320
ANALYTICAL CHEMISTRY
The temperature coefficient of transmittancy of the osmiumthiourea system is so slight that n o difficulty is encountered from temperature variations of a few degrees. The tolerance of the osmium-thiourea system for moderate amounts of ruthenium is particularly fortunate, in that a very sharp separation of ruthenium from osmium would not be required. LlTERATURE CITED
(1) Ayres, G. H., ANAL.CHEM.,21, 652 (1949). (2) Chugaev, L., 2.anorg. Chem., 148, 65 (1925). (3) Crowell, W. R., and Baumbach, H. L., J . Am. Chem. Soc., 57, 2607 (1935). (4) Crowell, W. R., and Kirschman, H. D., Ibid., 51, 175, 1695 (1929).
(5) International Critical Tables, 1’01. T‘, p. 367, New York, hlcGraw-Hill Book Co., 1929. (6) Klobbie, E. A., Chem. Zentr., 11, 65 (1898). (7) Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. XT‘, p. 520, New York, Longmans, Green and Co., 1936. (8) Ogburn, S. C., Jr., J . Am. Chem. Soc., 58, 2493 (1936). (9) Ogburn, S. C., Jr., and Miller, L. F., Ibid., 52, 4 2 (1930). (10) Paal, C., and Amberger, C., Ber., 40, 1378 (1907). (11) Sandell, E. B., IND.ESG. CHEM.,AXAL.ED., 16, 342 (1944). (12) Steiner. B.. Mikrochemie. 16. 193 (1934). (13) YoeyJ. H.,‘and Overholser, L. G., I ~ DENG. . CHEM.,ANAL.ED., 14, 435 (1942). RECEIVED September 8, 1949. Condensed from a thesis submitted b y William N. Wells to the faculty of the Graduate School of the University of Texas in partial fulfillment of the requirements of the degree of master of arts, August 1949.
Spectrographic Determination of Potassium in Iron Catalysts by Fractional Distillation EDWIN FAST, Phillips Petroleum C o m p a n y , Bartlesville, Okra. A spectrographicmethod for the determination of potassium in iron catalysts has been developed. Potassium was found to distill quantitatively from a sample pellet during the initial arcing period. By photographing the spectrum during this period only, interference due to iron was eliminated. The length of the log sectored potassium line was found to be a linear function of the log concentration of potassium. An average deviation of from 5 to 10% of the amount present is indicated by repeated determinations on the same sample. Sodium and lithium can be determined in the same manner.
I
R O S catalysts containing potassium are important in am-
monia and Fischer-Tropsch syntheses. There may be a tendency for some of the potassium to be volatilized during the preparation of the catalyst, so that the final concentration of potassium is somewhat uncertain. Wet chemical methods for the determination of potassium are tedious; hence a spectrographic method was sought. Potassium has a spectrum relatively poor in sensitive lines in the region of the visible and ultraviolet, The sensitive lines available are the doublets of the fundamentaloseries of which the red lines of wave lengths 7699.0 and 7664.9 A. are the first and hence strongest members. However, because photography in this region is not very convenient and the lines are subject to strong self-reversal, the second or third members in the series are used more frequently-namely, the violet lines of wave lengt$s 4044.2 and 4047.2 A., and the ultraviolet of 3446.4 and 3447.4 A., respectiyely. The violet lines straddle the strong iron line a t 4045.8 A . ; thus they are easily masked in the case of the type samples under consideration. The ultraviolet lines in general do not have sufficient sensitivity. The problem thus resolved itself into one of maintaining or increasing the sensitivity of potassium lines while reducing that of iron lines (and of carbon if carbon electrodes were to be used). I n experimenting with various excitation conditions i t was observed that when a low current, direct current arc was used the sample burned in two stages. At first the arc was almost invisible and burned quietly. After a time it changed suddenly to the characteristic blue color of an iron arc accompanied by a slight hissing sound. The temperature of the sample increased rapidly as this point of change was approached until it formed a molten bead. Moving plate studies showed that during the first period few lines other than those due to potassium appeared, whereas during the latter period the potassium lines were absent and those of iron and other constituents were excited. Thus
