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Analytical and Bioanalytical Chemistry (v.360, #3-4)

Seventh International Symposium on Biological and Environmental Reference Materials (BERM-7) by Jean Pauwels; M. Stoeppler; Wayne R. Wolf (pp. 275-276).

Reference materials in the world of tomorrow by S. D. Rasberry (pp. 277-281).

Good projections about the use of reference materials (RMs) in the world of tomorrow are especially important to RM producers. They need to know what kinds of RMs will be required in the future, by whom, and for what purposes. They need to know what batch sizes to prepare of different kinds and how to allocate limited resources to best effect. The following steps may provide a useful view of the future of reference materials: (1) Review of trends, (2) Projection of challenges, (3) Analysis of driving forces and construction of scenarios, (4) Thinking “outside the box,” and (5) Selecting strategies. This paper will illustrate the use of these steps for the field of reference materials in order to provide a framework for the role of reference materials in the world of tomorrow.

Global activities in the world of reference materials including the needs of developing countries by Venkatesh Iyengar; Wayne Wolf (pp. 282-286).

Proceedings of previous BERM meetings have been used to assess emerging trends in the development of RMs to meet AQC requirements of clinical, food, nutrition, and environmental health areas. BRM-1 reflected a strong need to initiate and expand RM activities for certifying organic nutrients in foods. BRM-2 highlighted the distinction between primary (certified) and secondary (e.g. check samples for proficiency testing) RMs¹. BRM-3 identified the need for producing different levels of an analyte in a given matrix (spiked standards) to address matrix related measurement problems in foods. BERM-4 highlighted the need for a global vision in dealing with standards, illustrated by the activities of GESREM. Also, the logistics required for setting up intercomparison programs related to food safety monitoring programs were outlined. BERM-5 presented the changing outlook of the AOAC International in recognizing the usefulness of incorporating RMs for use in conjunction with their methods validation protocol. BERM-6 brought to the forefront the concern for traceability of chemical measurements to internationally recognized standards. BERM-7 recognized the need for multidisciplinary approaches for preparing certain types of CRMs, partly in response to the measurement needs arising from governmental regulations dealing with food safety and environmental health criteria. Finally, BERM symposia have promoted a meaningful dialogue on the RM needs of African, Asian and South American countries and provided the developing countries opportunities to discuss their problems with the international analytical community. The issue of health safety is involved in movement of foodstuffs between countries, and therefore, international efforts as voiced by the World Health Organization to provide guidance and assistance in AQC matters to the needy countries deserve consideration.

IAEA analytical quality assurance programmes to meet the present and future needs of developing countries by R. M. Parr; A. Fajgelj; R. Dekner; H. Vera Ruiz; F. P. Carvalho; P. P. Povinec (pp. 287-290).

For many years the International Atomic Energy Agency (IAEA) has been promoting analytical quality assurance and quality control in its Member States with emphasis on measurands that are amenable to analysis by nuclear and related techniques, i.e. radionuclides, trace elements, and stable isotopes. This paper reviews briefly the rationale for some of these activities, particularly in relation to the needs of participants in developing countries arising out of co-ordinated research programmes, technical co-operation projects and global and regional networks. Emphasis is given to biological and environmental reference materials with a matrix of natural origin. Also described are some activities arising out of the requirements of ISO-25 and other relevant international quality standards.

Development and use of reference materials in India – status and plans by R. S. Mahwar; N. K. Verma; S. P. Chakrabarti; D. K. Biswas (pp. 291-295).

Reference materials development activities in India started during the period 1955–1960 for quality control in the production and use of drugs and pharmaceuticals. While the practice of import and distribution gradually accelerated in some areas, including medical, environment etc., the earliest known development of Certified Reference Materials (CRMs) within the country began with the preparation of metallurgical CRMs somewhere around 1965. A few more area-specific programs involving preparation of CRMs for quality control in the electronic industries, food and food products etc., began in the past decade. A common national program covering these activities was initiated in 1996, through organization of a national workshop on the subject and formation of a National Task Force for the development and use of reference materials in the country. The existing status and the priority needs of reference materials have been compiled by the Task Force, and a program has also been prepared for development of some of the urgently required CRMs within the country.

Production and certification of environmental reference materials in Romania by S. Duţă (pp. 296-298).

Preparation techniques for single-element and multielement standard solutions, with special emphasis on the potential progress in this field are presented. A short review of locally available reference materials is given. Some aspects of the experience accumulated in Romania regarding the various certification approaches of reference materials are presented and the main characteristics of these certified reference materials are listed.

The production of powdered candidate biological and environmental reference materials in the laboratories of the Joint Research Centre by G. N. Kramer; H. Muntau; E. Maier; J. Pauwels (pp. 299-303).

The production of candidate biological and environmental reference materials in the laboratories of the Joint Research Centre, mainly on behalf of BCR, started in 1972 in Ispra and became concentrated in 1984 in Geel. Today, dedicated facilities for the transformation of biological and solid or liquid materials into dry powder samples are in use. The major guidelines followed in the conception of these facilities are described. Some typical examples of facilities developed or adapted to fulfil the specific requirements of professional CRM preparation are discussed, e.g. the whole-Teflon cryo-grinding equipment, the in-line controlled freeze-drier, the special facility for clean and dry handling of powders, the milling with classification equipment and the automation of bottling and labelling operations.

Certified reference materials for extractable trace metals in soils: effect of the particle size by A. Sahuquillo; H. Bosch; G. Rauret; H. Muntau (pp. 304-307).

Homogeneity of a soil reference material was tested at two different stages of production: in the bulk material and after bottling. To increase homogeneity in the bottle, the material may be ground thoroughly, but this may change the material and consequently the extractable trace metal content even the stability of the extractable contents over time may change. These effects were studied for Cd, Cr, Cu, Ni, Pb, and Zn using acetic acid and EDTA as extracting solutions. Hard grinding of the soil increased or decreased the extractability of some heavy metals depending on the metal and the extractant, whereas the stability of the material was not affected by this treatment, except for Cd when using EDTA. As the homogeneity achieved in bottle by a short manual shaking was sufficient for the procedure studied, no hard grinding is recommended.

A synopsis of different approaches to the certification of reference materials by Milan Ihnat (pp. 308-311).

Proliferation of Biological and Environmental Reference Materials (RMs), agencies and individuals preparing and characterizing them for a wide variety of inorganic and organic chemical constituents, makes it pertinent to look at the various certification approaches followed. This synopsis presents amalgamated versions of several of the major certification approaches, for natural-matrix RMs, alluding to some of the many factors that significantly affect the conduct and outcome of the analytical characterization exercises.

