Traceability and its role in interlaboratory comparisons (proficiency testing programmes), modeled on trace element determination in biological materials

 Traceability is not always evident in proficiency testing programs, although this is a requirement in ISO/IEC Guide 43-1. The assigned, or "true", value in most programs is not traceable to an independent entity. The test materials should generally be similar in nature to those routinely tested by participating laboratories. This is far from always the case and it is important to realize that if the difference is large, there may be no traceability to the testing program. It is also important that results from participation in proficiency tests are cited when papers are published, in order to enhance reliability/credibility of the published data.

     

Requirements vs acceptability in proficiency testing schemes and other interlaboratory comparisons

Many laboratories take part in proficiency testing schemes, external quality assessment programmes and other interlaboratory comparisons. These have many similarities but also important differences in their modus operandi and evaluation of performance of participating laboratories. This paper attempts to highlight both the similarities and differences. It also puts particular emphasis on requirements called ”target values for uncertainty” and their meaning. Received: 24 January 2001 Accepted: 25 January 2001     

The determination of adsorbable organically bound halogens (AOX) in soil: interlaboratory comparisons and reference materials

The interlaboratory variability in the quantification of adsorbable organically bound halogens (AOX) in industrially contaminated soil is presented. Three consecutive rounds of a proficiency testing scheme, in which between 88 and 119 routine laboratories participated, yielded relative reproducibility standard deviations between 7 and 20% at AOX contents between 10.9 and 268 mg kg⁻¹. Nineteen laboratories with established proficiency were invited to participate in the certification of the AOX content in three soil reference materials meant for the internal quality control in analytical laboratories. The certified values are (1349 ± 59) mg kg⁻¹, (80 ± 7) mg kg⁻¹ and (102 ± 8) mg kg⁻¹, respectively.     

Mercury speciation and total trace element determination of low-biomass biological samples

Current approaches to mercury speciation and total trace element analysis require separate extraction/digestions of the sample. Ecologically important aquatic organisms--notably primary consumers such as zooplankton, polychaetes and amphipods--usually yield very low biomass for analysis, even with significant compositing of multiple organisms. Individual organisms in the lower aquatic food chains (mussels, snails, oysters, silversides, killifish) can also have very low sample mass, and analysis of whole single organisms is important to metal uptake studies. A method for the determination of both methyl Hg and total heavy metal concentrations (Zn, As, Se, Cd, Hg, Pb) in a single, low-mass sample of aquatic organisms was developed. Samples (2 to 50 mg) were spiked with enriched with (201)MeHg and (199)Hg, then leached in 4 M HNO(3) at 55 degrees C for extraction of MeHg. After 16 h, an aliquot (0.05 mL) was removed to determine mercury species (methyl and inorganic Hg) by isotope dilution gas chromatography inductively coupled plasma mass spectrometry (ICP-MS). The leachate was then acidified to 9 M HNO(3) and digested in a microwave at 150 degrees C for 10 min, and total metal concentrations were determined by collision cell ICP-MS. The method was validated by analyzing five biological certified reference materials. Average percent recoveries for Zn, As, Se, Cd, MeHg, Hg(total) and Pb were 99.9%, 103.5%, 100.4%, 103.3%, 101%, 97.7%, and 97.1%, respectively. The correlation between the sum of MeHg and inorganic Hg from the speciation analysis and total Hg by conventional digestion of the sample was determined for a large sample set of aquatic invertebrates (n = 285). Excellent agreement between the two measured values was achieved. This method is advantageous in situations where sample size is limited, and where correlations between Hg species and other metals are required in the same sample. The method also provides further validation of speciation data, by corroborating the sum of the Hg species concentrations with the total Hg concentration.     

Application of neutron activation analysis for trace element determinations in biological materials

Over the past three decades, more and more interest has been focused on trace eleemnts in biological materials. This increasing interest has gone hand in hand with the continuous improvement of analytical techniques. Neutron activation analysis has proven to be a most suitable method for the quantitative determination of a wide variety of trace (0.01–100 μg g^?1) and ultratrace (<0.01 μg g^?1) elements in biological materials. This technique has even played a preponderant role in this field.     

