The enrichment of water in l8O leads to the enrichment in deuterium as well. However, there are quite a number of experiments for which H,180 with natural deuterium abundance is needed since the isotope effect of deuterium exceeding that of l80 by an order of magnitude may present considerable inconvenience. To eliminate this disturbing effect the water must be "normalized".
Normalization by the techniques reported so far, such as isotopic exchange with H,, H,S, NH, by catalysis; electrolysis, requires operations of more than one step and an expensive apparatus. Thus these techniques are hardly practicable for small samples, except the method which involves an alternate oxidation and reduction on iron catalyst (l),
Considering that a gas-liquid chromatographic column has already been successfully applied for isotopic exchange by several authors ('4 sp 4 9 5), this method was chosen for varying the deuterium concentration of '*O enriched water samples while the l 8 0 concentration remains unchanged.
The experiments were performed on U-shaped glass columns, 2 m in length and 20 mm in diameter. The column was packed with 25% diglycerol (B. D. H. for gas chromatography) on celite. I S 0 enriched water samples of 0.3 ml were injected into the column heated to 95OC. The fiow rate of the purified nitrogen carrier gas was set to get a 30-40 min. retention time. It was found that up to the exchange of 80% of the exchangeable hydrogen atoms of digiycerol with deuterium, the deuterium content of the water samples did not exceed the natural isotopic abundance. The concentrations of D and lSO were determined in the normalized samples with the use of mass spectrometer, type MI-] 305. The column was regenerated and stabilized as soon as a sample with deuterium content was observed at its outlet. An example of the isotopic analysis of a typical normalization process is the following. Before the treatment the D-, and I6O-content of a water sample was 7.0 & 0.1 at%, and 70 & 1.3 at%, respectively; after the treatment 0.02 & 0.001 at%, and 70 & 1.3 at"/,, respectively. There was neither l8O isotopic dilution, nor any "memory" in the column due to the exchange.
The advantages of this method over the earlier techniques can be summarized as follows. Normalized H,lsO samples of high chemical purity can be obtained from l80 enriched water at any concentration of deuterium.