LITERATURE CITED
( 1 ) Bachmann, L., Bechtold, E., Cremer, E., J . Catalysis 1, 113 (1949). (2) Barrer, R. M., DiscussiOns Faraday SOC.7, 135 (1962). (3) Barrer, R. M., Gibbous, R. &I., Trans. Faraday SOC.59, 2569 (1963). (4) Basila, M. R., J . Phys. Chem. 11, 2223 (1962). ( 5 ) Brunauer, S., Emmett, P. H., Teller, E., J . Am. Chem. SOC.60,309 (1938). ( 6 ) Gant, P. L., Yang, K., Ibid., 85, 5063 (1964). ( 7 ) Hersh, C. K., “Molecular Sieves,” Chap. 4, Reinhold, New York, 1961. (8) Jones, K., Halford, P., Nature 202, 1003 (1964).
(9) King, J., Jr., J . Phys. Chem. 67, 1397 (1963). (10) King, J., Jr., Benson, S. W., J . Chem. Phys., 44, in press. (11) Lambert, M., Phys. Rev. Letters 4, 555 (1960). (12) Landolt Bornstein, “Zahlenwerte
-
und Funktionen aus Physik, Chemie, Astronomic, Geophysik, und Technik, 6th ed., Vql. 1, 509-512, SpringerVerlag, Berlin, 1951. (13) Langmuir, I., Colloid Symp. Monogr.
3, 72 (1925). (14) Lard, E. E., Horn, R. C., ANAL. CHEM.32, 878 (1960). (15) McBain, J. W., Colloid Symp. Monogr. 4, 7 (1926). (16) Martin, A. J. P., Synge, R. L. M., Biochem. J . 35, 1358 (1941).
(17) Mohnke, M., Saffert, W., “Proc. 4th International Gas Chromatography Symposium,” M. Van Swaay, Ed., Butterworth, Washington, D. C., 1962. (18) Moore, W. R., Ward, H. R., J . Am. Chem. SOC. 80, 2909 (1958). (19) Mortensen, E. A., Eyring, J., J . Phys. Chem. 64,433 (1960). (20) Sandler, Y . L., Ibid., 58, 58 (1954). (21) Scott, C., “Proc. 4th International
Gas Chromatography Symposium,” bl. Van Swaay, Ed., p. 36, Butterworth, Washington, D. C., 1962. (22) Spencer, C. F., J . Chromatog. 1 1 , 108 (1963).
RECEIVEDfor review August 4, 1965. Accepted October 11, 1965.
Formamide as a Stationary Phase in Gas Chromatography JOSEF NOVAK and JAROSLAV JANAK Institute of Instrumental Analytical Chemistry, Czechoslovak Academy o f Sciences, Brno, Czechoslovakia
b Formamide is the most polar known stationary phase for gas chromatography. It has a substantially lower volati‘ity than N,N-dimethylformamide or acetylacetone and produces a very low signal in the flame ionization detector. One mole of formamide gives a signal equivalent to 0.3 gram atom of paraffinic carbon. It is suited for the separation of highly volatile polar substances. The retention indices according to Kovbts, corresponding to the polar functional groups, are two to three times higher than on other known polar phases. The peaks of strongly polar substances possessing small moleculessuch as methanol, acetone, etc., are symmetrical even with untreated supports which have relatively high surface areas-e.g, Sterchamol, crude firebrick, aluminum silicates, etc. The values of the C term of the Van Deemter equation are half to one fifth of those obtained for phases commonly used. Formamide is well suited as a stationary phase when capillary columns are used, as well as in trace analysis. The use of formamide as a stationary liquid for the gas chromatographic analysis of complicated mixtures of oxygen-, SUIfur-, nitrogen-, or halogen-containing compounds, is demonstrated by chromatograms.
