levels. I n an effort to learn whether other metals known to occur with titanium would interfere, two analyses were made on mixtures of oxides of eight metals. To the weighed samples of Ti02, containing 0.0766 and 0.0764 mg. of Ti, respectively, were added 0.06 to 0.1 mg. amounts of each of the following: ZrOz, HfOz, NbzOs, Taz05, Fez03, SnOz, and h1203. The found values were 0.0790 and 0.0830 mg. of Ti. If the boiling point data on the metal chlorides are examined, it will be seen that none of the other chlorides would be expected to have the same retention time as TiC14. If this is true the only other readily apparent source of error is interference with the chlorination process in some manner. Extension of Technique. It seems quite likely t h a t this technique could be adapted for the analysis of mixtures of other volatile metal chlorides. Figure 3 is a chromatogram of SnC14 and TiCl, obtained from the reaction products of a mixture of the metal oxides and cc14. The technique should be amenable to extension to other ores and ceramic materials, particularly those that are primarily oxides. Bardawil, Collier, and Tyree ( 2 ) have shown that sulfide ores can also be chlorinated using this technique. Estensive attempts have been made to adapt the analyticd procedure to a chromatographic systcbm with an elec-
tron capture detector. The electron capture detector is extremely sensitive to electronegative species such as chlorine; consequently, it should be capable of detecting much smaller amounts of titanium tetrachloride than the thermal conductivity detector. But some experimental difficulties must be overcome before the method can be adapted to the more sensitive detector. I n particular, a way must be found to eliminate poisoning of the detector by the excess carbon tetrachloride in the reaction mixture. Efforts to do this by causing the bulk of the carbon tetrachloride to by-pass the detector or by substituting other chlorinating agents have been unsuccessful. LITERATURE CITED
(1) Albert, D. K., ANAL.CHEM.36, 2034 (1964). (2) Bardawil, A. B., Collier, Jr., F. N., Tyree, Jr., S. Y., Inorg. Chem. 3, 149 (1964). (3) Barksdale, J., “Titanium, Its 07;
currence, Chemistry, and Technology, Ronald Press. New York.
77., The .1949.
D.
(4) Camboulives, & P.,‘I Compt. . Rend. 150, 175 (1910). ( 5 ) Eisentraut, K. J., Sievers, R. E., J . Am. Chem. SOC.87, 5254 (1965). (6) . . Freiser,. H.,. ANAL. CHEM.31, 1440 (1959). (7) Juvet, R. S., and Wachi, F. M., Ibid., 32, 290 (1960). (8)Keller, R. A,, J. Chromatog. 5, 225 (1961). (9) Knox, K., et al., J . Am. Chem. SOC.
79, 3358 (1957) and references cited therein. (10) Morie, G. P., Sweet, T. R., ANAL. CHEM.37, 1552 (1965). (11) Moshier, R. W., Schwarberg, J. E., XXth International Congress of Pure and Applied Chemistry, Moscow, U.S.S.R., July 1965. (12) Moshier, R. W., Schwarberg, J. E., Morris. M. L.. Sievers. R. E.. 14th Conference on’ Analytical Chemistry and A plied Spectroscopy, Pittsburgh, Pa., d a r c h 5, 1963. (13) Moshier, R. W., Sievers, R. E., “Gas Chromatography of Metal Chelates,” Pergamon Press, Oxford, 1965. (14) Ross, W. D., ANAL.CHEM.35, 1596 (1963). (15) Ross, W. D., Sievers, R. E., Wheeler, Jr., G., Ibid., 37, 598 (1965). (16) Ross, W. D., Wheeler, G., Jr., Ibid., 36, 266 (1964). (17) .Scribner, W. G., Kotecki, A. M., Ibzd., 37, 1304 (1965). (18) Scribner, W. G., Treat, W. J., Weis, J. D., Moshier, R. W., Ibid., p. 1136. (19) Tadmor, J., Ibid., 36, 1565 (1964). (20) Tadmor, J., Bull. Res. Council Israel 11 Sec. A, No. 2, 144 (1962). (21) Tadmor,. J.,. J . Gas Chromatoa. ” 2.. 385 (1964). (22) Wachi, F. M., Thesis, University of Illinois, L. C. Card No. Mic. 59-2061 (1959). (23)-Weller, A., Chem. Ber. 15, 2593 (1882).
RECEIVED for review July 7, 1965. Accepted December 6, 1965. Research supported in part by the ARL In-House Independent Laboratory Research Funds, Office of Aerospace Research, U. S. Air Force. Third International Symposium, Advances in Gas Chromatography, Houston, Texas, October 1965.