potassium was distilled from the catalj-st almost completely before the spectrum of iron was excited. The total energy of the potassium lines was found to be a function of the concentration of potassium. Therefore, in the procedure developed, arcing was continued just long enough to volatilize all the potassium-Le., until the arc assumed a blue color. The principle described is essentially that of the “total energy” method advocated by Slavin ( 2 ) , and in some respects similar to the “carrier distillation” method for the analysis of uranium ores developed bv Scribner and Mullin ( 1 ) . EXPERIMENTAL
ri summary of the experimental conditions under which spectra were obtained is given in Table I. The sample pellet was chosen to be large enough to handle ronveniently but small enough so that the arcing time was not excessive. For the concentration range above 0.25%, the sample ~
Table I. Sample Spectrograph Spectral region Filter Optioal system Slit width Lower electrode Upper electrode Gap Multisource Voltage Arc current Polarity Exposure Emulsion Development Density calibration .4nalysis line
Experimental Conditions
0.100 gram S/u-inch diameter cylindrical pellet, grain size to pass 140-mesh. 21-foot Jarrell-Ash grating Second order 4000 A. Corning No. 774 19.7-cm. focal length plano-convex lens on slit, source 2 1 . 5 om. from slit 30 micions 0.25-inch carbon with flat end to support pellet 0.125-inch graphite, pointed Maintained a t approximately 0.5 mm. C = 60 mfd., L = 560 p h , R 300 ohms Primary 230, secondary 940 2.5 amperes Pellet made positive Until 5 seconds after arc changed Eastman spectrum analyais No. 1 2 minutes in D-19, 20’ C..mechanical agitation Rotating logarithmic apiral sector K 4047 A.
-
321
V O L U M E 22, NO. 2, F E B R U A R Y 1 9 5 0
tensity of distribution along spectral lines was most nearly uniform in this region. The logarithmic spiral sector was rotated as close to the slit as possible. The lengths of the wedge-shaped lines were measured as projected on the screen of an Applied Research Laboratories densitometer-comparator with a magnification of over 20 times. A specially prepared catalyst was analyzed by the well known chloroplatinate method to provide a standard for spectrographic work. (The chemical value of 0.21% potassium in this sample was used throughout this work. A flame photometer analysis gave the result as 0.26% based on synthetically prepared potassium standards.) This standard was diluted with the pure iron oxide as previously described to make a working curve (Figure 1). However, because no internal standard was used, several spectra of the standard catalyst were usually included with a set of analyses to check the work curve. A working curve was also made which relates the arcing time required to volatilize the potassium as a function of the concentration of potassium (Figure 2 ) . This is a convenient rough check, but is not as reliable, because the presence of other alkalies will increase the time required.
Table 11. Analyses of Some Iron Catalysts % ’ K, Repeated Catalyst Magnetite ore 76 108-7
0.01
,,
I I
3
4
108-7 (reduced)
I Figure 1.
~
122-1
5
7 LENGTH OF K 4047, MM.
6
8
9
10
Working C u r v e for Potassium
122-1 (reduced)
1.0
cy
w n
from Time Curve
0.23
9
0 345
1.4 0.22
2 12
1 2 0.22
0.12
6
0.14
0.7:
4
0.845
0.70
4
0 80’L
Average Deviation
0.04 0.03 .. Magnetite ore was used a s starting material for 122-1 and coutains about 0.15% sodium: hence, the apparent per cent potassium as determined from t h e time of arcing is high.
