Anal. Chem. 19a2. 54, 338-339
338
Flgure 4. Flekl desorptlon mass spectrum of 2deoxyguanosine loaded onto the FD emltter wlre by electrospray in rnethanokwater (8:2).
loss of methanol, and loss of water are not observed if the sample is heated above room temperature during the loading process. Figure 4 is the field desorption mass spectrum of 2deoxyguanosine which was loaded on the FD emitter by electrospray. In addition to the molecular and cationized species at m / z 268, 290, and 306, strong ion currents were observed at masses corresponding to dimerized species: 2M H+, 2M Na+, and 2M K+.Considering the difficulties that can be encountered in obtaining the FD spectra of this compound, the electrospray procedure does not damage the FD emitter needles. The exact origin of the ions at m / z 441 and 373 is currently unknown.
+
+
+
CONCLUSIONS The method of electrospray loading of DCI probes and FD emitter wires has been demonstrated to be a useful technique for highly efficient transfer of sample. The electrospray apparatus is extremely simple to construct and operate. Elec-
trospray is a rapid and gentle technique which causes no damage to the very delicate carbon microneedles of the high temperature activated FD wires. Furthermore, the surface which is exposed to the electrospray plume corresponds to the surface juxtaposed to the extractor plate in the FD ion source and from which ions are desorbed. Thermally sensitive and easily oxidized samples can be loaded with this technique making this approach readily applicable to the analysis of most biological molecules by DCI and FD mass spectrometry.
ACKNOWLEDGMENT The authors thank J. Rokach, Merck Frosst Laboratories for the synthetic methyl ester of leukotriene A4. LITERATURE CITED (1) Reynolds, W. D. Anal. Chem. 1979, 51, 283 A-293 A. (2) Cotter, R. J. Anal. Chem. 1979, 51, 1589 A-1606 A. (3) Beckey, H. D. Int. J . Mass Spectrom. Ion Phys. 1969, 2 , 500-503. (4) Beckey, H. D. Hendrichs, A,; Wlnkler, H. Int. J. Mass Spectrom. Ion Phys. 1970, 3, App. 9. (5) Olson, K. L.; Cook, J. C.; Rinehart, K. L. Biomed. Mass Spectrom. 1974, 7 , 358-362. (8) McNeal, C. J.; Macfarlane, R. D.; Thurston, E. L. Anal. Chem. 1979, 57,2036-2039.
RECEIVED for review August 25,1981. Accepted October 26, 1981. This work was supported through grants from the National Institues of Health (HL25785 and RR001152). Presented in part at the Annual Conference of the American Society for Mass Spectrometry, Minneapolis, MN, 1981.
Demountable Holder for Modlfied Electrodes Brigitte Bolsseiler-Cocollos, Etlenne Lavlron,* and Roger Gullard" Laboratoire de Synthke et d'Electrosynth8se Organom6talllque assocl6 au C.N.R.S., LA 33, 6, Boulevard Gabriel, 21 100 Djion, France
Redox modified electrodes have recently been the object of much interest (1-4).Use of these electrodes for examining catalysis or charge transfer reactions requires durable attachment of the molecules containing the redox centers to the surface of the electrode. One of the best means of achieving this result consists in creating functional groups on the surface of an electrode and in using them to form a covalent bond with the molecules via an appropriate reaction (5-26). In some of the procedures which have been described for the functionalization (5-16), the electrode is subjected to rather drastic conditions (for example, in the case of carbon electrode, oxidation by O2a t 450 "C (5-12)) or plasma etching (7, 14), followed by reaction with SOClzin boiling toluene). Ordinary disk electrodes in which a cylinder of the electrode material is set in a tubing of a nonconducting material (glass, Teflon, -) do not withstand such treatments. This difficulty can be circumvented by treating a piece (usually a