Bromocresol purple, a non-specific colour reagent for the determination of serum albumin.

The determination of serum albumin with the dye reagent bromocresol purple was investigated. We found that bromocresol purple is not a specific reagent for albumin, but that serum proteins in the alpha-, beta-, and gamma-globulin fractions also react with this dye. Similar results were obtained for bromocresol green. Furthermore there is a great difference in absorbance between human and bovine albumin solutions (having the same concentration) when using the bromocresol purple reagent. Most probably this is a result of the difference in interaction of the reagent with the substrate. Although the standard curves with the bromocresol purple method were more linear (especially at higher albumin concentrations) than those obtained with the bromocresol green method, we still prefer the bromocresol green technique to the bromocresol purple technique, because its results are more comparable with those of other methods. Moreover in quality control and calibration procedures, strong deviations from the recommended values are obtained when non-human sera are analyzed with the bromocresol purple method. For reasons of accuracy more specific methods are preferable.