Separation of Gaseous Mixtures Using Yorous Polyaromatic Polymer Beads 0. L. HOLLIS Basic Research, The Dow Chemical Company, Texas Division, Freeport, Texas
b Outstanding separations of volatile compounds have been achieved with columns of polyaromatic polymer beads which were synthesized by suspension with a diluent to give a highly porous structure. Notably sharp, symmetrical peaks, and low retention volumes were found for water, alcohols, and glycols. These polymer packings have the partition properties of a highly extended liquid surface without the problems of support polarity, liquid-phase volatility, or freezing point which hamper gasliquid chromatography. These porous polymers have been synthesized from monomers such as styrene, tertiarybutylstyrene, and ethylvinylbenzene with divinylbenzene as crosslinker. Applications of porous gel polymer columns have ranged from the analysis of the oxides of nitrogen to the determination of diethylene glycol in dipropylene glycol. The analysis of trace
quantities of water in a variety of materials has been greatly facilitated because water is eluted very rapidly with good peak shape from these columns. These columns have proved to be particularly useful where the adsorptive properties of the stationary phase contribute to tailing or skewing of the peak from materials such as carbon dioxide and acetylene on gas-solid chromatographic systems and water on most gas-liquid chromatographic systems.
P
their synthesis, and some of their properties were described by Lloyd and Alfrey (3, 4). More recently, Moore (6) described the use of porous polymer beads of styrene divinylbenzene as columns for separating polymers by a technique called “Gel-Permeation ChromatogOROUS POLYMER BEADS,
raphy” (GPC). For use in this technique, the bead is specifically tailored to have a given permeability (pore size) according to the size of molecule to be separated. The bead polymer was synthesized by suspension polymerization (1). It was found that on drying certain of the porous styrene divinylbenzene beads they retained the size and presumably much of the physical structure within the bead which they had when wet. This retention of shape was dependent upon the amount of crosslinking and upon the character of the diluent used in the polymerization. Samples of the dried GPC beads were obtained from J. C. Moore of The Dow Chemical Co. Texas Division, and were tested as column packings for separation of gaseous mixtures. Unusual separations were obtained, and the evidence indicates that the partition process with with porous polymers is different from VOL. 38, NO. 2, FEBRUARY 1966
309
~~
Table 1.
Polymer 1 2 3 4 5 6 7 8 9 10 11 12 13
Monomers EVBb-DVB sx2 SX8* EVB-DVB EVB-Styrene-DVB EVBStyrene-DVB tButylstyreneEVB-DVB EVB-Styrene-DVB EVB-Styrene-DVB EVB-Styrene-DVB EVB-Styrene-DVB EVB-Styrene-DVB EVB-DVB
Permeability by GPC (A.) lo6 150 40 400 400 lo4 105 106 106 106 lo6
14 EVB-Styrene-DVB 5 15 EVB-Styrene-DVB 5 16 ET'B-DVB 17 EVB-DVB 18 EVB-Styrene-DVB 19 EVB-DVB a ppf.-Plates per foot. S X 2 and SX8 are styrene-divinyl
Bulk density, g. per cc. 0.220
528.6 0.48 119.8
0.489 0.39 0.60 0.246
291.4 121.5 55.8
0.388 0.199 0.187
15.1 282.4
X lo5 X 105
0.268 0.160 0.222
106 400
505.0 615.0 660.0
0.254
G. C. utility Very good No separation No separation Very slow elution No separation Good Fair Good Usable, fair Poor Not good Not good Good separations; too fragile for general use Fair Fair Very fragile Good separation Good separation Very good
components in our laboratory gas (methane, ethylene, and ethane) when run at 50' C. The temperature was raised to 100' C. and the separation of natural gas components mas still complete. Several low-boiling compounds including methylene chloride, ethylene oxide, propionaldehyde, and chloroform were run. All had long retention times, relative to what was expected from previous gas chromatographic experience, but the peak shapes were good. I n the chloroform samples a small symmetrical peak (eluted in about one third the time of chloroform) appeared which was thought to represent about the amount of ethanol used as an inhibitor. This would be very rapid elution of the alcohol relative to chloroform. A sample of methanol was run, and the methanol was eluted from the column in about the same time as propane. Many other results were
-32' C.'tb Column Polymer Polymer No. 6 No. 13 (8.57) (4.88) 0.06 0.08 1.00 1.00 0.08 0.10 0.16 0.17 0.26 0.30 0.30 0.30 0.42 0.36 2.04 1.02 2.69 1.62 2.46 1.77
Relative Retention Data at
Compound
Polymer No. 1 (4.90)
Polymer KO.19 (5.93) 0.05 1.00
Water retention t,ime (minutes) 0.08 Air 1.00 Water 0.08 0.10 Methane 0.19 0.18 Carbon dioxide 0.39 0.30 Ethylene 0.39 0.30 Acetylene 0.56 0.41 Ethane 2.75 ... Propylene 3.57 2.17 Propane 3.23 2.32 Methyl chloride H20 = 1.00. b Data taken with 6-foot X 3/~6-inchcolumn operating a t approximately 32' C. with 50 t o 55 cc. per minute hydrogen carrier flow. 0
310
ANALYTICAL CHEMISTRY
Approx. column efficiency, PPf." ~~
0 0 316 0
n-Propyl Ethylenee and t-butyl acetylen alcohol sepn. sepn. Good No
Poor
Yes
Poor Poor Poor
No Ye8 Slight
Good
No
Good
No
135 400-800
benzene polymers commercially available from Dow Midland.
