made in the present work to separate the small amount of 1-olefin which remained in the isomerized product. The gas-liquid chromatographic separations of the cis and trans fractions of dodecene and octadecene are shown in Figures 2 to 5. Identifications were made on the basis of the order of elution and comparison of the area per cents with values from the oxidative cleavage of the same fractions. These comparisons are shown in Tables I and 11. The agreement is satisfactory considering the precision of the two procedures. The disadvantage of gas-liquid chromatography is the coelution of some isomers. This is not a problem except when a detailed analysis is required. The cis-3 and 1-olefin can be partially
separated on a butanediol succinate coated capillary column. LITERATURE CITED
(1) Asinger, F., Fell, B., Steffan, G., Chem. Ber. 97, 1555 (1964). (2) Blouri, B., Fauvet, J.-E., Rumpf, P., Bull. Soc. Chim. France 1963. D. 1855.
(3) DeVries, B., Chem. Ind. ’(London) 40
30
35
TIME /MINUTES
Figure 5. Gas-liquid graphic separation of isomers, cis fraction 1. 2. 3.
chromatooctadecene
cis-8 and cis-9
cis-7
cis-6 cis-5 5. cis-4 6. cis-3 7. cis-2
4.
+ 1-olefin
1962, p. 1049. (4) DeVries, B., J . Am. Soc. 40, 184 (1963).
Oil Chemists’
( 6 ) Kuemmel, D. F., ANAL. CHEM.36, 426 (1964). (. 5,) Kuemmel. D. F.. Miami T’allev Laboratories, The Proctor & Gam6le Co., Cincinnati, Ohio, unpublished data, 1961.
L. R. CHAPMAN D. F. KUEYMEL Mami Valley Laboratories The Procter & Gamble Co. Cincinnati, Ohio
Ultraviolet Spectrophotometric Determination of Mixtures of Vanadium(1V) and Vanadium(V) SIR: I n a study of the reactions of vanadium(V) that have occurred in molten LiCl-KC1 eutectic the need arose to analyze the reaction products for vanadium(1V) and vanadiunl(V). A literature search revealed no established method for determining separately the vanadium present in both oxidation states. A fairly rapid method was needed so large numbers of samples could be processed routinely. The following method was applied only to unknown solutions of vanadium(1V) and (V) in dilute H2S04. Most standard methods for the determination of vanadium involve Oxidation or reduction of all the vanadium present to a single oxidation state before the analysis can be performed (1, 2 ) . Warren, Hazel, and McNabb (3) have shown that the spectrophotometric absorbance maximum of vanadium(V) a t 270 mp in 1W sodium hydroxide can be used to determine small amounts of vanadium. We found that vanadium (IV) exhibited the same absorbance maximum and absorptivity a t this wavelength. This allowed the quantitative determination of total vanadium without first oxidizing any vanadium(1V) present to the (V) state. The oxidation of vanadium(1V) t o vanadium(V) by titration with standard potassium permanganate solution was quantitative for determining vanadium (IV) in the presence of vanadium(V). This enabled us to determine the amount of vanadium(1V) in mixtures of vanadium(1V) and (V). Subtraction of the vanadium(1V) from the total vanadium gave the vanadium(V) content. Visual end point detection in the titration of vanadium(1V) with potassium permanganate is difficult because of the 1600
ANALYTICAL CHEMISTRY
yellow color of vanadium(V). The reaction is slow near the end point, even when the solution is heated, unless a n excess of permanganate is present. To overcome these difficulties, a spectrophotometric method was devised to detect the end point. Data for a complete determination can be obtained on a routine basis in less than 15 minutes using the following method. EXPERIMENTAL
Apparatus. The absorbance measurements were made with a PerkinElmer Model 202 dual-beam recording spectrophotometer. One-centimeter
SAMRE SOLUTION
Figure 1.
Flow system
square quartz cells were used in t h e total vanadium determinations. A specially made borosilicate glass flow cell with a 4-em. light path was used in the spectrophotometric detection of the vandium(1V) titration end points. The flow cell was a part of a flow system (Figure 1) used to eliminate sampling errors which resulted when aliquots were taken from the titration beaker for spectrophotometric measurements. Small bubbles of air in the light path of the flow cell caused erratic absorbance readings and variations of the absorbance with flow rate, These bubbles were purged from the cell by rapidly changing the flow rate a few times. The sample solution was stirred with a magnetic stirrer and circulated through the flow cell at a rate of approximately 1 liter per minute during the titration. Distilled water was used as the reference in vanadium(1V) determinations. Solutions. Standard 0.02M vanadium(1V) and vanadium(V) solutions were prepared by dissolving vanadyl sulfate, VOSOZ. 5H20, and vanadium pentoxide, VpOr, respectively, in 1.8N sulfuric acid. T h e vanadium(1V) solutions were filtered t o remove small amounts of insoluble impurities. Both vanadium solutions were standardized by titration with potassium permanganate both before and after quantitative reduction by sulfur dioxide to vanadium(1V). The vanadium(1V) solutions consumed more permanganate after the sulfur dioxide reduction than before. The analysis showed 98 i 3% VOSOl 5H20content for the vanadyl sulfate used to prepare the solution. The reducible impurity was assumed to be vanadium(V). With the same procedure, the vanadium (V) solutions were found to contain no oxidizable impurities. The analysis showed 103 =t3% Vz05 content for the vanadium pentoxide used to prepare the solutions.
