QUANTITATIVE DESORPTION OF HUMIC SUBSTANCES FROM AMBERLITE XAD RESINS WITH AN ALKALINE-SOLUTION OF SODIUM DODECYL-SULFATE

Microgram quantities of humic or fulvic acid are quantitatively adsorbed on a small amount (ca. 1 ml) of pulverized Amberlite XAD-2 and XAD-8 resins. A sodium hydroxide solution, aqueous ammonia, or a mixture of methanol and aqueous ammonia leads to very low desorption recoveries of the humic substance, however. Pre-saturation of strong adsorption sites of the resin with some surfactants increases the desorption recovery, but it is not quantitative. The desorption efficiency is tremendously improved with the aid of an anionic surfactant. Humic and fulvic acids retained on the XAD resins are completely desorbed with 200 mg of sodium dodecyl sulfate in 10 ml of 0.1 M sodium hydroxide solution. The surfactant does not interfere with the spectrophotometric determination of humic substances. Further, it can be removed from the solution as a precipitate by increasing the alkalinity to 0.25 M.