Keulemans, Kwantes, and Zaal (10) have recommended dimethylformamide as an extremely polar stationary phase for gas chromatography. Retention data of some hydrocarbons on formamide a t 0” C. were reported by Podbielniak and Preston (17). Later, diethylformamide (15) and diphenylformamide (22) were recommended for separation of both saturated and unsaturated hydrocarbons. The use of dimethylformamide is confined to temperatures of about 0’ C. (4, IO),and to detectors of low or medium sensitivity-e.g., a katharometer. The vapor pressure of dimethylformamide is about 9 mm. of Hg (9, 18) a t 40’ C. I n textbooks on gas chromatography, dimethylfonnamide is referred to as a typical phase of extremely high polarity, but in practical work it is rarely used because of its high vapor pressure. These properties of dimethylfonnamide probably were the reason for neglecting the possibility of utilizing unsubstituted formamide, with the exception (17) referred t o above. Thus, other important recently described properties of amides (6, 14) have so far escaped attention. Consideration of the properties of amides induced us to reopen the investigation of formamide as a stationary phase for gas chromatography. EXPERIMENTAL
T
HE lower carboxylic acid amides are strongly associated and exhibit anomalous polarity and vapor pressure (9). These properties make them an interesting subject for chromatogaphic studies.
Apparatus. Measurements were carried out on Chrom 11, a chromatograph of Czechoslovak origin (Laboratory Instruments, Prague), using flame ionization detection. This instrument is intended for work with either packed or capillary columns (16).
The experiments were devised to furnish information on some of the abovementioned aspects of exploiting formamide as a stationary phase in gas chromatography. The packed columns were stainless steel tubes, 85 cm. long and 6 mm. in i.d.; the capillary columns were 50 meters long and 0.2 mm. in i.d. The V , values were measured a t 10” intervals over a range from 30” to 70” C. For practical applications, the working range was from 30” to 40” C. The injection Dort was maintained a t 100” C: throughout. Substances Used in Column Preparation and Analysis. For the preparation of packed columns four types of support were used, including one of high activity. The supports were chosen with regard t o their typical properties, as revealed by electron microscopic examination ( 8 ) . Celite 545 (Johns-Manville Co., Ltd., London, England), particle size 0.170 to 0.149 mm., specific surface area 1 to 2 sq. meters per gram. Crude firebrick (Calofrig, N.E., Borovany, Czechoslovakia), particle size 0.25 to 0.35 mm., specific surface area 10 to 15 sq. meters per gram; raw material for production of Rysorb supports (8)’
S t e r c h a m o 1 (St e r c h a m o 1we rk e G.m.b.H., Dortmund, West Germany), particle size 0.25 to 0.35 mm., specific surface area 7 to 8 sq. meters per gram. Xlusial (Slovnaft, N.E., Bratislava, Czechoslovakia), a technical product used as an inorganic ion exchanger, substantially a sodium aluminum silicate containing 8.5% &03,specific surface area 120 to 160 sq. meters per gram. Alusil is more polar than silica gel or aluminum oxide ( 7 ) . Formamide (VEB Laborchemie, Apolda, East Germany) was applied in the amount of 25% (w./w.) directly, VOL. 38,
NO. 2,
FEBRUARY 1966
265
The calculations were made, assuming the concentration of formamide vapor when the supports had a high load of formamide to be equal to the concentration of saturated vapor. Then, the molar ionization efficiency of formamide can be expressed by the relation
without using a solvent. An intimate mixture of formamide and support was sealed in a glass ampoule and heated a t 180' C. for about 2 hours. The capillary column was coated using a 10% solution of formamide in methanol. Model substances-i.e., n-heptane, benzene, dimethyl ether, l12-dichloroethane, acetone, n-butyl acetate, and methanol-were of C.P. grade (Lachema, N.E., Brno, Czechoslovakia).
q f = I,RT/P'f,T(dV/dt)
(amp. sec. mole-')
Chromatographic Characteristics of Formamide. T o establish the signal
where I f is the ionization current caused by the passage of formamide through the flame, R is the gas constant, T is the column temperature, P'~.T is the pressure of saturated formamide vapor a t column temperature, and dV/dt is the rate of carrier gas flow a t the column outlet-i.e., burner jet orifice. For the estimation of the ionization efficiency of 1 gram atom of paraffinic carbon, qc, the relation
of formamide in the flame ionization detector, its molar ionization efficiency q,, was measured. Because of the dependence of the ionization efficiency upon working conditions, the molar ionization efficiency of formamide was related to the ionization efficiency of 1 gram atom of paraffinic carbon. The measurements were carried out in the following manner: First, an empty column was inserted into the apparatus, and the ionization current, Io, flowing through the flame was determined. Thereafter, the empty column was replaced by a column packed with 30y0 (w./w.) formamide on Sterchamol and the ionization current, 10 I t , was measured under identical conditions. Into the latter column, 10 pl. of a standard containing 3.41 X lo-' mole of acetone (dissolved in MeOH) were injected, and the area under the chromatographic curve of acetone, Fa, was evaluated. These measurements were carried out a t 40°, 50', and 60' C., respectively. During all these measurements, the gas flow rates-Le., H2 80, N2 60, and air 750 ml. per minute as existing a t the burner jet orificethe electrode voltage (250 volts), and burner jet diameter (0.25 mm.) were kept constant.
qc =
IO,
Temp., C. 40 50 60
Table It.
amp.