Certification strategies for health-related SRMS at NIST by M. Welch; Jennifer Colbert (pp. 312-316).

Inaccuracy in health-related measurements raises overall health care costs, results in misdiagnoses, leads to inaccurate conclusions in clinical studies, and results in inaccurate nutrition labeling. NIST has an extensive program aimed at providing the health measurements community with standard reference materials (SRMs) to assist them in making accurate measurements. A variety of approaches are used to certify health-related SRMs. For pure crystalline SRMs used as primary standards, direct assays of purity are often not possible. Thus numerous techniques including differential scanning calorimetry, mass spectrometry, chromatography, and others may be used to assess purity. For matrix SRMs used to assess the accuracy of measurement systems, the approaches for certification depend upon the needs of the users and NIST capabilities. When accuracy needs are the highest and the methods exist, NIST uses definitive methods, primarily involving isotope dilution mass spectrometry. These methods have been applied to the certification of serum-based SRMs for a number of the common clinical analytes. For many analytes, definitive methods have not been developed, so NIST uses other strategies for certification. In some cases, such as for drugs of abuse, two independent methods are used for the measurements. For nutrients such as vitamins, in-house methods are used along with results from outside laboratories having extensive experience with a particular analysis. The paper includes tables with examples of many of the health-related SRMs that are available.

Uncertainty-based evaluation of certification study data by W. Hässelbarth; W. Bremser; R. Pradel (pp. 317-321).

An alternative procedure for the evaluation of certification study data is proposed. The aim of this proposal is to incorporate the concepts and methods proposed by the “Guide to the Expression of Uncertainty in Measurement” (ISO 1993, 1995) into the certification of reference materials. The proposed procedures, which are well established in metrology, basically use the technique of inverse-variance weighted means.

Reference material certification by prompt-gamma activation analysis by Richard M. Lindstrom (pp. 322-324).

Neutron-capture prompt-gamma-ray activation analysis (PGAA) shares most of the virtues of instrumental neutron activation analysis (INAA) for reference material certification: highly penetrating probe and response radiation, simple physics, and few interelement interferences or matrix related non-linearities. PGAA complements INAA in determining a different suite of elements using the same tools: a neutron source and gamma-ray spectrometry. Several important elements that are difficult to measure by other techniques are measurable by PGAA, notably H, B, C, N, and S. A survey of published applications and NIST Standard Reference Material certification work shows over thirty different SRMs analyzed by PGAA, including biological materials (botanical and food), coal and fly ash, metals, and several other matrices.

The work of ISO-REMCO’s accreditation task group by Ronald F. Walker (pp. 325-326).

This paper discusses some of the work of ISO-REMCO’s Task Group 4 (TG4) – the Accreditation TG, giving firstly a brief account of the recently published ISO Guide 34 – which gives guidance on the type of quality system a reference material producer should have in place. Secondly, work on the future development of Guide 34 to produce a document against which it will be possible for producers to be accredited without reference to ISO Guide 25 is discussed, and thirdly, the possible formation of an international register of CRM producers, which will provide users with information about the quality status of different producers, is considered.

Consensus values for NIST biological and environmental Standard Reference Materials by I. Roelandts; E. S. Gladney (pp. 327-338).

The National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards or NBS) has produced numerous Standard Reference Materials (SRM) for use in biological and environmental analytical chemistry. The value listed on the “NIST Certificate of Analysis” is the present best estimate of the “true” concentration of that element and is not expected to deviate from that concentration by more than the stated uncertainty. However, NIST does not certify the elemental concentration of every constituent and the number of elements reported in the NIST programs tends to be limited.Numerous analysts have published concentration data on these reference materials. Major journals in analytical chemistry, books, proceedings and “technical reports” have been surveyed to collect these available literature values. A standard statistical approach has been employed to evaluate the compiled data. Our methodology has been developed in a series of previous papers. Some subjective criteria are first used to reject aberrant data. Following these eliminations, an initial arithmetic mean and standard deviation (S.D.) are computed from remaining data for each element. All data now outside two S.D. from the initial mean are dropped and a second mean and S.D. recalculated. These final means and associated S.D. are reported as “consensus values” in our tables.

Consensus values for NIST biological and environmental Standard Reference Materials by I. Roelandts; E. S. Gladney (pp. 327-338).

Interlaboratory quality assurance studies: Their use in certifying natural waters for major constituents and trace elements by H. Alkema; Jayne Simser; Lisa Hjelm (pp. 339-343).

Environmental programs throughout North America have demonstrated a strong awareness of the usefulness of interlaboratory studies for disclosing the quality of analytical results. The Ecosystem Interlaboratory Quality Assurance Program offered by the National Water Research Institute has a wide participation base of laboratories. Many of these laboratories are accredited and employ a number of recognized analytical methods. The interlaboratory study data archives contain a wealth of data for natural surface and rain waters from across the continent. These archives have proven to be a reliable means of characterizing a variety of constituents. Data assessments from these studies accurately identify the variability of data and the presence of any outliers. Repeated use of selected samples in a regular QA program confirms their stability. Time charts and statistical techniques are used to illustrate this stability and yield the precision of pooled analyses. The availability of archived data from interlaboratory studies has enabled the Institute to develop and certify natural water and trace element standards. The natural water CRM, ION-911, has been available for several years. Its historical aspects are discussed as well as the processes leading to the certification of TMRain-95, a soft water standard certifying 22 trace elements. This paper focuses on the use of select laboratories in round-robin evaluations to provide accurate values for constituent concentrations. Natural water and fortified trace element CRMs meet a recognized need in the generation of accurate data for environmental programs.

Results of a complex round robin test with four river sediments by P. Heininger; J. Pelzer; R. Henrion; G. Henrion (pp. 344-347).

The results of a round robin test with four river sediments representing typical contamination levels in the Elbe river system are presented. Altogether 102 laboratories took part and were tested for stability and reliability of their results. A number of 54 inorganic and organic parameters were analyzed. The advantages of multivariate data evaluation compared with the univariate method are demonstrated.

Soil analysis: Western States Proficiency Testing Program for 1996 by D. Hanson; J. Kotuby-Amacher; R. O. Miller (pp. 348-350).

