The determination of chromium in human serum and urine.

A critical evaluation of the published data for chromium levels in serum and urine shows major discrepancies, indicating that further work to establish normal values for these parameters is necessary. Methods have been developed for the determination of total protein-bound, and alpha-2-globulin-bound, chromium in serum, and chromium in urine. The sample pretreatment for serum is based on concurrent protein precipitation and dehydration using propan-2-ol for the total protein-bound chromium, and 0.5M hydrochloric acid in propan-2-ol for the alpha-2-globulin-bound metal. The precipitates are washed in propan-2-ol, then in toluene. Urine aliquots equivalent to 20 umol creatinine are dried at 75° C. Acetic acid (plus 7.5% v.v. sulphuric acid) and 1,1,1,5,5,5-hexafluoropenta-2,4-dione are added to the serum precipitates and urine residues. The chromium in the specimens is converted to the beta-diketonate at 75° C, and the complex extracted with petroleum spirit. The excess diketone is removed by washing with phosphate buffer. The chromium is back-extracted with ammonia in EDTA solution and, after an evaporation step, dissolved in ammonium acetate solution. Atomic absorption spectrometry with electrothermal atomisation is used to measure the chromium, and because of the matrix simplification achieved, background correction is not necessary. The mean results on serum from normal subjects were 0.11 ug/L for total protein-bound chromium, and 0.07 ug/L for alpha-2-globulin-bound chromium. The detection limit was 0.03 ug Cr/L for both serum parameters. The mean normal value for urinary chromium was 0.44 ug/ 10 mmol creatinine, with a detection limit of 0.05 ug Cr/10 mmol creatinine. The analytical relative standard deviations for the three parameters at the above levels were: 7%, 9% and 13%respectively. The serum chromium parameters did not show a significant response to a glucose challenge. Precautions against sample contamination were taken, and techniques for reagent purification, and equipment cleaning to a high standard were developed.