X 10-10 0.82 1.14 1.43
Csf)o
(amp. sec./g. atom paraffinic C) can be used, where T is the attenuation factor, S is the current range of recorder scale a t full sensitivity, Fa is the area of the acetone peak, p is the length of recorder scale, N a is the number of moles of acetone in the chromatographic zone, dl/dt is the chart speed, and (ZC,,), is the effective carbon number of acetoneLe., (21). The results obtained are summarized in Table I, where c, denotes the concentration of formamide, in moles per milliliter, in the saturated formamide vapor. This value can serve as a guide for estimating the column life a t various working temperatures, in case no saturation precolumn was employed.
+
Table 1.
rSF, PN,(dlldt
Flame Ionization Characteristics of Formamide
I,, P',,T, amp. x 10-l" mm. Hg. 1.68 3.56 7.16
0.107 0.240 0.480
qr1
cf,
mole/ml. X 0.548 1.109 2.310
QCl
amp. sec. amp. sec. mole mole
X 3.06 3.00 3.10 fi = 3.055
G/qc,
X 10-*
C./,/mole
10.2
0,299
Now, let us presume a column containing a quantity of packing corresponding to 10 grams of formamide. If the incipient rate of bleeding of formamide from the column is taken as linear, then, a t a carrier gas flow rate of 60 ml. per minute, the loss of the stationary phase from the column amounts to 2%, corresponding to a 2% reduction in V , at O', 20°, 40°, and 60' C. within about 8000, 1300, 230, and 53 hours of operation, respectively. The measured values of specific retention volumes of model substances were transformed into empirical equations of the known Antoine form (1)Le., log V , = A / T B-indicating the temperature dependence of retention values. The symmetry of peaks (ZOO),and, in the case of methanol, the packing separation efficiency dependence on the rate of carrier gas flow, were also determined. The peak asymmetry, A,, is given by the ratio of intercepts of the base line by the perpendicular drawn a t the peak maximum, and by tangents drawn a t the points on the fore and rear part of the chromatographic curve at half-height of the peak. The values obtained for constants A and B of the Antoine equation, the asymmetry factors, A,, the C terms of the Van Deemter equation, and the H E T P values, H , measured a t a mean carrier gas flow rate of 60 ml. per minute, are summarized in Table 11. The values of C, A,, and H hold true a t 40' C.
+
DISCUSSION
The A , values, summarized in Table 11, indicate that all types of model substances-nonpolar and nonpolarizable (n-heptane), nonpolar but polarizable (benzene), less or more pronounced proton acceptors (ethyl ether, acetone, and n-butyl acetate), proton donors (l12-dichloroethane), and strongly hydrogen-bonded compounds (methanol) -gave peaks, symmetric for analytical purposes, on all solid supports used. The chromatogram in Figure 1, obtained with fonnamide on Sterchamol, may serve as an example. In Table 111,the A , values, measured when using fonnamide, are compared with data previously obtained for vari-
Values of Constants A and 6 in the Antoine Equation, Peak Asymmetry Factors, A,, and C Terms of Van Deemter Equation
Support Sterchamol Substance n-Heptane Ethyl ether Benzene 1,2-Dichloroethane Acetone Butyl acetate Methanol
266
0
A 1620 1605 1490
-B 4.86 3.967 3.15
1545 1970 2320 2380
2.869 3.92 4.85 4.673 HETP = 0 . 8 3 mm. C = 0.004 sec.
ANALYTICAL CHEMISTRY
Firebrick A,
A
1.0 0.8 1.0
1793 1739 1389
0.85 0.9 1.0 0.95
1510 2004 2220 2342
-B 5.363 4.388 2.847
2.750 4.002 4.543 4.580 HETP = 0 . 9 4 mm. C = 0.007 sec.
A.
