Anal. Chem. 1980, 52, 1777-1778
sential. Without cleanup of the resin, the identification of di- and trichlorophenols is difficult. There will, however, be some contamination from the resin that is, a t this time, difficult to remove. Even with cleanup, some interfering peaks from t h e resin co-elute with 2,4,6- and 2,4,5-trichlorophenol on DSB-DEGS, b u t these interferences were resolved on SB-BDS.
Koloff, R. H.; Breukiander. L. J.; Barkley, L. 8. Anal. Chem. 1963, 35, 1651. Ross, J.; Higginbotham, G. R. J. Chromatogr. 1970. 47, 474. Chadwick, R. W.; Freal, J. J. Bull. Environ. Contam. Toxicol. 1972, 7, 137. Freal, J. J.; Chadwick, R . W. J. Agric. Food Cbem. 1973, 21, 424. Chadwick, R . W.; Chuang, L. T.; Williams, K. Pestic. Biochem. Physiol. 1975, 5,575. Chriswell, C. D.; Chang, Richard C.; Fritz, J. S. Anal. Chem. 1975, 47, 1325. Junk, G. A.; Richard, J. J.; Geizer, M. D.; Witiak, D.; Witiak, J. L.; Arguelb, M. D.; Vick, R.; Svec. H. J.; Fritz, J. S.; Calder. G. V. J. Chromatogr. 1974, 99, 745. Burnham, A. K.; Calder, G. V.; Fritz, J. S.; Junk, G. A,; Svec, H. J.; Willis, R. Anal. Chem. 1972, 44, 139. Mule, S. J.; Bastos, M. L.; Jukofsky, D.; Saffer, E. J. Chromatogr. 1971, 63,289. Zaika, L. L. J. Agric. food Chem. 1968, 77, 893. Musty, P. R.; Nickless, G. J. Chromatogr. 1974, 89, 185. Coburn, J. A.; Valdmanis, I. A,; Chaw, A. S. Y. J. Assoc. Off. Anal. Chem. 1977, 60, 224. Riley, J. P.; Taylor, D. Anal. Chim. Acta 1969, 46, 307. Edgerton, T. R.; Moseman, R. F. J. Chromatogr. Sci. 1980, 18, 25-29. Moseman, R. F. J. Chromatogr. 1978, 166, 397. Thurman, E . M.; Malcolm, R . L.; Aiken, G. R . Anal. Chem. 1978, 50, 775.
ACKNOWLEDGMENT T h e authors acknowledge Elizabeth Yarbro and Steven Todd for their technical assistance in the development of this methodology and L. H. Wright for confirmation of the chlorinated phenols by high performance liquid chromatography/mass spectrometry. LITERATURE CITED Kohli, J.; Weisgerber, I.; Klein, W. Pestic. Biochem. Physiol. 1976, 6 , 91. Engst, R.; Macholz, R. M.; Kujawa, M.; Lewewenz, H. J.; Plass, R. J. Environ. Sci. Health B11 1976, 95. Kohli, J.; Jones, D.; Safe, S. Can. J. Biochem. 1976, 54, 203. Chau, A. S. Y.; Terry, K. J. Assoc. Off. Anal. Chem. 1976, 59, 633. Makita, M.; Yamamoto, S.;Katoh, A.; Takashita, Y. J. Chromatogr. 1978, 147, 456. Shafik. T. M.; Sullivan, H. C.; Enos, H. R. J. Agric. Food Chem. 1973, 21, 205. Edgerton. T. R.; Moseman, R. F.; Linder, R. E.; Wright, L. H. J. Chromatogr. I97g9 170, 336.
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RECEIVED for review March 24,1980. Accepted May 28,1980. Use of trade names is for identification purposes only and does not constitute endorsement by the 1J.S.Environmental Protection Agency.
Determination of Carbon Content in Carbides by an Elemental Analyzer Peter P. Borda' and Peter Legzdins Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Y6
Because of their physical properties, carbides have found wide application in various fields of technology ( I ) . Knowledge of their chemical composition, particularly the carbon content, is of primary importance during the manufacture of materials for specific applications ( 2 ) . At present, the quantitative determination of carbon in these materials is principally carried out on macrosamples by combustion techniques employing oxidizing fluxes at high temperatures ( 3 , 4 ) . These procedures, however, are cumbersome and time-consuming; a n d difficulties are often encountered with those carbides whose decomposition is troublesome, particularly S i c , B4C, a n d Cr3C2 (2). We now wish to report t h a t such assays can be effected simply and quickly with a n elemental analyzer of t h e type used routinely for the microdetermination of C, H, a n d N in organic compounds (5) if the carbide samples are first homogenized with a n appropriate oxidant.
EXPERIMENTAL In a typical assay a 0.5-2.0 mg sample of the powdered carbide (obtained from Ventron Corporation) was weighed into a silver capsule (manufactured by H. Reinhardt Labor-Service, Riehen, Switzerland) containing 20 mg of an oxidant whose composition depended on the nature of the carbide. For covalent carbides, a 7:l by weight mixture of Pb304:NaFwas employed, whereas ionic and metallic carbides were treated with pure, powdered CuO. The sample was then covered with an additional 10 mg of the additive, and the capsule was pinched shut. The sealed capsule was rapidly shaken on a vibrator for 5 s t o ensure complete mixing of its contents and was then transferred to the sample feeder of a Carlo Erba Model 1106 analyzer. Finally, the determination of carbon was carried out in the conventional manner using the instrumental parameters recommended by the manufacturer. RESULTS AND DISCUSSION As evidenced by t h e representative results presented in Table I, satisfactory analyses have been obtained for all 0003-2700/80/0352-1777$01 .OO/O
Table I.
