Representative results of these experiments are shown in Figures 2 to 5 , in which the initial burst, amounting to about 10% of the total material on the column, is omitted. Figure 2 shorn the separation of t'he eight bromo esters a t 35" C. by elution with alcohol from 40 to 707,. From the eight esters, seven peaks were separated, two with 50%,, one each with 55 and GO'%',, and three with 70% alcohol. Figure 3 s h o w the separation of the iodo esters a t 45" C. with alcohol from 40 to 95%. From the eight esters, five peaks w r e obtained, each equivalent to one ester. Apparently three of the esters were not detached from the column, w e n nith 95% alcohol. Figure 4 shows the srparation of the ehloro esters a t 30" C. by gradient elution, in which 957, alcohol was added dropwise to 1 liter of 40% alcohol. Seven peaks were obtained from the eight esters. Preliminary expcriments with indi-
vidual esters and with the reagent showed. that the reagent is eluted with 40% alcohol and the esters appear between 50 and 75% in the sequence of decanoic, lauric, myristic, linolenic, linoleic, oleic, palmitic, and stearic acids. Apparently the fifth peak contains both linoleate and oleate. Figure 5 shows that these two esters can be separated completely by elution with 60% alcohol. At present the special reservoir shown in Figure 1 or a similar constant pressure device is required to combine the separation of linoleate and oleate with that of the other six esters in one chromatographic experiment. However, it may be possible to adjust the gradient so that these two esters, as well as the other esters, mi!l be separated in one continuous gradient elution. LITERATURE CITED
(1) Bothner-By, A. A., J . Am. Chem. SOC. 77, 3293 (1955).
( 2 ) Calvin, RI., Heidelbergpr, C., Reid,
J. C., Tolbert, B. M., Yankwich, P. F., "Isotopic Carbon, Techniques in Its Measurement and Chemical Rfanipulation," p. 178, Wiley, Neiv York, 1949. (3) Isbell, H. S., Science 113, 532 (1951). (4) Judefind, W.L., Reid, E. E.) J . i i m . Chem. SOC.42, 1043 (1920). (5) Keston, A. S., Udcnfriend, S.,Cannan, R. K., Zbid., 68, 1390 (1946); 71, 249 (1949). (6) Kimura, K . , Ber. 67B, 394 (1934). ( i )Rather, J. B., Reid, E. E., J . A m . Chem. SOC.41, 75 (1919). (8) Ruliffson, K.R., Lang, H. L., Hammond, J. P., J. Biol. Cheni. 201, 839 (1953). (9) Sorensen, P.,ANAL. CHEM.26, 1581 (1954). (10) Stokes, W. RI., Hickey, F. C., Fish, W. A., Zbid., 28, 207 (1956).
RECEIVEDfor review March 13, 1933. Accepted August 28, 1959. Preliminary report presented at the Annual hfeeting of the Division of Biological Chemistry, 134th Meeting, ACS, Chicago, Ill., September 1958.
Determination of Trace Hydrocarbon Impurities in Petroleum Benzene and Toluene by Gas Chromatography F. A. FABRIZIO, R. W. KING, C. C. CERATO, and J. W. LOVELAND Sun Oil Co., Marcus Hook, Pa.
b Gas chromatographic methods for the determination of trace hydrocarbon impurities in benzene and toluene are rapid, sensitive, and precise. An accuracy of 0.01 volume in the range of 0.06 to 0.40 volume is obtained. The chromatographic chart record indicates that as little as 0.01 volume % of a hydrocarbon impurity is detectable. A comparative study clearly shows that these methods are superior to the physical property and differential infrared methods that have often been used. In this work, the saturated hydrocarbon impurities (mainly cycloparaffins) in a sample of petroleum benzene were separated and identified.
