Research On Rapid Quantitive Determination Of Tannins In Tannery Wastewater

Tannins, also named Plant polyphenols, are complex mixture and widely used in various fields. The complexities cause difficulties on research of tannins, and also bring about the diversity of tannin-determination. Quantitive gross determination of tannins has more extensive significance in practice. Different results to samples would be got from diverse reaction mechanisms or test methods. It is very important to select appropriate method from various methods considering about the accuracy and the properties of samples. Considering on the characteristics of tannery wastewater and the practical application demands of prompt tannins analysis, two methods of rapid quantitive determination of tannins, combining flow injection analysis, were established and studied, based on redox reaction and complex reaction, respectively. A flow injection spectrophotometry method based on redox reaction for determining tannins was developed. The procedure was based on the reduction of Fe³⁺ to Fe²⁺ in acid by tannins, and then the complex Fe²⁺-1,10-phenanthroline was formed.The maximum absorbance of the complex was 510nm. A linear calibration curve was obtained at the concentration range of 0.10⁵.00mg/L, and the R2 was 0.9991. The relative standard deviation was 0.492%. The detection limit was 0.05mg/L. The test results agreed well with the currently used industry standard method for the determination of tannins in tannery wastewater.Another flow injection spectrophotometry method based on complex reaction for determining tannins was also developed. The procedure was based on the complexation of VO²⁺ with tannins in acid. The absorbance of the complex was 585nm. A linear calibration curve was obtained at the concentration range of 1.00⁷0.00mg/L, and the R2 was 0.9982. The relative standard deviation was 0.725%. The detection limit was 0.31mg/L. Accurate test results of vegetable-tanning wastewater and tea drinkings were proved. The test results of comprehensive tannery wastewater were obviously influenced by interference.The first method was better at anti-jamming capability and could be used to determination of both vegetable-tanning wastewater and comprehensive tannery wastewater, while the second method could only be used to determination of vegetable-tanning wastewater. The reagents of the former method would be easily got and stored. The latter method owned a wider range of concentration, a simpler flow-path and a higher analytical frequency. Proper choice of analytical methods should be made in practice.