ANALYTICAL CHEMISTRY
1778 Table IX. Sample No.
19137a
Description
A P I , Fresh Natural Catalyst VanaIronb Nickel dium
Constituent
X-Ray Spectrographic Results for Analysis of Catalysts 33966“
9234@
~
Iron
A P I , Artificially Contaminated Synthetic Catalyst VanaSickel dium Iron
Kickel
21261- __
21715
Vanadium
Iron
0,0670 0,0670 0 0700 0.0710 0,0743 0.0726 0 0700 0.0725 0.0690 0.0700 0.0704 0.0048
0 2444 0 2444 0 2422 0 2422 0 2467 0 2450 0 2444 0 2450 0 2430 0 2460 0 2443 0 0028
Regular Production Catalyst VanaNickel dium Iron Sickel
~T’ann-
dirini
% Found
AV. Precision,2#
0 . 8 9 5 0 0050 0.920 0 0050 0.885 0 0060 0.900 0 0045 0 . 9 2 0 0 0055 0.895 0 0050 0.895 0 0045 0 . 9 0 0 0 0060 0 . 9 1 5 0 0055 0.885 0 0050 0,901 0 0052 0 . 0 2 6 0.0010
0 0 0 0
0080 0113 0110 0098
0 0085 0 0110 0 0095 0 0115 0 0100 0 0100 0 0101 0.0023
0.4550 0.4725 0.4726 0.4600 0.4555 0.4550 0.4600
0 1009 0.1012 0 1018 0 1027 0 1008 0 1015 0 1018 0.4550 0 1020 0.4555 0 1000 0 . 4 6 0 0 0 1010 0.4601 0.1014 0.014 0.0015
1012 I005 1015 1008 0 1006 0 1006 0 1015 0 I005 0 I010 0 1010 0.1009 0.0008 0 0 0 0
0.2500 0.2550 0.2525 0.2498 0.2560 0.2500 0.2525 0.2450
0835 0890 0825 0825 0835 0825 0830 0880 0.2550 0 0835 0 . 2 5 0 0 0 0835 0.2514 0 0842 0.0063 0.0047 0 0 0 0 0 0 0 0
0 0123 0 0180 0 0110 0 0130 0 0120 0 0125 0 0130 0 0110 0 0115 0 0120 0.0126 0 0044
0112 010.5 0124 0115 0 0123 0 0115 0 0120 0 0115 0 0112 0 0120 0 0116 0.0011 0 0 0 0
0125 0950 1025 0950 0925 0925 0950 0 0960 0 0920 0 0950 0 0948 0.0061
0 0 0 0 0 0 0
0.0113 0.0120 0 0115 0.0145 0.0130 0 0115 0.0120 0.0115 0.0110 0.0115 0.0120 0.0022
Chemical< 0.947 0.0026 0.0081 0.416 0.119 0 101 0 251 0.086 0.070 0.239 0.0109 0.0072 ... . a These samples and chemical analyses were received through courtesy of Committee on .inalytical Research of American Petroleum Institrite. I, Obtained by extrapolation of calibration curve. C Average of replicate determinations in several laboratories.
fluorescence has been developed. The method has shown to be rapid, about 15 minutes being required for a complete analysis. When proper sampling techniques are employed, excellent precision is obtained, and the precision, measured by the standard deviation a t the 95% confidence level, can be expected to be of the following orders of magnitude: Element Iron Nickel Vanadium
Range, W t . 0 . 1 -1.0 0.002-0.10 0.002-0.10
Precision, 2 0 3% (relative) 0,002 0.002
With recognition of rapidity, the accuracy of the x-ray method aa determined by comparison with analyzed synthetic samples
is reasonably good.
.
0 0575 0 0600 0 0565 0 0560 0 0580 0 0570 0.0560 0 0575 0 0580 0 0565 0 0573 0 0024
...
deep interest and helpful criticisms which have made this work possible. LITERATURE CITED (1) Brissey, R.
JI.,ANAL.C H E M .24, , 1034 (1952).
