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Anal. Chem. 1882. 54, 2388-2390
fluorescence. If this noise could be minimized so that the limiting noise is the shot noise of the PM tube, then the detection limits could possibly be lowered by up to 4 orders of magnitude. This problem has been effectively dealt with by several groups (5-9), through the use of optical fibers. By use of the fiber to collect the analyte fluorescence along the axis of the capillary tube, collection of the quartz fluorescence is minimized. Another way to minimize the unwanted signal is to time resolve one fluorescence signal from the other. Work toward these improvements is progress.
LITERATURE CITED
Flgure 1. Schematic diagram of the nanollter cwene cell
The detection ability of this system is limited by the blank noise. The blank noise was 4 orders of magnitude higher than the shot noise from the dark current of the PM tube and remained unchanged when the empty cuvette was illuminated or when it was filled with solvent and illuminated. The blank signal peaked at 450 nm, which led us to believe that it was not due to scatter from the laser and was more likely quartz
(1) Diebald. 0. J.; &re. R. N. Scknce 1977. 196, 1439-1441. (2) Volglman. E.; Jurgensen. A,; Winetordner. J. D. Anal. Chem. 1981, 53, 1921-1923. (3) Hershberger. L. W.; Galls. J. 8.; Christian. G. D. Anal. chem.1979, 51, 1444-1446. (4) Folestad, S.; Johnson. L.: Josefsson, 8.; Galle, 8. Anal. Chem. 1982, 54, 925-929. (5) smim. R. M.; Jackm. K. W.; AldOus. K. M. Anal. Chem. 1977. 49, 2051-2053. (6) Vurek. 0. 0. Anal. chem.1982, 54. 840-842. (7) Sepaniak, M. J.; Yeung. E. S. J . Chromatog. 1980, 190. 3 3 7 3 8 3 . (8) Thacker. L. H. J . Ghromatogr. 1877. 136, 213-220. (9) Vurek, G. 0.; Bawman, R. L. Anal. Biochsm. 1969. 29, 238-247. (10) Vurek, 0. 0.; Pegram, S. E. Anal. Bicchem. 1966. 16, 409-419.
RFCEIYEDfor review June 11,1982, Accepted August 9,1982. This work is supported totally by NIH-GM-11373-20.
Coupling of Fused Silica Capillary Gas Chromatographic Columns to Three Mass Spectrometers Trescott E. Jensen, Ray Kaminrky, Bruce D. McVeety, Timothy J. Wozniak, and Ronald A. Hites' School 01 Publk and Environmental A i f a h and L%pamnt 01 Chemlstty, Indiana Univers& Bbomlngton. Indiana 47405
The connection of the effluent of a gas chromatograph with the ion soulce of a mass spectrometer (GC/MS) has provided the analyst of organic compounds with an instrument more powerful than the s u m of its parts. For the last 15 years, this connection has been achieved by devices that separate the organic compounds from the gas chromatographic carrier gas (I, 2). These devices were a very succeasful strategy when used with packed GC columns. The advent of flexible fused silica capillary GC columns, however, has made such GC/MS interface devices obsolete. Unfortunately, few commercially available instruments are designed fo-r such modern GC columns. We h v e . herefoe. m(dified three H w l e n - p a c M ( ~ pGC/MS ) ins&,mente in our labratory that the end of the GC column directly entersthe ion source, hi^ paper will show that this strategy has been very successful, Thus, we will demonstrate that the best GC/MS interface is no interface.
