Anal. 0. 1988, 60, 191-192
pensive Wollaston wire-a single 2-cm length of Wollaston wire frequently can be used to produce several microelectrodes by our fabrication technique (vide supra). A higher success rate also means a savings in time. In addition, we found that the steps leading to the point where it can be determined if the electrode will be functional are simpler and less time consuming compared to other methods. Another advantage is the ruggedness of our electrodes. Due to sealing of the cylinder in glass tubing (Figure 2C), the insulating glass surrounding the electrode tip is much thicker than in previously described microelectrodes. It is also worth noting that the electrical connection of the platinum microwire is via a mercury pool and does not depend on a solder connection to another (thicker) wire.
ACKNOWLEDGMENT We are grateful to M. Sosnowski of the Physics Department, Brown University, for obtaining the scanning electron micrographs. C.D.B. is grateful to Providence College for granting a sabbatical leave (1986-1987). Registry No. Pt, 7440-06-4; Hg, 7439-97-6; Fe(0EP) (NMeIm)z+,60151-09-9;HN03, 7697-37-2. LITERATURE CITED (1) Bond, A. M.; Fleischmann, M.; Robinson, J. J. Nectroanal. Chem. Interfacial Electrochem. 1984, 168, 299.
(2) Flelschmann, M.; Lasserre, F.; Robinson, J.; Swan, D. J. Necfroanal. Chem. Inferfaclal Electrochem. 1984, 177, 97.
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Cassldy, J.; Khoo, S. B.; Pons, S.;Flelschmann, M. J. fhys. Chem. 1985, 8 9 , 3933. Blxler, J. W.; Bond, A. M.; Lay, P. A.; Thormann, W.; van den Bosch, P.; Flelschmann, M.; Pons, B. S. Anal. Chim. Act8 1988, 187, 67. Dibble, T.; Bandyopadhyay, S.;Ghoroghchlan, J.; Smith, J. J.; Sarfara21, F.; Fleischmann, M.; Pons, S. J. fhys. Chem. 1888, 9 0 , 5275. Montenegro, M. I.; Pletcher, D. J . Electroanal. Chem. Interfacial Nectrochem. 1986, 200, 371. Feidman, B. J.; Ewing, A. G.; Murray, R. W. J. Necfroanal. Chem. Interfacial Electrochem. 1985, 194, 63. Ewing, A. G.; Fekiman, E. J.; Murray, R. W. J. fhys. Chem. 1965, 69, 1263. a n g , L.; Ewlng, A. G.: Jernlgan, J. C.; Murray, R. W. Anal. Chem. lB86, 58, 8521 Geng, L.; Reed, R. A,; Longmire, M.; Murray, R. W. J. fhys. Chem. 1987., 91. 2908. . -. .. Howell, J. 0.; Wlghtrnan, R. M. Anal. Chem. 1984, 56, 524. Wehmeyer, K. R.; Wightman, R. M. Anal. Chem. 1985, 57, 1989. Scharifker, B.; Hills, G. J. Nectroanal. Chem. Interfacial Nectrochem. 1981, 130, 81. Aoki, K.; Aklmoto, K.; Tokuda, K.; Matsuda, H.; Osteryoung, J. J. Nectroanal. Chem. Interfacial Electrochem. 1984, 171, 219. Fitch, A.; Evans, D. H. J. Elecfroanal. Chem. Interfacial Electrochem. 1986, 202, 83. O'Brien. P.; Sweigart, D. A. J. Chem. SOC., Chem. Commun. 1986, 198. Bond, A. M.; Swelgart, D. A. Inorg. Chim. Acta 1986, 723, 167. Stone, N. J.; Swelgart, D. A.; Bond, A. M. Organometallics 1986, 5, 2553.
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RECEIVED for review August 7,1987. Accepted September 14, 1987. This work was supported by grants to D.A.S. from the National Institutes of Health (DK30145) and the National Science Foundation D*A*S.is the recipient of a NIH Research Career Development Award (1983-1988).
