Clinical determinations, trace elements

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

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. 

Caroli S, Forte G, Iamiceu AL, Galoppi B 1999) Determination of essential and potentially toxic trace elements in honey by inductively coupled plasma-based techniques. Talanta 50 327-336. Chiswell B, Johnson D (1994) Manganese. In Seiler HG, Sigel A, Sigel H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York. 

Adequate supplies of vitamins and trace elements are extremely critical in maintaining the health and development of humans. These nutrients occupy the attention of those concerned with the physical well being of a public made increasingly aware of the need for the quality and the quantity of their dietary intake. The general principle regarding assessment of nutritional status is to determine the extent to which the metabohc demand for nutrients has been or is currently being met by the supply. In clinical practice, this requires balancing supply and demand. 

In clinical analysis, flame AAS is very useful for serum analysis. Ca and Mg can be determined directly in serum samples after a 1 50 dilution, even with microaliquots of 20-50 pL [314]. In the case of Ca, La3+ or Sr2+ are added so as to avoid phosphate interferences. Na and K are usually determined in the flame emission mode, which can be realized with almost any flame AAS instrument. The burner head is often turned to shorten the optical path so as to avoid self-reversal. For the direct determination of Fe, Zn and Cu, flame AAS can also be used but with a lower sample dilution. Determination of trace elements such as Al, Cr, Co, Mo and V with flame AAS often requires a pre-concentration stage, but in serum and other body fluids as well as in various other biological matrices some of these elements can be determined directly with furnace AAS. This also applies to toxic elements such as Ni, Cd and Pb, which often must be determined when screening for work place exposure. When aiming towards the direct determination of the latter elements in blood, urine or serum, matrix modification has found wide acceptance in working practices that are now legally accepted for work place surveillance, etc. This applies e.g. for the determination of Pb in whole blood [315] as well as for the determination of Ni in urine (see e.g. Ref. [316]). 

The editors sincerely hope that this book will, with its introduction into the basic principles and limitations of the presently available trace analytical methodology and its detailed description of reliable procedures and quality control measures, serve as a valuable aid for all those who are involved in trace element analysis. It should be especially beneficial for analysts and researchers in clinical chemistry, toxicology, biochemical and environmental research first as a general overview and second to serve as a collection of elaborated methods for the reliable determination of the above-mentioned elements and some of their species in selected (human) biological specimens. 

In clinical practice, most trace element determinations are not done by neutron activation analysis but by other techniques, in the first place atomic absorption spectrometry -a technique having a good sensitivity for numerous elements and better suited for routine application. Nevertheless, neutron activation analysis played an important role as illustrated by the observation that somewhat more than 50% of the selected reference values advanced by Versieck in his 1985 CRC Critical Review were obtained by this technique. 

The rates and extents of trace element dependent metabolic reactions are controlled by the activities of the relevant element-containing species. Determinations of total trace element concentrations in a compartment are of limited value because these represent the sum of all species involved in storage and transport of the trace element in addition to the physiologically active species. It is necessary to identify and quantify all of these species in order to understand at the molecular level the roles of these elements in human metabolism. Areas of clinical chemistry which would benefit from such investigations are ... 

In the last decade, there has been a marked increase in the toxicological and clinical demand for trace element analysis which has been reviewed by a number of authors (Delves, 1987 Kruse-Jarres. 1987 Versieck and Cornells, 1989). This places big demands on the reliability of such analyses and highlights the importance of quality control in the determination of trace elements (Boyd. 1983 Brown. 1982 Inhat et al., 1986a,b Delves. 1987 Ihnat, 1988 McKenzie and Smythe, 1988 Versieck and Cornells, 1989 Brown, 1991). Early interlaboratory comparison studies revealed that there were serious difficulties in achieving precise and unbiased quantitative measurements of trace metals in biological materials. Moreover, reported normal concentrations of some trace metals varied by several orders of magnitude when results from so-called specialised laboratories were compared (Versieck, 1984 Ihnat, 1988 Versieck and Cornells, 1989). In the last... 

Schmidt. P.F. (1984). Localization of trace elements with the laser microprobe mass analyzer (LAMMA), Trace Elements in Medicine, 1,13-20 Sherwood. R.A., Rocks, B.F., and Riley, C. (1984). The use of flow-injection analysis (FIA) with atomic absorption detection for the determination of clinically relevant elements. Paper presented at 2nd BNAAS Symposium, Leeds, July 1984 Triebig, G., and Schaller, K.H. (1984). Copper, in Alessio, L, Berlin, A., Boni, M., Roi, R., Biological indicators for the assessment of human exposure to industrial chemicals, p. 57-62, EUR 8903 EN, Commission of the European Communities Van der Vyner, F.L, Verbreuken, A.H., Van Grieken, R.E., and DeBroe, M.E. (1985) Laser microprobe mass analysis A tool for evaluating histochemical staining of trace elements, Clin. Chem., 31. 351... 