EXPERIMENTAL SECTION Model 5985B Modification. The capillary column isolation valve assembly was removed from the transfer box heated zone and replaced with a length of in. stainless steel tubing running from the GC oven to the transfer line prohe assembly. A in. Swagelok tee was welded into this length of tubing to provide an entry for chemical ionization reagent gases that would sweep past the end of the column and into the ion source. Reagent gas flow was controlled by a flow controller needle valve and a shut off valve between the GC flow monitor and the tee fitting. A in. Swagelok union was welded to the end of the in. tube in the GC oven. By threading the column through the tube in the GC oven to the exit of the GC/MS probe within the connecting
bellows unit to the souce (and clipping off the column end), the end of column can he brought to within 2 cm of the electron beam. AU fittings are sealed with standard graphite vespel ferrules. With a 30 m x 0.25 mm i.d. J&W DB-5 column and He as the carrier gas at 25 cm/s, the source pressure is 4 X lo4 torr when the column is at ambient temperature. We have found this pressure satisfactory and have not experienced any significant difficulty with background from neutrals. Model 5982 Modification. The direct injection prohe assembly was removed at the source manifold flange. An interface prohe with a '/,$in. Swaeelok fitting welded in one end and a seal flange plate welded on th; other pr&dru the vacuum seal and wnnertiun hetween the GC own and column and the ion oowce. To decrease dead volume and allow simple alignment of the column with the ion source, a stainless steel insert fills the space within the prohe and aligns with the ion souce inlet. To ensure an inert surface in contact with the column, we installed a glass-lined tube within the of this insert, Fused silica capillary column installation is directlv from the GC oven through the interface D r o k . the end is positioned next to the source plkger. In our instrument, the source preasure with He flowing at 25 cm/s through a HP 25 m X 0.22 mm i.d. SE-54 column is 5 X torr. Instrument tuning is done hy introduction of perfluorotrihutylamine (PFTBA) controlled by both a metering and a shut off valve through one of the original sample inlet lines. In a similar manner, chemical ionization reagent gas can be introduced to the source through the other original sample inlet line. Model 5995 Modification. To provide a direct path for the introduction of a capillary column into the ion source, we removed the large source isolation valve. This was done by cutting the valve unit off the interface stem of the vacuum manifold on the in. i.d. stainless manifold side of the valve body. A length of 'I8 steel tubing equivalent in length and diameter to the piece re-
0003-2700/82/0354-2388$01.25/0 0 1982 American Chemical SocieIy
ANALYTICAL CHEMISTRY, VOL. 54, NO. 13, NOVEMBER 1982
A
Ill
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'I I
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BEFORE
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TlME (MIN.)
Flgure 2. Total ion chromatograms from our HP 5995 GUMS system before and after the modification discussed in the text. The peak identifications are as follows: (1 1) BHT, (12) pentachlorophenol, (13) acridlne, (14) DDT. TIME (MIN.)
Flgure 1. Total ion chromatograms for the lasi 10 components of a 36-component test mixture obtained after the modifications descrlbed
in the text on (A) HP 5985B and (B) HP 5982 GWMS systems. Peak identifications are as follows;: (1) benzo[k]fluoranthrene; (2) benzo[elpyrene, (3) benzo[a Ipiyrene, (4) perylene, (5) 9, lo-diphenylanthracene, (6)dibenz[a ,h ]anthracene, (7) benzo[ghi]perylene,(8) dibenzo [def ,mno Ichrysene, (9)coronene, (10) dibenzo[a ,e]pyrene. moved (11 cm X 1.3 cm 0.d.) was welded in place of the valve. On the GC end of this interface connecting tube, a l/ls in. Swagelok fitting was welded. The chromatographic column (25 X 0.22 mm i.d. HP SE-54) was threaded through the interface connecting tube so that the effluent end of the column resides about 1cm from the ion sIDurce repeller. When the column flow is adjusted to 25 cm/s of helium at ambient temperature, the source pressure is about 13 x lo4 torr. GC/MS Performance Standard. For the HP 5985B and 5982, a 36-component standard containing 10 ng/pL of aromatic compounds with one to seven rings was used. GC conditions were 30 "C for 4 min, programrned at 8 "C/min to 280 "C held for 30 min for the HP 5985B and 40 "C initial temperature programmed at 4 "C/min to 280 "C held for 30 min for the HP 5982. Another standard mixture was used to evaluate the HP 5995. This standard contained 100 ng/pL of 2,6-bis(l,l-dimethylethyl)-4methylphenol (BHT), pentachlorophenol, acridine, and 1,l'(2,2,2-trichloroethylidene)bis [4-chlorobenzene] (DDT). For the HP 5995, the starting teinperature was 30 "C held for 1 min programmed at 15 "C/min to 90 "C where the program rate was changed to 6 "C/min to 280 "C held for 20 min. One microliter injections were made in the splitless mode with a load time of 0.7 min.