Under the auspices of the Western States Proficiency Testing Program soil samples were analyzed for thirty-five constituents and plant samples were analyzed for fifteen constituents. Statistical evaluations using robust statistical estimation techniques were provided to individual laboratory participants. Analysis of samples previously analyzed in other programs indicated that the accuracy of several soil analyses (pH, electrical conductivity, NO₃-N, extractable K and organic matter) are very reliable. Results of soil phosphorus independent of method and soil organic matter by loss-on-ignition were generally unreliable. Precision, measured by a replicated sample, indicated that a majority of laboratory participants are capable of reproducing analytical values within 10% through a twelve month period.

Survey of reference materials for trace elements, nuclides and organic microcontaminants by R. M. Parr; S. F. Stone; T. Bel-Amakeletch; R. Zeisler (pp. 350-353).

The International Atomic Energy Agency (IAEA), in co-operation with the United Nations Environment Programme (UNEP), has recently prepared a survey on internationally available analytical reference materials for trace elements, nuclides and organic contaminants in biological, environmental and related matrices. The purpose is to help analysts to select reference materials for quality assurance that match as closely as possible, with respect to matrix type and concentrations of the measurands of interest, the “real” samples that are to be measured. The present version of the survey, which is available in the form of two cost-free printed volumes [1], contains over 10,000 certified and information values in 650 reference materials from 27 different producers. The 455 measurands listed include trace elements, major and minor elements, organic contaminants, organometallic compounds, radionuclides and stable isotopes. Currently, the database from which the survey has been produced is being modified and extended so as to make the data available in electronic form via the Internet.

Role of NAA in the characterization of sampling behaviors of multiple elements in CRMs by Weizhi Tian; Bangfa Ni; Pingsheng Wang; Huiling Nie (pp. 354-355).

Taking the advantage of the high precision and accuracy of neutron activation analysis (NAA), sampling constants have been determined for multielements in several international and Chinese reference materials. The suggested technique may be used for finding elements in existing CRMs qualified for quality control (QC) of small size samples (several mg or less), and characterizing sampling behaviors of multielements in new CRMs specifically made for QC of microanalysis.

An investigation of homogeneity within micro-areas of IAEA Urban Dust reference materials by the scanning proton microprobe technique by Yuanxun Zhang; Yingmei Gu; Jifang Zhu; Jieqing Zhu (pp. 356-358).

In order to develop new reference materials for microanalytical nuclear techniques, the Scanning Proton Microprobe (SPM) technique was used to determine homogeneity levels within 100 × 200 μm² areas on small pieces of IAEA Urban Dust reference materials. The experimental methods are described in detail. The results show that IAEA-396A/M Vienna Urban Dust is homogeneous enough for an SRM (≤ 10% for Si, S, K, Ca, Fe, Cu, Zn) for small sample analysis.

The study of the stability of reference materials by isochronous measurements by A. Lamberty; H. Schimmel; J. Pauwels (pp. 359-361).

An alternative method for stability testing of candidate certified reference materials (CRMs) utilizing “isochronous” measurements based on a storage design (storing samples at different temperatures for different time periods), which allows all measurements to be done at the same time, i.e. at the end of the study, is compared to “classical” designs of stability studies using reference time or reference temperature. The execution of stability studies using “isochronous” measurements only requires repeatability conditions, whereas classical designs require both repeatability and long term reproducibility conditions. Consequently, the new design allows the quality of results to be improved.

Influence of storage time and temperature of air-dried soils on pH and extractable nutrients using 0.01 mol/L CaCl2 by V. J. G. Houba; I. Novozamsky (pp. 362-365).

The stability of pH and certified amounts of nitrate, ammonia, total soluble nitrogen, total soluble organic carbon, magnesium, sodium, potassium and phosphorus obtained by extraction from air-dried (40 °C) soil samples by 0.01 mol/L CaCl₂ solution during storage at –18 °C, 4 °C, ambient temperature, 40 °C and 70 °C was investigated in one calcareous soil and one acid sandy soil. Even at storage times of 45 and 90 days, extractable amounts changed. Extractable amounts of P, NH₄-N, total soluble N and soluble organic C increased even at a storage temperature of 40 °C. The pH was lower for samples stored at a temperature of 70 °C and also the Mg concentration became lower at elevated storage temperatures after 45 days in both soils. It is suggested that reference materials certified for values using unbuffered extractants should be stored at a temperature not higher than 4 °C.

Are certified reference materials a victim of quality systems? The need for working matrix-certified reference materials by P. J. Jenks; A. Henk Boekholt; John F. N. Maaskant; Robert D. Rucinski (pp. 366-369).

The use of natural matrix-certified reference materials by commercial environmental laboratories is increasing rapidly. These materials are now an essential component of the quality systems of most commercial environmental laboratories. The use is increasing faster than existing producers, principally government agencies, can meet. The use of data from well established laboratory proficiency schemes is shown to be one alternative way of producing natural matrix-certified reference materials designed for use as day-to-day within-batch control materials.

Non-use and misinterpretation of CRMs. Can the situation be improved? by Lars Jorhem (pp. 370-373).

A survey of 82 scientific papers on trace elements in foods found the use of Certified Reference Materials to be less than anticipated. Less than 50% of the papers reported use of CRMs. When used, the evaluation is usually very crude and provides the user with very little information about his analytical performance. This is mainly due to lack of information/communication between the producers of CRMs, the users and those writing guidelines for the use of CRMs. Several specific problems are pointed out and remedies to improve the situation are described.

Ensuring accuracy in spreadsheet calculations by R. M. Lindstrom; C. Asvavijnijkulchai (pp. 374-375).

Spreadsheet programs have become ubiquitous and indispensable in the laboratory. Data may be easily entered and manipulated without the need to learn a programming language or consult a statistician. Spreadsheets are numerically robust and easily altered with a few mouse-clicks to accommodate changing needs. Ease of use, however, implies ease of making errors. Data can be entered in place of equations when a sheet is expanded, sometimes without immediately obvious consequences. Errors can be made less likely to occur by paying attention to the design of the worksheet as it is constructed. Input cells can be formatted to delineate input clearly from output. The sheet can be annotated with titles and notes. Named variables aid understanding and error tracing. Modular blocks of code can add clarity. Logical tests should be included to allow for the occurrence of blank cells, zeroes, and negative numbers. The output should display the values of the important parameters used in the calculation as well as the final result. A finished worksheet needs to be tested to assure accuracy. Standard test data should be used to recheck a sheet‘s reliability after it is modified

Reference materials for small-sample analysis by R. Zeisler (pp. 376-379).

