Determination of molybdenum in biological materials

Abstract

-The accurate determination of molybdenum in biological materials is of considerable importance because of the essential role played by this element in human metabolism. However, data on the Mo content in biological samples and especially in clinical materials are often contradictory due to the inadequate sensitivity and reliability of the instrumental techniques used and to insufficient control of contamination during the analytical procedure. Despite recent developments in Mo determination by electrothermal atomic absorption and plasma atomic emission spectrometry, measurements in human blood and serum remain beyond the scope of most hospital laboratories involved in the usual routine testing. Further development of atomic spectrometric methods or a wider availability of neutron activation analysis may provide more data which is required for a better understanding of the nutritional role of Mo and its metabolism in humans. Advantages and limitations of the analytical techniques used for the determination of Mo in biological materials are critically discussed with particular attention given to clinical samples. The most common sources of analytical error are discussed and methods for their reduction are given. BIOCHEMICAL A N D CLINICAL BACKGROUNDAs early as 1953 (ref. 1) molybdenum was recognized to be an essential trace element for many species including man. It is a component of many enzymes responsible for the initial stages of nitrogen, carbon and sulfur metabolism of plants, animals and man and participates in a large number of enzymatic reactions (ref. 2,3).There is an absolute dependence by plants on Mo as it plays a vital role in the earth nitrogen cycle where it is involved both in nitrate reduction and nitrogen fixation.Although molybdenum is essential for animals it shows evidence of toxicity at high levels. General symptoms of excess doses of Mo for ruminants are: retarded growth, decreased milk and meat production, osteoporosis, severe gastroenteritis and coma (ref. Molybdenum intoxication depends on its speciation and is also influenced by the uptake of other elements such as S"' , W"', Cu, Pb and Zn.In humans, a deficiency of Mo in the diet may lead to some healths deffects. Diets with a low Mo content (20 pg/kg) adversely effect growth and may lead to neurogical disorders and even early death (ref. 6). Molybdenum also seems to play a positive role in the prevention of tooth decay (ref. 7). On the other hand, excess doses of Mo can be detrimental, persons having a diet rich in Mo being susceptible to gout, uricemia and xanthinuria and often suffer from an inflammation of extremities due to excess uric acid deposition (ref. 8,9).The practice of supplementing human diets with trace elements has stimulated studies of Mo as an essential nutrient. Several studies using diets providing between 1 and 14 pg of Mo per kg body weight per day report that an optimal diet should provide about 2 pg Mo per kg body weight per day (ref. 7). This result is comparable with a daily intake of 128 pg Mo prop...

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