QUANTITATIVE-ANALYSIS OF TOTAL RESIN ACIDS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OF THEIR COUMARIN ESTER DERIVATIVES

A method for the quantitative analysis of resin acids in effluent and water samples using high-performance liquid chromatography is described. Resin acids in aqueous samples are extracted by passage through C-18 solid-phase cartridges at pH 9. The (7-methoxycoumarin-4-yl) methyl (MMC) and (7-acetoxycoumarin-4-yl) methyl (MAC) esters are quantitatively formed at room temperature by the reaction of resin acids with 4-bromomethyl-7-methoxycoumarin and 4-bromomethyl-7-acetoxycoumarin respectively, in the presence of potassium carbonate. The effect of potassium carbonate particle size, exposure to light, presence of residual water, and derivatisation reagent: resin acid ratio on their formation are described. The MMC esters of resin acids may be detected by UV absorption at 318 nm al concentrations > 20-mu-g l-1, while the (7-hydroxycoumarin-4-yl) methyl esters, obtained by post-column alkaline hydrolysis of the resin acid MAC (RAMAC) esters, enable the detection of resin acids by fluorescence spectrophotometry to levels below 1-mu-g l-1. The method has been compared to gas chromatographic analysis of the carboxylic acid methyl esters and shows no evidence of any interferences by other carboxylic acids. The method is routinely used by two newsprint mills for environmental monitoring of resin acids in effluent.