Gas Chromatographic Analysis of Aliphatic Amines Using Aromatic Polymers J. R. Lindsay Smith and D. J. Waddington Department of Chemistry, University of York, England Aromatic polymer beads have been used to separate a wide range of simple aliphatic amines by gas chromatography. To reduce peak tailing, polyethylene imine, tetraethylene pentamine, or potassium hydroxide have been used as coating materials, and their roles as modificants are compared and discussed. It appears that the peak tailing arises because of two types of active sites on the polymer: simple acidic sites which can be neutralized by treatment with base, and metal ions which must be deactivated by addition of an involatile complexing agent, for example, the polyamines. However, if an excess of the polyamine is used, separation of the amines appears to be by a combination of gas-solid and gas-liquid chromatography.
POLYETHYLENE ( I ) and cross-linked aromatic polymer beads (2) are remarkably effective in separating volatile organic compounds. In studies using aromatic polymers, Hollis included results for the separation of some aliphatic amines and he reported that severe peak tailing was eliminated by coating the beads with either polyethylene imine (PEI) or tetraethylene pentamine (TEPA) ( 2 , 3 ) . This paper is concerned with several aspects of this important advance in gas chromatography, for example to establish whether the polymer beads are successful in resolving complex mixtures of aliphatic amines (Cl-C6), many of which are difficult to separate using conventional gas-liquid columns. Further, it is uncertain what role PEI and TEPA play for PEI itself has been used as a liquid phase for the separation of amines (4), while TEPA, although itself unsuccessful as a liquid phase, when mixed with tetrahydroxyethylethylenediamine (THEED), is able to separate some mixtures (5). TEPA also reduces tailing on diglycerol and Carbowax 400 columns (5). EXPERIMENTAL
Operating Conditions of the Gas Chromatograph. All results were determined isothermally. The retention times for amines were determined on a Pye 104 gas chromatograph equipped with a flame ionization detector coupled to an R E 51 1 (Goerz Servoscribe) recorder. To find the rate of elution of the carrier gas (nitrogen), a Pye 104 gas chromatograph with a thermal conductivity cell was used. Glass columns (1.6m X 4-mm id.) were used. The flow rate for nitrogen was 25 ml min-'. Materials. AMINES.Commercially available amines were used whenever possible. Where necessary, they were purified either by conventional fractional distillation or by using a spinning band column (Buchi). N,N-Dimethylethylamine and N,N-dimethyl-sec-butylamine were prepared from the parent primary amines (6), N-methyldiethylamine from diethylamine (6) and N-methyl-sec-butylamine from N,N-dimethyl-sec-butylamine(7). Neopentyl(1) E. H. Baum, J. Gas Chromatog., 1,13 (1963). 38,309 (1966). (2) 0. L. Hollis, ANAL.CHEM., (3) 0. L. Hollis and W. V. Hayes, J . Gas Chromatog., 4,235 (1966). (4) K. Grob, J. Gas Chromatog., 2,80 (1964). (5) Y. L. Sze, 31. L. Borke, and D. M. Ottenstein, ANAL.CHEM., 35, 240 (1963). (6) T. D. Perrine, J. Org. Chem., 16, 1303 (1951).
