Simultaneous determination of inorganic mercury,methylmercury, and total mercury concentrations in cryogenic fresh-frozen and freeze-dried biological reference materials

Two speciated isotope dilution (SID) approaches consisting of a single-spike (SS) method and a double-spike (DS) method including a reaction/transformation model for the correction of inadvertent transformations affecting mercury species were compared in terms of accuracy, method performance, and robustness for the simultaneous determination of methylmercury (MeHg), inorganic mercury (iHg), and total mercury (HgT) concentrations in five biological Standard Reference Materials (SRMs). The SRMs consisted of oyster and mussel tissue materials displaying different mercury species concentration levels and different textural/matrix properties including freeze-dried (FD) materials (SRMs 1566b, 2976, and 2977) and cryogenically prepared and stored fresh-frozen (FF) materials (SRMs 1974a, 1974b). Each sample was spiked with (201)iHg (Oak Ridge National Laboratory, ORNL) and Me(202)Hg (Institute for Reference Materials and Measurements. IRMM-670) solutions and analyzed using alkaline microwave digestion, ethylation, and gas chromatography inductively coupled plasma mass spectrometry (GC/ICP-MS). The results obtained by the SS-SID method suggested that FF and FD materials are not always commutable for the simultaneous determination of iHg, MeHg, and HgT, due to potential transformation reactions resulting probably from the methodology and/or from the textural/matrix properties of the materials. These transformations can occasionally significantly affect mercury species concentration results obtained by SS-SID, depending on the species investigated and the materials considered. The results obtained by the DS-SID method indicated that the two classes of materials were commutable. The simultaneous and corrected concentrations of iHg, MeHg, and HgT obtained by this technique were not found to be statistically different form the certified and reference concentration together with their expanded uncertainty budgets for the five SRMs investigated, exemplifying the robustness, the accuracy, and the improved commutability of this method compared to SS-SID measurements.     

Methyl mercury determination in environmental and biological reference and other materials by quality control with certified reference materials (CRMs)

Summary Two concentration methods — HCl extraction and extraction followed by water vapour distillation — prior to anion exchange separation and cold-vapour atomic absorption spectrometry were used for the quantification of methyl mercury in a number of reference materials of biological and environmental origin with reference or certified total mercury contents. The applied methods were validated by the analysis of three marine reference materials, certified for methyl mercury. The results obtained in the materials with methyl mercury contents ranging from less than 1 g/kg to a few hundred g/kg showed good agreement between both methods for biological materials, whereas extraction/anion exchange resulted in somewhat too high values for a number of environmental materials. These findings, however, require further confirmation by additional methods and by other laboratories.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Non-destructive determination of zinc in biological certified reference materials

Non-destructive neutron activation analysis was employed to determine zinc in ten biological standard reference materials from the National Bureau of Standards and the National Research Council of Canada. The use of a 4 h. irradiation at a medium neutron flux allows excellent accuracies, precision and sensitivities to be attained for all the samples analyzed. It is suggested that neutron activation analysis be one of the benchmark methods for the determination of zinc in biological reference materials for concentrations as low as the one part per million level.     

A rapid ultrasound-assisted thiourea extraction method for the determination of inorganic and methyl mercury in biological and environmental samples by CVAAS

A rapid ultrasound-assisted extraction procedure for the determination of total mercury, inorganic and methyl mercury (MM) in various environmental matrices (animal tissues, samples of plant origin and coal fly ash) has been developed. The mercury contents were estimated by cold vapour atomic absorption spectrometry (CVAAS). Inorganic mercury (IM) was determined using SnCl₂ as reducing agent whereas total mercury was determined after oxidation of methyl mercury through UV irradiation. Operational parameters such as extractant composition (HNO₃ and thiourea), sonication time and sonication amplitude found to be different for different matrices and were optimized using IAEA-350 (Fish homogenate), IM and MM loaded moss and NIST-1633b (Coal fly ash) to get quantitative extraction of total mercury. The method was further validated through the analysis of additional certified reference materials (RM): NRCC-DORM2 (Dogfish muscle), NRCC-DOLT1 (Dogfish liver) and IAEA-336 (Lichen). Quantitative recovery of total Hg was achieved using mixtures of 5% HNO₃ and 0.02% thiourea, 10% HNO₃ and 0.02% thiourea, 20% HNO₃ and 0.2% thiourea for fish tissues, plant matrices and coal fly ash samples, respectively. The results obtained were in close agreement with certified values with an overall precision in the range of 5-15%. The proposed ultrasound-assisted extraction procedure significantly reduces the time required for sample treatment for the extraction of Hg species. The extracted mercury species are very stable even after 24 h of sonication. Closed microwave digestion was also used for comparison purposes. The proposed method was applied for the determination of Hg in field samples of lichens, mosses, coal fly ash and coal samples     