RESULTS AND DISCUSSION Performance of HP 5985B. After making the modification discussed above, we have been successful in using our HP 5985 system almost contiinuously for a 5-month period using a single capillary column. More than 600 injections were made into this column for electron impact (EI), positive chemical ionization (CI), and negative ion chemical ionization (NCI) experiments. Not less than half of these experiments were of the chemical ionization type. At about the midpoint in this time, the data shown in Figure 1 were obtained. After connecting the column directly to the ion source, we were able to detect and resolve coronene (peak 9, Figure 1A) and other compounds of similar difficulty. Before removing the isolation valve assembly, it was not possible to detect any of the compounds eluting after perylene (peak 4, Figure 1A). This limitation was not acceptable for our work. After the H P 5985B was successfullly modified as described above, its
performance became a goal for the improvement of the other two instruments in our laboratory. Performance of the HP 5982. The Hewlett-Packard 5982 gas chromatograph mass spectrometer was originally designed for packed column use. Column effluent passed through a heated, glass-lined transfer tube into the source housing flange. With this configuration, the transfer lines within the source were sealed against the flange by means of a spring loaded "shoe". Often this "shoe" failed to seat tightly against the flange and some of the column effluent was pumped away, never reaching the ionization chamber. When the flow rate is reduced with capillary columns, the limitations of the instrument's physical design prevented detection of less than 200 ng of n-alkanes. To adapt the H P 5982 to accept a fused silica column, the simplest approach was insertion of the capillary column into the ''shoe". Due to the curvature of the transfer lines internal to the ion source, it was difficult to assess the location of the column end. Also, adsorbtion in the transfer line itself, due to microfissures in the glass-lined connecting tube, reduced sensitivity. Samples of 200 ng were detected with this configuration, but smaller quantities were not reproducible or were not detected. Analysis of 200,100, 50, and 10 ng by direct probe, indicated that the mass spectrometer sensitivity was adequate and that the observed loss of sensitivity using capillary columns was occurring between the column end and the ion source. An acceptable solution was achieved by coupling the gas chromatograph column to the mass spectrometer through the probe flange. This allowed insertion of the column directly into the ion source. Figure 1B is the total ion chromatogram of the aromatic standard showing the resolution and detection of 10 ng of coronene (peak 9). The sacrifice of the direct injection probe of this instrument was not a limitation for us because we have two other instruments with this capability. Performance of the HP 5995. Our unit was received from the manufacturer with capillary column capability. We had only been using the instrument a short time when we determined that we were not able to resolve benzo[e]pyrene and benzo[a]pyrene and compounds that eluted after them were not detected a t all. Of even more concern, the instrument appeared to selectively adsorb some compounds and to chemically modify others. The total ion chromatogram (Figure 2 "before") of a solution of BHT, acridine, pentachlorophenol, and DDT shows only the elution of three of these compounds into the mass spectrometer. The loss of pentachlorophenol (100 ng) was virtually complete (compare peak 12 in Figure
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Anal. Chem. 1982,5 4 , 2390-2392 212
BEFORE
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235
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~,
’
of the problem, and we concluded that the GC/MS isolation valve was. In fact, in an early attempt to solve this problem we dismantled the instrument and cleaned the valve. Afterward, we were able to detect acridine, which had previously been undetectable. Following the modification of the interface region, as described above, the same four-component standard produced the total ion chromatogram shown in Figure 2 “after”. All four compounds were successfully eluted into the mass spectrometer ion source with increased sensitivity and with no chemical alteration (see Figure 3 “after”).
282
237
I65
I = I
R
L
I
m/e Flgure 3. Mass spectra DDT observed before and affer modification of the HP 5995. Only the after spectrum is correct.
