Graphitized Carbon Black as a Support for Gas Lisuid Chromatog ra phy THOMAS F. BRODASKY Research Laboratories, The Upjohn Co ., Kalamazoo, Mich.
b Overcoming the troublesome adsorption effects of polar compounds in gas liquid chromatography has involved the use of specialized supports or chemical treatment of normal supports to deactivate the surface. The latter may involve lengthy chemical procedures, leading to certain limitations which can b e disadvantageous. This paper describes the use of highly graphitized carbon black as a support for gas liquid chromatography. It requires no special treatment and has no temperature or mechanical limitations. Using a nonpolar stationary phase, several support materials representing the classes including silazined supports, perfluorocarbon polymers, and untreated diatomaceous earth were compared with graphitized carbon black in their ability to reduce peak asymmetry of homologous series of alcohols, ketones, and amines. Graphitized carbon black effected the greatest reduction of peak asymmetry. The column efficiency in terms of HETP and resolution of three alcohols was also evaluated.
T
of polar compounds on gas liquid chromatographic supports, especially as pertains to severe tailing of peaks, has plagued the analyst to the point where extensive research has been carried out to solve this problem. This has generally followed three approaches: chemically treating normal supports (3, 20, I S ) , using steam or gases other than helium, nitrogen, or argon as carrier gas (2, 7 ) , and using particulated fluorinated polymers (1, 28). Since the use of steam requires special equipment and is somewhat limited with respect to conditions under which it may be used, it is not dihcussed in relation to the present btudy. Chemical treatment of normal supports initially consisted of deactivating high energy surface sites on diatomaceous earth or firebrick with trimethylchloro- or dimethyldichlorosilane. This was soon replaced by he\amethyldisilazane (HMDS) because it is much less volatile and less toxic, and showed less tendency to undergo undesirable reactions a t the support surface. Although H I I D S alleviated HE ADSORPTION EFFECTS
1604
ANALYTICAL CHEMISTRY
the tailing problem, supports treated in this manner usually show specific surfaces two to three times lower than untreated supports, which can lead to a reduction of column efficiency (4, 9 ) . I n limited applications, washing normal supports with strong acid or base has reduced adsorptive effects: however, the difficulty of handling suspensions of support materials in hot acid or base renders this method somewhat undesirable ( I S , 29, 20). The use of particulated perfluoro carbon polymers has been successful in reducing tailing of polar compounds ( 9 ) . These have the advantage over treated supports in that no specific treatment is necessary before their use. However, the severest limitation is their inability to withstand mechanical stress. Coating and column packing with these supports require much more care than with normal supports. I n any event, silanized supports and particulated perfluoro carbon supports cannot be used above certain minimum temperatures without degradation. As stationary phases with higher minimum operating temperatures are discovered, this can become a serious problem. Based on these considerations, t,he ideal support would display efficiency comparable to normal fine-mesh supports, require no special chemical treat,ment, and show little or no tailing with polar compounds, especially when coated with nonpolar stationary phases. A finely divided solid displaying an essentially homogeneous energy surface or, more precisely, a homotactic surface (17) would fulfill the requirements mentioned. Highly graphitized carbon black more nearly falls into this category than any other solid thus far investigated. This substance has been used for some time as an adsorbent in the study of static isotherms and adsorption phenomena (8, 11, 16, 16). More recently, Ross, Saelens, and Olivier (14 ) have employed graphitized carbon as an adsorbent in the determination of isosteric heats of adsorption by gas solid chromatographic techniques. Since the present study was initiated, Halitsz and Horvath (6) and Pope (12) have reported the use of graphitized carbon as a matris for analytical gas solid chromatography. The present investigation was initiated
to evaluate graphitized carbon black as a support for gas liquid chromatography. The ability of various supports to reddce tailing was measured using a modification of asymmetry factors as described by Dal Sogare (4). The efficiency of the columns in separating a series of alcohols is alco described. EXPERIMENTAL
