Interpretation of ESCA binding energy data for these metal oxides should be made mainly from the binding energy differencesof the various oxygen and metal transitions, since these ABE’s are the ones free from charging complications (39). It is clear that it is very difficult to distinguish the intermediate oxidation states of Sn and In from the fully reduced and oxidized forms. Linear correlations of binding energy and oxidation number are not observed for the SnOz, SnO, Sn system. The N o / N Mratios, however, serve to distinguish the partially reduced metal oxide, since they are consistently lower than those computed for SnOz. Decomposition of SnO to Sno by ion etching also serves for identification purposes. The quantitations reported herein are important prerequisites for a detailed understanding of the surface composition of SnOz and Inz03electrodes, which are reported in a subsequent paper.
ACKNOWLEDGMENT We greatly appreciate the assistance of J. Lumsden (OSU) for use of the Varian Auger instrument and Paul Uglum and Nick Winograd (Purdue University) for obtaining ESCA spectra on the Hewlett-Packard ESCA instrument.
(13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35)
LITERATURE CITED (1) C. R. Brundle, J . Eiectron Spectrosc. Relat. Phenom., 5, 291 (1974). . (2) 0. C. Allen, P. M. Tucker, A. Capon, and R. Parsons, J , E l e c h o a ~ lChem. Interfacial Electrochem., 50, 335 (1974). (3) A. Cimino and B. A. DeAngelis, J. Catal , 36, 11 (1975). (4) N. S.McIntyre and M. G. Cook, Anal. Chem., 47, 2208 (1975). (5) J. S.Hammond, S . W. Gaarenstroom, and N. Winograd, Anal. Chem., 47, 2193 (1975). K. S. Kim and N. Winograd, J. Catal., 35, 66 (1974). K. S. Kim and N. Winograd, Surf. Sci., 43, 625 (1974). K. S.Kim, A. F. Gossmann, and N. Winograd, Anal. Chem., 46, 197 (1974). K. S.Kim, T. J. O’Leary, and N. Winograd, Anal. Chem., 45, 2214 (1973). K. S. Kim and R. E. Davis, J . Electron Specfrosc. Relat. Phenom., 1, 251 (1972/3). K. S. Kim, N. Winograd, and R. E. Davis, J. Am. Chem. Soc., 93, 6296 (197 1). T. Robert, M. Bartel, and G. Offergeld, Surf. Sci., 33 123 (1972).
(36) (37) (38) (39) (40) (41)
G. Schon, Surf. Sci., 35, 96 (1973). M. Seo, J. B. Lumsden, and R. W. Staehle, Surf. Sci., 42, 337 (1974). M. P. Seah, Surf. Sci., 40, 595 (1973). M. P. Seah, Surf. Sci., 32, 703 (1972). W. J. Carter and G. K. Schweitzer, J. Electron Spectrosc. Rebt. &nom., 5, 827 (1974). R. S.Swingle and W. M. Riggs, Crit. Rev. Anal. Chem., 5, 267 (1975). N. R. Armstrong, A. W. C. Lin, M. Fujlhira, and T. Kuwana, Anal. Chem., 48, 741 (1976). T. Kuwana and N. Winograd, “Spectroelectrochemistry at Optically Transparent Electrodes,” in “Electroanalytical Chemistry, ’ Vol. 7, A. J. Bard, Ed., Marcel Dekker, New York, N.Y., 1974, and references therein. R . Holm and S.Storp, Appl. Phys., 9, 217 (1976). J. B. Bosnell and R. Wagnorne, Thin Solid Films, 15, 141 (1973). C. D. Wagner and P. Bioen, Surf. Sci., 35, 82 (1973). G. E. McGuire, G. K. Schweitzer, and T. A. Carlson, Inorg. Chem., 12, 