that in conventional gas-liquid or gassolid chromatography. Apparently the components to be separated partition directly from the gas phase into the solid amorphous polymer of which the porous beads are composed, whereas in conventional gas chromatography the partition is from gas to a solid adsorption surface or from gas into a thin film of liquid supported on an impervious solid. The conventional partitions are thin film phenomena, involving only a small part of each packing particle, while porous-polymer bead chromatography appears to involve the entire particle. Initially a '/*-inch X 10-foot column was prepared and a sample was tried to determine whether the column would perform separations at all. Natural gas was used to determine dead volume since the column was coupled to a flame ionization detector. Surprisingly, there was a very large separation between the
Table II.
Properties of Porous Polymers
Surface area, m.2 per g. 119.8
unexpected. The same column might possibly be used to separate inorganic gases, water, alcohols, and glycols. EXPERIMENTAL
Apparatus and Materials. The equipment used included a PerkinElmer Model 800, a Barber-Colman Model 10 with a n argon-diode detector with strontium-90 source, and a homemade thermal conductivity apparatus. To deliver a small sample to t h e column when either the argon or flameionization detectors were used, a front-end splitter was used. Liquids were used to modify the porous polymers to achieve specific separations; these included polypropylene glycol P-2000, tetraethylenepentarnine, polyethylenimine (hIW2000), and polyphenyl ether 5P4E from The Dow Chemical Co. The porous polymers were obtained from a number of laboratories within The Dow Chemical Co. and from Waters Associates, Inc., but we synthesized most of the ones used in these studies. The most useful of these porous gel beads are now available from Waters Associates, Inc., 61 Fountain Street, Framingham, hIass., as Gel P and Gel Q (which correspond to gels S o . 6 and No. 19). This paper deals only with bead polymers, which are essentially polyaromatic. We have done extensive work on porous-bead polymers of other chemical natures and hope to report on these in the future. Preparation of Columns. I n general, the polymer beads were rigid and as strong or stronger t h a n most diatomaceous earths which are commonly used in gas chromatography. The dried polymers could be used directly or could be modified with suitable liquids t o perform specific separations. They were packed into columns by vibration and slight tamping.
To modify the beads with a liquid, the liquid dissolved in a solvent was added to the beads, and the solvent was removed. Both the modified and unmodified beads were easily handled during packing except for the static charge build-up on glass or plastic. In metal columns the beads were probably more easily packed than most gas chromatographic column packing materials, RESULTS AND DISCUSSION
Table I lists some of the porous polymer gels that we have tried as column packings. Not all polymer gels which are available for Gel Permeation are usable for gas chromatography. For a gel to be useful it must retain most of its structure on drying. Rigidity and surface area are important factors which affect the separation performances of porous polymers. A high degree of crosslinking is one way of preserving the uniformity of structure on drying or, in other words, preventing the collapse of the mechanical structure of the bead. A large surface area is necessary for good separations; this dlows rapid equilibrium. The surface area is dependent upon rigid structure but can also be affected by the kind and amount of diluent used. The strength of the polymer beads or aggregates is important for their use. If the particle is too fragile to withstand the handling during size separating and particularly during packing, it is of little use. Some such polymers are noted in Column 6 of Table I. The fragility of the polymer is dependent upon the internal structure, which is dependent on the nature of the diluent used in its preparation and on the diluent to monomer ratio. Tables 11, 111, and IV show the relative retention times of representative compounds which have been separated on porous-polymer columns at three different temperatures. Of particular note is the separation of hydroxyl-containing compounds, particularly water, alcohols, and glycols. On a .