| In recent years, with the rapid development of industry in our country, water pollutionis increasingly serious, the eutrophication problem of rivers lakes and sea water is moreand more serious, which is seriously affect human health and economic development.Nitrogen is an important element in the water and it is one of the elements which willcause eutrophication. Therefore it is of great importance for the monitoring of totalnitrogen in water. At present, the monitoring of total nitrogen is mainly manual samplingand laboratory analysis, and the operation of this analysis method is cumbersome and theanalysis cycle is long. So this method can’t meet the need for real-time monitoring. Withthe development of science and technology, automation, intelligent, real-time on-linemonitoring has become the development direction of monitoring technology. Therefore itis improtment to research a submersible apparatus for the determination of total nitrogen,which can put into the water and measurement directly, and realize the continuous, onlineand in situ measurement of the total nitrogen in water. It is of great significance toimprove the level of water monitoring in our country.This paper studied the process of digestion, reduction and chromogenic measurementbased on sequential injection apparatus. The optimum digestion conditions, reductionconditions and chromogenic conditions are ensured by experiment. And based on thismethod and conditions to design a submersible apparatus for the determination of totalnitrogen.The method of ultraviolet light catalysis-potassium persulfate oxidation is used in theprocess of digestion, and the digest of water is occurred in the pipeline.This methodcombined the UV radiation and the oxidability of the oxidizing agent and produced newfree radical which has stronger Oxidation ability, and improve the ability of digestion. Theoptimum digestion conditions obtained by the experiment is as follows, the ratio ofK2S2O8solution with NaOH solution is2:7, the concentration of K2S2O8is6g· L-1,digestion temperature is95℃, Digestion time is210s.After digested, the nitrate are reduced by copper coated cadmium column, the bestreduction conditions obtained though the experiment are as follows, the length of filledcadmium column is10cm, pump speed is15μL·s-1, residence time is60s. The solution iseasy to vestigital in the cadmium column, so it is important to cleaning the cadmiumcolumn in time after determined. It need to replace a new one when the column is old. After reduction, using azo dyes spectrophotometric method to determine. The bestchromogenic condition are as follows, the concentration of sulphanilamide is5g·L-1, theconcentration of N-ethylenediamine is1g·L-1, the concentration of hydrochloric acid is1mol·L-1, the sample volume is60μL, chromogenic agent volume is100μL, thechromogenic time is15s, tthe velocity of determination is45μL·s-1.The Nicotinic acid solution of different concentration, the tap wanter, the lake water inthe park and the waste water in the pipeline are determined under the best digest condition,the best reduce condition and the best chromogenic condition. The relative standarddeviation less than3%, the precise is satisfactory, the detection limit is0.0086mg·L-1, thestandard addition recovery of actual water was greater than97%.On the basis of preliminary experiments we preliminary designed the submersibleapparatus for the determination of total nitrogen, and come up with the fluid passage andoverall appearance. Which can realize automatic in situ determination of total nitrogen.It’s laid a solid foundation for the research of submersible apparatus for the determinationof total nitrogen. |
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