Anal. Chem. 1982, 5 4 , 2397-2398 (6) Rlch, E. S.;Wampier, J. E. Clin. Chem. (Wlnston-Salem, N.C.) 1981, (7) (8)
(9)
(IO) (11)
27, 1558-1568. Furman, 6. K.; Morrison, G. H. Anal. Chem. 1980, 52, 2305-2310. Lester, E. P.; Lemkin, P. F.; Llpkln. L. E. Anal. Chem. 1981, 53, 390A-404A. Glanelll, M. L.; Callls, J. 6.; Anderson, N . H.; Christian, G. D. Anal. Chem. 1981, 53, 1357-1361. DuNouy, P. L. J. Gen. Physlol. I S I S , 1, 521. Wllhemy, L. Ann. Phys. 1863, 119, 177.
2397
(12) Cayias, J. L.; Schecter, R. S.;Wade “Adsorption at Interfaces”;Mittal, K. L., Ed.; American Chemical Soclety: Washington, DC, 1975; ACS Symp. Ser., Vol. 8, p 234. (13) Porter, A. W. Philos. Mag. 1933, 15, 163. (14) Andreas, J. M.; Hauser, E. A,; Tucker, W. B. J. Phys. Chem. 1938, 42, 1001-1019.
RECEIVED for review June 7,1982. Accepted August 16,1982.
Etching Borosilicate Glass Caplllary Columns T. L. Peters,” T. J. Nestrlck, and L. L. Lamparski Do w Chemical USA, Michlgan Division, 574 Building, Midland, Michigan 48640
The uniform coating of organic liquids on glass has long been known to be difficult except when using silicones or hydrocarbons ( I ) . For this reason most of the first glass capillary columns were coated with apolar liquid phases such as SE-30. Attempts to coat columns with more polar liquid phases usually resulted in a low efficiency column with the phase being deposited in the form of minute droplets rather than a uniform film. The necessity to increase the “wettability“ of the glass by decreasing the wetting angle of liquid phases was recognilzed as early as 1962 ( 2 ) . Giddings (3)also suggested roughening the interior of the glass capillary as a means of decreasing the wetting angle and obtaining a more uniform liquid film. Golay (4) had proposed a roughened surface earlier to increase the gas-liquid interfacial area which would also improve capacity. An experimental study of the relationship between surface roughness and contact angle demonstrated the validity of the Wenzel equation linking these two parameters (5). The procedures used for roughening the interior of the column are varied. When using soda-lime or “soft” glass columns, the most popular procedure has been deposition of the sodium chloride crystals through high-temperature treatment with anhydrous hydrogen chloride (6). “Dendrites” of sodium chloride have also been obtained via an aqueous coating technique employing a salt solution (7). Grob used a unique procedure to grow barium carbonate crystals on the interior of the capillary both to promote coating of liquid phases and to deactivate (8). Other roughening procedures include carbon deposition (9), formation of amorphous silica (IO), and reaction with an aqueous solution of potasisium bifluoride (21). One of the more frequently reported procedures for roughening borosilicate glass capillary columns is the formation of silica “whiskers” on the walls through the action of anhydrous hydrogen fluoride a t elevated (-400 “C) temperatures (12-14). Our technique which is simple and reproducible, results in a thin, uniform etch in borosilicate glass capillary columns. We have accomplisihed this through a room-temperature treatment of the column with a solution of ammonium bifluoride in methanol. Although the now widespread availability of fused silica columns has diminished the need for borosilicate capillary columns, numerous applicadions still require them. Certain polar phases or column internal diameters significantly greater than 0.3 mm will continue to require the use of borosilicate columns.