%foot column, water and all of the C1to Ca saturated alcohols were separated and a mixture of the 16 CI to CS saturated alcohols gave 14 peaks. The separation of the C1 to Cs alcohols is shown in Figure 1. I n Table I, Columns 8 and 9 refer to separations which with the separation of water from ethane and propane (Figure 2) were used as criteria for comparison of one polymer with another. I n general, the polymers made from ethylvinylbenzene-divinylbenzene (EVB-DVB) would separate n-propyl from t-butyl alcohol easily b u t would not separate ethylene from acetylene. The ethylvinylbenzene-styrene-divinylbenzene polymers were suitable for a partial acetylene-ethylene separation, b u t not for a clean separa-
Table 111. Relative Retention Data at 100' C a s * Compound Column 1-Propanol Retention Polymer No. 1 Polymer No. 6 Polymer No. 13 Polymer No. 19 time (min.) (8.90) (7.70) (34.0) (29.4) Air 0.03 0.04 0.012 0.01 Water 0.08 0.13 0.045 0.04 Methane 0.04 0.05 0.015 0.02 0.05 ... Carbon dioxide ... Ethylene 0.06 0.07 0 026 0.03 0.026 Acetylene 0.06 0.07 0.03 Ethane 0.07 0.07 0.032 0.03 Propylene 0.14 0.073 ... ... 0.085 Propane 0.14 0.13 0.10 0.14 0.16 Methyl chloride 0.11 0.08 0.70 0.72 Methylene chloride 0.66 0.50 Vinyl chloride 0.21 0.21 0.19 0.14 Ethyl chloride 0.37 0.35 0.24 0.33 Methanol 0.15 0.18 0.10 0.10 Ethanol 0.33 0.37 0.28 0.28 2-Propanol 0.65 0.67 0.60 0.63 1-Propanol 1.00 1.00 1.00 1.00 &Butyl alcohol 1.25 1.00 1.35 1.34 Butadiene 0.31 0.31 0.24 0.27 Pentane 0.97 0.87 ... ... 1.27 1.32 Cyclopentane ... ... Hexane 2.76 2.29 ..* ... Cyclohexane ... 3.07 ... Benzene 3.19 ... ... Nitroethane ... 2.73 2.04 ... Acetone 0.61 0.69 0.54 0.59 Diethyl ether 0.94 0.86 0.84 1.02 Acetonitrile 0.45 0.64 0.36 0.41 Acrylonitrile 0.60 0.71 0.62 0.91 Formic acid ... 0.48 Acetic acid .., 1.18 Propionic acid ... 3.57 a I-Propanol = 1.00 Data taken with 6-foot X 3/la-inch column operating with 50 to 55 cc. per min. hydrogen carrier flow.
:
.
I
.
Table IV. Relative Retention Data at 157' C . a v b Compound Column 1-Propanol retention Polymer No. 1 Polymer No. 6 Polymer No. 13 Polymer No. 19 time (min.) (2.10) (1.21) (3.96) (5.05) Air ... 0.23 0.093 0.06 Water 0.25 0.40 0.23 0.13 Methane 0.07 ... ... 0.10 ... ... 0.16 ... Carbon dioxide Ethylene ... ... 0.17 0.10 Acetylene ... ... 0.17 ... Ethane ... ... 0.19 0.11 Propane 0.23 ... ... 0.30 0.24 Methyl chloride 0.28 ... 0.30 ... 1.00 0.74 0.83 Methylene chloride Vinyl chloride 0.34 ... 0.32 0.34 0.50 Ethyl chloride ... ... 0.50 Ethylene oxide ... ... 0.34 ... Methanol 0.32 0.44 0.32 0.22 Ethanol 0.51 0.62 0.43 0.43 2-Propanol 0.14 0.78 0.71 0.75 1-ProDanol 1.00 1.00 1 00 1.00 &Butyl alcohol 1.15 1.04 1.60 1.21 Butadiene ... 0.60 0.42 ... Pentane 0.98 0.92 0.92 1.11 Cyclopentane 1.31 1.08 1.62 1.41 Hexane 2.10 1.71 2.17 2.65 Cvclohexane 2.73 1.94 2.83 3.38 Benzene 2.58 2.20 2.60 .. 2.88 Nitroethane 1.75 2.11 2.52 1.92 Acetone 0.71 0.83 0.70 0.69 Diethyl ether 0.95 0.77 0.90 0.98 Acetonitrile 0.65 0.90 0.57 0.64 Acrylonitrile 0.84 1.01 0.78 0.82 Ethylene glycol 2.02 2.55 3.11 2.12 Propylene glycol 3.28 3.34 3.97 3.66 Formic acid 0.29 ... 0.53 0.41 Acetic acid 0.84 ... 0.97 0.85 Propionic acid 1.80 ... 3.05 2.85 1-Propanol = 1.00. Data taken with 6-foot X a/,e-inch column operating- with 50 to 55 cm. Der min. hydrogen carrier flow. ~
5
VOL 38, NO. 2, FEBRUARY 1966
31 1