70
T
%
amount of hydrocarbon impurity in high purity benzene and toluene is important to the consumer from a processibility standpoint. Sensitive and accurate analytical methods are needed for specification and process control testing. I n 1958, Wood, Martin, and Lipkin ( 7 ) published a physical property HE
2060
ANALYTICAL CHEMISTRY
method for the determination of saturated hydrocarbon impurities in aromatics for levels of sensitivity below those attainable by the ASTIT method (1). Differential infrared methods used for the determination of trace aromatic hydrocarbon impurities in aromatics can be made sensitive. However, the instrumentation is expensive, and supplementary methods ( 1 , 7 )are needed if the concentration of the saturated hydrocarbon impurities is desired. T h e inherent high sensitivity of gas chromatography makes it ideally suited for analytical control methods concerned with the detection of low levels of impurities. Martin and Smart (6) have used gas chromatography for the detection and estimation of small amounts of impurities in hydrocarbon gases. Bennett, Dal Nogare, Safranski, and Lewis ( 2 ) have described instrumentation suitable for the detection of trace components in liquids. More recently, Boggus and Adams (3) have described a chromatographic method for trace impurities in ethyl chloride. The lower limits of detectability of
the chromatographic methods described in this study are 0.01 volume % for either saturated or aromatic hydrocarbon impurities in either benzene or toluene. This is approximately a fiftyfold sensitivity advantage over the A S T N test method ( I ) . A tenfold sensitivity advantage over the physical property method ( 7 ) and a significant sensitivity advantage over the routine differential infrared methods are shown. I n addition, the chromatographic methods simultaneously determine both the saturated and the aromatic hydrocarbon impurities in a single sample. APPARATUS
A Perkin-Elmer Vapor Fractometer, Model 154 B, and a Leeds & Korthrup Speedomax G recorder (0 to 5 mv.) were used. Constant volume samples were charged with an Agla micrometer syringe. Helium carrier gas flow was controlled by a conventional regulator a t the cylinder and a null regulator supplied with the Fractometer. Two columns were used. Column 1. Column 1, copper tubing, 25 feet long, and inch in outer
I
II
1
, r , . -; MI
Figure 1.
, r , . 7
5
v v -rS
TVE
Separation of components of a test blend
diameter was packed with a stationary phase consisting of 20 weight % ' of 2,4,7-trinitro-9-fluorenone on 30- t o 60-mesh C-22 firebrick. T h e stationa r y phase was prepared b y sprinkling powdered 2,4,7-trinitro-9-fluorenone onto firebrick which had been preheated to 200' C. in a n evaporating dish. During addition the support was stirred thoroughly to ensure even distribution. The column packing was also prepared b y deposition of the 2,4,7-trinitro-9-fluorenone from a solvent consisting of equal volumes of benzene and acetone. T h e characteristics of the columns prepared by either method were equivalent. The packings were resieved before introduction into the column. Column 2. This column, 10 feet long, copper tubing, '/4 inch in outer diameter, was packed with two separate stationary phases. T h e inlet half of the column contained 40 weight yo of a saturated solution of picric acid in di-n-butyl phthalate on 30- to 60mesh C-22 firebrick ( 5 ) . The exhaust half of the column contained 15 weight yo of di-n-decyl phthalate on 30- to 60mesh C-22 firebrick. The exhaust half provided a section of column capable of retaining any picric acid which might distill from the inlet section.
Y M
~~-
~
-7
I,
Hydrocarbon impurities in petroleum toluene
Hydrocarbon Impurities in Benzene. Attempts to use column 1 for thc analysis of hydrocarbon impuritiw i i i benzene were largely unsuccessful I)(,cause of t h e poor resolution of t r n w s of toluene from benzene. This (I?creased t h e sensitivity for trnc-c toluene. Concentrations greater tlinii 0.10 volume yo were needed t o obtniii a measureable area. However, tlic saturated hydrocarbon impurity content could be determined wit,h adequate sensitivity. The separation shown in Figure 3 was obtained with column 2 operated a t 120" C. with a carrier gas flow rate of 165 ml. per minute. A sample charge of 0.20 ml. was used. A t these conditions. 0.01 volume yoof each impurity was detectable. These limits and calibratioiis were established with synthetic calibration blends prepared to simulate actual samples. Known amounts of satu-
Table I. Precision of G a s Chromatographic Methods Volume % Saturates Volume yo Toluene Calcd: Found Deviation Ca1cd.a Found Deviation Impurities in Benzene 0.065
The trace saturate and the trace benzene impurities in a sample of petroleum
Figure 2.
toluene are shown in Figure 2 (conditions same as Figure 1). T h e sensitivity was X1. Benzene was the only aromatic impurity found in any of the toluene samples examined in this study. T h e lower limit of detectability for each impurity is 0.01 volume yo. These limits and calibrations for each impurity were established with synthetic calibration blends prepared to simulate actual samples. Known amounts of saturated hydrocarbons and benzene were added t o a base stock toluene (Eastman White Label, from toluenesulfonic acid). No detectable quantities of hydrocarbon impurities were present in the base stock. The area under t h e saturate impurity peaks was measured and plotted against t h e known saturate concentration of the calibration blends. The same was done for the benzene impurity. This resulted in linear calibrations in each case.
