Open-Tubular Columns - ACS Publications - American Chemical Society

Instrumentation L. S. Ettre The Perkin-Elmer Corporation Norwalk, Conn. 06859-0090

Open-Tubular Columns: Evolution, Present Status,andFuture Open-tubular (capillary) columns were invented almost 29 years ago. The past quarter of a century has been characterized by a slow, steady evolution, with continuous improvements of this wonderful tool. Although the invention of these columns can be attributed to a single person, their continuous improvement is the result of contributions from scores of chromatographers around the world. The story of the evolution of open-tubular columns is also the story of the achievements of all of these scientists. However, it is virtually impossible to give credit to all the individuals who contributed to this progress. Therefore, although noting the more important achievements, I will particularly emphasize work with which my colleagues and I have been more closely related. Discussion of a scientific evolution represents a chapter in the history of science. History is always interesting. It is, however, even more useful if it not only discusses the past, but relates it to the present and the future. Obviously, the latter is subjective. Still, it is useful, particularly if it gives the reader ideas for possible improvements. I hope that I can achieve this.

day as he was 29 years ago. In the fall of 1956, Golay was considering the separation process that takes place in a gas chromatographic column which, at that time, naturally meant a packed column. He thought about how uncontrolled it was having the sample molecules strolling randomly around the particles. The logi-

cal conclusion of this thinking process was to replace the unorganized packed column by a simple, empty tube with the liquid phase coated as a uniform film on its inside wall, with an open, unrestricted path in the middle. He immediately tried it, and on Nov. 15, 1956, he reported some favorable results (i). Figure 2 shows one of Golay's

The beginnings Open-tubular gas chromatography can be traced back to a single person, Marcel Jules Eduard Golay (Figure 1). He is not a chemist but a physicist; actually, he likes to call himself an information scientist. Dr. Golay was 83 years old on May 3,1985; but he still has not retired, and he is as active to0003-2700/85/A357-1419$01.50/0 © 1985 American Chemical Society

Figure 1. M.J.E. Golay (right) with L.S. Ettre in 1965 at an international symposium in Athens, Greece ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985 · 1419 A

Figure 2. One of Golay's first chromatograms (winter of 1956-57) 12-ft X 1.44-mm i.d. open-tubular column, coated with Carbowax 1500 polyethylene glycol. Micro thermal-conductivity detector; Sanborn high-speed recording galvanometer. Sample: Phillips 37 hydrocarbon mixture. Total analysis time was only a few seconds

also showed two chromatograms that became the sensation of the meeting. The first chromatogram showed the full separation of the three xylene isomers on a partition column with an analysis time of about 1 h; the second illustrated the separation of CQ hydrocarbon isomers in 9 min (see Figure 4). These two chromatograms represent the practical start of open-tubular column gas chromatography. Early pioneers

Other work immediately followed Golay's. In particular, I will mention here the activities of four pioneering groups: Al Zlatkis at the University of Houston, Sandy Lipsky at Yale University, Dennis Desty at British Petroleum, and my colleagues at PerkinElmer. Both Zlatkis and Lipsky benefited from the small-volume version (5) of the argon ionization detector invented by Jim Lovelock. Figure 5 shows what is probably the first chromatogram obtained at the University of Houston, dated Nov. 16,1958. It was signed by Zlatkis and Lovelock, as well as by M. C. Simmons (then with Shell), R, E. Johnson, and H. Lilly (both with Barber-Colman). Zlatkis and Lovelock submitted their first paper to ANAFigure 3. Early chromatogram obtained by Golay (spring of 1957)

LYTICAL C H E M I S T R Y on Dec. 2,1958,

16-ft X 0.25-mm i.d. open-tubular column, coated with Carbowax 1500 polyethylene glycol. Micro thermal-conductivity detector; oscilloscope readout/Peaks: 1 = air, 2 = acetone, 3 = carbon disulfide, 4 = chloroform, 5 = methylene chloride. Retention time of last peak: 15 s

on the use of open-tubular columns for the analysis of C1-C5 alcohols, C5-C7 paraffins, p/m-xylene, and the olefins (6). Lipsky immediately tackled one of the most difficult applications of gas chromatography: the separation of fatty-acid methyl esters. His paper, coauthored with Landowne and Love-

first chromatograms. In the next step Golay used an oscilloscope as the readout. Figure 3 is a photograph of one of these chromatograms (2). These two examples show that wide-bore chromatography columns and highspeed analysis certainly do not represent new inventions. Golay's first paper on open-tubular columns was presented at the 1957 Lansing Symposium (3), giving the first approximation of the theory. During this presentation he showed three chromatograms of a simple, three-component mixture run on a

packed column and on two 0.25-mm i.d. columns of 100- and 300-ft lengths. The chromatograms were not very exciting, although the one obtained on the 300-ft column was probably the first ever to show more than 10,000 theoretical plates. In subsequent months, Golay and his co-workers improved both the theory and the practice of these columns. And, at the 2nd International Symposium on Gas Chromatography, held in May 1958 in Amsterdam (4), Golay not only presented the complete theory of opentubular column chromatography but

1420 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985

lock, was submitted to A N A L Y T I C A L C H E M I S T R Y on Feb. 8,1959 (7).

One cannot speak about the pioneering period of open-tubular column gas chromatography without mentioning D. H. Desty of British Petroleum. He built his first capillary GC immediately after the Amsterdam Symposium, using the new flame ionization detector, which was also intro-

Sample Preparation

Bombs In Many Styles and Sizes

Acid Digestion Bombs, Teflon lined, for treating inorganic samples in HF, HCI and other strong mineral acids, or for digesting organic samples in strong alkalis or oxidizing acids at temperatures well above normal boiling points. Available in five different styles for various applications.

