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ANALYTICAL CHEMISTRY, VOL. 50, NO. 9, AUGUST 1978
State University, Groningen) for his interest and advice in this study.
LITERATURE CITED L. Meites, "Polarographic Techniques", 2nd ed., Interscience Publishers, New York, N.Y., 1965. H. H. Willard, L. L. Merritt, and J. A. Dean, "Instrumental Methods of Analysis", 5th ed., D. van Nostrand Co., New York, N.Y., 1974. A. A. Cernik, Chem. Br., 10, 58-61 (1974). I. L. Larsen, N. A. Hartmann, and J. J. Wagner, Anal. Chem., 45, 1511-1513 (1973). J. Mandei and F. J. Linnig, Anal. Chem., 29, 743-749 (1957).
(6) Ch. K. Mann, Th. J. Vickers, and W. M. Guiick, "Instrumental Analysis", Harper & Row, New York, N.Y., 1974. (7) B. A. Kubrak, A. A. Kaplan, and V. N. Polyakova, S b . T r . Molodykh. Uch., Tomsk. Politekh.'lnst., 11-13 (1973); Chem. Absh., 8 2 , 50922 f 19751 -.-, (8) W. H.Reinmuth. Anal. Chem., 2 8 , 1356-1357 (1956). (9) E. C. Fieller, J . R . Stat. Soc., Suppl., 7 , 1-64 (1940). (10) P. D. Lark, 6.R. Craven, and R. C. L. Bosworth, "The Handling of Chemical Data", Pergarnon Press, New York, N.Y., 1968. ( 11) J. P. Franke, P. M. J. Coenegracht, and R. A. de Zeeuw, Arch. Toxicol., 34, 137-143 (1975). \
RECEIVED for review January 26,1978. Accepted May 17,1978.
CORRESPONDENCE Effect of Gas Burner Conditions on Lithium Tetraborate Fusion Preparations for X-ray Fluorescence Analysis Sir: Automated instruments are now available which perform fusions of one or more samples with a suitable fluxing agent such as lithium tetraborate. This procedure produces a glass disk(s) which after grinding and polishing can be directly analyzed by x-ray fluorescence spectrometry. The heat source in these instruments is usually a modified Meker burner fed with either natural gas/air or propane/air gas mixtures. T h e purpose of this communication is to report some results we have obtained when fusing mixtures consisting of various concentrations of calcium and iron with a constant amount of flux under conditions where the flow rates of propane and air fed into the burner were varied.
~~
Table I. Concentrations of Ca and Fe Added in Standard Disks Gas burner conditions I(1125 "C)
Bead No. 1
2 3 4 5 6 I1 (1100 " C )
1
2 3
4
EXPERIMENTAL Apparatus. An automated fusion device was employed to perform the fusions (Angstrom, Inc., P.O. Box 248, Belleville, Mich. 48111). An energy-dispersive x-ray spectrometer was used in these experiments and has been described elsewhere ( I ) . Procedure. Samples were prepared for fusion by adding known amounts of CaC03 (previously dried @ 260 "C) and Fe203 (dried at 110 'C) to 6.7 g of lithium tetraborate and 1.5 g of ammonium nitrate. All materials were of analytical reagent quality. The samples were then fused under two different gas burner conditions for 40 min each in platinum-5% gold alloy crucibles (Matthey Bishop Inc., Malvern, Pa. 19355). The resultant glass disks were then ground and polished and analyzed directly by energy-dispersive x-ray spectrometry. Temperature calibration of the glass melt was performed with an NBS calibrated Pt-10% Rh thermocouple. The temperature of the fusion mixture was set at 1125 "C by varying the flow rates of propane and air entering the burner by adjustment of the respective flow controllers. The air-to-propane ratio was the highest that could be obtained without causing the flame to extinguish (condition I). After a number of glass disks were prepared, the propane flow was increased and the air decreased so that a temperature of 1100-1110 "C was obtained (condition 11). Under these conditions, several glass disks were prepared. A summary of the concentrations of calcium and iron in the disks prepared under tE.e two gas burner conditions is tabulated in Table I.
RESULTS AND DISCUSSION T h e relative differences found in the determination of calcium and iron obtained under t h e two sets of fusion conditions are plotted in Figures 1and 2, respectively. Three replicate measurements of each binary glass disk were made with relative standard deviations of a single measurement of
5 6 7 8
0
10
20
30
%Ca 2.91 2.89 5.85 5.85 7.26 7.28 1.44 1.44 2.89 2.99 2.88 2.89 7.25 7.25
40 50 96 Ca in disk
60
% Fe
1.01 1.01 0.51 0.52 0.25 0.25 2.00 2.00 1.01 1.01 1.01 0.99 0.26 0.26
70
80
Figure 1. Effect of burner conditions on calcium in standard disks (A) I ( 0 )Condition I1
Condition
0.3 to 1.0%. T h e results shown were corrected for x-ray absorption in the glass disks using an NBS data reduction procedure (2). Figure 1 shows that the difference in fusion conditions had no effect on calcium. However, Figure 2 illustrates that under condition I, iron was markedly affected. T h e low values obtained are believed to be due to the partial chemical reduction of iron to the metal which subsequently alloys with the platinum crucibles (3). I t was also found that glass disks could not be prepared without cracking under condition I when the iron concentration was greater than 1.5% in the disk. These disks usually appeared very dark brown
This article not subject to U S . Copyright. Published 1978 by the American Chemical Society
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fusion under condition I did not appear to prevent reduction. These results illustrate the importance of maintaining proper oxidizing flames for accurate sample preparation by fusion. It has been suggested that a nickel crucible of the same size as the platinum crucible be used in an identical position in the flame t o determine the oxidizing or reducing conditions of t h e flame. We found that the use of a nickel crucible for determining these conditions was not always satisfactory. This work suggests t h a t observation of the color of a few fused samples of mixtures containing calcium and iron may serve as a more sensitive test of flame conditions.
