CHROMATOGRAPHY COLUMN

Abstract: A highly flexible glass chromatographic capillary col­ umn includes moisture impervious coating upon the external surface thereof and a stationary phase layer overlying the internal surface thereof.

Description: CHROMATOGRAPilY COLUMN Background of the Invention The present invention generally relates to a chromatographic column and, in particular, relates to a flexible glass chromatography column. As used herein the term "glass" is intended to include those glass materials which have a melting point of less than 11000C. More specifically, the term *glass" as used herein includes such compositions as borosilicate glass, soda lime glass and clearly excludes silica glass, i.e., fused quartz, which has a melting point on the order of about 16000C. As well known in the chromatographic arts in particular, the art engendering gas chromatography, the separation of the constituents of the sample material is dependent upon, inter alia, the length of the separation column. While this may appear to be an overly simplistic statement it is nevertheless a lflajor consideration in all gas chromatographic column analysis. Because of the high mobility of gas, compared to liquid, and because many gas chromatographic columns are of the "oiven-tube" type, i.e., without a packed bed, gas ci,rolnatography columns are often quite long, e.g. 5G meters or more. Consequently, such columns, generally capillaries, must be coiled to allow insertion into chromatographic ovens. To date, it has been necessary to heat the glass capillary after its formation in order to form a useful column. The process for forntiny such a coil is described in an article entitled Construction of Long lengths of Coiled Glass Capillary; Analytical Chemistry, 1960, p. 302. One major disadvantage of such a coiled capillary is its fragility, i.e., it is easily broken due to its rigidity. In fact, it has been believed by persons in the field, that the wall thickness of even the rigid heat-formed glass coiled columns had to be relatively large to avoid fracturing the glass. The rigidity of the glass columns, even though slightly flexible in the axial direction of the coil, required that the ends be straightened by heating in order to be inserted into a gas chromatographic instrument oven. This heating, in addition to being tedious and frustrating, was also a frequent source of column deterioration, at least insofar as it deteriorated the integrity and usefulness of the stationary phase near the ends of the column. Such deterioration was quite impossible to measure and thus the analytical results were inherently questionable. Exemplary of such a belief is U.S. Patent No. 4,293,415, issued October 6, 1981, which specifically recites the abovestated disadvantages and goes on to describe a chromatographic column niade from quartz, i.e., silica. Another primary disadvantage, which has deterred those in the art from continuing investigating the broad usefulness of glass columns has been the generally held belief that glass columns excessively distort even slightly acidic and basic sample materials. This effect is believed to be caused by the chemical activity of tlle surface of the glass. Such chemical activity is believed to result in sample components being irreversibly or non-linearly adsorbed by the column and thus not eluting from the column at all or to elute with so seriously distorted peak shapes as to be useless for analytical purposes. Summary of the Invention Accordingly, it is one object of the present invention to provide a highly flexible glass chromatographic capillary column capable of use in modern gas chromatographic analyses. This object is accomplished, at least in part, by providiny a highly flexible glass column of capillary dimensions having an outer moisture protective coating and having an inner chromatographic separation and surface passivating layer. Other objects and advantages will become apparent to those skilled in tie art from the following detailed description in conjunction with the attached drawing and the appended claims. Brief Description of the Drarring The attached drawing includes: Figure 1, which is a schematic representation of a machine for producing highly flexible glass capillary column; Figure 2, which is a pictorial view of a means for coating a highly flexible glass capillary column during the production tl.reof; Figure 3, which its a cross-sectional view of a portion of a highly flexible glass capillary column; Figures 4A and 4B, which are cbronatograms demonstrating the efficacy of a highly flexible glass capillary column; and Figure 5, which is a tabulated comparison of the results shown in Figures 4A and 4B. Detailed Description of the Invention A highly flexible glass capillary column, generally indicated at 10 in Figure 1, embodying the principles of the present invention, can be produced by means of a modified conventional rigid glass column drawing machine 12, such as a Shimadzu Model GDM-1 manufactured and marketed by Shimadzu Instruments of Xyoto, Japan. The aforementioned modifications include, inter alia, first and second column coating means, 14 and 16 respectively, first and second curing means, 18 and 2b respectively, and a take-up drum 22 which drum is preferably driven by a dedicated motor, not shown in the drawing. The above-described apparatus is operated to faithfully produce the highly flexible glass capillary columns 1.0 and ensure that flexibility by.