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Anal. Chem. 1082, 54, 1646-1647
thus increasing the ionization efficiency of the source. Upon using the mass spectrometer to monitor extracted ion signals from the modified source, ion signal enhancements of 6-9 times were observed for the sputtered sample neutral atoms subsequently post-ionized in the discharge. Table I presents typical data for mass scans with and without the magnetic field on. In this example, a polycrystalline copper sample was subjected to ion bombardment in an argon discharge. The ion signals from background contaminant species (N+,HzO+) and ions arising from the discharge sputter gas (Arz+)also increased with application of the magnetic field. The Cu+:Ar+ ion ratio maintained approximately the same value when the magnetic field was applied as when the source was operated without the magnet. For elements whose nominal mass positions are not masked by interferences, enhanced GDMS trace detection sensitivites are expected owing to the increase in ion yield. The analytical value of this magnetic coupling has yet to be fully evaluated for mass spectrometry. The dc electromagnet employed,while easy to construct, may not represent the optimum configuration of the magnetic field in the source. This gives expectation of developing more efficient source models which have different magnetic field distributions which could improve the ionization interactions. It has been reported that in the glow discharge, the concentrations of ionic species (both atomic and molecular) vary spatially throughout the body of the discharge (17,181. A redesigned electromagnet with properly defined and controlled magnetic field geometry might allow the observation of selective ion enhancements as the position of discharge regions changes with magnetic field
application.
LITERATURE CITED (I) Coburn, J. W.; Harrison, W. W. Appi. Specfroso. Rev. 1981, 17,
95-130. (2) Coburn, J. W.; Taglauer, E.; Kay, E. J . Appl. Phys. 1974, 45, 1779-1786. (3) Coburn, J. W.; Kay, E. Appl. Phys. Left. 1971, 19, 350-352. (4) Bruhn, C. G.; Bentz, B. L.; Harrison, W. W. Anal. Chem. 1978, 50, 373-375. (5) Bruhn, C. Q.; Bentz, B. L.; Harrison, W. W. Anal. Chem. 1979, 51, 673-678. (6) Hofmann, D.; Wechsung, R. Proc. ISPC-4 1979, 2, 622-627. (7) “Plasma Discharge Source”; Vacuum Generators Analytical Ltd.: Cheshire, England, Product Details Bulletln, April 1981. (8) Wiilett, C. S. ”Introductlon to Gas Lasers: Population Inversion Mechanisms”; Pergamon Press: Oxford, 1974; Chapter 3. (9) Maisel, L. In “Handbook of Thin Flim Technology”; -. McGraw-Hi11: New York, 1970; Chapter 4. ( I O ) Kay, E. J. Appi. Phys. 1963, 3 4 , 760-768. (11) Bentz, B. L.; Bruhn, C. G.; Harrlson, W. W. Inf. J . Spechom. Ion PhW. 1978. 28. 409-425. (12) Harrlson, W.W.’; Bentz,B. L. Anal. Chem. 1979, 51, 1853-1855. (13) Kip, A. F. “Fundamentais of Electrlclty and Magnetism”; McGraw-HIII, New York, 1969; Chapter 8, (14) Chapln, J. S. ResJDev. 1974 (Jan), 37-40. (15) Coblne, J. D. “Qaseous Conductors, Theory and Engineerlng Appllcations”; Dover: New York, 1941. (16) Thornton, J. A. J . Vac. Sci. Technd. 1978, 15, 171-177. (17) Howarka, F.; Llndlnger, W.; Pahl, M. I n f . J . Mass Specfrom. Ion Phy6. t973, 12, 67-77. (18) Knewstubb, P. F.; Tlckner, A. W. J . Chem. Phys. 1982, 36, 684-693.
RECEIVED for review July 1,1981. Resubmitted February 8, 1982. Accepted April 14, 1982. Support is gratefully acknowledged from the Department of Energy, Division of Chemical Sciences, and the National Institutes of Health.
