Polarographic determination of benzaldehyde in benzyl alcohol and sodium diclofenac injection formulations.

A rapid and sensitive polarographic method was developed for qualitative as well as quantitative analysis of the neurotoxic contaminant benzaldehyde in Na-diclofenac injections and in benzyl alcohol used for parental formulations. A well-defined differential pulse (DP) polarographic peak or a sampled direct current (SDC) wave was obtained at -1.39 V (vs. silver-silver chloride reference electrode) in Britton-Robinson buffer (pH 9.15) and at -1.41 V in 0.1 M LiCl solution. The reduction step involves a two-electron process, corresponding to the formation of benzyl alcohol. No peaks were observed in the anodic branch of the cyclic voltammogram, emphasizing the occurrence of an irreversible process. The peak current versus concentration relationship was found to be linear up to 50 microg/ml with the detection limit of 10 ng/ml and quantitation limit of 30 ng/ml. The relative standard deviations (S.D.) obtained for concentration levels of benzaldehyde as low as 25 microg/ml with the SDC and DP methods were 1.5 and 0.78% (n=10), respectively. Benzyl alcohol and Na-diclofenac are not electrochemically active, and metabisulfite reductions at -0.664 and -1.240 V do not interfere with the benzaldehyde reduction peak. The proposed methods (DP and SDC polarography) have been applied satisfactorily to the determination of benzaldehyde traces in benzyl alcohol and in different pharmaceutical products such as Na-diclofenac injectable formulations.