ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979
(42) K. Danzer, Z . Cbem., 13, 69 (1973). (43) K . Danzer, Z . Cbem., 13,229 (1973). (44) K . Danzer. Z . Cbem.. 14. 73 (1974). i45j K. Danzer: Z . Cbem.; 15, 158 (1975). (46) K. Danzer, Z . Chem., 15, 326 (1975). (47) K. Danzer, Z . Chem., 18, 104 (1978). (48)D. L. Massart, J. Chromatogr., 79, 157 (1973). (49) J. T. Clerc, R. Kaiser, J. Rendl. H. Spitzy, J. Zettler, G. Gottschalk, H.
Malissa, E. Schwartz-Bergkamp, and R. Werder, Fresenius' Z . Anal. Cbem., 272, 1 (1974). (50) D. L. Massart and R. Smits, Anal. Cbem., 46, 283 (1974). (51) . . R. Smits. C. Vanroeten. and D. L. Massart, Fresenius' 2. Anal. Chem., 273, (1975). (52) F. Dupuis and A. Dijkstra, Anal. Cbem., 47, 379 (1975). (53) St. Grys, Fresenius' Z . Anal. Cbem., 273, 177 (1975). (54) A. Eskes, F. Dupuis, A. Dijkstra, H. De Clercq, and D. Massart, Anal. Cbem., 47, 2168 (1975). 155) J. J. Fitzaeraid and J. D. Winefordner. Rev. Anal. Cbem.. 2. 300 (1975). i56j E Palm,-Fresen,us Z Anal Cbem , 256, 25 (1975) (57) G Ehrlich, Cbem Anal (Warsaw), 21, 303 (1976)
1995
(58) G. van Marlen and A. Dijkstra, Anal. Cbem., 48, 595 (1976). (59)G.L. Ritter, S. R. Lowry, H. B. Woodruff, and T. L. Isenhour, Anal. Chern., 48, 1027 (1976). (60) Yu. I. Belyaev and T. A. Koveshnikova, Zhur. Anal. Kbim., 27, 429 (1972). (61)T. Michalowski, A. Parczewski, and A. Rokosz, Chem. Anal. (Warsaw), 21, 979 (1976). (62) D. L. Massart, H. De Clercq, and R. Smits, "Reviews on Analytical Chemisry", Euroanalysis Conference 11, August 1975,Budapest, Akad6miai Kiado, Budapest, 1977. (63) C. Liteanu and I. Rk5, "Statistical Theory and Methodology of Trace Analysis", E. Horwood, Chichester, 1979,Chap. 3. (64) G. E. P. Box and K. B. Wilson, J . R. Stat. Soc. Ser. R.,13, l(1951). (65)G. E. P. Box, Biometrics, I O , 16 (1954). (66) W . Spendiey, G. R. Hext, and F. R. Himsworth, Technometrlcs, 4, 441 (1962). (67)J. A. Nelder and R. Mead, Comput. J., 7, 308 (1965).
RECEIVED for review November 7 , 1978. Resubmitted March 23, 1979. Accepted June 6, 1979.
Solvent Solubilization, Characterization, and Quantitation of Aliphatic Carboxylic Acids in Oil Shale Retort Water Following Chemical Derivatization with Boron Trifluoride in Methanol Robert G. Riley," Kazumi Shiosaki, Roger M. Bean, and Donald M. Schoengold Pacific Northwest Laboratory, Richland, Washington 99352
Boron trifluoride in methanol (BF,/MeOH) is an excellent reagent for transforming organic solvent insoluble components of oil shale retort water into derivatives which are easier to characterize and quantitate by classical analytical techniques. Treatment of a sample of freeze-dried retort water from the Paraho Oil Shale Demonstration Project (Rifle, Colo.) with BF,/MeOH converted 28% of the organic carbon in the sample to a benzene soluble form. Capillary gas chromatographic/ mass spectrometric analysis of the benzene extract revealed the presence of homologous series of aliphatic monocarboxylic and dlcarboxylic acids at concentratlons ranging from 3.2 to 138.4 ppm, based on original retort water. These results suggest that this technique in combination with other derivatization techniques can be used to characterize and quantitate water soluble classes of organic components of aqueous process wastes and other environmental samples.