Automated Cryogenic Collection of Carbon Dioxide for Stable Isotope Analysis and Carbon-14 Accelerator Mass Spectrometry Dating C. A. M. Brenninkmeijer
Institute of Nuclear Sciences, Department of Scientific and Industrial Research, Private Bag, Lower Hutt, New Zealand Manipulation of gases and vapors is often done in glass vacuum systems. The incompatibility of glass systems with the recent demand for laboratory automation has been a major drawback. With the development of a pneumatically operated glass high-vacuum valve (1)this problem was largely overcome. Thus by using automated glass valves, and an automated variable temperature cold trap (2), a process like converting organic matter to Hz for 2H mass spectrometric analysis could be automated (3). The more recent invention of a va:uumpowered high-vacuum glass valve (4)not only offers an elegant alternative to the pneumatic high-vacuum glass valve, but in addition makes it possible to fit gas sample bottles with automated taps. This allows automated gas collection in glass bottles (5). In order to quantitatively collect COz in a gas sample bottle, the bottle is commonly immersed in liquid nitrogen. This step can be automated by placing a Dewar with liquid nitrogen on a motorized labjack. Yet, when a larger number of sample bottles is involved this procedure becomes impracticable. Such an instance arose when we had to recover COz samples after mass spectrometric 13Canalysis in order to perform 14CTAMS (tandem accelerator mass spectrometry). A sample bottle as depicted in Figure 1 can be used successfully for automated COz collection. It consists of a mass spectrometer sample bottle fitted with a 5-mm-bore Vacutap. Vacutaps are vacuum operated, seatless, 0-ring-type, highvacuum glass valves. (Vacutaps are manufactured by Louwers Hapert, 5527 ZG Hapert, The Netherlands.) Inside the bottle is a tube through which liquid nitrogen can be passed. By reducing the pressure a t the exhaust tube, liquid nitrogen is
drawn into this tube and a small quantity is collected in the bottom. Sufficient liquid nitrogen can be collected to last for several minutes, thus allowing COz to be frozen into the bottle. Although the principle is simple, the procedure had to be optimised and its limitations established. With the bottle shown, and by using a 1-m-long plastic filling tube of 1.6-mm bore (urethane tubing X 1/16 in.) while pumping the exhaust at a rate of roughly 30 L/min, the tube can be filled with 1.7 cm3 of liquid nitrogen, up to level A indicated in Figure 1,in less than 1min. This amount of nitrogen will last for 6 min. in an evacuated tube. If COz is present, this will form an insulating and reflective layer around the liquid nitrogen, stretching this time to about 12 min. Not much condensation of water vapor on the outside of the bottle occurs and the condensation of COz can be observed. It appears that the height difference between the bottle and the liquid nitrogen supply has no significant effect on the performance. However, increasing the length of the filling tube rapidly increases the time it takes to collect the nitrogen. The reason is that boiling of liquid nitrogen in the filling tube creates so much nitrogen gas that the pressure drop is insufficient. The use of a larger diameter filling tube does not necessarily improve this situation, and often merely cold nitrogen gas was sucked through the assembly. Therefore, for bridging larger distances, a thermally insulated tube with a bore diameter of 3 mm or more is recommended. Two laboratory compressors have been used during experiments. A Thomas Model 917CD18 (34 L/min) was satisfactory, whereas Model 004CD33 (12 L/min) did not always provide enough suction.
0003-2700/88/0360-0191$01.50/00 1988 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 60, NO. 2, JANUARY 15, 1988
5rnm Vacutao
exhaust
inlet
Figure 1. Vacutap sample bottle with cooling insert. The inlet tube diameter was about 1 mm. The inlet tube points slightly downward on the inside. The exhaust tube diameter was 5 mm. The cooling tube diameter was 10 mm.
As mentioned above, the cooling time was less than 1 min. For automating the procedure, suction can be applied for a fixed period of 1-1.5 min. After the tube is filled with liquid nitrogen up to level A, a mixture of gas and liquid flows from the inlet tube straight into the exhaust tube. When pumping is interrupted, no liquid remains above level A. Further suction only causes unnecessary loss of liquid nitrogen but eventually the pump may be damaged by embrittlement of interior parts. After completing a sample freeze-back it takes
about 1 min for the filling tube and the plastic tube connected to the exhaust to warm up sufficiently to be detached from the sample bottle. For testing the freeze-back procedure we used a Vacutap freeze-back bottle on our automated Nuclide stable isotope mass spectrometer. One sample of I O cm3 COz gas was analysed and frozen back automatically for 28 times. The spread in 613C (la)was 0.02%0,and no systematic change in isotopic ratio could be detected. The loss of COP,primarily due to pumping of the sample after freezing back, amounted to 3%, equivalent to 0.1% /cycle. The cause of this loss of COzis that part of the C 0 2 is condensed near level A indicated in the figure. As the system is pumped some COz escaping from this position due to a lowering of the liquid nitrogen level is pumped away instead of condensing on the lower part. If this is considered undesirable, some additional liquid nitrogen can be drawn into the tube during pumping. The consumption of liquid nitrogen was 30 cm3/cycle. The bottle described also can be used to automatically collect condensable gases such as COz and SO2 from preparation systems. Another useful application can be achieved by constructing U-shaped sample bottles with two Vacutaps and a cooling insert. Such sample bottles can be used to automatically trap the condensables from the effluent gas of gas chromatographs. Registry No. COz, 124-38-9.
LITERATURE CITED (1) Brenninkmeijer, C. A. M. I n t . J . Appl. Radlat. h o t . 1981, 32, 679-680. (2) Brennlnkmeijer, C. A. M. Anal. Chem. 1882, 54, 2622. (3) Brenninkmeijer, C. A. M. Thesis, Unlverslty of Groningen, The Netherlands, 1983. (4) Brennlnkmeijer, C. A. M.; Louwers, M. C. Anal. Chem. 1885, 57, 960. (5) Brenninkmeijer, C. A. M.; Morrison, P. D. Isot. Geosc. 1987, in press.
RECEIVED for review July 15,1987. Accepted September 14, 1987.
CORRECTION Ion-Pair Chromatographic Determination of Anions Using an Ultraviolet-AbsorbingCo-Ion in the Mobile Phase Brian A. Bidlingmeyer, Carmen T. Santasania, and F. Vincent Warren, Jr. (Anal. Chem. 1987,59, 1843-1849). In the Results and Discussion section, the first two sentences of the second paragraph should read as follows: The conductometric monitoring of the separation shown in Figure 1B is similar to one previously reported that used a “dynamically coated” reversed-phase column with a tetramethylammonium salicylate (TMA-SAL) eluent (33). In that work cetylpyridinium chloride was used to “coat” the bonded phase column prior to using the low conductivity, aqueous eluent of 0.5 mM TMA-SAL at pH 6.3. The following reference corrections should also be noted: (3)Dreux, M.; LaFosse, M.; Pequignot, M. Chromatographia 1982,15, 653. (15) Vera-Avila, L. E.; Caude, M.; Rosset, R. Analusis 1982, 10, 36. (33) Cassidy, R. M.; Elchuk, S. J. Chromatogr. 1983,262, 311.
