Analytical quality control by solid sampling GFAAS in the production of animal tissue reference materials: lead and cadmium in bovine liver reference materials

Summary The function of solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) in the laboratory-internal preparation, production and standardization of bovine liver reference material is described. Analytical quality assurance was achieved by using a wet digestion decomposition procedure and GFAAS (WD-GFAAS) as well as three different methods of SS-GFAAS. It will be shown, that SS-GFAAS is an adequate and efficacious method of analytical quality control in the production of reference materials. Details are given about the preliminary steps of sample selection and preparation, applying SS-GFAAS both as a screening method and for the detection of contamination during the production of the reference materials. The element contents of the four bovine liver materials measured after decomposition with nitric acid in the open system by GFAAS and also by Flame-AAS, using the slotted tube atom trap, are compared statistically with the results obtained by SS-GFAAS. In solid sampling analyses three different systems were applied: a solid sampling ZAA-spectrometer with platform-boat, a D₂AA-spectrometer with solid sampling graphite tube and platform-drawer and an autoprobe-D₂AA-spectrometer with solid sampling autoprobe and graphite tube.     

Solid sampling ZAAS determination of endogenous Pb contamination in muscle tissue caused by calcification

Summary Focal endogenous Pb contamination in bovine muscle tissue can be caused by Cysticercus bovis (C. bovis), the larval stage of Taenia saginata. 79 samples of cysts and the respective muscle tissues were analyzed by means of solid sampling Zeeman atomic absorption spectrometry (SS-ZAAS). In calcified cysts of C. bovis, the Pb content was up to 1864 times higher than in the directly surrounding muscle tissue. The maximum Pb content of the cysts was 3.0 mg/kg, that of the muscle tissue 0.02 mg/kg. There is a significant positive correlation between the stage of calcification and the Pb content in the cysts (Spearman rank correlation: r=0.869, P0.01). Compared to the surrounding muscle tissue, even in non-calcified early stages of the cysticeri, there is a distinctly elevated Pb content. Non-focal endogenous Pb contamination in muscle tissue can be caused by calcification of the tissue itself or by calcification of its blood vessels. In the latter case the difference in the Pb content of muscle tissue (myocardium) and that of the regions which are prone to calcification (endocardium, endocardial platelets) proved to be highly significant with a ratio of up to <50.SS-ZAAS proved to be well suited for the determination of Pb in endogenously contaminated muscle tissue where sample decomposition methods may lead to incorrect results due to larger sample sizes and sample homogenization.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

The preparation of codfish candidate reference material to be certified for Pb, Cd, Hg, Fe, and Zn

Summary Since 1985 the conditioning of fresh seafish muscle reference materials to be certified for trace metals has been studied by CBNM at the request of BCR. This paper describes the study of the production process of a codfish reference material to be certified for Pb, Cd, Hg, Fe and Zn and its subsequent preparation. In particular, the collection of the base material, its transformation into powder by cryo-grinding in all-teflon equipment, the production of dry powder by freeze-drying and the conditioning and bottling of the candidate reference material. Production control and final homogeneity assessment were carried out by solid sampling Zeeman atomic absorption spectrometry. Analyses at different stages in the production process indicate that heterogeneities existing in the starting material are gradually eliminated in the subsequent production stages and that no external contamination occurs.     

Determination of lead, cadmium, zinc, copper, and iron in foods by atomic absorption spectrometry after microwave digestion: NMKL Collaborative Study

A method for determination of lead, cadmium, zinc, copper, and iron by atomic absorption spectrometry (AAS) after microwave digestion was subjected to a collaborative study in which 16 laboratories participated [including users of inductively coupled plasma (ICP) and ICP-mass spectrometry (MS)]. The types of samples included in the study were minced fish, wheat bran, milk powder, bovine and pig liver, mushroom, 2 simulated diets, and bovine muscle; the last 4 were certified reference materials. These were analyzed as single (4 samples), double blind (1 sample), or split level (2 samples) samples. Before the collaborative study, a pretrial was conducted in which 4 ready-made solutions and one fish tissue sample were analyzed for Pb and Cu. The reproducibility relative standard deviation (RSDR) values, for results above the detection limit, ranged from 59% at 0.155 mg/kg to 16% at 1.62 mg/kg for Pb, from 28% at 0.0124 mg/kg to 11% at 0.482 mg/kg for Cd, from 9.3% at 35.3 mg/kg to 1.7% at 147 mg/kg for Zn, from 39% at 0.241 mg/kg to 3.0% at 63.4 mg/kg for Cu, and from 17% at 7.4 mg/kg to 5.9% at 303 mg/kg for Fe. The RSDR values agreed well with the norms described by the International Union of Pure and Applied Chemistry. As a complement to the AAS determinations, a number of laboratories analyzed the samples either by ICP or by ICP-MS. The results of these analyses agreed well with the AAS results. On the basis of the results of the collaborative study, the method was adopted Official First Action by AOAC INTERNATIONAL.     

