Paper chromatographic determination of trimethyloctadecyl quaternary ammonium chloride in dimethyldioctadecyl quaternary ammonium chloride

A quantitative paper chromatographic method was worked out for determining small amounts of trimethyloctadecyl quaternary ammonium chloride in dimethyldioctadecyl quaternary ammonium chloride. With a mixed solvent containing methanol, acetone, and water, the trimethyl‐type quaternary travels just behind the solvent front, whereas the dimethyl‐type quaternary and other components move very little. The trimethyl quaternary spot is developed with bromphenol blue and the resulting color is measured photometrically at 607 mμ. Standards are run on either side of the sample spot and are used for quantitative calibration. Accuracy and reproducibility of the method appears to be within 0.4% absolute.