(2) Ibid., 25, 190 (1953). (3) Brissey, R. M., Liebhafsky, H. A,, and Pfeiffer, H. G.. “Exami-
nation of Metallic Materials by X-Ray Emission Spectrograph,” Symposium on Fluorescent X-Ray Spectrographic Analysis -4STJl Meeting, Atlantic City, N. J.,June 1953. (4) Compton, A. H., and Allison, S. K., “X-Rays in Theory and Experiment,” 2nd ed.. Piew York, D. Van Nostrand Co.. 1935. (5) Davis, E. N., and Van Nordstrand, R. 8.. . ~ X A L . C H E X . ,26, 973 (1954).
ACKNOWLEDGMENT
(6) Friedman, H., and Birks, L. d.,Rev. Sci. Instr., 19, 343 (1948).
The authors wish to express their gratitude t o E. L. Baldeschwieler of the Esso Laboratories, Research Division, for his
RECEIYEn for reriew hfay 26, 1954. Accepted August 19, 1954. Presented before the meeting of the American Petroleum Institute, Houston, Tex., 1954.
Photometric Determination of Magnesium in Electronic Nickel C. L. LUKE and M A R Y E. CAMPBELL Bell Telephone Laboratories, Inc., M u r r a y
Hill, N. 1.
In the manufacture of vacuum tubes it is necessary to control the magnesium content of the nickel from which the cathodes are made. -4 new photometric 8-quinolinol-chloroform extraction method for the determination of 0.001 to 0.1% of magnesium in electronic nickel has been developed. After removal of interfering metals by hydroxide, oxalate, sulfide, and carbamate separations, butyl Cellosolve and ammonium hydroxide are added and the magnesium is extracted into a solution of 8-quinolinol in chloroform and determined photometrically.
B
ECBUSE one of the important factors which determine the
life expectancy of a vacuum tube is the magnesium content of the nickel used in the manufacture of its cathode, an accurate analytical method for the control of the magnesium content is required. As the amount of magnesium present is usually in the range of 0.001 t o O . l % , and the sample size is often limited, the method used must be very sensitive. The Titan Yellow photometric method has been used in this analysis, but it has not proved satisfactory because of its inade-
quate sensitivity and poor reproducibility. I n view of the fact that aluminum and several other metals have been determined by photometric 8-quinolinol (exine)-chloroform extraction methods, it seemed probable that magnesium might be determined in the same manner, following the removal of all interfering metals by suitable separations. Experiments showed, however, that whereas magnesium can be quantitatively precipitated in ammoniacal solution by 8-quinolinol, it is very incompletely extracted from ammoniacal solution by a solution of 8-quinolinol in chloroform. rin attempt was made, therefore, to find a suitable water-immiscible solvent for the magnesium quinolinate. Of all those investigated, only acetophenone was found to be a good solvent for the magnesium compound. The analytical results obtained with it, however, were not reproducible and its odor was objectionable. The possibility of improving the chloroform extraction was next considered. Experiments have shown that this can be done by the addition of a water-miscible organic solvent to the aqueous solution. It has been shown that butyl Cellosolve improves the extraction of antimony-rhodamine B compound by benzene (1), and that the addition of butyl Cellosolve to the aqueous solution
