1886
Anal. Chem. 1986, 58, 1886-1887
CONCLUSIONS
Registry No. Bauxite, 1318-16-7;fluorspar, 14542-23-5.
The microwave oven, mixed acid digestion system is a suitable dissolution technique for a wide range of geologic sample types. It has proved to be a rapid, inexpensive method for decomposing rocks and soils in preparation for multielement determinations. This method is particularly useful for volatile elements, which are normally lost during decomposition procedures using open vessels. The solutions prepared by this procedure are compatible with analysis by ICPOES and AAS, although the resulting 1:lOOO dilution factor may preclude determination of certain elements by these techniques. Approximately 100 samples can be prepared for analysis in a single day. Refractory minerals, such as chromite, corundum, quartz, rutile, and zircon, and other materials known to be resistant to attack by mineral acids and HF are only partially dissolved by this technique. Except for Ti and Cr, the transition elements contained in most geologic samples can be completely dissolved by this technique.
ACKNOWLEDGMENT We are grateful to R. C. Erd, who performed the X-ray diffraction analyses. We also thank L. Jassie and H. M. Kingston, US.National Bureau of Standards, Gaithersburg, MD, for many helpful discussions and enthusiastic support.
LITERATURE CITED Thompson. M.;Waish, J. N. A Handbook of Inducthe& Coupled Plasm Spectrometry; Chapman and Hail: New York. 1983; Chapter 4. Summerhays, K. D.; Lamothe, P. J.; Fries, T. L. Appl. Spectrosc. 1983, 3 7 , 25-28. Crock, J. 0.;Lichte, F. E. Anal. Chem. lB82, 5 4 , 1329-1332. Slavin, W.; Carnick, (3. R.; Manning, D. C.; Ruszkowska. E. At. Spectrosc. IB83, 4 , 69-86. Abu-Samra, A.; Morris, J. S.; Koirtyohann, S. R . Anal. Chem. 1975, 4 7 , 1475-1477. Barrett, P.; Davidowski, L. J.; Penaro, K. W.; Copeiand, T. R. Anal. Chem. 1978, 50, 1021-1023. Matthes, S. A.; Farrell, R. F.; Mackie, A. J. Tech. Prog. Rep. U.S. Bur. Mlnes 1983, 120. Nadkarni, R. A. Anal. Chem. 1984, 56, 2233-2237. Fries, T.; Lamothe, P. J.; Pesek, J. J. Anal. Chim. Acta 1984, 159, 329-336. Myers, A. T.; Havens, R. G.; Dunton. P. J. U . S . Gem/.Surv. Bull. IB81, 1084-1, 207-229. Abbey, S. Geol. Surv. Can. Pap. IB83, 83-15. Allcott, G. H., US. Geol. Survey, private communication, 1985. Streckheisen. A. L. Geotlmes 1973, 18, 26-30.
RECEIVED for review December 3,1985. Resubmitted March 26,1986. Accepted March 26,1986. Any use of trade names and trademarks in this report is for descriptive purposes only and does not constitute endorsement by the U.S.Geological Survey.
CORRESPONDENCE The Unimportance of Stationary-Phase Viscosity in Gas-Liquid Chromatography Sir: An error in the theory of zone broadening was established early in the history of gas chromatography, e.g., in ref 1. It was amerted that since diffusivity in the stationary phase is inversely proportional to ita viscosity then the mass transfer term in the equation for plate height increases linearly with viscosity. This led to the practical advice to avoid stationary phases with high viscosity. This error was reinforced in a series of papers by this author (2-6) in which the theory was refined, elaborated, and delimited. It is perpetuated in manufacturers’literature and even in textbooks. A retraction and explanation is therefore desirable. The error arose from the theory of diffusion in liquids that was then current, based on models using spherical molecules. The chemical physics of viscosity and of diffusion in such system was and is described in textbooks and will not be elaborated here, but all theoretical relations based on such models lead to the inverse proportionality of diffusivity and viscosity. A number of contemporary chromatographers pointed out verbally that such models did not necessarily apply to the long-chain molecules used in chromatography, and this was eventually put into print by Giddings (7). The theory of diffusion in polymers was still in its infancy. It is now understood (8)that diffusion is related to movements of segments of polymer chains and that these are not related to what is normally understood by the term “Viscosity“. They are related to “high-frequency viscosity”, i.e., the resistance 0003-2700/86/035&1886$0 1.50/0
felt by a mechanical device vibrating at high frequency in the medium. However, there is usually no data on this for polymers used in gas chromatography, and it is not related in any simple way to the regular viscosity based on resistance to flow. The actual relations are discussed at length by Ferry (8).