A
Celite -B
Ai
A
Alusil -B
A,
1.0 1.0 1.0
1700 1712 1397
5.100 4.335 2.870
1.0 0.9 1.0
1980 1660 1720
5.230 3.866 3.797
1.0 1.0 0.9
1.0 0.95 0.9 0.9
1779 1834 2340 2228
0.9 0.95 1.05 0.95
1802 1721
3.617 3.010
1.0 1.1
3.586 3.491 4.919 4.226 HETP = 0 . 9 3 mm. C = 0,009 sec.
. ..
2280
41284 HETP = 1 . 1 4 mm.
C
= 0.008sec.
...
0.95
3
3 1
Table 111. Peak Asymmetry Factors of Various Compounds on Formamide and Other Stationary Phases on Sterchamol
7
2
B
1
Dinonyl Squa- phthal- Digly- FormSubstance lane" ate" cola amideb n-Hexane 1.2 1.1 . . . 1.p Benzene 1.4 ... ... 1.0 Ethyl ether 6 1.5 1.5 0.9 Acetone 8 5 1.6 0.9 Methanol 8 5 1.4 1.0 a At 70' C. At 40' C. c n-Heptane.
adsorption in the stationary liquid, as described by Martin (IS), plays a part. The results confirm that, in the case 1 1.91 grams of 25% (w./w.) N C O N H on SterchamaL Column length of conventional supports, formamide is 8 5 cm. 1.d. 0.6 cm. Temperature 40' C. Rate of carrier gas flow capable of effectively blocking the polar 1 3 2 ml. Na/min. Inlet pressure 1.67 kg./sq. cm. Ambient temcomponent of the adsorptivity of the perature 23' C. F.I.D. attenuation factor X 500. Sample 1 ml. of vapor a t 20' C. support, irrespective of the type of the A. Chart speed 1 cm./min. contributing adsorption forces. As a 6. First three Deaks at chart m e e d 6 cm./min. result, coated Sterchamol and Celite 1. Methane 6. 1;2-Dichloroethane have shown substantially identical sorp7. Acetone 2. n-Heptane 8. n-Butyl acetate 3. Ethyl ether tion characteristics, in spite of the gross 4. Benzene 9. Methanol differences in their physical structure 5. Unknown (8)and in the character and area of their active surfaces (3, 7, 8). Selectivity of Formamide. The ous other stationary phases on Stercompares the specific retention volselectivity of the stationary phase chamol (20). umes of test compounds, measured toward substances belonging to a Symmetric peaks were obtained even using the supports a t 40" C. Whereas certain homologous series is often when the strongly polar adsorbent Alusil with Sterchamol, firebrick, and Celite, expressed by retention indices accordwas used as solid support. In this case, the differences were insignificant, these ing to KovAts ( I @ , or, sometimes, by only n-butyl acetate yielded a severely constants differed considerably in the Bayer's coefficients ( 2 ) , U, defined as the asymmetric widespread zone, almost ratio V,(z)/V,(p) for hypothetical subcase of aluminum silicate support having coinciding with the base line. stances z and p , having the same boiling a specific surface area of 140 sq. meters The asymmetry of the n-butyl acetate points, where p stands for a paraffinic per gram. The influence of adsorption peak was encountered also after a longer hydrocarbon. is most pronounced in the case of the period of column operation, and found In Table V, the values of Bayer's least polar compound, and a minimum to increase gradually with both columns influence can be found with 1,2-dichlorocoefficients, u, corresponding to a boiling prepared by using conventional supports ethane, which is a proton donor. temperature of 50' C., are given, toand stainless steel capillary columns. The above relations become obvious gether with the Kovitts bZ values for the This effect was eliminated by injecting when expressed as (V,,, - Vo,2)/Vg.2, members of different classes of com10 ~ l of. formamide into the strongly where V,,, is the specific retention pounds on formamide and some other heated injection port (approximately to volume measured using a formamide-onliquids as stationary phases. 