fusion vary in their importance to gas chromatographic performance with different sample materials. This is illustrated in Figure 3, which shows acomparison of alcohols run on polymer No. 13 (which was efficient for all components) us. alcohols run on polymer No. 12 (which gave good efficiency for the normal alcohols, but very poor efficiency for the t-butyl alcohol). The retention of water may be dependent upon internal structure, as indicated by the data in Column 3, Table I, and Figure 2, which show the water eluted immediately behind ethane on polymer No. 19 (which had a 400-A. permeability as measured by GPC) and just in front of propane on polymer No. 13 (which had a 106-A. permeability). We hope to investigate further the effects on minor physical structure changes. Specific Separations. HYDROCARBONS. The surprising separation of methane, ethylene, and ethane, in that order, led t o investigation of hydrocarbon separations. The separation of the C1 to C3 hydrocarbons can be accomplished on a 6-foot column of polymer No. 6 in the order, methane, ethylene, acetylene, propylene, propane, propadiene, and niethylacetylene a t 30' C. By programming the temperature, paraffins through Ce can be separated and appear to be eluted according to carbon number, and such a separation is shown in Figure 4. As seen from Table
b'x3116" ~olyrner93
Column:
Conditions: 17f C
. 3 0 ~519.Argon
I
I
5
10
25
20
15
35
30
TIME IN MINUTES
Figure 1.
Separation
of
C1 to
CSalcohols
171 ' C., 30 p.r.i.g. argon; column 6-foot X */le-inch Polymer No. 13
Conditions:
mer may give access to a greater proportion of its weight even though the surface areas are essentially the same. This implies that some of the more extended, less rigid structures originally formed had collapsed on drying and thereby became inaccessible; selectivity changes may be produced in this way, as surface adsorption, solubility, and dif-
tion of the alcohols. The ethylvinylbenzene-divinylbenzene polymer was better for most applications, but the ethylvinylbenzene - styrene - divinylbenzene polymer gave more rapid elution (compare polymer No. 6 with other polymers in Table 11,111,and IV). This indicates that the structure of ethylvinylbenzene-divinylbenzene poly-
I
bl
K
%
e
n
I
oi
c P
1 0
Figure 2.
1
2
2
3
0
1
¶
101 ' C., 55 cc. per minute HZ
ANALYTICAL CHEMISTRY
3
4
5
6 1 0 TIME (MINUTES)
Conditionrr
150' C., 20
1
¶
3
4
5
Comparison of polymers
Figure 3.
Effect of structure on water separation
Conditions
312
3 0 1 TIME (MINUTES)
CC.
per minute He; Columns 6-feet
X
'/pinch
b
Condition,: 45' to 170' C., 2 0 cc. per minute He; 2 4 ' C. per minute, column 6-foot X l/*-inch Polymer No. 1 3
Relative Retentions of Cl to C4 Alcohols at 170" C . Q , ~
Table V.
Figure 4. Temperature-programmed chromatogram-C1 to CShydrocarbons
.!
Q
Column Polymer Polymer No .13 ComDound NO. 13 5%P-2000 Methanoi 0.292 0.250 Ethanol 0.488 0.440 2-Propanol 0.765 0.662 1-Propanol 1.00 1.00 2-Methyl-2-propanol 1.17 0.825 2-Butanol 1.66 1.45 2-Methyl-1-propanol 1.87 1.65 1-Butanol 2.24 2.28 2-Methyl-2-butanol 2.76 2.09 or 1-Propanol = 1.00. Data taken with 6-foot X 8/lginch column operating with 30p.s.i.g. argon carrier.
+
.F
I -
0
11, the hydrocarbons are retained much longer on the column than are hydroxyl compounds with similar boiling points. ALCOHOLS. The C1 to CS alcohols are separated very well on the No. 1 polymer bead column. On this column n-propyl alcohol was eluted before t-butyl alcohol, and the tm-o were well separated, but on a S o . 6 polymer bead column, the n-propyl and t-butyl alcohols were not well separated. By modifying the beads with a liquid such as has been normally used for gas-liquid chromatography, the separating characteristics of the column can be altered. A comparison of two 6-foot columns of polymer ]so. 13 (one column of untreated
> 4
4
beads and one modified with 5% P-2000 polypropylene glycol) is shown in Table V. When No. 6 polymer was modified with 4.85% polyphenyl ether 5P4E, the t-butyl was eluted before the n-propyl.