EXPERIMENTAL
Hydrocarbon Impurities in Toluene. Column 1 was used for t h e determination of hydrocarbon impurities in toluene. T h e 2,4,7-trinitro-9-fluorenone had t o be melted b y heating t o and maintaining a temperature of 190OC. for 30 minutes. Then the column was cooled t o the operation temperature of 160" C. The, separation of the components of a test blend containing eightand nine-carbon saturates and six- to eight-carbon aromatics is shown in Figure 1. A sample charge of 0.030 ml. and a carrier gas flow rate of 85 ml. per minute were used. The sensitivity was X32. This stationary phase is extremely selective for aromatic hydrocarbons. n-Xonane (boiling point 151O C.) is eluted before the first aromatic hydrocarbon, benzene (boiling point 80' C.), emerges.
__-
0.083 0,119 0,191 0.303
Std. dev.
0.066 0.065 0.087 0.095 0.123 0.133 0.200 0.197 0,313 0.311
+0.001 0.000 $0.004 +o. 012 +0.004 + O . 014 +o. 009 +0.006 $0.010 $0.008
Repeatability
Accuracy
0.004
0.211 0.175 0.139 0.103 0.063
0.203 0.198 0.165 0.168 0.140 0.138 0.105 0.103 0.070 0.063
Repeatability
-0,008 -0.013
-0.013 -0.007 +0.001 -0.001 +o, 002 0.000 +0.007
O.OO0 Accuracy
0,003
0.008
0.007
Impurities in Toluene Volume % Benzene 0.441 0.291 0,191 0.121 0.061
0.428 0.425 0.306 0.287 0.182 0.182 0.134 0.121 0.055 0,070
-0,013 -0.016 +0.015 -0.004 -0.009 -0.009 +0.013 0.000 -0.006 +o. 009
0.060 0.120 0.190 0.290 0.440
0,050 0.060 0.118 0.120 0.175 0.185 0,280 0.277 0.415 0.406
-0.010
O.Oo0 -0,002 0.000 -0.015
-0.005 -0,010 -0.013 -0.025 -0.034
Repeatability Accuracy Repeatability Accuracy Std. dev. 0.008 0.011 0.005 0.014 Includes added impurities and impurities found in base stock. 0
VOL. 31, NO. 12, DECEMBER 1959
2061
I
25
1 2
Sr(l.iATES
,
r
Figure 4.
n 6.
10
31
1c
55 TIVE
Figure 3.
