Atomic Spectrometry in Clinical Chemistry

Abstract

Atomic absorption spectrometry (AAS) and optical emission spectrometry (OES) are two closely related instrumental techniques that have many applications in many different fields. In clinical chemistry, these techniques are well established for the quantitative measurement of essential and nonessential elements found in body tissues and fluids. For most practical purposes, the elements that are routinely measured with modern commercial instrumentation include almost all of the metallic elements of the s, d, and p blocks of the periodic table. The exceptions in the p block include the halogens, the noble gases, and the elements C, H, N, O, and S. Above atomic number 83 (Bi), only U is measured in absorption. Over the last two decades, the increasing use of inorganic mass spectrometry in clinical laboratories has opened up new possibilities and commercial instrumentation based on inductively coupled plasma mass spectrometry (ICPMS) is now the dominant technique. Clinical chemists are now able to measure the multielement composition of biological specimens at ultra‐trace concentrations, i.e. <10 μg L −1 . With ICPMS, the halogens become detectable, along with B, C, N, and Th. The coupling of ICPMS with separation technologies has opened up new possibilities in clinical laboratory medicine in the field of chemical speciation analysis. In some areas of clinical chemistry, older atomic spectrometric techniques may still be considered the reference method for selected clinical applications, e.g. the determination of serum K and serum Na by flame atomic emission spectrometry ( FAES ). In other areas, flame atomic absorption spectrometry (FAAS) remains feasible for serum Mg and serum Cu because of its sensitivity, rapid throughput, and the relatively low cost of instrumentation. Graphite furnace atomic absorption spectrometry (GFAAS), also known as electrothermal atomic absorption spectrometry ( ETAAS ), while more complex than flame atomization methods, is still fit for purpose for routine applications such as blood Pb and serum Al, where physiological concentrations are too low to be measured in the flame without laborious preconcentration efforts. Robust procedures for quality assurance (QA) and quality control (QC) are now well established within the clinical laboratory and cover the entire spectrum of clinical laboratory activities. These include preanalytical issues, personnel training, and education, and also the appropriate use of certified reference materials (CRMs) for method validation purposes. Participation in proficiency testing (PT) programs and external quality assessment schemes (EQAS) for trace elements in biological fluids have also contributed to improved clinical laboratory performance. Despite the advent of ever more sensitive techniques and robust procedures, the quality of results is still only as good as the specimen collected. Contamination can occur at the preanalytical stage of the analysis and also during the analysis. Selection of the appropriate specimen is critical to obtaining meaningful clinical information about nutritional trace element status or exposure to toxic elements.