2 “before” and “after”). Even real time monitoring of the major chlorine cluster ion of m / e = 264 failed to produce a peak. Even more alarming, the mass spectrum of the last peak (see Figure 3 “before”) was not that of DDT as it should have been. It was, in fact, the combined mass spectra of 1,l’-(dichloroethenylidene)bis[4-chlorobenzene] (mol wt = 316) (mol (DDE) and l,l’-(chloroethylidene)bis[4-chlorobenzene] wt = 282). Since we could obtain a correct mass spectrum of DDT when it was introduced through the direct probe, it appeared that the GC/MS interface device was dehydrochlorinating this compound. Thus, the chemical activity of the interface presented real concerns about the use of this instrument. We suspected that the GC/MS isolation valve was responsible for these losses and compound alteration for three reasons: (a) When the four test compounds were introduced into the mass spectrometer via the direct probe the correct spectra with good sensitivity were obtained. (b) The same incorrect DDT spectrum and total ion chromatogram were obtained using the jet separator and an open-split interface (3). (c) All four of these compounds were correctly detected with the H P 5985B. Both the H P 5985B and H P 5995 had the same type of injector and column. Therefore, the injector, column, and mass spectrometer could not have been the source
CONCLUSIONS We have described our successful modification of H P 5985B, H P 5982, and H P 5995 GC/MS units for direct introduction of fused silica columns in close proximity to the ionizing beam in the ion source of the instrument. For the H P 5985B and H P 5982, the modification increased transmission of compounds with long GC retention times. Not only was sensitivity improved for the H P 5995 but, more importantly, the chemical reactivity and selectivity of the isolation valve were eliminated by its removal. In all three cases, we are confident that our approach was the best available solution. Though the manufacturer’s designed flexibility of use (packed or capillary columns) and ion source vacuum isolation have been sacrificed, these losses have been inconsequential in view of substantial gains in data quality and sensitivity. (Sketches of the hardware modification are available on request to R.A.H.) ACKNOWLEDGMENT We thank the Hewlett-Packard Gorp. for the gift of their 5995 GC/MS system, John Dorsett and the staff of the Chemistry Department Machine Shop for skilled craftsmanship, and Walter E. Reed (of UCLA) for helpful discussions. LITERATURE CITED (1) Watson, J. T.; Blemann, K. Anal. Chem. 1965, 37, 844. (2) Ryhage, R. Anal. Chem. 1964, 36, 759. (3) Kenyon, C. N.; Goodley, P. C. Presented at 29th Conference on Mass Spectrometry and Allied Topics; Minneapolis, MN, May 24-29, 1981.
RECEIVED for review May 21, 1982. Accepted July 23, 1982. The U.S. Department of Energy (Grant No. 80 EV-10449) and the U S . Environmental Protection Agency (Grant No. R808865) supported this work.
Automated System for Solvent Extraction Kinetic Studies Hltoshl Wataral,’ Larry Cunnlngham, and Henry Frelser” Department of Chemistry, University of Arizona, Tucson, Arizona 8572 1
Growing attention to the study of solvent extraction kinetics requires increasingly more convenient apparatus for extraction rate measurements. The apparatus reported previously (1) by our laboratory has given less equivocal data than has been obtained by other methods (2) used for extraction kinetic studies such as Lewis cell (3),falling drop method (4),in-liquid ejection method (5), and the AKUFVE apparatus (6),as a consequence of the highly efficient two-phase mixing necessary for rapid mass transfer between two phases. The apparatus described here is a further significant improvement incorporating continuous monitoring of the rate of extraction and essentially instantaneous data analysis, which are accomPresent address: Department of Chemistry, Faculty of Education, Akita University, Akita, Japan.
plished by introduction of a Teflon phase separator and an on-line minicomputer. A chemical system used to illustrate the efficacy of the automated system is the extraction of Ni(I1) with dithizone (dithiophenylcarbazone), which was studied earlier in this laboratory (7).
EXPERIMENTAL SECTION The schematic diagram of the extraction kinetic apparatus is shown in Figure 1. The extraction vessel is a 200-mL Morton flask fitted with a high speed stirrer (0-20 000 rpm) (Cole-Palmer Instrument Co.) and a Teflon phase separator. Stirrer blades are made of Teflon and the stainless steel stirrer shaft is covered with irradiated polyolefin tubing t o prevent contamination from the underlying stainless steel. The phase separator consists of a bored Teflon cylinder (9 mm 0.d. and 24 mm in length) wrapped with
0003-2700/82/0354-2390$01.25/00 1982 American Chemical Society