Production of oil from oil shale using presently available above-ground retorting technology will result in the production of wastes requiring ground disposal ( I ) . Major wastes produced include retorted shale and water which arises from pyrolysis of the kerogen, release of free and inorganically bound water, and combustion of organic material. Some of this water condenses with the oil and partially separates during storage. Preliminary investigations have indicated that a large percentage of the organic components comprising this retort water are polar and hydrophilic, since they are poorly extracted from water-immiscible organic solvents (2). This is despite the fact that studies have shown the organic carbon content of some retort waters t o be as high as 4.2% (2, 3 ) . Shale oil, unlike crude petroleum, contains greater amounts of complex mixtures or orgnnonitrogen, organosulfur, and organooxygen compounds. 0003-2700/79/0351-1995$01.~0/0
There is thus a need for development of new analytical techniques t o characterize the intractable compounds comprising retort waters. Examination of those compounds in shale oils that could be soluble in aqueous solution has given insight into the nature of the types of compounds to be found in retort water. Such compound classes include phenols, acids, and amines (4-6). Previous studies directed toward the chemical characterization of compound classes in retort waters include analysis of volatile carboxylic acids by gas chromatography ( 4 , 7 , 81, analysis of water soluble components by high pressure gel permeation chromatography (9) and reverse-phase liquid chromatography (IO). We have been working to develop chemical methods which transform water soluble organic compounds of retort waters into chemical forms which are easier to characterize and quantitate by classical analytical techniques. In this study we report on the action of boron trifluoride in methanol IBF3/MeOH) on the freeze-dried retort water obtained from operation of a n above-ground retort.
EXPERIMENTAL Chemicals and Reagents. Distilled in glass hexane, benzene, carbon tetrachloride, and methanol (Burdick and Jackson) were used throughout these studies. The derivatization reactions were conducted using BF3/MeOH (14% w/v, Alltech Associates). Phosphorus pentoxide (P20J was obtained from J. T. Baker Co. and potassium bromide (KBr) for IR analysis was obtained from Harshaw Chemical Co. 14C-methanol (58 mCi/nimol) was obtained from Amersham Searle Co. Samples were screened for radioactivity using phase combining solution (PCS) obtained from the same company. Standardization of the organic carbon analyzer was conducted using potassium hydrogen phthalate obtained from Matheson, Coleman and Bell. Mono- and dicarboxylic acid methyl ester standards were obtained from Analabs and Chem Services Corp. Preservation a n d Preparation of Samples. Retort water was obtained from the Paraho Oil Shale Demonstration Project, operated by Development Engineering Incorporated, near Rifle, C 1979 American Chemical Society
1996
ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979
Colo. The retort was being operated in the direct mode at the time the retort water was produced, i.e., retort gases recycled to the retort and combustion of a portion of the carbonaceous fraction provided the heat for the process. The untreated retort water exhibited a pH of 8.60. Prior to use, it was filtered through a glass wool and a 0.45-pm millipore filter. Filtered samples were stored in capped bottles a t 2 "C when not in use. Prior to derivatization or IR analysis, the retort water samples were frozen at -20 "C. The frozen samples were freeze-dried overnight a t reduced pressure (- 100 pm), transferred to watch glasses, and further dried in the presence of Pz05for 1 h under vacuum. These dried samples were either analyzed by IR for functional group characterization or subjected to chemical derivation with BF3/MeOH. Twenty-milliliter samples of this retort water produced 4.17 g of freeze-dried residue of which 20% was organic carbon. Chemical Derivatization. Approximately 0.5 g of the freeze-dried retort water was introduced along with 5.0 mL of BF,/MeOH into a 50-mL round-bottom flash fitted with a Friedrich condenser. The solution was gently refluxed for 18 h after which the excess BF3 was decomposed