Preliminary assessment of homogeneity of new candidate agricultural/food reference materials

Summary In an effort to bring to the analytical community new natural matrix reference materials (RM's) for elemental composition quality control, ten new agricultural/food candidate reference materials prepared previously, were characterized for homogeneity. The materials include bovine muscle powder, whole egg powder, corn bran, microcrystalline cellulose, wheat gluten, whole milk powder, corn starch and three wheat flours representing a wide range of matrix types and elemental composition. Characterization was for up to some twenty five major, minor, trace and ultratrace elements of nutritional, toxicological and environmental significance. Solid sampling electrothermal atomic absorption spectrometry was applied to the determination of copper and lead in sub-milligram subsamples. A variety of other analytical techniques via an interlaboratory cooperative effort was used to determine many other elements in 100–2000 mg subsample sizes. Good material homogeneity was observed for virtually all materials and analytes with the exception of Cr and Pb in limited instances. The materials were thus deemed suitable for detailed characterization of elemental concentration to lead to recommended values and to bring these biological products to reference material status.     

Direct analysis of solid samples by GFAAS – determination of trace heavy metals in barytes

Solid sampling graphite furnace atomic absorption spectroscopy (SS-GFAAS) has been used for the determination of traces of heavy metals (Cd, Pb, Cu, Cr, Ni, V and As) in barytes over a wide concentration range, e.g. Cd from 0.023 to 27.0 μg/g and Pb from 1.54 to 3509 μg/g.The necessity of determining heavy metals in commercial barytes (naturally occurring barium sulfate), a mineral important to the oil industry because of its use in drilling muds, is discussed. The problems presented by the analysis of this difficult matrix are elegantly solved by using SS-GFAAS for the direct determination of heavy metals. A high-performance graphite furnace AAS with D₂-background correction system and a transversely heated graphite atomizer was used for the investigations. The spectrometer was combined with a mechanical sampling module and an ultramicrobalance. The transfer of solid samples (sample weights 0.031–0.686 mg) into the atomizer was carried out by using an optimized graphite platform as the sample carrier. Calibration curve techniques and standard addition methods were employed using external standards (CRMs). Problems associated with signal deformations like multiple peaks, tailing or shoulders are also discussed and possibilities to solve the problems are given. The influence of the homogeneity of solid samples on the precision and accuracy are shown in a real example. The results obtained by SS-GFAAS were compared with results by other methods like X-ray fluorescence spectroscopy (XRF) and flame AAS after aqua regia microwave extraction. This study has demonstrated that SS-GFAAS is a very powerful and easy-to-use method for quick and accurate analysis of barytes. Received: 9 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Direct analysis of solid samples by GFAAS – determination of trace heavy metals in barytes

Solid sampling graphite furnace atomic absorption spectroscopy (SS-GFAAS) has been used for the determination of traces of heavy metals (Cd, Pb, Cu, Cr, Ni, V and As) in barytes over a wide concentration range, e.g. Cd from 0.023 to 27.0 μg/g and Pb from 1.54 to 3509 μg/g.The necessity of determining heavy metals in commercial barytes (naturally occurring barium sulfate), a mineral important to the oil industry because of its use in drilling muds, is discussed. The problems presented by the analysis of this difficult matrix are elegantly solved by using SS-GFAAS for the direct determination of heavy metals. A high-performance graphite furnace AAS with D₂-background correction system and a transversely heated graphite atomizer was used for the investigations. The spectrometer was combined with a mechanical sampling module and an ultramicrobalance. The transfer of solid samples (sample weights 0.031–0.686 mg) into the atomizer was carried out by using an optimized graphite platform as the sample carrier. Calibration curve techniques and standard addition methods were employed using external standards (CRMs). Problems associated with signal deformations like multiple peaks, tailing or shoulders are also discussed and possibilities to solve the problems are given. The influence of the homogeneity of solid samples on the precision and accuracy are shown in a real example. The results obtained by SS-GFAAS were compared with results by other methods like X-ray fluorescence spectroscopy (XRF) and flame AAS after aqua regia microwave extraction. This study has demonstrated that SS-GFAAS is a very powerful and easy-to-use method for quick and accurate analysis of barytes. Received: 9 November 1998 / Revised: 29 January 1999 / Accepted: 2 February 1999     