Apparatus. XI1 chromatography was carried out using the F & M Model 500 chromatograph equipped with a hot-wire thermal conductivity cell. Reagents. The following liquids were chromatographed to obtain mean values for tables presented in this study. The temperature ranges ("C.) in which each solute was chromatographed, depending upon the colun~n used, are: alcohols: met,hanol (30" to 5 3 " ) , ethanol (40" to 80"), 1-propanol (50" to loo"), and 1-butanol (70" to 120'); ketones: acetone (30" to 75"), methyl ethyl ketone (30" to 125"), diethyl ketone (35" to 150")) and ethyl propyl ketone (50" to 175'); and amines: n-amylamine (pentylamine) (40" to 125"), n-hexylamine (60" to 155"), and n-octylamine ( l 0 0 " t o 180"). Procedure. The support materials were coated with stationary phase to give a constant film t,hickness. Chromasorb W (F8rlI Scientific Co.; ,\vondale, Pa.) 60- to 80-mesh, Haloport F (F&N Scientific Co.)' 30- to 60-m~sh, .\nakrom (Ainalytical Laboratories, Hamden, Conn.) 90- t,o 100mesh, and Sterling FT-2700" C. graphitized carbon (Godfrey L. Cabot, Co., Cambridge, Mass.) were slurried with silicone oil DC 200 (F&N Scientific Co.) in acetone. The weights of stationary phase per column were Chromasorb W, 0.048 gram (0.9%); .hakroni, 0.058 gram (1.24y0); Haloport, 0.059 gram (0.6273; and Sterling FT-2700" C., 0.51 gram (5.07,), yielding 0.0059 gram per sq. meter of stationary phase on each support. The solvent was stripped off using a rotary flash evaporator with a minimum of tumbling after the solvent had evaporated. .\fter drying, the carbon was sieved and the 60- t,o 100-mesh fraction was selected. The packing.3 were loaded into 3- to 4-foot lengths of standard 1/4-inch 0.d. (0.20-inch i d . ) stainless steel tubing. The columns were preconditioned a t 200" for 3 hours with helium as a purging gas. The samples \$-ere introduced with a
100-
8.0-
\
6.0 4.0
0
4
.B
1.2
I6
2.0
2.4 2 8 3.2 TR i m n t
3.6 4.0 4.4
measures only the deviation of the peaks from a true gaussian distribution and does not effectively indicate the presence or absence of severe tailing in the lower 10% of the peak. For this reason, the asymmetry factor A , 6 O was selected to measure this effect. The temperatures at which each compound was chromatographed were selected so that the residence time of each solute on the column was approximately the same, in the range 0.8 to 1.1 minutes. The low retention times were chosen because there was reason to believe that asymmetry effects were more pronounced with fast-moving peaks (4,2 1 ) . This was bubsequently established by plotting # q a 6 0 (calculated from data obtained on all four columns) against retention time for amylamine (Figure 1). This relationship held true for diethyl ketone as well. The estimated standard errors of the means, S;, do not have statistical significance in the number of experiments performed, but are included in Table I merely to indicate the variation experienced in values of retention time and asymmetry factors encountered with the various members of the homologous series. For example, the estimated standard error of the mean of the asymmetry factor for alcohols on Haioport indicates a rather wide range in the asymmetry of the individual members of this series going from methanol through butanol. There is a rather small variation in asymmetry in going from one series to another on Anakrom, which indicates the lack of specificity in its interaction with various functional groups. All columns other than graphitized carbon were less specific at a constant weight ratio of 5oj,, indicating the increased influence of the stationary phase at higher loadings. Consideration of Figure 2 indicates that graphitized carbon shows somewhat more adsorption than the other supports; however, the A , 6 O data reveal superior performance in prevention of asymmetry. This ability may result from one of two sources, approsimate equilibrium conditions in the graphitized carbon column with a resulting nearlinear isotherm or more uniform desorption because of the homotactic surface. Giddings (5) has recently demonstrated that linear chromatography does not preclude the presence of ~
Figure 1 . Semilog plot of ?A (calculated from data on all four columns) v5. retention time for amylamine
10-p1. Hamilton syringe such that the peak height for all samples varied between 6.0 and 10.0 scale units (10.0 full scale). This required between 0.5 and 1.0 ~ 1 a. t the following conditions: injection port temperature, 325" C.; detector block temperature, 255" C.; helium flow, 35 ml. per minute; inlet column pressure, 3.4 atm.; outlet column pressure, 1.0 atm. Retention volumes are expressed as specific retention volume, V g , measured from the air peak. RESULTS A N D DISCUSSION
The asymmetry factors for a series of alcohols, ketones, and amines on four dissimilar column packings appear in Table I. All values of A,60 and efficiency fact,ors (Table 11) were computed from dat,a obtained on a single column of each packing. Since the principal object of the study was a comparison of the asymmetry characteristics of the packings a t constant stationary phase film thickness, no attempt was made to compare the packings on the basis of constant particle size. This should be kept in mind, especially when considering the efficiency data. The asymmetry factors (.-I:") were computed using a modification of the equation: :I* =
b+f b+f-AW
where
From a chromatographic peak, b and f are defined as the base-line half widths measured from a perpendicular through the peak maximurn to the inflection point tangent ( 4 ) . The is a modification of .-I8, inasmuch as the b value is measured from the perpendicular through the peak maximum to a 60" tangent a t the tailing edge of the peak. The asymmetry factor, A,,
Table II.
