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expected that this will be extended to liquid chromatography. This indeed enables studies of elements in ecosystems as shown impressively by a paper from the Molecular Ecology Beach, CA, Institute (Long U.S.A.). The current developments in the field of optical atomic spectrometry instrumentation, its use for the analysis of real samples as they are encountered in all fields of industry, technology and science, the state-ofthe-art of plasma mass spectrometry and the use of plasmas for elementspecific detection in chromatography were elucidated in five panel dis-

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cussions at the end of each day. In addition, a number of short courses given by experts on various topics (ICP-MS, advanced sample introduction techniques, sample preparation, etc.) were organized before and after the conference and attracted much interest. The next meeting will be held in Florida (1990).

The explosive growth of supercritical fluid chromatography (SFC) over the past few years has been paralleled by a growth in symposia and workshops with SFC as theme. One of the largest to date, the 1988 Workshop on Supercritical Fluid Chromatography, was held January 12-14, 1988, in Park City, Utah. Though three world-class ski areas were (nearly) within sight of the Workshop location, there was little time for skiing. The meeting format was intense. SFC was generally the topic of conversation over the 8:00 a.m. breakfast, and was still the subject of lively debate during the final discussion period of the day, which ended between 10 and lo:30 p.m. Interest in SFC remains high in academia, but attendance at the workshop illustrates SFC’s move from an academic curiosity to a problem-solving tool in government and industrial laboratories. Of the 158 attendees, 41% represented industrial laboratories, 31% were from acade-

More polar and higher-molecularweight applications Two methods were discussed in the attempt to move SFC toward more polar and higher-molecularweight applications: the use of novel or modified mobile phases, and the use of derivatization chemistry. Mobile phases

J.A.C. BROEKAERT J.A.C. Broekaert is at the Gesellschaft zur Fiirderung der Spectrochemie und angewandten Spectroskopie E. V., Institut fiir Spektrochemie, Postfach 778, 4600 Dortmund 1, F.R. G.

Supercritical fluid chromatography,

A report on the 1988 Workshop on Supercritical Fluid Chromatography, held in Park City, UT, U.S.A., 12-14 January, 1988

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alive and well

mia, 22% represented instrument manufacturers, and 6% were from government laboratories. Fourteen nations were represented. One preponderant theme of the Workshop was the growing list of SFC application areas. This was illustrated in a very concrete manner by a compilation of chromatograms contributed by the attendees and assembled by the Workshop organizers (no small feat). The final volume was nearly 2 cm thick. The chapter headings illustrate the breadth of applications: drugs, enantiomers, foods and natural products, fatty acids and derivatives, triglycerides, steroids, biomolecules, explosives, pesticides and herbicides, fossil fuels and aromatic compounds, polymer additives, polymers, miscellaneous chemicals and products. The compilation is a valuable reference tool and is available from Professor Milton Lee, Department of Chemistry, Brigham Young University, Provo, UT 84602, USA. The first speaker was appropriately the author of the first SFC publication, Ernst Klesper. Before the talk he was presented with a plaque in recognition of his work in SFC. Klesper discussed the power of simultaneous pressure, temperature, and mobile phase composition programming in SFC.

Many, such as Levy, have investigated the use of carbon dioxide modified with polar species. Propylene carbonate is the strongest modifier used to date. The critical parameters and phase behaviour of these modified mobile phases are largely unexplored topics but are crucial to good separations. Denyszyn discussed his work in characterizing certain mixtures. For example, up to 12% methanol in carbon dioxide yields a homogeneous phase to 140 atm and 30°C. Smith described his work in an area of modified mobile phases which has and will command much attention: the use of reverse micelles. These modified fluids will not only be of interest in SFC but also in supercritical fluid extraction (SFE). Smith and coworkers have demonstrated efficient solvation of large proteins in supercritical fluids containing reverse micelles. The road leading to the use of more polar, neat mobile phases is promising but fraught with technical difficulties and potential pitfalls. Griffiths described how sulfur dioxide found minuscule imperfections in the protective gold plating of a carefully treated flame ionization detector. As he described it, the experiment would have been a success had they been on a search for an efficient method of preparing sulfate salts of iron. Others such as Smith and Wright, Grolimund and Lee discussed the use of supercritical ammonia. It is an efficient solvent for many common materials, among them being the polyimide capillary-column coating and ferrules so prized by chromatographers. Derivatization

Novotny and Sandra advocated a different route to SFC of polar, ionic, or higher-molecular-weight compounds. Why not use the tried and