Oxygen Combustion Bombs for breaking down any solid or liquid combustible sample quickly and completely by oxygen combustion in a sealed bomb, for immediate conversion to soluble forms and complete recovery of all elements.

Figure 4. Chromatogram shown by Golay at the 1958 Amsterdam Symposium (4) 150-ft X 0.25-mm i.d. open-tubular column, coated with didecyl phthalate. Column temperature: 40 °C. Carrier gas (He) flow rate: 0.96 mL/min. Micro thermal-conductivity detector. Sample: mixture of isomeric C6 hydrocarbons. Courtesy of Butterworths, Inc.

duced in 1958 (8). His first report (9) was presented at the Symposium on Gas Chromatography, held in Leipzig, Oct. 9-11,1958. In subsequent years, Desty and his co-workers have reported on a large number of investigations covering almost every aspect of opentubular column GC. Probably his most impressive chromatogram was presented at the 1961 Lansing Symposium; it was obtained on a column al-

most 300 m long with an i.d. of 0.15 mm, showing the total analysis of a Ponca crude sample. In the proceedings of the symposium (10) only part of the chromatogram was included, as the whole chromatogram had the length of a full recorder chart roll. At Perkin-Elmer, Dick Condon had already been involved in open-tubular column work, even prior to the 1958 Amsterdam Symposium. He had a

General Purpose Bombs in sizes from 21 m I to 2 gallons for a wide range of laboratory applications.

Our 16-page Bulletin 1100 details these bombs and their many unique applications. Write or phone for your copy.

PARR INSTRUMENT COMPANY 211 Fifty-third Street Moline, Illinois 61265 Phone: 309/762-7716 TWX: 910-225-1753

Figure 5. One of the first chromatograms, obtained Nov. 16, 1958, at the University of Houston 150-ft X 0.25-mm i.d. open-tubular column, coated with squalane. Micro argon ionization detector. Sample: hydrocarbon mixture. Signatures (left to right): A. Zlatkis, J. E. Lovelock, M. C. Simmonds, R. E. Johnson, H. Lilly

CIRCLE 164 ON READER SERVICE CARD 1422 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985

Figure 6. Chromatogram of a mixture of C 2 -C 5 alkanes, alkenes, and alkynes, shown by Condon in his paper presented at the 1959 Pittsburgh Conference (11) Open-tubular columns: 200-ft X 0.25-mm i.d., coated with dimethyl sulfolane, and 100- ft X 0.25-mm i.d., coated with polypropylene glycol, connected in series. Column temperature: 33 °C. Carrier gas (He) flow rate: 0.5 mL/min. Flame ionization detector

major presentation at the 1959 Pittsburgh Conference, which was soon published (11). This paper contained a large number of impressive chromatograms showing, among others, the separation of C2-C5 hydrocarbons (Figure 6) and aromatics including the xylene isomers. He also used the new flame ionization detector. Warren Averill joined Perkin-Elmer in 1960 and, for a decade, he was probably the one who knew best how to coat a stainless-steel capillary tube. Figure 7 shows one of his chromatograms of peppermint oil; this was shown during his paper presented at the Annual Meeting of the Institute of Food Technologists, in Miami Beach, Fla., on June 11,1962 (12). Another field that we at PerkinElmer became very much involved in was the analysis of fatty-acid methyl esters on open-tubular columns coated with polyester phases. Figure 8 shows one chromatogram from 1962 (13). Note that it was obtained on a 0.50-mm i.d. column, widely used at that time. There is now renewed interest in such columns, and many consider them an entirely new invention, which, obviously, they are not. Tube material

Figure 7. Chromatogram of peppermint oil from Yakima Valley, Wash, (from Averill's paper presented in 1962 [ 12]) 150-ft X 0.25-mm i.d. open-tubular column, coated with Ucon oil 50-HP-2000 polypropylene glycol. Temperature: programmed, as given. Carrier gas (He) flow rate: 1.4 mL/min. Flame ionization detector. Peaks: 1 = a-pinene, 2 = /3-pinene, 3 = eucalyptol, 4 = menthone, 5 = menthofuran, 6 = menthyl acetate, 7 = menthol

Figure 8. Chromatogram of a fatty-acid methyl ester mixture (from the publication of Ettre, Averill, and Kabot, 1962 [ 13)) 200-ft X 0.50-mm i.d. open-tubular column, coated with butanediol succinate. Temperature: 196 °C. Carrier gas (He) flow rate: 10 mL/min. Flame ionization detector. Peaks correspond to the methyl esters: 1 = caprylate, 2 = caprate, 3 = laurate, 4 = myristate, 5 = palmitate, 6 = stéarate, 7 = oleate, 8 = linoleate, 9 = linolenate 1424 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985

Early columns were made both of plastic and glass tubing, and, by 1960, glass capillary drawing machines had already been described (14,15). In spite of this, however, metal columns were used almost exclusively at that time. The main reason for this was that methods for the preparation of a stable coating on the inside of a glass capillary tube had not yet been developed. This situation was well summarized in the discussions at the 1961 Lansing Symposium, particularly by Halâsz. He stated that they could use a copper tube coated with squalane more than eight hours per day for more than seven months, whereas a squalane-coated glass open-tubular column lasted no longer than two to three days: "On glass coated with squalane, you can see with your eyes after two days that your film is not in one piece" (16). Of the metal tubes, stainless steel became the most widely used. Naturally, such columns also had their problems, mainly because of an uneven inside surface and the activity of the material. To overcome these problems, in 1961 Averill proposed the use of special additives to the liquid phase, which would block the active sites (17). This technique was generally accepted for the coating of stainless-steel tubing. In the 1960s our knowledge about glass slowly increased, and techniques were developed to modify the inside tube wall, making it amenable to coat-

HOT!

