D/H Ratio Determination Of Cellulose Nitrate From Tree Rings

Scientists have already handled the determining of hydrogen isotope composition from tree ring cellulose nitrate since 1970s, but due to analytical problems, in China, the research in this field is at the starting point. The elemental zinc reduction method was utilized to analyze the hydrogen isotope composition of water, and the sealed-tube high temperature combustion method coupled with the zinc reduction method was used for the analysis of hydrogen isotope composition of organic matter and cellulose nitrate. The following conclusions are draw from the results:CD The ratio of cellulose nitrate to zinc must be fixed, e.g., the ratio of water produced by cellulose nitrate combustion to zinc should be not less than 2 μL (ca, 112 μ mole) of water to 100 mg zinc. CH7 samples were loaded into the silicate reaction tubes based on two kinds of ratios, 1 and 0.7. The results showed that samples with ratio of 0.7 are enriched (-95.6‰), whereas the results (-100.2‰) of samples with ratio of 1 are nearly equals to the given value (-100.3‰) by the IAEA.(2) Long time heating (1 hour at 80℃) in a vacuum line is necessary for removing the absorbed moisture in cellulose nitrate. The analytical precision is quite good (1.6 ‰) in the last day for determining the D/H ratios tree ring cellulose nitrate LN-31. Prolonging the heating time from 45 min to 75 min is the main reason.(3) Addition of copper makes no effects on the hydrogen isotope analytical precision. Except for the addition of copper or not, the other experimental conditions such as sample amount, water/ zinc ratio, heating time are the same, but the experiment results of CH7-5 and CH7-3 (31-08), CH7-16 and CH7-18 (8-09), CN-1 and CN-2 (31-08), are very similar. Therefore, these comparing results show that copper does not improve the analytical precision.(4) Water produced by cellulose nitrate combustion should be transferred as soon as possible into the zinc tubes and sealed. Long time contact of water, CO₂ and copper oxide may lead to formation of water-containing minerals, which will significantly alter the hydrogen isotope composition of water. Sample CN-3 is enriched by 14‰ compared to CN-1 and CN-2 just because of the transfer time was prolonged for two days.The analytical precision of the determination of the hydrogen composition of tree ring cellulose nitrate was 2.2‰ for sample DN-27 and 1.6‰ for sample LN-31, which very close or even better than the accept international precision (2.0‰). Therefore, the experimental conditions of sealed-tube high temperature combustion method coupled with the zinc reduction method for the analysis of hydrogen isotope composition of organic matter and cellulose nitrate was built with the normalization of hydrogen isotope data. This thesis constitutes a technical base for the extraction of highly evolution East Asia monsoon variation information from tree ring, peat, lake sediments, paleo soils and so on, and also it provides a better platform for Chinese plant physiologist using hydrogen isotope technique to trace the plant physiology process.