1774
ANALYTICAL CHEMISTRY
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the original perchloric arid solution, thus avoiding the necessity of weighing out a separate s:tmple. T h e comparative method (graphic measurement and comparison with a standard) was used in all cases in calculating the aluminum or zinc concentration of u n k n o m solutions. Taylor (8) has examined the comparative and absolute methods and concluded that the former is more suit,able for routine analytical application, as it is not necessary to exercise a rigid control over conditions if standards are run with each series of samples. Polarographic maxima v-ere not seen in any of the polarograms recorded. Methyl red and bromophenol blue are acting as maximum suppressors as xvell as indicators in t’his case. T h e use of methyl red as a maximum suppressor has been discussed by Kolthoff and Lingane (4). This met,hod was intended for use in the study of segregation of major constituents in magnesium alloys. S n illustration of the effectiveness of this method in showing differences in the composition of adjacent samples is given in Figure 1. Drilling8 were taken from a magnesium casting and analyzed according t o the above procedure. I n this figure, the results of these analyses are plotted against the posit’ion of the sample in the casting. The percentage of magnesium as determined by difference is included and s h o w a typical inverse segregation effect. Results of the colorimetric manganese determination are also shon-n. ACKNOWLEDGMENT
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This work was carried out a t the Naval Research Establishment of the Defence Research Board of Canada as part of Project Kumber D12-75-35-02. T h e permission of the board to publish this work is gratefully acknowledged.
0.5 1.5 2.5 DISTANCE THROUGH CASTING ( INCHES) Figure 1.
Segregation of major constituents in a magnesium casting
chrome Garnet 1-m d Pontochronie Blue Black R. T h e latter is often supplied in the form of a zinc salt and a polarogram of the pure dye qhould be checked for a zinc wave before proceeding with the determination of this element. I n the cource oi this 11-ork, it was found that manganese can be determined toloi imetrically with periodate in an aliquot of
LITERATURE CITED
(1) (2) (3) (4)
Gull, H. C., J . SOC.Chem. Ind. 56, 177 (1937). Heller, B. A., Zan’ko, 8 . AI., Za.~odsizayaLab. 8 , 1030 (1939). Ibid., 9, 513 (1940). Kolthoff, I. RI., Lingane, J. J., “Polarography,” vol. 1 , p. 162, Interscience, Xew York, 1952. ( 5 ) I b i d . , vol. 2, p. 515. (6) Zbid., p. 617. (7) Stenger, V. il., Kramer, W. R., Beshgetoor, d. ti-., ISD. EX. CHEW, ANAL.ED. 14, 797 (1942). (8) Taylor, J. K., Awat. CHEU.19, 368 (1947). (9) Willard, H. H., Dean, J. A , , Ibid., 22, 1264 (1950). RECEIVED for review February 27, 19.56.
Accepted June 25, 1936.
Spectrochemical Analysis of Fabricated Steel with the Rotating Electrode J. P. PAGLIASSOTTI Research Department, Standard
Oil Co. (Indiana), Whiting, lnd.
h simple. rapid, and accurate procedure for the spectrochemical anal?=isof steels in acid solutions has been deieloped. Condensed-spark excitation is used w-ith a rotating graphite electrode. Chromium, copper, manganese. inol?bdenuni, nicLe1, silicon, and vanadium are determined with a precision within 2 to 4qc. The procedure is particularly suited to the needs of the steel consunier, because he cannot control the physical form or metallurgical history of his samples. The steel producer may find the procedure useful for classifying scrap. Extension to the analysis of samples of other metals an dalloy is possible.
C
OXVENTIONAL spectrochemical methods, in which the sample itself serves as one or both of the electrodes, are often of little use for analyzing fabricated steel. Serious problems arise because the steel consumer is not able to control the physical form or metallurgical history of his sample. The steel producer may encounter similar difficulties in the classification of scrap. A method that analyzes steels in solution would not suffer these disadvantages. Several methods have been described for introducing metal solutions into the excitation zone. Electrode carbons have been impregnated with steel solutions (7), a continuous flon- of metal solution has been fed through a capillary
1775
V O L U M E 2 8 , N O . 11, N O V E M B E R 1 9 5 6 hole drilled in an electrode along its axis ( 4 ) ,and porous-cup electrodes (Z), through which the sample solution seeps, have been used for analyzing bronze in acid solution (6). il rotating electrode has been used successfully in these laboratories for determining metals in catalyst solutions ( 5 ) . Investigations of the applicability of this device to the analysis of steel solutions has led to the development of a simple, rapid, and accurate method for determining chromium, copper, manganese, molybdenum, nickel, silicon, and vanadium. METHOD
Ordinary laboratory glassxare and equipment is used for the preparation of samples and standard solutions. The spectrographic equipment (commercially available through Applied Research Laboratories, Glendale, Calif .) includes a grating spectrograph providing a dispersion of 5.2 8.per mm. in the first order, a high-precision source unit (S),a Universal arc-spark Etand equipped with a rotating-electrode attachment, and a comparator-densitometer. The rotating-disk apparatus is illustrated in Figure 1. A disk 0.125 zJ= 0.005 inch thick, cut from a high-purity graphite rod 0.5 inch in diameter, is mounted on a tapered rotating carbon shaft. ,4 stream of air is directed through the excitation zone by positioning a '/r-inch gas-inlet tube ahove the optical axis inclined toward the excitation zone. The current of air directs the vapor cloud am-ay from optical surfaces.