Analysis of marine biological certified reference material by various non-destructive neutron activation methods

By the use of non-destructive neutron activation analysis (NAA) twenty-four trace (Ag, As, Br, Cd, Ce, Cr, Co, Cu, Eu, Fe, Hf, I, La, Mn, Ni, Rb, Sb, Sc, Se, Sm, Sr, U, V and Zn) and six minor (Ca, Cl, Mg, K, Na and S) elements were determined in a certified marine tissue standard reference material. Four non-destructive methods including thermal, epi-thermal, prompt-gamma ray and delayed neutron counting activation analyses were performed. Results when compared to the certified values showed the reliability of employing these methods in such standards program.     

A novel preconcentration technique using crosslinked chitosan for the determination of mercury by CVAAS

A novel crosslinked chitosan (CCTS) has been synthesized by the reaction of water-soluble chitosan with epoxy chloropropane. In the presence of the chelating EDTA and in the pH range between 4–10, CCTS selectively adsorbed trace inorganic Hg in water samples with enrichment factors of 100. Inorganic Hg could be directly reduced using KBH₄ without preceding elution and determined by CVAAS. Accordingly, the total mercury could be determined after all species of mercury in water samples were transformed into Hg²⁺. The detection limit (3σ) for mercury was 12 ng L^–1 and the relative standard deviation less than 5% at the 50 ng L^–1 level. Beer’s law was obeyed over the range 30–400 ng L^–1 of mercury and the preconcentration method was applied to environmental water samples with the recoveries between 92–96%.     

Selection of reference methods for the determination of selenium in biological materials

Summary Over the period 1985–1989 the European Community Bureau of Reference (BCR) has certified 7 biological reference materials for selenium with concentrations ranging from 0.03 to 10 mg/kg. Certification analyses were carried out by the most experienced laboratories in the Member States, using Fluorimetry, Hydride formation, combined with ICP or AAS, Electrothermal AAS with or without Zeeman-background correction, Instrumental or radiochemical NAA. Results from these exercises are available in a form suitable for estimating the experimental precision of the various methods as a function of concentration. With the same number of replicates for all analyses the logarithm of the observed standard deviations have constant variance, independent of concentration; for each method the absolute and relative standard deviations can therefore be estimated by means of non-linear regression. Analytical bias was monitored plotting results and their estimated standard deviations from individual laboratories versus certified confidence intervals. For concentrations of Se <0.3 mg/kg fluorimetry was selected as a reference method; above this level INAA is recommended; both are capable of producing unbiased results.     

Estimation of uncertainty for the determination of mercury in food by CVAAS

This paper is aimed at reporting a full validation of a Cold Vapour Atomic Absorption Spectrometry (CVAAS) method for mercury determination in fishery products. Method precision, trueness, limit of detection and limit of quantification are evaluated. The uncertainty of measurement is estimated following the bottom-up approach in conjunction with the validation data as suggested for complex analysis. The precision is evaluated using a pooled relative standard deviation and the recovery is added to the measurement uncertainty budget. Uncertainties of weight of sample, dilution factor, calibration, work solution and analyte amount are also assessed. The most relevant uncertainty sources result those associated to amount of mercury determined in the final sample solution, to method precision and to recovery. The relative contributions have different weights according to the analyst decision regarding recovery correction of results. In conclusion, the adopted CVAAS method fully complies with EU requirements. Presented at AOAC Europe/Eurachem Symposium March 2005, Brussels, Belgium     

