Stevens W B, Mulvaney R L, Khan S A, Hoeft R G
University of Illinois, Department of Crop Sciences, Urbana 61801, USA.
J AOAC Int. 2000 Sep-Oct;83(5):1039-46.
Simple methods are described that permit the use of either H3BO3 indicator solution or acidified filter disks to collect NH3 liberated by treatment of Kjeldahl digests with NaOH. These methods incorporate modifications to improve reliability, analytical capacity, and convenience. A semimicro digest was diluted to 25 mL with deionized water, and a 10 mL aliquot, containing up to 4 mg N (150 microg N for diffusions into acidified disks), was transferred to a shell vial, which was placed inside a 473 mL (1 pint) Mason jar containing 10 mL 10N NaOH. The NH3 liberated by overturning the vial was collected after 12 to 48 h at ambient temperature, or after 4 h at 45 to 50 degrees C on a hotplate, for quantitative and/or isotope-ratio analyses. With either H3BO3 indicator solution or acidified filter disks, recovery of diffused N was quantitative. Isotope-ratio analyses of diffused N from 15N-labeled chemical, plant, and soil samples were within 3% of analyses using steam distillation.
本文描述了一些简单的方法，这些方法允许使用硼酸（H₃BO₃）指示剂溶液或酸化滤纸片来收集通过用氢氧化钠处理凯氏消化液所释放出的氨。这些方法进行了改进，以提高可靠性、分析能力和便利性。将半微量消化液用去离子水稀释至25 mL，取10 mL等分试样（含氮量高达4 mg，扩散到酸化滤纸片中的氮为150 μg）转移至贝壳形小瓶中，该小瓶置于一个473 mL（1品脱）梅森罐内，罐中装有10 mL 10N氢氧化钠。翻转小瓶释放出的氨在室温下收集12至48小时，或在45至50摄氏度的热板上加热4小时后收集，用于定量和/或同位素比率分析。使用硼酸指示剂溶液或酸化滤纸片时，扩散氮的回收率均为定量。对来自¹⁵N标记的化学、植物和土壤样品中扩散氮的同位素比率分析结果与使用水蒸气蒸馏法的分析结果相差在3%以内。
