These IQC procedures have been applied during routine antidoping analyses of more than 5000 samples per year in a laboratory accredited by the International Olympic Committee (IOC) and meeting the requirements of the quality standard ISO 17025.     

Method of comprehensive and accurate rheological material characterization

A new rheological test procedure is described, which provides a comprehensive, precise and reliable characterization of the material at reasonable cost, and which was developed specially for rubber polymers. It is based on the established Defo test and is largely automatic including evaluation and recording.The six rheological characteristics values are described, together with control values which automatically arise. The new test values have a good selectivity. The work shows that raw polymers examined so far, from a narrow Mooney range of 46–56 ML (1+4) 100°C, can be divided into some 400 different rheological classes because of this high selectivity in viscosity and elasticity alone.The test can be conducted on the virtually unstrained ‘virgin’ polymer. Its high selectivity (difference in test values for change of quality, relative to repeatability inaccuracies) makes it suitable also for examining rheological change in the polymer under thermal, mechanical, or combined loads by testing before and after loading. Empirically determined relationships between macrostructural features and the new rheological test values are set out. Details must await later publication because of present space limitations. Some examples of relationships with processing properties are discussed.     

Geochemical investigation of alluvial sediments: validation of ICP-OES determination of heavy metals. A case study from the Utrata River Valley (central Poland)

The development and validation of a reliable analytical procedure for the determination of selected metals (Cd, Cr, Cu, Pb, Zn and Mn) in sediments accumulated in the Utrata River (Poland) is described. The aqua regia extraction followed by inductively coupled plasma optical emission spectrometry (ICP-OES) was used for this purpose. The optimized analytical procedure was validated, and adequate quality control actions were implemented in order to provide reliable data. The precision under’ within-laboratory’ reproducibility conditions was estimated from duplicate analysis. Certified reference material (CRM) was used in order to evaluate the accuracy of the results regarding the sewage sludge amended soil CRM 143R. The detection limits for all elements of interest were well-below their content in the investigated sediment samples. The obtained reliable data could be used for assessment of the relationship between human economic activity in the past and the geochemical features of the sediments.     

Decreasing analysis time in capillary electrophoresis: validation and comparison of quantitative performances in several approaches

Capillary electrophoresis (CE) can be used for the rapid determination of pharmaceuticals, particularly in routine quality control analysis. This paper focuses on several approaches aimed at decreasing the analysis time with commercially available instrumentation by (i) application of a high electric field through a reduced capillary, (ii) use of a dynamically coated capillary to increase the electroosmotic flow, (iii) short-end injection (SEI) technique, and (iv) application of multiple sample injections. Moreover, SEIs were combined with the three other approaches. A pharmaceutical formulation containing lidocaine as an active component was selected, and the methods were validated according to the ICH guidelines. The seven approaches investigated fulfilled different statistical requirements and demonstrated their linearity and trueness, with good recoveries and confidence limits always inferior to 1.5%. Furthermore, relative standard deviation (RSD) values for repeatability and intermediate precision were inferior to 1.1 and 1.8%, respectively. These results confirmed that each approach is of utmost interest to increase the analyte throughput in CE.     

Selenium in electrolytic manganese as a reference material for the quality control of aluminium melts

Electrolytic manganese is an important alloying element for aluminium and steel melts. It is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of manganese and aluminium powders). Selenium derivates are usually added during the production of electrolytic manganese, so some selenium is present in the alloys produced when electrolytic manganese is added to the aluminium furnace. Since the selenium contents of many alloys are of concern from health and environmental perspectives, their values should be provided. In this work, a laboratory reference material (LRM) based on electrolytic manganese was produced to assure our routine quality control method, where selenium is analysed by hydride generation followed by optical emission spectrometry with inductively coupled plasma (HG–ICP–OES). Therefore, the present paper describes in detail the preparation procedure for and the results from homogeneity and stability studies performed on electrolytic manganese LRM. For this purpose, a commercial electrolytic manganese lot was selected and the main factors involved in the preparation of the material (pretreatment step, homogenization, bottling and storage) were carefully studied and established in order to guarantee the long-term stability of the LRM. The results obtained showed that the LRM developed was a fit-for-purpose material for the quality control of the routine analysis of selenium.     

Instability and heterogeneity: a new approach needed!

