Evaluation of methods for trace-element determination with emphasis on their usability in the clinical routine laboratory.

Commonly used techniques for trace-element analysis in human biological material are flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Elements that form volatile hydrides, first of all mercury, are analysed by hydride generation techniques. In the absorption techniques the samples are vaporized into free, neutral atoms and illuminated by a light source that emits the atomic spectrum of the element under analysis. The absorbance gives a quantitative measure of the concentration of the element. ICP-AES and ICP-MS are multi-element techniques. In ICP-AES the atoms of the sample are excited by, for example, argon plasma at very high temperatures. The emitted light is directed to a detector, and the optical signals are processed to values for the concentrations of the elements. In ICP-MS a mass spectrometer separates and detects ions produced by the ICP, according to their mass-to-charge ratio. Dilution of biological fluids is commonly needed to reduce the effect of the matrix. Digestion using acids and microwave energy in closed vessels at elevated pressure is often used. Matrix and spectral interferences may cause problems. Precautions should be taken against trace-element contamination during collection, storage and processing of samples. For clinical problems requiring the analysis of only one or a few elements, the use of FAAS may be sufficient, unless the higher sensitivity of GFAAS is required. For screening of multiple elements, however, the ICP techniques are preferable.

Trace element reference values in serum determined by inductively coupled plasma atomic emission spectrometry.

Serum reference values for Ba, B, Cd, Cu, Fe, Mn, Li, Se, Sr, and Zn in 141 healthy Norwegians were determined. The trace element concentrations were determined by the inductively coupled plasma atomic emission spectrometry technique that we have recently validated. The reference intervals were established according to the recommendations of the International Federation of Clinical Chemistry and Laboratory Medicine. Also coverage intervals with coverage uncertainties were calculated according to the International Union of Pure and Applied Chemistry. The population studied consisted of 69 men and 72 women of the ages 21-87 years. The effects of gender, age, smoking, and oral contraceptives on serum levels of trace elements were investigated. Median concentrations of the different trace elements in (micromol/l) were as follows: Ba (0.44), B (1.50), Cd (0.004), Cu (17.1), Fe (21.4), Li (0.06), Mn (0.003), Se (1.26), Sr (0.17), and Zn (13.3). An increase in serum Ba and Sr was detected with age. These metals and Se were also significantly higher in women over 50 years of age in comparison to younger women. Women had higher serum Cu than men and those on oral contraceptives had higher serum Cu and Fe. Serum B tended to increase with age, while it was significantly reduced with smoking.

Validation of inductively coupled plasma atomic emission spectrometry technique (ICP-AES) for multi-element analysis of trace elements in human serum.

The use of inductively coupled plasma atomic emission spectrometry (ICP-AES) for the simultaneous determination of Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Se, Sr and Zn in human serum in a clinical laboratory was validated. Samples were digested and then analysed using yttrium as an internal standard and a serum-matched calibration standard. The criteria used to assess the analytical performance of the ICP-AES were detection and quantification limits, linearity, sensitivity, recovery, interference from alkali and acid, trueness and precision. Detection limits were 0.002-0.003 micromol/L for Mn, Sr, Ba, and Cd; 0.014-0.07 micromol/L for Co, Zn, Fe, Be, Li, Pb, Cu, Ni, and Cr; and 0.2-0.9 micromol/L for B, Se, and Al. Trueness, as controlled by analysis of bovine serum certified reference material, was acceptable for Co, Cu, Se and Zn, while Fe was 5.1% and Mn 6.2% below the lowest limit of the certified material interval. We conclude that ICP-AES can be used for multi-element analysis of B, Ba, Cu, Fe, Li, Se, Sr and Zn in serum. Serum levels of Al, Be and Co were below the detection limits while serum levels of Cd, Cr, Ni and Pb were below the quantification limits of the ICP-AES. These trace metals cannot be analysed as routine by the ICP-AES. However, in cases of intoxication with elevated serum concentrations mean recovery of 100+/-10% was obtained at an addition of 2.22 micromol/L for Al, 0.11 micromol/L for Be, 0.03 micromol/L for Co, 0.39 micromol/L for Cr, 0.14 micromol/L for Ni, and 0.12 micromol/L for Pb.