An Inexpensive Sample Holder for Storage and Introduction of Air-Sensitive Organometallic Compounds into a Mass Spectrometer with lnert-Atmosphere Blanketing Louis Messerle, Larry M. Mallis, and Peter J. Hatch University of lowa, lowa City, IA 52242 Mass spectrometry is a powerful tool for the characterization of organic and inorganic compounds. For solid and liquid compounds the mass spectrum is often obtained via introduction of the compound in a glass capillary into a direct inlet probe which may or may not be heated to increase s a m ~ l volatilitv. e The air and moisture sensitivity of solid and liquid orga~ometalliccomplexes has limited~the applicability of mass spectrometry to the characterization of this important class of compounds. The often extreme air sensitivities of oreanometallics have led mass spectrometrists toward a variety of approaches for sample handling, la cement into a direct inlet probe, and introduction into ihe spectrometer ion source. These approaches range from blanketing samples with a stream of inert gas from ruhber tuhing (often a two-person operation on sophisticated spectrometers) t o temporarily enclosing the spectrometer inlet with a polyethylene glove hag and doing repeated, timeconsuming glove-hag purges before sample handling and introduction into the suectrometer can commence. We wish to describefa simple sample holder that provides a rigorous inert gas blanketing of air-sensitive samples without the need for elaborate inert atmosphere enclosures on the spectrometer inlet. In our studies of organotransition metal chemistry of the early transition metal^,^ electronimpact mass spectrometry (EI-MS) is frequently utilized in characterization of these air-sensitive complexes. Faced with the need for both short-term sample storage in air prior to analvsis and the need for rieorous inert gas blanketing glass sample duringsample introduction, we designed holderldelivery apparatus (see figure) that performs both functions while allowing one-person sample handling and introduction. This holder is designed tostore and then deliver a small (0.75- to 2-cm length)glass capillary that contains the sample. Two Teflon stopcocks (2-mm bore) enclose the 25-mm tuhing section in which the capillary resides; Teflon stopcocks are utilized in order to eliminate grease contamination and to prevent sticking of the capillary during its passage through the stopcock. The pressure equalizing arm allows eas flow around the enclosure to the holder's delivew end, wkch consists of a funnel-shaped stand joined via ring seal to aconstricted ti^ ~~-~~~~~~~~ so that the tip can be used . (thickened . to push the capillary farther into the inlet samile cup ot'the direct insertion nn)hej.'l'wo small holes in the s i d e d the tip &ow the blanketing inert gas to purge the funnel area. In actual use the capillary is filled in a glove box or glove bag and placed into the top of the sample holder through the opened top stopcock 1(with bottom stopcock 2 closed). The top stopcock 1 is closed and the holder brought out of the inert atmosphere enclosure; the holder can be placed into a
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screw-cap, wide-mouth jar under inert atmosphere if longer term storage is desired. Before sample introduction into the mass specirometer ion source, flexible rubber tubing connected to an inert gas source is attached to the top tube A and a gentle stream of inert gas is passed through the equalizing arm and bottom funnel for a short time. The holder is placed atop the direct insertion probe sample cup and the bottom stopcock 2 opened, allowing the capillary to fall into the cup; the holder tip can be used to push the capillary firmly into place. The holder is then used as a funnel to blanket the probe CUD area until the probe is inserted into the spectrometer inlet. For very sensitive samples, a purge line is ulaced inw thespectrometer inlet for a short timeand w i t h d k just prior to inserting the probe. A 10-fold increase in signallnoise has been observed using this more rigorous approach to sample handling and introduction when compared to simply placing a sample capillary into the direct insertion probe in air prior tointroduction into the ion source.' The holder is inexpensive, easy to construct, and also useful for enclosing hazardous samples in order to protect the spectrometrist. Acknowledgment
We would like t o acknowledge the support of the US. Department of Energy Pittsburgh Energy Technology Center (DE-FG22-85PC80513, to LM) and the University of Iowa, Office of the Vice President for Educational Research and Development, for partial support of this research. Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research (Grant 17193-G3,to LM). m m OD +Attachment point for Inert Gas (A)
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Mallis. L. M.; Ting. C.; Hammer, M. S.;and Messerle, L. Proceed ings of the 36th Annual Conference on Mass Spectrometryand Allied Topics. San Francisco, CA, June 5-10. 1988: pp 536-537. 2(a)Ting, C.; Messerle, L. J. Am. Chem. Soc. 1987, 109, 65066508. (b)Ting,C.; Baenziger, N. C.: Messerle, L. J. Chem. Soc. Chem. Commun. 1988,1133-1 135. 618
Journal of Chemical Education
l n m - a m p h e r e sample holdec tor mass spectrometry.