522
ANALYTICAL CHEMISTRY
amine was prepared from pivalic acid via the reduction of pivalamide by lithium aluminum hydride (8). PACKINGMATERIALS.Two polymer resins were used, Porapak Q (100-120 mesh) (Waters Associates Inc.) and PAR-1 (formerly Polypak 1) (80-120 mesh) (Hewlett-Packard). The coating materials included tetraethylene pentamine (TEPA) (British Drug Houses, Ltd.) and polyethylene imine (supplied by Kodak Ltd. as Montrek 18). Preparation of Coated Packings. When preparing polymers coated with PEI, TEPA, or potassium hydroxide, a weighed sample of coating material was dissolved in excess of methanol or ethanol, and a known weight of polymer beads was added to the solution. The mixture was evaporated on a rotary evaporator under reduced pressure and the column packing was subsequently dried in an oven at 110" for several hours. A similar procedure was adopted for the preparation of polymers to which metal salts were added. The solvent was water and the salts used were potassium dichromate, chromium(II1) sulfate, and iron(II1) citrate. The following packing materials were used : I. Porapak Q 11. PAR-1 111. Porapak Q PEI, (a) 1 %, (b) 5 %, ( 4 10% (d) 20%
+
WIW
+ +
IV. Porapak Q TEPA, 10% w/w V. Porapak Q potassium hydroxide, 10% w/w VI. PAR-1 PEI, 10% W/W VII. PAR-1 potassium hydroxide, (a) 5 %, (b) 10 % w/w metal salts VIII. Porapak Q (a) 20 ppm Cr(V1) (b) 40 ppm Cr(V1) (c) 1 % Cr(VI) (d) 20 ppm Cr(II1) (e) 20 ppm Cr(II1) 20 ppm Fe(II1)
+ +
+
+
RESULTS
Variation of Concentration of PEI and Potassium Hydroxide on the Polymers; Columns I and I11 (a)-(a); Columns I1 and VI1 (a) and (b). With untreated polystyrenes, there is gross peak asymmetry, particularly for primary and secondary amines. On coating Porapak Q with 1 w/w PEI, the symmetry of the peaks is somewhat improved, but on increasing the loading to 5 % w/w, the peaks are symmetrical. From 0 to 5 % w/w, there are only small changes in retention time, but on increasing the concentration of PEI further, the retention time decreases (Table I). Similar changes in the retention times and peak shapes from the amines are observed when the loading of potassium hydroxide on PAR-1 is increased from 0 to 10%. Comparison of PEI and TEPA on Porapak Q; Columns III(c) and IV. The retention times at 166" C for aliphatic amines on Porapak Q coated with the same weights of PEI or TEPA are given in Table 11. In general, the retention times for primary amines are longer on PEI than on TEPA, while those for tertiary amines are longer on TEPA. Similar effects were seen at temperatures between 133-200" C. It (7) H. T. Clarke, H. B. Gillespie, and S. 2.Weisshaus, J . Am. Chem. Soc., 55,4571 (1933). (8) S. L. Shapiro, V. A. Parrino, and L. Freedman, Zbid., 81, 3728 (1959).
~~
Table I. Adjusted Retention Times (Minutes) for Aliphatic Amines on Porapak Q Variation of Loading of PEI 200" c
Temperature Loading of PEI % w/w Ethylamine tert-Butylamine Diethylamine sec-Butylamine Isobutylamine n-Butylamine N- Methyl-sec-butylamine 1-Methyl-n-butylamine 2-Methyl-n-butylamine Triethylamine N,N-Dimethyl-sec-butylamine n-Pentylamine
0
1.1 3.5 3.5 4.8 5.2 5.9
...
8.0 9.2 9.2
...
14.3
1
1.2 3.0 3.6 4.1 4.4 5.1 6.8 7.9 8.9 9.5 10.3 10.2
5 1.5 3.2 4.0 4.3 4.6 5.3 6.5 7.8 8.9 9.5 9.9 10.0
186' C 10 1.0 2.3 2.5 3.0 3.3 3.8 4.2 5.1 5.8 5.0 5.6 7.1
20 0.7 1.5 1.8 2.1 2.3 2.7 3.0 3.5 4.2 3.5 4.0 4.7
1
1.4 3.7 4.7 5.2 5.7 6.6 9.1 10.7 12.2 13.2 14.2 14.1
5 2.3 4.2 5.1 5.9 6.4 7.4 10.8 11.3 12.9 13.0 16.4 14.8
10 1.4 2.9 3.6 4.1 4.5 5.3 6.3 7.4 8.6 7.7 8.6 9.9
20 0.9 1.8 2.3 2.7 3.0 3.5 4.0 4.8 5.7 4.8 5.5 6.5
