2174
Anal. Chem. 1900. 60. 2174-2176
by the MSD. Thus better than 99.999% of the sample flow may be diverted away from the vacuum chamber. This experiment was repeated, with similar results, after the restrictor line between the open-split fitting and the MSD had been changed, but has not been repeated with a different open-split fitting. Evidence that 100% of the sample passes throught the open-split cross when the divert flow is shut off can be found in the absence of peak broadening, as observed in the discussion on GC resolution, above. The only place that the sample can go, other than to the vacuum chamber, is out the vent line from the cross. If any of the sample were actually diffusing out the vent while makeup gas was flowing in from the vent line, peak broadening would be evident a t the IR or MS detectors. In fact, severe peak tailing has been observed in one situation, in the middle of runs in which the initial GC flow into the open-split cross is greater than the draw to the vacuum chamber. As the GC flow decreases with temperature programming, it becomes equal to the vacuum draw and eventually drops below the vacuum draw. At the beginning of such a run, the net flow from the GC into the open-split fitting and out the vent line adequately flushes all of the lines, and no broadening is observed. As the GC flow decreases, the flow from the cross to the vent tee drops to zero and then reverses direction. The components that pass through the open-split fitting during the several minute period when the vent line flow is reversing show severe tailing. As the GC flow decreases further so that makeup gas flows in from the vent line, the peak tailing disappears. We conclude that as long as there is makeup gas flowing in from the vent port, the sample is quantitatively passed on through to the vacuum chamber. By establishing a flow through the vacuum restrictor slightly greater than the maximum expected GC flow, quantitative sample delivery and zero peak broadening may be maintained throughout the GC run. Other Features and Limitations. Although this interface has been designed to minimize active sites and dead volumes, GC peak broadening or adsorption still might occur in the open-split fitting where the sample crosses the gap between the inlet and vacuum-restrictor fused silica tubes. The distance between these two tips is about 0.25 mm, and the walls surrounding this area are stainless steel. During operation, the entire carrier gas stream crosses this gap. Both the purge stream and the makeup gas stream enter the gap from right angles to the sample stream and join the sample stream as it flows down the restrictor tube to the vacuum chamber. These two auxiliary streams serve to buffer the sample from the metal surrounding the gap. Although no extremely rigorous experiment has been performed to detect minute effects from active metal, no broadening or tailing attributable to this intersection has been observed from the many GC runs that
we have performed on Grob and other column test mixtures passing through these interfaces. The purge and makeup streams provide a convenient means to introduce auxiliary material into the sample stream, downstream of the GC column. I t is customary in matrixisolation GC/IR work to mix the matrix gas (usually argon, a t a concentration of 1-2%) into the GC carrier gas supply. However, with combined GC/IR/MS, it is undesirable to have argon in the carrier gas, since it interferes with the mass spectrometer operation. In this case, we meter the argon flow into the matrix-isolation system through the makeup line to the IR open-split fitting. Other materials, such as MS calibration standards, could easily be introduced in a similar manner. We have observed two minor undesirable features of this interface. One, discussed above, is the peak tailing that can occur if the flow in the vent line is allowed to reverse directions during a temperature-programmed GC run. The second, characteristic of all open-split interfaces used to divert solvent peaks, is a small shift in retention times and split ratio when the sample is being diverted, relative to a run in which the sample is not diverted. The pressure at the open-split fitting is affected by the rate of flow of gas from the fitting out the vent line. This flow rate, and thus the pressure a t the open-split intersection, increases when the divert flow is turned on. This decreases the total effective pressure drop across the GC column and thus increases the retention times. In addition, the relative pressure drop across the two arms of the splitter changes, causing the split ratio to change in going from pass through to divert mode. These changes are usually minor and reproducible, with the retention times typically increasing from 1 to 15 s over the course of a totally diverted run relative to a totally nondiverted run. These effects can be minimized by constructing the vent line with the lowest restriction consistent with maintaining a good purge (typically 0.5 mm internal diameter vent lines will serve well) and using the lowest effective divert flow rate.
LITERATURE CITED Henneberg, K.; Henrichs. U.; Schomburg, G. J. Chromatogr. 1975. 112, 343. Henneberg, K.; Henrichs, U.; Schomburg, G. Chromatographia 1975, 8 , 449. Stan, HansJurgen: Abraham, Bernd Anal. Chem. 1978, 50, 2161-2 164. Hurley, Rupert B., Jr. HRC C C , J . High Resolut. Chrometogr. Chromatogr. Commun. 1980, 3 , 147-148. Jordan, S. W.; Karger, B. L.; Kruil, I. S. Chem., Biomed. Environ. Instrum. 1982, 12, 263-274. Arrendale, R. F.; Severson. R. F.; Chortyk, 0. T. Anal. Chem. 1984, 56, 1533-1537. Bourne, Sdney; Reedy, Gerald T.; Coffey, Patrick J.; Mattson, David R. Am. Lab. (Fairfield, Conn.) 1984, 16, 90-101.
