the combustion products of the vapor may already be so high as to bring about alterations in the properties of the flame and, consequently, in the magnitude of the net response. This may also constitute a factor contributing to the decrease of the net response. If the decrease were due to some variations in the working parameters (detector temperature, flow rate of the gases), it should be the same with both types of stationary phase. The above account indicates that the enhancement of the
decrease in the net response due to the background one is likely a case applying especially to the flame ionization detector. Since this effect cannot be suppressed by any method of compensating for the background response, it is advisable that the use of stationary phases producing a high background signal be avoided in accurate quantitative analysis by gas chromatography. RECEIVED for review July 19, 1971. Accepted August 30, 1971.
Evaluation of Dendritic Salt as a Support for Gas-Liquid Chromatography R. D. Schwartz, R. G . Mathews, J. E. Rountree, and D. M. Irvine Pennzoil United, Inc., P.O.Box 1407, Shreoeport, La. 71158 A commercially available dendritic salt has been evaluated as an inert support for packed column gas-liquid chromatography. The results obtained indicate that efficient columns may be prepared with this material. Further, polar compounds may be separated with nonpolar liquid phases when salt i s used as the support. The pressure drop of salt columns is low and no tailing, loss by adsorption, or reaction of polar compounds with this support were noted.
SILICIOUS MATERIALS, of high pore volume and low surface area, are currently employed for nearly all packed column gas-liquid chromatography ( I ) . These silicas, often treated with acid and/or alkali, as well as with silanes, are called “inert solid supports.” Their function is to hold the liquid phase utilized to provide the desired separation. In practice, the silicas have certain disadvantages, particularly when polar molecules are being separated. The surface of silica is reactive and can yield tailing peaks, nonquantitative recovery, and chemical decomposition or reaction of labile molecules. These problems, could, perhaps, be minimized if a nonpolar inert solid support were available. Inorganic salts such as sodium chloride have been utilized as supports and as modifiers of other adsorbents (2,3). Recently, a dendritic form of sodium chloride became commercially available. Dendritic crystals are branched or starlike in form. This particular Torm of sodium chloride is a six-pointed star crystal with an extremely jagged and irregular surface and an interior containing millions of cavities of only several microns diameter ( 4 ) . The material has the ability to hold liquids in its pores. An investigation was initiated to study the gas-liquid chromatographic behavior of packed columns prepared with dendritic salt as an inert solid support. EXPERIMENTAL
Materials. Dendritic sodium chloride-obtained as a sample from the Morton Salt Co.-was screened prior to use ( I ) D. M. Ottenstein, J . Gus Clrromutogr., 1, 11 (1963). (2) F. R . Cropper and A. Heywood, Ncrture, 174, 1063 (1954). ( 3 ) C. G. Scott and C . S. G . Phillips 111 “Gas Chromatography 1964,” A. Goldup, Ed., Institute of Petroleum, London, 1965,
C6 t a C i 0 t Benzene
i n j e c t i o n Paint
Tlme in Mlnutes-
7. 0
1
2
Figure 1. Column B. Room temperature; 20 psi helium. Cgto CloNparaffins plus benzene to 60-80 mesh and dried at 120 “C. Gas Chrom Q, 60-80 mesh, a silanized silicious support material, was obtained from Applied Science Laboratories, State College, Pa. The tubing used for the columns was l/s-in. 0.d. Type 316 Stainless Steel, from Handy & Harman Co., Norristown, Pa. Reagents. Squalane was obtained from Eastman Chemical Co. Carbowax-400 was a sample from Union Carbide Chemical Co. PZ-110, a polyimide, (5) was prepared at Pennzoil United, Inc. Igepal CO-210 was a sample from General Aniline and Film Corp. The chloroform used in preparing the column packings was Baker Analyzed Reagent Grade. Column Preparation. The screened support materials, Dendritic Salt and Gas-Chrom Q, were coated by slurrying with a chloroform solution of the liquid phase and subsequent
p 266. (4) “The Unique Physical Properties of Star Flake Dendritic
Salt,” Morton Salt Company, Chicago. 111. 60606. 2000
( 5 ) R . G . Mathews, R. D. Schwartz, M. Novotny, and A. Zlatkis, ANAL.CHEM., 43, 1161 (1971).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1971
Figure 2. Column A. Room temperature; 20 psi helium. C6 to CUI N-paraffins plus benzene
Injection Point
I n j e c t i o n Point-')
-1
-
1_1
Time in Minutes
Trme ~n Mlnutes-
'
1
0
1
I
I
2
3
I
4
I
5
I
I
6
7
Figure 4. Column C. Temperature: 80 "C. Pressure: 10 psi helium
evaporation to dryness. These dried materials were packed steel columns for evaluation. into 6 f t X Apparatus. A Barber-Colman Series 5000 gas chromatograph equipped with a flame ionization detector and a BarberColman Model 5340 with a TC detector were used for this study. Columns. The following columns were prepared and tested during the course of this study. All were of */8-in. 0.d. stainless steel.
