Simultaneous Determination of Naphazoline Nitrate and Tetramethylthionine Base in Eye Drops by First-Derivative UV Spectrophotometry

A rapid first-derivative spectrophotometric method for the simultaneous determination of naphazoline nitrate and tetramethylthionine base in eye drops by using zero-crossing measurements is described. Solutions of this drug combination in water were analysed by measurement of the amplitudes at 257.2 and 247.5 nm, respectively. Good linearity, accuracy, precision and selectivity were found, and the method is proposed for routine quality control purposes.