The ACCUSPEC # 2 0 is the estab lished basic tool for high tempera ture infrared studies. Designed to operate with both dispersive and FT-IR spectrometers, the #20 provides the facilities for infrared analysis of samples at temperatures of up to +700°C in controlled atmospheres. Current user applica tions include catalyst research, thermal stability, gas-solid reactions, etc. The # 2 0 is essential for all research laboratories using infrared analysis.

& HEAVY! Figure 9. Chromatogram of a "pure" o-butyl acetate sample on a wide-bore column (from the publication of Jentzsch and Hovermann, 1962 [26]) 100-m X 1-mm i.d. open-tubular column, coated with polypropylene glycol. Temperature: 80 °C. Carrier gas (He) flow rate: 37.3 mL/min. Flame ionization detector. Packed column injector; 1-μί sample. The large peak indicated with an arrow corresponds to η-butyl acetate; the rest represent impurities in the sample

The new ACCUSPEC # 2 0 0 0 pro vides an exceptional range of experimental parameters for FT-IR. Within the # 2 0 0 0 , the sample can be subjected to temper atures f r o m - 1 7 0 ° C t o +700°C and pressures from high vacuum to 2000psig. Three optical modes are available for sample analysis so that even the most difficult samples can be readily analysed in either trans mission or reflectance modes. The new # 2 0 0 0 is a must for researchers working on materials research, reaction mechanisms and high temperature/high pressure topics.

ACCUSPEC USA:

3375 Park Avenue Wantagh, NY 11793 Tel: (516) 783-9380

EUROPE: Sandyford Estate Foxrock, Dublin 18 Tel: (Dublin) 953221 Τ LX: 24474

ing. In particular, Grob, Liberti, and Novotny and Tesarik pioneered in this field. From their methods, etching with gaseous HC1 or HF (first de scribed by Novotny and Tesarik) be came the most widely accepted meth od. In addition, detailed investigations by scores of scientists in both Europe and the United States were carried out before glass replaced stainless steel as the most widely used column material (for a summary of this evolu tion, see References 18-20). This tran sition did not take place until the ear ly 1970s. The introduction of fused silica as the column tube material in 1979 rep resented another breakthrough in the continuous improvement of open-tu bular columns. The first report was presented by Dandeneau and Zerenner at the 1979 Hindelang Symposium (21); since then considerable work has been carried out in this field (for a summary, see Reference 22). Today, fused silica has replaced nearly all other column materials. Column diameter and length In the early period of open-tubular column GC, column diameter depend ed mainly on the availability of suit able metal tubing. The 0.25-mm (0.010-in.) i.d. tubing became the most


popular and remained so, even after the introduction of glass columns. De pending on the drawing machine, the actual internal diameter of the most frequently used tubing varied between 0.20 and 0.27 mm. As already mentioned, 0.50-mm (0.020-in.) i.d. columns had also been widely used practically since the be ginning of open-tubular column GC. In addition to these columns, the utili ty of tubing with even wider diameters was also investigated in the 1960s. For example, in 1964 Teranishi and Mon (23) described the use of 0.76-mm (0.030-in.) i.d. columns, which they used in GC/MS applications. In the early 1960s Kovâts had widely used 1.8-2-mm i.d. columns in the investigation of essential oils (24, 25). Kovâts even used these columns with thermal-conductivity detectors. In the early 1960s, we were also very much interested in larger diameter open-tubular columns. Jentzsch and Hovermann, my German colleagues, extensively investigated the possibility of 1-mm i.d. columns (26-28); Figure 9 shows one of their chromatograms. In fact, such columns have been marketed for a number of years under the name of "macro Golay columns." At Perkin-Elmer we investigated the performance of 1.55-mm i.d.

THE DEFINITIVE STANDARDS FOR CHLORINATED AND BROMINATED

DIBENZODIOXINS DIBENZOFURANS PREPARED BY

CAMBRIDGE ISOTOPE LABORATORIES, INC. and

RADIAN C O R P O R A T I O N

NOW AVAILABLE BROMODIBENZODIOXINS • ISOTOPE LABELED STANDARDS FOR GC/MS • UNLABELED CHEMICAL STANDARDS FOR GC AND HPLC

BROMODIBENZOFURANS • ISOTOPE LABELED STANDARDS FOR GC/MS • UNLABELED CHEMICAL STANDARDS FOR GC AND HPLC PLEASE CALL OR WRITE FOR OUR COMPLETE CATALOG ON:

DIBENZODIOXIN/ DIBENZOFURANS POLLUTANTS/RESIDUES PESTICIDES/PCBs

Contact: CAMBRIDGE ISOTOPE LABORATORIES 20 Commerce Way Woburn, MA 01801 USA 1-800-322-1174 (617) 938-0067 (in Mass.)

