Effects of temperature variation on the zero, second and fourth derivative ultraviolet absorption spectra of benzenoid drugs

The effect of temperature in the range 0–40 °C on the absorbance at three wavelengths of maximum absorption and two wavelengths of minimum absorption in the zero-order ultraviolet absorption spectra and on the second- and fourth-derivative amplitudes of eight benzenoid drugs, displaying fine vibrational structure in the region 250–270 nm, was studied. All of the drugs show a linear increase in absorbance at the λmin. between the bands of the fine structure with an increase in temperature, with temperature coefficients ranging from +0.06 to +0.325% per degree. A concomitant linear reduction occurs in the second- and fourth-derivative amplitudes with temperature coefficients in the range from –0.60 to –1.12% and –0.7 to –1.2%, respectively. The implications of these high temperature coefficients on the accuracy and precision of derivative spectrophotometric assay procedures for benzenoid drugs are discussed.