1979 Volume 28 Issue 6 Pages 341-346
A fluorometric method was described for the simultaneous determination of lignine sulfonate and humic acid. The fluorescence peaks of lignine sulfonate and humic acid due to excitation at 320 nm have intensity maxima at different wavelengths (near 400 nm, 500 nm, respectively). The concentration of lignine sulfonate and humic acid were determined by a dual wavelength procedure from the emission at 400 nm and 500 nm. Fulvic acid in the extracted solution from sediments was also determined by the dual wavelength procedure, using as the reference a standard solution of lignine sulfonate which gave the similar emission peak as fulvic acid. A typical procedure was as follows. Free humic acid and free fulvic acid in sediment {(0.10.5) g} were extracted with 10 ml of a 0.1 N sodium hydroxide solution, and the combined humic acid and combined fulvic acid in the residual material were also extracted with 10 ml of a 0.1 M sodium pyrophosphate solution. Four milliliters of a 0.1 M EDTA solution and 2 ml of 1 M sodium acetate buffer solution were added to the extracted solution, and pH of the solution was adjusted to 9.0 with sodium hydroxide solution. The fluorescence intensity of the solution was measured at 400 nm and 500 nm depending on excitation 320 nm, and calculated by following equation.
CNaLS = IF400k2' - IF500k2/k1k2' - k2k1', CHA = IF500k1 - IF400k1'/ k1k2' - k2k1'
where IF400 and IF500 are the relative fluorescence intensitites at the two wavelengths; CNaLS and CHA are concentrations of lignine sulfonate and humic acid; k1 and k1' are the lignine sulfonate constants at 400 nm and 500 nm, and k2 and k2' are the constants for the humic acid at the two wavelengths. This method was applied to sediment samples containing less than 10 ppm of two humic conponents. Precision of the method was studied using a mixed standard solution of lignine sulfonate (5.0 ppm) and humic acid (1.0 ppm), and the recovery was 98% (c.v. 0.6%) and 97% (c.v. 2%), respectively.
