30 NORMALITY HCI
Figure 3. Wed of acidity on color development of o-tolidine-chlorate solutions
Table II. Comparison of Colorimetric and PolarographicAnalyses of Various Well Waters
Well
Chlorate Found, P.P.M. Colorimetric Polarographic - . 5.7 1 .o 7.1 1 :2 0.9 11.4 1.1
4 0.5 6 2 0.8 14 1
using cells of longer light path length. The average deviation is 0.02 p.p.m. in the 0.5- to 2.5-p.p.m. range. The maximum concentration that can be measured for a 4-ml. sample is of the order of 10 p.p.m. when measured at 490 mp. When concentrations of this order or higher are encountered, only 1 or 2 ml. of sample should be used. Color development is independent of o-tolidine concentration provided that the amount of o-tolidine present is a t least six times the amount of chlorate on a weight basis. Because o-tolidine dihydrochloride is only slightly soluble in strong hydrochloric acid solutions, the concentration of the reagent as described in the method does not provide a large excess of o-tolidine.
45
60
TIME MINUTES
Figure 4. Effect of time on color development of o-tolidine-chlorate solutions
Development of color with chlorate does not noticeably occur a t acidities of less than 2N in hydrochloric acid. Figure 3 shows the maximum amount of color developed within a %hour period a t various acid strengths. From 3 to 6N the color development is incomplete and slow. At normalities above 6, color development is reasonably rapid. The described method gives a final solution which is approximately 6.3N. Figure 4 shows the variation of color absorptivity with time under the conditions of the method. Table I gives quantitative data on interferences from various substances in the forms of their sodium or chloride salts. Essentially, chloride and nitrate ions do not interfere. Ferric ion and chlorine have additive effects which can be corrected. Nitrite ion forms a yellow diazo compound with o-tolidine giving an additive effect. Yet, in acid solutions, this compound decomposes somewhat slowly. Unreacted nitrite reduces chlorate, resulting in an over-all lowering of the chlorate results. Other colored, oxidizing, or reducing agents bring about the same general effects (9). Table I1 lists some actual analyses of representative well waters by both the outlined method and by the mod-
ification of the Meites and Hofsass polarographic method (7). The well waters were of highly varying composition, originating from wells of a few feet to more than 100 feet in depth. In spite of this, the results are reasonably comparable. The reliability of the polarographic method was not better than *l p.p.m. because of a varying blank. LITERATURE CITED
(1) Am. Pub. Health Assoc., Am. Water
Works Assoc., Fed. of Sewage and In$; Wastes Assoc., “Standard Methods, 10th ed., p. 65, Waverly Press, Inc., Baltimore, Md., 1958. (2) Ibid., p. 66.
(3) Ibid., p. 68. (4) Bray, W., Z . amrg. Chem. 48, 217 (1906); 2.phys. Chem. 54,569 (1906). (5) Hallinan, F. J., Thompson, W. R., J . Am. C h m . SOC.61,265 (1939). (6) Hovorka, V., Holabeoker, Z., Collection Czechoslov. Chem. Communs. 14, 490 (1949). (7) Meites, L., Hofsass, H., ANAL.CHEM. 31, 119 (1959). (8) Mellor, J. W., “A Comprehensive
Treatise on Inorganic and Theoretical Chemistry,” Vol. 11, p. 313, Longmans, Green, and Co., London, 1922.
RECEIVED for review February 15, 1960. Accepted June 27, 1960. This study was supported in part by a research g a n t from t h e U. S. Army Chemical Corps.
Determination of Aldehydes from Hemiacetal Formation J. S. FORRESTER ESSO Research laboratories, ESSOStandard, Humble Oil & Refining Co., Baton Rouge, l o . The temperature-sensitive equilibrium reaction between aldehydes and
1668
ANALYTICAL CHEMISTRY
can serve as a useful analytical tool. Detection of carbonyl compounds in
RIGACTION of carbonyl comDounds to form hemiacetals has
T
HE
b Figure 2. Equilibrium constant, K, for formation of CIS hemiacetal plotted against 1 / T
The extent of hemiacetal formation was reversibly t e m p e r a t d e p e n d e n t . While at room temperature, a C ~ O aliphatic aldehyde is approximately 50% associated as the hemiacetal; an increase in temperature r e v e m the reaction and increases the aldehyde concentration. This provides a means of differentiating the carbonyl compound in the presence of interfering background absorption. 0.2 Heat of Reaction. To estimate the heat of reaction, the equilibrium Figure 3. constant 0 7
CALUDIlL
