Table 111.
Relative Error Associated with Various Matrices
Relative error, yo 0-5
6-10
11-15
16-20
21-25
>25
Fez03 NaCl ZnO PbOi NiO
HaBOa MgO coo
SnO (NHa)zHPO4
CUO
Si02 CrzOa
AlzOa
The addition of graphite powder t o the fused sample was necessary to improve sparking characteristics. Europium oxide was chosen as an internal standard chiefly because it was not likely to be encountered in samples. Initially, samples were fused with K2S207 in platinum crucibles over a burner. It soon became evident that while replicate analysis of a given fusion showed good reproducibility, analysis of the same sample over separate fusions varied widely. A study of the effect of fusion temperature, from 400' to 1000' C., on relative intensity ratios of a few elements to Eu verified this fluctuation. T o counteract this effect, all samples were fused for 30 minutes in a muffle furnace a t 650' C. This temperature was chosen because it was on the flat portion of the curve for most elements tested and because samples fused a t this temperature could be removed easily from the crucible. A precision and accuracy study was made using NBS sample 168, a high
temperature alloy. The sample was put into solution with aqua regia, evaporated several times with HNOI and ignited at 800' C. The sample was ground and portions taken through the procedure each day for 10 days. The results are shown in Table 11. These indicate that a relative error of less than &20% and a relative standard deviation of better than &lo% was obtained. The same type of study was also performed on a limestone, NBS l a , and an aluminum alloy, XBS 86C. The results for the limestone were comparable to that for the high temperature alloy. However, the aluminum alloy showed definite evidence of a matrix effect. On the basis of this a more extensive matrix effect investigation was indicated. Accordingly, synthetic samples containing Al, Be, Co, Cr, Fe, Mg, Mn, Mo, Ni, Pb, Si, Sn, Ti, V, and Zn were prepared at the 1% level in each of 14 representative matrices. They were then analyzed by the procedure. The mean value of the concentration of the 15 ele-
ments in each matrix was calculated to detect any overall bias. These results are summarized in Table 111. This study indicates that for some matrices, such as Fe203, ZnO, PbOs, NaCl, and K O , the standard working curves give average accuracies approaching experimental error. It is possible that, by increasing the amount of potassium pyrosulfate, matrix effects may be reduced further with a concomitant sacrifice of sensitivity. Special standards can be prepared when necessary for samples containing matrices Ivhich experience s h o m give large biases. LITERATURE CITED
(1) A.S.T.M., Philadelphia, "Methods
fy
Emission Spectrochemical Analyses,
1957. (2) Danielson, A., Lundgren, F., Sundkvist, G., Spectrochim. Acta 15, 22 11959).
(3j-Feldman, C., Ellenburg, J., ANAL. CHEM.27, 1714 (1959). (4) Hargis, D. C., Smith, G. W.,Ibid., 36, 824 (1964). ( 5 ) Neuhaus, W. R., A p p l . Spectry. 15, 54 (1961). ( 6 ) Wang, %I.S., Ibid., 17, 76 (1963).
~ I A U R IG. C ATWELL E GERALD S. GOLDEN Research Laboratories United Aircraft Corp. East Hartford, Conn.
PRESENTED at Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1965.
Liquid-Solid and Capillary Gas-Liquid Chromatography of Internal Olefin Isomers SIR: The composition of a high molecular weight internal olefin (Clz t o C,) such as that produced by isomerization of a 1-olefin is difficult to determine because of the multiplicity of positional and geometrical isomers present. The literature is almost completely void of analytical methods for such samples. Blouri and coworkers (2) analyzed 1-, 2-, 3-, and 4-decenes by capillary gas chromatography but no resolution of cis and trans isomers was reported. Using a packed p,p'-oxydipropionitrile column, Asinger et al. (1) obtained separation of the cis and trans isomers of a given positional undecene, but only partial separation of all the possible isomers when present in a complex mixture. S o references to separations of higher molecular weight olefin isomers could be found. Gas chromatography with polyester partition liquids (particularly ethylene glycol adipate) in '/(-inch packed columns has been successful in this laboratory in determining the cis-2 and trans-2 isomers in a complex mixture of internal 1598
ANALYTICAL CHEMISTRY
olefins, but resolution of other isomers could not be obtained (6). Oxidative cleavage of the olefin to carboxylic acids or other fragments with subsequent gas chromatographic analysis of the fragments accurately determines the bond position but gives no information as to the geometry of these positions. I n the present work, high molecular weight internal olefins produced by the isomerization of 1-olefins (of a single carbon number) were first separated into cis and trans fractions by liquidsolid chromatography on alumina impregnated with silver nitrate. The fractions were then analyzed by capillary gas chromatography t o determine the bond position. Oxidative cleavage with periodate-permanganate was performed on the same fractions to provide reference analyses. EXPERIMENTAL
Liquid-Solid Chromatography. T h e technique used here was a modification of that reported by De Vries (3, 4) for fatty acid methyl esters. Alumina
impregnated with 30%, silver nitrate was used in 39- X 2-em. columns containing 130 to 135 grams of adsorbent. Pentane was used to elute the paraffins; 99: 1 pentane-ethyl ether to elute the trans olefins; and 97 :3 pentane-ethyl ether to elute the cis olefins. Small amounts of oxygenated products in the original olefin are eluted with eluants of much higher ethyl ether content. For dodecene the number of individual fractions collected was kept to a minimum and the solvent was removed on a Rinco evaporator to reduce evaporation losses. The adsorbent mas prepared by rotating on a Rinco evaporator a slurry consisting of 200 grams of aluminum oxide Woelm (neutral, activity grade I) and a solution of 100 grams of silver nitrate in 180 ml. of water. The flask, a 2000ml. 24/40 Morton stirring flask (Corning S o . 94200), was rotated in a 50' to 60" C. water bath under 100 mm. of pressure until no further water was being removed and the material appeared caked. After drying overnight in a 180" C. forced-draft oven and blending on a Patterson-Kelley yoke type blender, the alumina contains 18
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.
0.4
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 4. cis-5 5. cis-4 6. cis-3 7. cis-2
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.
+ 1-olefin
L. R. CHAPMAN D. F. KUEYMEL M a m i 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. T o 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. T h e 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 p a t h 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 b y 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.