-providing a coating thereon which protects the glass from deterioration generally believed to be the result of interaction between the glass and moisture or other materials. In one preferred mode, a rigid glass tube 24 having an outside diameter of about 4 millimeters and an inside diameter of about 2.5 millimeters is used as the feed stock. The rigid glass tube 24 is initially cleaned, for example, with a 108 hydrochloric acid solution which is rinsed with water and subsequently dried. Preferably, thereafter, the tube 24 is handled with a gloved hand. The cleaned tube 24 is fed into the drawing nachine 12 via a set of feed pulleys 26. Title tt:rt)peratue of the drawing mashine 12 is set at about 6700C for soda lime glass. The resultant capillary column 10 is drawn from the inaciine 12 via a set of draw pulleys 28. The driving motors, not shown, for the feed pulleys 26 and the draw pulleys 28 must be carefully adjusted to ensure a smooth, continuous linear movement of the drawn capillary column 10. The majority of highly flexible glass capillary columns 10 drawn to date have been with a drawing ratio, i.e., the ratio of the drawn length to the feed length, of about 110 to 1 and have resulted in capillary columns 10 having outside diameters of about 0.3 millimeters and inside diameters of about 0.2 millimeters. In order for the column 10 to retain its strength and, most importantly, its flexibility, it must be provided with an external coating as rapidly as possible after it is formed. Such coating serves to protect the external surface from the deleterious effects of moisture and other materials which can make the glass friable. Further, the internal surface must also be treated with an appropriate coating to prevent the drawn column from becoming friable. However, this coating canbe applied subsequent to the entire length of the capillary being drawn. The permissible hiatus in applying such treatment to the internal surface is granted from the reduced diffusion rate of moisture bearing gas, e.g., the atmosphere or ambient, therethrough because of the capillary dimension of the column 10. The external coating which, in the preferred embodiment, comprises a first and a second column coating, 30 and 32 respectively, shown in Figure 3, is applied by the aforementioned first and second coating means, 14 and 16 respectively. As clearly shown in Figure 2, the coating means, 14 and 16 includes a cup 34 having a bore 36 through which the column 10 is drawn. Preferably the cup 34 is made from a pair of semicircular members 38 and 40 which are united by means of, for example, a hinge 42. The cup 34 is rigidly affixed to a stationary base member, not shown, so that the bore 36 is axially aligned with the drawn column 10. In operation, the cup 34 is provided with a column coating material preferably Prdlin PI-2550, a polyrnide manufactured and marketed by DuPon Corp. of Deiaware. The Pyralin PI-2550 can be applied either in its pure form or it can be diluted, for example, with N methyl-;-pyrrolidone. Although other materials, including metals, can be used for the first and second coatings, 30 and 32 respectively, the Pyralin PI-2550 is preferred. In order to prevent leakage of the coating material through the bore 36 the mating surfaces, 44 and 46, respectively, of the semicircular members, 38 and 40 respectively, are provided with a layer of resilient material, for example, a strip of Teflon, a material manufactured and marketed by DuPont Corp. of Delaware. In order to effectively bond the Pyralin PI-2550 to the column 10, the wet coated column 10 is passed through the first curing means 18 substantially immediately upon exiting the. first column coating means 14 and the second curing means 20 substantially immediately upon exiting the second column coating means 16. In this instance, the curing means 18 and 20 are effectively constant temperature ovens. The first curing means 18 is set to a temperature of about 3000C, +- 50 C, whereas the second curing means 20 is set to a temperature of about 3500C -+ 50"C. The higher temperature of the second curing means 2S, in addition to removing the solvent of the second column coating 32, further cures the first column coating 30. As stated above, the internal surface of the highly flexible glass capillary column 10 must also be treated to avoid friability. To this end, the internal surface is flushed with n-butanol and, in order to be useful as a chromatographic column, is subsequently passivated or deactivated. This deactivation may be accomplished by techniques well known in the glass chromatographic column coating art. Preferably, the internal surface is first subjected to an n-butanol flush and thereafter a static leach with gaseous hydrochloric acid prior to applying a film of Carbowax 20M, a polyethylene glycol nianufactured and marketed by Union Carbide of Danbury, Connecticut. Thereafter, in the columns formed to date, the column 10 wasvsubjected to a dichioromethane rinse and a stationary phrase layer of Carbowax 20M was applied by conventional techniques. Referring particularly to Figure 3, a resultant highly flexible glass chromatoraphic capillary column 48 is shown in cross-section. As shown, the column 48 includes a highly flexible glass capillary tube 50 having an external surface 52 and an internal surface 