V O L U M E 2 6 , N O . 11, N O V E M B E R 1 9 5 4 greatly improves the extraction of magnesium quinolinate by chloroform. As a result, a very satisfactory photometric method for the determination of magnesium in electronic nickel has been developed. The extraction of the magnesium quinolinate is controlled by the pII of the solution, the concentration of the butyl Cellosolve in the aqueous solution, and the concentration of the 8-quinolinol in the chloroform layer. By arranging to extract from a 5y0 butyl Cellosolve solution having a p H of 10.0 to 10 2 15 ith a 3Y0 solution of 8-quinolinol in chloroform, the extraction of the magnesium compound is made almost quantitative. The three variables mentioned must be carefully controlled if reproducible results for magnesium are to be obtained. Because of the lack of specificity of 8-quinolinol as a reagent for magnesium, the magnesium must be almost completely isolated before its determination is attempted. Electronic nickel usually contains small amounts of cobalt, iron, manganese, copper, aluminum, titanium, silicon, sulfur, and carbon, and traces of boron, lead, calcium, chromium, and zinc may also be found. Experiments have shown that aluminum and other members of the ammonium hydroxide group can be quantitatively removed by precipitation with ammonium hydroxide if a small amount of ferric iron is added as a collector. Magnesium is lost by copreciptation if too much iron is added, or if nickel precipitates. A sufficient amount of ammonium salts must be present t o prevent precipitation of magnesium, but the salt concentration must not be so great as to prevent the subsequent attainment of a high p H a t the time of the 8-quinolinol extraction. Following the ammonium hydroxide separation, nickel, cobalt, copper, zinc, and lead can be removed by an ammonium sulfide separation. Calcium, if present, will interfere with the determination of magnesium, as some calcium quinolinate is extracted by chloroform when magnesium is present. Strangely enough, little or no extraction occurs when magnesium is absent. The interference can be eliminated by removing the calcium as oualate. Barium and strontium do not interfere. Follon ing the oxalate and sulfide separations, the solution is still contaminated by traces of nickel, manganese, and other metals which may have escaped the sulfide separation. I n order to eliminate the interference of these impurities in the 8-quinolinol extraction it was necessary to resort t o a carbamate separation. Whereas manganese is incompletely precipitated by sodium diethyldithiocarbamate in acid or ammoniacal solution, precipitation is virtually complete in neutral solution. The carbamate separation removes all interfering trace impurities without carrying down magnesium. Both 8-quinolinol and magnesium quinolinate in solution in chloroform exhibit absorption in the near ultraviolet spectral region. Experiments show that the optimum wave length for the measurement of the concentration of the magnesium compound is 400 mw. At this wave length the absorption due to the 8-quinolinol is relatively low, while that due to the magnesium compound is sufficiently great t o provide high sensitivity in the analysis. By using a narrow band width in the photometric measurements, calibration curves t h a t are almost linear can be obtained. I n the present work a Beckman Model €3 spectrophotometer was used. REAGENTS
Standard Magnesium Solution (10 y of magnesium per m1.L Dissolve 0.0500 gram of pure magnesium metal by warming gently with 5 ml. of nitric acid (1 t o 2) in a covered conical flask. When dissolution is complete, heat to expel oxides of nitrogen. Transfer to a 500-ml. volumetric flask, dilute t o the mark with distilled water, and mix. Transfer a 25.0-ml. portion of this solution to a 250-ml. volumetric flask, dilute t o the mark with distilled water, and mix. Ferric Nitrate Solution. Dissolve 0.10 gram of pure iron in 5 ml. of nitric acid (1 to 2), heat t o expel oxides of nitrogen, and dilute to 100 ml. with distilled water. Oxalic Acid Solution. Dissolve 5 grams of oxalic acid in 100 ml. of distilled water.