All infants, on admission to the neonatal intensive care unit, were established on parenteral fluids within the first hour of day 1 at 80 ml/kg/day with a solution of electrolytes, dextrose 10%, amino acids (Vaminolact, Fresenius Kabi, Cheshire, UK) and a phosphate supplement (Addiphos, Fresenius Kabi, Cheshire, UK). Fluid intakes were thereafter managed on the basis of clinical requirements. On day 2 of life, and thereafter, the solution was further supplemented with water-soluble vitamins (Solvito N, Fresenius Kabi, Cheshire, UK) and trace elements (Peditrace, Fresenius Kabi, Cheshire, UK), to the levels recommended by the manufacmrer. In tandem, a fat emulsion solution (Intralipid 20%, Fresenius Kabi, Cheshire, UK) with added fat-soluble vitamins (Vitfipid, Fresenius Kabi, Cheshire, UK) was infused, initially at 8ml/kg/ day, increasing maximally to 18 ml/kg/day by posma-tal day 5. Enteral feeds were started, when the condition of the infant was stable, as hourly boluses of 0.5—1 ml/h. Thereafter enteral feed volumes were gradually increased as determined by the infants clinical condition, with reciprocal reductions in the volume of parenteral nutrition infused. No infant progressed beyond hourly bolus feeds for the duration of the study. 

Biochemistry, Clinical Chemistry, and Medicine Foods and beverages of many types have been analyzed by ICP-MS. Solid or semisolid samples are generally digested with mineral acid, as are some beverages. Peanut butter, commercial breakfast cereal, dried milk, fish and shellfish, wine, beer, and the like have been analyzed for trace elements such as Cu, Fe, Se, and Zn for nutritional purposes as well as for toxic metals like As and Pb. Al has been determined in many foods because dietary Al was being studied for a possible link to Alzheimer s disease. 

The determination of trace elements such as Pb, Cd, Zn, Cu, As, Se, and Hg in environmental or clinical samples is often required at sub p.p.m. levels, the extreme limits of sensitivity for conventional AAS. At these low concentrations these elements can be readily determined by graphite furnace AAS. However, GF-AAS is relatively expensive, time-consuming, and in some cases too sensitive (for example, Zn in serum) a method. Typically, the measurement takes 2 to 3 minutes by GF—AAS, while by FAAS it takes 10 seconds or less. 

Trace Elements in Clinical Chemistry Determined by Neutron Activation Analysis... 

In recent years life science researchers have become more earnest in their considerations that trace elements have important roles in physiology and pathology. So far, some of these experimenters have used activation analysis (1) to measure the elemental contents of biological tissues and fluids (2) to determine if a correlation exists between abnormal trace element concentration and certain types of diseases (3) as an investigational method for epidemiological functions (4) to measure metabolic functions (5) as a clinical and investigational method for toxicology (6) in total body in vivo studies (7) in in vivo studies with stable tracers and (8) in individual identifications for forensic requirements. 

Almost all trace elements of interest in clinical chemistry have been determined in body fluids and various tissue samples using ETA AS. A recent review article published by Delves and Shutder [22] or a textbook on AAS [23] may serve as a source of references for detailed information. In spite of the very large number of publications in this field an attempt was made to select a few representative examples. 

Dietary intakes of many essential trace elements are being determined by NAA, and results may serve as a basis for improved recommendations of safe and adequate daily average intakes of these elements. As a next step, possibly deficient or toxic intakes, the influence of the environment on dietary intake, correlations with tissue concentrations and clinical symptoms, and so forth may be investigated. A special example of such studies is the correlation of low dietary intakes of selenium with a particular syndrome known as Keshan disease in China. 

Direct determination of solids may be performed by, e.g.. X-ray fluorescence spectrometry, or by arc or spailr emission spectrometry in case of powders. For special applications many surface techniques are available such as proton-induced X-ray emission (PIXE) and laser microprobe emission spectrometry (LMA). In the case of determination of trace elements on clinical material, however, most of these direct methods have detection limits that are too high to be useful. Moreover, as some of these methods are cormected to an accelerator or electron microscope, usage is somewhat limited for routine determination. 

Samples such as hair, nails, blood, urine, and various tissues are analyzed by NAA for both essential and toxic trace elements (Bhandari et al. 1987, Lai et al. 1987). The analysis can be related to determine their effect on disease outcomes. These authors have reported that the diet and environment contribute largely towards the trace elements in the human body. It is has been demonstrated in other works that the selenium concentration in human nails is an accurate monitor of the dietary intake of selenium. As a consequence, the nail monitor has been extensively used to study the protective effect of dietary selenium against cancer and heart disease in numerous prospective case-control studies. In another study by Kanabrocki et al. (1979) on human thumbnails in USA, using thermal NAA technique, the average concentration of metals studied in clinically symptom-free adult female and male subjects were found to be zinc, 184 vs. 153 ppm chromium, 6.8 vs. 4.2 selenium, 0.9 vs. 0.6 gold, 2.6 vs. 0.4 mercury, 1.9 vs. 0.4 silver 0.7 vs. 0.3 cobalt, 0.07 vs. 0.04. In another study, the fluorine concentration in bone biopsy samples was... 

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