Patton G W, Cooper A T, Tinker M R
Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Health Phys. 1997 Mar;72(3):397-407. doi: 10.1097/00004032-199703000-00007.
Ambient air samples for tritium (as HTO) can be collected using the solid adsorbent silica gel. The purpose of this study was to determine the maximum practical sampling volume and overall collection efficiency for water vapor collected on silica gel columns and to demonstrate the use of an impinger-based system to load water vapor onto silica gel columns. Breakthrough volumes (Vb) were measured and chromatographic efficiencies (expressed as the number of theoretical plates, N) were calculated for a 20 degrees C to 50 degrees C temperature range, with the relative humidity at approximately 30%. The tests yielded relative breakthrough volumes (air volume/adsorbent depth, m3 cm(-1)) of 0.36 for 20 degrees C, 0.20 for 30 degrees C, 0.15 for 40 degrees C, and 0.077 for 50 degrees C. For 18-cm columns, the average tritium tracer recoveries at 20 degrees C were 71% with no observed breakthrough for air volumes up to 5 m3, while at 40 degrees C mean tritium tracer recoveries dropped from 75% for volumes < or = 3.0 m3, to 0% for a volume of 5.0 m3. Frontal chromatographic profiles were measured for water vapor migrating through silica gel columns that were divided into 5 segments. The chromatographic efficiency of the silica gel columns was determined by graphical evaluation of the chromatography profiles. At a sampling rate of 0.25 L min(-1) and 30% relative humidity, the number of theoretical plates per adsorbent depth were 0.55 N cm(-1) at 20 degrees C, 0.68 N cm(-1) at 30 degrees C, 0.51 N cm(-1) at 40 degrees C, and 0.30 N cm(-1) at 50 degrees C. Chromatographic theory was used to estimate the overall collection efficiency of the silica gel columns as a function of the ratio of the sampling volume to breakthrough volume and the chromatographic efficiency. For a 9.5 m3 sample volume, 30% relative humidity, 0.25 L min(-1) sampling rate, and a 54-cm column, the overall collection efficiency was above 99.9% at 20 degrees C, above 95% at 30 degrees C, just below 80% at 40 degrees C, and <<80% at 50 degrees C.
可以使用固体吸附剂硅胶来采集环境空气中的氚（以HTO形式存在）样本。本研究的目的是确定硅胶柱上收集水蒸气的最大实际采样体积和总体收集效率，并演示使用基于冲击式吸收管的系统将水蒸气加载到硅胶柱上。在20℃至50℃的温度范围内、相对湿度约为30%的条件下，测量了穿透体积（Vb）并计算了色谱效率（以理论塔板数N表示）。测试得出，20℃时的相对穿透体积（空气体积/吸附剂深度，m3 cm-1）为0.36，30℃时为0.20，40℃时为0.15，50℃时为0.077。对于18厘米长的柱子，20℃时氚示踪剂的平均回收率为71%，空气体积达到5立方米时未观察到穿透，而在40℃时，体积≤3.0立方米时氚示踪剂的平均回收率从75%降至5.0立方米时的0%。对通过分为5段的硅胶柱迁移的水蒸气测量了前沿色谱图。通过对色谱图进行图形评估来确定硅胶柱的色谱效率。在采样速率为0.25 L min-1和相对湿度为30%的条件下，每吸附剂深度的理论塔板数在20℃时为0.55 N cm-1，30℃时为0.68 N cm-1，40℃时为0.51 N cm-1，50℃时为0.30 N cm-1。利用色谱理论估计硅胶柱的总体收集效率，该效率是采样体积与穿透体积之比以及色谱效率的函数。对于9.5立方米的采样体积、30%的相对湿度、0.25 L min-1的采样速率和54厘米长的柱子，总体收集效率在20℃时高于99.9%，30℃时高于95%，40℃时略低于80%，50℃时远低于80%。