The outcome of routine testing for instability and heterogeneity of materials used in proficiency tests tends to be weakly informative because of the unacceptable cost of obtaining enough data to support a suitably powerful statistical test. A better strategy would be to spend considerably more on a large initial validation of a type of material or a procedure for preparing it, and then to monitor all subsequent batches of material of that type by a much cheaper quality control system. The expense of a powerful validation would be quickly recouped by savings in the longer term. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

An attempt at quality control based on the recovery test in radioimmunoassay

Quality control sera for radioimmunoassay (RIA) are supplied commercially, as lyophilized sera will become more common due to the ease of their usage, good reproducibility and the constant supply. This paper demonstrates the improvement in accuracy and precision of analyses proved over the year by the tracking of recovered and recommend proper analysis simplified enough for routine application. The recovery test for quality control is described and can be used to control intra-day variation with R values and to control long-term intra and inter-day variation and suits the purpose that is not supported by commercial control sera well.     

The use of uncertainty estimates of test results in comparisons with acceptance limits

When a test is performed in order to qualify a material or a product for a certain use, the result is generally compared with an acceptance limit. The test result has an uncertainty which should be estimated and stated (e.g. in accordance with GUM). Very often this is not the case. Further, discussions often arise on the issue of how the uncertainty shall be considered in relationship to the acceptance limit. The intention of this note is to describe, in simple terms, the statistical background and to give some recommendations. In short, there are two clean-cut, extreme situations. The first case is when the uncertainty of the testing procedure is the dominating factor. Here it is found that the estimates of single laboratories cannot, generally, be used for comparisons with acceptance limits. One should have standardised, well-verified estimates based on comprehensive investigations of the method. It can also be concluded that comparisons between test results and acceptance limits have to be made with regard to the actual circumstances, as, e.g. how the acceptance limit is related to the risk. In the second case, the variation in the property of the material or product dominates and the uncertainty of the testing procedure is negligible. When the results are non-quantitative (go – no go), statistical methods can be used to estimate the risk taken with a certain sampling and acceptance strategy that a certain proportion of the batch to be delivered does not qualify. This should be considered more often in standardisation of product test methods. When the results are quantitative, a statistical analysis should be performed and the uncertainty should be compared with the acceptance limit as before, from the actual circumstances. When effects of testing uncertainty and product variation are comparable a sound treatment requires extensive experimental work. No short cuts can be made without loss of confidence! Received: 17 August 2001 Accepted: 21 March 2002     

Determination of cadmium,copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry

Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g⁻¹ for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g⁻¹ for lead, and 0.014 μg g⁻¹ for copper.     

External quality assessment schemes for clinical laboratories

 The clinical routine laboratory generally utilizes cheap, easy and rapid measurement procedures ("methods") in order to meet the requirement for the production of many analytical results (500–3000 per day) of hundreds of different types. The measurement procedures are optimized for the analysis of native patients' samples, but are frequently sensitive to deviation of the composition of the matrix from that in normal fresh samples. The inherent lack of stability of patient samples means that control samples need to be stabilized. The method of stabilization is critical. Furthermore, the method of "spiking" samples with pathological material is a matter of concern. Generally, minimally processed patients' samples should be used in external quality assessment (EQA) schemes. Consensus values are currently the most popular for use as a guide to the best results from participating laboratories in EQA schemes; these often work fairly well. However, the uncertainty and traceability of this type of value is unknown, and in some cases may even be misleading, tending to preserve bad routine methods when these are dominant in the participating laboratories. Reference measurement procedure (RMP) values are recommended to provide scientifically based information, to facilitate the proper choice of methods in the routine laboratories, and to validate the suitability of control materials in EQA schemes. The present paper provides selected examples from a study comparing consensus values with RMP values on lyophilized sera, and also presents results on a fresh frozen thawed serum for the study of commutability. Received: 8 November 1995 Accepted: 8 May 1996     

Estimation of limits of detection and determination in X-ray fluorescence analysis by the dependence of the relative standard deviation on analyte concentration

An experimental dependence of the relative standard deviation on analyte concentration of hyperbolic type, characterizing the precision of quantitative chemical analysis, was used to estimate the limits of detection and determination in the X-ray fluorescence analysis. A method is proposed for the determination of their values using the approximation of the experimental dependence of the relative standard deviation on the analyte concentration by a power function. The choice of the values of the relative standard deviation, being criteria for the estimation of these limits, is substantiated. A concept of the limits of detection and determination of an analytical procedure is formulated, according to which the limit of detection of an analytical procedure is an objective value depending only on the precision of determinations, and the limit of determination of an analytical procedure is a subjective value depending not only on the precision of determinations but also on the requirements to their limiting (admissible) accuracy. The limits of detection and determinations of an analytical procedure found by this approach completely characterize the possibilities of an analytical procedure in determining low concentrations of analytes. The proposed approach can be used for the estimation of the limits of detection and determination of analytical procedures and in other methods of chemical analysis with the hyperbolic dependence of the relative standard deviation on the analyte concentration.     