rod or a disk) of the material alone and by inserting it afterward into an appropriate holder. Murray et al. have used for example a heat shrinkable Teflon tubing to protect the cylindrical part of the carbon rod from the solution (7, 8, 9, 10, 13). We describe here an electrode holder which allows a rod of the electrode material to be mounted or demounted rapidly and which we think can be of service to electrochemists working in this field. It can also eventually be used as a rotating disk electrode. Holders of a different conception, in which carbon disks (11, 27) or cones (28) can be mounted have been described. EXPERIMENTAL SECTION Materials. The glassy carbon V25 was obtained from "Carbone Lorraine" (Paris, France) in the form of cylindrical rods which 0003-2700/82/0354-0338$01.25/0
were cut into pieces 4-5 mm in length. The poly(tetrafluor0ethylene) (PTFE) Gaflon was provided by Plastic Omnium (Sirem Division, Langres, France). Tetrakis (p-aminophenyl)porphyrin, TpNH2PPH2,was prepared by reduction of tetrakisb-nitropheny1)porphyrin according to the procedure described by Collman et al. (29) for the preparation of tetrakis(rn-aminopheny1)porphyrin. Dimethyl sulfoxide was freshly distilled under argon on active alumina. Tetraethylammoniumperchlorate was dried in vacuo in the presence of PzOs. Apparatus. Current-potential curves were obtained by means of a commercial potentiostat (Tawse1PRT 30-0.1,Lyon, France) and recorded on an XY recorder (SeframTGM 101,Paris, France). A one-compartment cell was employed with a platinum wire auxiliary electrode. The saturated calomel reference electrode was separated from the main cell compartment by immersion in a glass tube terminated by sintered glass frit.
RESULTS AND DISCUSSION The holder, which consists of four parts in PTFE, is shown unassembled and assembled in Figure 1. The rod electrode is inserted from above part A into the cylindrical part (a) where it fits exactly. This ensures in particular that the modified part, which will be exposed to the solution, is not handled during this procedure. Part B is then screwed on part A, which, owing to its conical shape, ensures that a tight contact is made between the rod and the holder. A glass or a stainless steel tubing is then inserted in the upper part of the holder. Air tightness is provided by the biconical joint C, by screwing part D on the top of part A; this ensures in particular that oxygen which is present inside the holder (in F) cannot leak into the electrochemical cell. With, e.g., a carbon or a platinum electrode, electrical contact can be made 0 1982 Amerlcan Chemlcal Soclety
Anal. Chem. 1982, 5 4 , 339-340 -6.2-
DID
-! -.I
:---m 1
Figure 1. Cross sectlonal view of assembled and unassembled disk
electrode (all Indicated dimensions are In millimeters): (a) cyllndrical hole for rod electrode, (A) PTFE sleeve, (6,D) PTFE screws, (C) biconical joint, (E) glass or stainless steel tubing, (F) holder inside.
339
times without noting any deterioration. The carbon rod must be inserted carefully and smoothly in part (a) (Figure 1)in order to avoid damaging it. Tightness is ensured only by the slight pressure exerted by part B. In order to test its possibilities, we have repeated the experiments of Murray et al. (7-10).Carefully polished glass carbon rods were treated at 450 "C in an oxygen atmosphere and next refluxed in 5% SOClzin toluene. TpNHzPPHzwas then attached to the surface by following exactly the procedure given by Murray et al. (7-10).An example of voltammograms is shown in Figure 2. They present the same characteristics as those given by these authors (Figure 1, ref 8). ACKNOWLEDGMENT The authors thank Marcel Bartocci (Plastic Omnium, Departement Gaflon, Usine Sirem, 