Difference spectrophotometric assay of benzaldehyde in benzyl alcohol

A simple and rapid procedure is described for the selective determination of benzaldehyde in benzyl alcohol intended for use in the manufacture of parenteral dosage form. The assay is based upon the measurement of the difference absorbance between two equimolar solutions of benzaldehyde in buffer solution pH 5.75, one of which also contains sodium bisulphite. The difference absorbance which has a maximum at 248 nm is due to the different spectral characteristics of benzaldehyde and its adduct form with sodium bisulphite is proportional to concentration of benzaldehyde. The accuracy, precision, sensitivity and specificity of the procedure are discussed. Application of the assay is described for different batches of benzyl alcohol. The results are compared with the official (BP) GLC method.