Many modern analytical techniques use small solid samples and lack proper reference materials for their calibration and quality assurance. A remedy to this deficiency may be in the development of a new genre of highly homogeneous natural matrix materials, their properties being studied with analytical techniques such as PIXE and μ-PIXE, solid sampling AAS, scanning electron microscopy in combination with electron probe X-ray microanalysis, and INAA. Suitable natural materials may be obtained in form of single cell biological materials, finely dispersed suspensions and precipitates such as air particulate matter or sediments, and by appropriate particle size reduction of complex matrices. Initial studies have been carried out on single cell green algae biomass and air particulate matter, as well as several processed materials. Narrow particle size distributions with particles preferably below 10 μm diameter may assure the desired analytical homogeneity. The determination of sampling parameters for individual measurands will ascertain the utility of a material for small-sample analysis.

Microhomogeneity of candidate reference materials: Comparison of solid sampling Zeeman-AAS with INAA by M. Rossbach; P. Ostapczuk; H. Emons (pp. 380-383).

Homogeneity of certified reference materials (CRMs) is a crucial property especially when minimum sample mass of a certain material used for analysis is considered. Particularly in microanalytical techniques CRMs are frequently used to calibrate quantitative analysis, therefore reliable information on the confidence interval of reference values with regard to milligram or sub-milligram sample amounts is urgently needed. Relative element specific homogeneity factors H_e were determined in order to characterize a single cell algae candidate reference material issued by the IAEA, Vienna, for a number of elements. Solid sampling Zeeman AAS and micro-INAA were applied to determine H_e values in two batches of monocellular algae with considerably different concentrations of trace elements. It could be shown that the extremely low and narrow particle size distribution of the materials offers the opportunity to use such natural matrix materials for quantitative analysis with microanalytical techniques, such as PIXE, laser ablation MS, or solid sampling AAS, where milligram amounts or less of the material are analyzed. Such homogeneity factors in selected reference materials could be used to attach a precisely determined mass related confidence interval to the certified concentrations, reflecting the properties of the material. If a mass related homogeneity factor reflecting the material’s true heterogeneity could be applied, systematic bias of analytical procedures together with intermethod bias can be traced.

Virginia Tobacco Leaves (CTA-VTL-2) – new Polish CRM for inorganic trace analysis including microanalysis by R. Dybczyński; H. Polkowska-Motrenko; Z. Samczyński; Z. Szopa (pp. 384-387).

Preparation and certification of a new Polish reference material (CTA-VTL-2) for inorganic trace analysis including microanalysis is described. Virginia Tobacco Leaves of Bulgarian origin were hand picked, dried, comminuted and sieved at conditions preventing contamination of the material with metals. Ca. 13 kg of the material with particle size φ≤ 80 μm was prepared. Certification was based on world-wide interlaboratory comparison in which 60 laboratories from 18 countries participated. Data evaluation was done using an approach which includes rejection of outliers by concurrent use of four different outlier tests followed by calculation of overall means, confidence intervals etc. Several criteria were employed to qualify or disqualify the obtained overall mean as a certified or information value, respectively. 33 elements were certified and information values were established for 10 others. Particle size distribution of CTA-VTL-2 was investigated microscopically. The modal particle diameter was in the range of 15–35 μm. Extensive homogeneity checking by neutron activation analysis revealed that the material is sufficiently homogeneous for mg sample sizes.

Virginia Tobacco Leaves (CTA-VTL-2) – new Polish CRM for inorganic trace analysis including microanalysis by R. Dybczyński; H. Polkowska-Motrenko; Z. Samczyński; Z. Szopa (pp. 384-387).

Pure substances and a new generation of CRMs for chemical industry by Achim Boenke (pp. 388-392).

This article aims to link the certification of the purity of chemical substances with their possible new application in on- and off-line calibration and quality control/ assurance of process control chemo- and/or biosensors. In addition, it provides an overview on the development of and concludes with different quality and certification criteria for pure compounds, matrix CRMs, and transfer material standards which are needed for on- and off-line purposes as above. It finally proposes a flow diagram for the preparation and certification of CRMs for the quality control/assurance of process control chemo- and/or biosensors by including the necessary requirements for such CRMs.

Development of porous and dispersed CRM by B. Röhl-Kuhn; K. Meyer; P. Klobes; T. Fritz (pp. 393-397).

Porous and finely dispersed certified reference materials (CRM) were certified using the gas adsorption method. The special certification procedure for IUPAC isotherm classification types I, II, and IV is presented for meso- and macroporous materials with special emphasis on specific surface area, specific pore volume and pore width according to standards DIN 66 131, 66 134, and 66 135. Four CRMs (SiO₂, α-Al₂O₃, two transition aluminas) with a macro- and mesopore range are presented. Certification was made on the basis of BCR guidelines in connection with interlaboratory tests (altogether 38 participating laboratories, 44 various gas adsorption apparatus).

Reference materials for long-term environmental programs by H. Emons; P. Ostapczuk; M. Rossbach; J. D. Schladot (pp. 398-401).

The application of reference materials (RMs) for quality control in analytical chemistry within long-term environmental monitoring and banking programs is described. The profitable use of different levels of RMs, in particular the introduction of problem-designed internal control materials and internal reference materials at the German Environmental Specimen Bank is demonstrated. Moreover, further demands from biosphere-oriented programs for future developments of certified reference materials (CRMs) are discussed.

A set of four soil reference materials with certified values of total element contents and their extractable fractions by J. Kučera; V. Sychra; J. Koubek (pp. 402-405).

A set of certified reference materials of four natural soils denoted as CRM 7001-4 was prepared. They consist of light sandy soils with normal and elevated, silty clay loam with normal, and loam with elevated element levels. Certified and/or information values were established for the total contents of the elements As, Ba, Be, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, V, Zn, and their fractions, extractable with aqua regia, and boiling and cold 2 mol L^–1 nitric acid, from results of a 28 laboratory intercomparison using various methods of atomic absorption spectrometry, optical emission spectrometry, mass spectrometry, electrochemical methods, spectrophotometry, instrumental neutron activation analysis, and X-ray fluorescence.

An international interlaboratory study for the production of a sewage sludge certified reference material for routine use in inorganic quality control by J. F. N. Maaskant; A. H. Boekholt; P. J. Jenks; R. D. Rucinski (pp. 406-409).

Two existing interlaboratory schemes are used to certify a sewage sludge reference material. Data from the analysis (As, Cd, Cr, Cu, Pb, Hg, Ni and Zn) of the material using routine procedures, US EPA and Netherlands NEN, plus INAA and IDMS and an interlaboratory comparison in Eastern Europe have been examined. The Dutch results show significantly lower analytical results for As for the graphite furnace technique compared to HG-AAS, probably due to matrix-effects. The differences between the Dutch and USA results for Cr and Ni suggest that the USEPA 3050A digestion method for dissolution of the metals is less aggressive for this material compared to aqua regia destruction. For international comparability of analytical data it is essential to harmonize method dependent dissolution/extraction techniques. The preparation of reference materials which mimic real samples and certification by ILS result in useful materials for quality control.