t
c
I
P
0
I
0 P 4 (TIME MINUTES) Left ~ 0 . 0 5 - p l sample; . right, ~ 0 . 3 0 - p l .sample
4
Figure 5. Conditions:
1
'
I 6
Glycol and oxide separations on porous polymers X '/ls-inch Polymer No. 19
1 5 8 C., 60 cc. per minute H2, column 6-foot
L
I 0
I 1
I P
I 3 (TIME MINUTES)
I 4
Figure 6. Separations of Cl to CB monobasic acids Conditions: 196' C., 7 5 cc. per minute H2, column 6-foot X '/ts-inch Polymer No, 19
VOL. 38, NO. 2, FEBRUARY 1966
313
~~
0
1
Figure 8. nents
1 3 4 TIME (MINUTES)
5
~
6
Separation of air compo-
Conditions: -78' C., 9 0 cc. per minute Hz, column 16-foot X 3/ldnch Polymer No. 1 9 0
1
9
3
4
5
10
15
TIME (MINUTES)
Figure 7.
Separation of amines X 8/le-inch Polymer No. 19
Conditionrr 74' C., 75 cc. per minute Hz, column 6-foot
Very good peak shapes and efficiencies were obtained with all alcohol samples, and there was very little tailing. Most of the tailing was probably due to the apparatus and not the column. The efficiency of the column used to obtain the separation shown in Figure 1 was approximately 800 plates per foot for the see- and n-butyl alcohol peaks. GLYCOLS.One of the most surprising findings in working with the porous-
Table VI. Relative Retentions on Amine Modified Columns at 75' C . a , b
Column Polymer Polymer No. 19 No.19 10% TEPAc 10% PEId 0.050 0.032 ... 0.046 *.. 0.080 *.. 0.094 ... 0.242 ... 0.550 ... 0.732
+
+
Compound Air Methane Ethylene Ethane Propane Isobutane n-Butane Water 1.00 1.00 Ammonia 0.107 0.095 Carbon dioxide ... 2.41 Methylamine 0.325 Dimethylamine 0:5i8 0.714 Trimethylamine ... 0.945 Ethylamine ... 1.06 Diethylamine 2.38 4.10 Isopropylamne 1.00 ... a Water = 1.00. Data taken with &foot x */lcinch column operating with 75 cc./min. hvdrogen carrier flow. Tetraethylene pentamine. Polyethylenimme.
314
ANALYTICAL CHEMISTRY
+ 1 0 % PEI
polymer beads was the elution of ethylene glycol before propylene glycol, as shown in Figure 5. Diethylene glycol is eluted in front of dipropylene glycol. All of the glycols through Cq could be separated on a %foot column of polymer No. 1. ACIDS. The lower monobasic acids were eluted from the beads with good peak shape, except for a slight amount of tailing, as shown in Figure 6. Formic, acetic, and propionic acids were well separated from each other, but acrylic acid was not separated from the propionic acid. NITROGENCOMPOUNDS.The amines which were separated on the porous polymer beads all had bad tailing characteristics, particularly the polyamines such as ethylenediamine. Ethylenimine and diethylamine gave reasonably good peak shapes; however, a column made of polymer No. 19 beads, modified by adding tetraethylenepentamine or polyethylenimine, gave very good peaks for ammonia and the lower amines, as shown in Figure 7. Retention data from such a column are shown in Table VI The lower nitriles which were tried gave very good peak shapes, and the separation of aceto- from acrylonitrile could be accomplished in a relatively short time as shown in Tables I11 and IV. CHLORINATED HYDROCARBONS. The chlorinated hydrocarbons gave good peak shapes in all cases. Most of the separations achieved were not outI
standingly different from those possible by usual gas-liquid chromatographic columns. I n the lower boiling members such as methyl, vinyl, and ethyl chloride, the separations relative to hydrocarbon gases and carbon dioxide niight prove useful. The separations were good, as is shown in Tables 111 and IV. INORGANIC COMPOUXDG.The inorganic compounds which have been separated have been gases. It should be noted that a t temperatures from 30" to 100' C. many compounds such as nitrous oxide (SzO), carbon dioxide (CO*), and carbonyl sulfide (COS)can be effectively separated on porous polymers. These compounds give poor gas chromatographic characteristics, such as bad tailing, gross adsorption, or reaction, when separated using solid adsorbents or gas-liquid chromatography with diatomaceous earths as solid support. The components of air can be separated a t -78' C. as shown in Figure 8. The nitrous oxide-carbon dioxide separation which was accomplished with some difficulty by DeGrazio (2) can be done on a 12-foot column of polymer No. 19, as shown in Figure 9. ~IISCELLANEOUS APPLICATIOSS.The porous polyaromatic beads are thermally stable up to 250' C., as indicated by thermal gravimetric analysis. Therefore, columns of the polymer beads work quite well for temperature-prograinmed operations. This is illustrated in the analysis of water, acetone, and phenol as shown in Figures 10 and 4. The behavior of water on these polymers was probably the most interesting of many unique separations. Figure 11 s h o w the separation of a low-boiling chloride, oxide, ether, and ketone from
L
io
'
Figure 9.
