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

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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.