with 20 mL of a saturated NaCl solution. The aqueous reaction product was extracted with two 10-mL portions of CCl,. The CCll extracts were combined and evaporated under nitrogen to 0.1 mL. The sample was analyzed by IR for the presence of solvent solubilized organic compounds. The residual aqueous layer was freeze-dried and analyzed for residual organic carbon. For sequential organic carbon analysis, samples (2.0 g) of freeze-dried retort water were refluxed overnight in 20 mL of BF3/MeOH. Excess BF3 was decomposed in 20 mL of H20 and extracted first with 20 mL followed by 2 X 10 mL portions of benzene. The combined benzene extracts were analyzed by GC and GC/MS without further concentration. The aqueous fractions were freeze-dried and analyzed for organic carbon content. Chemical derivatization reactions involving the incorporation of ''C-methanol used 0.5 g of freeze-dried retort water, 5 mL of BF3/MeOH amended with 1pCi of l4C-MeOH,8 mL of water for hydrolysis of the excess BF3, and 1 X 5 mL and 2 X 3 mL extractions with benzene. Infrared Analysis. The IR analyses were performed on a Beckman Acculab 6 infrared spectrophotometer scanning from 4000 cm-' to 250 cm-'. Solid samples were incorporated in KBr pellets for analyses. Approximately 0.7 mg of the solid sample and 200 mg of KBr were mixed and pelletized in a KBr die (Barnes Engineering) under 5 tons of pressure for 2 min. Carbon tetrachloride extracts of BF3/MeOH treated freezedried retort water were analyzed between NaCl plates or in a 9-pL NaCl micro-cavity cell (Barnes Engineering). Gas Chromatographic Analysis. Two microliters of the combined benzene extract of the derivatized sample was analyzed on a Varian Model 2800 gas chromatograph fitted with a 30-m OV-101 glass capillary column (Supelco, Inc.) and equipped with a flame ionization detector. The chromatographic conditions were as follows: helium carrier gas flow, 1.2 mL/min; split ratio, 10 to 1; program, 70 to 250 "C a t 4 "C/min; injector temperature, 300 "C. The acid methylesters were quantitated using hexamethylbenzene as an internal standard. Mass Spectrometric Analysis. Mass spectrometric analysis of benzene extracts containing derivatized compounds was conducted on a Hewlett-Packard 5992A GC/MS system operating in the argon chemical ionization mode. Two microliters of the sample were chromatographed on a 30-m SP2100 glass capillary column initially held a t 70 "C for 4 min and then programmed a t 4 "C/min to a final temperature of 260 "C. Analysis for '4c Radioactivity. Aliquots of aqueous samples from radiochemical experiments were suspended in PCS and analyzed on a Nuclear-Chicago Mark I1 Model 6847 liquid scintillation system. No quench effects were observed in the analysis of the samples. Organic Carbon Analysis. Samples were analyzed for organic carbon content on an Oceanography International Carbon Analyzer equipped with a direct injection module.
-
RESULTS Action of BFJMeOH o n Freeze-Dried R e t o r t Water. T h e major organic fraction of several retort waters has been reported to consist of hydrophilic and hydrophobic acids (11);
l
a 4000
3000
2000
1800
1800
1400
1200
1000
800
800600400300
WAVENUMBER CM '
Figure 1. (1) Infrared spectrum (KBr pellet) of freezedried retort water (pH 8.6); (2) infrared spectrum of CCI, extract of freeze-dried retort water after reaction with BF,/MeOH. Note appearance of new absorbances at 1740 crn-' and 1697 cm-'
Table I. Organic Carbon Content of Freeze-Dried Retort Water before and after Treatment with BF ,/MeOHa
sample A. BFJMeOH blank B. freeze-dried retort water (PH 8 . 6 ) C . freeze-dried aqueous residue after reaction with BF,/MeOH D. freeze-dried aqueous residue after reaction with BF,/MeOH and after correction for 14C-MeOH incorporation
organic carbon concn, mg/mL -0.01b 38.9 I2.2'
organic carbon solubilized in benzene, 70
__
__
32.0
I
1.1
17.6
t
3.7
27.9
i
0.8
28.2
i
2.7
a Standard deviations based on n = 3. Organic carbon concentration of the residue obtained from the decomposition, benzene extraction and freeze-drying of a solution of 20 mL of BF,/MeOH according t o the same procedure used for freeze-dried retort water samples. ' Total carbon concentration in retort water was 42.6 i 0.1 mg/mL of which 3.4% was inorganic and of which 5.5% of the organic carbon was lost upon freeze-drying.