Septumless Injection Port for Capillary Gas Chromatography Joachim Greter” and Goran Sttihle Department of Clinical Chemistry, University of Gothenburg, 5 4 13 45 Gothenburg, Sweden
In capillary gas chromatography, problems arising from the injection port septum are quite common and very disturbing in routine on-column injection work. The main problems encountered are bleed from the septum at elevated injector block temperatures and particles torn from the septum into the column by the injection needle. These particles are deleterious to column performance and in the worst case may clog the column. For some injection ports with a septum, devices have been designed to overcome problems from septum bleeding, but as far as we know none of these devices safely prevent septum particles from coming into the column, if on-column injection is to be applied. Two years ago the only commercially available septumless on-column injector for capillary columns (1) did not fit our budget and, like other septumless injection devices known to us, did not seem to be suitable for a trouble-free continuous use with an autosampler. We therefore designed, built, and tested the injection port shown in Figure 1which can be made in 2 days at a material cost of less than $30 by any skilled technician. The injection port was easily fitted to different gas chromatographs (Carlo Erba, Hewlett-Packard, Varian) in our laboratory, the only difference being the thread cut into the block (Figure 1F). To prevent carrier gas and sample from leaking out during the injection, we fitted the syringe with a piece of high-temperature septum (Figure 1B) which is tightly pressed against 0003-2700/82/0354-1646$0 1.25/0
the injector block (Figure IC)at least 20 s before and after the injection. A representative chromatogram obtained with this injection port is shown in Figure 2 (chromatogramB). The comparison with the chromatogram obtained using an injection port septum under otherwise identical conditions (chromatogram A) reveals the absence of septum bleeding but no significant differences in peak shapes, heights, and separation. The high-temperature septum was obtained from Varian (Part No. 69-000179) and had been conditioned 8 h at 350 “C. Flash heater block and FID detector temperatures were 350 OC (3770 gas chromatograph with manually switchable constant flow and constant pressure regulators, Varian, Palo Alto, CA), and the temperature in the injection port measured a t the rotating stainless steel disk (Figure 1E) was 120 “C. The needle was guided about 4 cm into a 15 cm long, 0.7 mm i.d. glass-lined stainless steel tubing (SGE, Melbourn, Australia) to which capillary columns of different internal diameters can be attached by the reversed cone principle without any dead volume (not shown in Figure 1). Since the sample is not really injected into the column but into a glass-lined tube attached to the column, we call this type of injection ‘‘quasi on column”. The oven temperature was programmed from 40 “C to 300 OC a t a rate of 10 “C/min. The final temperature was held for 5 min. The carrier gas was hydrogen a t a flow rate of 20 mL/min during injection (constant pressure regulated), and 2 mL/min during the temperature program (constant flow 0 1982 American Chemical Society
Anal. C M . 1982, 54.
1647
1647-1650
lETLrnHlWIIYE..l"
Fbun 2. Comparison of the FID chromatograms obtained Wlth (A) and wlthout (6) Injection p a l septum of an alkane mixture dissolved In n-haptane. From left to right the main peaks are solvent peaks. nundecane. ndodecane, n-mecane, n-tebadecane. nhexadecane. n-wtadecane, n-eicosane, and ndocosane.
O
L
-
ncE.. 1. Schemstk drawings (explodedview and vwtkal cut) of the sepbn*as h pat. A stahless steel bsk (E) wlth an exammcaly positioned hole of a slightly greater diameter than Um outer diameter of the 1n)ecUon madb (A) used is enclosed between two TeRon disks (D). At injection time the disk (E) is rotated about 45' from the closed psmon to a ked open pmM. The two halves (C and F)of the brass metal bk& are hdd toSeUmr by spfbq (I) loaded screws (J) and ~ealed against the gas chomatogaph (H) wtlh an aluminum dm (G). A piece of septum (E) pressed against the metal block by Um syrlnw prevents leakage during the injection. regulated), hut comparahle resulta are obtained if the carrier gas flow is presaure regulated all the time to give a flow rate of 3 mL/min at 300 "C. The temperature program was started 30 s after the flash heated, hot needle, solvent flush (2), splitless 'quasi on column" injection. The injection volume waa 0.2 i.L containing about 50 ng of each component and the flushing solvent (ca. 0.7 NL)was n-pentane. The column was a 28 m, 0.5 mm i.d Pyrex column statically coated (except for the first meter of the column) with crosslinked SE-54 principally according to Grob and Grob (3) to yield a film thickness of 0.15 fim. The chromatographic conditions given are those currently used in our laboratory hut are not critical for the performance of our injection port, as long as an effective trapping of the
sample onto the column is ensured to prevent hack-flushing when withdrawing the syringe. The injection port is gastight even at mum temperature and can thus he used for cold on column injection as well. Recently we have started to use our injection port for hot needle, flash heated 'quasi on column" injection in conjunction with a modified autosampler (Model 8o00, Varian, Palo Alto, CA) with very satisfying results. One of the reviewers directed our attention to a device marketed by Perkin-Elmer ("septum swinger") which looks similar to our device hut cannot be modified to he used in the way we use our device. ACKNOWLEDGMENT We thank Nils Ekendahl for the skillful electronic modification of the autosampler. LITERATURE CITED (1) u.ob. K.; Orob. K.. Jr. J . chromamg. i878. f51, 311-320. (2) @ob. K.. Jr.; Rennhard. S. HSC CC J . H&h Resolut. Chromatogr. Uvomemg. C o r n . 1880. 3. 627-633. (3) Orob, K.: Upb, 0. J . Chromsfogr. 198i. 213. 211-221.
RFCEIVEDfor review February 8, 1982. Accepted April 12, 1982. This work was supported hy a grant (13X-5853 from the Swedish Medical Research Council and a grant (80/1385) from the Swedish Council for Planning and Coordination of Research.
Determination of Boric Oxide by Ion Chromatography and Ion Chromatography Exclusion John P. Wllshlre' and Wlllla A. Brown U.S. Bwax Research Cmpcintiw?,412 Crescent Way, Anaheim. Callrornia 92801-6794 Ion chromatography is a relatively new technique (I),which is rapidly gaining stature as a method for trace anion and
cation analysis (2). Although used principally in the determination and quantitation of simple anions and cations in
o o o ~ z ~ o o 1 8 ~ 1 0 3 5 c 1 ~ ~ 5 0 1 . 2e35 /1982 o ~mericanC h a m b l Soclew