Development of clenbuterol reference materials: lyophilized bovine eye samples free of clenbuterol (CRM 673) and containing clenbuterol (CRM 674)

The certification by inter-laboratory testing of two candidate reference materials (RMs) for the mass concentration of the anabolic agent clenbuterol in bovine eye material is described: RM 674 with ca 10 microg clenbuterol per kg of eye matrix and RM 673 clenbuterol-free eye matrix as the negative control (<0.50 microg kg(-1)). Both candidate RMs were certified by eleven EU laboratories, and sixty-six accepted replicate measurements were included in the "Certification Study". The precision of the measurement process was assessed by calculation of the standard variation determined within each laboratory during the certification step. The study was performed according to the "Guidelines for the production and certification of BCR reference materials" and to "ISO guide 31, 33, and 35". The certified clenbuterol mass concentration for clenbuterol-free eye material CRM 673 (calculated on the basis of clenbuterol as the free base) was <0.50 microg kg(-1). The corresponding concentration for clenbuterol-containing eye material CRM 674 was 9.42 +/- 0.88 microg kg(-1). These certified values are very close to the desired target concentration of <0.5 microg kg(-1) and ca 10 microg kg(-1). This study has demonstrated that successful certification of clenbuterol-containing and clenbuterol-free bovine eye materials is possible.     

Preparation of bovine muscle, bovine liver and pig kidney reference materials and the certification of the contents of nine elements of toxicological and nutritional interest

Summary The preparation of 3 meat reference materials (bovine muscle, bovine liver and pig kidney) and the steps taken to confirm their homogeneity and stability are described. Details are presented of a preliminary intercomparison and of the final collaborative exercise which led to the certification of the contents of 9 elements of toxicological and nutritional importance. Indicative values are given for the contents of a further 9 elements in these materials.

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Herstellung von Referenzmaterial aus Rindermuskel, Rinderleber und Schweineniere sowie Zertifizierung der Gehalte an neun Elementen von toxikologischem und ernährungsphysiologischem Interesse

     

Development of candidate reference materials for the measurement of lead in bone

The production of modest quantities of candidate bone lead (Pb) reference materials is described, and an optimized production procedure is presented. The reference materials were developed to enable an assessment of the interlaboratory agreement of laboratories measuring Pb in bone; method validation; and for calibration of solid sampling techniques such as laser ablation ICP-MS. Long bones obtained from Pb-dosed and undosed animals were selected to produce four different pools of a candidate powdered bone reference material. The Pb concentrations of these pools reflect both environmental and occupational exposure levels in humans. The animal bones were harvested post mortem, cleaned, defatted, and broken into pieces using the brittle fracture technique at liquid nitrogen temperature. The bone pieces were then ground in a knife mill to produce fragments of 2-mm size. These were further ground in an ultra-centrifugal mill, resulting in finely powdered bone material that was homogenized and then sampled-scooped into vials. Testing for contamination and homogeneity was performed via instrumental methods of analysis.

Development of bovine muscle, liver and urine reference materials for zeranol – preparation, homogeneity and stability

 Samples of bovine muscle, liver and urine, zeranol-free (RM 508, RM 509 and RM 510, respectively) and zeranol-containing (RM 511, RM 512 and RM 513, respectively) were prepared and tested as candidate reference materials. Preliminary studies on achievement of target zeranol content, intercomparison of analytical methods (HPLC-RIA and GC-MS) and effects of lyophilisation and irradiation on zeranol content are described. The preparation of the materials and testing for homogeneity and stability of zeranol in the materials are discussed. The coefficients of variation for zeranol determinations for between-vial homogeneity (4.0%, 4.4% and 4.6% for muscle, liver and urine, respectively) are similar to those for the analytical method (4.0%, 7.3% and 6.8% for muscle, liver and urine, respectively) indicating that the materials are homogeneous. Stability data over a 12-month storage period at temperatures ranging from −18 °C to +37 °C indicate that the materials are sufficiently stable for use as reference materials. This paper is dedicated to the memory of Dr Hilary Stevenson (The Queen’s University of Belfast/DANI) who, together with Mr. W. Graham, facilitated the irradiation of the lyophilised materials.--> Received: 18 June 1996/Revised: 19 August 1996/Accepted: 23 August 1996     