thus we selected BF3/MeOH as a means of rendering these components more organic solvent soluble. Figure 1 shows a comparison of the infrared spectrum of freeze-dried retort water with the spectrum obtained from the CC14 extract of the same material after treatment with BF3/MeOH. T h e infrared spectrum of freeze-dried retort water showed a broad absorption at 1650 cm-' suggesting the presence of acid salts. However, further investigation revealed that the cationic and anionic species of NH4+,S20:-, S032-,and contributed, at least in part, to the major absorption bands appearing in this spectrum, including the band at 1650 cm-'. These cationic and anionic components have been shown to be major inorganic species present in this retort water ( 3 ) . Reaction with BF3/MeOH produced a new absorption band in the infrared spectrum at 1740 cm-' indicating the presence of the carbonyl stretch of acid esters along with bands at 1165 cm-', 1190 cm-', and 1240 cm-' indicative of methyl esters (12). Samples of freeze-dried retort water were reacted with BF3/MeOH to determine the extent to which this reaction
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979
1997
Table 11. Aliphatic Monocarboxylic and Dicarboxylic Acids Identified and Quantitated from Paraho Retort Water"
! ,IS
TIME M N i
Capillary gas chromatogram of benzene extract of freezedried retort water after reaction with BF,/MeOH. (A) Heptanoic acid, (B) butanedioic acid, (C) octanoic acid pentanedioic acid, (D) nonanoic acid, (E) decanoic acid, (F) heptanedioic acid, (G) octanedioic acid, (H) nonanedioic acid, (I) decanedioic acid, (J) hendecanedioic acid. IS = hexamethylbenzene internal standard Figure 2.
+
solubilizes organic carbon in retort water. The results of the analysis are listed in Table I. Analysis of samples indicated that about 5.5% of the organic carbon was lost in the process of freeze-drying retort water. Determination of the carbon remaining after treatment of freeze-dried retort water samples with BF3/MeOH and extracting with benzene indicated a loss of about 17.6% of the organic carbon as a result of the chemical treatment. This value, however, is low because it does not account for the methanol incorporated into the residue during the derivatization reaction. Thus an experiment was conducted to measure the amount of incorporation using BF3/14C-methanol. T h e use of 14C-methanol demonstrated that 12.9 & 0.9% of the organic carbon remaining in the water soluble residue after reaction of freeze-dried retort water with BF3/14C-MeOH was due to incorporation of methanol. Based on this value, the percent organic carbon solubilized in benzene as a result of the reaction of freeze-dried retort water with BF3/MeOH was calculated to be approximately 28.2%. I d e n t i f i c a t i o n a n d Q u a n t i t a t i o n of A l i p h a t i c Acids. Gas chromatographic-mass spectrometric analysis of the benzene extracts of freeze-dried retort water after reaction with BF3/MeOH revealed the presence of a homologous series of aliphatic monocarboxylic and dicarboxylic acids (Figure 2). The compounds that were identified and quantitated are listed in Table 11. Aliphatic dicarboxylic acids from butanedioic acid to hendecanedioic acid with the exception of hexadecanedioic acid were identified. Their concentrations varied over almost two orders of magnitude from 3.2 to 138.4 ppm. Although they were not quantitated, trace amounts of the dicarboxylic acids from dodecanedioic acid to tetradecanedioic acid were also present. No attempt was made to quantitate the lower molecular weight dicarboxylic acids (ethanedioic and propanedioic acid) because of their obscurity in the maze of very early peaks and the solvent front. Aliphatic monocarboxylic acids from heptanoic acid to decanoic acid were also identified and found to be present a t levels within this concentration range. Monocarboxylic acids of chain length greater than Clo were not detected a t the minimum detectability levels of the analysis with no concentration of the sample. The low molecular weight monocarboxylic acids, although most likely present, were not analyzed owing to similar difficulties as encountered with the low molecular weight dicarboxylic acids. DISCUSSION While other workers have reported the presence of monoalkanoic acids in other retort waters ( 4 , 7 , 8 ) ,we have found no previous reporting of the presence of aliphatic dicarboxylic acids in such waters. Although it is likely t h a t these acids
compound
concne
CH,(CH,),COOH CH,(CH,),COOH~ CH,( CH,),COOH CH,(CH,),COOH HOOC(CH,),COOH HOOC( CH 2),COOHC HOOC(CH,),COOH~ HOOC(CH,) ,COOH HOOC(CH,),COOH HOOC(CH,),COOH HOOC(CH2),COOH HOOC(CH ,),COOH
16.0 t 1.1 55.7 t 3.2 18.4 t 0.4 4.4 t 0.3 50.7 i 1.5 138.4 * 11.0 .._ 3.2 t 0.2 10.2 t 1.0 15.5 t 2.1 11.1i 0.9 9.5 t 0.9
a Concentrations in parts per million of whole retort water. b , c Octanoic acid and pentanedioic acid had identical retention times on capillary chromatographic system. Concentration reported for each assumes the absence of the other compound. Only trace amounts indicated present by chemical ionization mass spectrometry. e Concentrations are not corrected for recovery. However, samples of hexanedioic and dodecanoic acids of known concentration when amended to retort water and quantitated by the described procedure were recovered in high yield: 92.0 2 13.0% and 107.6 i 17.276, respective!y.
