羟胺浸提-可见分光光度法测定土壤无定形铁

采用羟胺浸提-可见分光光度法测定了土壤无定形铁。与草酸-草酸铵浸提法相比，羟胺浸提法排除磁性铁矿物的干扰，克服了原方法实验结果偏高的缺点。该法相对标准偏差RSD<2.0％，回收率为97.5％～101.5％，实验的精密度稍好于草酸-草酸铵法，且具有快速、简便、显色时间短等特点。同时进行了土壤厌氧恒温培养实验，结果显示铁还原启动期、快速期和稳定期的还原速率分别为0.030～0.053 g·d-1·kg-1,0.186～0.333 g·d-1·kg-1和0.015～0.030 g·d-1·kg-1。回归分析结果表明，羟胺浸提法测定结果与土壤培养实验中测得的快速期铁还原速率显著相关(r=0.990 7，p＜0.01)，说明在浸提土壤无定形铁的过程中，羟胺法比草酸-草酸铵法具有更好的选择性。

Determination of Amorphous Iron Oxides in Soil by Hydroxylamine Extraction-Spectrophotometry

Amorphous iron oxides in soil were determined by hydroxylamine extraction-spectrophotometry. The results showed that hydroxylamine extraction eliminates interference of magnetite and the defect of results being on the high side was overcome to a certain degree compared with oxalic acid-oxalic acid ammonium extraction. The hydroxylamine extraction-spectrophotometry for the detection of amorphous iron oxides in soil was highly precise (relative standard deviation was less than 2.0%) and highly reliable (recovery rates ranged from 97.5％ to 101.5％). Other advantages of the method were rapidness，simplicity and a shorter chromogenic time. In addition, soil incubated anaerobically at constant temperature under laboratory condition was investigated. The results suggested that iron reduction rates during initiation, rapid reaction and steady phases in the soil samples anaerobic incubation were 0.030-0.053, 0.186-0.333 and 0.015-0.030 g·d-1·kg-1, respectively. Significant relationship between the concentrations of hydroxylamine extraction iron and iron reduction rates during rapid reaction phase in soil incubation (r=0.990 7, p＜0.01) indicated that hydroxylamine had a higher degree of selectivity in amorphous iron oxides extraction than oxalic acid-oxalic acid ammonium extraction.