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sample m i g h t , liquid volume, and acid content mill not affect the accuracy of the method. Chemically analyzed steels dissolved in the same manner as the samples serve as standards. Alternatively, synthetic standards may be prepared by dissolving pure metal constituents.
A portion of the prepared sample or standard solution is transferred to a small porcelain combustion boat and placed on the lower electrode clip of the arc-spark stand. The clip is raised until the lov-er quarter inch of the rotating disk dips into the solution. B fresh disk is used for each exposure. The disk, which is of positive polarity, is rotated a t 5 r.p.m. A hemispherically tipped counterelectrode cut from a graphite rod 0.25 inch in diameter is used. The clip holding the counterelectrode is watercooled. Ten liters of air per minute are directed through the excitation area. High-voltage condensed-spark excitation is used. Excitation and exposure constants are shoivn in Table I. Spectrum Analysis KO.1 film is used for recording spectra; film processing, photometrj-, and calculation of results are carried out in the conventional manner. Spectral lines used and related data are shov n in Table 11.
Table I.
Excitation and Exposure Constants
Added inductance, p h . Current, amperes Analvtical pan. mm. Electrode siekh, r.p.m. Electrode diameter, inch Electrode thickness, inch Primary slit width. p Air flow, literelmin. Pre-exposure period, see. Exposure period, see.
360 2 3 5
0.5 0.125 60 10 20 60
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Table 11. Analytical Lines and Related Data (Internal standard. Analytical Line,
Index&,
Cr Cr Cu Mn hlo h-i Ni Si V (I
line.
Figure 1.
2 4 0
0.15 2.3 0,045 0 61 0.25 0.20 0.93 0 32 0.28
1
4 8 0 6 0
70
0.07
0 023 0.27 0.15 0.10
...
0.10 0.17
Concentration a t which intensity of analysis line equals t h a t of standard
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Rotating-disk apparatus
2677 2822 3274 2933 3170 3414 3012 2881 3184
Limit of Detection,
Range, 3,73 0.07 -0.6 0 . 5 -3.5 0,023-0.15 0.27 -1.2 0.15 -0.7 0 . 1 -0.7 0 . 5 -3.5 0.17 -0.4 0.1 -0.5
%
.I.
F e 3205.4 A.)
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INTERNAL STANDARD: Fa 3 2 0 5 . 4
4
The steel samples are prepared as drillings to obtain material in convenient form for weighing and dissolution; 0.50 =t0.05 gram of the sample is weighed into a 125-ml. Erlenmeyer flask and treated with acid t o dissolve it. No single acid or acid mixture is satisfactory for all steels. If silicon is not t o be determined, a usually satisfactory treatment is: 10 ml. of a mixture of 1 volume of 70% perchloric acid plus 2 volumes of 85% phosphoric acid, followed by 15 ml. of a mixture of 1 volume of 70% pefchloric acid plus 2 volumes of 80% sulfuric acid (8). If silicon is to be determined, 25 ml. of 6A' nitric acid is often satisfactory. The particular acid used does not appear to be critical, provided samples and standards are treated alike and solution of the elements t o be determined is complete. No attempt has been made to find a dissolution procedure for those steels not soluble in nitric acid but requiring a silicon determination. When solution is complete, the volume is adjusted to 50 ml. Because the iron serves as a n internal standard, 10% variation in
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CONCENTRATION, X
Figure 2.
Analytical curves
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A N A L Y T I C A L CHEMISTRY Table 111.
Analytical Line, A. C‘r 2677 2 Cr 2822 4 C u 3274 0 &In 2933 1
Mo 3170 4 Xi 3414 8 Ni Si V
3012 0 2881 6 3184 0
Precision of Steel .4nalysis s o . of Detns.
