DISCUSSION
It nil1 be noted in the manipulation procedure that this sampling de\ice ii not immediately removed from the flash heater section of the gas chroniatogi aph. This can be advocated since uncontrolled needle “boil out” and “blon by“ as is sometimes experienced nith the conventional microsyringe IS liiiiited in the case of “boil out” and eliminated in the case of “blow by” (eacape of sample between plunger and barrel). Further, some fractionation of the sample has occasionally been obscwed n ith -ample introduction by means ot the conven-
tional microsyringe. Such fractionation could result in the loading of the gas chromatograph column nith a sample of erroneous composition. While fractionation may occur during sample introduction with the needle cup sampling device, the extended injection period apparently minimizes this difficulty. Under the conditions employed, volatilization of the sample from the cavity of the needle cup mas essentially complete and no difficulties n-ere encountered with peak tailing or column efficiencies. I n conclusion, introduction of ester
samples derived from edible fats and oils with the needle cup sampling dcrice into gas chromatography syeteins using highly sensitive detectors (such as P-ray ionization detectors) was foiiiid very satisfactory. If the present day trend for even more sensitive detectors continues, it is apparent that some forni of thiq sampling de\-ice and procedure could he of considerable use. The needle clip sampling device is easily const,ruct,ed, simple to manipulate, and in many ea-es requires lit,tle or no modificat,ion of the conventional SI .‘l‘iconer;ibber-iealed injection ports.
Column Rejuvenation in Gas Chromatography by Means of Reservoir Sections Irving R. Hunter and M a yo K. Walden, Western Utilization Research and Development Division, Agricultural Research Service, U. S. Depa,rtment of Agriculture, Albany, Calif.
AS CHROhfATOGRBPHIC CO1UIllllS
de-
I
G teriorate mith extended use. Among probable factors for auch deterioration is a leaching action of the carrier gas and injectsd sample< on the stationary phase at the column head. Samples injected into an old column, therefore, diffuse over a longer distance than in a new column before reaching a n effective portion of the stationary phase. The result is a spreading of the peak with accompanying 1 0 s in efficiency. When the former becomes excessive, the column is usually discarded. Since column prepwation i> both an a r t and a science, extension or rejuvenation of the life of a good column is highly desirable. A simple method for doing this, utilizing v h a t we call reservoir sections, has bel:n devibed in our laboratory. A chromatographic colunin [16 feet long X 1 / 8 inch in diameter filled n-ith Johns-hlanville brick duat (60to 80-mesh) coated isith 17 of L.1C I-R-2961, which initially gave excellent results for the separation of a mixture of carbonyl compounds. gradually declined after a period of uqe (isothermally and with programming) to the point where it. separating efficiency had dropped dra~ticallv. -1 short column inch X 1 foot) containing 5% of the same stationary phase used in the longer volumn on brick dust (reservoir section) n as then mounted between the carrier pa. inlet and the main columr~ so that the carrier gas passed through the reservoir section before reaching the niain column. Injected samples bypaa-ed the reservoir section. With this modification, the efficiency of the original column was restored.
A
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a a W
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Sample I nj e c t ed -I
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B
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RETENTION T I M E
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Figure 1. Chromatograms of a mixture of carbonyl compounds made on A. A freshly p r e p a r e d column 6. The same column after extended use
C. The used column with the reservoir section
in
place
Figure 1-4 illustrates the separation of a mixture of aldehydes and ketones made with a freshly prepared LAC 1-R296 column. Figure 1B illustrates a separation of a n identical injection made on the same column after it had been in use for several months. S o r mally i t would be discarded as no longer capable of making practical
separat’ions. Figure 1C illustrates a chromatogram of the mixture on the same column after a reservoir qection had been in place in the system for 30 minutes. It’ is obvious from the illu5trat’ion t’hat the c~olumn had heen restored to its original efficiency. The example cited i i particularly striking since it appears to he a case in which the u n c o a t d solid .support at the head of the deteriorated column (Figure 1B) diq1ay.i considerithle nrtivity. (Most of the sample i? actually lost.) Rejur-enation, in this cn+, ,?erves to rrwoat the active -it?> and to prrniit only the desired partition process t o occur. It i> el-o extremely likely that the stationary phase Ta])lJr in the carrier streani ser\-e> effrctiwl>s to displace adsorbed -ample ~ n p o r from the wall^ of the injection c h s m l w :ind inlet tubing, thus enhancing the l w formance of w e n brand new colunin+. ;Is a result’ new coliuiin.5 with the adtlrrl column section had tlouhle the numlicr of theoretical plate- calculated without the reservoir in place. Reservoir section. may bc usrd a t room tempcmture. or the:- may he placed in the oven of the gas chromatography apparatu. where they receive t h r same heat treatinpnt as the main column. Rejuvenation of a column hi al-0 been achier-ed by reversing a >!wit column. This temporarily residteil in an efficiency eyiial to that, obtainrtl when the column was new. Hon-c.v(~, ivit’h time the efficiency onci? q a i n declined. REFERESCEt o a company or produc*t name does not imply approval or rwoiiiniendation of the product by the U. 4. Department of .igricnlture t o t k e\clusion of others that may be suital~le.
VOL. 35, NO. 1 1 , OCTOBER 1 9 6 3
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