Separation of COz from
NzO Conditions: 2 7 ' C., 50 cc. per minute He, column 12-foot X 3/~o-inch Polymer No. 1 9
water, methanol, and ethanol. The water is eluted first, well separated. This means it can be determined in low concentrations in practically all volatile organic compounds. Its early elution eliminates the usual problems of interference from substances other than CI to C P ,and perhaps C3 hydrocarbons. The advantages of the porous polystyrene beads are most apparent in the analysis of highly hydroxylated compounds. Because the hydroxylated compounds are usually strongly adsorbed by most other packings, they have been difficult to analyze by commonly used gas chromatographic techniques, particularly when present in trace amounts. The porous polystyrene beads are highly nonsorptive and nonreactive to the hydroxylated compounds. They can be prepared with high surface areas per unit weight, and their structures can be made rugged enough to allow handling and packing into columns. The beads by themselves are quite useful, or they can also be used in combination with a liquid to achieve results which are not possible with the beads alone or the liquid phase on the usual inert supports. The quantitative determination of water, carbon dioxide, and lower alcohols in lorn concentrations has been one of the prime uses of gas-gel chromatography. Because of the lack of adsorption on the porous polymer gels, the loss of components which have strong adsorptive properties is negligible. With standard hot wire thermal conductivity detectors, water has been determined a t 50 p.p.m. (full scale) with a 10 pl. liquid sample of a
chlorinated hydrocarbon; carbon dioxide can be determined a t 50 p.p.m. (full scale) with a 5 c c . gas sample. The capacity of the porous polymer gel columns is not large. Recovery, however, is rapid from the flood condition of overloading the column with excess sample. Baseline operation is quickly re-established and there is very little tailing of peaks due to nonlinear adsorption, as seen with many gas chromatographic column systems. The chromatogram in Figure 11 was obtained on a 3.5-mm. i.d. column from a 0.2-pl. sample with a thermal conductivity detector. The peak shape begins to distort with about 0.2 pl. of a single component, but the shape remains fairly good up to 1 pl. Larger samples can be handled as long as the separation is adequate-eg., the analysis of a trace quantity of ethanol in chloroform or diethyl ether. The water peak in Figure 10 was on a 2-mm i.d. column from a 0.75-pl. sample. This illustrates the rapid recovery from flooding with water. In a system employing temperature programmed operation, beads give little or no "bleed" of materials due to column deterioration until the decomposition temperature of the polymer is reached, and then the column is ruined. If 10' to 20' C. below the decomposition temperature is set as the limit of a temperature program, these columns can be used with very high sensitivity
Y
I
0 to 50" C.
PROGRAMMED
Figure 10. Temperature programmed analysis of water, acetone, and phenol Conditionr: Programmed to 200' C. at maximum rate, column 6-foot X 3/~6-inch Polymer No. 1
detectors operating at or near their maximum sensitivity. Good flow control is required, however, because thermal expansion of the polymer
t I
0
I 1
1 2
I
!
I
3
4
5
1 6
I 7
TIME (MINUTES)
Figure 1 1 . Conditions: 1 15'
Separation of organic compounds from water CC. per minute Hz, column 6-foot X a/~6-inch Polymer No. 1 9
c., 6 0
VOL 38, NO. 2, FEBRUARY 1 9 6 6
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changes the flow of carrier gas during temperature programming unless adequately controlled. From the elution data for water, alcohols, glycols, and hydrocarbons, it appears that the solubility in the polymer is the most important factor in determining the order of elution, and boiling point or volatility is of less consequence. As seen by the order of elution for ethylene glycol before propylene glycol and n-butyl alcohol before t-amyl alcohol, the addition of a methyl group greatly increases the retention time, although the boiling points are actually lowered. The effect of the permeability (Table I, Column 3); as measured by GPC, on the separations and/or utility has not been thoroughly studied. It is apparent that if the permeability is too great or too small, the polymer is of little use.