Figure 3. Column E. Temperature: 80 "C. Pressure: 20 psi helium
A
Length
Support
Coating
loft
Gas-Chrom Q Dendritic Salt Dendritic Salt Dendritic Salt Dendritic Salt Dendritic Salt Dendritic Salt Dendritic Salt
None None 1 Carbowax-400 1 % Squalane 3 % Squalane 2 % Carbowax-400 2 % Igepal CO-210
B
loft
C D
6 ft 6 ft 6 ft 6 ft 6 ft 6 ft
E F G H
0 . 5 % PZ-110
DISCUSSION
T i m e i n Minutes-
b
i
;
;
i
The results obtained, see Figures 1 through 7 and Table I, indicate that dendritic salt is suitable as a support for gasliquid chromatography. The salt has sufficient pore volume t o hold up to 3% of liquid. Packings prepared with more than 3 liquid were tacky and very difficult to pack. The pressure drop of typical columns, prepared with dendritic salt is shown in Table I. For comparison, the flow rate is shown for Column A packed with a silicious support.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1971
2001
Table I. Column Flow Rates Flow rate in ml/min, 20 psi helium Column 17.4 A 27.3 40.0 30.0
B C D E
5 6 '
'8
30.0
Injection
T i m e ir M m u t e s
-'
0
I
I
I
I
1
2
3
4
Figure 5. Column F. Temperature: 80 "C. Flow: 60 ml/min helium z Injection Point
*
w
+
L
- # m e in Minutes
P
-
I
0
1
I
I
I
I
I
I
1
2
3
4
5
6
7
I 8
Figure 7. Column H. Temperature: 190 "C. Pressure: 10 psi helium. Fatty acid methyl esters 1
carbons than the silicious support. Because the salt does not undergo dehydration or dehydroxylation a t elevated temperatures (300-400 " C ) ,it is expected to provide a good support for high-temperature gas-liquid chromatography. Further, because it is inert toward polar compounds without silane treatment, it is expected to perform well for the separation and analysis of such compounds. It should be pointed out that the deterioration of silane-treated silicas (6) a t elevated temperatures causes serious problems in many analyses. This investigation is being continued in order to study further application of dendritic salt and other nonsilicious materials as solid supports.
m
Time ~n M l n u t e s
-'
0
I
1
I
I
L
1
2
3
4
5
Figure 6. Column G . Temperature: 100 "C. Pressure: 23 psi helium Chromatograms of a variety of compounds are shown as Figures 1 through 7. These results indicate that the column efficiency and peak shapes obtained are comparable to those of conventional support columns. It should be noted, Figures 1 and 2, that the uncoated salt is more inert toward hydro-
2002
ACKNOWLEDGMENT
The authors thank Pennzoil United, Inc. for permission t o publish these results. RECEIVED for review July 12, 1971. Accepted August 16, 1971.
( 6 ) Aiialabs Researclz Notes, 11, 28 (1971).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 14, DECEMBER 1971