54 and having a continuous bore 56 there through. The external surface 52 has a moisture impervious coating 58 which includes a first and a second layer, 60 and 62 respectively, of a polymide. The internal surface 54 has an adhesion layer 64 adjacent thereto which layer 64 has a chromatographic stationary phase layer 66 thereover. The efficacy of the above-described highly flexible glass chromatographic capillary column 48 was investigated both for its acid/basic separation capability and the possible irreversible adsorption ofqeither acidic or basic components. Although only soda-lime glass columns have been drawn to date, it is anticipate that similar results are achievable with other glass columns, e.g., borosilicate glass or the like. The results are shown in Figures 4 and 5. Figures 4A and 4B are chromatograms representing the capabilities of the column and Figure 5 is a companion table interrelating the chromatograms. A test sample was prepared which included a base/acid pair of compounds and a substantially ileutral pair of compounds in a toluene solution. The base/acid pair selected was 2,4dimethylaniline (DA) and 2,6-dimethylphenol (tip) whereas the reference compounds were heptadecane (C17) and octadecane (Cl8). All of these compounds are chromatograph standards for evaluating the efficacy of gas chromatographic columns The sanple solution was 0.75% w/vol and the column 48 was about 17.5 meters long. A Perkin-Elmer Sigma 115 Gas Chromatograph was used for the testing. The response time of the detector w snodified to enable the output signal to more rapidly Lj)ond to the chromatographic peaks characteristic of any small capillary column. The test conditions were: helium carrier gas, u (linear velocity) of 6 cm/sec; 600:1 split ratio; and temperature of 1200C. The only operating condition cl.ange between the test represented in Figure 4A and that shown in Figure 4B was a 1:10 dilution of the test sample prior to the test shown in Figure 4B and a four-fold decrease in detector attenuation. The primary column characteristic, amply demonstrated by the chromatogram of Figure 4A, of interest is the polarity of the internal surface of capillary column. As shown there is -very little wailing" of the component peaks. Tailing is a term of art used to indicate the lopsidedness of a chromatographic peak. Tailing usually results from a sample component being retained on the stationary phase material in a non-uniform manner. Thus, as shown in Figure 4A, the stationary phase of the highly flexible glass chromatographic capillary column 48 is, for all intents and purposes, neutral. In order to determine the presence of any acidic or basic adsorption sitesthe solution was diluted so that the peaks were just above the noise level of the chromatogram. Again, as shown in Figure 4B1 there is no serious tailing of the peaks. A close comparison of the two chromatograms, in -con3unction with the data set forth in Table I in Figure 5, clearly demonstrates that there is no discernable loss of either the acidic or basic compound at its lowest concentration. That is, the column 48 does not irreversibly adsorb either acidic or basic compounds. In fact, since the stationary phase coating 66, in this instance, was quite thin, on the order of about 0.1 micrometers, any irreversible adsorption of either acidic or basic compound would have been demonstrable. Thus excellent chromatographic results have been obtained from a relatively inexpensive highly flexible glass capillary calumn. Although the present invention has been described with respect to an exemplary embodiment, the invention is. not deemed to be so limited. Other configurations and embodiments are clearly possible within the scope and spirit of the present invention which is deemed limited only by the appended claims and the reasonable interpretation thereof.

Claims: What Is Claimed Is: 1. A chromatographic column, comprising: a highly flexible glass capillary tube; said tube being hollow and having an external surface and an internal surface; a first coating overlying substantially completely all of said external surface, said first coating being impervious to moisture; and a second coating of surface passivating material overlying substantially completely all of said internal surface. 2. Column as claimed in Claim 1 wherein: said first coating is a polymide. 3. Column as claimed in Claim 1 or 2 wherein: said first coating includes first polymide layer adjacent said external surface of said tube and a second polymide layer overlying said first layer. 4. Column as claimed in Claim 2 wherein: said polymide is Pyralin PI-2550. 5. Column as claimed in Claim 1 or 2 wherein: said second coating includes a chromatographic stationary phase. 6. Column as claimed in Claim 1 wherein: said second coating includes a passivating layer adjacent said internal surface and a chromatographic stationary phase layer overlying said passivating layer. 7. Column as claimed in Claim 1 wherein: said tube has an inside diameter of about 0.2 millimeters and a wall thickness of about 0.05 millimeter. 8. Column as claimed in Claim 1 wherein: said highly flexible glass capillary tube is substantially comprised of soda-lime.

Inventors: OGAN, KENNETH LEE, REESE, CHARLES EDWIN, SCOTT, RAYMOND PETER WILLIAM
Applicants: THE PERKIN-ELMER CORPORATION
Application year: 1983
Main classification: G01N30
IPC codes: G01N30