207
was diluted with a pure iron oxide sample prepared in the same way as the catalysts but without potassium. This concentration required an arcing time of about 2 minutes. The pointed upper electrode and small gap were chosen to keep the arc centered on the pellet itself. The flat-end lower carbon electrode served simply as a conducting support for the pellet. No significant differences in results were obtained, holvever, when graphite was used in place of carbon. The condenser lens and source were so positioned that an image of the arc was thrown on the collimating mirror of the large Jarrell-Ash grating spectrograph. The second-order spectrum was used because of the greater dispersion and because the in-
Determinations 0.26, 0.21, 0.24, 0.21, 0.24, 0 20 1.4.. 1.3.. 1 . 4 0.20, 0.18, 0 . 2 2 , 0 . 2 5 , 0 24. 0.21, 0.24, 0 . 2 0 0.12, 0.14, 0 . 1 2 , 0.12,0.11,0.11 0.75, 0 . 7 2 , 0.74, 0 . 7 2 . 0.69, 0 . 8 0 , 0.80 0.74, 0.70, 0.68. 0 . 6 5 , 0.74, 0 . 7 2 0.02, 0.035
%K
%
Average %K
a
RESULTS
The analyses of several catalyst’s are given in Table 11. A number of repeat determinations are given in each case to show what reproducibility is attained. The reported values include both those for which the sample \vas arced as received, and those for which the sample was diluted. The agreement in general is good between the potassium concentration determined from the length of lines and from arcing time. The samples whose time values are high were found to contain about 0.15% sodium, which behaves in a similar manner in the arc. Most samples contained a trace of sodium (usually less than 0.01%) including the standard. The method described is applicable down to about 0.0170 potassium. For lower values it is usually not possible to observe the initial arcing period during which only potassium is volatilized. A definite upper limit was not established, but an anaiysis (without dilution) can be made for samples having up to 1.5Yc potassium-for example, the direct analysis of a commercial ammonia synthesis catalyst ( S o . 76 in Table 11) gave consistent results with that obtained upon dilution of the catalyst to one tenth its original concentration of potassium. However, the arcing time of neaily 8 minutes n-ould be inconveniently long for routine analysis. DISCUSSION
0.01
Figure 2.
Working C u r v e for Potassium Using Arcing Time
The method described here is not applicable to catalysts containing several per cent of carbon. Such samples burned erratically and did not have an initial period during which only potassium was volatilized. Catalysts that have been used in hydrocarbon synthesis will generally have enough carbon deposit to behave in this way. Reduced catalysts may be analyzed, although there is a slight sputtering a t the outset. (The oxide !Then treated with hydrogen is reduced to the metallic state.
322
ANALYTICAL CHEMISTRY
Any subsequent exposure to air results in a partial oxidation. Thus the reduced catalysts which are analyzed are not fully reduced.) A lower arc current would be preferable in this case. No serious attempt was made to find a suitable internal standard in applying this method because the accuracy attained otherwise was deemed satisfactory. Obviously the major constituent, iron, is not a satisfactory standard. Elements found to behave in the same way as potassium were sodium and lithium when added to the iron catalyst. Keither has lines in the immediate neighborhood of the violet potassium lines, but they could possibly be used. Sodium would be less desirable because it occurs as a variable impurity in the samples. Lead and calcium have lines favorably located, but, although they are excited, they are not completely exhausted during the initial arcing period. The possibility of using the arcing time as a measure of the
concentration of potassium is intriguing because of its simplicity. The apparatus required is a stop watch, a controlled direct current arc source, and means for making the sample pellets. The analysis may be performed in a few minutes. The presence of appreciable quantities of yodium (or lithium) could readily be detected by the color of the discharge, and hence such samples could be analyzed spectrographically. Because sodium and lithium behave in the same manner as potassium, a spectrographic analysis niay be made simultaneously for the three elements. LITERATURE CITED
(1) YciihiieI, B. F., and Mullin, H. R., J . Research A-atl. BUT.Standards, 37, 379-89 (1946) ; Research Paper 1753. ( 2 ) Slayin, XI., IXD. EKG.CHEM.,A h - k ~ED.,10, 407-11 (1938). RECEIVED
July 14, 1949.