240' C.). The phenomenon may be The W terms represent the difference Alusil packing and Vu,2is the average caused by flushing the volatilized of the specific retention volumes of the between the retention indices of two formamide from the entrance portion same compound, measured on the other different substances, determined on the of the packing, or from the inlet part of three packings. The extent of deviasame stationary phase and a t the same the capillary wall, thus exposing the tions of the V a . l values suggests that temperature. In the present paper, the surfaces. The effect can be entirely eliminated by using a small saturation precolumn before the analytical column. The properties of the formamide film, used as stationary phase, can be deduced Table IV. Specific Retention Volumes and Discrepancies Caused by Support from data characterizing the dependence Support of column separation efficiency on the Sterrate of carrier gas flow. The values of chamol, Firebrick, Celite, Alusil V,,l - Va,* the C term of the Van Deemter equaSubstance Va 8, V, Va,z Vg = VQ81 Va,2 tion, expressing the resistance to mass n-Hept ane 2.06 2.63 2.14 2.28 12.3 4.40 transfer, are approximately half or one Ethyl ether 14.6 14.5 13.0 14.0 27.2 0.94 fifth of those in the literature (6,11). Benzene 40.7 38.7 38.9 39.4 50.5 0.28 1,2-DichloroInfluence of Adsorption on Retenethane 118 123 124 122 139 0.14 tion. The influence of adsorption Acetone 245 251 239 245 309 0.26 can be estimated from the differences Butyl acetate 355 360 361 358 ... ... in the constants of the Antoine equaMethanol 845 794 774 804 990 0.23 tion of model substances. Table I V Figure 1. Chromatogram of model mixture on formamide as stationary phase
~~~~
VOL. 38, NO. 2, FEBRUARY 1 9 6 6
267
Bayer's Coefficients for Members of Various Homologous Series and Corresponding Kovdts d/
Table V.
2,PDimethylsulfolane"
Polyethylene glycol 400b U dI
p,B'-Oxydipropionitrile U dI
Dimethylformamideo U aI
Formamide U aI U a1 Compound type Alcohols ,.. ... 17.4 650 ... ... ... ... 327 1750 Methyl n-alkyl ... ... ... 13.2 390 ... ... ..* 178 1360 ketones Methyl isoalkyl ketones ... ... ... ... ... ... ... 160 1250 n-Aldehydes ..* *.. 13.jd 415 ... ... ... ... 104 1255 ... ... ... ... n-Alkyl acetates 12.4 400 ... ... 82 1200 Benzene methylhomologs 8.0 27 1 14.8 295 ... 485 ... 568 24 765 Cyclohexane methyl homologs 1.67 87 2.34e 120 ... 180 ... 220 2.43 245 Values calculated from ( 4 ) . b Values calculated from (19). c (82), temperature 55" C. d Straight line representing relation V , = .f( T)b constructed by drawing a line, passing through only one known point lying at 50.29' C. and parallel to rectilinear plot for estersi.e., as experimentally verified in case of formamide. e Straight line passing through point for cyclohexane, at same angle to straight line for paraffins, as in case of formamide.
+
+
5
Activity Coefficients of Cs to Cg Members of Various Classes of Compounds (S'ery dilute solutions in formamide a t 50' C.)
Table VI.
Type of substance n-Alcohols Methyl n-alkyl ketones Methyl isoalkyl ketones n-Aldehydes n-Alkyl acetates Benzene methyl homologs Cyclohexane methyl homologs n-Paraffins
C5 18.1
26.4
54.4
4.03
,..
..,
21.9
40.3
71.5
118
...
... ... ...
... ... ...
20.3 37.2 43.9
36.2 66.5 77.3
70.5 123 143
126 226 267
...
*..
...
46.9
90.0
175
304
...
...
... ...
2080 3110
4480 5171
C4
+
...
110
IO 2
10
'
2
3
4
5
6
7
8
9
Figure 2. Plot of activity coefficients vs. carbon number for individual members of various homologous series on formamide at 50" C. 1. 2. 3.
4. 5. 6.
268
n-Paraffins Benzene methyl homologs +Alkyl acetates n-Aldehydes n-Alcohols Methyl n-alkyl ketones
+
ANALYTICAL CHEMISTRY
Ce
455 925
825 1710
CS 108
CQ
11.0
6.01 8.54
+
c7
C3 6.38
...