400r
! I T 1 103
Figure 2. Semilog plot of specific retention volume vs. reciprocal of a b solute column temperature
A X
0
Crophitized carbon Chromosorb W Anakrom Haloport F
Table 1. Performance Characteristics of GLC Supports in Reducing Peak Asymmetry
-
Tr,
Solute
min.
Si0
-
Si
A
Chromosorb Water Alcohols Ketones Amines
0 9 10 0 9 10
Water 0 Alcohols 0 Ketones 0 Amines 1 Sterling FT Water 0 Alcohols 1 Ketones 1 Amines 1
b 8 00 ( 2 00)
5 1 7 80 3 0 4 90 0 0 5 90
16 7 18 3 17 8
Haloport F 1 86 5 5 2 25 29 1 7 5 4 78 13 5 1 3 8 4 79 13 3 2700" C. Graphitized Carbon 8 2 67 1 6 5 1 70 6 5 1 2 3 1 65 5 3 4" 4 1 2 33 14 2 7 9 9
Anakrom Water 0 8 3 94 Alcohols 0 8 11 7 3 31 14 Ketones 1 0 2 7 3 45 7 Amines 1 0 2 9 3 78 2 a Estimated relative standard error mean 100 S l &
7
1 4
of
(&).
Value in parLntheses obtained after first injection of water and probably results from deactivation of support Average % could not be reduced without excessive increase of temp.
Column Efficiencies
Column Rirz Chromosorb W 0 066 (0 SO) Haloport F 0 11 ( 2 0 0 ) Graphitized carbon 2 00 Anakrom 0 1 6 ( 1 30) Rl.z = resolution of EtOH, PrOH peaks. R2,3= resolution of PrOH, BrOH peaks
R2,3
0 30 ( 1 92) 0 28 ( 2 90) 2 60 0 33 (2 40)
H E T P , inm 6 1 8 6
VOL. 36, NO. 8, JULY 1964
4 3 6 2
1605
kinetic tailing resulting from highly active adsorption sites. The infrequency of such sites on graphitized carbon would lead to more complete desorption of the solute molecules. The other supports may differ from graphitized carbon and each other only in the degree of heterogeneity of their surfaces. The efficiencies of the columns with respect to H E T P and resolution of a series of alcohols (ethanol, propanol, butanol) appear in Table 11. With experimentally obtained data, the resolution and H E T P were calculated using the following equations:
L
HETP= V2 16
Y b
where Ay = difference between retention volumes y1.2 = base-line peak widths V , = retention volume of peak i y E = base-line peak width of peak i ' L = column length, millimeters
The greater adsorption on graphitized carbon is beneficial a t this column loading, inasmuch as it aids in resolution. The values presented in parentheses are
those obtained with columns packed at constant weight ratio (5%) rather than constant film thickness and are included merely to indicate the increase in efficiency with increase in column loading of the other columns. The H E T P values are the means of the individual H E T P for ethanol, propanol, and butanol. CONCLUSIONS
The advantages of using Sterling FT-2700' C. graphitized carbon as a stationary support include the elimination of prior chemical treatment to prevent tailing even in the presence of low loadings of nonpolar stationary phases, excellent efficiency, and the absence of temperature limitations with respect to the support itself. The principal disadvantage is the necessity of sieving the coated support and the care necessary in packing columns to obtain normal gas velocities by preventing large pressure differentials. ACKNOWLEDGMENT
The author expresses his appreciation to S. Ross, Rensselaer Polytechnic Institute, Troy, N . Y., for discussions which helped to initiate this study and t o W. R.Smith, Godfrey L. Cabot Co., Cambridge, Mass., for supplying the author with Sterling FT-2700' C. graphitized carbon.
