Modification of the serum bromide assay for the measurement of extracellular fluid volume in small subjects.

Serum bromide has been used in the past to measure extracellular fluid volume in infants. In this report, a modification and refinement of a previously described spectrophotometric assay suitable for determining bromide levels in blood is presented. The assay involves sample deproteinization with perchloric acid followed by spectrophotometric analysis of the complexes formed by the reaction between sodium bromide and gold chloride. Linear standard curves were obtained by diluting 1:2 with pooled serum at the following bromide concentrations: 10, 20, 30 and 40 mg%. Intra- and interassay variation using this technique was extremely small (n = 6, correlation coefficient, 0.995, and n = 5, correlation coefficient, 0.988, respectively). For toxicological analysis, a linear standard curve was derived from sodium bromide standards at the following concentrations: 40, 60, 80, and 100 mg%. The reproducibility and reliability of this assay have been excellent and the correlation with neutron activation analysis was excellent. The assay is easily adapted for the analysis of large numbers of samples, is easy to perform, and requires only small sample volumes.