Determination Of Permanganate Index In Water Based On Spectrophotometry And Electrochemical Method

Permanganate index is one of the main pollution indexes of surface water in China,which comprehensively reflects the pollution degree of oxygen consumption organic matter in water body.Although the national standard method(GB 11892-89,Determination of Permanganate Index of Water Quality)is a mature and reliable method for the determination of permanganate index,it has the disadvantages of long time-consuming,tedious operation and unsuitable for determination of large quantities of water samples.Therefore,it is of great significance to explore the determination method of permanganate index which is fast and easy to operate and suitable for mass sample analysis.This paper investigated the reaction kinetics of the main factors affecting the determination of the permanganate index in the national standard method(GB 11892-89).Based on the kinetics data,two new methods are explored and studied to determine permanganate index,which are the sealed digestion spectrophotometric method,and the method based on photoelectrocatalysis of TiO2-Au nanocomposite particle modified electrode.The contents and results are summarized as follows:(1)The reaction kinetics of main influencing factors for the determination of permanganate index in the national standard method(acidity)were investigated by continuous circulating flow device,including heating time,(1+3)H2SO4 addition and heating temperature.The results show that when other conditions remains constant,with the heating time prolonging,KMnO4 oxidizing organic matter is gradually consumed,the longer heating time is,the more KMnO4 consumed,the measured permanganate index will be larger,conversely,the measured value will be smaller.The addition of(1+3)H2SO4 has little effect on the digestion reaction,but the addition is too small,which will reduce the oxidation capacity of KMnO4 and lead to the slow digestion rate,and the measured value will be low at a fixed time.The water bath temperature has great influence on the digestion reaction.With the increase of the water bath temperature,the digestion rate is accelerated.Therefore,the determination of permanganate index should be strictly in accordance with the requirements of the national standard method,so as to achieve the same digestion efficiency.(2)A sealed digestion spectrophotometric method was developed for the determination of permanganate index.Based on the maximum absorbance of the remaining KMnO4 after digestion in the 526 nm wave length,the relationship between the absorption of the remaining KMnO4 and the permanganate index of water samples was established.The optimized analysis conditions are as follows:adding water sample 20 mL,(1+3)H2SO4 solution 1.00 mL,0.01 mol/L KMnO4 solution 2.00 mL,the sealed digestion time is 22 min,and removal MnO2 by filtering.The detection limit is 0.1 mg/L,the quantitative limit is 0.4 mg/L,upper limit of detection is 5.0 mg/L,and the method has good linearity(R2>0.990).The recovery rate of the actual water sample is 91.0-117.2%,and it has high sensitivity and good precision.This method has been successfully applied to the determination of permanganate index in actual water samples.Compared with standard method,this method is efficient,fast,and can be used to analyze a large number of water samples,and the method will not be affected when the Cl-content is less than 900 mg/L.(3)A method for determination of permanganate index based on photoelectrocatalysis of TiO2-Au nanocomposite particle modified electrode was developed.Compared with pure TiO2 nanoparticle modified electrode,TiO2-Au nanocomposite particles modified electrode has better photocatalytic oxidation performance.For the P25 Ti02 used in this experiment,the optimized Au nanoparticle load is TiO2 and Au mole ratio of 250:1;the optimum analysis conditions are:the application voltage 1200 mV,the solution pH in the 5-9 range,the electrolyte solution of 0.15 mol/L Na2SO4.Based on the current produced by photocatalytic oxidation of TiO2-Au nanoparticles with organic compounds,the relationship between net photo oxidation current and permanganate index was established.The detection limit is 1.3 mg/L,the quantitative limit is 4.1 mg/L,upper limit of detection is 40 mg/L,and the method is linear(R2 ?0.990).The method is simple,rapid and environmentally friendly.It can be used as a pre-judgement for determination of permanganate index.