Analysis of Trace Elements in Biological Samples

Biological samples are potentially excellent records of their environment and are being examined by inorganic and biomolecular mass spectrometry to an increasing extent. Biomaterials such as carbonate shells, fish otoliths and fish scales or tree rings that increase their mass regularly on an annual basis may record changes in their environment via the concentrations of metals or non-metals and the isotopic composition of elements.2 

A homogeneity and stability study of the candidate reference materials for trace element analysis (As, Cd, Cu, Cr, Fe, Mn, Ni and Zn) on the Antarctic bivalve Admussium colbecki (IRMM 813) is discussed by Caroli and associates.7 The scallops were collected at Terra Nova Bay (Ross Sea) during the 2000-2001 Italian expedition to Antarctica. 

Multi-element analysis on 57 tree bark samples collected at different locations (near power plants, closed to a motorway, in urban or in uncontaminated rural areas) in the UK in order to study environmental contamination was performed by quadrupole based ICP-MS (Elan 6000, Perkin Elmer Sciex) after microwave induced digestions of samples and dilution. The measured concentration ranges of 52 elements varied from the sub-ngg-1 range (e.g., Hf or Pt) to the low % range (e.g. for Ca) and are summarized in Table 9.24.4 Oriental Tobacco Leaves SRM (CTA-OTL-1) was employed to validate the analytical ICP-QMS method. 

Element Concentration range, pgg 1 Element Concentration range, pgg-1 

In addition to ICP-MS for the multi-element analysis of aqueous solutions, LA-ICP-MS allows the direct determination of trace elements in biological samples and due to this feature it is a well suited analytical technique for microlocal analysis with spatial resolution. In 1995, Outridge el al.lg reported on the performance of an LA-ICP-MS analysis for studying incremental biological structures as archives of trace element accumulation. The use of LA-ICP-MS for several biological (and environmental) applications is reviewed by Durrant and Ward.19 Selected examples for determination of trace elements and species in biological samples are summarized in Table 9.25. 

Sanz-Medel and co-workers reported on selenium determination in biological samples by isotope dilution analysis in ICP-QMS with an octopole collision cell. The argon based isobaric interference arising during measurements of °Se was eliminated by using a hydrogen flow of 4 ml min in the octopole cell, so that it is possible to determine Se with a detection limit of 14pgg.  

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Hydrochloric and nitric acids have been used as preservatives for urine specimens for metal analyses, and mineral acids are extensively used in graphite furnace analysis of trace elements in biological specimens (e.g. Gills et al., 1974 Stoeppler and Brandt, 1980). Historically, concentrations of trace elements in commercially available acids have been incompatible with analysis of trace elements in biological samples (Kuehner et al., 1972). However, present commercial ultra pure hydrochloric, nitric, sulphuric and perchloric acids have been reported to be suitable for trace element analysis in urine without further purification (Golimowski et al., 1979 Brown et al., 1981 Veillon et al., 1982). 

Sansoni B and Iyengar V (1978) Sampling and Sample Preparation Methods for the Analysis of Trace Elements in Biological Material. Spezielle Berichte Kemforschungsanlage Jiilich, JUL-Spez-13. 

FIG. 6.22. PKE analysis of trace elements in environmental and biological samples. 

Lasers have been used in mass spectrometry for many years. Trace elements in biological samples [90] can be determined by using laser microprobes (LAMMA, laser microprobe mass analyzer) or a combination of laser ablation with ICPMS. For the analysis of bulk materials, techniques such as resonance ionization mass spectrometry (RIMS) and laser ablation MS (LAMS) are employed for a review see [91]. 

Neutron activation analysis. New methods of quantitative analysis based on the formation of radioactive nuclei by neutron capture have been developed. The sample is exposed to neutrons, each constituent element forms a specific radioisotope with a characteristic half-life, and from the activity of the radioisotope, the mass of the element from which it was formed may be calculated. The sensitivity of the method, about one part or less per billion, makes it very useful for the nondestructive analysis of trace elements in complex biological systems, in archeological samples, in meteorites, and in lunar rocks. 

