黄土-古土壤沉积物中酸溶相硼的分离及其同位素测定

Separation and isotopic determination of boron in the acid soluble fractionof loess and paleosol

用0 5mol/LHCl提取黄土、古土壤中的酸溶相成分 ,并用混合树脂法和硼特效树脂法两种方法叠加对硼进行分离和纯化 ,Cs2BO2+法测同位素比值。结果表明,虽然混合树脂法和硼特效树脂法都是较成熟的方法 ,但用来处理杂质离子含量相对高而硼含量低的样品溶液并不成功。两种方法叠加处理后能达到理想的效果 ,重复处理黄土 古土壤样品的精度(2RSD)在0 4‰～0 6‰之间 ,这与标样(NISTSRM951)水平(0 3‰)接近 ,说明处理方法是可行的。用此方法首次测定了洛川黄土

A procedure was established for determination of boron isotopic composition in acid soluble fraction of loess and paleosol. Samples were leached by 0 5 mol/L HCl. Most of the impurities in the leaching solution were removed by a mixture of strongly acidic cation exchange resin in hydrogen form and weakly basic anion exchange resin (Ion ExchangeⅡ) in bicarbonate form. Then the boron was separated by boron specific ion exchange resin (Amberlite IRA 743), eluted with 0 1 mol/L HCl. Boron isotopic ratios were determined by PTIMS technique. The relative standard deviation (2RSD) of samples was 0 4‰～0 6‰, which is similar to the reproducibility, obtained from a large number of analyses ofthe NIST 951 standard, 0 3‰. This precision is consistent with that reported by others, e.g. Spivack and Edmond (1986) of 0 4 and Xiao et al. (1988) of 0 1‰, and higher than the sodium tetraborate technique of 0 5‰(Oi et al., 1989) and NTIMS technique of 0 5‰to 0 7‰(Barth, 1997). The average measured absolute, oxygen corrected 11B/10B of NIST SRM 951 was 4 053 80±0 001 06, which is similar to the certified value of 4 043 62 Using IDMS method, a total procedural blank of about 62 ng was determined. Concentrations of total dissolved boron of our samples were 10～20 μg, determined by spectrophotometric method using the reagent azomethine H. Hence, the contribution of blank boron tothe isotopic composition of boron in samples could be neglected. According to our experiment, it is concluded that our proposed procedure is a suitable method for determining the boron isotopic composition of low boron concentration and high ion strength samples. Using the procedure described in this paper, the boron isotopic compositions of acid soluble fraction of loess and paleosol from the Luochuan Section, in central China are successively measured.