F
LITERATURE CITED 02
04
06
08
10
12
14
16
18
20
22
X IC 8n dtrk
Figure 2. Effect of burner conditions on iron in standard disks. (A) Condition I. ( 0 )Condition I1
and opaque. At lower iron concentrations, the disks exhibited a greenish blue coloration in contrast to the yellowish brown obtained with disks having t h e same iron content prepared prior to under condition 11. T h e addition of more “,NO3
(1) P A Pella. R. H Mvklebust. M M Darr. and K F J Heinrich. N B S I R ’ 77-1211, June 197:. (2) R. L. Myklebust. C. E. Fiori. D. N. Breiter, and K. F. J. Heinrich, FACSS Abstracts (3rd Annual Meeting) N o . 241, Philadelphia, Pa., 1976. (3) C. 0. Ingamells, Anal. Chim. Acta, 52, 323 (1970).
P.A. Pella National Bureau of Standards Washington, D.C. 20234
RECEIVED for review February 12, 1978. Accepted April 13, 1978.
Solvent Extraction of Coal-Derived Products Sir: T h e recent interest in separating and characterizing coal-derived oils has revealed an intriguing problem. There is, a t present, no standard method or technique that is widely used to separate and characterize liquefied or solvent refined coal products. Most investigators in the field, and those just getting started, are however using a host of similar terms to define dissimilar fractions from coal products. For example, the word asphaltene(s), as it pertains to coal-derived products, can mean a solvent separated material t h a t is benzene or toluene soluble and pentane insoluble ( I ) , or hexane insoluble (21, or cyclohexane insoluble (3) or even derived by specific mixtures of toluene and pentane ( 4 ) . Beside all of these differences, there are a host of techniques being used t o characterize coal-derived products by solubility distribution analysis (5,6),chromatographic analysis (7-9), and by the use of distillation (10). Finally, there is also a redefinition of asphaltenes as being specific chromatographic fractions with one functional group present per molecule (8). The situation for t h e analyst is one of mass confusion. When a chemist wishes to separate coal-derived oils for the first time, he can find two, three, and in t h e case of “asphaltenes” as many as ten different methods, all of which arrive at supposedly the same product. A common separation method should be used on all coal-derived products t o serve as a guide post for comparison by process engineers, chemists, and management. T h e method we present here should be used only as a guide t o t h e development of a standard separation analysis of coal-derived material. We feel it is important that the finally accepted method be rapid (hours), suitable to analytical (1-10 g) a n d preparative (10-100 g) batch size, and not require sophisticated instrumentation. Our procedure can provide an analytical separation of three or four major solvent-defined solubility fractions from the multicomponent coal-derived oil. Separation is carried out a t just below room temperature with solvents of increasing orientation solubility (polarity) parameter as defined by Hildebrand (11). Each fraction is also defined with respect t o the volume of solvent used. We have found that 1 liter of solvent per fraction per 3 grams of starting material is sufThis article not subject to
ficient to define the separation. It has also been our experience that Soxhlet extraction a t elevated temperatures requires days to complete and the “soluble” final product of each extraction contains some insoluble material. Finally we wish to introduce a pre-treatment step of the coal-derived oil prior t o solvent extraction. By freezing the oil in liquid nitrogen, one can grind the solid pieces into a fine powder of great surface area. This contributes to rapid and efficient extraction of the pentane soluble material a t the onset of the procedure.
EXPERIMENTAL A coal-derived product is chosen and mixed well if it has been standing for more than 1 h after processing. Most liquefaction products may be warmed to 60 “C and stirred to obtain a uniform mixture. Solids may be chipped or broken. Three to four grams of the product are weighed into a tared 250-mL Pyrex heavy wall or a 315-mL stainless steel (DuPont No. 00522) centrifuge tube to =k5 mg or less. Add liquid nitrogen to the centrifuge tube slowly until 100 mL can remain as a quiet solution-no rapid evaporation. The now frozen product is ground with a thick glass rod into a fine powder. As the liquid nitrogen nears complete evaporation, place the centrifuge tube in a 50-watt ultrasonic bath and sonicate while adding 240 mL pesticide grade n-pentane and stirring rapidly with a glass or Teflon rod. Continue to sonicate and stir until no large particles are present-only a fine powder-approximately 5 min. When sonication is complete, centrifuge for 10 min at 2500 rpm (up to 10000 rpm have been used), 25 “C. The resulting supernatant is decanted into a tared 250-mL round bottom flask and pentane removed under dry nitrogen flush on a Rotovap from a warm (50 “C) water bath until 5 min after the last drop of pentane is observed to condense. The centrifuge tube is washed with 200 mL n-pentane, sonicated, stirred, and centrifuged again, decanting the supernatant into the same distilling flask. The solvent recovered from the Rotovap should be used as part of the next wash to reduce loss. Washing is continued until 1 L of n-pentane is used. After the last wash, pesticide grade benzene is added to the residue and the sonication and washing process repeated for a total of 1 L of solvent decanting into a second distilling flask. The water bath temperature is raised to 80 “C. The final benzene wash may be followed by a 50-mL n-pentane
U S . Copyright. Published 1978 by the American Chemical Society