Standardization of methods for the determination of traces of mercury : Part I. Determination of total inorganic mercury in inorganic samples

A method is described for the routine determination of mercury in the process and product streams of chlor alkali electrolysis plants (with the exception of chlorine) and also in the plant waste waters. The procedure is based on flameless atomic absorption spectrophotometry. Results for interlaboratory trials involving up to 37 participating laboratories are presented. Both synthetic and technical samples were analysed with mercury contents varying between 20 μg kg^-1 and 20 mg kg^-1. Statistical evaluation of the results gave a value of from 4 to 8% for the repeatability and from 6 to 22% for the reproducibility.     

A new neutron activation technique for simultaneous determination of inorganic and total mercury contents in human hair

A simple method for simultaneous determination of inorganic and total mercury contents in human hair by neutron activation analysis (NAA) has been developed. The method is based on the selective extraction of methylmercury from hair by hydrochloric acid. Thus, the residual phase containing inorganic mercury can be determined by NAA. Further, the methylmercury contents in hair samples are easily calculated by subtracting the inorganic mercury contribution from the total Hg simultaneously given by INAA. Several reference materials of human hair, including IAEA hair RM 085 and 086, Chinese hair RMs GBW 09101 and 07601, were analyzed by this method. Our results show that the method is reliable.     

Evaluation of botanical reference materials for the determination of vanadium in biological samples

Three botanical reference materials prepared by the National Bureau of Standards have been studied by neutron activation analysis to evaluate their suitability with respect to the determination of vanadium in biological samples. Various decomposition methods were applied in connection with chemical or radiochemical separations, and results for vanadium were compared with those found by purely instrumental neutron activation analysis. Significantly lower results indicate losses or incomplete dissolution, which makes SRM 1575 Pine Needles and SRM 1573 Tomato Leaves less satisfactory than SRM 1570 Spinach. A reference value of 1.15 mg/kg of this material is recommended, based on results from 3 different methods. All three materials are preferable to SRM 1571 Orchard Leaves, while Bowen's Kale remains the material of choice because of its lower concentration.     

The determination of the uncertainty of reference materials certified by laboratory intercomparison

A pragmatic method is proposed for the implementation of the Guide to the expression of uncertainty in measurement in the certification of reference materials by laboratory intercomparison. It is based on the establishment of a full uncertainty budget for each laboratory result and the estimation of the impact of various laboratory standard uncertainties and of between-units variability on the certified reference material (CRM) uncertainty.     

Radiochemical separation methods for the determination of some toxic elements in biological reference materials

The present paper describes radiochemical separation procedures developed for the determination of the elements As, Cr, Hg, Sb and Se in biological reference materials. The methods chosen utilize ion exchange, retention on inorganic exchangers and solvent extraction techniques for the isolation of the elements of interest. These procedures are more rapid than previously used methods, such as distillation and precipitation. As to the sample dissolution, the following procedures were tested using radioactive tracers and reference materials: treatment of the materials in teflon bombs with a mixture of HNO₃+H₂SO₄ or HNO₃ only in a normal oven, and with HNO₃ in a microwave oven using specially designed digestion bombs.     

Reference materials and certified reference materials for spectrometry in Romania

Several reference materials (RMs) and certified reference materials (CRMs) are widely used in Romania as measurement standards in different spectrochemical measurements. Among them, single element standard solution certified for their mass concentration play a key role in ensuring the required traceability of results expressed in this measurement unit. A short review of the locally available elemental RMs and CRMs used in atomic spectrometry or in other analytical techniques where aqueous standard solutions are required (usually called RMs or CRMs for spectrometry) is given. The experience of the INM in preparation and certification of such materials is described. Some aspects regarding their use for ensuring the accuracy and for confirmation of the traceability of analytical measurements, especially through calibration and metrological validation of main instrument performances, are discussed.     

Overview about biological and environmental certified reference materials in the database COMAR

The Database COMAR now includes data from more than 8640 CRMs supplied by 180 producers in 24 countries. These data are divided into 8 main categories, containing up to 10 sub-categories. Quality of life as well as biological and clinical CRMs are two main categories where a great increase could be observed in the past years. These fields represent approximately 20|X% of the data records. Therefore it will be possible to gather different statistical information from these data.     