LITERATURE CITED
(1) Bevilacqua, E. M., English, B. S., Gall, J. S., AKAL.CHEM.34, 861 (1962). ( 2 ) Chem. Eng. S e w s 40, 50 (July 16, 1952). (3) Cieplinski, B. W., ANAL.CHEY.35, 2n6 119631. (4) u a l Sogare, S., Chin. S. J., Zbid., 34, 890 (1962). ( 5 ) Giddings, J. C., I b i d . , 35, 1999 (1963). (6) Halitsz, I., Horvath, C., .Yature 197, 71 (1963). (7) K'arrneri, A,, PvlcCaffrey, I., Bowman, R., Zbid., 193,575 (1962).
(8) Kiselev, -4.V., Gazo. Khrom., Tr. 1-02 (Peruoi) Vses. Konf., A k a d . .Yauk SSSR L~Ioscow1959, 45 (1960). ( 9 ) Landault, C., Guiochon, G., J . Chromatog. 9, 133 (1962). (10) Pefrett, R. H., Purnell, J. H., Zbid., 7 , 430 (1962). (11) Polley, M. H., Shaeffer, W. D., Smith, W. P., J . Phys. Chem. 57, 469
(1953). (12) Pope, C. G., A x . 4 ~ .CHEM.35, 654 (1963). (13) Purnell, H., "Gas Chromatography," p. 235, Wiley, New York, 1962. (14) Ross, S., Saelens, J. K., Olivier, J. P., J . Phys. Chem. 66,696 (1962). (15) Sams, J. R., Jr., Constabaris, G., Halsey, G. D., Jr., I b i d . , 64, 1689 (1960j. (16) I b i d . , 65, 367 (1961). (17) Sanford, C:, Ross, S., Ibid., 58, 288 i1964). (18) Sawyer, D. T., Ben, J. K., A x . 4 ~ . CHEM.34, 1518 (1962). (19) Smith, B. D., Radford, R. D., Zbid., 33, 1160 (1961). (20) Sze, Y. L., Borke, M. L., Ottenstein, D. SI., Zbtd., 35, 240 (1963). (21) Reinstein, A. W., I b z d . , 33,18(1961). RECEIVEDfor review July 29, 1963. Accepted hpril 16, 1964.
Simultaneous Determination of Crude Oil Boiling Range Distribution and Hydrocarbon-Type Distribution by Gas Chromatography V. F. GAYLOR, C. N. JONES, J. H. LANDERL,' and E. C. HUGHES Research Departmenf, Sfandard Oil Co. (Ohio), 4440 Warrensville Center Road, Cleveland 28, Ohio
b A rapid crude oil analysis procedure yielding both boiling range distribution and hydrocarbon type composition in less than 2 hours has been devised. Distil1a:ion-type yields up to 725' F. are calculated from gas chromatographic peak areas. Relative concentrations of aromatics and naphthenes in fractions boiling to about 390" F. are calculated from peak height measurements. Analytical procedures and computations are readily adaptable to routine refinery use. Crude oil chromatograms are obtained from a '/r-inch packed column with a thermal conductivity detector. A timeof-flight mass spectrometer was used for preliminary characterization of chromatographic separations and 1606
ANALYTICAL CHEMISTRY
showed that the poorly resolved peaks representing the lower boiling fractions of crude oil could be related to hydrocarbon-type composition. Quantitative calibration was effected by chromatographing naphtha fractions of known composition. The gas chromatographic technique for composition analysis has also been applied to reformer feed naphthas and is a reliable replacement for more expensive methods.
T
HE NUMEROUS APPLICATIONS of gas chromatography to analysis of petroleum streams are well known. Widespread routine uses have, however, been generally limited to the relatively
simple C1 through C7 hydrocarbons. Outstanding successes in analyzing more complex mixtures have been achieved, using specialized techniques and equipment, which often involve increased costs and analysis time. Methods which retain the speed and simplicity features of the original chromatographic technique may require a new approach to interpretation of complex chromatograms. This paper describes such an approach to crude oil analysis, based on research with a mass spectrometer used as a chromatographic detector. Previously reported applications of gas chromatography to quantitative Deceased.