A pilot study for the preparation of a new Reference Material based on antarctic krill by S. Caroli; O. Senofonte; S. Caimi; P. Pucci; J. Pauwels; G. N. Kramer (pp. 410-414).

The preparation of new Certified Reference Materials (CRMs) of antarctic matrices forms the backbone of an ongoing project in the framework of the Italian National Program for Antarctic Research. The first CRM of this kind (MURST-ISS-A1 Antarctic Marine Sediment) is already available. The second phase focuses on the certification of antarctic krill, a small shrimp extremely abundant in the Southern Ocean. The total mass of krill available for this purpose is approximately 44 kg and results from the combination of three different catches (Ross Sea, Marguerite Bay and Livingston Island, respectively). The quantification of the following elements in the raw mass appears to be affordable by current analytical techniques, values being in the range of (in μg/g) 0.11–0.30 for As, 0.03–0.12 for Cd, 0.06–0.23 for Cr, 6.1–21 for Cu, 5.7–7.6 for Fe, 0.005–0.008 for Hg, 0.7–1.2 for Mn, 0.013– 0.077 for Ni, 0.04–0.57 for Pb and 12–16 for Zn. On the other hand, the average values ascertained in freeze-dried krill are as a rule one order of magnitude higher, i.e., (in μg/g), 3.2 for As, 0.6 for Cd, 1.8 for Cr, 75 for Cu, 61 for Fe, 0.025 for Hg, 4.6 for Mn, 0.7 for Ni, 2.1 for Pb and 81 for Zn. Information on the pretreatment of krill and details on the planned certification campaign are also given.

Low uncertainty determination of manganese and vanadium in environmental and biological reference materials by instrumental neutron activation analysis by J. Kučera; Ladislav Soukal (pp. 415-418).

The elements Mn and V were determined by INAA in about 5 mg and 100 mg aliquots of NIST SRM 1648 to elucidate discrepancies between our previous results for the 0.5 mg to 15 mg aliquots and the NIST certified and/or information values. Simultaneously, other NIST SRMs 1633a, 2704, and BCR CRMs 038, 101 and 143 were also analyzed. Special attention was given to evaluating and minimizing uncertainties of all steps of analysis. Our results compared very well with the respective certified and/or information values (if available) of all SRMs and CRMs studied, except for NIST SRM 1648. For this SRM we have found significantly lower results than the NIST values which suggests that the NIST values are positively biased by about 10%. A new value for V in BCR CRM 143 was also obtained.

Certification of two human hair reference materials issued by the International Atomic Energy Agency by S. F. Heller-Zeisler; R. M. Parr; R. Zeisler (pp. 419-422).

Two new human hair reference materials, with different levels of mercury and methylmercury, have been developed and characterized by the International Atomic Energy Agency, for use in validation of measurements for mercury exposure. The set of materials consists of IAEA-086, with a low level of methylmercury, and IAEA-085, with an elevated methylmercury level. An international intercomparison exercise was carried out, and 68 institutes from 40 countries have contributed data. Based on the evaluation of the results from the intercomparison and analyses by expert laboratories, values of 23.2 and 0.57 mg/kg total mercury are recommended for IAEA-085 and IAEA-086, respectively. Values for methylmercury are recommended at 22.9 mg/kg, MeHg as Hg, for IAEA-085, and at 0.26 mg/kg, MeHg as Hg, for IAEA-086. Recommended and information values are also given for other selected trace elements.

Determination of 24 elements in four algae reference materials by neutron activation analysis and inductively coupled plasma mass spectrometry by Xiaolin Hou; Chunsheng Li; Wenjun Ding; Qinfang Qian; Chifang Chai (pp. 423-426).

Four algae reference materials, IAEA-391, 392, 393 and IAEA-140, prepared by the International Atomic Energy Agency for intercomparison under different preparation conditions were analyzed for 24 elements. Conventional neutron activation analysis (NAA) was used to determine Al, Ca, Cl, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Sb, V and Zn and epithermal NAA using BN and Cd as shielding material for I, Br, As, Ni, Mo and Cd. Inductively coupled plasma mass spectrometry (ICP-MS) as a complementary and comparative method was applied to determine Pb, Sn, Ni, Sr, Rb, As, Co, Cr, Cu, Mn, V, Mo and Zn. Two analytical quality control standard reference materials IAEA-V-10 (hay powder) and IAEA-331 (spinach) were analyzed simultaneously with real samples. The results agree quite well with each other and with the certified values.

A quantitative infrared spectral database of hazardous air pollutants by P. M. Chu; G. C. Rhoderick; D. Van Vlack; S. J. Wetzel; W. J. Lafferty; F. R. Guenther (pp. 426-429).

Open-path monitoring of the atmosphere using Fourier transform infrared spectrometry has recently become a useful real-time in situ analytical technique. The U.S. Environmental Protection Agency (EPA) is currently formulating Method TO-16, a protocol for infrared remote sensing of the hazardous air pollutants (HAPs) identified in EPA’s Clean Air Act of 1990. To support infrared based sensing technologies, the National Institute of Standards and Technology (NIST) is currently developing a standard quantitative spectral database of the HAPs based on gravimetrically prepared samples. This paper presents the protocol used to prepare the gravimetric mixtures and initial results.

Single cell green algae reference materials with managed levels of heavy metals by R. Zeisler; R. Dekner; E. Zeiller; J. Doucha; P. Mader; J. Kučera (pp. 429-432).

Three batches of single cell green algal biomass have been produced as model substances for green biomass reference materials with the aim of arriving at three different concentration levels for selected heavy metals in the same matrix. The green algal biomass is produced in a water based culture medium in open and closed bioreactors. An outdoor open bioreactor technology was used to produce a batch of “natural level” algae as well as a batch with elevated levels of As, Cd, Cr, Hg, Ni, and Pb. A photoreactor constructed without metal parts and employing artificial light sources was used in a clean air environment with high purity chemicals to reduce heavy metal concentrations in the third batch of algal biomass. For the above elements, the depleted level material, with exception of Hg, showed about one order of magnitude lower concentration than the natural level, while concentrations in the enriched material were up to four orders of magnitude higher. Analysts can use these materials to sustain verification of calibration and analytical quality over the entire operational range of the analytical work.

