Certification of Elements

Milan Ihnot, Anthony R Byrne, Jan Kucera and Philippe Quevauviller 3.2.1 

An extremely wide variety of analytical methods are used by RM producers and developers in the certification of RMs for inorganic elemental content. These methods range from the classical, through current instrument based methods to highly specialized definitive methods. 

In general, a typical method contains three basic stages  

Minimal pretreatment such as pelletizing, briquetting, grinding Acid digestion/dissolution in open vessels (atmospheric pressure) 

Acid digestion/dissolution in closed vessels (under pressure) 

---

Kucera j, Mader P, Miholova D, Cibulka J, Faltejsek J and Kordik D (1995) Preparation of the bovine kidney and bovine muscle reference materials and the certification of element contents fi om interlaboratory comparisons. Fresenius J Anal Chem 352 66-72. 

Certification of Element Contents by Neutron Activation Analysis... 

It can be concluded that, in the field of RM certification, NAA represents a major analytical technique contributing significantly to the certification of element contents in environmental and biological RMs, as was also pointed out earlier (Dyb-czynski 1980 1995), and also provides the bulk of the hterature data on NIST SRMs (Gladney et al. 1987,1993). NAA also has a similar position in the field of geological RMs (Roelandts 1991). It possesses unique quality assurance and self-verification aspects (Becker 1993 Byrne 1993 Byrne and Kucera 1997), though these in-built features are rarely exploited in fuU at present. It should be reahzed that the advanta-... 

Ihnat M, Byrne AR, Kucera J and Quevauviller P (2001) Certification of Elements. In Stoeppler M, Wolf WR and Jenks PJ, eds. Reference Materials for Chemical Analysis - Certification, Availability and Proper Usage, pp. 60-75 (refs pp. 101-110). Wiley-VCH, Weinheim. 

The audit plan must include all elements of the supplier s quality system that meet the needs of those customers recognizing ISO/TS 16949 certification of their suppliers, even when these requirements go beyond ISO/TS 16949. 

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). 

Two challenging, but very difficult tasks have been tackled mainly or increasingly during the last two decades the certification of organometallic species and valency states of elements (see Section 3.3), and organic compounds (see Section 3.4). But doubtless this was just the beginning and a wealth of work waits in the future to serve all needs of the analytical community (Quevauviller and Maier 1999)-... 

Versieck J, Vanballenberghe L, de Kesel A, Baeck N, Steyart H, Byrne AR and Sunderman FW Jr. (1988) Certification of a second-generation biological reference material (freeze dried human serum) for trace element determinations. Anal Chim Acta 204 63-75. 

Benoliel MJ. Quevauviller P, Rodrigues E, Andrade ME, Cavaco MA, Cortez L (1997) Certification of reference materials for quality control of major element determinations in ground-water Part i Feasibility study, fresenius J Anal Chem 358 574-580. 

Fraser CA, Gardner GJ, Maxwell PS, Kubwabo C, Guevremont R, Siu KWM, Berman SS (1995) Preparation and certification of a biological reference material (CARP-i) for polychlorinated dibenzo-p-dioxin and dibenzofliran congeners. Fresenius J Anal Chem 352 143-147. Gardiner PE (1993) Consideration in the preparation of biological and environmental reference materials for use in the study of the chemical speciation of trace elements. Fresenius J Anal Chem 345 287-190. 

Tab. 3.3 Methods for the certification of RMs for elemental content Initial stages pretreatment, preconcentration, isolation and separation...

Multi-method certification of 25 elements with information provided on another 22 elements was performed in NIST SRM 2704 (Buffalo River sediment) by NIST laboratories with four co-operating laboratories from USA and Canada (Epstein et al. 1989). 

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). 

Byrne AR, Camara-Rica C, Cornelis R, de Gobi JJM, Iyengar GV, Kirkbright G, Knapp G, Parr RM, and Stoeppler M (1987) Results of a co-ordinated programme to improve the certification of IAEA milk powder A-ii and animal muscle H-4 for eleven difficulf trace elements. Fresenius Z Anal Chem 326 723-729. 

Delfanti R, Di Casa M, Gallorini M, and Orvini E (1984) Five years activity in determining trace elements for the certification of standard reference materials by neutron activation analysis. Mikrochim Acta [Wien] L239-250. 

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. 

Other authors used a simple 2 standard deviation criteria or an outlier test (F-test) to check for significant differences between within-bottle and between-bottle results (Martin-Esteban et al. 1997 Quevauviller et al. 1995). The degree of homogeneity of elements and compounds in the materials tested in these studies does not seem to be adequately described and, hence, the asigned uncertainties in the mean values may represent only the bias between the analytical methods used in the certification. 

As micro-analytical techniques (performing direct analysis on a <10 mg sample mass) have a particularly distinct demand for very homogeneous CRMs, it becomes necessary to provide element-specific homogeneity information in the CRM certificates. The distribution of elements in a material can be evaluated experimentally by repetitive analysis. The scattering of results from a method with known intrinsic precision is related to the mass of sample consumed for individual analysis. The... 

The enormous difference in certified values between methods and between analytes illustrates well how much care is needed in matrix/method matching. Further evidence of the importance of matrix matching is provided by an interlaboratory study on trace elements in soil reported by Maier et al. (1983) and the certification of a sewage sludge described by Maaskant et al. (1998). 

---