Determination of tannins in tannery wastewaters by flow injection—Folin-Denis
WEI Liang, DAI Yi-chun, ZHANG Xin-shen,et al
1. School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China;
2. Institute of Mechanical Manufacturing Technology, China Academy of Engineering Physics, Mianyang 621900, China;
3. College of Light Industry & Textile & Food Engineering, Sichuan University, Chengdu 610065, China;
4. Sichuan Fushun Agricultural Bureau, Fushun 643200, China
Abstract：In sodium tetraborate-sodium hydroxide buffer solution at pH 12.4, tannins could reduce Folin-Denis reagent to form blue compound with the maximum absorption wavelength at 760 nm. Based on this, a rapid flow injection spectrophotometric method was proposed for determination of tannins in tannery wastewaters. A discussion was conducted on the impact of reagent flow rate, injection volume, amounts of Folin-Denis reagent, pH of the solution, dosage of buffer solution and the length of reaction coil on the determination and the optimal experimental conditions had been obtained. The results showed that Beers' law was obeyed in the concentration range of 0.2-10 mg/L and 10-50 mg/L for tannins respectively, and the detection limit of the proposed method from three times of baseline noise was 16.84 μg/L. The relative standard deviation was 3.2% and 2.1% for fourteen parallel determinations of 500 μg/L and 20 mg/L tannins standard solution, respectively. Commonly co-existing ions except SO32- (which could eliminated by heating pretreatment) in tannery wastewaters had no interference with determination of tannins, so it could be applied for the on-site online analysis. The proposed method had been applied to the determination of tannins in tannery wastewaters. The results were consistent with those obtained by standard method GB/T 15686-2008 and the relative standard deviations（RSDs，n=8）were less than 4%.
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