Determination of chlorine and pentachlorophenol in wood by G. Bartelt; H. G. Buge; W. Görner; T. Win (pp. 433-434).

Chlorine in wood was determined in connection with the development of a reference material (RM) of pentachlorophenol (PCP) in wood. The element was determined by photon activation analysis (PAA) using bremsstrahlung of 19 MeV electrons from an electron linear accelerator. The initial overall Cl content as well as the Cl remaining after extraction with methanol and subsequent extraction with water were determined. Moreover, the PCP fractions in the organic and in the aqueous extracts were analyzed by gas chromatography (GC). The results show that at least three quarters of the overall chlorine is bound in PCP and that PCP can be extracted to a high degree.

Examination of a procedure for the production of a simulated filter-based air particulate matter reference material by S. F. Heller-Zeisler; Ales Fajgelj; Gabriel Bernasconi; Antonella Tajani; R. Zeisler (pp. 435-438).

An approach for producing simulated air particulate matter (APM) deposited on filters has been developed and investigated as to its usefulness for yielding large batches of filters as a future reference material. The APM deposited on the filters was a material collected from an urban industrial area, and had been milled to approximate a material of PM-2.5 particle size distribution. The milled APM material was loaded onto filter substrates (Nuclepore) through the deposition of aliquots from a liquid suspension via vacuum filtration. It should be noted that these filters do not represent a typical PM-2.5 elemental composition, since the milling increased the proportion of crustal materials and the suspension in liquid decreased the sulfate content. Homogeneity between filters was tested using INAA (whole filter analysis) and ED-XRF and PIXE and was estimated to be in the 5% range (relative standard deviation). Homogeneity within the filters and among the filters was also tested using micro-XRF and found to be acceptable for the elements tested. The results of the tests carried out on the filters indicate that this approach is appropriate for large-scale production of similar filters for distribution as reference materials.

Proficiency tests using four batches of green alga with controlled levels of cadmium by J. Kučera; P. Mader; D. Miholová; J. Száková; I. Stejskalová; V. Štěpánek (pp. 439-442).

A set of test materials of the green alga Chlorella vulgaris with different levels of naturally bound Cd and about the same levels of other 13 essential or trace elements (BIOMA 1–4) was produced for proficiency testing of laboratories involved in elemental analysis of food. Criteria of the laboratories’ performance, such as the z-score and combination scores RSZ and SSZ were evaluated and discussed in terms of their suitability for proficiency testing using a set of test materials with the same matrix. The use of the test materials as a set of internal reference materials has also been suggested.

Particle size determination of some IAEA and NIST environmental and biological reference materials by A. Fajgelj; Rolf Zeisler (pp. 442-445).

Particle size distributions in fifteen International Atomic Energy Agency (IAEA) and sixteen National Institute of Standards and Technology (NIST) reference materials (RMs) were measured with the basic aim to investigate the potential of these materials to be used as reference or quality control materials in analyses where a small sample mass is required (< 100 mg). Most of the investigated materials are commercially available environmental or biological natural matrix RMs with certified values for trace elements, radionuclides, or organometallic compounds. The laser diffraction technique was used in all measurements. From the point of particle size distribution, materials IAEA-390 (Algae, a set of three materials), IAEA-396m (Urban Dust, 3x air jet milled), NIST-SRM 1515 (Apple Leaves), NIST-SRM 1547 (Peach Leaves), NIST-SRM 1566a (Oyster Tissue), NIST-SRM 1570a (Spinach), NIST-SRM 1573a (Tomato Leaves), and NIST-SRM 1648 (Urban Particulate) can be considered appropriate for small sample mass analysis. However, additional analytical tests are needed to confirm the appropriate homogeneous distribution of chemical composition, the level of heterogeneity for individual elements, at this sample mass level.

Comparison of some additives used in the preparation of freeze-dried lemon juice candidate reference materials by W. Ooghe; G. N. Kramer; H. Schimmel; J. Pauwels (pp. 445-448).

The stability, storage, and distribution of certified reference materials which consist of liquid or frozen fruit juices is rather problematic. As a better alternative a stable orange juice powder has been obtained by freeze-drying to a moisture content below 0.4%. However, freeze-drying lemon juices resulted in unstable materials which collapsed into lumps after standing some weeks in brown bottles under argon. An additive was sought which can be used to obtain stable lemon juice powders without influence on important analytical parameters as amino acids, sugars, organic acids, minerals and flavanone glycosides. The additives pectin, hydroxy ethylcellulose, and hydroxypropyl methylcellulose were examined. Powders containing pectin quickly showed a loss of structure (collapse) and resulted in non-acceptable changes in amino acids, sugars or minerals compared to the original lemon juice. The addition of up to 3% hydroxypropyl methylcellulose seemed more promising, although some minor changes in the sugar and sodium concentration occurred.

Trace element analysis in CRM of plant origin by inductively coupled plasma mass spectrometry by R. Koplík; E. E. Curdová; M. Suchánek (pp. 449-451).

Three CRMs of plant origin (SRM 1515 Apple Leaves, SRM 1570a Trace Elements in Spinach Leaves, and SRM 1575 Pine Needles) were used for analytical quality assurance of Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, and Pb determination by ICP-MS. The samples were decomposed using microwave assisted pressurized digestion by HNO₃ and HNO₃ + H₂O₂ mixture and temperature programmed dry ashing. Concentrations of elements in samples were evaluated by external calibration. All samples, blanks, and standards were spiked to 100 μg/L concentration of In and Bi as internal standards. During the measurement, signals of ⁵²Cr, ⁵³Cr, ⁵⁴Fe, ⁵⁵Mn, ⁵⁹Co, ⁶⁰Ni, ⁶²Ni, ⁶³Cu, ⁶⁵Cu, ⁶⁶Zn, ⁹⁵Mo, ¹¹¹Cd, ¹¹²Cd, ¹¹⁵In, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb and ²⁰⁹Bi were monitored. Results of Pb, Cd, Cu, Zn, Mo and Co determination were in good agreement with certified values. In order to obtain accurate results for As at low levels, it was necessary to mathematically correct the analytical signal. This correction effectively eliminates the influence of interfering ArCl⁺ ions. For Cr analysis it is advisable to use as powerful oxidizing conditions during sample decomposition as possible.

Experience with wheat and wheat flour CRMs by J. Budai; J. Fükő (pp. 452-453).