originate from the oil shale kerogen, they may also be formed by oxidation during the retorting process. No assignment of structural type has been made for the absorbance a t 1697 cm-' (Figure 1); however, compounds which contain nitrogen in close proximity to a n acid ester absorb in this region. An example of this is indole-3-acetic acid ethyl ester (13). Further clarification of this and other possibilities awaits more detailed characterization of other compounds in the benzene extract by GC/MS. The retention of 14C-methanolin the aqueous residue suggests the presence of benzene insoluble carboxyl-containing components possibly generated through the partial degradation of kerogen. Chemical derivatization with BF3/MeOH is applicable to the characterization of organic acids in other fossil fuel wastes, e.g., those generated in the solvent refined coal processes (14). The technique is also applicable to acid-containing samples generated from the fractionation of aqueous environmental and process waste samples according to compound type (11, 15). Difficulties are observed in attempting to apply this technique to the quantitation of low molecular weight acids; however, this could be remedied by generating less volatile derivatives through the use of butanol instead of methanol as the esterifying agent. The utilization of combinations of selective chemical derivatizing reagents, each specific to a particular functional group type, increases the likelihood that the majority of the environmentally significant components contained in complex mixtures of this type can be investigated using classical chemical techniques. LITERATURE CITED R. C. Routson, R. E. Wildung, and R. M. Bean, "A Review of the Environmental Impact of Ground Disposal of Oil Shale Wastes", J . Environ. Qual., 8, 14 (1979). R. E. Wildung, R. G. Riley, T . R. Garland, R. M. Bean, and Shu-mei W. Li, "TenestrialEffects of Oil Shale Development", BNWL-2100 P t 2, Battelle Northwest, Richland, Wash., 1977. R. E. Wildung, T. R. Garland, R. G. Riley, D. J. Silviera, J. E. Rogers, R. M. Bean, and S. W. Li, "Terrestrial Effects of Oil Shale Development", BNWL-2500 Pt. 2, Battelle Northwest, Richland, Wash., 1978. C. H. Ho, B. R. Clark, and M. R. Guerin, J , Environ. Sci. Health, 7, 481 (1976). R. E. Poulson, J . Chromatogr. Sci., 7, 152 (1969) R. E. Poulson, H. B. Jensen, and G. L. Cook, "Nitrogen Bases in a Shale Oil Light Distilbte", Prepr., Div. Pet. Chem., Am. Chem. Soc., 18, A49 (1971). E. W . Cook, Chem. Ind., 485 (1971). C. S. Wen, T. F. Yen, J. B. Knight, and R. E. Poulson, "Study of Soluble Organics in Stimulated In-Situ Oil Shale Retort Water by Electron Impact
1998
(9) (10) (11)
(12)
ANALYTICAL CHEMISTRY, VOL. 51, NO. 12, OCTOBER 1979 and Chemical Ionization from a Combined Gas Chromatograph-Mass Spectrometer System", 172nd National Meeting, American Chemical Society,Division of Fuel Chemistry, Vd. 21, No. 6 (Aug. 29-Sept. 3, 1976). J. T. Kwan, J. I.S.Tang, W. H. Wong, and T. F. Yen, "Application of Liquid Chromatography to Monltw Biological Treatment of Oil Shale Retort Water", Prepr., Div. Pet. Chem., Am. Chem. Soc., 22, 823 (1977). W. D. Felix, D.S.Farrier, and R. E. Poulson, "High Performance Liquid Chromatographic Characterization of Oil Shale Retort Waters", USERDA, Omega-9 CIP Document No. 3 (1977). H. A. Stuber and J. A. Leenheer, "Fractionation of Organic Solutes in 011 Shale Retort Waters for Sorption Studies on Processed Shale", presented at the 175th National Meeting of the American Chemical Society, Anaheim, Calif., March 12-17, 1978. R. M. Silverstein, G. C. Bassler, and T. C. Morrill, "Spectrometric Identification of Organic Compounds", John Wiley and Sons, New York, 1974.
