Anal. Chem. lS88, 60, 1365-1369
the future. Therefore, the SSJ/SSL technique has definitely better selectivity in comparison with chromatography. This SSJ/SSL technique has several additional advantages. The observed wavelength is a spectral parameter, so that it is independent of the experimental conditions used. While, the retention time in chromatography is frequently changed by the conditions, for example, by a separation column, the temperature of an oven, the flow rate of a carrier, etc., the experimental condition should strictly be kept constant in chromatography. The time for the measurement is similar or slightly shorter than chromatography, since the time for high-resolution chromatography sometimes requires more than 1 h. It is worth mentioning that the time for recording the SSJ/SSL spectrum can be shortened to a second by increasing the scanning speed of the dye laser wavelength in the future. The detection sensitivity of SSJ/SSL spectrometry in the concentration unit is comparable to chromatography. SSJ/ SSL spectrometry has, of course, some disadvantages. The amount of the sample required for the measurement is 200 pL, so that the detection limit in the amount unit (100 ng) may be poorer than a picogram detection limit for capillary gas chromatography. The chromatograph technique can be combined with the other spectrometric method such as mass spectrometry, which is quite useful for assignment of the sample molecule. A similar hyphenated technique is also possible in SSJ/SSL spectrometry. The use of a spectrometric multichannel analyzer allows the repetitive measurements of the fluorescence spectrum (11). It is useful for sample identification from the spectral feature. A combination with multiphoton ionization/mass spectrometry gives us additional information con-
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cerning molecular weight and chemical structure of the molecule (3,6). If a rapid wavelength scan becomes possible in the future, this SSJ/SSL spectrometry might be combined even with chromatography. This approach may provide us much greater selectivity in chemical analysis. Registry No. Anthracene, 120-12-7; 2-methylanthracene, 613-12-7; 2-ethylanthracene, 52251-71-5; 1-chloroanthracene, 4985-70-0; pyrene, 129-00-0; 9-methylanthracene, 779-02-2; 9chloroanthracene, 716-53-0; 9,10-dimethylanthracene,781-43-1; 9,10-dichloroanthracene, 605-48-1.
LITERATURE CITED Hayes, J. M.; Small, G. J. Anal. Chem. 1983, 55,565A. Johnston, M. V. TrAC Trends Anal. Chem. 1984, 3,58. Lubman, D. M. Anal. Chem. 1987, 59,31A. Imasaka, T.; Shigezumi, T.; Ishibashi, N. Ana/yst (London) 1984, 109, 277. Imasaka, T.; Okamura, T.; Ishibashi, N. Anal. Chem. 1986, 58, 2152. Imasaka, T.; Tashiro, K.; Ishibashi, N. Anal. Chem. 1986, 58, 3242. Hayes, J. M.; Small, G. J. Anal. Chem. 1982, 54, 1202. Pepich, B. V.; Callis, J. B.; Danielson, J. D. S.; Gouterman, M. Rev. Sci. Instrum. 1988, 57,878. Pepich, B. V.; Callis, J. B.; Burnes, D. H.; Gouterman, M.; Kalman, D. A. Anal. Chem. 1986, 58, 2825. Stiller, S. W.; Johnston, M. V. Anal. Chem. 1987, 59,567. Imasaka, T.; Tanaka, K.; Ishibashl, N. Anal. Sci. 1988, 4 , 31. Beck, S. M.; Powers, D. E.; Hopkins, J. B.; Smalley, R. E. J. Chem. Phys. 1981, 73,2019. Beck, S. M.; Hopkins, J. B.; Powers, D. E.; Smalley, R..E. J. Chem. Phys. 1981, 74,43. Yang, Y.; D’Silva, A. P.; Fassei, V. A. Anal. Cham. 1981, 53,2107.
RECEIVED for review November 7,1987. Accepted March 3, 1988. This research is supported by Grant-in-Aid for Scientific Research from the Ministry of Education of Japan and from the Nissan Foundation.
Evaluation of a Supercritical Fluid Chromatograph Coupled to a Surface-Wave-Sustained Microwave- Induced Plasma Detector Debra R. Luffer, Leonard J. Galante,’ Paul A. David, Milos Novotny,* and Gary M. Hieftje
Department of Chemistry, Indiana University, Bloomington, Indiana 47405
A capillary supercritical fluid chromatograph (SFC) was coupled to a surface-wave-sustained microwave-induced plasma (MIP) sustained wlth a surfatron. The chromatographic system, interface, and plasma source are described. The plasma was optlmlzed for sulfur emisdon at 921.3 nm and used to detect a mixture of sulfur-containing polycyciics that had been separated by SFC. The linear dynamlc range for these compounds is 3 orders of magnitude with detection iimlts of 25 pg/s sulfur for thlophene. The relative standard deviations for repetltlve injections are typlcaiiy I-5% at concentrations well above the detection limit.
Capillary supercritical fluid chromatography (SFC) has been recognized as the separation method of choice for compounds that are not easily amenable to either gas or liquid chromatographic analysis (2-3). The former is ultimately limited by ICurrent address: Glaxo, Inc., Crown I1 Bldg., 1035 Swabiz Ct., Morrisville, NC 27560. 0003-2700/88/0360-1385$01 S O / O
the involatility of large compounds or thermal lability a t the high temperatures required in gas chromatography (GC). The latter suffers from a lack of element-selective detection methods (4)due to solvent interferences. A supercritical fluid mobile phase has been able to overcome some of these limitations because. it can operate optimally at significantly lower temperatures than GC, its viscosity and solute diffusivities are between liquid and gaseous phases, and its solvating power approaches that of a liquid ( 5 ) . In addition, the column effluent at atmospheric pressure is compatible with many GC detectors that offer sensitive and selective detection. It is for this reason that many detection schemes are being borrowed from GC and adapted to SFC. Some examples of this include SFC/MS (6,7), SFC/FTIR (8),and SFC/FID (9-12), as well as thermionic (12), dual flame photometric (13), and ion mobility (14). Of the many varied detection methods for chromatography that have been investigated, those based on atomic spectroscopy have become increasingly attractive due to their inherent selectivity, freedom from interferences, and multielement detection capability (15). In particular, plasma 0 1988 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 60, NO. 14, JULY 15, 1988 COLUMN
SWAGELOK UNION
IWEGRAL RESTRICTOR
PLASMA
PM TuQe (1102)
QUARTZ NOZZLE
'
I
L! F@re 1. Schematic diagram of the supercritical fluM chromatograph,
interface, and microwave-induced plasma detector. detectors possess several characteristics that make them even more appealing than flame-based photometric systems: these include improved sensitivity, a wide dynamic range, and fewer spectral interferences. Most importantly, with respect to chromatographic analyses, the plasma detector will often tolerate co-elution from a column because it is virtually element-specific (15). Microwave-induced plasma (MIP) (16,17)has been successfully employed as an element-specific detector for GC (15, 18-20). The surface-wave-sustained MIP (surfatron) is particularly attractive due to its stable, reproducibly long, small-diameter plasma (21). In addition, it is relatively inexpensive, is easy to construct, and produces an annular plasma in helium (22), which is believed to make it less likely to be extinguished by the high mass flow of the mobile phase. This type of plasma can operate under low pressure or atmospheric conditions with argon or helium as the support gas, typically at relatively low flow rates (