32 8’ G4 64 47 32 32 15 15
Average Concn.,
Coefficient
5%
Variation
0.76 4.00 0.087 0.68 0.38 0.44 1.75 0.23 0.23
2.1 1.8 2.1 1.9 1.7 2.7 1.9 4.1 1.5
Of
silicon separates from nitric acid solution; it is probably colloidally dispersed and can be determined accurately. Sensitivity of the method is shown in Table 11. h spectralline-plus-background intensity 1.5 times that of the adjacent background was considered limiting in arriving a t these values. These sensitivities are generally satisfactory for the inspection of fabricated steel parts and for classifying scrap. Increased sensitivity, if desired, can be obtained either by increasing t h e concentration of the steel samples in the test solution or by using interrupted-arc excitation. LITERATURE CITED
DISCUSSION
Precision of the method is shoxn in Table 111. Expressed as coefficient of variation, the precision for all the metals but silicon is within about 2T-that is, the 95% confidence limit of a single analysis is about 4 q of the amount present. Two questionable results of 235 determinations were rejected in preparing Table 111. Criterion for rejection was a 95% confidence as shonn by the statistical Q test ( 1 ) . The error for silicon, although twice that for the other elements, is within acceptable limits, Good accuracy is indicated by comparative testing of synthetic standards and of steel standards certified by the Sational Bureau of Standards. The analytical curves for manganese and nickel, shown in Figure 2, indicate good agreement. The slope of the curve for silicon and the precision data indicate that little
(1) Dixon, W. J., llassey, F. J.. “Introduction t o Stati-tical dnalysis,” p. 146, NcGraw-Hill. Sew York, 1951. (2) Feldman. C.. dsar.. CHEST.21. 1041 (1949). (3j Hasler, i l . F., Kemg. J. IT.,~Iiller,‘W.H., J . Ol,t. SOC. Anm-. 37, 990 (1947). (4) llilliman, S., Kirtchik. K. H., .Is.AI.. (‘HEM. 26, 1392 (abstract)
(1954).
( 5 ) Pagliassotti, J. P., Porache, F. W., I t i d . , 2 4 , 1403 (1952). (6) Scribner, B. F., Ballinger. J. C., J . Reseuch S a t l . B u r . Standards 47, 221 (1951). ( 7 ) Sloviter, H. .I., Sitkin, .I., J . Opt. SOC.Amer. 34,400 (1944). ( 8 ) Smith, G. F., “llixed Perchloric, Sulfuric and Phosphoric .kids and Their Applications in bnalysia,” 2nd ed., G. Frederick Smith Chemical Co., rolumhus, Ohio, 1942. RECEI!-ED for review h-ovember 14, 1955. Accepted J u n e 28. 195fi. Pittsburgh Conference on .Inalytical Chemistry and Applied Spectroscopy, March 4. I!755,
Determination of Carbon and Hydrogen in Organic Fluorine Compounds Microcombustion Method for Gases, liquids, and Solids R. N. MCCOY and E . L. BASTIN
Shell Development Co., Emeryville, Calif.
A conventional microcombustion procedure for the determination af carbon and hydrogen was frequently found unsatisfactory for the successive anal)-sis of highly fluorinated organic materials. A modified combustion tube filling, maintained at 900” C. and containing two sections of magnesium oxide separated by a section of copper oxide, ensures complete oxidation of the sample and removal of fluorine from the combustion products. The precision found was somewhat better for hydrogen and somewhat poorer for carbon than that for the nonfluorinated samples using a conventional procedure. Because the apparatus includes a system for measuring and transferring gaseous samples to the combustion tube, it can thus be used for samples ranging from gases to solids.
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ARIOUS workers have shown that conventional procedures for the determination of carbon and hydrogen in organic fluorine compounds are often not satisfactory because the fuorine-containing combustion products react with the‘silica combustion tube to form silicon tetrafluoride. This gas passes into the absorption train and is retained, causing high results ( 2 , 15). Throckmorton and Hutton ( 1 6 ) recently reviewed a number of combustion procedures for this determination and subsequently used magnesium oxide placed in the sample end of the microcombustion tube for removing fluorine from the combuetion products.
Because fluorinated organic materials may contain little or n o hydrogen, their hydrogen content is a sensitive measure of t h e extent of fluorination and i t must be determined accurately. It is well known t h a t lead peroxide, frequently used in combustion tube fillings to absorb oxides of nitrogen, is partially hydrated. Close control of the amounts of water produced by the sample and the volumes of carrier gases passed over the lead peroxide is necessary t o maintain a steady state and to obtain quantitative transport of water to the absorption train ( 5 , 7 , 9 ) . Thus, samples containing little or no hydrogen produce little or no water and dehydrate the lead peroxide, causing high hydrogen results (16). Subsequent analyses of compounds containing more hydrogen give low results for hydrogen, because the dehrdrated lead peroxide absorbs some of the water. The physical properties of highly fluorinated organic materials are such t h a t many of them are gases. For this reason a general method for the analysis of these compounds should include provision for measurement and transfer of gaseous samples to the combustion tube. The procedure described here makes use of magnesium oxide as part of the combustion tube filling as suggested by Throckmorton and Hutton. However, TTith the types of compounds analyzed and the apparatus and procedure used, it was found nece3sary to place the magnesium oxide differently to ensure complete retention of fluorine. The lead peroxide section in the combustion tube filling used by Throckmorton and Hutton was omitted, as they suggested, t o avoid the hydration problems mentioned above and thus to achieve greater accuracy for hydrogen