RECEIVED for review May 9, 1988. Accepted June 13, 1988.
Hollow-Drill Mass Spectrometric Technique for Determination of Volatile Compounds Trapped in Solid Matrices G . J. Kallos* and J. C. Tou Analytical Sciences, The Dow Chemical Company, Midland, Michigan 48667 The sampling and identification of gas content in bubbles and/or blisters in polymers or metals by mass spectrometry have been quite challenging for many years. Over a period of many years, different approaches have been implemented in our laboratory to accommodate these types of problems. Polymer samples containing bubbles would be evacuated in
a special container and then crushed or melted to release the volatiles into the mass spectrometer. Also, bubbles would be loaded in the mass spectrometer through the batch inlet system developed by Caldecourt ( I ) to introduce the sample into a heated reservoir system up to 200 "C without breaking vacuum. In recent years Grayson et al. (2) have reported on
0003-2700/88/0360-2174$01.50/00 1988 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 60, NO. 19, OCTOBER 1, 1988 Drill Press
000
-
2175
2024
4
SINGLE ION CHROMATOGRAM ml2 18
^^
.
2255
t - t I
Regular MS or API MS
Fused silica capillary (100 microns I D )
Iib
R'C
t
t
mu
2000 7 19
'
t1
ION CHROMATOGRAM
I
I
1
I
i
I
2050 7 30
2100
2150 7 12
2200 B 03
2250
2300 8 21
741
8 14
Total ion and single ion chromatograms of drilled epoxy resin. The arrows denote the time of drill penetration into the bubbles. Flgure 2.
Drill 1/8 Bit "
s-
Hole through Drill Blt 0.012''
,,-
Bubbles in Plastic
1000
r
28
-
I
"12
I
28
I
I
225
Figure 1.
EXPERIMENTAL SECTION A diagram of the drill device is shown in Figure 1. A 'j8-in. X 12.5-cm oil hole drill (Hayden Twist Drill Sales, Co., Inc., Warren, MI) is inserted through a lj8-in. stainless steel tee that was fabricated to contain two Viton O-rings ('18 X X lj16in.) compressed with metal ferrules to form a seal. The tee was machined to include a flat surface to accommodate the O-rings. Packing ferrules were fabricated to compress the O-ring in the modified fitting. The two longitudinal holes through the drill bit are 0.012 in. in diameter. The openings of the end connecting to the drill press were sealed with Dow Corning RTV silastic sealant. A 0.010-in. hole was bored with an electric discharge machine (EDM) approximately 3.5 in. from the top so that it would connect to the holes of the drill bit. A 4 ft, 100 pm i.d. fused silica capillary was inserted at one end through a special drilled Teflon plug in the tee and the other end was connected
I
mlz 32
I-
Schematic diagram of drilling device.
precision abrasion mass spectrometry where samples are precisely abraded inside the ion source housing and mass analyzed. The qualitative and quantitative distribution of the volatile compounds trapped in a polymeric material could be measured. However, the complexity, alignment of the system inside the ion source, and availability of instrumentation may pose some problems for wide applications. We have developed a practical sampling technique based on drilling the sample outside the mass spectrometer. The evolved gas is sampled immediately into the ion source via a 100-pm fused silica capillary for detection. By use of appropriate drill speeds and sample handling techniques, either qualitative or depth profile of the trapped volatile compounds in the matrix of the polymeric material can be determined. Soft polymer samples may be penetrated with a syringe needle for sampling directly into the mass spectrometer but hard polymers or metals require a mechanical drill. This technique was found to be practical in the identification of volatile components in polymeric and metallic materials and is also expected to provide useful information on the profiling of indigenous volatile compounds in a polymer matrix.
r
1
1
1325
-
RIC
-
TOTAL ION CHROMATOGRAM
200 110
Figure 3. Total ion and
film.
400
2 20
600 3 30
800 L 40
000 5 50
single ion chromatograms of a drilled composite
to the ion source via a hollow solids direct probe. The drill bit is connected to a bench top drill press Model SP-30 (Sterling Industrial Machines) that had been modified to accommodate a speed control Model MM-1 (Lourdes)to provide various speeds of operations. A Finnigan-MAT (San Jose, CA) Model 4500 quadrupole mass spectrometer with an Incos data system was used in this study. In a normal operation the drill bit may be moved up or down through the tee for approximately 1.5 cm distance between the two O-rings. The preferred mode of operation is that the tee move vertically with the drill bit without rotating. This mode of operation eliminates the chance of creating any leaks through the Viton O-ring seals. The pressure in the ion source is controlled with the length of the fused silica capillary so that electron impact conditions are maintained during the experiment. Several compounds tested through this inlet were found to respond in the mass spectrometer at
