known (6) and is indicated by the presence of a 3.32-micron band in the infrared spectrum (Perkin-Elmer Infracord) of evaporated sampling solution which had been oxidized by hydrogen peroxide. This band was not found in the spectrum of either phenolphthalin or phenolphthalein (Eastman Kodak) . However evaporation of the sampling solution by boiling may have caused the degradation. Further work is necessary before definite conclusions can be reached. Absorption Maximum. T h e absorption maximum (Beckman Model DB spectrophotometer) was found to be at 550 2 mp rather than a t 530 mfi as has been reported (1).
*
LITERATURE CITED
(1) California State Dept. of Health,
Conference-Workshop, Berkeley, Calif., “Chemical Methods in Air Pollution,” November 1958. (2) Chemical Rubber Publishing Co., Cleveland, Ohio, “Handbook of Chemistry and Physics,” p. 1624, 1953-4. (3) Goto, Hidehiro, Musha, Soichiro, J . Chenz. SOC.Japan 66, 37 (1945); C . A . 43, 16829 (1949). (4) Haagen-Smit, A. J., Brunelle, M. F., Intern. J . Air Pollution 1, 51 (1959). (5) Hubacher, M. H., J . Am. Chem. SOC. 65,2097 (1943). (6) Kastle, J. H., Shedd, 0. M., Am. Chem. J., 26,526 (1901). (7) Kolthoff, I. M., Lehmicke, D. J., J . Am. Chem. SOC.70,1879 (1948). (8) Lecoq, H., Bull. SOC. Chim. Belges 54, 186 (1945); C . A . 41,2346.1’(1947). (9) McCabe, L. C., Ind. and Eng. Chem. 45, 111.4 (1953). (10) Meyer, H., Muench. Med. Wochschr. 50,1492 (1903); in Lecoq. (11) Okac, A., Celechovsky, J., Chem. Listy 45, 52 (1951); C . A . 45, 65300 (1951).
(12) Scholes, O., Ber., 71, 447 (1938). (13) Thomas, P., Carpentier, G., Compl. rend. 173, 1082 (1921); C.A. 16, 538 (1922).
DANIELF. BENDER^ ANDREW W. BREIDENBACH~
Division of Air Pollution Technical Assistance Branch Air Pollution Training Activities U. S. Department of Health, Education, and Welfare Cincinnati 26, Ohio *Present address, Division of -4ir Pollution, Robert A. Taft Sanitary Engineering Center, Cincinnati 26, Ohio. 2 Present address, Division of Water Supply and Pollution Control, Department of Health, Education, and Welfare, 1014 Broadway, Cincinnati 2, Ohio. DIVISIONof Waste and Water Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
Improved Gas Chromatographic Column for Barbiturates Kenneth D. Parker, Charles R. Fontan, and Paul L. Kirk, School o f Criminology, University of California, Berkeley 4, Calif.
work has been done C on the gas chromatography of the barbiturates. Brochmann-Hanssen and ONSIDERABLE
Baerheim-Svendsen (1) treated the solid support with hexamethyldisilazane (HMDS) to reduce tailing, and Cieplinski (2) used acidic additives in conjunction with HMDS to obtain sharp peaks. Table I lists the relative retention values a t two ternperatures for 28 barbiturates, phenacetin. salicylic and acetylsalicylic acids, and a metabolite of amobarbital. Although symmetrical peaks were obtained with Carbowax 2011 alone, the column employed for the collection of these data had two liquid phases: SE 30 and Carbowax 2OiLI. The Hy-Fi gas chromatograph (Wilkens Instrument and Research Co., Walnut Creek, Calif.) with hydrogen flame ionization detector, Aerograph Model 600, and the Leeds and Northrup Speedomax H, 0- to 1-mv. recorder, Model S, were used. The chromatographic column was a stainless steel tube of l/e-inch o.d., 0.093-inch i.d., 21/2 feet in length. It was packed with 100to 120-mesh firebrick, acid-washed, coated with SE 30 [1.5% (w./w.)], and Carbowax 20M 12% (w./w.) I. The stationary phase was prepared in two steps. First a slurry was made of the firebrick and the SE 30 in chloroform; the solvent mas evaporated a t 41 8
.TANALYTICAL CHEMISTRY
once on a steam bath, with the air over the slurry being aspirated b y vacuum. When the material was dry, i t was mixed with a solution of Carbowax in chloroform and treated in the same manner. The operating conditions were: injector temperature 30’ C. above column temperature, oven temperatures 210’ and 230’ C., flow rate of carrier gas (nitrogen) 30 cc. per minute.
Table 1.
Since Carbowax 2011 is polar, the order of emergence of the barbiturates is different from that observed on a column utilizing SE 30 only ( I , 4 ) or Apiezon L (1) as the liquid phase. The effect of first coating the firebrick with SE 30 was not eutenskely investigated. However, i t i= possible that the high temperature niasimum of this column (240’ C.), an? the cor-
Relative Retention Values of Barbiturates
Temperatures,
O
C.
Official names Metharbital Narconumal Barbital Hexobarbital Butabarbital Probarbital
230 0.27 0.14 0.27 0.20 0.70 0.66 0.88 0.73 0.96 1.04 1 , 00 ( 5 . 6 ) 1.OO ( 2 . 3
Butethal Allylbarbituric acid Methallatal Amobarbital ADrobarbital D’lallvlbarbituric acih. Mephobarbital Pentobarbital Butalbital Thiopental Secobarbital
1.01 1 02 1 09 1 11 1 12 1.14
1.04 1 00 1.17 1.17 1 09 1.13
1.20 1.25 1.26 1.27 1 55
1.23 1.30 1.39 1.30 1.56
210
min.)
Temperatures, C. Official names 210 230 1.57 Thiamylal 1.57 1.52 Vinbarbit’al 1.59 1.69 Hexethal 1.82 2.91 Cyclo a1 3.26 3.48 Pr opaEy lonal 3.99 3.70 Cyclobarbital 4.14 4 .25 Butallylonal 4.87 4,g.j Kemithal 5.55 4.95 Heptabarbital 5 70 5.65 Phenobarbital 6 79 S.05 ;Ilphenal 9 72 4.74 Amobarbital meta- 6 27 bolite 0.09 Salicylic acid 0 2; 0.09 Acetilsalicylic acid 0 34 0.65 Phenacetin 0.46 Data obtained with a mixed liquid phase: Carbowax 2011 ( 2 9 ) and SE 30 O
(1.551.
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. Helium Carrier gas 40 p.s.i. Inlet pressure 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
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