超声交换-抽滤淋洗-全自动凯氏定氮法测定土壤中阳离子交换量北大核心CSCD

当土壤样品pH≤7.5时,取2.00 g样品,用1 mol·L^(-1)乙酸铵溶液冲洗至土壤无结块,并定容至50 mL,超声交换6 min。当土壤样品pH>7.5时,取2.00 g样品,加入1 mol·L^(-1)氯化铵溶液50 mL,在电炉上煮沸,直至表面皿上蒸出的水的酸度达到pH 7(依此判断氨已煮尽),再加入1 mol·L^(-1)乙酸铵溶液,超声交换6 min。启动抽滤模式,将超声好的样品倒在布氏漏斗上,用40 mL乙醇洗涤沉淀,重复洗涤4次,直至无NH_(4)^(+)洗出(用纳氏试剂检测)。将沉淀、滤纸和约1 g预先高温灼烧好的固体氧化镁试剂置于全自动凯氏定氮仪上,设置盐酸溶液浓度为0.05 mol·L^(-1)、20 g·L^(-1)硼酸吸收液(内含甲基红-溴甲酚绿指示剂)用量为20 mL,蒸馏时间为5.0 min,自动完成消化、蒸馏和滴定操作,仪器输出结果即为测定值。结果表明:方法检出限(3.143s)为0.083 cmol·L^(-1);按照试验方法分析土壤有效态成分分析标准物质,测定值的相对标准偏差(RSD,n=5)均小于5.0%,且测定值均在认定值的不确定度范围内;方法用于分析不同来源地不同类型的样品,所得测定值的RSD(n=5)小于标准(LY/T 1243-1999)方法的,相对误差为-1.5%~6.6%,t检验结果(0.0419)小于临界值(t;=2.228),两种方法无显著性差异。     

全自动淋洗样品预处理-气相分子吸收光谱法测定土壤阳离子交换量

称取经风干并过2mm筛孔的网筛的土壤样品2.000g置于反应瓶中,采用全自动淋洗仪,加入1.00mol·L~(-1)乙酸铵溶液80mL对土样进行处理。经过前处理,土样中的阳离子全部被NH_4~+离子所取代。此时,仪器将自动吸入乙醇对土样进行反复淋洗。淋洗结束后,将土样完全转移至蒸馏瓶中进行蒸馏。馏出液接收于预置有20g·L~(-1)硼酸吸收液20mL的100mL比色管中,待管中溶液总体积达到90mL时,取下比色管,加水定容至100.0mL。此吸收液中氨氮的含量用气相分子吸收光谱法进行测定。此吸收液最长可放置24h,在24h以内测定结果不受放置时间的影响。标准曲线系用氨氮标准溶液(0.10～2.00mg·L~(-1)范围内)按气相分子吸收光谱法进行测定并制作。土样的阳离子交换量(CEC)系根据所测得的氨氮含量按公式换算求出。按此方法分析了4种土壤标准物质,所测得的CEC值与认定值相符,其测定值的相对标准偏差(n=6)均小于2.0%。     

全自动凯氏定氮仪在测定干旱区土壤中全氮量的研究

本实验采用了UDK159全自动凯氏定氮仪对干旱区土壤全氮量的方法以及试验部分影响因素进行研究,结果表明：精密度试验中RSD在0.01919%～0.1073%之间(≤1%),用标准物质硫酸铵进行回收率检验,其回收率达99.5% 以上,检测准确度和精密度都符合国家标准的要求;在消化时间的选择上,变异系数为0.0088,表明土壤中有机物在30 min时已完全消化;而关于硫酸用量在10~15mL时为最佳值,干旱区土壤中氮一般含量为(0.260±0.003) %(P =0.95)。     

Determination of total phosphorus and nitrogen in turbid waters by oxidation with alkaline potassium peroxodisulfate and low pressure microwave digestion, autoclave heating or the use of closed vessels in a hot water bath: comparison with Kjeldahl digestion

The evaluation of the use of alkaline peroxodisulfate digestion with low pressure microwave, autoclave or hot water bath heating for the determination of total phosphorus and nitrogen in turbid lake and river waters is described. The efficiency of these digestion procedures were compared to a Kjeldahl digestion procedure with sulphuric acid-potassium sulfate and copper sulfate. The final solution before digestion was 0.045 M in potassium peroxodisulfate and 0.04 M in sodium hydroxide. Procedures were evaluated by the analysis of suspensions of two reference materials, National Institute of Environmental Science, Japan, no. 3 Chlorella and no. 2 pond sediment and natural turbid waters. Best recoveries of phosphorus and nitrogen by microwave heating were obtained when solutions were digested at 95 °C for 40 min. Quantitative recoveries of phosphorus from Chlorella suspensions up to 1000 mg/l were obtained by all three heating procedures, but incomplete recoveries of nitrogen occurred above 20 mg N/l in the digested sample. Good recoveries of phosphorus and nitrogen from suspended sediment suspensions were obtained only from solutions containing <150 mg/l of suspended sediments. Recoveries of phosphorus from phosphorus compounds containing COP and CP bonds added to distilled water were quantitative (94-113%) except for polyphosphates (microwave, 34±8; autoclave, 114±6; water bath, 96±4) and aluminium phosphate (8-23%). Recoveries of nitrogen compounds containing CN bonds added to distilled water were quantitative (94-96%). The analysis of a range of natural turbid water samples by alkaline peroxodisulfate and microwave, autoclave and water bath heating gave similar total phosphorus and nitrogen results. All procedures using alkaline peroxodisulfate underestimate phosphorus concentrations at high suspended sediment concentrations (>150 mg/l) and are only suitable for the analysis of very turbid samples when the turbidity is due to organic matter (algal cells, plant detritus). Underestimation of nitrogen occurs when samples contain more than 20 mg N/l.