The Chemical Section of OHM [1–2] embarked on the preparation of a wheat sample series as CRMs in 1992. The certification process has been carried out according to the recommendations of ISO. Since then a series of wheat flour samples has been developed as well. The investigations of the long-term stability and the application of wheat and flour CRMs are presented.

Bank of reference samples of blank urine from livestock by S. Sterk; Frederike van Tricht; Anneke van Soeren-Kieft; H. Herbold; Rainer Stephany; Leendert van Ginkel (pp. 454-455).

From three species of livestock, bovine, ovine and porcine, samples of urine from each 10–20 different animals were collected. The animals originated from a governmental experimental farm and differed in race, age, sex and were fed with different types of feed. Fifty different samples of urine were lyophilised in units of 5 mL in sealed amber glass bottles. After lyophilisation of the samples, several quality control tests were performed. The variation in net weight of the units of urine and the lyophilisates ranged from 0.01%–1.7% and 0.1%–10%, respectively. Most values did not exceed 0.1% for urines and 1% for lyophilisates. The residual water content of the lyophilisates was determined by the Karl-Fisher titration method. The average percentage of residual water ranged from 1.0%–7.0% for bovine, from 1.3%–3.0% for porcine and from 1.6%–5.5% for ovine urine lyophilisates. Further, all different samples were analysed for the presence of anabolic compounds with a multi-residue procedure developed at the CRL. In two samples of bovine urine the presence of α-boldenone was detected and confirmed. In most porcine urines the endogenous steroids α-testosterone and α-estradiol were detected. In a number of porcine and ovine urine samples α- and β-zearalenol were detected. The origin of these compounds is the f2-toxin produced by a Fusarium fungus. In ovine samples α-testosterone and α-estradiol were detected.

Recent SRMs for organic and inorganic nutrients in food matrices by K. E. Sharpless; M. J. Welch; R. R. Greenberg; G. V. Iyengar; J. C. Colbert (pp. 456-458).

The National Institute of Standards and Technology (NIST) has recently introduced several reference materials for organic and inorganic nutrients in food matrices to assist the food industry in complying with nutrition labeling laws; the food industry and other government agencies have collaborated with NIST in this endeavor. Two food-matrix SRMs were issued in 1996: SRM 1544, Fatty Acids and Cholesterol in Frozen Food Composite; and SRM 1846, Infant Formula. Concentration values in SRM 1544 are provided for six fatty acids, cholesterol, and proximates (fat, protein, carbohydrate, etc.). Values are assigned for proximate and caloric content as well as the concentrations of sixteen vitamins and nine minerals and trace elements in SRM 1846. In 1997, NIST expects to issue two additional food-matrix SRMs: SRM 1548a, Typical Diet, and SRM 2383, Baby Food Composite. SRM 1548a will replace SRM 1548, Total Diet, and will have values assigned for proximates, major and minor inorganic nutrients, and toxic trace elements. SRM 2383 will have values assigned for proximates, vitamins, carotenoids, and inorganic nutrients.

Sampling constants for niacin content in standard reference material 1846 Infant Formula by W. R. Wolf; Denis E. Lacroix (pp. 459-464).

Modern measurement systems for food components often require use of ever smaller sample sizes, down to mg for some new microtechniques, which puts a stronger demand on development of reference materials with defined homogeneity for subsampling. One approach to evaluate the homogeneity of materials is the characterization of sampling constants, defined as that amount of material that gives a 1% error for subsampling. This approach was developed for geological sampling and has been applied in a limited way for inorganic components in food/biological materials. We have extended this approach to the determination of the sampling constants for an organic component, niacin, in the SRM 1846 Infant Formula material. This material was produced by blending of a dry vitamin mix (5% weight) into the bulk spray dried powder, for long term stability purposes. By analyzing similar aliquots of a reconstituted homogeneous fluid solution of a large sample size, in comparison to smaller portions of dry powder, an estimate of the variation due to sampling can be separated from estimates of variation due to analysis. Using either the AOAC microbiological method or a newly developed HPLC method, sampling constants for the niacin content of SRM 1846 are in the range of 1–3 g; use of smaller sub-samples can introduce significant variation into determinations using this SRM.

Karl Fischer titration A method for determining the true water content of cereals by K. Schmitt; Heinz-Dieter Isengard (pp. 465-469).

A variation of the Karl Fischer titration was developed to measure the water content of cereals such as various grains and flours. The presented method is based on an elevated working temperature. It can even reach the boiling point of the working medium which contains methanol as solvent. The influence of different sample preparations is also discussed. A standardized procedure could be found to achieve highly reproducible and statistically safe results. The proposed titration method can be carried out with titrators of different manufacturers. The method may serve as a reference technique for these products and, by consequence, as calibration method for other more rapid methods, which may then be used in the daily laboratory practice or in industrial production lines.

Availability and need of microbiological Reference Materials in India by R. S. Mahwar; Shriance Jain; S. P. Chakrabarti (pp. 470-472).

A survey was conducted to identify the sources of availability and make an assessment of the need of microbiological Reference Materials in India, as a part of the programme initiated by the Microbiological Reference Materials Committee of the AOAC International’s Technical Division on Reference Materials (TDRM) in 1996. The data collection process involved circulation of copies of the questionnaire received from TDRM (AOAC) to 120 institutions in India. The findings of the study indicated that, although India has made tremendous progress in the establishment of microbial culture collection centres, the use of Proficiency Test Samples (PTS) or Certified Reference Materials (CRM) in microbiological measurements is yet being introduced in a meaningful manner, and there is a strong need for introduction of national level quality assurance programmes for the microbiological laboratories in the country.

The preparation of International Biological Standards by Peter Phillips (pp. 473-475).

The National Institute for Biological Standards and Control (NIBSC) plays a key role in providing International Biological Standards and Reference Materials. The focus is on providing Standards that are needed by manufacturers of biological medicines and, increasingly, biological diagnostic assays. These Standards need to be credible, stable over a long period of use, widely available and of suitable potency.

International Standards for growth factors and cytokines by C. Jane Robinson (pp. 476-478).

Growth factors and cytokines are polypeptides with a wide range of potential therapeutic and diagnostic applications. They are complex biological molecules which cannot be completely characterized by physicochemical analysis alone, and require some form of bioassay to determine their potency. Bioassay systems are themselves inherently variable, so comparison of the potency of a growth factor or cytokine preparation with that of a common reference standard is necessary to permit interassay and interlaboratory comparison of results. The National Institute for Biological Standards and Control (NIBSC) is engaged in a program to develop World Health Organization (WHO) International Standards (IS) for growth factors and cytokines. These are preparations ampouled following WHO guidelines, characterized in an international collaborative study for their potency, stability and suitability to serve as standards, assigned a unitage in International Units (IU), and established by WHO as the IS for that growth factor or cytokine. IS are are available, on request, for use, usually through calibration of local standards, in defining the potency in IU of therapeutic products, in calibration of diagnostic immunoassays and calibration of biological assays and immunoassays in biological and medical research.