23
15
0.065 0.083 0.119 0.191 0.303
I 5
05
"OURS
Identification of saturates
5
v ..,-E5
Hydrocarbon impurities in petroleum benzene
rated hydrocarbons and toluene m-ere added to a base stock benzene, which had been purified by repeated slow crystallization. The base stock contained 0,015 volume 70 saturates and 0.027 volume 70 toluene after purification. Linear calibrations were obtained by following the same procedure as used for the toluene samples. Identification of Saturated Hydrocarbon Impurities in Petroleum Benzene. T h e identification of saturated hydrocarkon impuiitics in petroleum henzene was of interest, as four distinct peaks n ere obtained for these impurities (Figure 3). It n-as also necessary to establish the absence of seven- and eight-carbon saturates. If present, they would be under the broad henzene peak. The qualitative procedure used in the identification work proved that seven- and eight-carbon saturates were absent. A concentrate of the hydrocarbon hipurities in petroleurn benzene was obtained by repented don. crystallization of this material. Four successive crystallizations resulted in about a tenfold
Calcd.0
0
I 2 0
TllE,
increase in the impurity concentration of the supernatant liquid. The concentrate was charged to column 1 and the saturated hydrocarbons eluted were collected in a liquid nitrogen cold trap. V i t h this column traces of saturates containing as many as eight carbons are eluted prior to benzene. The collected saturated hydrocarbons were identified by charging them to a 50-foot column of squalane on Pelletex carbon black. This column has been described by Eggertsen, Knight, and Groennings (4).It is capable of resolving all of the six- and most of the seven-carbon saturates. Figure 4 shows the results of this work. n-Pentane (trace) cyclopentane, methylcyclopentane, and cyclohexane were identified. These four peaks correspond to those observed in Figure 3. Because no seven- or eight-carhon saturates were present, Column 2 was acceptable for the analysis of saturated hydrocarbon impurities in benzene RESULTS A N D DISCUSSION
The gas chromatographic precision
data presented in Table I were obtained with blends other than those which were used for calibration, These synthetic blends were prepared by adding known amounts of hydrocarbon impurities t o benzene and toluene base stocks. The benzene base stock contained 0.015 volume 70saturates and 0.02i volume % toluene. The toluene base stock contained 0.041 volume yGsaturates and 0.040 volume % benzene. The accuracy standard deviation for the trace inipurities is of the order of 0.01 volume % for both benzene and toluene samples. The repeatability standard deviation is approximately 0.005 volume %. The slightly improved precision and accuracy for the benzene samples are attributed mainly to the larger sample size used with the benzene procedure. A comparison of the chromatographic results with those obtained using the physical property method ('7) and differential infrared methods is given in Table 11. These data show that the chromatographic methods are more sensitive. There is approximately a tenfold increase in sensitivity over the physical property method for the trace saturate impurity and a significant increase in sensitivity over the differential
Table 11. Comparison of Gas Chromatographic and Other Methods Volume yo Toluene Volume yo Saturates Found6 Deviation Calcd.0 De Foundb viation Phys. Phys. Diff. Diff. GC infrared GC infrared GC Prop. GC Prop. Impurities in Benzene 0.066 0.13 $0.001 $0.06 0.211 0.201 0.24 -0,010 $ 0 . 03 -0.03 -0,008 0.091 0.13 +0.008 +0.05 0.175 0.167 0.15 -0.03 0.10 +o. 009 -0.02 0.130 0.139 0.11 0.000 0.128 $0.001 -0.03 0.109 0.10 +0.008 -0.09 0.103 0.104 0.07 -0.01 10.004 0.18 +0.009 -0.12 0.063 0.067 0.05 0,312 Std. dev. 0.008 0.09 0.006 0.03
Impurities in Toluene -0.014 -0.07 0.37 0.427 0.441 +0.006 -0.07 0.22 0.297 0.291 -0.009 -0.08 0.11 0.182 0.191 +0.007 -0.03 0.09 0.128 0.121 +0.02 0.08 +0.002 0.061 0,063 Std. dev. 0.009 0.06 Includes added impurities and impurities found in the base stock. * Average of duplicate determinations.
5
2062
ANALYTICAL CHEMISTRY
0.060
0.120
0.190 0.290
0.440
Volume yo Benzene -0,005 0.06 -0,001 0.14 0.119 -0.010 0.21 0,180 -0.011 0.32 0.279 0.411 0.47 -0,029 0.015
0,055
0.0 0 $0.02
$0.02 +0.03 +0.03
0.02
infrared methods for the trace aromatic impurity. In addition, the gas chromatographic methods use relatively inexpensive equipment and they are rapid, require a single sample, and provide a permanent record of each analysis. ACKNOWLEDGMENT
The authors thank W, B. AI. Faul-
(4) Eggertsen, F. T., Knight, A. S., Groennings, S., Ibid., 28, 303 (1956).
coner for his assistance in obtaining many of the data.
(5) Keulemans, A. I. hl., Kwantes, A., Zaal, P., Anal. Chim. A c b 13, 357 (1955). (6) hlartin, A. E., Smart, J., Nature 175, 422 (1955). (7) Wood, J. C. S., Martin, C. C., Lipkin, M.R., ANAL.CHEII.30, 1530 (1958).
