Mixture 3. This mixture was composed of t h e kinds and relative amounts of monocarbonyls identified in t h e steam distillate of a n unheated rancid pork fat ( 3 ) . Table I11 shows the absorbance values of the standard solutions used in preparing the mixture. The solution analyzed was made up b y combining 1.00 ml. of each of the standard solutions. Data represent amounts found in 14.00 ml. of mixture. I n general, results were similar t o those found in the preceding experiments but recoveries were much more uniform. There was good agreement between the proportions of individual compounds present and those found. Mixture 4. This mixture was composed of t h e proportions of steamvolatile monocarbonyls found (3) in t h e rancid park fat after heating a t 165' C. Two milliliters of each of the standard solutions shown in Table I V were used t o make 22.00 ml. of mixture. Quantities shown in the data are those found for that volume of mixture. Recoveries showed the same trend observed in the previous experiments. Again there was good agreement between the proportions
of individual compounds present and those found. However, proportions were high for the saturated, and low for the alk-2,4-dienal class. Table V surveys the results of the four experiments. Mean recoveries in the class separation. individual separation, and over-all were consistent and showed small variations. Mean recoveries for the classes in the two separations were also consistent and had low deviations. I n the class separation, there were very definite differences in recovery between the classes. Recovery decreased from the 2-alkanones to the alk-2,4-dienalsa This was due to differences in stability of the classes, and is the chief cause of error in the method. There was much less difference in class recoveries in the separation into individual compounds. It is probable that chromatography on the impregnated paper gives some degree of protection to the sensitive classes. Results indicate that the method is flexible and consistent, and possesses good reproducibility and precision. The paper chromatographic methods require only simple equipment (1, 2 ) .
Class separation requires 11/4 hours ($), and the separation into individual compounds ( I ) 13/4 hours for low molecular weight compounds and 6 hours for the derivatives of higher molecular weight. Time of analysis is naturally influenced by the proportions of compounds present, but generally a complete analysis can be mad? within 3 days. ACKNOWLEDGMENT
The authors thank George T. Currie of this laboratory for spectrophotometric measurements. LITERATURE CITED
( 1 ) Ellis, R., Gaddis, A . M., Currie, G . T., ANAL.CHEM.30, 4 i 5 (1958). ( 2 ) Gaddis, A. M., Ellis, R., Ibid., 31, 870 (1959).
(3) I., ~, Gaddis, A. &Ellis, , R.,. Food Research, inpress. ' ( 4 ) Gaddia, A. M., Ellis, R., Science 126, 745 f19571.
(5) Gaddis,'A. M., Ellis, R., Currie, G. T., Food Research, in press. (6) Konaka, M., Pippen, E. L., Bailey, G. F., ANAL.CHEM 31, S i 5 (1959).
RECEIVEDfor review July 16, 1959. Accepted August 24, 1959.
Separation of C, and Lighter Hydrocarbons by Gas-Liquid Chroma tog rap hy T. A. McKENNA, Jr., and J. A. IDLEMAN Firestone .Synthetic Rubber and latex Co., Orange, Tex. The accuracy of chromatographic peak area measurements of concentration is enhanced by completely separating the peaks. This investigation was designed to screen available liquids suitable for columns and to select the optimum solid support. A combination of liquid and solid has been found such that the normally encountered hydrocarbons through Cq are all separated within the &I3 sigma limit of the normal error curve, or 99.7 area yo at room temperature. Methods for selecting the liquid and solid are described.