Table 11. Adjusted Retention Times for Aliphatic Amines on Porapak Q and PAR-1 Coated with Either P E I or TEPA or Potassium Hydroxide, Relative to n-Butylamine (1.00); 166' C Porapak Q Porapak Q Porapak Q Porapak Q Porapak Q PAR-1 PAR-1 PAR-1 PAR- 1 Polymer 10% PEI 5 Z K O H lO%KOH ,.. 5 Z P E I lO%PEI 20zPEI lO%TEPA lO%KOH Loading wjw VI VII(a) VII(b) Column No. III(b) III(c) III(d) IV V I1 0.34 Ethylamine 0.32 0.31 0.18 0.20 0.26 0.21 0.17 ... 0.27 0.27 0.25 Dimethylamine 0.16 0.21 ... ... 0.15 ... 0.26 Trimethylamine 0.27 0.28 0.22 0.25 ... ... 0.21 ... 0.41 0.44 0.34 Isopropylamine 0.33 0.33 0.33 ... 0.28 0.38 0.58 rz-Propylamine 0.59 0.53 0.43 0.46 0.45 0.49 0.43 0.50 0.42 N,N-Dimethylethylamine 0.44 0.41 0.50 0.50 0.52 0.51 0.44 0.30 0.42 0.44 0.47 rerf-Butylamine 0.51 0.50 0.52 0.53 0.51 0.50 ... Diethylamine ... 0.59 0.65 0.66 0.68 0.67 0.61 0.66 0.65 0.71 0.70 sec-Butylamine ... 0.77 0.76 0.77 0.76 0.76 0.83 Isobutylamine ... 0.79 0.85 0.83 0.84 ... 0.84 ... 0.70 N-Methyldiethylamine 0.74 0.66 1.oo 0.88 0.78 ... 0.95 0.68 1.00 1.00 1 .oo n-Butylamine 1 .oo 1.oo 1.00 1 .oo 1.00 1.oo 0.94 0.88 0.93 (err-Pentylamine 1.24 1.15 ... ... 1.23 ... N- Methyl-sec-butylamine 0.93 1.00 0.94 1.35 1.23 1.15 1.30 1.32 ... 0.83 0.94 0.84 Diisopropylamine 1'65 1.39 1.11 ... 1.57 0.80 1.17 1.21 1.16 1-Methyl-tz-butylamine ... 1.70 ... 1.60 1.48 1.38 0.96 Triethylamine 1.09 0.97 1.63 1.50 1.25 1.80 1.82 ... N,N-Dimethyl-sec-butylamine 2.10 1.10 1.27 1.16 1.73 1.43 1.94 2.03 1.10 2-Methyl-rz-butylamine 1.45 1.44 1.41 ... 1.99 1.55 1.88 1.73 1.63 n-Pentylamine 1.73 1.73 1.70 2.28 2.25 1.97 2.11 2.41 ... Di-n-propylamine 1.55 1.68 1.50 2.86 2.41 1.87 ... 3.00 1.68 ti-Hexylamine 2.93 3.18 2.75 4.69 4.53 3.20 ... 5.30 3.11 Di-sec-butylamine 2.27 2.47 2.25 ... 7.82 2.57 6.60 5.19 3.71 t, for tz-butylamine (min.) 2.9 3.4 3.2 10.3 8.0 5.5 7.2 17.2 5.6 was found that the column coated with TEPA tended t o give an unstable base line, presumably because of the relative volatility of TEPA. Comparison of Porapak Q and PAR-1 Coated with PEI; Columns III(c) and VI or with Potassium Hydroxide; Columns V and VII(b). The retention times using PAR-1 are consistently shorter than those on Porapak Q when modified with either PEI or with potassium hydroxide (Table 11). In general, both polymers separate similar mixtures of amines, but by modifying the polymer with the same amount of base, one of the polymers may be able t o separate a mixture more effectively (Table 11). Comparison of PEI and Potassium Hydroxide as Modificants for PAR-1; Columns VI and VII(b) and for Porapak Q; Columns III(c) and V. The retention times for amines on both polymers when coated with potassium hydroxide are longer than when the corresponding polymer is coated with the same amount w/w of PEI (Table II), and the inorganic alkali is not as successful as PEI in removing the tailing experienced when using the unmodified resin. Addition of Transition Metal Ions to Porapak Q; Columns When small amounts (20-40 p.p.m.) of chroVIII(a)-(e). mium(III), (VI), and iron(II1) salts are added t o Porapak Q,
the peaks obtained from primary and secondary amines show increased tailing over those from the untreated polymer and their areas are markedly reduced; tertiary amines are relatively unaffected. These effects can be removed by saturating the column with amine from several large injections. The peak symmetry and areas obtained from primary and secondary amines after this treatment are approximately the same as those obtained from columns of Porapak Q coated with PEI or TEPA. Very large amounts of chromium(V1) ( l z w/w) enhance the effects described above. DISCUSSION
The separation of aliphatic amines by gas-solid chromatography on unmodified cross-linked polystyrenes, such as Porapak Q and PAR-1, is severely limited by tailing and peak asymmetry. These problems are also encountered in conventional gas-liquid chromatographic separation of amines and have been overcome by treatment of the solid support, either by action of a silane or, more usually, by action of a n inorganic or organic base. VOL. 40, NO. 3, MARCH 1968
523
I
I
I
25
50
I
I
75
100
I
125
b.p. of amine, “C
Figure 1. Plot of log t, against boiling point of the amine. Porapak Q 5 x PEI (w/w)166”C 0 Primary amines
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
Methylamine Ethylamine Isopropylamine tert-Butylamine n-Propylamine sec-Butylamine Isobutylamine tert-Pentylamine n-Butylamine Neopentylamine 1-Methyl-n-butylamine Isopentylamine 2-Methyl-n-butylamine n-Pentylamine 1,3-Dimethyl-n-butylamine(12) n-Hexylamine
@
1. 2. 3. 4. 5. 6. 7. 8. 0
1. 2. 3. 4. 5.