bl values represent the difference between the retention index of any of the Cs compounds tested, and the retention index of n-hexane, as measured on the same stationary phase and at the same temperature (50" C.). Thus, the bI values reflect the contribution of oxygen present in the functional group, as well as the contribution of aromaticity and of a cyclic structure, t o the ['apparent number of paraffinic carbons.,' For comparison, the corresponding values for some of the above compounds were taken from the literature (4) for 2,4-dimethylsulfolane and dimethylformamide a t 25.5" C. and for p,@'oxydipropionitrile at 55" C., as stationary phases (4, $2). The selectivity of formamide for benzene is exemplified by a positive increment in dI, which is about 200 higher on formamide a t 50" C. than on dimethylformamide at 25.5' C., and about 470 higher than on PEG 400 at 50" C. To gain a better insight into the behavior of solutions of the chromatographed substances in formamide, the activity coefficients have been calculated for the system-solute vapor equilibrated with the very dilute formamide solution,
a t 50" C., using the well-known relation y = ~~~R/MLP"V The , . activity coefficients are summarized in Table VI. The sharp increase in the values of the activity coefficients of the successive members of a homologous series illustrates, for all compounds tested, the major role played in the sorption in formamide by polar interactions. The increment of dispersion forces is to a considerable degree compensated by the increasing positive deviations from Raoult's law. From data of Figure 2, obtained by extrapolation, it can be seen that only solutions in formamide of polar substances with the lowest number of carbon atoms approach an ideal solution. The extremely high values of the activity coefficients for hydrocarbons and for polar substances with longer paraffinic chains permit the separation of these compounds a t a relatively low temperature. Even for the extremely
f
1
0
1
1
2
1
1
1
4
1
1
1
6 min. 8
Figure 3. Separation of benzenetoluene-p-xylene-styrene mixture at 31 C. Conditions of Figure 1 1. Benzene 3. 2. Toluene 4.
p-Xylene Styrene
L
0
I
S
2
I
,
4
Figure 4. benzene
,
8
8
6
,
8
I
!
“
10
,
‘
12
‘
‘
14
‘
1
16 r n n
Chromatogram of technical
Conditions of Figure 3 1. Aliphatic hydrocarbons 2. Benzene 3. Toluene
4. Thiophene 5. Xylenes
polar formamide, the increase in retention with an increasing number of carbon atoms, is very similar for all types of compounds tested. Analytical Utilization. The practical possibilities of using formamide are illustrated by chromatograms. Figure 3 presents the separation of a mixture of styrene, benzene, toluene, and p-xylene a t 30” C. Figure 4 illustrates determination of thiophene in technical benzene. Figure 5 shows a gas chromatogram of a crude product from the dehydrogenation of Zpropanol, containing a rich mixture of oxygenated compounds, The chromatogram in Figure 6, obtained for the separation of the components of a cellulose lacquer thinner on a capillary column, is a further example of the utilization of formamide as stationary phase. CONCLUSIONS
Formamide is suitable as a liquid phase for gas chromatography. It is an extremely polar substance, because of its electrondonating and accepting
3 5
Figure 6.
groupings, has a relatively small molecule and low viscosity, and gives a low signal in the flame ionization detector. Because of these properties formamide can be used to obtain new separation effects. For a formamide film, the C term of the Van Deemter equation has a value half t o one fifth of those for other stationary phases. Thus, a higher number of theoretical plates per unit length of the column can be achieved. The volatility of formamide at 40’ C. [vapor pressure 0.107 mm. of Hg ( 9 ) ] is lower than the volatility of dimethylor diethylformamide a t 0” C. Formamide as stationary phase is an extraordinarily powerful tailing reducer, and thus it is possible to use conventional materials as solid supports without pretreatment even for analyses of most polar substances. These properties of formamide evidently cause an effective blocking of the active sites of the support. Formamide is a suitable stationary phase in the separation of complex mixtures of highly volatile compounds of polar character, and can be used to good advantage for their separation from hydrocarbons. The values of the retention indices according to Kovhts, for polar functional groups, are substantially higher than when conventional polar stationary phases are used-e.g., 2,4-dimethylsulfolane, polyethylene glycols, oxydipropionitrile, and dimethylformamide. The minor role of dispersion forces in the sorption in formamide (enormous increase in activity coefficients with increasing number of carbon atoms in the hydrocarbon part of the molecule for all classes of compounds tested) makes it possible to analyze on formamide members of homologous series having relatively higher numbers of carbon atoms a t a lower temperature than on other polar stationary phases. Because of the very strong sorption of
?