Telex 951935

columns (29). Because of their increased sample capacity, these wider diameter columns could be used with direct sample introduction (without any split) and even with standard thermal-conductivity detectors. In addition, because of the smaller capacity factors (due to the higher phase ratios), these columns were particularly suited for the rapid analysis of highboiling compounds. For example, Quiram could analyze n-cetyl alcohol in 8 min at 175 °C (i.e., 169 °C below its boiling point) using a 250-ft X 1.55-mm i.d. column and a flow rate as high as 800 mL/min (30). This result, of course, is not surprising; in fact, in 1960 Golay had pointed out (31) that the pipeline from Texas to Maine (which certainly does have a very high phase ratio) actually may be an excellent "open-tubular column" for highboiling compounds. Until now, I have surveyed only the development of columns with a wider diameter. The pioneering work on small-diameter (less than 0.2 mm) columns was carried out by Desty in 1960-61 (10, 32). Until recently, very little work was done in this field, mainly because of the unavailability of such tubing and problems with the introduction of extremely small samples. However, over the past five years, there has been renewed interest in such columns. With regard to the length of opentubular columns, for more than two decades most were made of relatively long tubes—usually 100-300 ft. Some were even longer. The record in column length belongs to Al Zlatkis; in 1959, he prepared and tested a onemile-long open-tubular column made of nylon tubing with an i.d. of 1.676 mm, and obtained an HETP of 1.61 mm (33). Shorter columns have also been used since the beginning of open-tubular column GC, although less frequently. I have already mentioned that Golay's first columns were less than 20 ft long. Desty has also reported on short (1-10 m) columns (10,32). In 1964 Marco demonstrated the analysis of C1-C12 alcohols on a 9-m X 0.50-mm i.d. column in less than 5 min (34). In our laboratories, Johansen carried out a detailed study in 1977 (35) that demonstrated some possibilities for short (10-15 m) open-tubular columns. They greatly reduced the analysis time while still providing adequate efficiency. Such short columns, especially those with 0.50-0.53-mm i.d., are of particular interest now as a replacement for packed columns in routine applications.

Coating technique and liquid phases Basically, two methods have been used to coat the inside wall of the col-


umn tubing with liquid phase: the dynamic and the static method. In both cases, the liquid phase is in a solution. In the dynamic method, the solution is passed through the tube, wetting the inside surface; in the static method, the tube is completely filled with the liquid phase and the solvent is allowed to evaporate slowly. The dynamic method was first mentioned by Dijkstra and De Goey (36); the static method was first used by Golay (4). Later, Bouche and Verzele (37) simplified the static method by using a vacuum to evaporate the solvent slowly from the filled column tube. Both the dynamic and static methods exist in many variations. Just as with packed columns, commonly available organic compounds, such as plasticizers, hydrocarbons, polyalcohols, and polyesters, were used at the beginning as the liquid phase for open-tubular columns. The basic problem with these, however, is their relatively low molecular weight (resulting in excessive bleeding) and the presence of impurities. Slowly, higher molecular weight polysiloxanes (silicones), made specifically for gas chromatography, replaced the older phases, thereby extending the usable upper temperature limit. However, an apparent contradiction soon became evident: To reduce bleeding and further extend the upper temperature limit, high-molecular-weight polymers were desired. On the other hand, the higher the molecular weight of the polymer, the poorer its solubility. The solution to this problem is to coat the column with a relatively low molecular weight substance and then repolymerize this prepolymer in the column, creating a high-molecularweight, cross-linked liquid phase. The final polymer coating can also be partially bonded to the Si-OH groups of the inside tube surface. Madani, in 1976 (38,39), was the first to prepare such columns, and he was soon followed by a number of other researchers including Blomberg, the Grobs, Lee, Lipsky, Sandra, and Schomburg. This development is still continuing.

Film thickness In the past, relatively little was done on controlled changes to the liquidphase film thickness. This was mainly for three reasons: • For a long time, the dynamic coating method was used most frequently. With this method, it is difficult to know the actual film thickness. • Until the advent of immobilized, cross-linked stationary phases, films thicker than about 1 Mm were unstable: The excess phase was soon lost through bleeding. • Metal columns had to be coated with a somewhat thicker film to re-

CHROMATOGRAPHY SPECIALISTS SPECIFY ALLTECH

Figure 10. Chromatogram of a C^Cg hydrocarbon mixture (alkanes, alkenes, cycloalkanes, and aromatics) on a SCOT column (from the publication of Ettre, Purcell, andBilleb, 1966 [50]) 100-ft X 0.50-mm i.d. SCOT column, prepared with squalane liquid phase; phase ratio: 67. Flame ioniza tion detector. The first five peaks: 1 = methane, 2 = ethane, 3 = propene, 4 = propane, 5 = 2-methylpropane. Courtesy of Marcel Dekker, Inc., New York, N.Y.

You're a specialist, and so are we. It takes a specialist to keep up with the changes and advancements in the field, and it takes a specialist to pioneer those changes. Alltech does both. For 30 years, Alltech Associates, Inc./Applied Science Labs has been the leader in innovative chromatography products. Our Gas Chrom Q is an industry standard; we pioneered the use of Vespel ferrules; we developed the Microbore HPLC column; and our new NON-PAKD GC columns are fast replacing Packed GC columns in labs around the world; and on and on and on; product after product, innovation after innovation. It takes a specialist to understand what another specialist needs, both now, and in the future. At Alltech, we understand. For your free copy of our catalog, please contact us at:

ALLTECH ASSOCIATES APPLIED SCIENCE LABS 2051 Waukegan Road Deerfield, II. 60015 TEL: 312-948-8600 CIRCLE 5 ON READER SERVICE CARD

Figure 11. Chromatogram of an oil of marjoram sample obtained in a GC/MS system using a SCOT column (from the investigations of Averill and Struck, 1966; see Ref erence 49) 50-ft X 0.50-mm i.d. SCOT column, prepared with OS-138 polyphenyl ether liquid phase. Phase ratio: 50. Temperature: programmed, as given. Total ion current recording

duce the activity of the inside tube surface. Thus, conscious variation of the liquid-phase film thickness was not plausible until the advent of glass columns. According to the theory of open-tu bular columns, columns prepared with a thin film have a higher absolute effi ciency. This was the primary reason why most of the glass columns were prepared with a relatively thin (about 0.2-μΐη) film. However, it had been understood for a long time that it is advantageous to select the film thick ness according to the type of sample: This had been pointed out as early as 1961-63 by Jentzsch and Hôvermann (27,28). In 1974 in our laboratories, Averill and March (40) illustrated the differences in the separation of early peaks in complex natural samples, such as gasolines and essential oils, when


changing the film thickness from 0.25 μΐη to 0.50 μπι; in fact, columns with a 0.50-μπι film (in addition to 0.25μΐη film columns) were commercially introduced at that time. Continuing these investigations, in 1979 Johansen (41) published his pioneering study on the characteristics of 0.27-mm i.d. col umns coated with l-μΐη film. The introduction of immobilized phases finally permitted the prepara tion of open-tubular columns with film thicknesses well above 1 μιη. The first detailed reports on such columns, with film thicknesses up to 8 μπα., were published in 1983 almost simulta neously by the Grobs (42), Sandra (43), and ourselves (44,45). Such col umns, particularly with the simulta neous increase of the tube diameter, represent an exciting new field in the application of open-tubular columns. Although this discussion dealt only

INTERESTED IN SIMPLIFIED THERMAL ANALYSIS SET-UP?

with simultaneous TG-DTA?

