Study On FI Fast Determination Of Chemical Oxygen Demand

Flow Injection Analysis (FIA), put forward by Ruzika and Hansen in 1975, has developed rapidly in a short time after its appearce. It made the traditional operation could be completed on-line, quickly, sealed, and automated, especially in the field of flow injection analysis combined with atomic absorption spectrometry and spectrophotometry. In this thesis two methods of indirectly determined chemical oxygen demand (COD) by flame atomic absorption spectrometry (FAAS) with flow injection on-line preconcentration and separation have been established respectively with the traditional heating digestion and the ultrasonic digestion. Another method is directly determined COD by spectrophotometry (SP) with FIA, on the basis of merging zones technique and stop flow technique. There are two parts in this thesis.· Part one: ReviewThe new development in traditional determination method of COD isreviewed.The application of flow analysis in the determination of COD is introduced.· Part two: Research paperIn this part, three new determination methods have been established by FIA.Firstly, A method is described for the determination of COD in environmental waters by FIA-FAAS. The method uses acid potassium permanganate solution as oxidant reagent and glucose as a standard. The produced Mn2+ is retained on a cation-exchange resin microcolumn, then eluted by 3 mol/L HC1 and measured by FAAS. When the reaction tube is 5 m, reaction time is 30 s and reaction temperature is 95℃, the linear range of determination COD is 8-200 mg/L and the detection limit is 2.6 mg/L with a sampling frequency of 24/h. Cl- up to 100 mg/L level does not interfere, Mg2+ up to 1000 mg/L level does not interfere. The relative standard deviation of 7 replicate determinations is 3.37 %. The method has been applied to the on-line determination of COD in river water, pool water,slight contaminative industrial water and the results are in agreement with traditional method using potassium dichromate.Secondly, we know that sonochemistry, as a new branch of subject, can quicken chemical reaction and enhance productivity. A new method of determination COD is proposed on the basis of on-line ultrasonic digestion and FIA-FAAS. The use of ultrasonic wave not only quickens the reaction and improves the completion of this reaction, but also the acidity drops to a great extent, and makes the reaction suit for quick determination in the system of FIA. The method uses acid potassium permanganate solution as oxidant reagent and glucose as a standard. After ultrasonic digestion, the produced Mn2+ is retained on a cation-exchange resin microcolumn, then eluted by 3 mol/L HC1 and measured by FAAS, When the reaction tube is 5m, reaction time is 30 s and reaction temperature is 80癈, the linear range of determination COD is 3-300 mg/L, and the detection limit is 1mg/L with a sampling frequency of 24/h. Cl- up to 1000 mg/L level does not interfere, Mg2+ up to 1000 mg/L level does not interfere. The relative standard deviation of 9 replicate determinations is 2.7 %. The method has been applied to the on-line determination of COD in river water, pool water, and the results are in agreement with traditional method using potassium dichromate.Finally, we have designed a new method of determination COD. In this method, stop flow technique and merging zones technique are used in the spectrophotometry of acid potassium permanganate solution as an oxidant reagent. When the reaction temperature is 70℃ and stop flow is 60 s, the linear range of determination COD is 3-150 mg/L and the detection limit is 1mg/L with a relative standard deviation of 1.2% and sample frequency of 30/h. Cl- up to 10000mg/L level does not interfere. The method has been applied to the on-line determination of COD in river water, pool water and the results are in agreement with traditional method using potassium dichromate.