(13) H. A. Szymanski and R. E. Erickson, "Infrared Band Handbook", Vol. 1. Plenum Press, New York, 1970. (14) C. D. Becker, W. G. WoodfieM, and J. A. Strand, "Solvent Refined Coal Studies: Effects and Characterization of Treated Solvent Refined Coal Effluent", PNL-2606, Pacific Northwest Laboratory, Richland, Wash., 1978. (15) J. A. Leenheer and E. W. D. Huffman, Jr., U . S . J. Res. U.S. Geol. Survey, 4, 737 (1976).
RECEIVED for review February 5 , 1979. Accepted March 29, 1979. This work was supported by the US.Department of Energy under Contract EY-76-C-06-1830. Brand names are used for reader convenience but use does not constitute endorsement by Battelle Memorial Institute.
Noble Metal Field Ionization/Field Desorption Emitters Generated by Electrochemical Deposition Guenter Semrau and Joachim Heitbaum" Institute of Physical Chemistry, University of Bonn, Wegelersrr. 12, 0-5300Bonn, West Germany
An ion emitter for field ionizatlon and desorption mass spectrometry is presented consistlng of a 10-Cc.m Pt wire covered with Pt microneedies formed by cathodic metal deposition from an aqueous 1.5 M sodium hexachioropiatinate solution at 85 O C using a galvanic pulse technlque. The emitter has good mechanical strength and can be used several times when standard cleaning procedures are applied. Its emission properties are comparable to that of the well known carbon dendrite emitter produced at high temperatures.
properties, although the peak intensities are one to two orders of magnitude smaller than those obtained with the carbon dendrite emitter used as a reference standard. The formation of MeOH layers in the case of the Ni and Co emitters can be well understood having in mind that hydrogen evolution occurs parallel to the cathodic metal deposition. Thus, the pH of the solution is locally increased near the electrode because of the H30+ consumption or OHformation, respectively, according to
H30++ eSince the invention of field ionization (FI) and field desorption (FD) mass spectrometry, special attention was given to the development of ion emitters. Up to now, there has been an almost exclusive use of wire emitters covered with carbon dendrites generated by pyrolysis of benzonitrile at low pressure and high electric field (1-3). Their advantages of high mechanical strength and chemical resistivity compete with the long time needed for preparation (almost 8 h). For this reason, alternative methods have been proposed recently such as the "high-rate growth of dendrites" ( 4 ) or the "high temperature growth of silicon whiskers on gold coated tungsten wires" ( 5 ) . Although the times of preparation were reduced to several minutes with the latter methods, all three types of emitters mentioned so far have to be formed under vacuum conditions and rather complicated temperature programs have to be observed under careful gas pressure control. These experimental difficulties can be avoided and even shorter preparation times (less than 1min) can be achieved when dendritic deposits are produced electrochemically as was pointed out by Goldenfeld (6). Using a programmable pulse generator, Bursey et al. (7-9) prepared F I / F D emitters by cathodic metal deposition on tungsten wires from aqueous solutions of simple Ni or Co salts. These emitters, however, exhibit almost insulating or semiconducting properties a t room temperature because they contain intrinsic oxide layers of the respective metal (10). Electrically conductive microneedles are obtained only when the Ni or Co emitters are heat treated in vacuum. Therefore, only heat activated emitters show satisfactory ionization 0003-2700/79/035 1-1998$01.OO/O
or
H 2 0 + e-
-
;H2 1
+ H2O
1 2
+ OH
-H2
This causes hydrolysis of the metal ions resulting in the formation of, for example, colloidal NiOH which occasionally may be incorporated into the deposit. The formation of metal hydroxides will not take place when noble metals are deposited such as Pt group metals or Au. Therefore the generation of Pt emitters for FI/FD applications was studied and is described below. These emitters are free of intrinsic oxide, no heat treatment being necessary. They are easy to prepare and the dendrites show good mechanical strength and adhesion to the underlying wire. Moreover, the Pt emitters can be used several times and standard cleaning procedures may be used such as washing in organic solvents or even in chromic acid. Furthermore, their morphology can easily be adjusted to the analytical problem in question by varying the number of cathodic pulses. And finally, they may be of special interest for the investigation of surface reactions.
EXPERIMENTAL Electrolytic Cell and Solution. The experimental setup for the electrochemical metal deposition is schematically shown in Figure 1. Emitter bases were constructed from two 1.0-mm diameter Vacon ports rigidly held approximately 1.5 mm apart by a glass spacer with glass to metal seals. A 10-bm length of platinum wire was spotwelded to this base and mounted in a holder which allowed accurate and reproducible adjustment of distance between the emitter wire and the counter electrode 0 1979 American Chemical Society
