冷空气蒸馏分离酸滴定法测定复合肥中铵态氮

Acidimetric Determination of NH_4^+-Nitrogen in Compound Fertilizers After Separation by Cold-Air Distillation

提出了用冷空气蒸馏分离酸滴定法在多种形态氮共存时测定复合肥料中铵态氮含量的方法。取适量复合肥料样品于蒸馏瓶中,与550g.L-1碳酸钾溶液60mL反应,溶液总体积以不宜超过110mL。通过空气在流量为3L.min-1和不加热条件下蒸馏8h,生成的氨馏出并先后吸收于相互连接的3个吸收瓶中,每一吸收瓶中预置硼酸吸收溶液50mL,用0.05mol.L-1盐酸标准溶液滴定3溶液至指示剂呈暗红色,记录所耗盐酸标准溶液的总量。将吸收瓶重新按装在蒸馏系统中继续蒸馏1h后再进行滴定,以所耗盐酸标准溶液量不超过0.03mL认为测定完成。根据滴定所耗盐酸标准溶液的总量计算样品中铵态氮的含量。根据3个样品各5次测定结果计算,得到方法的回收率在99.7%～100.1%之间,相对标准偏差在0.12%～0.55%之间。

Ammonium nitrogen in compound fertilizers in the presence of nitrogen in various species was determined by acidimentry with 0.05 mol·L-1 HCl standard solution after separation by cold distillation.Appropriate amount of the sample was reacted with 60 mL of 550 g·L-1 K2CO3 solution in a distillation flask,to form gaseous NH3 which was carried over by cold air with flow-rate of 3 L·min-1 and absorbed in 3 portions of 50 mL of boric acid solution previously added into 3 separate absorption flasks conrected in series,during the course of 8 h.The solutions in the 3 flasks were titrated with HCl standard solution to a dark red color of the indicator.The cold distillation was carried on again for another one hour.The distillates were titrated again and if the consumption of HCl standard solution was less than 0.03 mL,the determination was concluded and content of NH4＋-nitrogen was calculated on the base of the total volume of standard HCl solution consumed in the titration.From the results of 5 determinations each in analysis of 3 samples by the present method,values of recovery were found in the range of 99.7% to 100.1% with RSD′s（n=5） ranged from 0.12% to 0.55%.