LITERATURE CITED
‘(1) .4m. SOC. Testing Materials, Philadelphia, Pa., ‘‘ASTLM Standards on Benzene, ,Toluene, Xylene, and Solvent Naphtha, D 851-47 (1952). (2) Bennett, C. E., Dal Nogare, S., Safranski, L. w., Lewis, c. D., ANAL. CHEM.30, 898 (1958). (3) Boggus, J D., Adams, N. G., Ibid., 30, 1471 (1058).
RECEIVED for review hIay 8, 1959. Accepted September 18, 1059. Division of Analyticnl Chemistry, 135th Meeting, ACS, Boston, Mass., April 1959.
Solvent Effects in the Spectrophotometric Determination of Weak Organic Acids in Alkaline Solution Application to Aromatic Primary Amine and Carbonyl Derivatives E. SAWICKI, T. R. HAUSER, and T. W. STANLEY Air Pollution Engineering Research, Robert A. Taft Sanitary Engineering Center, Public Health Service, U. S. Department of Healfh, Education, and Welfare, Cincinnati 26, Ohio
In the colorimetric determination of weak organic acids in alkaline solution, the striking effect of the solvent on the absorption maximum and the color intensity of the anion has been studied. The organic anion absorbs a t a longer wave length and usually with greater intensity than the weak acid from which it is derived. Many conjugated organic anions absorb a t longest wave length and with greatest intensity in the more basic solvents. In solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethylsulfoxide, and N,N-dimethylacetamide, the bands are a t their longest wave length and greatest intensity. At the other extreme, in hydroxylic solvents such as water and ethyl alcohol, the bands are at relatively shorter wave lengths and usually at decreased intensity. The application of these solvent-effect phenomena to the analysis of aromatic primary amines and ketones i s described.
T
colorhetric analysis of many organic compounds has been carried out in alkaline media. I n most cases the use of an alkaline solvent is of great value n hen the organic compound can forni an anion. as the anion will usually absorb a t a longer wave length and with greater intensity than the analogous n e u t r d compound. The advantages of these spectral changes are the decreased interference from other compounds a t the longer wave lengths (and consequently, greater specificity) HE
dye derived from phenol gave a band a t 567.5 nip in alkaline alcohol and a t 475 m p in alkaline nater. This same solvent effect was found for 14 other 4nitrophenylazo dyes derived from various phenols. The solvent effect of the anion of 2-bcnzaniido-1-nitroanthraquinone has also been reported ( I ) . This compound has a wave length maximum a t 520 mp in pyridinp, a t 505 mp in alkaline acetone, a t 483
and the increased sensitivity derived from the greater absorption intensity. The solvent effects of diverse alkaline media on the wave length maxima and the color intensities of various anions have never been thoroughly studied. Palkin and Wales (4) have spectrally identified phenols by reacting them with p-nitrobenzenediazonium chloride to form azophenols which were then d e t e r m i n d in alkaline solution. The
Table 1.
Compound Dimethylsulfoxide N-Methyl-2-pyrrolidone lOYc aqueous tetraethylammonium hydroxide 40% methanolic benzyltrimethylummonium methoxide
Solvents and Reagents
P22l,t%b. ... ...
.,. . . ,
2-~lethgl-4-hydroxyazobenzene 100-101 3-~Zethvl-Ph~-drox~azobenzene 125-126
Phenol “ l-Saphthol
42-43 96
2-S~ipllthol Pxitrophenol 1-Hydroxyanthraquinone PHydrosychalcone
122-123 112-113 194-195 182-
Isatin
200-201
183 5-
N-Perfluorobutgryl-Pnitro-
aniline
4Trifluoroacetglaminoazoben-
zene
85-86
173-175
Source Remarlis J. T. Baker Donated Antara Donated Distillation Products Sumner hlatheson Recrystallized from hexane Matheson Recrvstnllized from hexane Fisher Recrtstnllized from pentaw Distillation Recrystallized from heptane Products Fisher Fisher .ildrich 4ldrich Distillation Products Synthesis Prepared by reacting p nitroaniline with perfiuorobutyric anhydride in benzene (K calcd., 8.4; S found, 8.3) Synthesis Prepared by reacting 4aminoazobenzene Kith trifluoroacetic anhydride in benzene ( N calcd., 14.9; S found, 14.7)
VOL. 31, NO. 12, DECEMBER 1959
2063
