- Ki.i-1.-
+
the rapid interchange between the complexes. ci+iKi+i,i Qi+i - Qi Determination of Ferrous-Ferric Ratios. Another application of the Qi-in - Qi" ci- iKi- t,i (7) method is the determination of the Qi-1 - Qi APPLICATIONS ratio of ferrous to ferric iron. Such The method described above is of where an analysis is of interest since ferrous special value for the analysis of a solusulfate solutions are widely used as Qi = ( 1 - Ki.i-1 - Ki.i+l)(l - Pi) a number of so~uks tion radiation dosimeters (1). The amount which fulfill the following conditions: Thus, of trivalent iron formed, which .is proAll solutes must contain the same portional to the radiation dose,' has to (cI), = (yi)n p i = xi (8) tracer isotope, which must be in radiobe measured. In this case the comactive equilibrium with respect to the ponents can be regarded as independent i i different solutes. of each other. Furthermore, many A solvent must be found, into which with methods of analysis-for instance, titrations and spectrophotometric methods-are available, a t least if the amount of iron is not too small. NeverQi Qi Qi theless, the method of repeated exci p c l K , . c l c i ~ i Ki.i+, + ~ ci-ipi Ki-1.i Qi+i - Qi Qi-1 - Qi Qci- Q i tractions might be used to advantage, since it is accurate and very simple to the compounds are extractable, even carry out ( 5 to 6 extractions.are suffiEvidently this case can be treated as after the addition of some reagent, with cient). The method is also independent before. Log (C& is plotted us. n, different partition coefficients. of the amount of iron, which can be and all values of Qiand Xi are deterThe components must depend on each extremely small. A suitable extraction mined by a subtraction procedure. other, but the reaction rates should be system would be to extract isoamyl Now, for a determination of partition neither too great nor too small. A alcohol containing thiocyanate with coefficients and concentrations from suitable range of rate constants might 0.8N sulfuric acid (the iron originally these data, the rate constants for the be from about 0.01 to 0.2 minute-'. contained in the first water phase) Higher values of the rate constants mean interchange between the solutes have experimental difEculties because the using Fe59as tracer. It is important to to be determined. If they are known, experiment has to be carried out very keep the thiocyanate concentration in Qi will give the partition coefficients fast. If the rate constants are lower, the water phases constant and in directly. The concentrations are then other separation methods can usually equilibrium with the thiocyanate conobtained by solving a system of linear be applied. The method of repeated centration in the organic phase since equations. The rate constants are extractions is still of great value, howthe partition coefficients depend strongly determined from kinetic experiments. ever, because it is simple to carry out, on the thiocyanate concentration. They have to be evaluated by successive and furthermore, because other chemical The method should be useful also for approximations. A convenient starting separation methods might introduce other branches of chemistry-eg., for harmful changes into the system. point might be to assume all components the analysis of a mixture of labeled to be independent and to calculate the Nitrosylruthenium Complexes. Niorganic compounds. concentrations as functions of time trosylruthenium forms several difusing this assumption. The rate conLITERATURE CITED ferent nitrato complexes in nitric acid stants are then calculated from the time(1) Bildstein, H., Atompuzis 4, 164 solutions (2'). Since these complexes dependence of the concentrations. These (1958). interchange with reaction half-times rate constants are used for the deter(2) Fletcher, J. M., Brown, P. G. M., Gardner, E. R., Hard C . J., Wain, of the order of 10 minutes or longer, mination of effective rate constants to A. G., Woodhead, J. J : Inorg. & they can conveniently be analyzed by be introduced into Qiand X,. The conNuclear Chern. 12,.154 (1959). the method of repeated extractions centrations and rate constants are then (3) Rudstam, G., Acta Ghem. Scund. 13, (9). A suitable solvent is tributyl re-evaluated until further approxima1481 (1959). phosphate. In this case other methtions do not change the results. RECEIVED June 16, 1960, Accepted Auiust 23, 1960. ods of analysis are difficult owing to It is not always possible to neglect (Yi). = ci (1
Ki.i+i)Qi"-' Qi+l" - Qi +
terms containing two (or more) rate constants as factors. A calculation to the second approximation is given in a previous paper (3).