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true derivatization methods, many developed for gas chromatography (GC), to increase the solubility (not volatility) of polar solutes in the widely used non-polar SFC mobile phases such as carbon dioxide and pentane? Sandra described methods for phospholipids, and neutral and quaternary amines. Novotny discussed derivatization with a heteroatom-containing group and elementselective detection. Furthermore, the mild elution conditions possible in SFC make derivatization reactions yielding thermally sensitive products practical. Reinhold commonly uses derivatization to study biologically important species, such as oligosaccharides and steroids, by SFC. Developments in SFC instrumentation Injection techniques

SFC instrumentation continues to evolve rapidly. Chester, Greibrokk and Richter discussed exciting results from their efforts to develop direct injection techniques for capillary SFC. Split injection is generally used in capillary SFC to reduce the amount of sample injected on-column and to narrow the solvent front. But split injection has made quantitation and trace analysis difficult. Special precautions must be taken for quantitation with split injection, as discussed by Nichols. The direct injection methods discussed attempt to focus solutes at the head of the column and eliminate the solvent rapidly. One approach (Chester, Greibrokk) is to vent the solvent with a system of valves, bypassing the flow restrictor. Chester’s approach also allows for control of the flow-rate on column independent of the applied pressure. Richter’s method takes advantage of the compressibility of the mobile phase by using an injection at low pressure and a rapid ramp to higher pressure. The mobile phase is compressed during the ramp and the solvent is rapidly forced through the column. These advances are significant as capillary SFC will become a legitimate trace and ultratrace analysis tool with direct injection of microliter or near-microliter volumes.

SFE-SFC

Trace analysis is already a reality with SFE-SFC, where the injection solvent is the supercritical mobile phase and no solvent elimination is required. King, Yocklovich, Engelhardt and Hawthorne dicussed coupling chromatographic methods with SFE. Computer Chemical Systems has put an extractor/injector on the market. Richter revealed that Lee Scientific is developing a SFE-capillary SFC system. Packed or capillary?

Injection has never been a drawback in packed-column SFC. Direct injection is typically the method of choice. The storm that raged between the proponents of packed-column SFC and those of capillary-column SFC at previous symposia seemed to have calmed in Park City. Henion echoed the feelings of most when he asserted that both packed and capillary have unique advantages and are appropriate in different situations. Packed-column SFC has been used for quantitative, rapid analyses. Injected amounts without column overload can be much higher than in capillary SFC. Though impressive separations have been produced using packed columns, it is generally accepted that capillary SFC is best suited for very complex mixtures. Flow restrictors

Which type of flow restrictor is best? This continues to be the subject of lively debate. Campbell performed an empirical comparison of the three most widely used restrictors: the integral, the robot-pulled tapered, and the frit, using polyethylene glycol with an average molecular weight of 600. All three gave equivalent results in terms of molecular weight range and freedom from spiking. The three particular restrictors chosen did yield different flowrates. (Fine tuning of the flow-rate is difficult with the integral and robotpulled tapered restrictors.) This translated to differences in column efficiency and dissimilar chromatograms. Raynie discussed a restrictar/make-up-flow design that would allow higher flow-rates through the

final restriction and control of the linear velocity on the column. Packings and stationary phases

The activity of column packings has often limited the molecular weight range of packed-column SFC. Taylor, in cooperation with Henry, is attempting to develop well deactivated packings which have less retention and greater molecular weight range. A new cross-linked cyanopropylpolysiloxane on silica, called ‘deltabond’, is promising. Hirata discussed recent progress in packed capillary-column SFC. Jones discussed capillary-column stationary phase selection in SFC. Most analyte-stationary phase interactions in capillary-column SFC are relatively non-specific. Chang detailed the very specific interactions between a new smectic liquid crystal polysiloxane stationary phase and planar molecules such as polynuclear aromatic hydrocarbons (PAHs). The phase is also able to resolve positional isomers, such as cis and trans fatty acids. Multi-dimensional separations

Such a liquid crystal column might be useful in a two-dimensional SFC (2D-SFC) system. Of the two-dimensional chromatographic techniques, those involving SFC may be the most challenging to develop. Yet they are being reduced to practice in a few laboratories. Sandra has coupled an apolar column with an OV-225 coated column for analyzing triglycerides by 2D-SFC. Levy has approached multidimensional separations involving supercritical fluids from a number of directions. He has coupled SFC and GC, packed and capillary SFC, and SFE with both GC and SFC. SFC detectors

SFC detectors are the subject of a great deal of research. Not surprisingly, those which have the best potential for providing structural information for unknown analytes command the most attention. Mass spectrometry (MS) edged out Fourier transform infrared (FTIR) spectroscopy during this Workshop with seven talks vs. four.