Since gas-liquid chromatography (GLC) is now conducted almost exclusively with polymeric liquid phases, the regular viscosity is irrelevant. To the limited extent that short-chain molecules are used, there is a viscosity dependence but it is less than linear (3) and the dependence on viscosity decreases as chain length increases. In general, therefore, viscosity should not be considered in choosing a stationary phase. Indeed, it has been shown that diffusivities in dimethylsilicones of molecular weights used in gas chromatography not only change very little with increasing viscosity but actually increase (5,6). This is because the higher molecular weight dimethylsilicones have lower density (4)and therefore greater free volume. Two trifluoropropylsilicones of very different viscosities showed the same diffusivities within experimental error (5). Nothing said here should be interpreted to imply that polymers can be used below their glass temperature. A t this temperature the segmental motions causing diffusion of substances in the molecular weight range of GLC samples are slowed or stopped and diffusion becomes very slow (8). This prevents the use of silicone gums at low temperatures, but in no way hinders the use at subambient temperatures of 0 1986 American Chemical Society
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silicone oils with the narrow molecular weight range customary in stationary phases prepared specially for use in gas chromatography.
LITERATURE CITED (1) Keuiemans, A. I. M.; Kwantes, A. Vepour Ph8se Chrometogf8phy; Desty, D. H., Ed.; Butterwofths: London, 1957; pp 22-23. (2) Hawkes, Stephen, J.; Mooney, Eric F. Anal. Chem. 1864, 3 6 , 1473- 1477. (3) Hawkes, S. J.; Carpenter, D. J. Anal. Cheffl. 1967, 39, 393-395. (4) Kong, John M.: Hawkes, Stephen J. Macromolecules 1975, 8, 685-687. ( 5 ) Kong, John M.; Hawkes, Stephen J. J. Chromfogr. Sci. 1976, 14. 279-287.
(6) Mlllen, William; Hawkes, Stephen J. J . Chromtogr. Sci. 1977, IS, 148- 150. (7) W i n g s , J. C. D y ~ f f l l c sof Chromtogaphy; Marcel Dekker: New York, 1985; p 235. (8) Ferry, John E. Visccelestic Pfopeftlesof Po&rnefs, 2nd ed.; Wlley: New York, 1970 pp 332-333, 371-375, 466-480.
Stephen J. Hawkes Department of Chemistry Oregon State University Corvallis, Oregon 97331
RECEIVEDfor review Janumy 27,1986. Accepted April 1,1986.