π» netzsch STA m 1. Weigh sample. Place in furnace. 2. Set system balance to zero. (2 simple controls) 3. Program furnace microprocessor (Less than 60 seconds) 4. Press start, T6 and DTA readouts are automatic! « Temperature range: -1 BOX to +1700^ • Vacuum capability to 5 χ 10~4 Torr. • Inert gas atmosphere • Corrosive gas atmosphere • Steam atmosphere to +1700°C • Thermal analysis software • Mass spectometer interfacing available For more information on the STA 409 or any otter Netzsch Thermal Analysis Instruments, please call or write today.

N E T Z S C H INCORPORATED Thermal Analysis Division 119 Pickering Way Exton, PA 19341-1393 TEL: (215) 363-8010 TWX: 510-663-9340 CABLE: NETZSCHINC CIRCLE 151 ON READER SERVICE CARD

with increasing the film thickness, it should also be mentioned that in some cases decreasing it may be desirable, particularly when analyzing very high boiling samples. For example, Adams and co-workers demonstrated in our laboratories, in 1977, the use of col umns with a 0.05-Mm-thick film for the analysis of amino acid derivatives (46). Porous-layer open-tubular (PLOT) columns

In his 1958 paper (4), Golay had al ready indicated the advantages of in creasing the inside surface area to be coated; he elaborated on this in I960 in more detail (31). The advantage of such columns is a decrease in the phase ratio of the column while keep ing a very thin liquid-phase film. The inside surface area can be increased by building up a porous layer on the in side tube wall, either by chemical treatment or by deposition of porous particles from a suspension. The latter method was developed in 1962-63 by Horvâth (47,48), then at the University of Frankfurt, in the laboratory of Dr. Halâsz, by adopting Golay's original static coating method. Because these columns were prepared by coating the inside tube wall with a porous support layer, they are commonly called support-coated open-tubular (SCOT) columns. In the latter half of the 1960s we continued Horvath's work, extensively studying these columns and making them commercially available (for a summary, see Reference 49). Figures 10 and 11 show typical chromatograms; the latter was obtained with a GC/MS system and represents a total ion current recording. SCOT columns were very popular for at least a decade because of their advantages: higher sample capacity, higher flow rates, the need for fewer plates for the separation of early peaks (cf., e.g., Figure 10), and very good efficiency. The only limitation of these columns was the residual activity of the particles used in building up the porous layer. However, overall column performance was still good, comparable to that of metal columns used at that time. With the advent of highly sophisticated and efficient glass and fused-silica columns in the second half of the 1970s, the importance of SCOT columns diminished. The wider diameter thicker film columns developed recently seem to have completely replaced them. This may, however, not necessarily remain so, as the theoretical background of SCOT columns is sound. In fact, a comparison of a SCOT column and a smooth-walled column with the same inside gas volume and total liquid-phase volume should favor the SCOT column as-


suming, naturally, that proper inert particles are found for building up the porous layer. This certainly is not an insurmountable task. In addition to increasing the inside surface area of partition columns, porous-layer open-tubular columns represent the only way to prepare opentubular adsorption columns. A number of researchers prepared such columns in the 1960s by creating the porous adsorbent layer either by chemical treatment or by the deposition of the porous adsorbent particles (see Reference 49). Figure 12 illustrates the performance of such a column, prepared by depositing bentonite particles on the inside wall of the column (51). At present there is renewed interest in adsorption-type porous-layer open-tubular columns. Instrumentation for open-tubular columns

The subject of this paper is column development. However, columns do not exist in themselves; they are always part of a system, and one cannot split them apart. This is especially true for open-tubular columns; their small sample capacity and the low carrier gas flow rates used with these columns create special requirements for the system, particularly concerning the way in which samples are introduced. The problems associated with sample introduction were recognized practically since the beginning of open-tubular column GC. In fact, the first papers describing the application of open-tubular columns already dealt with the possibility of split sampling (6, 7,9,11,32). Split sampling refers to dividing the mixture of the sample vapor and the carrier gas into two highly unequal parts, the smaller one being conducted into the column. Although early split systems represented a simple tee design, their construction was soon refined, adopting the so-called concentric tube design. It is safe to say that by 1961-62, reliable split sample introduction systems were described and made commercially available (52-55). In addition, the two basic requirements of linear splitting were also soon recognized: that no sample loss should be encountered during evaporation, e.g., due to thermolysis, and that sample vapor and carrier gas must be homogeneously mixed prior to splitting. Later complaints about the apparent nonlinearity of split-type sample introduction can all be traced back to disregarding these two basic requirements. Naturally, in the past 20 years, split sample introduction systems have been significantly improved, and a number of other systems have been introduced permitting, for example, direct, on-column sample introduction

Ifj union

GIKEH

First choice for

STOPPED FLOW reaction analysis

Union Giken apparatus achieves a dead time as short as lA millisecond for measurement of fast reactions. Gas pressure is directly applied to the surface of the reactants in each reservoir, mixing and flow being controlled from the end of the system by a high-response stop valve. The RA-401 STOPPED FLOW SPECTROMETER is the ideal match for fast reactions.