Secondary amines Dimethylamine Diethylamine N-Methyl-sec-butylamine Diisopropylamine N-Methyl-n-butylamine Di-n-propylamine Di-sec-butylamine Diisobutylamine Tertiary amines Trimethylamine N,N-Dimethylethylamine N-Methyldiethylamine Triethylamine
N,N-Dimethyl-sec-butylamine (13)
For boiling points, see references (14) and (19, except where indicated above.
The peak tailing observed with untreated polymers indicates that there are sites on the surface of the solids which strongly adsorb amines, particularly the primary and secondary compounds. Hollis has shown that when the aromatic polymers are coated with PEI or TEPA, the symmetry of the peaks from amines is greatly improved. However, treatment of the polymer with potassium hydroxide is not so effective as with PEI or TEPA, suggesting that although some of the active sites are acidic groups, there is another type of site that is holding back some of the amine molecules. Since transition metal salts are used in the production of the polymers, it is possible that traces of these ions might be present and be the cause of some of the peak tailing. Chemical analysis showed the presence of both chromium and iron in Porapak Q. The peaks from primary and secondary amines on columns to which transition metal salts had been added were highly asymmetric and their areas were greatly reduced. It is interesting to note that the different behavior of primary, secondary, and tertiary amines on untreated polymer and on 524
0
ANALYTKAL CHEMlSTRY
polymer to which transition metal ions are added, parallels their ability to act as ligands to transition metal ions (9). If the columns packed with metal ion-treated polymer are saturated with amines, the symmetry and size of the peaks from subsequent injections of primary and secondary amines are greatly improved. Thus it is clear that peak tailing can arise from traces of transition metal ions on the polymers and this interference can be largely removed by saturating the column with an amine prior to the injection of the sample, possibly because all the available coordination sites of the metal ions are filled. However, the metal ions may have different effects depending on whether they are trapped in the polymer (as they may be during the preparation of the polymer) or whether they are deposited on the surface. If the principal mode of separation
(9) “Stability Constants of Metal-Ion Complexes,” special publication No. 17, The Chemical Society. London, 1964.
0
2 5
5 0
75
100
125
b.p. of amine, “C
Figure 2. Plot of log f, against boiling point of the amine. Porapak Q 20 0 Primary amines
Secondary amines
of organic compounds by the polymer is due to passage of the sample through the resin, the metal ions trapped inside the polymer may have a more important role than those added to the surface, as in the materials described above. That the metal ions are trapped inside the polymer is indicated since they cannot be removed by frequent washings with either dilute mineral acids or organic solvents. An example of deliberate addition of metal ions to a packing material for the separation of amines is seen in the work of Sawardeker and Lach (IO). They were unable to separate nbutylamine, diethylamine, and triethylamine on silicone oil, but in the presence of silver nitrate, these amines were eluted in the order, tertiary, secondary, and primary. As in the present work, the addition of metal ions increases tailing. In this work, since the order of elution of the amines was not markedly altered by the addition of metal ions to the polymer, the metal ions are not playing a major role in the separation of amines. The retention times of aliphatic amines depend on the structure of the amine, their order of elution being somewhat similar to that observed in gas-liquid chromatography when a nonpolar solute is used, [for example, paraffin oil (141; this indicates that the separation of amines is brought about principally (IO) J. S . Sawardeker and J. L. Lach, J. Pharm. Sci., 52, 1109
(1963). (11) R. V. Golovnya, G. A. Mironov, and I. P. Zhuravleva, Dokl.
