Simultaneous Determination of Barbiturates and Salicylates by Ultraviolet Spectrophotometry.

A rapid method based on UV spectrophotometry is described for simultaneous determination of salicylates and barbiturates in serum. While barbiturates have no absorbance above 280 m and extracted normal serum has insignificant absorbance, salicylate has a maximal absorbance peak at 296 mjh, which is proportional to concentration. The barbiturate concentration can be calculated from absorbance differences between pH 10 and pH 2, pH 13 and pH 2, or pH 13 and pH 10, at wave lengths 239 rn/h, 253 m , and 259 rn/h respectively. These absorbance differences can be shown to relate linearly with concentration. The error involved in barbiturate determinations performed when salicylate is present is discussed, and a compensation for the presence of salicylate is derived from absorbance measurements at 296 m/h. The extraction and the various factors involved (e.g., pH, and presence of Na2SO4) in obtaining quantitative recovery of both barbiturates and salicylates are described. As the UV absorption spectra of some barbiturates but not of salicylates are changed during alkaline treatment, a partial differentiation of barbiturates based on the rate of alkaline hydrolysis is made possible. Criteria for the presence of salicylates and barbiturates and the detection of interference from other drugs such as bemegride, glutethimide, and sulfonamides are discussed.