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. SFC-MS. Major themes of the SFC-MS talks were applications, the investigation of methods providing structural information similar to that provided by electron ionization (EI), and the move toward higher-perfor(exmance mass spectrometers tended mass range and/or higher mass resolving power). Miller discussed applications of a direct interface SFC-MS system to PAHs, PEG 600, and porphyrins. Henion described three different methods which provide more structural information than chemical ionization. He used atmospheric pressure ionization and tandem MS, charge exchange with carbon dioxide as reagent gas, and a ‘momentum separator’, based upon the monodisperse aerosol (MAGIC) interface for LC-MS, where true EI conditions are obtained in the ion source. Buchner revealed that Extrel is also working on its version of the MAGIC interface for SFC-MS during a discussion period. Both Berry and Lane discussed use of a moving belt interface for packed-column SFC-MS of biologically and pharmaceutically important compounds. All types of traditional EI or CI methods are available, since the eluent is sprayed on the belt, the mobile phase is pumped away, and the analytes are flash-vaporized from the belt as it moves into the ion source. Berry also discussed direct-introduction EI SFC-MS and packed-column work using a thermospray interface. Pinkston discussed an evaluation of several extended mass range quadrupoles or SFC-MS. The highest massed ions observed were just below 4000 dalton. Huang described their SFC-MS interface to a highvoltage sector instrument. He and his co-workers in Lee’s group had achieved true El conditions using 25 iurn I.D. capillary columns and keeping the restrictor at 400°C. They achieved an impressive detection limit for heptachlor of 200 fg. Wright summarized the Pacific Northwest Lab’s high-flow rate interface and their version of the high voltage SFC-MS interface for a VG ZAB sector instrument. He also gave his working definition for ‘non-volatile’, a term which has been used rather

loosely in SFC circles: a species which yields a signal by direct probe MS is volatile; a species that does not is non-volatile. SFC-FTIR. Both schools of thought in SFC-FTIR, mobile phase elimination and flow cell, were well represented. Wiebolt described Nicolet’s approach using a 1.491 flow cell. The only important spectral region obscured by carbon dioxide is the C-H stretch region. Spectra do differ slightly from condensed phase and gas phase spectra, however. Morin used flow-cell SFC-FTIR for thermally labile analytes. Griffiths discussed the relative merits of flow elimination cell and solvent SFC-FTIR and has opted to pursue the latter. No restrictions are placed on the supercritical mobile phase when the solvent elimination approach is used. Bartle has also used the solvent elimination technique for packed and capillary SFC-FTIR. Twenty-one polymer additives ranging in molecular weight up to 1200 were resolved by capillary SFC. Other SFC detectors. Three other detectors were highlighted by talks. Hill discussed his most recent work with the ion mobility detector. He stressed that this relatively simple instrument provides the type of information one might expect from a UV detector, not from a mass spectrometer. Bornhop discussed progress in UV detection for capillary SFC. Jinno analyzed metal-containing compounds using micro-packed columns and inductively coupled plasma atomic emission spectroscopic detection . Applications and conclusions A few notable applications should be mentioned. Macaudiere used chiral stationary phases and made a number of direct comparisons between HPLC and SFC. Given the same degree of resolution between isomers, the SFC separations were invariably much quicker than the LC separations, often by a faktor of two or more. Wright revealed that the group at Pacific Northwest Laboratory has successfully chromatographed sodium salts of carboxylic acid containing ionophores such as imagermiacin.

He suggested that the molecule may fold to hide the polar group from the non-polar mobile phase. Mathiasson described the use of nitrous oxide and nitrogen-specific detection for SFC analysis of amines. There was a good deal of discussion on whether carbon dioxide could be used in the analysis of primary amines. The ‘primary amine’ peaks which have been eluted have yet to be investigated with a spectroscopic detector. Later discussed a comparison of aldicarb analysis by SFC with analysis by more traditional methods. The SFC methods yielded comparable results in less time. Raynie made an impassioned plea, which was well received by this author, for better standardization of the units and terminology used by the practitioners of SFC. We should all work toward this goal as the field of SFC expands rapidly. Campbell emphasized the potential of SFC for growth in a discussion of the results of an internal survey he conducted at Dow. The final talk was presented by Ishii. He showed how GC, SFC, and LC are thermodynamically related and how different ,retention mechanisms predominate in different temperature and pressure regions. This type of informal workshop, away from the distractions of the lab and office, is vital to the health of a fast-growing field such as SFC. This three-day immersion in SFC will undoubtedly stimulate new developments in the field. The organizers of the Workshop, Milton Lee and Karin Markides, are to be commended for performing a job which is crucial to the vitality and growth of SFC, and for performing it well. J. DAVID PINKSTON

J. David Pinkston is at the Procter & Gamble Company, Miami Valley Labs., P. 0. Box 398707, Cincinnati, OH 45239, U.S.A.