Experience of the National Institute of Metrology (INM) in development and certification of reference materials used in the metrological assurance of clinical laboratory measurements by Mirella Buzoianu (pp. 479-485).

In order to provide quality assurance in the field of clinical chemistry, required by European Standards, the Romanian national metrological infrastructure has to be improved. The main objectives of this important activity are metrological assurance of concentration measurements, the assessment of the uncertainty, and the traceability of measurements. Within this framework, reference materials play an important role. The experience of INM in the preparation, certification and use of reference materials and in metrological assurance of clinical laboratory measurements (especially when absorption photometric devices are used) is described. The combined uncertainty associated with chemical preparation of these reference materials is estimated.

A review of silicon and silicone determination in tissue and body fluids – a need for standard reference materials by S. J. Lugowski; Dennis C. Smith; Joanna Z. Lugowski; Walter Peters; John Semple (pp. 486-488).

The role of Si in nature is briefly described, especially the toxic properties of inorganic and organic Si for humans. The use of different forms of silicones in medicine and food industry is noted and potential consequences of their use are discussed. Since Si is an essential trace element there is need for establishment of the “normal” level of Si in blood, other body fluids and tissues and development of speciation of Si forms in biological samples. Numerous difficulties in the determination of Si are described and the need for SRM is stressed. The results of the determination of Si in blood of patients with Si breast implants and controls, Si in milk and blood of nursing mothers – with and without Si breast implants and extractable Si in capsules – are summarized. The obtained data reinforce the need for a reliable SRM.

Control materials for selenium in serum suitable for speciation studies by G. Morisi; A. Menditto; F. Chiodo; A. Minoprio; M. Mosca; M. Patriarca (pp. 489-493).

Selenium is an essential element which importance for human health is widely recognised. At present, Se status is assessed by either determination of total Se or glutathione peroxidase activity, but increasing attention is paid to the dosage of other Se species. From an analytical point of view, the presence of different Se species may influence even the determination of total Se. Most analytical techniques suffer from interferences and require control (CMs) and reference (RMs) materials for their validation. At present, the preparation of materials with different Se concentrations mainly relies on the addition of inorganic Se compounds to human or animal serum. However, the analytical behaviour of added inorganic Se may be different from that of native organic Se species, thus affecting the evaluation of method and laboratory performances. CMs at different Se concentrations were prepared without the addition of inorganic Se by pooling batches of serum with low and high Se content obtained from two different animal species (cow and horse) and used for two years in the Italian External Quality Assessment Scheme (EQAS) for trace elements in biological fluids. The results obtained in this EQAS are reported and compared with those obtained by the same laboratories on CMs spiked with inorganic Se. CMs prepared according to this protocol could be suitable for the assessment of methods for the speciation of Se in serum.

Importance of the definition of catalytic properties for the commutability of an enzyme reference material: example of lipase by J.-M. Lessinger; J.-L. Dourson; G. Férard (pp. 494-497).

Assays for pancreatic lipase activity in serum need the use of calibrators, but there is a lack of a reference method and of a reference material. Under routine conditions, comparability of lipase catalytic activities was found to be poor when lipase was determined in 50 patients’ specimens by a turbidimetric (Boehringer) and a colorimetric (Sigma) assay. Mean values of the results differed by a ratio of 2.39. Catalytic properties of three materials, two commercial calibrators and a home-purified preparation of human pancreatic lipase (HPL), have been compared in titrimetry at constant pH. Optimal common conditions were defined for the titration of lipase activity in the three materials. When using these titres for each calibrator, comparability was greatly improved (ratio = 1.25). This result indicates that a significant part of between-method discrepancy was due to the lack of a reference method for the titration of lipase calibrators. The inter-method behavior of each material was compared to that of patients’ specimens. Using HPL as calibrator, the comparability of patients’ results was still dramatically improved (ratio = 1.01). This study shows the importance of verifying the similarity of catalytic properties of an enzyme reference material to those of the corresponding enzyme in human specimens, in order to ensure its commutability. The use of validated commutable calibrators, traceable to certified reference materials, is an opportunity to improve the inter-method comparability of results in clinical enzymology.

Preparation of doubly 13C-labelled benzylpenicillin as internal standard for residue analytical use with GC/MS and LC/MS by Joachim Schlösser; Armin Mehlich; Frank Ballwanz; M. Petz (pp. 498-501).

A simple and rapid method is described for the preparation of doubly ¹³C-labelled benzylpenicillin for use in isotope dilution analyses of benzylpenicillin residues. The product is characterized by IR, NMR, GC/MS and LC/MS. Tissue analyses demonstrate its advantage with residue analytical methods using mass spectrometric techniques for measurement. Different fragmentation patterns are observed when using GC/EI-MS or LC/electrospray-MS. The consequences for residue analysis are discussed.

Feasibility of a recombinant human apolipoprotein E reference material by F. Schiele; A. Barbier; A. Visvikis; L. Aggerbeck; M. Rosseneu; L. Havekes; M. Hüttinger; C. Profilis; G. Siest (pp. 501-504).

The aim of this work was to prepare a recombinant apo E material and to determine its suitability as a reference material. We produced human apo E3 using recombinant DNA technology. The cDNA of human apo E3 was cloned in the pARHS bacterial expression vector and used to transfect E. Coli BL21 (DE3) cells. The recombinant protein was then purified in one step by affinity chromatography on a Ni-chelated agarose column under denaturing conditions. The purity of the protein estimated by SDS PAGE was greater than 96%. The physicochemical properties and biological and immunological reactivity of the purified recombinant apo E3 were shown to be close to those of the protein purified from human plasma VLDL. A limited batch of lyophilized apo E material was then prepared. The stability of the lyophilized apo E material examined by temperature accelerated degradation was acceptable. No degradation of the measured apo E was observed after storage of the lyophilized material at +4° C and –20° C for 11 months. The reconstituted lyophilized material, in comparison with human fresh serum samples and with apo E purified from human VLDL, showed no major alteration of its immunological reactivity when assayed by immunoturbidimetry or ELISA.

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Analytical and Bioanalytical Chemistry (v.360, #3-4)