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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: δ~(18)O_(MCO_3)=δ~(18)O_(M-CO_2)+(△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CO_2,情况就较为复杂。如果标样和样品两者有一个为非碳酸盐CO_2,则可按下式校正δ~(18)O_(X-PDB(CaCO_3))=(α一1)×10~3+αδ~(18)O_(X-PDB(CO_2))如果标样和样品均为非碳酸盐或全为碳酸盐CO_2,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~(13)C/~(12)C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。
In carbonate carbon and oxygen isotope analysis, isotope kinetic fractionation occurs due to the release of carbon dioxide by decomposition of carbonate with 100% phosphoric acid and retention of the other oxygen in carbonate by the so-called 2/3 oxygen and total oxygen Isotopic fractionation between. This fractionation is different for different reaction temperatures and different minerals and must be corrected. In the actual calibration often used a simple approximation algorithm: δ ~ (18) O_ (MCO_3) = δ ~ (18) O_ (M-CO_2) + (△ l- △ M) This correction is actually 2 / 3 oxygen isotopes converted into oxygen isotope values. In mass spectrometry, the standard used and the sample to be measured are not necessarily all carbonate CO 2, the situation is more complicated. If there is a non-carbonate CO_2 between the standard sample and the sample, we can correct δ ~ (18) O_ (X-PDB (CaCO_3)) = (α_1) × 10 ~ 3 + αδ ~ 18) O_ (X-PDB (CO_2)) If both the standard and the sample are non-carbonates or all carbonates CO_2, they can be directly measured without conversion. Mass spectrometry measures molecular ion ratios, such as 45/44 rather than ~ (13) C / ~ (12) C, so the effect of other isotopes must be deducted. The calibration formula depends on the mass spectrometer receiver type and the standard used. In practice, different mass spectrometry methods can also be used according to the situation.