Assays of
carbide covalent carbides B4C -4'4C3 Sic ionic carbides Lac, BaC, metallic carbides TaC ZrC NbC TIC Mo,C Hf C
Various Carbides carbon, % found automated other additive methoda methods
calcd
Pb,O,/ NaF Pb,O,/ NaF Pb,04/ NaF
20.22
20.41
21.74
25.60
25.90
25.03
c u0 c u0
13.88 14.38
13.98 14.50
14.74 14.89
c u0 c u0 c u0 CUO CUO CUO c u0 CUO
6.32 11.54 11.21 19.39 5.87 6.25 13.31 6.16
6.23 11.75 11.10 19.55 5.87 6.31 12.85
6.22 11.64 11.45 20.05 5.89 6.30 13.34 6.13
29.88
29.96
a These values are the average of a t least six determinations, none of which differed by more than * 0.2 from the mean.
samples examined to date. T h e accuracy of the carbon determinations is confirmed by comparison of the values obtained during this study with those obtained by classical techniques. The latter values were kindly provided by James Guy of Ventron Corporation. The procedure described above appears to be applicable to all types of carbides whether they 0 1980
American Chemical Society
Anal. Ghem. 1980, 52, 1778
1778
be covalent, ionic, or metallic in nature. Indeed, we have assayed a number of other carbides (including mixed-metal species) supplied to us by commercial manufacturers and have obtained agreements between automated and classical carbon values comparable to those shown in Table I. However, we have not been granted permission by these firms to publish these data. Obviously, an assay of a standard carbide sample t o place our results on an absolute scale would have been desirable. Unfortunately, to the best of our knowledge, no such standard sample is available a t the present time. T h e principal advantage of this automated method is its speed. A complete determination requires 10 min, meaning that 30 to 40 samples can be analyzed easily during a working day. Furthermore, no difficulties arising from incomplete combustion are encountered if the oxidants indicated are used. However, utilization of additives such as CeOp,MnOz, Co304, WOS, V z O j , NiO, and CrOs affords lower apparent carbon
contents. Hence, the experimental procedure outlined seems to encompass the optimum conditions for effecting these assays. This method should also prove to be of use during the elemental analysis of organometallic complexes which have a proclivity for forming carbides during thermal decomposition (6).
LITERATURE CITED (1) Kosolapova, T. Ya. “Carbides”; Plenum: New York, 1971; Chapter 9. (2) Kieffer, R. In “Encyclopedia of Chemical Technology”; Kirk, R. E., Othmer, D. L., Eds.; Wiley: New York, 1964; Vol. 4, p 90. (3) Kriege, D. H. Los Alamos, N.M., 1959, AEC Rep?. 2306. (4) Annual Book of ASTM Standards, Part 45, 1979, pp 550-574. (5) Pella. E.; Colombo, B. Mikrochim. Acta ( W e n ) 1973, 697-719. ( 6 ) Crease, A. E.; Legzdins, P. J . Chsrn. SOC.,Datfon Trans. 1973, 1501-7.
RECEIVED for review March 27,1980. Accepted May 28,1980. This work was made possible by a grant from the Natural Sciences and Engineering Research Council of Canada to P.L.
Two-way Valve for Control of Liquid Pressures up to 50 Kilograms per Square Centimeter Kenneth E. Collins” and Carol H. Collins Instituto de QGmica, Universidade Estadual de Campinas, Caixa Postal 1170, 13.100 Campinas, SP, Brasil
T h e cost of commercial valves for regulating the flow of fluids is a limiting factor for low-budget laboratories, particularly when the fluids are corrosive and/or must be handled a t elevated pressures. The valve shown in Figure 1 is simple, inexpensive and effective in many such applications. Its body and rotor pieces may be made of nearly any hard, machinable plastic or metal. We have used both Plexiglas and stainless steel for the body and nylon for the rotor. The valve employs the “pinch clamp“ concept with ordinary or 1/16-inch polytetrafluoroethylene (PTFE) chromatography tubing. It is serviceable to at least 50 kg/cm2 and can be added to an existing line made of PTFE tubing without cutting or installing new connections. On-off flow (0.001-1.0 mL/s) control of gases or liquids can be achieved by “finger power” using l/*-inch PTFE tubing. A small wrench is useful when using ‘/,6-inch tubing in the “on-off’ mode. I n flow-control situations. a “freshly squeezed” valve typically gives a flow-rate which decreases slightly over a period of 24 h , perhaps due t o “cold-flow” of the tubing around the rotor. Thus, occasional readjustment of the flow may be necessary for long-term applications. T h e valves have been used for hundreds of “on-off‘ cycles without loss of effectiveness. Although the squeeze action probably does result in some thinning of the tubing walls after repeated use, “containment” by the valve body and rotor give adequate support for such repeated use at pressures up to 50 kg/cm2. Obviously, care should be taken to avoid overtightening the rotor in “on-off’ operations to prevent excessive thinning of the tubing. 0003-2700/80/0352-1778$01 O O / O
/aTOR
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