Chromatogram of cellulose lacquer thinner
Stainless steel capillary, 50 meters long. 1.d. 0.2 rnrn. 1. Paraffins and cycloparaffins 2. Benzene 3. Toluene 4. Xylenes 5. Ethyl acetate
Temperature 40’ C. Sample 1 pg. of liquid 6. Acetone 7. n-Butyl acetate 8. Ethonol 9. Propanol 10. Butanol
i5
2
R I
0
I
I
J
I
j
,
20
I
,
40
’
(
I
”
,
60
1
80
’
8
1
min,
Figure 5. Chromatogram of crude product from 2-propanol dehydrogenation 4 7 . 6 grams of 25% (w./w.) HCNOHz on Sterchamol. Column length 3 4 0 cm. 1.d. 0.6 cm. Temperature 40’ C. Sample 1 ml. of vapor, F.I.D. attenuation factor X 50 1. Nonaromatic hydrocarbons 2. Ethyl ether 3. Diisopropyl ether 4. Ethanol 5. Propionaldehyde 6. n-Butyraldehyde 7. Ethyl acetate 8. Acetone
alcohols and water, formamide is a phase especially suited for the analysis of various admixtures present in these compounds. ACKNOWLEDGMENT
The authors are indebted to Olga Hainova and 0. Pospichal for technical assistance. LITERATURE CITED
(1) Ambrose, D., Keulemans, A. I. AI., Purnell, J. H., ANAL.CHEM.30, 1582 (1958). (2) Bayer, E., “Gas-Chromatographie,” p. 20, Springer-Verlag, Berlin, 1959. (3) Blandenet, G., Robin, J . P., J . Gas Chromatog. 2, 225 (1964). (4) Bloch, M. G., in “Gas Chromatography 1959,” H. J. Noebels, R. F. Wall, N. Brenner, eds., p. 133, Academic Press, New York, 1961. (5) Brass, S. J., Nashan, W. I., Meighan, R. M., Cole, R. H., J. Phys. Chem. 6 8 , 509 (1964). (6it Dal Nogare, S., Juvet, R. S., Jr., Gas-Liquid Chromatography,” p. 138, Interscience, New York, 1962. (7) Janitk, J., Collection Czech. Chem. Commun. 20, 1241 (1955). (8) Janitk, J., Stassewski, R., J. Gas Chromatog. 2, 47 (1964). (9) Jordan, T. E., “Vapor Pressure of Organic Compounds,” p. 189, Interscience, New York, 1954. (10) Keulemans, A. I . M., Kwantes, A., Zaal, P., Anal. Chim. Acta 13, 357 (1955). (11) Keulemans, A. I. >I., Kwantes, A., Zaal, P., in “V;pour Phase Chromatography 1956, D. H. Desty, ed., p. 15, Butterworths, London, 1957. (12) Kovitts, E. Z., Z. Anal. Chem. 181, 351 (1961). VOL. 38,
NO. 2,
FEBRUARY 1 9 6 6
269
(13) Martin, R. L., ANAL. CHEM.33, 347 (1961). (14) Meighan, R. M., Cole, R. H., J. Phys. Chem. 68, 503 (1964). (15) Morrow, H. M., Buckley, K. N., Petrol. Refiner 36, 157 (1957). (16) Novhk, J., JanAk, J., Chem. Listy 57, 371 (1963). (17) Podbielniak, W. J., Preston, S. T., Petrol. Refiner 35, 215 (1956).
(18) Preston, S. T., Jr., J. Gas Chromatog. 1, No. 319 (1963). (19) Raupp, G., 2. Anal. Chem. 164, 135 (1958). (20) Stazewski, R., Janhk, J., Collection Czech. Chem. Commun. 27, 532 (1962). (21) Sternberg, J. C.,. Gallaway, W. S., Jones, D. T. L., in "Gas Chroma-
tography," N. Brenner, J. C. Callen, M. D. Weiss, eds., p. 231, Academic Press, New York, 1962.
(22) Tenney, H. M., ANAL. CHEM.30, 2 (1958).
RECEIVEDfor review July 12, 1965. Accepted November 3,1965. Third International Symposium on Advances in Gas Chromatography, Houston, Tex., October 1965.