Procedure. Obtain a representative sample containing vanadium(1V) and (V) and subject i t to treatment necessary to prepare a solution containing not more than 1 gram per liter total vanadium in 1.8N sulfuric acid. Substances oxidized by dilute potassium permanganate must be removed prior to analysis. Chloride ion, for example, may be precipitated from the sample solution as silver chloride. Transfer a 10-ml. aliquot of the sample solution to a 400-ml. beaker and add 300 ml. of 1.8,V sulfuric acid. Titrate a t 45-55’ C. with standardized 0.015~V potassium permanganate using the flow system described in Figure 1. Stop 0.5 to 1.0 ml. beyond the estimated end point, stir for 2 minutes, measure, and record the absorbance of the permanganate ion at 525 mp. Then add successive 0.5-ml. increments of permanganate, determining the absorbance a t 525 mp after each addition. Plot the absorbance us. the volume of permanganate added and extrapolate to zero absorbance to obtain the volume of permanganate consumed. Calculate the vanadium(1V) content of the sample. Transfer a 0.5-ml. aliquot of the sample solution containing vanadium (IV) and (V) to a 100-ml. volumetric flask and dilute to the mark with 5N sodium hydroxide. Measure the absorbance of this solution a t 270 mp and calculate the total vanadium content. Calculate the amount of vanadium(V) from the difference between the results of the total vanadium and vanadium(1V) determinations. RESULTS AND DISCUSSION
The permanganate absorbance peak a t 525 m p can be detected photometrically with no interference from vanadium when the sample concentrations are less than 0.05 mg. per ml. of total vanadium. The manganese(I1) produced by the reaction of the permanganate with vanadium(1V) does not absorb a t 525 mp. The absorbance of other impurities a t the end point is blanked out by using a portion of the untitrated sample solution in the reference cell. Impurities oxidized by permanganate, such as chloride ion, must
1.5
IA
-
1.3
-
1.2
-
-
1.1
as 0” 0.7 1.0
0.9
a 0.6 -
2 0.5 0
U
0.4
-
0.2
-
0.1
-
0.3
o i
I
d
250
200
Reference, 5N N a O H
-------.VanadiumIV) - Vanadium(lV) be removed by precipitation or other means prior to titration. Figure 2 is a plot of absorbance us. wavelength for various concentrations of vanadium(1V) and vanadium(V) in 5N sodium hydroxide. At low concentrations, both ions exhibit the same ultraviolet absorption spectra near 270 mp. A straight-line least squares fit of the absorbance a t 270 mp us. the concentration of vanadium in milligrams per milliliter yielded an absorptivity value of 147 ml. mg.-l cm.-l with a standard deviation of 5 ml. mg.-l cm.-’ which is within the limits of experimental error. At concentrations of total vanadium above 0.02 mg. per ml., the reaction to produce the absorbing species was not quantitative for either vanadium(1V) or (V). There was a slight dependence of the absorbance a t 270 mp on the sodium hydroxide concentration. At concentrations of sodium hydroxide greater than 6 N and
+
B C D
0.88 0.78 0.49 0.20
0.86 0.80 0.48 0.20
-.02 +.02 -.01 0.0
0.12 0.22 0.51 0.80
(MILLIMICRONS)
Figure 2. Absorbance vs. wavelength for vanadium(V) and vanadiurn(1V) a t various concentrations in 5N N a O H
Table 1. Analyses of Known Mixtures Composition of standard vanadium(1V) solution used to prepare mixtures below was: 0.98 mg./ml. V(1V) 0.02 mg./ml. V(V) = 1.00 mg./ml. total V. Composition of standard vanadium(V) solution was: 1.00 mg./ml. V( V). Vanadium(IV), mg./ml. - Vanadium(V), mg./ml. Total vanadium, mg./ml. Present Found Error Present Found Error Present Found Error
A
300 WAVELENGTH
0.16 0.20 0.49 0.81
+.04 -.02 -.02 +.01
1.00 1.00 1.00 1.00
1.02 1.00 0.97 1.01
+.02 0.0 -.03 +.01
less than 1N some deviation from the Bougert-Lambert-Beer law occurred. Samples of known mixtures of vanadium(1V) and (V) were analyzed using the above analytical procedure. Solutions of vanadium(1V) and (V), prepared and standardized as described, were mixed in definite ratios to prepare the known mixtures. The results of analysis, given in Table I, indicate that the method is accurate and precise to approximately 5’% of the total vanadium content because 3% error is involved in t.he standardization. However, the calculated value for vanadium (V) is poor when the fraction in the solution is small because this value is obtained as a difference. Table I is based on single determinations. LITERATURE CITED
(1) Furman, N. H., ed., “Scott’s Standard Methods of Chemical Analysis,” 5th ed., Vol. 1, pp. 1030-53, Van Nostrand, New York, 1938. (2) Rasmussen, S. W., Rodden, C. J.,
“The Analvtical Chemistrv of the Manhattan Project,’’ C. J.-&dden, ed.; Chap. 19, McGraw-Hill, New York, i9.w
(3) Warren, R. J., Hazel, J. F., McNabb, W. W., Anal. Chim. Acta 21,224 (1959).
CHARLES B. ROOT Electrochemistry Division U. S. Naval Ordnance Laboratory White Oak Silver Spring, Md. PERFORMED for the Bureau of Naval Weapons under Task No. NOL732/SP019.
VOL. 37, NO. 12, NOVEMBER 1965
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