Simultaneous spectrophotometric determination of humic acid and iron in water

A simple and rapid method for the determination of humic acid and iron in solution is described. Two absorbance measurements are required, one on an untreated sample aliquot, and the other on an aliquot treated to enhance iron absorptivity. The method requires sample volumes of less than 15 ml and is sensitive enough for direct application to most natural waters. Limits of detection for each component vary with concentration of the other, but 0.01 mg 1^?1 for humic acid and 0.04 μM for iron can be achieved. For six natural waters, determinations based on independent calibration curves for each component gave results 6–40$ higher for iron, and 6–29% higher for humic acid, than results obtained by the proposed method. The interference of fulvic acid and the use of different humic acid standards are examined.