有机酸释放暗棕壤磷素养分中显色时间对磷测定的影响

Effects of Chromogenic Time on Phosphorus Determination During Phosphorus Mobilization of Dark Brown Forest Soils by Organic Acids

向磷标准溶液中加入不同浓度草酸和柠檬酸溶液,并用不同浓度草酸/草酸盐和柠檬酸/柠檬酸盐浸提暗棕壤,分别用森林土壤磷测定的标准方法(简称"土显法")、水和废水中磷的钼蓝比色法(简称"水显法")做显色的时间序列,探讨上述过程中显色时间对磷测定的影响,确定磷的最佳测定方法和显色时间。结果表明,用"水显法"测定时,较低浓度(柠檬酸≤0.6mmol/L,草酸≤0.4mmol/L)有机酸不影响磷标准溶液显色;较高浓度时(柠檬酸≥7.2mmol/L、草酸≥2.8mmol/L)影响严重,延长显色时间对消除影响已不起作用;上述浓度内,延长显色时间能有效消除其影响,且有机酸浓度越高所需时间越长。用"土显法"测定时,影响磷标准溶液显色的有机酸浓度低于"水显法",所以,"水显法"测定效果强于"土显法",特别是较高浓度有机酸处理下。用草酸/草酸盐和柠檬酸/柠檬酸盐浸提A1层和B层暗棕壤时,对于浸出液中磷的测定,"水显法"效果也明显强于"土显法",应优选"水显法"测磷,当有机酸浓度≤10.0mmol/L时直接测定,20mmol/L时则稀释2倍后测定,显色时间均定为15min。

By adding different concentrations of oxalic acid and citric acid solutions to phosphate standard so- lution, extracting dark brown forest soils by different concentrations of oxalic acid/oxalate and citrate/cit- rate, the time series of phosphorous coloration and the effects of chromogenic time on phosphorous determi- nation were studied by standard method for phosphorus measurement of forest soil （referred to as soil colora- tion）, molybdenum blue method for phosphorus measurement of water and wastewater （referred to as water coloration）, so as to choose the best method and chromogenic time. The results showed that, when deter- mined by ＂water coloration＂, organic acids of lower concentrations （citric acid≤0.6 mmol/L, oxalic acid≤ 0.4 mmol/L） had no effect on phosphorous coloration of phosphate standard solution. Solutions of higher concentrations （citric aeid≥7.2 mmol/L, oxalic acid≥2.8 mmol/L） had a serious impact, and extension of chromogenic time had no effect. Between the concentrations above, extension of chromogenic time could ef- fectively eliminate the effects, and the higher organic acids concentrations longer the time required for. When determined by ＂soil coloration＂, the organic acids concentrations had impact to the coloration of phosphate standard solution and the effects were lower than those of ＂water coloration＂. So ＂water coloration＂ was bet- ter, especially at higher organic acids concentrations. When oxalic acid/oxalate and citric acid/citrate extrac- ting A1 and B horizons of dark brown forest soils, for phosphorus determination in leaching solution, ＂water coloration＂ was better than ＂soil coloration＂, and the former should be preferred. When organic acids con- centrations ≤10.0 mmol/L, phosphorus could be measured directly, when it was 20 mmol/L measured after 2-fold dilution, and chromogenie times were all set at 15 min.