激光同位素分析仪测定液态水的氢氧同位素及其光谱污染修正

Measurements of hydrogen and oxygen isotopes in liquid water by isotope ratio infrared spectroscopy (IRIS) and their spectral contamination corrections

氢氧稳定同位素示踪技术是研究土壤-作物-大气连续体(SPAC)水分循环的重要手段。激光同位素分析仪以其独特的优点逐渐得到广泛应用,但其在测量植物水时,与同位素质谱仪的测量结果存在差异。本文采用Los Gatos Research公司生产的激光同位素分析仪DLT-100分别测定植物水、土壤水、雨水和地下水等共19个样品,并用其开发的光谱污染矫正软件标记和量化水样品的污染,修正污染水样品的同位素值,然后与同位素质谱仪进行比对。结果表明:土壤水、雨水和地下水等样品均未受到污染,而植物样品均受到一定程度的光谱干扰;植物水的δD和δ18O修正范围分别是1.21‰～26.65‰和0.50‰～18.27‰。该修正方法消除了δD测定的差异,并大大降低了δ18O的偏差。可见,激光同位素分析仪法在测量土壤水、雨水和地下水同位素时可以有效地代替传统的同位素质谱仪法,但对植物水的测量时,则首先需要判断样品是否受到光谱干扰,如果受到污染,仍需同位素质谱法进行确认。

Hydrogen and oxygen isotope tracing is an important means in studying the hydrologi- cal cycle in soil-plant-atmosphere continuum （SPAC）. Isotope ratio infrared spectroscopy （IRIS）, with its unique superiorities, has been widely applied to investigate the stable isotopes of water from different sources, but some discrepancies in the measurement results are reported between IRIS and isotope ratio mass spectrometry （IRMS）. In this paper, 19 water samples in- cluding 6 plant waters, 4 soil waters, 1 groundwater, and 8 min waters were collected, with their hydrogen and oxygen isotopes measured by IRIS and IRMS. It was observed that all the samples except plant waters presented a well agreement in the measured results between IRIS and IRMS. The plant waters were contaminated during the cryogenic vacuum distillation process. By using the spectral contamination identifier, the δD values were well corrected, whereas the δ18O values still showed minor difference, as compared with those measured by IRMS. It was suggested that IRIS could be applied to replace IRMS to measure the stable isotopes of liquid waters which are not contaminated.