Akad. Nauk. S.S.S.R., 163, 369 (1965). (12) P. Karrer and P. Dinkel, Helo. Chim. Acra, 36, 122 (1953). (13) E. Grovenstein, E. P. Blanchard, D. A. Gordon, and R. W. Stevenson, J. Am. Chem. SOC.,81,4842 (1959). (14) “Handbook of Chemistry and Physics,” 46th ed., The Chemi-
cal Rubber Co., 1965. (15) “Dictionary of Organic Compounds,” Eyre and Spottiswood Ltd. and E. and F. N. Spon Ltd., 1965.
PEI (w/w)166“C 0
Tertiary amines
by adsorption on the nonpolar polystyrene and not the polyamine. Thus, there is a relationship between the boiling point of the amine and log tr (Figures 1 and 2). (The lines are drawn through the points that represent amines with normal alkyl groups.) Three separate lines can be drawn for primary, secondary, and tertiary amines. There are also divergencies from the line within each of these series. In general, if the line for primary n-alkyl amines is taken as a standard, the greater the degree of branching, and the closer the proximity of this substitution to the nitrogen atom, the greater is the divergency. This can be accounted for by assuming that there is some interaction between the amine and the polymer and thus deviation from a simple distillation process. The part played by PEI can be seen most clearly by considering the results at different loadings. Changing the amount of the base on Porapak Q from 1 to 5 % w/w has little effect on the retention times, and the polymer is separating amines by a gassolid distribution between the polymer and carrier gas with the PEI serving to deactivate the active sites on the polymer, The results using Porapak Q with 20 w/w PEI show that a high loading of polyamine reduces the retention times of all amines, although the primary amines are less affected than the secondary, less than the tertiary. This observation is illustrated in Figures 1 and 2 and in the relevant data in Table 11. In the plots of boiling points against log t p the lines for primary, secondary, and tertiary amines cross over either at three points close to each other (Figure 1 and data from Table 11) or at one point (Figure 2). The effect of increasing the PEI loading is twofold; first, it lowers the positions of the lines on the log fr scale, illustrating the general reduction of the retention times of all amines with increased PEI loading, and, second, it VOL. 40, NO. 3, MARCH 1968
525
Table 111. Adjusted Retention Times for Isomeric Aliphatic Amines on Porapak Q Coated with PEI For each series of isomers, adjusted retention time of the straight-chain primary amine is taken as 1.00 200" c 186" C 0 1 5 10 20 1 5 10 I III(a) III(b) III(c) III(d) III(a) III(b) III(c)
Temperature PEI % w/w Column No. Cp amines N,N-Dimethylethylamine fert-Butylamine Diethylamine sec-Butylamine Isobutylamine n-Butylamine C6amines N-Methyl-sec-butylamine 1-Methyl-n-butylamine N-Methyl-n-butylamine 2-Methyl-n-butylamine n-Pentylamine
20
IIi(d)
0.63 0.63 0.63 0.83 0.89 1.00
0.63 0.63 0.74 0.83 0.94 1.00
0.63 0.63 0.78 0.83 0.88 1.oo
0.65 0.65 0.68 0.81 0.88 1.00
0.63 0.63 0.72 0.81 0.88 1 .OO
0.59 0.59 0.72 0.80 0.87 1.OO
0.59 0.59 0.70 0.80 0.86 1.oo
0.59 0.59 0.69 0.78 0.86 1.oo
0.57 0.57 0.70 0.78 0.86 1 .OO
...