2450 (1973). V. I. Nefedov, B. F. Druzsinszklj, N. P. Szergusin, J. V. Szalin, and Gyula 6s GBti, Magy. Kem. Foly., 81, 495 (1975). P. A. Grutsch, M. V. Zeller, and T. P. Fehlner, Inorg. Chem., 12, 1431 (1973). W. E. Morgan and J. R. VanWazer, J. Phys. Chem., 77, 964 (1973). P. W. Palmberg, J . Vac. Sci. Techno/., 13, 214 (1976). D. J. Pocker, R. W. Springer, F. E. Ruttenberg, and T. W. Haas, J . Vac. sci. Techno/., 13, 507 (1976). H. E. Bishop and J. C. Riviere, J. Appl. Phys., 40, 1740 (1969). F. Meyer and J. J. Vrakking, Surf. Sci., 33, 271 (1972). J. T. Grant, T. W. Haas, and J. E. Houston, Surf. Sci., 42, 1 (1974). J. J. Vrakklng Bnd F. Meyer, Phys. Rev. A , 9, 1932 (1974). G. E. Theriault, T. L. Barry, and M. J. B. Thomas, Anal. Chem., 47, 1492 (1975). K. Siegbahn, C. Vordling, A. Fanlman, R. Nordberg, K. Hamrin, J. Hedman, G. Johansson, T. Bergmark, S. E. Karlsson, I. Lindgren, and B. Lindberg, “ESCA-Atomic, Molecular, and Solid State Structure Studied by Means of Electron Spectroscopy,” Almquist and Wiksells, Uppsala, Sweden, 1967. P. W. Palmberg, J . Nectron Spectrosc. Re/. Phenom., 5, 691 (1974). N. Beatham and A. F. Orchard, J. Electron Spectrosc. Re/. Phenom., 9, 129 (1976). J. H. Scofield, J . Necfron Spectrosc. Rei. Phenom., 8, 129 (1976). C. D. Wagner, Faraday Discuss. Chem. Soc., 60, 291 (1975). G. W. Grynkewich, B. Y. K. Ho, T. J. Marks, D. L. Tomaja, and J. J. Zuckerman, Inorg. Chem., 12, 2522 (1973). R. A. Pollak, L. Ley, F. R. McFeely, S. P. Kowalczyk, and D. A. Shirley, J . Nectron Spectrosc. Re/. Phenom., 3, 381 (1974).
RECEIVED for review February 16, 1977. Accepted April 25, 1977. The financial support provided by NSF grants C H E 73-04882 and C H E 76-04911 is gratefully acknowledged.
Determination of Organic Carbon By Thermal Volatilization-Plasma Emission Spectrometry D. G. Mitchell,” K. M. Aldous, and E. Canelli Division of Laboratories a n d Research, N e w York State Department of Health, Albany, N e w York
Organic carbon is determined by differential volatilization and plasma emission spectrometry. Water or suspended particulate samples are dispensed into platinum boats acd dried at 85 ‘C for 10 min. Oxidant is added, then the boats are injected Into a furnace at 850 ‘C, at which temperature organic carbon volatilizes several seconds before inorganic carbon. The resulting vapor is fed to a microwave-excited plasma, and carbon emission at 193.0 nm is measured. For a 400-pL allquot, callbration curves are linear up to 16 pg C, the detection limit is 0.4 kugl dissolved organic carbon, and the relative standard deviation is typically 3% at the 5 pg C level. The instrument has a number of advantages for routine organic carbon analysis: (i) Analysis is rapid, typically with an elapsed tlm@of 10 min and an analysis rate of 20 samples per hour. (ii) Samples usually do not require pretreatment other than drying. (iii) Moderate amounts of inorganlc carbon do not interfere. (iv) Refractory organic compounds can be determined with excellent recoveries.
