Development of an analytical technique for isotopic ratio of carbon and oxygen in carbonates using a laser-probe method.

该项目的目标是开发一种方法，在显微镜观察过程中分析任何选定的碳酸盐样品点的碳和氧同位素比率。为接近这一目标，开展了以下工作。该真空线的建造是为了在真空下用Nd-YAG激光点火样品，并对产生的二氧化碳进行净化。样品室是用石英和铝制成的，用来存放要烧制的样品。尝试将碳酸盐粉末和氯化钠粉末混合压制成固体标准碳酸盐样品，其同位素组成已知。该方法制得的碳酸盐颗粒强度较高，但在激光的照射下，除了二氧化碳外，还产生了未知气体，影响了后续的同位素分析。以碳酸钙为原料，研制了一种新的标准微丸。这是非常易碎的，但被证明有足够的强度在激光发射中幸存下来。激光脉冲间隔越小，二氧化碳的产率越高，说明样品中的二氧化碳和氧化钙发生了复合反应。功率越大，产量越高，但功率越大，增产幅度越小。碳、氧同位素比值随产量的变化而变化，接近恒定值，与常规方法测得的预定值接近，但仍相差不大。在常规方法中，氧同位素比值不需要施加偏压。重现性差于常规方法，重现性仅为0.5permil，取得了满意的结果，表明该方法具有较好的应用前景。

The objective of this project is to develop a method to analyze the isotopic ratio of carbon and oxygen in any selected spot of carbonate samples during microscopic observation. Following works were carried out to approach the objective.1. The vacuum line was constructed to fire sample with an Nd-YAG laser under vacuum and to purify produced carbon dioxide. The sample chamber, to hold samples to be fired, was made using quartz and aluminum.2. A solid standard carbonate sample, whose isotopic composition was known, was attempted to prepare by pressing the mixture of carbonate powder and sodium chloride powder. This procedure produced the carbonate pellets with good strength, but by the radiation of the laser, unknown gases were generated besides carbon dioxide, which impaired the following isotopic analysis.3. A new standard pellet was made using calcium carbonate only. This was very brittle, but was proved to have strength just enough to survive the laser firing.4. The yield of carbon dioxide increased with smaller interval of laser pulses, implied the re-combination of carbon dioxide with calcium oxide in the fired sample. The higher power tended to give the greater yield, but the increasing rate became the smaller with the higher power.5. The isotopic ratio of carbon and oxygen varied with the yields, approaching constant ratios, which are fairy closed to the pre-determined values obtained by the conventional method, but are still different by a few permil. The bias was not needed to apply in the oxygen isotopic ratio, which was necessary in the conventional method. The reproducibility is as much as 0.5 permil, which was poorer than the conventional method.Fairy satisfactory results were obtained to show that the new method was promising.