EXPERIMENTAL SECTION Reagents. The solvents used were distilled-in-glass quality obtained from Burdick and Jackson Laboratories (Muskegon, MI). The ammonium bifluoride used was purchased from J. T. Baker Chemical Co. The etching solution is made by saturating methanol with ammonium bifluoride. Etching the Column. A borosilicate glass capillary is first flushed with 5 column volumes of methanol followed by methylene chloride and then dried with purified nitrogen. Five column volumes of the etching solution is very slowly pushed through the column such that the total contact time is 8-12 h. The column is then rinsed with 5 column volumes of methanol followed by 5 column volumes of water. The transition from methanol to water should take place in the form of a gradient over a volume of >20 mL of mobile phase. After the capillary is dried with purified nitrogen, the etch is evident in the form of an easily perceptible opaqueness. RESULTS AND DISCUSSION
A 50 m X 0.5 mm Pyrex column was etched by this procedure, “leached” with concentrated hydrochloric acid (15),
I
Flgure 1. Chromatogram of EPA priority pollutant phenolics (in order of elution): 2-chlorophenol,phenol, 2,4dimethylphenol,2-nitrophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenoI, 2,4-dinltrophenol, 4-nitropheno1, 4,6-dinitro-2-methylphenol, penta-
chlorophenol.
0003-2700/82/0354-2397$01.25/0 0 1982 American Chemical Society
23S8
Ami. Chem.
1982, 54. 2398-2399 Before deactivation and coating these columns should be "leached" with hydrochloric acid. This W N ~ the S dual purpose of removing trace metals and destroying any residues from the etching solution. Although the etch is very fme structured, no problems with air entrainment have been encountered aa with whisker columns (17) making the columns suitable for d standard coating procedures.
ACKNOWLEDGMENT The authora wish to express their sincere appreciation to H. L. Garrett for microscopy characterization of the etched capillary columns.
LITERATURE CITED Fox. H. W.; Have. E. F.: Zlsmsn. W. A. J . W s . chan. 1955. 59, 1097-1106. (2) Fame RIw. F.: bnnker. J.: Guiochon. 0. N a m( L m ) 1962. 196. 63-84. (3) Giddlw.J. C. Anal. Chsm. 1962. 34, 458-485. (4) Golay. M. J. E. '"asChromatography": Caaty. 0. H.. Ed.; A C B d "
(1)
Flgure 2. SEM photograph of etched Pyrex capillary at nification.
1940X mag
thermally deactivated with a cyclic siloxane (16).and s t a t i d y coated with a 0.2-pm fdm (calculated thirkness) of OV-I7 oil. After the column was ronditioned overnight at 220 "C, the chromatogram in Figure 1 was obtained. The calculated column efficiency of 1620 effective plates/m had not deteriorated after more than a month of temperature programmed operation. A SEM photograph reveals the etch to be extremely uniform and fine structured (Figure 2). The depth of the etch, as measured by a Tencor Alpha-Step Profilier, ranges from 0.05 to 0.4 pm with a distance of 243 pm between "peaks". Problems with this procedure occur whenever an air bubble is allowed into the column between the methanol and water in the final washing step. Particles of ammonium hexafluorceilicate dislodged by the water will move forward through the liquid. If there is an air bubble present, these particles will collect there and meventually plug the column. Plugging can also occur if the transition from methanol to water in the washing step is made too abruptly.
Press: New Y a k . 1958; pp 38-53. (5) TamI. Y.: Aralani. K. J . phyr. Chem. 1972. 76,32674291. (8) Frankm. J. J.: Runen. 0. A. F. M.: RIBS. J. A. J . C h m m a g . 1076, 126.
117-132.
(7) Sandra. P.: Vsrstapp. M.; Verzeie, M. Ummatcgaddn 1976. i i . 223-226. (8) @ob. K.; clob. 0. J . Ummatog. 1976. 125.471-495. (9) Gweni. Q. C.: ubatl. A,: Nola, 0. ChrMlamgaPhla 1975. 8 .
476-490.
V a W Pol. J. J. G.: Wasink. J. D. M C CC. J . Hgh Resolut. UmmaIcq. Chmmatog.. Can".1979. 2 . 297-302. (11) Heckman. R. A.; em. C. R.: Best. F. W. Anal. CI". 1976. 50. (10) Badingo. H. T.;
- ._. ,,e.-,,=.*
(12) Sandra. P.: V s n e l a . M. UmmaIOgapMa 1977. 70, 419-425. (13) Onuska. F. 1.: Comb. M. E. J . Chrometog.. 1976. 126. 133-145. (14) Schkke. J. D.: Comina. N. R.: Retwius. V. J . Chmmatog.. 1975. 1.1)
,,