The chemical speciation study of trace elements in life sciences has been paid more and more attention in recent years, mainly because it can provide more significant information on the pathway, distribution, accumulation, excretion, and functions of trace elements in biological systems of interest than the traditional bulk composition study. Almost all speciation techniques consist of two steps. The first step involves the separation of species from the sample followed by the second step of element specific detection. The so-called molecular neutron activation analysis (MoNAA) or speciation neutron activation analysis (SNAA) is, in fact, a combination of conventional NAA with physical, chemical, or biological separation procedures in order to meet the ever-increasing need for chemical species study. 

The information on the chemical speciation of trace elements in biological systems is much needed to evaluate their biological significance. Although a number of analytical techniques based on atomic behavior are available for the analysis of chemical speciation of trace elements, neutron activation analysis, as a nuclear analytical technique, can be successfully used in chemical speciation studies, after appropriate fractionation steps. Table 2.5 lists some typical applications of NAA in chemical speciation analysis of metalloproteins. The main advantages of NAA are of its high sensitivity and the absence of matrix effects inherited from the conventional neutron activation analysis. It can, therefore, be used to analyze the chemical species of trace elements in very small samples or complicated matrices, which is often impossible for non-nuclear techniques. 

The ability to measure the concentration of the exact form of the analyte present in the sample yields important information regarding the chemical and biological reactivity of the material. Because of the significant differences in toxicity between various forms of trace elements in the sample, occurrence standards are often estabhshed by regulatory agencies specific to a particular form of the analyte. This speciation analysis approach provides the information required to study and monitor these toxic compounds. In addition, to determine the fate of specific compounds in chemically reactive situations, quantitative information about the specific forms of the materials present is required to understand the process chemistry and kinetics that are occurring. 

There are many examples of relatively straightforward use of ICP-MS for the analysis of biological fluids. Antimony has been measured in blood after a 14 1 dilution [236]. Cesium serum levels were found to be elevated in patients with alcohol dementia but not in Alzheimer s disease patients [237]. Cobalt levels in rat serum depended on the form of cobalt [238] ingested. Bismuth levels were measured in human blood and urine by using a direct injection nebulizer [239]. Lead was measured in the blood and blood plasma of smelter workers and the general population [240]. The measurement of trace elements in serum by ICP-MS has been compared to results from neutron activation analysis and proton-induced x-ray emission [241]. Semiquantitative analysis can also be used to obtain a rapid screening of samples [242]. 

Other Metal-Peptide and -Protein Interactions.—The determination of protein-bound trace elements in biological material by neutron activation analysis has been described Zn, Hg, Cu, and Se were accurately detected in human liver samples, provided that most of the element concerned was protein bound. An interaction of mercury with a protein or a protein-DNA complex has been invoked to explain the partitioning of the metal in euchromatin over heterochromatin (from mouse liver nuclei) by a 10 1 ratio. " Bovine retinas, isolated rod outer segments and emul-phogene extracts of rod outer segments have been shown to contain appreciable amounts of Zn ", Ca and the zinc levels being light sensitive. 

Kotz etal. (1972, Decomposition of biological materials for the determination of extremely low contents of trace elements in limited amounts with nitric acid under pressure in a Teflon tube) Hartstein et al. (1973, Novel wet-digestion procedure for trace-metal analysis of coal by atomic absorption) Jackson etal. (1978), Automated digestion and extraction apparatus for use in the determination of trace metals in foodstuffs) Campos etal. (1990, Combustion and volatilization of solid samples for direct atomic absorption spectrometry using silica or nickel tube furnace atomizers) Erber et al. (1994, The Wickbold combustion method for the determination of mercury under statistical aspects) and Woit-tiez and Sloof (1994, Sampling and sample preparation). 

Examples of applications of X-ray spectrometric analytical techniques to elemental determinations in a variety of materials are presented in Table 2.12. Some recent applications papers may be mentioned. Total reflection XRF has been applied by Xie et al. (1998) to the multielement analysis of Chinese tea (Camellia sinensis), and by Pet-tersson and Olsson (1998) to the trace element analysis of milligram amounts of plankton and periphyton. The review by Morita etal. (1998) on the determination of mercury species in environmental and biological samples includes XRF methods. Alvarez et al. (2000) determined heavy metals in rainwaters by APDC precipitation and energy dispersive X-ray fluorescence. Other papers report on the trace element content of colostrum milk in Brazil by XRF (da Costa etal. 2002) and on the micro-heterogeneity study of trace elements in uses, MPI-DING and NIST glass reference materials by means of synchrotron micro-XRF (Kempenaers etal. 2003). 

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