【摘要】 碳酸盐岩碳氧同位素分析中,由于用100%磷酸分解碳酸盐放出二氧化碳,碳酸根中另一个氧留在水中,这就产生了同位素动力学分馏,即所谓2/3氧和全氧之间的同位素分馏。这种分馏对于不同反应温度和不同矿物是不同的,因此必须进行校正。在实际校正时常用一种简便的近似算法: δ¹⁸O_MCO3=δ¹⁸O_M-CO2+（△l-△M）这种校正实际上是将2/3氧同位素换算成全氧的同位素值。在质谱测量中,所使用的标样和待测的样品不一定全是碳酸盐CO₂,情况就较为复杂。如果标样和样品两者有一个为非碳酸盐CO₂,则可按下式校正δ¹⁸O_{X-PDB（CaCO3）}=（α一1）×10³+αδ¹⁸O_{X-PDB（CO2）}如果标样和样品均为非碳酸盐或全为碳酸盐CO₂,则无需进行换算就可直接测量。质谱测定中测量的是分子离子比,如45/44,而不是¹³C/¹²C之比,因此必须扣除其他同位素的影响。校正公式决定于质谱仪接收器类型和所用的标准。实际工作中还可根据情况采用不同的质谱测量方法。更多还原

【Abstract】 In the carbon or oxygen isotope analyses of carbonate rocks, when thephosphoric acid （100%） is used to decompose the rocks and release CO₂, thereis one oxygne atom to be left from carbonate root and it will be transfered towater, this process is called as "mechanical isotopic fractionation" i. e. thefrationation between whole oxygen and 2/3 oxygen. It is necessary to correct this frationation effects according to concretecouditions because the fractionation processes differ under different reactiontemperatures and in different minerals. Usually using a simple approximatecalculation to realize the corrections: δ¹⁸O_M-CO3=δ¹⁰O_M-CO2+（Δ₁-Δ_M）this processing is, actually, to convert 2/3 oxygen isotope into whole oxygenisotope. If not all the standard samples and those to be examined are carbonaterocks, a complex aspect appears in mass spectrometric analyses. If only one ofthe samples （the standard sample or the sample to be examined） is not carbo-nate rock, the correction can be realized by the following equation: δ¹⁸O_{X-PDB（CaCO3）}=（α-1）×10³+α¹⁸δO_{X-PDB（CO2）}If both of the samples mentioned above are carbonate rocks or not, we canexamine directly without any correction. In additin, the influences from other isotope fractionations should be eli-minate because only the molecular ion ratio such as 45/44 is measured but no¹²C/¹³C. The correction equation as above depond on the kind of receive plateof mass spectrometer and the standard sample. Therefore, we have to selectedifferent mass spectrometric method according to the different eases in practice.更多还原