C
0
Figure 1 shows the partial separation of a mixture of barbiturates introduced into the gas chromatograph with a solid injector (3). Use of t h e solid injector permits concentration of samples and detection of compounds whose responses would otherwise be obscured by the solvent peak. Metharbital, for example, would be so obscured if i t were injected in solution. A &foot column utilizing neopentylglycol succinate (3%) as the liquid phase, prepared by the evaporation technique described above, but coated on Chromosorb K, acid-washed, 60t o 80-mesh, also gave sharp peaks for the barbiturates.
G
5
15
10
M inulrs
Figure 1. Tracing from a chromatogram showing the partial separation of seven barbiturates Solid injection; mixed stationary phase A . Acetone (trace remaining from solution) B . Metharbital C. Barbital D. Butabarbital
responding reduction of bleeding, are due to thc mixing of the two liquid phases and the consequent lowering of the mlinr pressure of the Carbowax
LITERATURE CITED
( 1 ) Brochmann-Hanssen,
E.
F. G.
H. x.
Amobarbital Pentobarbital Secobarbital Phenobarbital Attenuation X 1 6
20RI. A 6-foot column utilizing the same packing at 210’ C. almost completely separated butabarbital. amobarbital, and pentobarbital.
E., BaerheimSvendsen, A., J. Pharm. Sci. 51, 318
(1962). (2) Cie linski, E. W., ANAL.CHEM.35,256 (19637. (3) Parker, K. D., Fontan, C. R., Kirk, P. L., Ibid., p. 356. ( 4 ) Parker, K. D., Kirk, P. L., Ibid., 33, 1378 (1961).
WORKsupported by grants from Yational Institutes of Health, U. S. Public Health Service IEF 21 (C3)1, and the Research Committee, University of California. meeting, California Association of riminalists, San Diego, Calif., May 1962.
Backflush Applied to Capillary Column-Flame Ionization Detector Gas Chromatography Systems E. R. Fett, Union Oil Co. of California, Union Research Center, Brea, Calif.
w
the technique of backflushing packed ga. chromatographic columns is ne11 known and estensively applied. this has not been the case for capillaiy columns. It is assumed t h a t the main reason for this is the extremely m a l l allowable dead volume in capilla~v cystem$, requiring valves which ni F :lot conimercially available. The method presented here will allow backflushing a capillary column-flame ionization detector system with almost a n y coinm~rciallyavailable valve. I n many ea-PS this method will both provide increased detector sensitivity and minimize effective dead volume in the detection system. The niodification which makes this method poqsible is the addition of an a u d i x r y cupply of carrier gas a t the outlet end of the capillarycolumn. This stream, usually 30 to 100 ml. per minute, ip added bj- means of a tee constructed to present the column end directly into this n u d i a r y flow. The resultant minimizing of downstream dead volume b y this relatively large flow is selfevident and makes possible both the addition of a backflush valve with no loss of resolution due t o valve volume HILT:
and the removal of excess dead volume found in some detector Systems. The effect of carrier gas flow on t h e response of a flame ionization detector has been published by Sternberg et al. ( 2 ) who conclude that “for a given carrier gas flow, there is a hydrogen flow which results in maximum average molecular energy in the reaction zone and in optimum response.” Sternberg has subsequently pointed out (1) that the converse must be true-e.g., an optimum carrier gas flow exists for a given hydrogen flow, and t h a t this condition is not being fulfilled in most capillary systems. Therefore, the auxiliary flow of carrier gas proposed t o facilitate backflushing not only is harmless but, when carefully chosen, is a means of attaining optimum detector response and will, in some cases, provide a n order of magnitude increase in detector sensitivity. Figure 1 shows two possible modes for backflush plumbing with resulting chromatograms. Mode A is the basic system and is adequate where only column cleaning is the desired result. While the backflushed sample has been sent to the detector primarily for il-
lustration, this sample portion can be vented to the atmosphere at the splitter, eliminating the need for heated transfer lines. When the backflush is sent to the detector, Mode A causes the column effluent to travel through the relatively large volume splitter, injector, and transfer line, resulting in a poorly resolved backflush chromatogram. Mode B is a refined scheme which,
Table I. Operating Conditions
x 0.010’’ i.d. stainless Stationary phase Hexadecene Temperature 25” C. Carrier gas Helium Inlet pressure 40 p.s.i. Flow rate (outlet) 2.5 ml./min. Sample size Approximately 5 cLg. of gasoline cut from crude oil Efficiency (n130,000 plates heptane) Auxiliary flow 36 ml./min. rate Flame detector: t , Air flow 400 ml./min [ Hydrogen flow 23 ml./min. Column
200‘
VOL. 35, NO. 3, MARCH 1 9 6 3
419
AUXILIARY HELIUM
MODE E
DETECTOR
1
I
i'
I HYDROGEN
"-GI0
n;C9
n-
\
1 0
~
10
20
30
TIME
Figure 1 .
