or manometric measurements of the Table IV.
Additive Na2COs Graphite
co*.
Analysis of Sodium with Added Carbon Micrograms of carbon
Sodium wt., g. 0 . 294a 0.309" 0.313" 0.230b
In sodium 9 10
10 31 33 31
In
additive 23 23 29
Total 32 33 39 105 72
74
39 0.224b 119 150 4 Carbon content 32 p.p.m. (av. of previous analyses). Carbon content 137 p.p.m. (av. of previous analyses). 0.244b
To establish the precision of the method and to determine the carbon level in a sodium sample to be used for standard additions, replicates were burned with the results shown in Table 11. The relative standard deviation of this series with approximately 0.5-gram samples was *19%,. To establish the accuracy of the method, a series of tests was conducted on carbon standards alone (Table 111) and then in the presence of the sodium on which the carbon level had been obtained (Table IV). Quantitative recovery of the added carbon was obtained. Sodium carbonate, graphite, and "Leco" carbon standards were employed. The latter may be obtained from K&L Scientific Co., Columbus, Ohio. I n view of the good accuracy demonstrated, it is possible that the
Found 36 33 42
103 77 155
Dev. +4
0
+3 -2 +5
s5
precision observed reflects to some degree the fact that impurities are not necessarily uniformly distributed in sodium. Larger samples might improve precision but would be more difficult to handle in the combustion. It is felt that the precision and accuracy obtained are quite satisfactory for monitoring the carbon level in molten sodium systems. -4dry combustion method for carbon analysis was chosen for this study because it provides a simple and accurate method for the determination of total carbon. Low blanks are obtained and it provides, via gas chromatography, a positive identification of the COz. Oxides of nitrogen are observed in the gas chromatogram but are resolved by the silica gel column. They would be a potential interference in conductometric
Stoffer and Phillips ( 3 ) pointed out that the dissociation of sodium carbonate begins around 700" C.; however, the pressure does not exceed l mm. of mercury until about 950" C. It was found in the recovery experiments that a temperature of 1100" C. is needed for complete recovery of carbon from sodium carbonate in the time allotted for this analysis. Combustion tube mortality is lower when quartz protective sleeves are employed. A new quartz sleeve and boat are used with each analysis since the old one is destroyed by the hot sodium oxide. It has been found useful to rinse the combustion tube periodically with 1:l HC1 solution and then with distilled water to remove any sodium oxide that has accumulated during combustion of the samples. LITERATURE CITED
(1) Ayers, Cora W., Belcher, R., West, T. S., J. Chem. SOC. (London), 1959
2582. (2) Pepkowitz, Leonard P., Porter, John T., AYAL.CHEM.28, 1606 (1956). (3) Stoffer, K. G., Phillips, J. H., Zbid., 27, 773 (1955).
(4)Vogel, Alfred M., Quattrone, Joseph J., Zbid., 32, 1754 (1960).
RECEIVEDfor review M a y 16, 1963. Accepted September 30, 1963. Division of Analytical Chemistry, 145th Meeting, ACS, S e w York, N. Y., September 1963.
Apparent Conformational Changes of Liquid Phases in Gas Liquid Chromatography CHIADAO CHEN and DIONE GACKE Department o f Biochemisfry, Northwestern University Medical School, Chicago 7 7, 111. The brief heating at high temperature (-200" C.) of diatomite packed columns coated with certain liquids just before use at low temperature (