Support Effects on Retention Volumes in Gas Chromatography PAUL URONE and JON F. PARCHER University of Colorado, Boulder, Colo. Four series of matched columns using deactivated and nondeactivated acid-washed firebrick as support materials and squalane and tri-o-tolyl phosphate as liquid phases were studied to determine the dependence of gas chromatographic retention volumes of polar solutes on surface active supports. Liquid surface effects were absent on both the squalane and tri-otolyl phosphate columns. Retention volume minima at 0.6% and maxima at 2% liquid phase were observed for the solutes on squalane-coated surface active AWFB columns indicating a wide variety of retention effects over a small liquid phase range for low-loaded columns. Zero sample size retention volumes obtained from a series of samples injected on columns being subjected to constant amounts of the same solute in the carrier gas gave straight line Freundlich-type plots for the low-loaded columns. The slopes of the lines, which indicated sample size effects, differed for different liquid loads, being steepest at the lowest liquid phase loads. Adsorption isotherms for acetone on squalane-coated AWFB columns were essentially Type I of the BET classification and paralleled the retention volume dependence upon the amount of liquid phase coating for their relative magnitude.
R
of polar solutes are affected by the type and amount of liquid phase, the type and the treatment of the solid support, the sample size, and the temperature (13). The difficulties of comparing the performance of different column supports have been discussed (1, 12). Martire (6) applied theory of solution techniques to the calculation of activity coefficients of gas chromatographic solutes through their dispersive, orientation, and induction forces. His final expression for the 270
ETENTION VOLUMES
ANALYTICAL CHEMISTRY
activity coefficient includes an empirical residue factor, K , which is probably due to support effects. Martin ( 5 ) , Pecsok et al. (IO), and Martire, Pecsok, and Purnell (7) studied the adsorption of solutes on liquid phase surfaces by gas chromatographic and surface tension measurements. Observed retention volumes were interpreted to be composed of liquid phase and liquid surface adsorption contributions. Previous studies by the author (16) showed that, although the type of solid support and its treatment greatly affected the specific retention volumes of polar compounds, relative retention volumes and activity and partition coefficients were remarkably repetitive from column to column for a given homologous series on a given liquid phase coated on different types of supports. The heats of solution, on the other hand, did not show a strong repetitive pattern from column to column. Further studies of the contribution of the solid support to the retention volumes of polar solutes have been undertaken by comparing the retentive characters of four series of matched columns using deactivated and nondeactivated acid-washed firebrick as support materials. Deactivation of the support was accomplished by intensively treating a portion of the firebrick used in the study with hexamethyldisilazane (HMDS) using a recently developed radiation-induced copolymerization technique called RIC (14). Surface area measurements showed little change in the surface area of the support caused by the treatment. EXPERIMENTAL
Each series of columns included eight to ten columns of the respective firebricks coated with 0.6 to 22% squalane and tri-o-tolyl phosphate (TOTP), respectively. Coating of the columns was accomplished by a special solution
coating technique which helped to give some assurance that columns coated with small amounts of liquid phase had a uniform distribution of the liquid (9). Retention data were obtained a t different liquid loads, sample sizes, under various conditions of column sweep time, and in the presence of known amounts of solute in the helium carrier gas. Each column was made of copper tubing 1 meter by 4-mm. i.d. All retention data were taken a t 75" C., and all retention volumes were corrected for pressure and air peak volumes. All columns were properly conditioned before use. Columns with no liquid phase were conditioned by heating to 200" C. over a half-hour period. Coated columns were conditioned overnieht a t 75" C. Sample injections for Figures 1 and 2 were obtained by using helium saturated a t 30" C. with the respective vapors and a 0.922-m1. gas sampling loop. Liquid sample injections of acetone less than 1.0 pl, were obtained by diluting the acetone with an inert solvent such as hexane. A 1000-cubic-inch (16.4 liter) stainless steel tank containing helium a t 80to 100-p.s.i.g. pressure and acetone a t approximately 50% of saturation pressure (100 to 160 mm.) was used as a source for a constant amount of acetone (Figure 3). The helium-acetone mixture was bled into the carrier gas stream with a capillary tube and controlled by a fine-control needle valve. The concentration of the acetone was determined by absorbing the acetone in a 1.ON NaOH solution, adding excess iodine, and back-titrating with thiosulfate (3, 8). RESULTS AND DISCUSSION
Figures 1 and 2 show the variation of the net retention volume per gram of coated support with the per cent of liquid phase. Reproducible values obtained from consecutive sample loop injections of the individual solutes at 5-minute intervals were used because the first injections in the low-loaded nondeactivated (AWFB) columns either
