García-Ruiz Silvia, Moldovan Mariella, García Alonso J Ignacio
Department of Physical and Analytical Chemistry, University of Oviedo, Julián Clavería 8, 33006 Oviedo, Spain.
J Chromatogr A. 2007 May 18;1149(2):274-81. doi: 10.1016/j.chroma.2007.03.048. Epub 2007 Mar 19.
Large volume injection, up to 5 mL, was evaluated and optimised for the on-line ion chromatographic separation of Rb and Sr before ICP-MS measurement of Sr isotope ratios. Flat-topped chromatographic peaks, ideally suited for multicollector ICP-MS isotope ratio measurements, could be obtained when the composition of the mobile phase (nitric acid and 18-crown-6 ether) was identical to the matrix of the sample. Under those conditions rubidium eluted at the dead volume of the column while strontium produced a flat-topped transient signal with several minutes of stable plateau. On-line data acquisition during several minutes at the plateau of Sr signal allowed high precision Sr isotope ratio measurement. The developed procedure was evaluated for Sr isotope ratio measurements on different types of samples, including cider, apples, apple leaves, and soil extracts, in the frame of a long-term project aiming at origin authentication using strontium isotope ratio measurements. It was observed that sample matrix caused broadening of the strontium chromatographic peak and loss of flat-topped peak profile. Under those circumstances the addition of the complexing crown-ether 18-crown-6 both to samples and chromatographic eluent provided two distinct advantages. First, a drastic increase in the retention of strontium was observed which could be modulated by increasing the concentration of nitric acid in the eluent up to 900 mM. This increase in the eluent HNO(3) concentration allowed the application of the method to acid soil digests and other high acidity samples. Second, the matrix of the sample did not affect any more the chromatographic peak profile and similar chromatographic separations could be obtained for samples and standards maintaining the flat-topped Sr peak profile. Sample preparation consisted of a simple 1:10 dilution of the cider or pre-treated solid samples by adding HNO(3) (900 mM) and 18-crown-6 ether (5mM) to obtain similar composition in the sample solution and the HPLC eluent.
在通过电感耦合等离子体质谱法（ICP-MS）测量锶同位素比值之前，对高达5 mL的大体积进样进行了评估和优化，以用于铷和锶的在线离子色谱分离。当流动相（硝酸和18-冠-6醚）的组成与样品基质相同时，可获得平顶色谱峰，这非常适合多接收ICP-MS同位素比值测量。在这些条件下，铷在柱的死体积处洗脱，而锶产生一个平顶瞬态信号，具有几分钟的稳定平台期。在锶信号的平台期进行几分钟的在线数据采集，可实现高精度的锶同位素比值测量。在一个旨在利用锶同位素比值测量进行产地鉴定的长期项目框架内，对所开发的方法进行了评估，用于测量不同类型样品中的锶同位素比值，包括苹果酒、苹果、苹果叶和土壤提取物。观察到样品基质导致锶色谱峰变宽和平顶峰形消失。在这种情况下，向样品和色谱洗脱液中添加络合冠醚18-冠-6具有两个明显的优点。首先，观察到锶的保留率大幅提高，可通过将洗脱液中硝酸浓度提高至900 mM来调节。洗脱液中硝酸浓度的增加使得该方法能够应用于酸性土壤消化液和其他高酸度样品。其次，样品基质不再影响色谱峰形，对于保持平顶锶峰形的样品和标准品可获得相似的色谱分离效果。样品制备包括将苹果酒或经过预处理的固体样品简单地按1:10稀释，加入硝酸（900 mM）和18-冠-6醚（5 mM），以使样品溶液和高效液相色谱洗脱液具有相似的组成。
