分光光度法测定水稻土中有机酸的研究

STUDY ON SPECTROPHOTOMETRIC DETERMINATION OF ORGANIC ACIDS IN PADDY SOIL

本文以三种有机酸为代表,研究并建立了测定水稻土中有机酸的分光光度法。结果表明,三种有机酸的有色络合物具有相同的吸收光谱,且具有相同的最大吸收波长(λ_(mss)=500um)和相近的表观摩尔吸光系数。水分对酯化反应影响很大,含水量达4ml时,吸光值下降85％。酯化温度在10℃以上时,酯化率达最大值且保持稳定。在25℃时,显色反应20min趋干稳定,且在1h内吸光值下降不超过1.2％。土样中的有机酸采用NaCl溶液为提取剂,以3:1的液土比振荡提取30min,NaCl溶液浓度为1％就能达到良好的提取、过滤效果。提取液在烘干前需进行碱化,否则有机酸将损失30％以上。本法平均回收率为92.2％(n=5),标准差为0-0.0478cmol k8^(-1)(n=2-6),平均0.0142cmol kg^(-1)(n=26);变异系数为0—10％(n=2-6),平均4.87％(n=26);线性范围为0—0.0018mol L^(-1)。

This paper studies and establishes a method for the spectrophotometric determination of organic acids in paddy soil by taking three kinds of organic acids as representatives. The results show that the coloured compounds of the three organic acids have the same absorption spectrum, maximum absorption wavelength(λ_(max)=500nm) and close apparent molar absorption coefficients. Water strikingly affects esterification of organic acids. Absorbance will drop down by 85% when the amount of water reaches 4 ml. When the temperature of esterification is above 10℃ esterification rate reaches maximum and remains stable. At 25℃ colour reaction trends to stableness in 20 minutes and absorbance drop is less than 1.2% within one hour. Organic acids in soil samples are extracted by shaking for 30 minutes using NaCl solution as an extractant at a 3 : 1 (solution : soil) ratio. Good extraction and filtration effect can be obtained when NaGl concentration reaches 1%. Sample solution has to be alkalized before oven drying otherwise the organic acids will loss more than 30%. The average recovery of the method is 92. 2% (n=5), the standard deviation 0—0.0478 cmol kg^(-1)(n=2—6) with an average of 0.0142cmol kg^(-1) (n=26), the coefficient of variation 0—10% (n=2—6)with an average of 4.87%(n=26) and the linear range 0—0.0018mol L^(-1).