L
in the refining and petrochemical industries are analyzing light hydrocarbons by gas-liquid chromatography. I n the writers' experience, none of these laboratories are using partition columns which separate the Ca hydrocarbons very well a t temperatures above 0" C. Several, however, have observed incomplete separation of these components a t higher temperatures (3, 4). I n this laborarory a numABORATORIES
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ANALYTICAL CHEMISTRY
ber of liquids have been screened; those best suited for specific applications are discussed in the present paper. Also discussed is the effect of the particle size of the solid support on column performance. APPARATUS
Perkin-Elmer Model 154-B Vapor Fractometers with thermistor-type thermal conductivity cells were used. Helium was the only carrier gas. The column support was Chromosorb (JohnsManville Corp.) as received or, in some cases, acid-washed or water-washed. Unless otherwise specified, the temperature of the sample loop, the column, and the detector cell was 23" to 26" C. Phillips standard hydrocarbon mixtures (Phillips Petroleum Co.) were used as analytical reference samples. The sampling procedure has been described (6). All columns were constructed with soft copper tubing 1/4 inch in outside diameter (0.030-inch wall thickness). A Straub 50.F 4 laboratoryhand -driven mill was used for grinding the Chromosorb to various particle sizes. A
Bausch & Lomb measuring magnifier was used to measure peak widths. PROCEDURE
Chromosorb, 30 to 60 mesh as re' ceived, was coated with 30 weight % liquid, with acetone as the solvent. The coated material was air-dried a t room temperature to the approximate calculated weight of solid support plus partition liquid and packed into 50-foot lengths of tubing to a density of 3.6 to 3.7 grams per foot. Because the 1butene and isobutene isomers are the most difficult to resolve, Phillips hydrocarbon mixture 36 was analyzed in all columns in either a 0.25-cc. or a 1-cc. gas sample. The measured separation of the I-butene-isobutene double peak was determined by measuring the ratio of the valley height and the 1-butene peak height. For these measurements a flow rate was selected that gave maximum peak separation. From the screening runs, two liquid phases that indicated maximum separation of the C4 hydrocarbons were selected: propylene carbonate (EK 7050) and y-butyrolactone (MCB 7042). Of the two, propylene carbonate was
-
0.5
0.4-
-
04
0 3-
d
0.3
5
-
,"o
2-
W
a.
6
2 0 2
I
-
.-
FER CENT LIQUID
v-
01MESH
V OL
SIZE
35
30
e-
23.1 1 1 - 167
32-40 40-50 50-60
0
I
I
I
I
I
I
2
3
4
5
1
I
1
1
2
3
I
I
6
I
8
7
Figure 2.
1
4 CMkEC.
1
1
I
5
6
7
I 8
Effect of liquid phase concentration on HETP
CM/sEC.
40-50-mesh Chromosorb
Effect of Chromosorb mesh size on HETP
Figure 1.
Table I.
STAR1
Figure 3. column
Chromatogram of Phillips hydrocarbon mixture 37, 16.7 weight
%
1.
5. lrobutene 6. trans-2-Butene 7. cis-2-Butene 8. 1,3-Butadiene
Air lrobutone n-Butane 1-Butene
tested further because it has a lower vapor pressure and smaller retention time for the C4hydrocarbons. RESULTS AND DISCUSSIONS
The liquids tested and the measured separation of the 1-butene peak are listed in Table I. Analysis of Phillips hydrocarbon mixture 40 indicated that propylene carbonate separated propene only about 30y0from the trailing edge of the isobutane peak. Therefore, if a proposed stream sample contains propene, a mixture is recommended for the separation. The mixture selected 13 as glutaronitrile (RICB 5769) and propylene carbonate in proportions of 30 to 70, respectively, for the following reasons. This mixture will place the propene peak between the isobutane and %butane peaks and completely separate all remaining C4 and lighter hydrocarbons. Any Cb's present nil1 be eluted in separate peaks, except that isopentane and n-pentane will be partially masked by 1-butene and trans-2-butene, respec-
Liquid Phase Hexamethylphosphoramide Diacetin 2,5-Hexanedione 0-Hy droxypropionitrile o-Kitroanisole B,p'-Oxydipropionitrile &Proplolactone Malononitrile Glutaronitrile Dimethylsulfolane 7-Valerolactone Adiponitrile Sulfolane r-Bu tyrolactone Propylene carbonate
Measured Separation, 1-Butene, 7 0 34.7 50.2
60.0 64.1
68.5
79.4 i9.6 81.3 83.8 86.3 86.6 88.4 89.4 92.3O 99.4a
a Apparently complete separation obtained a t 35 weight "/c concentration.