0.66 0.77 0.83 0.87 1.00
0.65 0.78 0.77 0.89 1.00
0.63 0.77 0.76 0.88 1.00
0.64 0.81 0.74 0.89 1.oo
0.65 0.76 0.76 0.86 1.00
0.72 0.76 0.76 0.87 1.00
0.64 0.75 0.76 0.87 1.00
0.61 0.74 0.74 0.88 1.00
0.56 0.55
0.65 1.00
Table IV. Adjusted Retention Times for Isomeric Aliphatic Amines on Porapak Q and PAR-1 Coated with Either PEI or Potassium Hydroxide; 166' C For each series of isomers, adjusted retention time of the straight-chain primary amine is taken as 1.00 PAR-1 Polymer Porapak Q Porapak Q PAR-1 PAR-1 Loading wjw 10% PEI 10% KOH 10%PEI 5 % KOH 10% KOH V VI Column No. III(c) VII(b) IVII(a) CI amines Trimethylamine 0.50 0.49 0.44 0.45 0.53 Isopropylamine 0.66 0.70 0.68 0.75 0.65 1.00 n-Propylamine 1.00 1.00 1.00 1.00 Cc amines N,N-Dimethylethyl0.50 0.44 0.42 amine 0.44 0.41 0.51 rert-Butylamine 0.50 0.42 0.53 0.47 0.66 ... 0.61 Diethylamine ... 0.59 0.76 0.76 0.65 sec-Butylamine 0.71 0.70 0.83 0.84 0.83 Isobutylamine ... 0.79 1.00 1 .OO 1.00 1.00 n-Butylamine 1.00 Cs amines N-Methyldiethylamine 0.40 0.44 0.39 0.42 0.39 rert-Pentylamine 0.51 0.54 0.57 ... 0.52 N-Methyl-sec0.55 butylamine 0.54 0.60 0.57 0.56 1-Methyl-n-butyl0.68 amine 0.70 0.73 0.69 0.69 2-Methyl-n-butyl0.84 0.82 0.83 0.85 0.82 amine 1.00 1.00 1.00 n-pentylamine 1.OO 1.00 Ce amines Diisopropylamine 0.31 0.30 0.29 0.29 0.31 0.33 Triethylamine 0.33 0.34 0.34 0.35 N,N-Dimethyl-sec0.38 0.39 butylamine 0.39 0.40 0.42 Di-n-propylamine 0.53 0.54 0.53 0.57 0.54 n-Hexylamine 1 .OO 1.00 1.00 1 .OO 1.00
changes the slopes of the lines and moves the cross-over (isodromos) points lower down the boiling point axis. Clearly at high loadings of the polyamine the simple gas-solid chromatography is replaced by a combination of gas-solid and gas-liquid chromatography, where PEI is acting as the liquid phase. The differential behavior of primary, secondary, and tertiary amines is to be expected since primary amines are more capable than secondary amines of forming hydrogen bonds to the polyamine, and tertiary least of all. That the polyamine is acting as a stationary phase at high concentrations is confirmed for when its loading is further in526
ANALYTICAL CHEMISTRY
creased the retention times begin to increase (16). Similar results are obtained when the polymers are coated with either Carbowax 20M or Apiezon L; as the loading of these stationary phases is increased up to 10% wjw the retention times of amines are reduced, but at higher concentrations the retention times increase (16). At first sight, Table I1 shows that the relative retention times for the amines vary with change of loading on Porapak Q. (16) J. R. Lindsay Smith and D. J. Waddington, University of York, unpublished results, 1967.
However, if each amine is classified into a group depending on the number of carbon atoms in the molecule, and the amine with the largest retention time in each group is taken as the standard, the relative retention times, within each group at a constant temperature are almost independent of the loading of PEI (Table 111), showing that Porapak Q is playing the major role. The importance of the polymer in the separation of the amines is further emphasized by comparing the results from the two polymers, Porapak Q and PAR-1 (Table IV) which show that the retention times, within each group of amines containing the same number of carbon atoms, remain independent not only of the loading of base, but also of the nature of the polystyrene. This suggests that the chromatographic separation depends on the solubility of each amine in the polymer, which depends in turn on the proportion of carbon to nitrogen in the molecule. It is possible that any surface modification of the polymer with a polar material, such as PEI, will affect the solubility of amines in the polymer, so that the solubility, and hence retention times, of amines with the same carbon to nitrogen ratio will be changed to the same extent. Amines with a different carbon to nitrogen ratio will have their retention times altered by different amounts. Although such a scheme would explain the observed results, further work is required to produce confirmatory evidence.