Chromatographic Estimation of Carotene in Feeds and Feed Ingredients -
3I-IXU-ELLL. COOLEY, Larro Reaeurch Farm Laboratory, General .Mills, Inc., Rossford, Ohio AlVD
R..IY\lOND C . KOEH\', Products Control D e p a r t m e n t , Generul 41ills, Jnc., .Minneapolis, ,Minn. irapid method for the estinlation of chroniatographic carotene in alfalfa meal, corn, corn products, and finished feeds is described. The nse of a combination of three solvents (toluene, ethjl alcohol, and ethyl acetate) results in improvement in the completeness of extraction of carotenoid pigments. The method estimates the total concentration of all the known \itamin .I-acti,e carotenoids.
A
XUMBER of methods for the estraction of carotene from alfalfa meal have been proposed.
Wall and Kelley (11) recommend refluxing the sample for 0.5 hour with 30% acetone and 70% Skellysolve B. The tentative Association of Official .%gricultural Chemists procedure ( 2 ) is essentially a modification of this method but uses a 1-hour reflux time. The extraction method of Silker et a l . (9) is to shake the sample with 1 part of acetone and 2 part,s of Skellysolve B in a tightly stoppered container, after which the mixture is allowed to stand in the dark for 16 to 18 hours. Although the A.0.B.C. phasic method (5) for carotene (crude carotene) is no longer official, provision is made ( 1 )for extraction of carotene from alfalfa meal and similar materials by refluxing with 12% alcoholic potassium hydroxide solution for 30 minutes. S o specific A.O.A.C. recommendation has been made for extraction of pigments from vellow corn and corn products such as corn gluten meal and corn gluten feed. However, Buxton (4)suggests refluxing ground yellow corn for 1 hour with 570 methanolic potassium hydroxide, and Fraps and Kemmerer ( 5 ) recommend 12% alcoholic potassium hydroxide (30 minutes) for extraction of pigments from ground yellow corn. The authors propose the use of a mixture of equal parts of toluene, ethyl alcohol, and ethyl acetate for the extraction of carotenoids and other pigments from plant materials. After the sample is refluxed with the solvent mixture, the solvents are evaporated and the pigments are dissolved in petroleum ether (Skellysolve B). This solution of pigments is passed through a magnesia-Hyflo Super-Cel adsorption column and the carotene is eluted from the column by means of 10% acetone in Skellysolve B. As compared with boiling in 12% alcoholic potassium hydroxide, refluxing alfalfa meal with 30% acetone in Skellysolve B (tentative A.0.rl.C. method) is a good method for extracting the carotene (Table I). Apparently, however, the proposed solvent mivture more completely extracts the carotene than does the 30%
acetone (Table 11). Furthermore, the tentative A.O.A.C. extraction is not applicable to corn and corn products nor to manufactured feeds (Table 111). Refluxing a variety of dried plant materials with 127, alcoholic potassium hydroxide according to the formerly official A.O.A.C. crude carotene method appeared to he the most effective procedure until this work on the new solvent
Table I. Extraction of Carotene chromatographic Carotene, ?/Gram Tentative A.O.A.C. chromatographic method'"
Alcoholic Crude Carotene, potash Phasic Method, through magnesia y /G. 45,4 36.0
Sainple Dehydrated alfalfa meal .I (over 1 year old) Dehydrated alfalfa meal 206.0 190.0 B (fresh) a Extraction \ \ i t h 30% acetone in Skellysolve B for 1 hour.
Table 11.
37.6 195.0
Chroniatographic Extraction of Carotene
Sainple Dehydrated alfalfa meal .An Dehydrated alfalfa meal Ba Dehydrated alfalfa meal C Western sun-cured alfalfa meal
Tentative d.0.A.C. Nethod
Proposed Method
Y/Q.
YIQ.
37.6 195 0 38.5 14.5
210.9 43.0
40.3 17.0 Additional Carotene in Residue) y/g. % of total 4.3 10.0 1.5 9.4
Dehydrated alfalfa meal 38.5 Western sun-cured alfalfa meal 14.5 4 Same sample as in Table I . b Residue from 30% acetone extraction re-extracted with proposed solvents mixture.