Highly efficient columns can be packed using good porous polymers. The measured efficiency for n-butyl alcohol (Figure 4) was greater than 800 plates per foot. Column efficiency is dependent partly upon the absence of tailing and partly upon fast equilibration. This is due to the structure, fast access to a large surface area, and absence of thick sections. Porous beads which combine this structure with low and linear sorption properties can then be given greater capacity and specific selectivity by using them as supports for the liquid phases commonly used in gas-liquid chromatography.
J. C. Moore for consultations on polymer synthesis, to W. L. Howard for
ACKNOWLEDGMENT
RECEIVEDfor review August 23, 1965. Accepted December 20, 1956. Third International Symposium, Advances in Gas Chromatography, Houston, Texas, October 1965.
Contributions of many other persons to these studies are gratefully acknowledged. Thanks are particularly due to
assistance in preparation of the manuscript, and to W. V. Hayes and 11. C. Arrington for technical assistance. LITERATURE CITED
(1) Billmeyer, F. W., Jr., “Textbook of
Polymer Science,” pp. 341-2. Interscience. New York. 1962. (2) DeGrazio, R.’P., J . Gas Chromatog. 3, 204 (1965). (3) Lloyd, W. G., Alfrey, T., Division of Polymer Chemistry, 139th Meeting, ACS, St. Louis, March 1961. (4) Lloyd, W. G., Alfrey, T., J . Polymer Sci. 62, 301 (1962). (5) Moore, J. C., Ibid., Part A, 2, 835 (1964).
Separation and Identification of Derivatives of Biologic Amines by Gas-Liquid Chromatography POMPEO CAPELLA’ and E. C. HORNING Department o f Biochemistry, Baylor University College of Medicine, Houston, Texas The separation of biologic amines, including catecholamines, by gas chromatographic techniques requires the preparation of suitable derivatives. A procedure has been developed which involves the treatment of amine mixtures with hexamethyldisilazanefollowed (after complete reaction) by the addition of an aliphatic ketone or cyclobutanone (not cyclopentanone or cyclohexanone). Hydroxyl groups are converted into trimethylsilyl ether groups and primary amines are converted into eneamines or Schiff bases. Secondary amino groups are unchanged. The structures of the reaction products were determined by gas chromatography-mass spectrometry. Effects of changes in the reaction conditions were studied by gas chromatographic and gas chromatographic-mass spectrometric analysis of reaction mixtures. By-products, including oxazolidines and N-trimethylsilylamines, were formed under some conditions. The separations were carried out with a 10% F-60 column with temperature programmed operation. Amines expected as products of human metabolic pathways gave appropriate derivatives and were separated under these conditions.
T
was to develop a method for the gas chromatographic separation of the bioHE OBJECTIVE OF THIS STUDY
316
ANALYTICAL CHEMISTRY
logic amines found in human or other mammalian tissues. Many pharmacological and physiological investigations have been concerned with the occurrence and physiological or biochemical action of these amines, particularly the catecholamines, and the literature of these fields bontains numerous descriptions of isolation and determination procedures. With few exceptions, these methods involve a purification or fractionation procedure leading to a final fraction containing one or more of the amines under study, followed by a colorimetric, fluorometric or spectrophotofluorometric determination of a single amine or of several amines as a group. However, these methods have little in common with gas chromatographic procedures. One of the major problems in the development of a GLC procedure for use with polyfunctional compounds, such as the catecholamines, is that multiple products may be formed at the stage of conversion to derivatives. If nonclassical reagents are used, leading to derivatives which are stable in the gas phase but which can not be isolated for classical analytical study, it may be impossible to characterize the reaction pathways by well established methods. I n the present study no reaction products were isolated. All compounds of uncertain structure were examined in a gas chromatograph-mass spectrometer (combined instrument), and structural
conclusions were drawn on the basis of gas chromatographic and mass spectrometric data. These conclusions mere used as a basis for developing a procedure applicable to all of the amines listed in Table I. This work, however, was not intended to be a systematic or exhaustive study of mass spectrometric behavior for amine derivatives. It would be desirable to carry out a more detailed mass spectrometric investigation if it is proposed to identify amines of unknown structure by this method. The reaction conditions described in the experimental section are suitable for many biologic amines. Hydroxyl groups, when present, are converted to trimethylsilyl ether groups. Primary amines are converted to ketone condensation products through reaction with acetone or cyclobutanone. Secondary amine groups are unchanged, although condensation products may be observed with certain ketones. Tertiary amines were not studied, but from other work it is known that the amine group would remain unchanged under these conditions. If only a few amines are under study, isothermal separation conditions may be used. If a number of amines are to be studied, a temperature programmed separation procedure is recommended. Examples of separations 1 Present address, Institute of Pharmacology and Therapy, University of Milan, Milan, Italy.
