Efficient Trapping of Gas Chromatographic Effluents via Solvent Co-condensation Thomas H. Parliment General Foods Technical Center, White Plains, N. Y . 70625
In studies on volatile natural materials, it is frequently necessary to collect selected fractions of the gas chromatographic (GC) effluent from a large matrix of undesired material. High collection efficiency is desired since sample preparation is normally difficult and time consuming. Numerous collection techniques have been described in the literature and include thermal gradient traps (I), electrostatic precipitation ( Z ) , total trapping of effluent ( 3 ) ,filter trapping ( 4 ) , and co-condensation with a solvent (5, 6). We felt this last concept possessed definite advantages, but the technique as described required a series of traps and a fraction collector. The device described herein extends the concept of co-condensation, with its concurrent high efficiency, and describes applicability to both major and minor components of a mixture.
EXPERIMENTAL The apparatus shown in Figure 1 consists of a pear-shaped flask of 5- to 10-mi capacity to which has been fused a short 3.5mm 0.d. side arm. This is connected to a 3-way valve (Type 3 MMM, Hamilton Company, Reno, Nev.) by means of a short Teflon (DuPont) tube. The distal end of the valve connects t o the exit port of the gas chromatograph. A micro spiral condenser placed above the flask is used. to provide highly efficient reflux. The valve is heated with heating tape to the temperature of the GC manifold to prevent premature condensation. In operation, 0.5 to 1.0 ml of solvent is placed in the flask and brought to reflux with an appropriate heating mantle. As undesired peaks pass through the exit port, they are vented to the atmosphere through the three-way valve. When the component of interest elutes, the position of the valve is adjusted to pass the
Figure 1. Gas
chromatographic trap
R. K. Stevensand J. D. Mold, J. Chrornatogr.. IO, 398 (1963). D. W . Fish and D. G . Crosby, J . Chrornatogr., 37, 307 (1968). D. Verdin, Anal. Chern.. 43, 1909 (19711. E. C. Schluter, Anal C h e m . . 41, 1360 (1969). J . H. Jones and C. D. Ritchie, J. Ass. O f f c Agr. Chern.. 41, 753 (1 958). (6) T. Tsuda and D. Ishii, J. Chrornatogr.. 47, 469 (1970).
(1) (2) (3) (4) (5)
1792
A N A L Y T I C A L C H E M I S T R Y , VOL. 45,
NO. 9,
entire effluent into the flask containing the refluxing solvent. After the completion of elution, the valve is returned to its vent position. The efficiency of this system was studied in several ways. In all cases, collection efficiency was determined by GC comparison of the trapped material to a solution of known composition. Sample fractionation was carried out in a Perkin-Elmer Model 900 gas chromatograph, normally using a 6-ft X Yg-in. 0.d. column packed with 10% DEGS on 80/90 Anakrom ABS. Carrier gas flow for this column was 30 ml/min. A Y,-in. 0.d. column was used for experiments with higher carrier gas flow rates. In each experiment, sample sizes of both 10 kg and 1 mg were injected to demonstrate recovery a t various concentration levels.
RESULTS AND DISCUSSION In order to relate collection efficiency with volatility, samples of widely differing boiling points were collected. Recoveries were over 95% for compounds as low boiling as ethyl acetate (bp 77 "C) and propanol (bp 98 "C) and as high boiling as methyl stearate (bp 215 "C a t 15 mm). The high collection efficiency of methyl stearate is particularly interesting since high boiling methyl esters are notorious for their tendency to form aerosols which are difficult to condense. To ascertain whether repetitive collections can be made over a period of time, four samples of methyl octanoate were injected and collected over a period of four hours while holding the solvent a t continuous reflux. Total recovery was over 95%. Such a procedure is important in the isolation of natural products where repetitive injections must be made to isolate significant quantities of a trace component. Recovery studies of methyl octanoate a t flow rates of 60, 100, and 150 ml/min were made and in each case recovery was over 95%, thus demonstrating the utility of trapping from larger diameter columns where higher flow rates are required. The solvent we generally use is Freon 113 (bp 47 "C) since this is low boiling, non-flammable and since this does not interfere in organoleptic evaluation of separated fractions. Obviously, other solvents such as carbon tetrachloride for IR studies or deuterated chloroform for NMR studies could be used. Thus it is evident that this technique allows essentially quantitative recovery of both low and high boiling eluates from a gas chromatograph. The technique is applicable over a wide range of sample sizes and carrier gas flow rates. Finally, it permits repetitive collections to be made while retaining high collection efficiency. Received for review April 26, 1973. Accepted May 21, 1973.
A U G U S T 1973
