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在50ml无缓冲的1M NH_4NO_3中浸出20g土壤2h以进行萃取,已成为估计微量元素流动形式和潜在危险形式的标准德意志方案(DIN19730)。利用加拿大草原诸省和安大略省所收集的黑土和灰壤特性控制土壤,考察了此方案。发现此法对于单位体积试剂的样品重量变化与接触时尚欠周密。将50ml试剂中的样品重量由10g减至1g,萃取的Cd增大3—15倍。在控制的样品中,随着土壤pH由5.2增至8.1,可萃Cd的这种变化更显著。浸出时间对测定结果影响不大,但延长时间(1—3h)常产生较少的可萃Cd,说明有反复吸附作用。借助浸出开始时添加Cd的掺杂试验,进一步证明了Cd在此试剂中的稳定性差。在土壤pH为6.1和6.9时,50和200ppb Cd的回收率<20%。用另一种无缓冲试剂1M NH_4Cl在类似的初始pH 5时操作,未见这样严重地吸附Cd。用NH_4Cl和0.1M Na_4P_2O_7从土壤中萃取的Cd含量差不多,可用于预测加拿大草原诸省硬粒小麦的吸收,而1M NH_4NO_3浸出的数据常接近于检测限0.1ppb(ng g~(-1))Cd。在1M NH_4NO_3萃取中Cd的重复吸附和欠平衡可能导致中性和碱性土壤中植物可获得Cd的低估。
Leaching 20 g of soil for 2 h in 50 ml of unbuffed 1 M NH 4 NO 3 for extraction has become the standard Deutsche Schemes (DIN 19730) for the estimation of the trace elemental mobile forms and potentially dangerous forms. This program was investigated using the characteristics of black and gray soils collected in the provinces of Canada and Ontario. Found that this method for the unit volume of the sample weight changes and contact fashion less well. The weight of the sample in 50 ml of reagent is reduced from 10 g to 1 g, and the extracted Cd is increased by 3 to 15 times. In the controlled samples, this change of extractable Cd is more pronounced as the pH of the soil increases from 5.2 to 8.1. Leaching time on the determination of little effect, but the extension of time (1-3h) often produce less extractable Cd, indicating repeated adsorption. With the addition of Cd at the start of leaching, the doping test further proves the poor stability of Cd in this reagent. The recovery of 50 and 200 ppb Cd was <20% at pH 6.1 and 6.9. With another non-buffered reagent 1M NH 4 Cl operating at a similar initial pH 5, no such severe adsorption of Cd was observed. The contents of Cd extracted from soils with NH 4 Cl and 0.1 M Na 4 P 2 O 7 are almost the same, which can be used to predict the absorption of durum wheat in the Canadian steppe provinces. However, the data of 1 M NH 4 NO 3 leaching are usually close to the detection limit of 0.1 ppb (ng g -1) Cd. Repeated adsorption and underbalance of Cd in 1 M NH 4 NO 3 extracts may lead to the underestimation of Cd available to plants in both neutral and alkaline soils.