中文摘要：

采用“样品-标准”交叉技术,以纯Mg试剂、水样和矿物岩石样品作为实验材料,尝试建立高精度多接收器等离子体质谱（MC-ICP-MS）测定Mg同位素方法。应用质谱仪上窄的进样狭缝,将来自Ar载气、空气和酸中的C2^＋、C2H^＋、C2H2^＋、CN^＋、NaH^＋等分子对Mg同位素的影响减至最小。当标准Mg浓度为3×10^-6时,保持样品与标准的浓度比在0.5-2之间,对Mg同位素比值测量没有影响。大量实验表明,不同基质的行为各异：Na、Fe和Al的基质效应使δ25Mg和δ26Mg偏负;Ca的基质效应使δ25Mg和δ26Mg偏正;Cr的基质效应使δ25Mg和δ26Mg波动。控制[元素]/[Mg]的浓度比在0.05范围内,可以忽略同质异位素的干扰和基质效应。通过对本实验室的两个工作标准CAGS1-Mg和CAGS2-Mg的长期测量,估计出Mg同位素测量的外精度（2SD）对于δ26Mg可达0.180‰,对于δ25Mg可达0.090‰。在25Mg/24Mg对26Mg/24Mg的同位素比值图上,所有样品的Mg同位素值都落在斜率约0.5的质量分馏线上,意味着建立的MC-ICP-MS测定Mg同位素方法既精确又无干扰。相对于DSM3国际标准,样品的Mg同位素组成大致变化范围是δ26Mg值为2.790‰,δ25Mg值为1.282‰。其中,CAGS1-Mg的δ26Mg值最大,为0.399‰,来自新疆喀纳斯湖水的δ26Mg值最小,为-2.091‰。

英文摘要：

A method for Mg isotope measurement using MC-ICP-MS has been set up. The authors tried to make a high-precision analysis of magnesium isotopes by MC-ICP-MS for Mg reagent, waters and minerals. The ＂sample-standard＂ bracketing technique was used to correct spectrometer mass-dependent fractionation. By arranging narrow entry slit on MC-ICP-MS, the interferences of such molecules as C2^＋ , C2H^＋ , G2H2^＋, CN^＋ and NaH^＋ from Ar gas, air and acid can be decreased to the minimum. Keeping the concentration of samples the same as that of the standard is a good way to obtain high-predsion Mg measurement. Through a lot of experiments on matrix dement interference, matrix effects on Mg measurement can be realized. Keeping [dement]/[Mg] concentration ratio lower than 0.05 can minimize isobaric interference and matrix effects. External repeatability （2SD） of Mg isotope measurement estimated by the authors＇ laboratory standard CAGS1-Mg relative to CAGS2-Mg is 0.180‰ for δ^26Mg and 0.090‰ for δ^25Mg in a long period. The data in three ^25Mg/^24Mg versus^26Mg/^24Mg plots all fall on the mass-dependent fractionation line with a slope of -0.5. This means the method put forward by the authors is of high precision and suffers no interference. Relative to DSM3, Mg isotope composition of samples changes at 2.790‰ for δ^26Mg and 1.282‰ for δ^25Mg. 0.399‰ of δ^26Mg from CAGS1-Mg is the maximum, whereas -2.091‰ of δ^26Mg from Kanansi lake water is the minimum.