Spectrophotometric study of the determination of boron by the carminic acid method

Abstract

Carminic acid has been investigated critically as a reagent for the spectrophotometric determination of boron. A new ultraviolet spectrophotometric method and two improved visible spectrophotometric methods have been developed. The composition of the complex and the effect of experimental variables have been evaluated. In 95% sulfuric acid medium the boron:carminic acid ratio was 1∶1 and in a sulfuric acid-acetic acid medium this ratio was 1∶2. The sensitivities for methods employing the 95% sulfuric acid medium are 1.5×10−3 and 7.0×10−4 μg of boron/cm2 when absorbance measurements are made at 615 nm and 300 nm, respectively. A sensitivity of 3.8×10−4 μg of boron/cm2 is obtained using a sulfuric acid-acetic acid solution and measuring the absorbance at 548 nm.