Peaks 2. 3. 4.
Liquids Tested for Applicability
tively. The propylene carbonate alone produces a better separation of the saturated C6's than does the mixture. The mixture does not measurably affect the degree of separation of 1-butene and isobutene. Various combinations of the liquids in Table I can be made by the procedure of McFadden ( 5 ) to suit specific stream requirements, as the various compounds have different separating properties. The propylene carbonate-glutaronitrile mixture was tested a t several concentrations 011 Chromosorb of the
same particle size and a t a single coiicciit'ration on Chromosorb of various particle size ranges. For each column the H E T P (height equivalent to a theoretical plate) us. average linear gas yelocity (a) curve was plotted (Figures 1 and 2). Peak separation (1-butene-isobutene) for these columns as measured or calculated ( 1 ) is listed in Table 11. De Wet and Pretorius ( 2 ) have discussed the influence of various column parametcrs on HETP. Chromatograms of various liqui(1 ('oncent,rat,ionsof this mixture arc shon-n in Figures 3, 4, and 5 , illustrating the separation of the butenes. The 23 w i g h t yo colunin is considcrctl thc optiinum
Table II.
Column X O
1 2
3
4 5
6 7
Comparison of Expression for Peak Separation 1-Butene Separation Chromosorb Mesh AIcasured, yc Cdcd. ( I ) 1.44 16.7 40-50 95.9 1.64 23.1 40-50 98.8 1.75 30.0 40-50 99.4 1.60 35.0 40-50 99.7 38.2 40-50 1.35 95.7 1.34 35.0 3230 96.0 35.0 50-60 1.67 99.3
Liquid, Wt o/o
VOL. 31 NO. 12 DECEMBER 1 9 5 9
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ANALYTICAL CHEMISTRY
4 Figure 5. Chromatogram of Phillips hydrocarbon mixture 36, 35 weight column
70
Peaks 1.
2. 3. 4.
Air lsobutane n-Butane 1-Butene
Temperature 18' C.
5.
6. 7.
lsobutene frons-2-Butene cis-2.Butene
A 2-mv. recorder used
no evidence of deterioration. Colunins of smaller particle size (60 to 80 mesh and 80 to 100 mesh) and shorter length (15 to 30 feet) will perform satisfactorily. A ao-foot column of 30 weight % of this liquid mixture on 60-SO mesh Chromosorb \\ill produce a 1-butene separation in excess of 97% a t room teinperature. Acid irashiiig of the Cliromosorb produced no noticeable iinprovement in column perforrnancc. ACKNOWLEDGMENT
concentration for speed plus resolution. .4column of this concentration has been in ccxntinuous use for over 8 months with
The authors are grateful to 11'. A. Wilson and h'. A. Adanison for their encouragement, and to The Firestone
r I.
l i r c arid Iiubiicr Co. foi. p(,riiiissioii to publish this paper, LITERATURE CITED
(1) Destt);,
D. H., "Gas C'hromatog.4cademic Press, S e w York,
mphy, 195s. ( 2 ) De \Vet, W. J., Pretoriiis, \:ic.tor, A S A L . CIIEY. 30, 325 (1958). (3: Fredericks, E. M., Brooks, F. R . , Ibid.,28,297 jl956). ( 4 ) Lichtenfels, D. H.; Fleck, E. A , , Uurrow, F. H., Coggeshtlll, N I)., l b i d . , 2 8 , 1376 (1956). ( 5 ) McFadden, W. H., Ibid., 30, 479 (1958). ( 0 ) RIcIienna, T. A , Jr., Idlem;in, J. Ii., Ibzd., 31, 1021 (1959). RECEIVEDfor review M:LY 7 , 1959. Accepted Septeinbcr 3 , 1959. Gulf Coast Spectroscopic Groiip \leetirig, Xfarch 13, 195'3.
