GasbenchⅡ-IRMS测定新鲜橙汁水中氧同位素方法

摘要

橙汁中水的氧（δ18O）同位素比值对于果汁真实性技术鉴别具有重要意义。文章分别考察反应瓶气密性、样品体积、平衡时间和乙醇等因素对橙汁中水的氧同位素影响分析；添加乙醇可有效抑制鲜橙汁的微生物发酵，避免测定过程因橙汁发酵产生CO2干扰橙汁水中氧同位素有效测定问题。经优化建立GasBench II-IRMS测定新鲜橙汁中水的δ18O比值在线分析方法。结果表明，当橙汁样品体积200μL～1000μL、加入10%乙醇、反应24 h~48 h后测定，同一样品中水的δ18O比值的重复性和再现性标准偏差（1σ）均小于0.1‰，完全符合测定要求，方法操作简便，可实现大批量连续测定。%Oxygen stable isotope ratio(δ18O) of water is currently applied for detecting illegal addition of exogenous water in juice. The method of determination of δ18O in water from orange juice samples by GasbenchⅡ-IRMS using on-line equilibration technique was reported in this paper, and the effects of sample volume, equilibration time and ethanol on the determination ofδ18O in water were discussed. Results showed that ethanol contribute to inhibit fermentation of fresh juice effectively, avoid a great influence on the determination ofδ18O of water by CO2 origined from fermentation, the method above was stable with a standard deviation (1σ) lower than 0.1 ‰following conditions: sample volume range from 200 μL to 1 000 μL with 10 % (V/V) ethanol added and equilibration time range from 24 h to 48 h. This method had an advantage of easy and rapid operating with a lowering Sample consumption, and especially can be used continuously for a large number of instances in batch.