Applications of mass spectrometry in the trace element analysis of biological materials

The importance of mass spectrometry for the analysis of biological material is illustrated by reviewing the different mass spectrometric methods applied and describing some typical applications published recently. Though atomic absorption spectrometry is used in the majority of analyses of biological material, most mass spectrometric methods have been used to some extent for trace element determination in biomedical research. The relative importance of the different methods is estimated by reviewing recent research papers. It is striking that especially inductively coupled plasma mass spectrometry is increasingly being applied, partly because the method can be used on-line after chromatographic separation, in speciation studies. Mass spectrometric methods prove to offer unique possibilities in stable isotope tracer studies and for this purpose also experimentally demanding methods such as thermal ionization mass spectrometry and accelerator mass spectrometry are frequently used.     

Survey and evaluation of available biological reference materials for trace element analysis

Summary A database recently prepared by IAEA contains information on 60 internationally available biological reference materials (BRMs) from 9 producers. The data recorded for each material include: name, code No., cost, list of elements, and minimum weight of material recommended for analysis. For each element the concentration and its confidence interval (CI) are recorded, as well as an indication of whether the concentration value is certified or noncertified (e.g. an information value).Large differences among producers are observed in respect of how the concentration values and their CIs are defined, and how other relevant information is reported in the certificates of analysis. International recommendations on how this should be done generally do not seem to be followed.For several elements of biomedical interest there is a serious lack of BRMs namely: Al, F, I, Mo, Si, Sn and V. In addition, the CIs for the following elements are generally excessively large: Al, As, Cd, Cr, Hg, Mo, Ni, Se and V.     

Preparation of the Bovine Kidney and Bovine Muscle reference materials and the certification of element contents from interlaboratory comparisons

Results obtained in interlaboratory comparisons on candidate reference materials Bovine Kidney and Bovine Muscle, in which more than 32 laboratories participated employing atomic spectrometry, electrochemical, and nuclear analytical techniques, have been evaluated using combined statistical and analytical considerations. Certified and/or information values for the elements Br, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, P, Pb, Rb, Se, and Zn have been established. Information on contents of the elements Al, As, Au, Cs, Li, Ni, Sb, Sn, Sr, and V is also presented.     

Quality control with CRMs for trace element determination in candidate reference materials

Summary Three soil samples and five candidate materials of biological origin (bovine muscle, bovine kidney, bovine blood, rye flour and wheat flour) and one already certified RM (Bovine Liver, 12-02-01) were analyzed for their contents of Cd, Cu, Cr, Pb and Zn. Pressure digestion with nitric acid in PTFE (at 180°C) and quartz (at 290°C) vessels was used for sample decomposition. The measurements were made by graphite furnance atomic absorption spectrometry (ET-AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and square wave voltammetry. The accuracy of analysis has been checked by simultaneous analyses of six similar CRMs. An excellent agreement between the found and certified values is illustrated by highly significant correlations.     

Radiochemical determination of some trace elements in biological materials using short-lived isotopes

A radiochemical procedure for the consecutive separation of vanadium and molybdenum, copper, manganese, rubidium and potassium is proposed for the analysis of biological materials. Vanadium and molybdenum are extracted together with 0.1% BPHA solution in toluene, copper followed by manganese are extracted as diethyldithio-carbamate complexes with chloroform and rubidium and potassium are precipitated as tetraphenylborates.     

水产品中呋喃唑酮代谢物AOZ的检测能力验证分析

介绍了全国多个行业51家实验室参加水产品中呋喃唑酮代谢物AOZ的检测能力验证计划的情况。选用活虾药浴暂养后制得并通过均匀性F检验和稳定性t检验的虾肉糜样作为测试样品,采用稳健统计技术对试验结果进行了分析。讨论了水产品中呋喃唑酮代谢物AOZ检测的一些关键点。     

A comparison of two separation techniques using NaI(Tl) and Ge(Li) spectrometry for trace element determination in biological materials by neutron activation analysis

A comparison of two group separation techniques using either NaI(Tl) or Ge(Li) spectrometry is presented for trace element determination in biological materials by neutron activation analysis. The capabilities of both procedures are described in terms of detection limits, precision and accuracy for the determination of the elements As, Cd, Co, Cr, Cu, Fe, Hg, Mo, Ni, Sb, Se, Sn, and Zn in various types of biological samples. For this purpose the (standard) reference materials NBS SRM-1577 Bovine Liver, Bowen's Kale, IAEA Pig Kidney H-7 and IAEA Milk Powder A-11 were analyzed. An attempt was also made to minimize blank values for several elements.     