MODE A
MINUTES
Two possible modes for backflush plumbing with resulting chromatograms
by adding the ausiliary gas a t the splitter during backflushing (additional valving required), reduces the effect of these large volumes and thus improves resolution. -1second advantage of Mode B i- that, through the uqe of the auxiliary carrier gas in the backflush, the detector remains in operation with optimum carrier flow. This approximately triple- the area response for this particular system. Operating conditions for the column are given in Table I.
The relatively large pressure drop across capillary columns produces teniporary flow instability 11-hen snitching from normal to backflush operation or vice ver5a. For the system shown it is necessary to .i\.ait about ten minute? betlveen successive runs to pro\ ide a stable base line. This problem is very apparent in the backflush mode where ba-e line drift makes quantitative mea-urenient difficult. A minor problem with some detectors is the fact
that thc immediate pressure surge associated with valve sn-itching extingui>heq the flame. LITERATURE CITED
(1) Sternberg, J. C., informal discussion,
Second Annual Research Conference on Gas Chromatography, University of California, Los Angeles, January 1962. (2) Sternberg, J. C., et al. Third International Symposium on Gas Chromatography, Instrument Society of America, Michigan State Universitj-, preprints pp. 169-84, June 1961.
Use of Chlorine for Quantitative Elution of Cu(ll) from Dowex 1 Resins John J. O'Connor,' Joseph R. Weiner, and Bernard Rubin, Air Force Cambridge Research Laboraiories, Electronics Research Directorate, L. G. Hanscom Field, Bedford, Mass.
side reactions betlveen ions that are being eluted on an ion exchange column and the resin have been studied or referred to by several investigators (1, 2 ) . These reactions usually involve the reduction of cation< or anionic oxidants, and may result in a decreased efficiency for the removal of the desired ion, a change in its elution characteristics, and interference b y the reduced species n-ith subsequent fractions. These phenomena were observed in the course of the development of a separation scheme for several trace elements on a Dowex 1 anion exchange column in a chloride medium. The NUESIRABLE
Present address, Tracerlab, a Division Laboratory for Electronics Inc., Waltham, Mass. 1
of
420
ANALYTICAL CHEMISTRY
qcheme under investigation involved separation of a copper fraction with 0.1F HC1. Copper did not elute quantitatively from the resin, perhaps caused by the reduction of Cu(T1) to Cu(1) on the resin. Reference to the copper adsorption functions (4)indicated that Cu(I1) should be eluted quantitatively under these conditions and that Cu(1) probably would be ad-orbed by the resin. I n an analogous situation, chlorine was used to ensure the oxidation of As(II1) to As(V) and as a holding oxidant on ion exchange columns ( 6 ) . Several investigators have observed this same effect on different resins with other cations (6,5 ) . On the basis of these facts i t was decided t o investigate the role of chlorine in stabilizing the
higher oxidation state of copper during its elution. EXPERIMENTAL
Adsorption columns were fabricated from Lucite, each with an area of 1.13 sq. cm., and plugged with gla- wool to retain the resin. The upper part of the column \vas in the form of a reservoir to permit easy addition of solutions and resin. Conditioning solution- were placed in a separatory funnel which was joined to the reservoir by means of a one-hole rubber stopper. The separatory funnel was capped with a rubber stopper containing a glass tube with a small hole to prevent rapid lo-s of chlorine gas. The columns were filled with resin [Bio Rad AG 1-XlO (200to 400-mesh), chloride form (purified
