ANALYTICAL CHEMISTRY, VOL. 50, NO. 14. DECEMBER 1978 -
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SPECTRU'd E G TI;EFi Figure 1. Schematic representation of the data digitizer The area wrthin the dotted line IS contained wrthin the Laboratory Peripheral System (LPS) of the minicomputer averaged 16.8 peaks each. Six calibration points were included with each spectrum (2.5, 5.0, and 15.0 pm, each a t 0 and 100% transmission) so that the peaks obtained in ADC counts could be converted to wavelength (or wave number) and percent transmission. These spectra were digitized a t the rate of about one spectrum per minute. An example of the effectiveness of this digitizer is shown in Table I which compares the results of computer vs. manual digitization for a typical spectrum. The correspondence is seen to be within six reciprocal centimeters (averaging 3 cm-') which compares well with the stated instrumental resolution of 4 cm-'. T e n replicate digitizations of four different peaks yielded spectral accuracies averaging within 1 cm-' and intensity
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accuracy averaging within 1 % transmission unit. For these measurements, the average standard deviation for the wavelengths was 2.6 cn1-l and 0.4% transmission unit for intensities. This corresponds to a physical displacement of about 0.2 mm. Once the computerized data set has been obtained, it can be tested for correctness and restructured or abstracted to fit the needs of the desired investigation. T h e VPIR library described herein is presently being used in several ways to study the effectiveness of vapor phase spectra as a n identification tool for gas chromatography, namely, by pattern recognition ( 3 ) ,by library searching (4), and by selection of optimal wavelengths for selective single wavelength monitoring.
LITERATURE CITED P. C. Uden, D. E. Henderson, and R. J. Lloyd, J . Cbromatogr., 126, 225 (1976). Specba 1-500 in "Atmospheric Pressure Vapor phase Infra-red Collection", Sadtler Research Laboratories, Inc., Philadelphia, Pa. M. F. Debney, P. C. Men, and D. E. Henderson, 29th Pittsburgh Conference on Anavical Chemistry and Applied Spectroscopy, Cleveland, Ohio, 1978. Paper 478. M. F. Delaney, P. C. Denzer, and P. C. Uden, to be presented at the Fifth Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies, Boston, Mass., 1978.
RECEIVED for review July 17, 1978. .4ccepted September 5, 1978. The award of an American Chemical Society, Division of Analytical Chemistry summer fellowship, sponsored by the Olin Corporation is gratefully acknowledged (M.F.D.). The computer was obtained through National Science Foundation Grant G P 42542 to the University of Massachusetts.
Etching and Deactivating Glass Capillary Columns for Gas Chromatography Robert A. Heckman,' Charles R. Green, and Freddie W. Best Research Department, R. J. Reynolds Tobacco Company, Winston-Salem. North Carolina 27 102
T h e first step in preparing an efficient, wall-coated glass capillary column generally involves modification (usually etching) of the interior surface. This step is frequently required in column preparation for the promotion of film spreading and stability. T h e use of gaseous or aqueous H F for etching untreated glass capillary columns is not widespread. Aqueous HF does not impart a matte etch to borosilicate glass, and treatment of flint glass with either reagent is extremely difficult to control. One technique ( I ) applied to wide-bore columns relies on silica whisker formation resulting from attack of gaseous hydrogen fluoride which is generated at 350 "C from a deposit of ammonium hydrogen difluoride. Since 1974 we have used a similar reagent, potassium hydrogen difluoride, but have employed it under entirely different conditions and with significantly different results. The present etching technique employs aqueous K H F 2 solutions and has been used successfully in etching both borosilicate and flint glass capillary columns. Aqueous etching procedures have been shunned by some research groups (2) because of problems associated with deactivation of the etched layers. However, when properly eroded, the glass surface obtained by use of K H F z is already extensively deactivated relative to untreated glass. T h e procedure yields columns that are readily amenable to further deactivation by Cronin's adaptation (3) of Aue's method involving Carbowax 20M and silanization techniques similar 0003-2700/78/0350-2157$01.00/0
to the hexamethyldisilazane procedure of Welsch and coworkers ( 4 ) . T h e resulting columns have been statically and dynamically coated with a variety of polar and nonpolar stationary phases with excellent results; they have also been used extensively in several GC-MS systems. T h e etching of a flint glass column requires the passage of one column volume of 10% aqueous KHF,. This treatment is performed with a n 80-mL plastic-lined reservoir similar in construction to that described by Nikelly ( 5 ) . T h e development of a matte etch from the beginning to the end of the column can be followed visually and by a rapid change in the p H of the effluent from 6.5to 2.5. This is followed by passage of 1.5-2 mL of water per meter of column length. The water wash erodes the etched surface. I t can be followed visually and results in a uniform etch throughout the column. Both of these steps are conducted under 50-100 psig nitrogen pressure, depending on column length and diameter. Etching of columns made from borosilicate glasses requires a more concentrated K H F 2 solution (20%) and may require several treatments for development of a matte etch. Deactivation of the etched columns can generally be accomplished by the passage of 6 N hydrochloric acid. followed by sealing the ends of the nearly filled column with 6 N hydrochloric acid and heating overnight a t 100-150 "C. I t is sometimes advantageous to repeat this step. T h e columns are then rinsed with water and acetone and dried under a flow Q 1978 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table I. KHF,-Etched WCOT Columns separation no. stationary phase ov-101 ov-101 OV-17 Poly A-103 UCON 50 HB5100 Carbowax 20M SPlOOO
length, mm 22 22 25 20
22 68 18
type of glass flint borosilicate flint borosilicate borosilicate flint borosilicate
Figure 2.