The retention times of amines on PAR-1 are shorter than those using Porapak Q under the same conditions (Table 11). Moreover, the isodromos point is at a lower temperature on the boiling point axis for PAR-1 (calculated from data in Table II), and this results in the retention times of tertiary amines being shortened relative to primary and secondary. Thus, there appear to be several mixtures which can be separated by one polymer but not by the other. In general, however, by varying the loading of PEI, TEPA, or potassium hydroxide, it is possible to resolve the same mixture on both polymers (Table 11). This difference in behavior of the two polymers presumably arises from their different structural properties (for example, cross-linking, surface area, and permeability). ACKNOWLEDGMENT
The authors are grateful to Mrs. M. V. Walker and Miss M. A. Warriss for much helpful technical assistance and to Dr. E. McIntyre, I.C.I. Fibres Limited, for the chemical analysis on the polymer. RECEIVED for review August 14, 1967. Accepted November 14,1967.
Capillary Gas Chromatographic Method for Determining the C,-C Hydrocarbons in Full-Range Motor Gasolines W. N. Sanders and J. B. Maynard Shell Oil Co., Research Laboratory, Wood Riuer, Ill. 62095 A capillary gas-liquid chromatographic method has been developed to determine the individual C3-C12 hydrocarbons in full-range motor gasolines. The analyses are conducted on a 200-foot squalane capillary column in less than 2 hours. Approximately 240 chromatographic peaks are observed in the analysis of an average gasoline; 180 of them (amounting to 9699% wt of the sample) have been specifically identified. The column temperature and column inlet pressure are both programmed to obtain resolution of close-boiling hydrocarbons. Standard deviations ahd the 95% confidence limits are given for the quantitative repeatability and reproducibility of the method. Chromatographic peak identifications and the detailed quantitative composition of typical premium and regular-grade gasolines are presented, as well as the detailed composition of the American Petroleum Leaded Institute Prototype Fuel No. 1-Premium Reference. Changes that can be made in the temperature and pressure programs to obtain resolution of specific groups of hydrocarbons are discussed.
THENEED for a method to determine the detailed hydrocarbon composition of full-range motor gasolines has been evident for some time. Previously, such information was either unobtainable or required an exorbitant amount of time and effort. Generally, the data were compiled from a series of analyses such as fluorescent indicator absorption (FIA) analyses, ASTM distillations, packed column gas-liquid chromatography, and mass spectrometry. However, with
the advent of capillary columns and ultrasensitive detectors (particularly the hydrogen flame ionization and electron capture detectors), it is now possible to obtain, by gas chromatography, detailed compositional data on complex gasoline range mixtures. Schwartz, Mathews, and Brasseaux have described capillary gas-liquid chromatographic (GLC) methods for the determination of saturated hydrocarbons in the 28" to 114" C portion of petroleum, as well as the individual components in the 80" to 180" C aromatic portion of petroleum (I, 2). Martin and Winters used 500- to 800-foot capillary columns to determine hydrocarbons through Cl0 in crude oil fractions; however, long analysis times of 4 hours were reported (3). Durrett et al. employed capillary GLC for the analysis of individual refinery streams including light reformer feed, reformate, and alkylate (4, 5). McEwen (6) has employed his exhaust gas analysis (1) R. D. Schwartz and D. J. Brasseaux, ANAL.CHEM., 35, 1 3 7 4 8 2 (1963). (2) R. D. Schwartz, R. G. Mathews, and D. J. Brasseaux, J . Gas Chromarog., 5 (3,251-53 (1967). (3) R. L. Martin and J. C. Winters, ANAL.CHEM., 35, 1930-33 (1963). (4) L. R. Durrett, M. C . Simmons, and I. Dvoretsky, Preprints, Division of Petroleum Chemistry, 139th National Meeting, ACS, St. Louis, Mo., March 1961, pp 63-71. ( 5 ) L. R. Durrett, L. M. Taylor, C . F. Wantland, and I. Dvoretsky, ANAL.CHEM., 35, 637-41 (1963). (6) D. J. McEwen, Ibid.,38, 1047-53 (1966). VOL. 40, NO. 3, MARCH 1968
527
