Eisenhut S, Heumann K G, Vengosh A
Institute of Inorganic Chemistry, University of Regensburg, Universitätsstrasse 31, D-93040, Regensburg, Germany.
Anal Bioanal Chem. 1996 Mar;354(7-8):903-9. doi: 10.1007/s0021663540903.
A technique for precise boron isotope ratio measurements with a high detection power has been developed by negative thermal ionization mass spectrometry (NTIMS). Relative standard deviations in the range of 0.03-0.3% have been obtained for the determination of the (11)B/(10)B isotope ratio using nanogram amounts of boron. Ba(OH)(2) has been applied as ionization promoter for the formation of negative thermal ions. By adding MgCl(2) better reproducibilities of the measurement have been achieved. A possible interference of BO(-)(2) ions at mass number 42 by CNO(-) could be excluded by the sample preparation technique used. Contrary to other NTI techniques no dependence of the measured isotope ratio on the boron amount used has been observed. Anthropogenic and natural saline influences in ground water have been successfully identified by boron isotope ratio determinations with this NTIMS method, due to the different isotopic composition of boron in natural and anthropogenic substances. In sewage, the boron isotope ratio is substantially influenced by washing powder, which contains low (11)B/(10)B ratios (expressed in delta(11)B values normalized to the standard reference material NIST SRM 951). In contaminated ground water, low delta(11)B values are normally correlated with high boron and high chloride concentrations. On the other hand, delta(11)B shifts to higher values in less contaminated samples. For ground water with saline influences, only the delta(11)B determination, and not the boron or chloride content, allowed the correct identification of this natural source of contamination.
通过负热电离质谱法（NTIMS）开发了一种具有高检测能力的精确硼同位素比值测量技术。使用纳克量的硼测定（11）B/（10）B同位素比值时，相对标准偏差在0.03 - 0.3%范围内。Ba(OH)₂已被用作形成负热离子的电离促进剂。通过添加MgCl₂，测量的重现性得到了更好的提高。所采用的样品制备技术可以排除质量数为42的BO₂⁻离子受到CNO⁻的可能干扰。与其他NTI技术相反，未观察到测量的同位素比值对所用硼量的依赖性。由于天然和人为物质中硼的同位素组成不同，利用这种NTIMS方法通过硼同位素比值测定成功识别了地下水中的人为和天然盐分影响。在污水中，硼同位素比值受洗衣粉的显著影响，洗衣粉中（11）B/（10）B比值较低（以相对于标准参考物质NIST SRM 951归一化的δ（11）B值表示）。在受污染的地下水中，低δ（11）B值通常与高硼和高氯浓度相关。另一方面，在污染较轻的样品中，δ（11）B值会向更高值偏移。对于受盐分影响的地下水，只有δ（11）B的测定，而不是硼或氯的含量，能够正确识别这种天然污染源。