Accuracy and precision in the determination of perfluorinated chemicals in human blood verified by interlaboratory comparisons

Perfluorinated chemicals (PFCs) are analyzed in laboratories worldwide to determine human blood levels and exposure pathways. The development of the analytical technique has been rapid in the last 10 years, and prerequisites for accurate and precise determination of PFCs in human blood at low ng/g concentrations are today readily available. The main contributing factors are the improved LC–MS instrumentations, the increased availability of native and mass labeled PFC standards, and new column materials available for chromatographic separations. The results of the first international interlaboratory study (ILS) in 2005 on PFCs revealed relatively better analytical results for human blood analyses when compared to analyses of a number of environmental matrices. The representative accuracy for the analyses of PFCs in human matrixes reported in recent years was established in the second human serum ILS in 2006. Interlaboratory standard deviations for the two human serum samples one low level concentration and one medium level concentration were found to be 12% and 16% for PFOS, respectively, and 47% and 21% for PFOA, respectively. Reported detections for all PFCs followed a frequency of PFOS > PFOA > PFHxS > PFNA > PFDA ? PFDoA ? PFDS ? PFHxA. Due to the small number of reported values for the other perfluorosulfonates and perfluorocarboxylates, standard deviations were not established.     

High-performance liquid chromatographic determination of clioquinol and its conjugates in biological materials

A method has been established for the determination of clioquinol (C) and its glucuronide (CG) and sulfate (CS) in biological materials. C and its internal standard were extracted with benzene-pyridine from samples. CG and CS were also hydrolyzed to C and extracted by the same method. The extracts were evaporated to dryness and redissolved in methanol. The methanol solution was subjected to HPLC using a column packed with Iatrobeads 6cp.2010 and a UV monitor (254 nm). The mobile phase was 0.1 M citric acid-methanol-n-hexane (8:86:6). The detection limit of C and 1 nmole and its recovery was above 92%.     

A new calibration method for the determination of trace amounts of mercury in air and biological materials

Summary A new calibration method for the determination of mercury by CVAAS using collector preconcentration is described. The main piece of a developed calibration device is a special valve which links a closed Hg — saturated gas flow with an open flow of the carrier gas to the AA — spectrometer. This principle allows the direct injection of defined Hg-saturated gas volumes into the sample gas-flow. In this way the known systematic errors of traditional methods by contamination and loss, caused above all by the manual handling of mercury vapor or solution, are avoided. Instrumental and procedural aspects of the application are discussed and the reliability relating to the mercury determination in air and biological materials is evaluated. The new method is superior to the other calibration methods in every way. In the 1 ng Hg range the within-run precision is better than 1%, and the day-to-day precision better than 2%. The accuracy was validated by determining various biological SRMs. All the results in the g/g and ng/g level corresponded well to certified values. The new method is also a simple and reliable way of carrying out the necessary internal quality control.     

Czechoslovakian biological certified reference materials and their use in the analytical quality assurance system in a trace element laboratory

Summary The Trace Element Laboratory of the University of Agriculture in Prague (CSFR) participated successfully in interlaboratory experiments on the determination of the contents of trace elements in seven Czechoslovakian reference materials. Czechoslovakian certified reference material CRM 12-02-01 (Bovine liver) was used for the development of a new analytical method using the Dry Mineralizer Apion as well as in analytical quality assessment of data in the determination of Cd, Pb, and Hg contents in routinely analyzed animal tissues.     

Analytical evaluation of comparative data on trace elements in biological materials

Large bodies of data on a given material from different sources appear a major advantage of intercomparison experiments and a sound basis for a straight statistical evaluation (as is the usual approach in the assignment of recommended or consensus values). On closer inspection of the results, however, it is usually found that only one or two techniques are represented in statistically significant numbers, most frequently AAS and NAA, and their distribution may not be normal. Correct results are sometimes hidden among laboratory means in the lower or upper part of the frequency distribution plots. Conventional statistics neglecting procedural details and the chemistry behind a procedure may result in incorrect assignment from the reported data, which can be affected by unidentified systematic effects. Generally, in the lowest concentration range contamination predominates as the systematic error determining the accuracy of results. Activation analysis being the least vulnerable to this type of error, it is, if applicable, in principle the most likely to give correct answers. Follow-up work was carried out in this laboratory on the IAEA reference samples of Milk Powder A-11, Muscle Tissue H-4, Fish Flesh MA-A-2 and the Soil-5, clearly demonstrating the potential of activation analysis as verification technique. By determining the same element in the destructive and nondestructive mode, and on the basis of two different isotopes, virtually independent approaches are achieved, often allowing the disclosure of different types of errors. Results are also reported for nickel by a new voltammetric technique enabling its determination at the microgram per kilogram level.