Title: Chromium Analysis
Key words: sodium heparin, spectrophotometer, matrix modification, contamination, chromium status, chromium body pool
Date: July 2000
Category: 14. Measurement
Author: Dr van Rhijn
Fasted samples (1012 hours) of urine (second morning sample) and blood (in sodium heparin), with the latter centrifuged & aliquoted, should be stored (lyophilised) at 20oC in sealed plastic bags containing ice to maintain humidity, if analysis is delayed.
Reputable laboratories1 ensure stringent sample preparation (non-powdered gloves), using Cr free containers (plastic cannula or siliconised needles) to prevent contamination2, ultra-pure reagents, acid-washed pipettes and sample cups, in a class-100 laminar flow hood high humidity atmosphere to reduce the build-up of static.
Cr analysis is best performed using a sensitive and specific Zeeman graphite furnace electrothermal atomic absorption spectrophotometer (GFAAS)3, measuring one item at a time by sample heating and vaporising. The results can then be compared with an external quality control reference standard4. Initial GFAAS5 systems, which measured background absorption from the sample matrix proved inaccurate. The improved analysis with Tungsten-halogen correctors has also now been superceded by Zeeman-effect background correction. Matrix modification, using Mg(NO3)2 & Pd(NO3)2 solutions, for the analysis of the microwave-assisted wet acid digested procedure improved measurement accuracy6.
Neutron activation analysis (enrichment by co-precipitation with metal carriers after irradiation) is also used7. Interpretation remains difficult due to low Cr levels in biological tissues8 which do not reflect chromium status or metabolically active chromium body pools9.
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