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Determination of organic carbon in natural waters, waste waters, suspended particulates, sludges, and sediments is one of the most important environmental analyses. Organic carbon levels indicate the potential oxygen demand. Monitoring of sewage treatment plant effluent and receiving waters is a common application and necessitates many routine determinations. Both particulate organic carbon (POC) and total organic carbon (TOC) are measured. In general, samples are acidified, and dissolved COPand COz from bicarbonate and carbonate are removed. Organic carbon is then (i) oxidized by combustion or wet oxidation to COP and detected using an infrared or a thermal conductivity detector or (ii) oxidized, then reduced to CH4 and determined using a flame ionization detector (1-6). These procedures are precise but they have several important practical disadvantages, particularly for routine analysis. The elimination of inorganic carbonates by treatment with acid is time-consuming, may introduce contamiANALYTICAL CHEMISTRY, VOL. 49, NO. 8 , JULY 1977
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nation, and may result in error due to incomplete carbonate removal (7) or loss of organic carbon. In addition, some compounds, such as pyridine and saturated fatty acids and esters, cannot be quantitatively oxidized t o C 0 2 by wet oxidation (Canelli and Adrat, unpublished data). A third disadvantage is that these methods involve multiple sample-handling operations and a t least 30 min elapsed time before analytical results are available. Even without a prior separation step, interferences from inorganic carbon can be prevented. For example, Telek and Marshall (7) using an F&M Model 185 CHN Analyzer, obtained a negligible response from CaC03 in untreated samples by limiting combustion time to 10 s and temperatures to less than 720 "C. Also, use of a carbon-specific detector, as in plasma emission spectrometry, may avoid systematic error due to incomplete conversion of organic carbon to COz or CHI. McCormack and co-workers (8)and Bache and Lisk (9-11) have successfully used low-power microwave-induced plasma emission discharges as specific detectors in gas chromatography. Taylor et al. (12),using a low-power plasma emission spectrometer to determine carbon compounds in argon, reported excellent sensitivity and precision for C, N, and H. Such an instrument should also be suitable for determining the total carbon content of the volatile carbon-containing species obtained after pyrolysis of organic carbon. In this paper we describe the design and performance of a thermal volatilization-plasma emission spectrometer for determining organic carbon in water or suspended particulates. Samples are aliquoted or weighed into platinum boats. The sample is dried, Vz05 is added, and the boat is injected into an oven a t 850 "C. Organic compounds are volatilized, oxidized to CO or COz, and passed to a plasma emission detector. Dissolved C 0 2 is removed during the drying step, and inorganic carbonates and bicarbonates either do not volatilize at 850 "C (Na2C03,KZCO3) or decompose and evolve COz after organic materials have volatilized (MgC03, CaC03). T h e plasma emission spectrometer does not require quantitative conversion to a single carbon species, since carbon emission is insensitive to moderate changes in the chemical composition of the sample vapor (12). I t should yield accurate and precise results providing the organic material is not lost during drying, is completely volatilized at 850 "C, and if a constant fraction of the volatilate is converted to atomic carbon. The procedure is very rapid; samples can be analyzed with an elapsed time of 10 min a t a rate of 20 samples per hour.
EXPERIMENTAL Materials. Reagent-grade chemicals were used throughout. Carbon-free water (CFW) containing less than 0.5 ppm organic carbon was obtained by distilling freshly demineralized or distilled water with H2S04and KMn04. The first 200 mL of distillate were discarded. All solutions were prepared with CFW, and Vz05 (50 mg) contained less than 0.4 pg apparent organic carbon. Potassium hydrogen phthalate (obtained from the National Bureau of Standards) was selected as a standard because it is easily oxidized to COz and water, it can be obtained in very pure form, and its aqueous solutions are stable over a long period of time. A stock solution containing 400 fig TOC/mL was prepared by dissolving 0.8509 g of KHC8H4O4in CFW and diluting to 1 L. Standard solutions containing 4-40 pg TOC/mL were prepared daily from this stock solution. High-purity amino acids and a standard solution of 17 amino acids (AA-S-18,lot No. 35C-7460-1) including phenylalanine, histidine, glycine, cystine, valine, and tyrosine, were obtained from Sigma Chemical Company, St. Louis, Mo. Methyl stearate (Applied Science Laboratories)was dissolved in CHC13 or dispersed in CFW. Suspended solids for POC analysis were collected by membrane filtration using HA-type, 0.45-pm pore, 47-mm diameter filters (Millipore Corp.) and a standard vacuum filtration apparatus. The filtration technique and the procedure for quantitative 1236
ANALYTICAL CHEMISTRY, VOL. 49, NO. 8 , JULY 1977
Figure 1. Schematic diagram of the thermal volatilization-plasma emission spectrometer for organic carbon analysis
removal of particulate from the filter are described elsewhere (13). Celite (Fisher No. C211,1% suspension in CFW) was used as a filter aid, and particulate matter was removed from the filter using 20 mL of CFW. Prior to analysis, the particulate suspension was homogenized using a Vortex mixer. With 2 mg Celite, blank values were typically
