Metal requirements, biological

The study of metals in biological systems requires techniques, some of them highly specific, some limited to certain aspects of the metal ion in question, some of more general applicability. Thus, Mossbauer spectroscopy in biological systems is restricted to iron-containing systems because the only element available with a Mossbauer nucleus is 57Fe. The EPR spectroscopic techniques will be of application only if the metal centre has an unpaired electron. In contrast, provided that crystals can be obtained, X-ray diffraction allows the determination of the 3-D structure of metalloproteins and their metal centres. 

It is of course important to realize that the technique of matrix isolation also has its limits, or that certain conditions must be fulfilled so that it can be applied. The first and most important one is that the precursor of the reactive intermediate to be studied must be an isolable substance and volatilizable without decomposition, which sets limits on the size of species that can be studied and/or on their thermal lability. Thus many interesting compounds (e.g. of biological relevance) are excluded, at least in their native forms. Also very nonvolatile substrates, such as metals, require special techniques such as Knudsen cells for controlled evaporation. 

In this chapter it is hoped to review in general terms the major subject of metals in biology, and to draw attention to appropriate further reading for the expansion of particular topics. The essential role of metal ions in a wide range of biological processes is now well known and hardly requires elaboration It should be noted that important advances have been made in the last two decades, and current studies are serving to demonstrate the breadth of the subject and the exciting prospect that lies ahead. 

Me tals and metallic compounds are among the toxic substances most often found in workplace environments (1,2), Industrial hygienists and hygiene chemists must accurately determine the presence and amount of toxic metals and their compounds in the industrial environment. Accurate methods for the quantification of metals in biological and atmospheric samples are required for the industrial hygienist to properly evaluate the environment. Atomic absorption spectroscopy (AAS) has been the primary method of analysis for toxic metals because AAS is sensitive, specific, and rapid especially compared to colorimetric analysis. 

The alkali- and alkaline-earth metals are widespread on earth (four of the eight most common elements in the earth s crust are 5-block elements) and their compounds are ubiquitous in daily life. Considering that an estimated one-third of all proteins require a metal ion for their structure or function," and that the most common metals in biological systems are from these two families... 

Atomic absorption spectrometry with flame (AA-F) or electrothermal atomization furnace (AA-ETA), inductively coupled plasma-emission spectroscopy (ICP-ES), inductively coupled plasma-mass spectrometry (ICP-MS), and high-performance liquid chromatography-mass spectrometry (LC-MS) are state-of-the-art analytical techniques used to measure metals in biological fluids. They are specific and sensitive and provide the cfinical laboratory with the capability to measure a broad array of metals at clinically significant concentrations. For example, ICP-MS is used to measure several metals simultaneously. Photometric assays are also available but require large volumes of sample and have limited analytical performance. Spot tests are also... 

This chapter presents the results of studies carried out for the determination of Pb, Cd, Hg and As using GC-MS. Since GC-MS requires a volatile form of the metal, suitable chelating agents were identified, prepared, and examined for the cross-over (memory) effect. Also the validation of isotope dilution GC-MS for the determination of these toxic metals in biological samples was carried out using suitable NIST certified reference materials. 

One of the main requirements of using GC-MS for the determination of metals is the preparation of a suitable metal chelate, which should have adequate thermal stability and should also be volatile. Further, the metal chelate should not introduce any memory effect or carry-over effect when injecting sequential samples of different isotopic compositions. We have been able to identify suitable metal chelates for the toxic metals Pb, Hg, Cd and As. Another requirement for the determination of toxic metals in biological samples is the development of a suitable digestion procedure, without introducing any contaminants from the reagents employed. 

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