Colorimetric Method for Determination of Vanadium Employing 1 - (2- Pyridy I a z 0)- 2 - na p ht ho I FRED W. STATEN and E. W. D. HUFFMAN Huffman Microanalytical laboratories, Wheatridge, Colo.
b The absorbance at 61 5 rnp of a chelate of vanadium with 1 -(2-pyridy1azo)-2-naphthol varies according to Beer's law in the range of 9 to 61 y of vanadium. The molar absorbancy index is about 16,900. The determination of vanadium based on this may b e made essentially specific b y employing a hydroxide separation and compensating for remaining traces of iron. The method has been applied to ferrous alloys and to ores and refractories having vanadium contents from 0.03 to 50%. The techniques are simple and feasible for routine use. The accuracy and applicability are shown by results on standard samples.
S.
colorimetric methods have rxen described for the determination of vanadium (2,9,11-13). This paper reports a new, sensitive, and selective analytical procedure. 1(2-PyridyIazo)-Znaphthol reacts with many heavy metals to form red chelates (1). Vanadium forms a blue chelate m d e r the proper conditions. I n chloroform solution the vanadium chelate has absorbance maxima a t 615 and 570 mq. T h e 615-mq maximum is outside the wave length range tor high absorbance of many of the'other metal chelates with 1-(2-pyridylazo)-2-naphthol (PAN) and of the reagent itself. Chelation with this reagent is the basis of a simple coloriEVERAL
metric method for the determination of vanadium. APPARATUS AND REAGENTS
Spectrophotometric measurements were made with a Beckman DK-2 ratio recording spectrophotometer using 1cm. silica cells. A Beckman Zeromatic p H meter was used for pH measurements. All water used was purified, first by distillation and then by passage through a deionizing column. Reagent grade chemicals were used, unless otherwise indicated. Standard vanadium solution of any convenient concentration can be used. The solution used contained 87 y of vanadium per ml. and was made up in water from C.P. ammonium metavanadate. The P A N was obtained from J. T. Baker Chemical Co. and was analvzed by micromethods for carbon, hydrogen, nitrogen, and ash. Analysis of other commercial samples of P A N gave aa high as 16.06% ash. Analysis of PAN, J. T. Baker Lot 6103 Theory, % Found,
C H N Ash
72.27 4.45 16,86 0.00
70.60 4.42 16,46 2.09
P A N Solution. Dissolve 50 mg. of P A N in 60 ml. of glacial acetic acid.
Add 6.8 grams of sodium acctate trihydrate and make to 100 ml. n i t h water. Standard iron solution, 0.05 mg. of iron per ml., was made froin standard iron wire in hydrochloric acid solution. Chloroform, reagent gradc was uscd as solwnt for the reaction product of vanadium and PAN. The chloroform was checked before usc to determine whether PAN would produce a colored reaction product with it alone. If a spectrophotometric curve shon ed any absorbance a t 615 mp on a chloroform solution of PAN, the chloroform was purified by distillation in thc prescnce of PAN. PROCEDURE
I n general, the proccdure consists of putting the sample into solution, separating interfering elements by hydroxide precipitation, treating the solution to put the vanadium into a reactable condition, chelating with PAN a t a chosen pH, extracting the chelate into chloroform solution, making the absorbance measurements on the chloroform solution, and calculating the vanadium concentration by the use of a standard curve or of knowns whose concentrations bracket that of the unknown. Preparation of Standard Curve. TO 25-ml. portions of water add 5 drops of 2 N hydrochloric acid and suitable amounts of the standard ammonium metavanadate solution. Add a n excess of saturated bromine water and boil off t h e excess bromine. Cool, adjust the p H to 3.5, and add an excess VOL. 31, NO. 12, DECEMBER 1959
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