【已撤稿】淡水磷监测中钼酸铵分光光度法的改进

我国现行淡水水体中磷测定方法为钼酸铵分光光度法（GB 118931989），该方法检测下限为0.01 mg/L，但我国南亚热带地区部分水体的总磷以及多数水体的溶解态磷浓度均低于0.01 mg/L，通过对标准试样和野外水样的测定，分析该方法在监测低磷浓度水体中可能出现的问题并提出改进方法.结果表明：对于磷浓度低于0.01 mg/L的水体，国标法灵敏度低，准确性差.通过3个方面的改进可提高该方法测定的灵敏度和准确性：1）将消解水样体积由25 ml增加到50 ml，消解后不再进行二次稀释定容；2）改变显色剂的配制，显色剂由14%硫酸溶液50 ml、酒石酸锑钾溶液5 ml、4%钼酸铵溶液15 ml和0.1 mol/L的抗坏血酸溶液30 ml混合而成，现配现用；3）将测定波长设置为880 nm.改进后方法的灵敏度有较大提高，能准确、有效地检测磷浓度在0.003~0.01 mg/L的水样.

[This article has been retracted.] Improvement of the ammonium molybdate spectrophotometric method for phosphorus monitoring in freshwater

Ammonium molybdate spectrophotometry(GB 11893-1989) has been widely used to determine phosphorus for fresh waters, with a detection limit of 0.01 mg/L. However, total phosphorus as well as dissolved phosphorus concentration in most fresh waters are lower than that in southern China. Here, we present an improvement of the method for monitoring low phosphorus concentrations in fresh waters after extensive testing of standard and field samples. The accuracy and sensitivity improved after changing three manipulations:1) increase the digested sample volume from 25 ml to 50 ml, without secondary dilution after digestion; 2) prepare the chromogenic agent as follows:mixing 50 ml of 14% H₂SO₄, 5 ml of antimony potassium tartrate solution, 15 ml of ammonium molybdate solution and 30 ml of ascorbic acid solution together just before addition; 3) set the determination wavelength to 880 nm. The improved method is able to accurately determine phosphorus concentrations of 0.003-0.01 mg/L.