Reference materials and certified reference materials for spectrometry in Romania

Several reference materials (RMs) and certified reference materials (CRMs) are widely used in Romania as measurement standards in different spectrochemical measurements. Among them, single element standard solution certified for their mass concentration play a key role in ensuring the required traceability of results expressed in this measurement unit. A short review of the locally available elemental RMs and CRMs used in atomic spectrometry or in other analytical techniques where aqueous standard solutions are required (usually called RMs or CRMs for spectrometry) is given. The experience of the INM in preparation and certification of such materials is described. Some aspects regarding their use for ensuring the accuracy and for confirmation of the traceability of analytical measurements, especially through calibration and metrological validation of main instrument performances, are discussed.     

Evaluation of high pressure oxygen microwave-assisted wet decomposition for the determination of mercury by CVAAS utilizing UV-induced reduction

The UV-induced cold vapor generation with formic acid coupled to AAS after high pressure oxygen microwave decomposition was developed for determination of total Hg in analytical samples. Certified reference materials were decomposed in 1.5 mol L^{− 1} HNO₃ and 0.6 mol L^{− 1} H₂O₂. Microwave decomposition with oxygen has allowed the use of diluted reagents. The oxygen at a pressure of ca. 15 bar was delivered during the mineralization to the closed vessel. Interference by unused residues of H₂O₂ and HNO₃ was observed. In order to overcome the negative effect of remaining oxidants pre-reduction with hydroxylammonium chloride at a concentration 0.75 mmol L^{− 1} was used. Recovery of mercury in four reference materials containing 0.20–1.99 µg g^{− 1} Hg were 99–104% of certificate values. The limits of detection and quantification in the sample solutions were determined as 0.12 and 0.38 µg L^{− 1}, which corresponds to absolute detection limits of 12 and 38 ng g^{− 1} for total mercury, respectively. The results were in good agreement with the t-test at a 95% confidence level of the certified values in the investigated reference materials. The relative standard deviation was better than 7% for most of the samples.     

Pyrolysis/CVAAS for the determination of mercury in solid environmental samples

Summary A CVAAS method is reported for the determination of mercury in solid environmental materials by pyrolysis and a two-stage amalgamation on gold. Interferences by pyrolysis products are eliminated by a purification section containing a catalytic converter and two specific adsorbers for organic substances. The detection limit of the method is 5 ppb for a 20-mg sample. The reproducibility highly depends on the homogeneity of the materials.

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Pyrolyse/Kaltdampf-Atomabsorption zur Hg-Bestimmung in festen Umweltproben

Zusammenfassung Ein Kaltdampf-Atomabsorptions-Verfahren zur Quecksilberbestimmung in festen Umweltproben durch Pyrolyse und Zwei-Schritt-Amalgamierung auf Gold wurde angegeben. Störungen durch Pyrolyseprodukte lassen sich durch eine Reinigungsvorrichtung beseitigen, die einen katalytischen Konverter und zwei spezifische Absorber für organische Substanzen enthält. Die Nachweisgrenze für eine 20-mg-Probe liegt bei 5 ppb. Die Reproduzierbarkeit der Ergebnisse ist weitgehend von der Homogenität des Materials abhängig.

     

Iodine determination in biological materials Options for sample preparation and final determination

This paper describes the development of various new acid sample decomposition methods, as well as an extraction (leaching) method and compares them with the “Sch?niger Combustion” technique. The methods have been developed as sample preparation techniques for iodine determination in biological materials, especially in solid samples. ICP-MS (inductively coupled plasma mass spectrometry) and a catalytic technique are employed and discussed for the final determination of iodine concentrations. Accuracy and reliability of the different analytical methods are shown in the examples of different CRMs (certified reference materials) available for iodine. The results of an interlaboratory comparison are specifically presented for the extraction (leaching) method. Received: 11 May 1998 / Revised: 14 June 1998 / Accepted: 16 June 1998