Development of bovine muscle, liver and urine reference materials for zeranol – preparation, homogeneity and stability

 Samples of bovine muscle, liver and urine, zeranol-free (RM 508, RM 509 and RM 510, respectively) and zeranol-containing (RM 511, RM 512 and RM 513, respectively) were prepared and tested as candidate reference materials. Preliminary studies on achievement of target zeranol content, intercomparison of analytical methods (HPLC-RIA and GC-MS) and effects of lyophilisation and irradiation on zeranol content are described. The preparation of the materials and testing for homogeneity and stability of zeranol in the materials are discussed. The coefficients of variation for zeranol determinations for between-vial homogeneity (4.0%, 4.4% and 4.6% for muscle, liver and urine, respectively) are similar to those for the analytical method (4.0%, 7.3% and 6.8% for muscle, liver and urine, respectively) indicating that the materials are homogeneous. Stability data over a 12-month storage period at temperatures ranging from −18 °C to +37 °C indicate that the materials are sufficiently stable for use as reference materials. This paper is dedicated to the memory of Dr Hilary Stevenson (The Queen’s University of Belfast/DANI) who, together with Mr. W. Graham, facilitated the irradiation of the lyophilised materials.--> Received: 18 June 1996/Revised: 19 August 1996/Accepted: 23 August 1996     

Determination of trace elements in biological materials using tetramethylammonium hydroxide for sample preparation

A method to prepare milk powder, bovine liver and bovine muscle samples for analysis by electrothermal atomic absorption spectrometry (ETAAS) is proposed. Samples are mixed with a small amount of tetramethylammonium hydroxide (TMAH) and a stable and homogeneous slurry is produced in ca. 2 h with heating at 60–70 °C. After such sample preparation and dilution with water, trace elements are determined in certified reference materials. Pyrolysis and atomisation temperatures are optimised for each element, and several modifiers are investigated. External calibration is used for every analyte. Limits of detection (LODs), precision and accuracy are reported for Cd, Pb, Ni, Cr, Cu and Ag and compared with those obtained after conventional acid digestion. The main advantages of the proposed method are the simplicity of sample preparation and the longer lifetime of the graphite tube.     

Certification of reference materials for Cd, Cr, Hg and Pb in polypropylene

Two reference materials, at relatively low and high concentrations (GBW08404 and GBW08405), for analysis of the mass fractions of Cd, Cr, Hg and Pb in polypropylene were developed. The reference materials were prepared by doping blank polypropylene base material with Cd, Cr, Hg and Pb in the form of oxides, salts or pigments. Homogeneity and stability studies were performed by inductively coupled plasma mass spectrometry. The certification of the four analytes was carried out by isotope-dilution mass spectrometry (IDMS) with microwave-assisted digestion. Combined uncertainties were calculated from the IDMS uncertainty evaluation budget and the uncertainty of the homogeneity. The mass fractions of Cd, Cr, Hg and Pb of the two certified reference materials (CRMs) were from 8 to 1,000 mg kg⁻¹. The two samples were also used in an interlaboratory comparison scheme in which National Institute of Metrology, China, National Metrological Institute of Japan and Korea Research Institute of Standards and Science participated. The agreement of the comparison results proved that the certification procedure of the CRMs is valid and that the certified values of Cd, Cr, Hg and Pb are accurate and reliable.     

Direct determination of Hg in polymers by solid sampling-graphite furnace atomic absorption spectrometry : A comparison of the performance of line source and continuum source instrumentation

This work explores the potential of solid sampling-graphite furnace atomic absorption spectrometry (SS-GFAAS) for the fast and direct determination of Hg in polymers. Eight certified reference materials with different composition (polyethylene-PE-, polystyrene-PS-, poly vinyl chloride-PVC- and acrylonitrile butadiene styrene-ABS-) were selected for the study, covering a wide Hg content range (from 20 to 1100 μg g^− 1).     