Multielement analysis with ICP-AES-possibilities for quality control with CRMs

Summary An analysis using Certified Reference Materials (CRMs) together with routine samples is by far the best approach for quality control in multielement analysis of environmental samples. The selection of the correct CRM is thus the first important step for all reliable analysis. The chosen material should have a similar matrix, similar concentration of the element(s) of interest and a sufficient number of well-certified elements. For the analysis of samples from the Environmental Specimen Bank only a few CRMs could be successfully used. These were analyzed for a considerable period of time, together with the routine samples for quality control. The results of these analyses were compared with the certified values.     

Auswahl,Vergleich und Bewertung optimaler Arbeitsbedingungen für die quantitative Mehrkomponenten-Analyse

Calibration and analytical measurements in spectrometric multicomponent analysis can be solved by linear algebra supposing the observed values being a homogenous linear function of the expected quantities. The increase of precision is one of the most important problems for the analyst. Using two-dimensional overdetermined systems of equations precision can be extended up to the outer limits. In calibration procedures both the number of calibration samples and wavelengths should be higher than the minimum, in analysis the overdetermination in the number of wavelengths is sufficient. Two alternative ways in producing the amount of overdetermination by “repetitive and additive measurements” respectively, are discussed on the basis of information theory. The metric functional term “sensitivity” can be derived from the matrix of the system. There exists an statistical correlation between this term and the precision of analysis. A stepwise maximisation procedure of the sensitivity in the system to be solved is used as a criterion of decision.     

Gas chromatographic method for assessing the dermal exposure of greenhouse applicators to dimethoate and malathion

An analytical method is developed to determine potential and actual dermal exposure to dimethoate and malathion for agricultural workers using whole body dosimetry. The methodology described includes three different aspects: the validation of the analytical method incorporating a matrix effect for establishing performance parameters such as recovery rates (between 92% and 103% for both pesticides), limits of detection and quantitation, and precision of measurements (RSD < 10%); a field sampling strategy developing a procedure for collecting samples and carrying out field spikes and field blanks in order to ensure the stability of samples during transport, storage, and analysis; and finally, a quality control procedure for ensuring that data are under statistical control. The method is applied to evaluate the potential and actual dermal exposure as well as its distribution for a pesticide applicator and the applicator's assistant after a greenhouse application. Operator exposure levels of approximately 68 mL/h, and 25 mL/h in the case of the assistant, are found. The body areas most exposed are the lower body and hands.     

Trueness, precision, and detectability for sampling and analysis of organic species in airborne particulate matter

Recovery, precision, limits of detection and quantitation, blank levels, calibration linearity, and agreement with certified reference materials were determined for two classes of organic components of airborne particulate matter, polycyclic aromatic hydrocarbons and hopanes, using typical sampling and gas chromatography/mass spectrometry analysis methods. These determinations were based on initial method proficiency tests and on-going internal quality control procedures. Recoveries generally ranged from 75% to 85% for all target analytes and collocated sample precision estimates were generally better than 20% for polycyclic aromatic hydrocarbons and better than 25% for hopanes. Results indicated substantial differences in data quality between the polycyclic aromatic hydrocarbons and hopanes. Polycyclic aromatic hydrocarbons demonstrated better collocated precision, lower method detection limits, lower blank levels, and better agreement with certified reference materials than the hopanes. The most serious area of concern was the disagreement between measured and expected values in the standard reference material for hopanes. With this exception, good data quality was demonstrated for all target analytes on all other data quality indicators.     

C2-C8 hydrocarbon measurement and quality control procedures at the Global Atmosphere Watch Observatory Hohenpeissenberg

A new automated on-line GC-flame ionization detection system for long-term stationary measurements of atmospheric C2-C8 hydrocarbons in the lower ppt range is described. The system is operated at the Global Atmosphere Watch Observatory Hohenpeissenberg (47 degrees 48'N, 11 degrees 01'E) in rural south Germany. Atmospheric mixing ratios of more than 40 different hydrocarbons can be continuously measured in 80 min time intervals. Corresponding detection limits are below 3 ppt, except for propene, butenes and benzene (about 10 ppt). Detailed quality assurance and quality control protocols are described which are applied to routine operation and data analysis. The various error contributions, overall precision, and accuracy for all measured compounds are discussed in detail. Typical ambient air mixing ratios are in the range of a few ppt to a few ppb, and corresponding measurement accuracies are below 10% or 10 ppt. For less than 20% of the analyzed compounds measurement accuracies are worse, mainly because of insufficient peak separation, blank values or reduced reproducibilities. The present system was tested in international intercomparison experiments (NOMHICE, AMOHA). For most of the C2-C8 hydrocarbons analyzed, our results agreed better than +/- 10% (20% NOMHICE phase 5) or +/- 10 ppt with the corresponding reference values.