Fading Spectrophotometric Methed for the Determination of Sodium Alginiate with Some Basic Triphenylmethane Dyes

The reaction conditions,the spectrophotometric characteristics,and the analytical properties of the ion association complex of sodium alginiate with the basic triphenylmethane dye such as ethyl violet(EV),crystal violet(CV),methyl violet(MV),malachite green(MG),methyl green(MeG) and brilliant green(BG) were studied.The method was based on the discoloration reaction between sodium alginiate and triphenylmethane dyes in the pH 4.0 HAc-NaAc medium.The reduction in absorbance is directly proportional to the concentration of sodium alginiate and Beer's law is obeyed in the range of 0～5.0 mg/ L sodium alginiate for EV and MV systems,0～3.0 mg/ L for CV system,and 0～2.0 mg/ L for MG system,respectively.The molar absorptivities(e) for different systems are between 3.6 ×10~5 and 4.8×10~6 L·mol~(-1)·cm~(-1),and the EV system's is the highest.Taking EV system for an example,the effect of coexisting substance was investigated and the result showed that the method has good selectivity.The method has been used to determine the sodium alginiate with satisfactory result.