High-Resolution Detection of Daughter Ions with a Hybrid Mass Spectrometer Sir: The technique known as mass spectrometry/mass spectrometry (MS/MS) or tandem mass spectrometry has become an accepted technique in analytical laboratories for the analysis of complex mixtures and a widely used technique for fundamental studies of gas-phase ion chemistry (1,2).The initial work in MS/MS was done on instruments of "reverse" geometry; i.e., the magnetic sector (B) preceded the electric sector (E) (3,4). As it became apparent that MS/MS was very useful for mixture analysis (5),new instruments were built to try to improve upon the performance of the BE instruments, especially the mass resolution. Daughter ion resolution was the f i t area that was improved upon with the application of triple quadrupole (QQQ) systems (6) to mixture analysis. While the triple quadrupole instrument was being developed, several triple sector instruments were also being constructed (7-10).All the latter had a geometry of EBE in which the EB portion of the instrument was a double-focusing mass spectrometer. Thus,they offered greatly increased parent ion resolution. However, the daughter ion resolution was no better than that of the BE instruments. Shortly thereafter, hybrid instruments, combining quadrupoles and sectors, were introduced to try to take advantage of the best resolution features of both triple quadrupole and triple sector instruments. The first of these was of BQQ geometry (11). Since the introduction of this instrument, other hybrids have been reported in the literature in which the sector portion of the instrument was a double-focusing mass spectrometer of EB geometry (12)or BE geometry (13). These instruments offer high parent ion resolution but still only unit resolution for the daughter ions. To improve the daughter ion resolution further, a magnet was added to one of the previously described triple sector instruments to produce an EBEB geometry, or essentially an instrument consisting of two double-focusing mass spectrometers in tandem (8). It was estimated that this instrument would have a daughter ion resolution of =lo OOO but this has yet to be reported experimentally. Recently a commercial instrument of BEEB geometry has been constructed (14). A daughter ion resolution of ~ 5 5 0 has 0 thus far been reported with this instrument (15). Both four-sector instruments use linked scanning a t a constant B/E (16,17),following high-energy collision activated dissociation (CAD), to obtain daughter ion MS/MS spectra. In taking data in this manner, these instruments do not suffer from the artifact peaks that are commonly observed in linked scan spectra obtained on two-sector instruments (18).This is due to the fact that a stage of mass separation occurs before 0003-2700/86/0358-1867$01.50/0
CAD in the four-sector instruments but not before the CAD process in the two-sector instruments, Another approach has been used to obtain high resolution of MS/MS daughter ions, namely, Fourier transform mass spectrometq (Fl'MS) (19).In the FTMS experiment, a single analyzer is used with the ionization, MS/MS reactions and mass analysis being separated in time. This is in contrast to conventional MS/MS instruments where the ionization, MS/MS reactions, and analysis are separated in space. In the first FTMS MS/MS experiment (191, low-energy CAD was used to form the fragment ions, and a resolution of =3000 was reported. Since then, resolution has been improved by approximately an order of magnitude (20). A variant of the FTMS experiment has been performed where a quadrupole is used as the first stage of mass analysis and a FTMS instrument as the second. With this system a resolution of 140000 (FWHM) has been shown (21). In this report, we describe experiments where high-resolution daughter ion spectra are obtained with a new hybrid MS/MS instrument of QEB geometry. These experiments were done by using low-energy CAD, although a unique feature of this instrument is its ability to also detect high-energy CAD daughter ions at high resolution. Thii latter mode of operation has yet to be implemented, however. The instrument will be described briefly here. A detailed description of the instrument will be reported elsewhere (22). Figure 1shows a block diagram of the instrument. The first stage of mass analysis is performed by a UTI lOOC quadruople mass fiter. The EB portion of the instrument is an AEI MS50 double-focusing, high-resolution mass spectrometer. There are three reaction regions in the instrument where ions can undergo reactions and subsequent mass analysis. The first of these is after the quadrupole but prior to acceleration into the EB portion of the instrument. Therefore, low-energy CAD MS/MS experiments can be performed by use of this reaction region. The other two reaction regions are located in the instrument after the accelerating region, and thus the ions have kiloelectronvolt energies in these regions. It is possible to perform high-energy CAD MS/MS and analyze the daughter ions at high resolution with the QEB by the linked scan procedure used on the four-sector instruments (8,14). This would involve mass selecting the parent ion with the quadrupole, performing collisional activation (kiloelectronvolt ion kinetic energy) in the second reaction region, and then link scanning the EB portion of the instrument at a constant r a t i o of B/E.Given the excellent transmission and resolution of the MS50, this should give results @ 1986 American Chemlcal Society
