电超滤浸提土壤养分的研究 Ⅳ.连续流动分析测定土壤电超滤氮和磷

STUDIES ON THE EXTRACTION OF SOIL NUTRIENTS BY ELECTRO-ULTRAFILTRATION(EUF)Ⅳ.DETERMINATION OF SOIL ELECTRO-ULTRAFILTRATION NITROGEN AND PHOSPHOROUS BY CONTINUOUS FLOW ANALYSIS(CFA)TECHNIQUE

研究电超滤-连续流动分析(EUF-CFA)联用技术测定土壤有效氮和磷的方法。在探讨紫外-过硫酸盐氧化土壤电超滤有机氮和 NH4-N 成为 NO_3^-以及氧化有机磷成为正磷酸根的机理和条件之后,研究并优化了 Technicon 自动分析仪测定 EUF-N_T,-N_(NO_3),-N_(org)和-P_T,-P_(min),-P_(org)的主要条件,提出了快速简便的方法,灵敏度和精密度都很高。

The electro-ultrafiltration-continuous flow analysis (EUF-CFA) combined technique used for determining soil available N and P is investigated. In this procedure the soil EUF-N and -P,including both soluble inorganic and organic compounds,are oxidized to nitrate and orthophosphate respectively,by means of ultraviolet irradiation-peroxydisulfate (UV-S_2O_3^(2-)) oxidation. Experimental evidence shows that the presence of sufficient soluble oxygen which can be provided by adding potassium peroxydisulfate to the solution,is necessary for the complete UV-oxidation of dissolved organic compounds.Ammo- nium salts and some known organic nitrogenous compounds tested,including tryptophan and nicotinic acid,can be rapidly UV oxidized to nitrate and nitrite in alkaline medium.But we have found that the N atoms in the quanido group of arginine molecule are only partially photo-oxidized to nitrate,which,how- ever,is of not much importance,as this compound is seldom found in EUF ex- tract.UV-oxidation of organic phosphorous compounds is much faster than that of nitrogenous compounds,but polyphosphate esters yield polyphosphate ion which is only depolymerized and hydrolyzed to orthophosphate in the presence of acid.Hence the total phosphorous (P_T) should be determined by UV-oxidation in acid medium.The NO_3^- in the solution is determined by the hydrazine reduction- Oriess method and PO_4^(3-) by the molybdate-antimonyl ascorbic acid method of Murphy and Rilley. The conditions of CFA determination of soil EUF-N_T,-N_(NO_3),-N_(org),and -P_T, -P_(min),and -P_(org) have been investigated and optimized,then,a rapid,convenient and precise method has been recommended based upon the Technicon AutoAna- lyzer II System.Because of the high sensitivity and precision of this method,it allows to pool the EUF anode and cathode extracts before analysis,so the errors of 'ion leakage' during the EUF extraction are avoided,and the accuracy of the values of EUF-N and -P may be improved.