The RA-451 DATA PROCESSOR gener ates a simulated reaction curve from the measured results and automatically calculates the rate constant.

The RA-415 RAPID SCAN A T T A C H MENT monitors the change in absorp tion spectrum during the reaction.

Other attachments are available for T-jump, P-jump, fluorescence and flash photolysis. Contact the sole export agent for more details:—

ATAGO BUSSAN CO., LTD. 7-23, 5-chome Shimbashi, Minato-ku, Tokyo 105, Japan Telex: 28421 Cable: TAGOA T O K Y O Phone: (03) 432-8741

with or without previous sample evap oration (56). The present

Today, interest in capillary columns is exponentially increasing. This is best demonstrated by the 700 partici pants at the 6th International Sympo sium on Capillary Chromatography, which was held May 13-16,1985, at Riva del Garda, Italy. The importance of this large number of attendees is even more evident if we consider that at the recent Biannual International Chromatography Symposium (Oct. 1-5,1984, Nurnberg, F.R.G.), which encompassed all branches of chroma tography, the total number of regis trants was only about 1000. The present status of open-tubular column GC can be characterized by three trends. The first is the change over from soda-lime or borosilicate glass to fused-silica tubing. This de velopment is practically complete in the United States and, although it is somewhat slower in Europe, the direc tion is clear. This is accompanied by two related events. The first is in creased use of well-defined crosslinked phases and, the second, reli ance on a few highly specialized sup pliers for high-quality fused-silica columns, replacing homemade glass columns based on individual and usu ally empirical technology. All of these developments led to a vast improve ment in the overall quality and perfor mance of the columns used in practice and ensure better uniformity of their characteristics. The second trend is characterized by the greater flexibility available in the selection of column variables. Pres ent-day columns have diameters from 0.05 to 0.75 mm, film thicknesses from about 0.2 μτη up to 5-6 μτη, and lengths from 10 m or even shorter up to 100 m. The availability of such a wide range readily permits the selec tion of the optimum parameters for a given application. Finally, the third trend is found in the application of open-tubular col umns. Until recently, they were pri marily considered tools for the analy sis of very complex samples, and chromatographers often tried to outdo themselves in "number counting," seeking to separate the largest number of peaks in a given sample. This, natu rally, did not mean that the essential advantage of the columns was not clear—that, compared with packed columns, one can either obtain better resolution in equal time or the same resolution in a much shorter time. However, this rule was frequently overshadowed by the illustration of very high absolute efficiencies. Most recently, analysts finally began to re alize that today's open-tubular col-


Figure 12. Chromatogram of an aro matic hydrocarbon mixture on an ad sorption-type PLOT column (from the publication of Ettre, Purcell, and Norem, 1965 [51]) 50-ft X 0.50-mm i.d. PLOT column prepared with Bentone 34, Celite, and DC-550 phenylsilicone oil. Temperature: 100 °C. Carrier gas (He) flow rate: 4 mL/min. Peaks: 1 = benzene, 2 = thiophene, 3 = toluene, 4 = ethylbenzene, 5 = p-xylene, 6 = m-xylene, 7 = o-xylene, 8 = isopropylbenzene, 9 = n-propylbenzene, 10 = fert-butylbenzene, 11 = sec-butylbenzene, 12 = 4-isopropyl-1-methylbenzene, 13 = n-butylbenzene. Courtesy of Preston Publishing Co., Niles, III.

umns have obvious advantages, even in relatively simple applications usual ly solved with packed columns. Be cause of their high sample capacity and excellent resolution capability, the larger diameter, thicker film col umns introduced in the past two years are particularly important in this re spect. They possess a degree of repro ducibility not found in packed col umns. They are flexible, inert, stable, and have a long lifetime. They do not have the inherent defects (rigid struc ture, active sites of the solid support, high inlet pressures, etc.) of the packed column. Thus, it seems obvi ous that they are ideal for a routine analytical laboratory. With this, we have arrived at the future of the opentubular GC column. (continued on p . 1436 A)

The future

How to increase precision in HPLC sample injection. Rheodyne's Tech Note 5 shows how you can maximize HPLC precision by using skillful sample injection techniques. The information is drawn from hundreds of closely controlled experiments using different types of sample injectors and different load ing methods. The 6-page summary of results is written to help both the beginner and the experienced chromatographer. The experiments yielded some surprising answers to highly practical questions. One question: How much sample must you waste to fill a sample loop "completely"? (It's more than you are likely to think.) Another question: When you are reading a syringe to judge the amount of sample being loaded, how much sample can you inject without impairing accuracy? (It's less than you may think.) Get the answers to these and other salient questions now

Send for Tech Note #5. Contact Rheodyne, Inc., PO. Box 996, Cotati, California 94928, USA. Phone (707) 664-9050.

