The Chemical Analysis of Argonne Premium Coal Samples
Edited by Curtis A. Palmer
U.S. Geological Survey Bulletin 2144
Determination of Carbon, Hydrogen, and Nitrogen in Eight Argonne Premium Coal Samples by Using a Gas Chromatographic Analyzer with a Thermal Conductivity Detector
By Carol J. Skeen and Zoe A. Brown
The carbon, hydrogen, and nitrogen contents of eight Argonne Premium Coals were determined by using the Perkin-Elmer 240B elemental gas chromatographic (GC) analyzer with a thermal conductivity detector (TCD). Precision for the analysis of these samples is within the accepted 0.1 percent relative standard deviation. The carbon content ranged from 56 to 86 percent; the hydrogen content ranged from 3.7 to 5.6 percent; and the nitrogen content ranged from 0.93 to 2.2 percent. Because these ranges are typical for coals, the NIST (National Institute of Standards and Technology) 1635 coal standard reference material was chosen as the control standard to evaluate the accuracy of the method.
Analysis of a substance for carbon, hydrogen, and nitrogen generally requires drastic treatment of the material in order to convert the elements into a form readily determined by routine analytical techniques. A common way to convert the carbon, hydrogen, and nitrogen to gaseous products is to carry out an oxidation in a quartz combustion tube through which is forced a stream of carrier gas. The stream transports the volatile products to the part of the apparatus where they can be separated for measurement.
The combustion train is packed with silver compounds to remove any halogen and sulfur compounds generated, because these compounds interfere with the determination of carbon dioxide and water. Before reaching the combustion train, the helium and oxygen flow through scrubbers packed with colorcarb and anhydron to remove extraneous contaminants.
The Perkin-Elmer 240B elemental gas chromatographic analyzer with a thermal conductivity detector gives excellent results for finely ground, dry materials, especially materials high in organic matter, with the following concentration ranges: 0.1-100 percent for carbon, 0.01-12 percent for hydrogen, and 0.10-18 percent for nitrogen.
ANALYTICAL PROCEDURE
Standard operating procedures for use of the Perkin-Elmer 240B and a revised statistical computer program (Abramowitz, 1964) were implemented for the analysis of the eight Argonne Premium Coals. Oxygen was the combustion gas, and helium was the carrier gas. The instrument was calibrated by oxidizing three samplings of standard acetanilide, all of approximately the same weight (1.0 to 1.3 mg). The furnace temperatures were 950°C for the combustion tube and 650°C for the reduction tube. The sample weights used were between 1.0 mg and 1.3 mg.
The NIST (National Institute of Standards and Technology, formerly the National Bureau of Standards) 1635 coal standard reference material (SRM) was analyzed as a control standard at the same time as the last three premium coals. Table 1 shows these results along with the NIST SRM values (National Bureau of Standards, 1978) and the analytical values of Gladney and others (1987).
RESULTS AND DISCUSSION
A study was made to ascertain the detection limits of this method (Filby and others, 1985). By diluting pure acetanilide with ultra-pure silica to prepare three analytical standards- (1) 7.1 percent C, 0.67 percent H, and 1.04 percent N, (2) 0.71 percent C, 0.067 percent H, and 0.104 percent N, and (3) 0.071 percent C, 0.0067 percent H, and 0.010 percent -- and by using acetanilide undiluted (71.07 percent C, 6.71 percent H, and 10.36 percent N), the lowest detection limits were calculated to be 0.1 percent C, 0.01 percent H, and 0.10 percent N. The experiment using various sampling weights also validated that the analytical curves were linear from the detection limit to the highest standard.
The results of these coal analyses were compared with the published data for the Argonne Premium Coal Sample Program (Vorres, 1990) for carbon, hydrogen, and nitrogen determined on dried whole coals. The values were in good agreement with all the coals except for the carbon values for the subbituminous coal (WY) and the lignite (ND). To verify the accuracy of this paper's results, analyses of these two samples were repeated with special attention given to proper drying of the samples before analysis. The carbon values obtained by the repeat analyses, 61 percent for WY and 57 percent for ND, are in agreement with values obtained by the initial analyses. Table 2 shows the results for the replicate analyses of these coals, the repeats, and Vorres' published data.
The differences between the results from Argonne National Laboratories (Vorres, 1990) and the data reported in this paper could be due to oxidation of these two coals. Argonne went to great lengths to seal these coals in an oxygen-free environment. Because analysis in the U.S. Geological Survey laboratories was not done immediately after the ampoules were opened, it is likely that the subbituminous coal and the lignite oxidized. Bituminous coals are characteristically more stable.
The precision of this method is within the 0.1 percent relative standard deviation, which is well within the accepted deviation for this type of analysis. The analysis of NIST 1635 indicates that the accuracy is also excellent.
Abramowitz, M., 1964, Elementary analytical methods, in Abramowitz, M., and Stegun, I.A., eds., Handbook of mathematical functions-National Bureau of Standards Applied Mathematics Series 55: Washington, D.C., U.S. Government Printing Office, chap. 3, p. 18.
Filby, R.H., and others, 1985, Evaluation of geochemical standard reference materials for microanalysis: Analytical Chemistry, v. 57, no. 2, p. 551-555.
Gladney, E.S., O'Malley, B.T., Roelundts, J., and Gilly, T.E., 1987, Composition of elemental concentration data for NIST clinical, biological, geological and environmental standard reference materials: National Institute of Standards and Technology Special Publication 260-111, p. 21-22.
National Bureau of Standards, 1978, National Bureau of Standards certificate of analysis, standard reference material 1635, trace elements in coal (subbituminous): Washington, D.C., National Bureau of Standards, 2 p.
Vorres, K.S., 1990, The Argonne Premium Coal Sample Program: Energy and Fuels, v. 4, no. 5, p. 420-426.
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