Figure 1. Electronmicrograph (6000 diameters) of a KHF,-etched capillary column
of nitrogen prior to examination in a gas chromatograph. Finally, the column should be further deactivated by techniques such as those previously described ( 3 . 4 ) . T h e entire deactivation process should be monitored at various stages by examination of the peak shapes of undecane, 2-octanone, and 1-octanol a t 190 "C (190 "C and 100 "C for short columns). Success at deactivation is indicated by improvement in the peak shapes of 2-octanone and 1-octanol. Alternatively, the testing procedure of Schomburg (6) may be used. We have examined the etched capillary surfaces a t various stages by scanning electron microscopy; whisker-like formations were not observed. The electron micrograph in Figure 1 is of an etched flint glass column that has been washed with water only. I t is logical that the crystalline material is K,SiF, which is sparingly soluble in water. However, we have not been able to confirm this. Ideally, a general column preparation procedure should meet certain requirements, such as those established by Grob
deactivation method silanization silanization Carbowax 20M Carbowax 20M Carbowax 20M Carbowax 20M none
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32 23 18 48 19
Chromatogram of Patchouli Oil
( 7 ) . We feel that the procedure described above comes close to satisfying these criteria. T h a t is, the method is applicable t o both flint glass and borosilicate glass columns, does not require sophisticated equipment or reagents, and is suitable for a wide variety of coating materials. However, as with other techniques, success with this method is somewhat sensitive to the nature of the glass in each length of capillary tubing. Table I shows some typical results for several 0.25-mm i.d. WCOT columns prepared by static coating of capillary columns that were etched and deactivated by the above method. T h e chromatogram in Figure 2 was obtained with a borosilicate glass column (0.33 m m i.d. x 40 m) that was etched with KHF, and coated with SP1000. T h e column had a separation number (C15-C1G)of 40 a t 100 "C. A flow rate of 3 mL/min was used with linear temperature programming from 50-210 "C @ 2'/min.
LITERATURE CITED (1) F. I. Onuska, M. E. Coneba, T. Bisticki, and R. J. Wilkinson,J. Chromatcgr., 142, 117 (1977). (2) M. Novotny and A . Zlatkis, Chromatogr. Rev., 14, 1 (1971). (3) D. A . Cronin, J , Chromatogr., 97, 263 (1974). (4) Th. Welsch, W . Engewald, and Ch. Klancke, Chromatographia, 10, 22 (1977). (5) J. G. Nikelly, Anal. Cbem., 46, 2249 (1974). (6) G. Schomburg, H. Husmann, and F. Weeke, Chromatographia, 10, 580 (1977). (7) K . Grob and G. Grob, J . Chromatogr., 125, 471 (1976).
RECEIVED for review July 5, 1978. Accepted August 11, 1978.
Compact, Variable Volume, Liquid/Liquid Extractor William A. Hoffman, Jr.' Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
"Continuous" liquid/liquid equilibration between two immiscible solvents provides a convenient way to exhaustively 'Permanent address,Department of Chemistry, Denison University, Granville, Ohio 43023. 0003-2700/78/0350-2158$01 OO/O
extract components from solution even if the distribution coefficients of the solutes are not favorable. Commonly, either the lighter or the heavier density liquid is boiled, condensed, and allowed to percolate repetitively through a companion solvent which contains the solute. Many continuous extraction C 1978 American Chemical Society