Reference materials for domoic acid, a marine neurotoxin

Summary Domoic acid was recognized recently [1, 2] to be a marine neurotoxin associated with shellfish harvested or cultured for use as human food. Evidence about the occurrence of domoic acid and its importance to shellfish industries is reviewed. The preparation and certification of two reference materials for the determination of domoic acid, an instrument calibration solution (DACS-1, released by the Marine Analytical Chemistry Standards Program [MACSP] in May, 1989), and a tissue reference material (MUS-1, homogenized soft tissues of Mytilus edulis, released by the MACSP in August, 1989) are described. We believe these are the first certified standards or reference materials to be available for the determination of shellfish toxins, a problem of increasing importance to aquaculturists and the seafood industry, as well as to agencies concerned with the safety of food. The tissue homogenate preparation techniques we have developed and used may be of general interest for the preparation of other tissue reference materials for the determination of other organic compounds, since the sealed, fluid homogenate samples seem acceptably stable without being continuously frozen or refrigerated.NRCC No. 31925     

Ultrasound-assisted pseudodigestion for toxic metals determination in fish muscles followed by electrothermal atomic absorption spectrophotometry: multivariate strategy

A simple and efficient procedure for the determination of arsenic (As), cadmium (Cd), and lead (Pb) in the edible parts of freshwater fish by ultrasonic-assisted acid pseudodigestion (USD) was developed. A Plackett-Burman experimental design was used as a multivariate strategy for the evaluation of the effects of several variables at once. Five variables--sonication time, sample mass of muscle tissue, temperature of the ultrasonic bath, mL of nitric acid, and mL of a mixture of acid and oxidant--were regarded as factors. From these studies, certain variables showed up as significant, and they were optimized by a 23+star central composite design, which involved 16 experiments. Optimum values of the variables were selected for the development of USD to determine the contents of As, Cd, and Pb in fish muscles used as pollution bioindicators from Lake Manchar (Sindh, Pakistan). The determination of the 3 toxic metals under study was performed by electrothermal atomic absorption spectrometry. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials BCR 185R bovine liver and by comparison with conventional wet acid digestion methodology. The result obtained by the optimized method showed good agreement with the certified values and sufficiently high recovery. No significant differences were observed for P = 0.05. Relative standard deviation values (average of 10 separate determinations) were 1.21, 5.52, and 5.32% for As, Cd, and Pb, respectively.     

Comparison of methods used for the preparation of biological CRM's

The starting material for two certified and one candidate reference material was obtained from dried grass specially cultivated on a selected and well prepared soil. The Community Bureau of Reference (BCR) of the Commission of the European Communities produced two certified reference materials (CRM's) from this dried grass: a rye grass material (CRM 281) certified in 1988 for the quality control of trace and toxic element analyses and a hay powder material (CRM 129) certified in 1989 for monitoring trace and minor elements. A fraction of the dried grass was used in 1993 for the preparation of a hay powder with a particle size of <63 m using newly developed grinding techniques.This paper compares the production methods of these three materials and the obtained particle size distribution of the powders. The analytical evaluation of these production methods was carried out by solid sampling Zeeman atomic absorption spectrometry for the determination of Cd, Pb and Zn.     

Direct analysis of coal by electrothermal atomization atomic-absorption spectrometry

A novel approach for trace element determination in coal samples is described, based on grinding the sample to less than 200 mesh, "pipetting" the material into a tube-cup furnace, and measurement by electrothermal atomization atomic-absorption spectrometry. Either solid standard reference materials or aliquots of solutions of Pb, Zn and Mn can be used to prepare analytical calibration curves. The SRMs are diluted with spectroscopic grade graphite prior to introduction into the tube-cup furnace. After the atomization and cleaning step, any remaining ash is removed with a Pasteur pipette. The measured values for Pb, Zn and Mn agree well with the certified SRM values. The method is rapid, and sufficiently precise (5-14%) and accurate (within 5-12% of standard reference values).     

NBS activities in biological reference materials

Summary NBS activities in biological reference materials during 1986–1988 are described with a preview of plans for future certifications of reference materials. During the period, work has been completed or partially completed on about 40 reference materials of importance to health, nutrition, and environmental quality. Some of the reference materials that have been completed during the period and are described include: creatinine (SRM 914a), bovine serum albumin (SRM 927a), cholesterol in human serum (SRM's 1951–1952), aspartate aminotransferase (RM 8430), cholesterol and fat-soluble vitamins in coconut oil (SRM 1563), wheat flour (SRM 1567a), rice flour (SRM 1568a), mixed diet (RM 8431a), dinitropyrene isomers and 1-nitropyrene (SRM 1596), and complex PAH's from coal tar (SRM 1597). Oyster tissue (SRM 1566a) is being analyzed and should be available in 1988.

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NBS-Aktivitäten in biologischen Referenzmaterialien