RHEODYNE THE LC CONNECTION COMPANY

Until recently, these columns were mainly considered tools for the analy sis of complex mixtures—in other words, for samples that could not be satisfactorily separated on a packed column. The newest developments in column technology finally have start ed to convert the chemists in routine analytical laboratories to using these columns, even for relatively simple ap plications. The advantages of the thicker film, wider diameter columns in most instances are so overwhelming that it does not seem far-fetched to predict that within the next few years they will replace the packed column in most routine applications. The new developments in open-tu bular columns are, however, not re stricted to these workhorse columns. There are also many advances in col umn technology for those who are ana lyzing complex mixtures. I am think ing particularly of the small-diameter columns providing very high absolute efficiencies. We shall certainly see a more widespread application of these columns. As I discussed earlier, apart from a few reports, very little was done in the past in the field of open-tubular ad sorption columns. I believe that in the future this will also change. Many advances can also be predict ed in the GC systems in which the col umns are used. We certainly will have smaller, fully automated and dedicat ed instruments for open-tubular col umn use only, including the use of ro botics for sample preparation. We will also see increasing use of open-tubular columns in hyphenated techniques such as GC/MS and GC/FTIR. Prediction of the future is always difficult. However, I feel it is safe to say that we are finally at the thresh old of the universal acceptance of open-tubular columns in every field. With this, 29 years after their inven tion, we are finally starting to fulfill the pioneers' dreams. I have tried to survey almost 30 years of open-tubular column develop ment. It represented a nostalgic jour ney for me, surveying the activities of a generation. For many of us, these ac tivities became our whole life. It was exciting, and it was interesting. But even more important, it was fun! Based on the Chromatography Award Address, presented at the 189th National Meeting of the American Chemical Society, Miami Beach, Fla., April 28-May 3,1985

References (1) Golay, M.J.E. "Progress Report of Gas Chromatographic Experimental Work for September and October 1956"; Per kin-Elmer Corp., Norwalk, Conn., Nov. 15,1956. Reprinted on p. 3 of Ettre, L.S. "Open-Tubular Columns in Gas Chromatography"; Plenum Press: New York, N.Y., 1965.


(2) See also Ettre, L.S. In "Applications of Glass Capillary Gas Chromatogra phy"; Jennings, W.G., Ed.; Marcel Dekker: New York, N.Y., 1981; pp. 1-47. (3) Golay, M. J.E. In "Gas Chromatogra phy (1957 Lansing Symp.)"; Coates, V.J.; Noebels, H.J.; Fagerson, I.S., Eds.; Aca demic Press: New York, N.Y., 1958; pp. 1-13. (4) Golay, M.J.E. In "Gas Chromatogra phy 1958 (Amsterdam Symp.)"; Desty, D.H., Ed.; Butterworths: London, 1958; pp. 36-55. (5) Lovelock, J.E. Nature (London) 1958, 182,1663-64. (6) Zlatkis, Α.; Lovelock, J.E. Anal. Chem. 1959,51,620-21. (7) Lipsky, S.R.; Landowne, R.A.; Love lock, J.E. Anal. Chem. 1959,31,852-56. (8) McWilliam, I.G.; Dewar, R.A. Nature (London) 1958,181,760. (9) Desty, D.H. Abh. Dtsch. Akad. Wiss. Berlin, KL Chem. Biol. 1959,9,176-84. (10) Desty, D.H.; Goldup, Α.; Swanton, W.T. In "Gas Chromatography (1961 Lansing Symp.)"; Brenner, N.; Callen, J.E.; Weiss, M.D., Eds.; Academic Press: New York, N.Y., 1962; pp. 105-38. (11) Condon, R.D. "Design Considerations of a Gas Chromatography System Em ploying High Efficiency Golay Col umns," presented at the 10th Pittsburgh Conf. Anal. Chem, Applied Spectrosco py, Pittsburgh, Pa., March 1959; Anal. Chem. 1959,31,1717-22. (12) Cieplinski, E.W.; Averill, W. "Gas Chromatographic Analysis of Essential Oils Using Golay Columns and a Flame Ionization Detector," presented at the Annual Meeting of the Inst, of Food Technologists, Miami Beach, Fla., June 11,1962. GC Applications No. GC-AP002; Perkin-Elmer Corp.: Norwalk, Conn., 1962. (13) Ettre, L.S.; Averill, W.; Kabot, F.J. "Gas Chromatographic Analysis of Fatty Acids," GC Applications No. GC-AP001; Perkin-Elmer Corp.: Norwalk, Conn., 1962. (14) Desty, D.H.; Haresnape, J.N.; Whyman, B.H.F. Anal. Chem. 1960,32, 302-4. (15) Kreyenbuhl, A. Bull. Soc. Chim. France 1960,2125-27. (16) "Discussion on Capillary Columns." In "Gas Chromatography (1961 Lansing Symp.)"; Brenner, N.; Callen, J.E.; Weiss, M.D., Eds.; Academic Press: New York, N.Y.,1962; p. 560. (17) Averill, W. In "Gas Chromatography (1961 Lansing Symp.)"; Brenner, N.; Callen, J.E.; Weiss, M.D., Eds.; Academ ic Press: New York, N.Y., 1962; pp. 1-6. (18) Novotny, M.; Zlatkis, A, Chromatogr. Rev. 1971,14,1-44. (19) Alexander, G. Chromatographia 1980, 13,651-60. (20) Jennings, W. "Gas Chromatography with Glass Capillary Columns"; Academ ic Press: New York, Ν.Υ., 1st ed. 1978, 2nd ed. 1980. (21) Dandeneau, R.D.; Zerenner, E.H. J. High ResoL Chromatogr. /Chromatogr. Commun. 1979,2, 351-56. (22) Jennings, W. "Comparisons of Fused Silica and Other Glass Columns in Gas Chromatography"; Huthig Verlag: Hei delberg, 1981. (23) Teranishi, R.; Mon, T.R. Anal. Chem. 1964,36,1491-92. (24) Kugler, E.; Kovâts, E. Helv. Chim. Acta 1963,46,1480-1513, (25) Kovâts, E. Helv. Chim. Acta 1963,46, 2705-31. (26) Jentzsch, D.; Hôvermann, W. "Die Anwendung von Makro-Golay Sâulen in der Gaschromatographie," No. 19-GC; Bodenseewerk Perkin-Elmer & Co.: Ueberlingen, 1962. (27) Jentzsch, D.; Hôvermann, W. In "Gas

