CRMs for trace elements

Four 680 L polyethylene containers (two for each solution) to be used for the sampling, preparation and homogenisation of the candidate CRMs were cleaned with detergent, rinsed with distilled water and soaked with diluted pro-analysis nitric acid (1 10). The containers were rinsed again with Milli-Q water and soaked with Milli-Q water for a period of at least one month prior to the use of the containers. Tubings used for filtration and homogenisation were also cleaned at the same time as the container cleaning procedure. 

The filters used for filtration were of the types Sartorius depth filter (particle retention size 0.7 pm) and Sartorius PH membrane filter capsule (particle retention size 0.45 pm). Polyethylene bottles produced by Nalgene were used for each of the reference material. 2600 pieces of 500 mL bottles were cleaned, using the following procedure  

SUBSTANCES ADDED FOR THE PREPARATION OF THE CANDIDATE CRMS AND CONCENTRATIONS EXPECTED UPON SPIKING 

Before spiking Amount added Before spiking Amount added 

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Accuracy and Analytical Quality Control Aspects The analysis of certified reference materials (CRMs) following the same analytical procedures was performed for assessment of the accuracy of the procedure and for quality control (QC). Yet, the available CRMs are mostly freeze-dried, not fresh or deep-frozen. In Table 22.3 an overview of CRMs in a seafood matrix with respect to organic Hg is given. It is certainly beneficial that more and more CRMs are becoming commercially available. Recently, a new CRM for trace elements in a matrix of lyophilized tuna fish (IMEP-20) has been produced [44]. Apart from total Hg (4.32 mg kg-1 dry mass) and Me-Hg (4.24 mg kg-1 dry mass), this material is also certified for other elements such as As, Pb, and Se. 

Krill is a small planktonic crustacean primarily living in the Southern Ocean and its total biomass is estimated to be at least 500 million tons (around 500,000 billion individuals). It feeds on phytoplankton and is one of the most important species in the Antarctic food chain. In fact, krill is the basic food for whales, seals, cephalo-pods, penguins and many other seabirds and is also used for direct human consumption (20-24). Moreover, krill seems to be a promising bioindicator of environmental pollution by trace elements and organic compounds. All these considerations called for the production of a CRM for trace elements based on this matrix (25). 

A candidate CRM for trace elements in Antarctic coastal marine sediment was prepared by coarse sieving, drying, jet-milling with ultrafine classification of particles and Turbula mixing. The material was found to be of appropriate particle size distribution, dryness and homogeneity to be certified as a stable and homogeneous CRM. 

BCR CRM 402 Trace Elements in White Clover 0, = 0.456 at 2i.r°C w.c. = 7.52 0.04%. Despite its relatively high value, the water activity is still in the range for long-term stability and major differences in the water content as a consequence of sorption processes are not to be expected. This is supported by the fact that no spoilage has been observed, even though the production was in 1987. 

It is clear that the available RMs certified for trace element species are not sufficient to cover present needs. As it is quite unlikely that producers of CRMs will ever be able to meet all demands, users are encouraged to produce their own RMs to guar-... 

Zambia, Thailand and USA (Florida) were analyzed by using the X-ray fluorescence method for elemental composition. These rock phosphates have also been evaluated for their agronomic effectiveness by means of radioisotope techniques (Zapata and Axmann, 1991). The samples were prepared as pellets and analyzed using the emission transmission method for trace elements (Markowicz and Haselberger, 1992). All samples were excited using an Mo tube with an Mo secondary target. For quality control of concentration data analysis of standard reference material CRM 032 (phosphate rock) produced by CEC, Brussels, has been used. Satisfactory agreement between certified and measured values was obtained. 

Table 10.1. Laboratories participating in the certification project for trace elements in the CRM MURST-ISS-Al Antarctic Sediment and the instrumental techniques employed...

Table 10.6. Informative concentrations for trace elements in the CRM MURST-ISS-A2 Antarctic Krill as obtained by NAA and other techniques as specified, wherever applicable...

In geochemistry, the introduction of RMs did not take place until 1951 but, once RM usage became a regular part of geochemical analysis, the consequences were not far short of amazing. For many years geochemical analysts had been concerned about the accuracy of their determinations of major elements in rocks, but it was the potential of emission spectrometry for the determination of trace elements which set off the production of the first rock Certified Reference Materials (CRMs),... 

Further afield, in 1978 the Japanese National Institute for Environmental Studies (NIES) started the production of a series of biological and environmental matrix CRMs, certified for a number of trace elements (Okamoto and Fuwa 1985). Recently also the certification of metal species in some materials was reported (Okamoto and Yoshinaga 1999). 