c
~
~
~
E.,
Colorimetric Determination of Chlorates in Well Waters PAUL URONE and ERIK BONDE Department of Chemistry, University of Colorado, Boulder, Colo.
b Chlorates react with o-tolidine in strong hydrochloric acid solutions to give a sensitive colorimetric method for their determination in waters used for drinking or irrigation purposes. The method is simple, rapid, and relatively free from interferences. Using a 4ml. sample, the proposed method quantitatively measures from 0.05 to 10 p.p.m. chlorate ion with an average deviation of 0.02 p.p.m. Higher or lower concentrations may be measured 1666
a
ANALYllCAL CHEMISTRY
with smaller samples or longer path length spectrophotometer cells. Except for very low concentrations, Beer's law is followed closely. Quantitative measurements are made with a spectrophotometer, but visual comparisons may be made in the absence of strongly interfering colors. Nitrite ion interferes while residual chlorine and ferric ion give additive effects that can be corrected. Chlorides and nitrates do not interfere.
D
a recent study, it became necessary to measure small concentrations of chlorate ion in well waters used for irrigation and household purposes. The commonly used iodide-thiosulfate method (1, 5) waa not sensitive enough to apply it directly to the waters. Concentrating the samples by boiling involved the possible high temperature reduction of chlorate by trace impurities. At first, a modification of the polarographic URING
concentration, and add d o u b l a e d water to make a total of 4.0 ml. of test solution.
CONCENTRATED HYDROCHLORIC Acm.
00
I
I
350
400
I *so
I
Sa0
WaVELENGTII,#w
Figure 1. Spectrophotometric curves of colors developed using o-tolidinechlorate rnefhod a. b. c.
0.5 p.p.m. CIOI- (asNaCIO1) 25 p.p.m. Fa+' (as FeClJ 25 p.p.m. Fef' plus 0.5 p.p.m.
CIOa-
method of Meites and Hofsass (7) was used. Although this.gave satisfactory results, the modification was somewhat time consuming and required a relatively high degree of laboratory skill. Because chlorate ion reacts with chloride ion in a highly acidic solution to yield chlorine (4, 8),it was felt that the *tolidine method used by many water and sewage laboratories to measure chlorine colorimetrically in water (2)could be adapted for use in measuring small concentrations of chlorate ion in water. Some preliminary studies were undertaken. The results were satisfactory, and, after a more detailed study, the method was developed.
Analytical reagent quality. Procedure. T o freshly cleaned and rinsed 20 x 150 mm. test tubes, add 4.0 ml. of sample and 1.0 ml. of 0tolidine solution in that order and mix. The solution should be approximately water white a t this point (see Note 1). Rapidly and with shaking in a stirring motion, add 5.0 ml. of concentrated hydrochloric acid. A yellow color develops if chlorate ion i s present. After a &minute period and within 1/2 hour measure the absorbance of the solution with a spectrophotometer a t 448 and 490 m p (see Note 2) for low and high chlorate ion concentrations, respectively. If chlorate concentrations are too high, use smaller volumes of sample. Use doubledistilled water to bring the volume of the sample to 4.0 ml. I n the absence of interfering colors, visual comparison with suitably prepared comparison standards may be
used.
