High frequency polarographic determination of p-toluenesulfonic acid: Study of the trace elements in food. IV

A high frequency polarographic method for the determination of p-toluenesulfonic acid was investigated by using a Yanagimoto PF-501 Polarograph. p-Toluenesulfonic acid gives a suitable wave for polarographic determination at a peak potential. -0.27 V (vs. Hg pool) in 1M ammonium sulfate-0.36N sulfuric acid and 1M magnesium sulfate-0.36N sulfuric acid solution (Fig. 1). The polarographic wave height obtained was proportional to the concentration of p-toluenesulfonic acid in the range 0.05 to 1 μmol/ml at 500 kHz-2.6 V with electrolytic cell and 0.01 to 0.2 μmol / ml at 250 kHz-2.0 V.The variation of values in a seriese of repeated experiments did not exceed 2%. The reducing wave appeared only when sulfate or phosphate is used as the supporting electrolyte and it was not observed in nitrate, perchrolate, halide or thiocyanate solutions. The peak potential was different when the acid added to the salt solution was different, that is, the potential shifted to the positive side by nitric, phosphoric and acetic acid but toward the negative side by sulfuric acid. The shift by the addition of sulfuric acid increased when the acid concentration enhanced, but it became stationary when the concentration reached 0.1N for ammonium sulfate and 0.3N for magnesium sulfate solution. Although the wave height was not influenced by an addition of sulfuric acid (Fig. 2), it was affected by the changes in the superimposed high frequency amplitude with electrolytic cell, as shown in Fig. 4. At each frequency, the wave height was linearly dependent on the amplitude, except when it is higher than 1.6 V at 250 kHz and 2.6 V at 500 kHz where the amplitude-wave height curve became a plateau. The concentration of supporting electrolyte had an effect on the peak height as shown in Fig. 5. When the concentration of sulfate was lower than 0.3M (250 kHz superimposed) or 0.7M (500 kHz), a linear relation was observed between the concentration and the height, but when it is higher than 0.8M (250 kHz) or 1M (500 kHz), no change in the wave height was observed even if the salt concentration was increased.