Trace elements in soils and sludges (CRMs 141R-146R 597) pp 225-232 (1998k) Chlorobi-phenyls in sewage sludge (CRM 392) pp 240-243 (1998I) Trimethyl-lead in urban dust (CRM 605) pp 274-278 In Production of Certified Reference Materials for Pollutants in Environmental Matrices. European Commission Report EUR 18157 EN, CCF Academic Press, Tarbes. 

Quevauviller Ph, Maier EA, Vercoutere K, Muntau H, Griepink B (1992a) Certified reference material (CRM 397) for the quality control of trace element analysis of human hair. Fresenius J Anal Chem 343 335-338. 

Lichens accumulate trace elements from the atmosphere and thus are frequently used instead of air filters for pollution monitoring. Certification of nine elements (Al, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, and Zn) by a group of ii selected laboratories was performed in BCR CRM 482 (Lichen) after an inter-comparison on trace elements in samples of this material (Quevauviller et al. 1996b). 

The list of elements and their species listed above is not exhaustive. It is limited to the relatively simple compounds that have been determined by an important number of laboratories specializing in speciation analysis. Considering the economic importance of the results, time has come to invest in adequate CRMs. There is a steadily increasing interest in trace element species in food and in the gastrointestinal tract where the chemical form is the determinant factor for their bioavailability (Crews 1998). In clinical chemistry the relevance of trace elements will only be fully elucidated when the species and transformation of species in the living system have been measured (ComeUs 1996 Cornelis et al. 1998). Ultimately there will be a need for adequate RMs certified for the trace element species bound to large molecules, such as proteins. 

Quevauviller Ph, Herzig R. and Muntau H (1996b) Certified reference material of lichen (CRM 482) for the quality control of trace element biomonitoring. Sci Total Environ 187 143-152 Quevauviller Ph, Lachica M., Barahona E, Rauret G, Ure A, Gomez A, and Muntau H (1997) The certification of the EDTA-extractable contents (mass fractions) of Cd, Cr, Ni, Pb, and Zn and of the DTPA-extractable contents (mass fractions) of Cd and Ni in calcareous soil by the extraction procedures given CRM 600. EUR Report 17555 Quevauviller Ph. Maier EA, and Griepink B, eds. (1995) Quality Assurance for Environmental Analysis. Elsevier. Amsterdam. 

There are a number of CRMs available for this group of elements in semm and urine (see Table 6.3). The most severe problems with the determination of these trace elements are contamination and loss. Therefore, strict protocols are necessary to prevent these problems. Contamination can be prevented by cleaning thoroughly all used utensils, and the use of highly purified chemicals. Loss is mostly due to exchange between the container walls and can be prevented by working at a pFI<2. 

In his survey of the use of CRMs in food related publications on the subject of trace elements for the years 1990-1996, Jorhem (1998) checked 82 papers published in five international journals. He found that in 42 papers there was no mention of CRM results and assumed that no CRMs were used. He wrote Since the importance of incorporating CRMs in the AQA-activities today is well recognized, it is surprising that firstly so many laboratories still do not use CRMs and secondly that scientific journals accept papers describing analytical results without the use of reference materials, as part of the verification of the analytical results . 

One approach to providing secondary RMs is the NIST Traceable Reference Material (NTRM) program for gas standards (Jenks et. al. 1998 NIST 1997). The NTRM program is to be extended to metals, trace elements and pure substances. It may be possible to extend this concept to other types of RM, but it is difficult to see how it can easily be applied to the production of complex matrix CRMs. 

Segura, M., Camara, G, Madrid, G, Rebollo, C., Azcarate, J., Kramer, G. N., Gawlik, . M., Lamberty, A., and Quevauviller, Ph. (2004), Certified reference materials (CRMs) for quality control of trace-element determinations in wastewaters, Trends Anal. Chem., 23,194-202. 

Certified reference materials (CRMs) are mainly applied to validate the analytical procedure developed for routine analysis in order to determine the accuracy of analytical data, the recovery for selected elements, the uncertainty of trace element determination and the detection limits. Otherwise, in solid-state mass spectrometric techniques, such as SSMS, LA-ICP-MS, GDMS, SNMS or SIMS, one point calibration using CRMs has been established as an important calibration strategy to obtain reliable analytical data. The one point calibration is performed using the experimentally determined relative sensitivity coefficients (RSCs) on a suitable CRM with a similar trace/matrix composition. An RSC of a chemical element is defined as the ratio of the measured element concentration (experimentally determined) divided by the certified element concentration (accepted or recommended value of element concentration) in a given matrix. 

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