52200 Langres, France) for his help in conceiving and constructing the electrode holder. LITERATURE CITED ( I ) Snell, K. D.; Keenan, A. G. Chem. SOC. Rev. 1079, 8 , 259-282. (2) Murray, R. W. Acc. Chem. Res. 1980, 13, 135-141. (3) Heineman, W. R.; Kissinger, P. T. Anal. Chem. 1978, 50, 166R173R. (4) Heineman, W. R.; Kissinger, P. T. Anal. Chem. 1080, 52, 138R. (5) Watkins, B. F.; Behling, J. R.; Kariv, E.; Miller, L. L. J . Am. Chem. SOC. 1075, 97, 3549-3550. (6) Firth, B. E.; Miller, L. L.; Mkani, M.; Rogers, T.; Lennox, J. C.; Murray, R. W. J . Am. Chem. Soc.1078, 08, 8271-8272. (7) Lennox, J. C.; Murray, R. W. J . Hectroanal. Chem. 1077, 78, 395-401, (8) Lennox, J. C.; Murray, R. W. J . Am. Chem. SOC. 1078, 100, 37 10-37 14. (9) Rocklin, R. D.; Murray, R. W. J . Nectroanal. Chem. 1970, 100, 271-282. ( I O ) Jester, C. P.; Rocklin, R. D.; Murray, R. W. J . Electrochem. SOC. 1080, 727, 1979-1985. (11) Koval, C. A.; Anson, F. C. Anal. Chem. 1078, 50, 223-229. (12) Elliott, C. M.; Marrese, C. A. J . Electroanal. Chem. 1081, 179, 395-401. (13) Elliott, C. M.; Murray, R. W. Anal. Chem. 1076, 48, 1247-1254. (14) Evans, J. F.; Kuwana, T. Anal. Chem. 1977, 49, 1632-1635. (15) Evans, J. F.; Kuwana, T.; Henne, M. T.; Royer, G. P. J . Electfoanal. Chem. 1077, 80, 409-416. (16) Willman, K. W.; Rockiin, R. D.; Nowak, R.; Kuo, K.-N.; Schuhz, F. A.; Murray, R. W. J . Am. Chem. SOC.1080, 102, 7629-7634. (17) Burt, R. J.; Leigh, G. J.; Pickett, C. J. J . Chem. SOC.,Chem. Commun 1076, 940-941. (18) Armstrong, N. R.; Lin, A. W. C.; Fujihira, M.; Kuwana T. Anal. Chem. 1078, 48, 741-750. (19) Moses, P. R.; Murray, R. W. J . €lectroanal. Chem. 1077, 77, 393-399 and references therein. (20) Untereker, D. F.; Lennox, J. C.; Wier, L. M.; Moses, P. R.; Murray, R. W. J . Electroanal. Chem. 1077. 81. 309-318. (21) Lenhard, J. R.; Murray, R. W. J . Am. Chem. SOC. 1078, 100, 7870-7875. (22) Abruna, H. D.; Walsh, J. L.; Meyer, T. J.; Murray, R. W. J . Am. Chem. SOC. 1080, 102, 3272-3274. (23) Sharp, M.; Petersson, M.; Edstrbm, K. J . Electroanal. Chem. 1970, 95, 123-130. (24) Armstrona, N. R.; SheDhard. V. R.. Jr. J . Hectroanal. Chem. 1080. . 175, 2531265. (25) Fujihara, M.; Matsue, T.; Osa, T. Chem. Lett. 1978, 875-880. (26) Fujihara, M.; Kubota, T.; Osa,T. J . Electroanal. Chem. 1981. 119. 379-387. - . - - -. . (27) Geiger, T.; Anson, F. C. Anal. Chem. 1080, 52, 2448-2450. (28) Harrington, G. W.; Lahlnen, H. A.; Trendafllov, V. Anal. Chem. 1073, 45,433-434. (29) Collman, J. P.; Gagne, R. R.; Reed, C. A.; Halbert, T. R.; Land, G.; Robinson, W. 7. J . Am. Chem. SOC. 1075, 97, 1427-1439.
.
flgure 2. Cyclic voltammetry of attached TpNH2PPH2 in dimethyl sulfoxide solvent with 0.1 M tetraethylammonium perchlorate. Sweep rate was 100 mvas-'.
by means of mercury and an iron wire; with other metals, it can be made directly with a metallic wire. This holder can be constructed easily and cheaply, and allows the electrode to be rapidly mounted and demounted. It gives very reproducible results. It is also very durable; we mounted and demounted the system at least several hundred
RECEIVED for review June 30, 1981. Accepted October 26, 1981.
Modlfication of Flanging Tool Used with Teflon Tubing Robert E. Barron Ames Laboratory and Department of Chemistry, Iowa State lJniversi@, Ames, Iowa 5001 1
When Teflon or polypropylene tubing is used for flowing stream applications,a small, circular flange is usually formed on the end of the tubing so that connections to fittings may 0003-2700/82/0354-0339$01.25/0
be made. Several companies market a resistively heated device for introducing a flange at the tubing end. The device consists of a tapered flanging tip whose shank is inserted in the core 0 1982 American Chemical Soclety
