Spectrophotometric Determination of Sodium Alginate by Decoloration of Some Basic Dyes

In a BR-buffer of pH 3.0,association compounds were formed between large anion of sodium alginate(NaAGN) and cation R+ of some basic dyes,e.g.victoria blue 4R(VB4R),victoria blue B(VBB) and night blue(NB),leading to color-fading of the dye reagents.Linear relationships between the magnitude of color-fading intensity(ΔA) and concentration of NaAGN were obtained in the ranges within 5.0 mg·L-1(for VB4R system) and 3.0 mg·L-1(for either VBB or NB system).Absorbance were measured at the absorption maxima 612 nm,616 nm and 614 nm for VB4R,VBB and NB respectively.Values of molar absorptivity for the 3 dyes were found in the range 4.8×106-9.5×106L·mol-1·cm-1,among which the value of VB4R was the highest.Detection limit of this method with VB4R as reactant was 21 μg·L-1.Selectivity was tested giving satisfactory results for determination of NaAGN.In applying the method to analysis of noodle sample,average values of RSD (n=7) and recovery obtained were 2% and 105% respectively.