Chromatography 1962 (Hamburg Symp.)"; Van Swaay, M., Ed.; Butterworths: London, 1962; pp. 204-15. (28) Jentzsch, D.; Hôvermann, W. J. Chromatogr. 1963, 77,440-51. (29) Ettre, L.S.; Cieplinski, E.W.; Averill, W. J. Gas Chromatogr. 1963, 7 (2), 7-16. (30) Quiram, E.R. Anal. Chem. 1963,35, 593-95. (31) Golay, M.J.E. In "Gas Chromatography 1960 (Edinburgh Symp.)"; Scott, R.P.W., Ed.; Butterworths: London, 1960; pp. 139-43. (32) Desty, D.H.; Goldup, A. In "Gas Chromatography 1960 (Edinburgh Symp.)"; Scott, R.P.W., Ed.; Butterworths: London, 1960; pp. 162-83. (33) Zlatkis, Α.; Kaufmann, H.R. Nature (London) 1959,184, 2010. (34) Marco, J.R.P. GC Newslett. (PerkinElmer Corp.) 1964, 7 (3), 1-2; see Ettre, L.S. "Open-Tubular Columns in Gas Chromatography"; Plenum Press: New York, N.Y., 1965; pp. 127-28. (35) Johansen, N.G. Chromatogr. News lett. 1977,5,14-16. (36) Dijkstra, G.; De Goey, J. In "Gas Chromatography 1958 (Amsterdam Symp.)"; pp. 56-58. (37) Bouche, J.; Verzele, M. J. Gas Chro matogr. 1968,6, 501-5. (38) Rigaud, M.; Chebroux, P.; Durand, J.; Maclouf, J.; Madani, C. Tetrahedron Lett. 1976, 3935-38. (39) Madani, C; Chambaz, E.M.; Rigaud, M.; Durand, J.; Chebroux, P. J. Chroma togr. 1976, 726,161-69. (40) Averill, W.; March, E.W. Chromatogr. Newslett. 1976,4, 20-23. (41) Johansen, N.G. Chromatogr. News lett. 1979, 7,18-21. (42) Grob, K.; Grob, G. J. High Resol. Chromatogr./Chromatogr. Commun. 1983,6,133-39.

(43) Sandra, P.; Temmerman, I.; Verstappe, W. J. High Resol. Chroma togr./Chromatogr. Commun. 1983,6, 501-4. (44) Ettre, L.S. Chromatographia 1983, 17 553—59 (45) Ettre, L.S.; McClure, G.L.; Walters, J.D. Chromatographia 1983, 77, 560-69. (46) Adams, R.F.; Vandemark, F.L.; Schmidt, G.J. J. Chromatogr. Sci. 1977, 75,63-68. (47) Horvâth, C. "Trennsàulen mit dûnnen porôsen Schichten fur die Gaschromatographie," Inaugural Dissertation, J.W. Goethe Universitàt, Frankfurt am Main, 1963. (48) Halâsz, I.; Horvâth, C. Anal. Chem. 1963,35, 499-505. (49) Ettre, L.S.; Purcell, J.E. In "Advances in Chromatography, Vol. 10"; Giddings, J.C.; Keller, R.A., Eds.; Marcel Dekker: New York, N.Y., pp. 1-97. (50) Ettre, L.S.; Purcell, J.E.; Billeb, K. Sep. Sci. 1966, 7, 777-802. (51) Ettre, L.S.; Purcell, J.E.; Norem, S.D. J. Gas Chromatogr. 1965,3,181-85. (52) Ettre, L.S.; Averill, W. Anal. Chem. 1961,33, 680-84. (53) Halâsz, I.; Schneider, W. Anal. Chem. 1961,33, 978-82. (54) Halâsz, I.; Schneider, W. In "Gas Chromatography (1961 Lansing Symp.); Brenner, N.; Callen, J.E.; Weiss, M.D., Eds.; Academic Press: New York, N.Y., 1962; pp. 287-306. (55) Gill, H.A.; Averill, W. "Design Considerations and Performance of a Linear Programmed-Temperature Gas-Liquid Chromatograph for Golay and Packed Columns," presented at the 13th Pittsburgh Conf. Anal. Chem. Applied Spectroscopy, Pittsburgh, Pa., March 5,1962; Reprint, Perkin-Elmer Corp.: Norwalk, Conn., 1962.

(56) See: Sandra, P., Ed. "Sample Introduction in Capillary Gas Chromatography, Vols. I—II"; A. Hûthig Verlag: Heidelberg, 1985.

Leslie Ettre earned a degree in chemical engineering and a technical doctorate from the Technical University of Budapest. In Europe, Ettre was active in industrial research, research management, and academic teaching. After emigrating to the U.S. in 1958, he joined the Perkin-Elmer Corporation, where he has served as an applications chemist, product specialist, and, in his present capacity, as senior staff scientist. His research interests include GC (trace analysis, detector response, selective detectors, retention indexes, and open-tubular columns), LC, and the history of chromatography.

It Had to Happen

Best Just Got Better

Manufactured By

ERMA INC. 2-4-5 Kajicho Chiyoda-Ku T o k y o 101, Japan T E L E X 2655671 ERMAIN J

ir&d IR&D PO Drawer H Kingston, MA 02364 617/585-5125 TELEX 881004

IR&D introduces the new 7510/D Refractive Index Detection System to enable you to achieve faster, easier, more reproducible results. The 7510/D marries the legendary ERMA Rl Detector with the unique 3000 series in-line solvent degasser to eliminate drift and reduce baseline noise caused by gasses entering the mobile phase. Contact IR&D for details on how the 7510/D will improve the performance of your HPLC system.

CIRCLE 49 ON READER SERVICE CARD


Open-Tubular Columns - ACS Publications - American Chemical Society

Recommend Documents