NOTE 1. Solutions may be colored at this point for a number of reasons. Each calls for its own corrective measures. The sample water may be colored as received. This may be the result of any number of coloring agents, organic matter, femc ion, etc. Filtering may help, and, if necessary, a comparison blank made from the original water plus all reagents except 0-tolidine may also be used. Ferric ion does not give a strong color with 0-tolidine (Figure 1). At 448 ma 1 p.p.m. of ferric ion has the same absorption as 0.008 p.p.m. of chlorate ion. If the ferric ion concentration is EXPERIMENTAL known, a simple correction factor can be applied. Apparatus. Satisfactory results Chlorine, or strong oxidizing agents were obtained with the Bausch and which release chlorine, would develop Lomb Spectronic 20, the Beckman ayellow color a t this point. StoichioDU, and the Cary Model 14 spectrometrically, 1 p.p.m. of chlorine should photometers. Reagents. 0-TOLIDINESOLUTION. have the same effect as 0.4 p.p.m. of chlorate ion. However, Table I shows Dissolve 0.400 gram of o-tolidine that 1'p.p.m. of chlorine has the same dihydrochloride (Eastman Kodak Co. effect as 0.55 p.p.m. under the condiNo. 250) in 700 ml. of double-distilled water. Then add 250 ml. of concentrated hydrochloric acid slowly and with stirring, let the solution cool t o room temperature, and make up t o 1 liter with double-distill2d water. The Table 1. Effects of Various Substances solution should be clear and slightly Chlorate Ion, yellow to colorless. Store in a plastic or Amount, P.P.M. dark bottle a t room temperature. Substance P.P.M. Taken Found C H ~ R A TSET m m s . Stock SoluNO*31 1.56 1.53 tion. Dissolve 1.2755 grams of reagent 1.50 1.56 grade sodium chlorate in 1 liter of 312 156 1.56 1.63 double distilled water. One milliliter NOI12 5 5.00 4.70 of this solution equals 1 mg. of chlorate 25 0.63 0.40 ion. Working Solutions. a. Just be88 0.63 0.57 fore use, dilute 10.0 ml. of stock solution to 100 ml. in a volumetric flask and c1125 0.63 0.62 2-50 0.63 0.60 mix thoroughly. b. Dilute 5.0 ml. of 875 0.63 0.62 working solution a to 100 ml. in a volumetric k k and mix thoroughly. One c12 0.40 0.60 0.86 milliliter of this latter solution equals 1.60 0.60 1.48 1.60 0.00 0.87 0.005 mg. of chlorate ion. If nechary, further dilutions of a or b may be made. Fe+J 25 0.63 0.85 Add proper aliquots of these solutions 31 1.56 1.73 62 1.56 1.80 to test tubes with proper micro techniques to give the desired chlorate io9 -
I 4 0 a L ~ l
Figure 2. Standardization curves for o-tdidine-chkxate method Measured with 10.0-mm. cdb on Cary Model 14 spectrophotometer
tions of the described method. Corrective factors can be appropriately applied. Nitrite ion, if present, forms a yellow color with &tolidine a t this point. The yellow color is due to the formation of the diaeo derivative of 0-tolidine. This is unstable in acidic solutions and decomposes to become colorless in l/* to 1 hour. Upon the addition of the reagents several competing reactions occur. These include diazotization, decomposition of the diazotized product, and reduction of the chlorate by unreacted nitrite. Fkmlts will be variable, depending on the time between addition of reagents and spectrophotometric measurements. The nitrite effect may be eliminated with sodium azide in weakly acidic solution (6). NOTE2. APELA "Standard Methods" (8) prescribes spectrophotometric settings a t 435 and 490 mp for the recommended method for determining chlorine in water. The absorption maximum of the o-tolidine color in this method undergoes a bathochromic shift to 448 (Figure 1) due to the higher ionic concentrations involved. The absorption curve a t 490 m p is rising aharply, and, as a consequence, the wave length setting and slit width must be carefully controlled in this region. DISCUSSION
Beer's law is followed rather closely (figure 2) except for very low concentrations. The slight curvature observed is possibly due to trace reducing agents remaining in the 0-tolidine solution or the concentrated hydrochloric acid. Straight line extrapolation indicates that this effect is of the order of 0.1 p.p.m. For accurate work in the low concentration ranges, careful treatment of these reagents with chlorate to a zero chlorate demand point as is done in chlorine determinations (3)would be in order. The sensitivity of the method as given is about 0.05 p.p.m. of chlorate. This is equivalent to 0.02 pg. of chlorate per ml. of final solution. A 0.1-p.p.m. chlorate solution gives an absorbance of 0.021 a t 448 mp with a lGmm. cell. The sensitivity can be increased by VOL 32, NO. 12, NOVEMBER 1960
0
1667
30 NORMALITY HCI
Figure 3. Wed of acidity on color development of o-tolidine-chlorate solutions
Table II. Comparison of Colorimetric and Polarographic Analyses 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 . A m . C h m . SOC.61,265 (1939). (6) Hovorka, V., Holabeoker, Z., Collec-
tion 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