1779 Carbamate Solution. Dissolve 1 gram of sodium diethyldithiocarbamate in 25 ml. of distilled water and filter through a medium texture paper. Prepare fresh just before use. Butyl Cellosolve Solution. Pipet 50.0 ml. of butyl Cellosolve into a 100-ml. volumetric flask, dilute to the mark with distilled n-ater, and mix. 8-Quinolinol Solution. Dissoh-e 3 grams of 8-quinolinol in chloroform and dilute to 100 ml. with chloroform in a volumetric flask. Prepare fresh just before use, PROCEDURE
Preparation of Calibration Curve. Transfer 0, 2.0, -4.0, 6.0, and 8.0 ml. of st,andard magnesium solution (10 y of magnesium per ml.) to 100-ml. beakers, add 2 ml. of nitric acid (1 to l), and dilute to 40 f 2 ml. Neutralize the solution to Congo red paper with ammonium hydroxide. Add 5.0 nil. of butyl Cellosolve solution and then 10 ml. of ammonium hydroxide. Transfer to a 125-ml. Squibb-type separatory funnel, add 20.0 ml. of 8-quinolinol solution, stopper, and shake vigorously for 1 minute. Allow the layers to separate and then filter about 18 ml. of the chloroform solution through a dry 5-cm. coarse-texture filter paper into a dry 50-ml. conical flask. Swirl and transfer a portion of the solution to a 1-em. absorption cell. Measure photometrically a t 400 mp, using pure chloroform as the reference solution. Prepare a calibration curve. Analysis of Nickel Sample. Depending on the magnesium cont,ent, transfer 0.0100 t,o 0.1000 gram of the sample to a 125-ml. Vycor conical flask. Carry a reagent blank through all steps of the procedure. Add 2.0 ml. of nitric acid (1 to l), cover, warm gently unt,il the action starts, and continue warming only as needed to keep the reaction going. Remove from the hot plate as soon as dissolution is complete. IgriorP any insoluble residue of carbon, silicon, or tungsten. Add 1 nil. of ferric nitrate solution and dilute to 40 ml. with distilled watw. Neutralize to Congo red paper with ammonium hydroxide and add 1.0 ml. in excess; this excess of ammonium hydroxide is great enough to prevent precipitation of nickel xithout permitting solution of aluminum or chromium hydroxide. Heat rapidly to 65' to 70 C. to coagulate the precipitate; the rate of heating and the temperature must be controlled to prevent loss of ammonium hydroxide with resultant precipitation of nickel. Filter into a 250-ml. Vycor beaker through a 9-em. medium-text,ure filtpr paper. Do not wash, but allow t o drain well and then carefully lift an edge of the paper so as to relpase the solution retained in the funnel st,em.
Table I.
Determination of Magnesium in Synthetic Samples RIg Added,
50.
Y
1
10 40 80 40 40 40 40
2
3 1 5 Cia
7 8
9 10 11 12
13 14
40 ti0
40 20 60 20 40
Impurities Added &-one
Mg Recovered, Y
8.9 37.7 78.7 39.6 89.4 39.6 41.0 38.9 61.9 39.6 18.8 58.6 19.0 44.6
a 15-nig. portion of pure nickel was taken t o determine if calcium is removPd when amount of NiS is smaii.
Add 2 nil. of oxalic acid solution to the filtrate. Pass in hydrogen sulfide for 5 minutes. Let stand for 5 minutes and then filter into a 250-ml. Vycor beaker through a 9-em. medium texture filter paper. Do not wash, but allow to drain well and then release the column of filtrate in the funnel stem by carefully lifting an edge of the paper. h d d a few siliron carbide granules to the filtrate, and boil uncovered donn to 20 ml. in order to expel ammonium sulfide. Cool to room temperature and add 5 ml. of carbamate solution. A l l o ~to stand 10 minutes, filter through a 9-cm. fine-texture filter paper, and n-ash once with a small amount of distilled XT-ater. Ignore any faint pink color in the filtrate. Dilute the filtrate to 40 zk 2 ml. with distilled water. Add 5.0 ml. of butyl Cellosolve solution and 10 ml. of ammonium hydroxide and proceed w i t h i h e extraction as directed above. With the
1780
ANALYTICAL CHEMISTRY
aid of the calibration curve, determine the weight of magnesium in the sample. EXPERIMENTAL
In order to test the accuracy of the method, synthetic samples of known magnesium content were prepared by dissolving 0.1gram samples of very pure nickel in the recommended manner, and then adding aliquots of standard magnesium solution plus aliquots of solutions of various other metal impurities. The aliquots of most of the metal impurities contained 100 y of the metal in question; in the case of cobalt, 500-7 portions were added. The results obtained by the recommended procedure are recorded in Table I. 'The values shown in the last column have been corrected for a small amount of magnesium (approximately 2 y ) found in the reagents plus nickel. I n order to test the reproducibility of the new method, magnesium was determined in several types of cathode nickel samples (Table 11). Sample Cathaloy A-31 contained about 4% of tungsten and the average value obtained several years ago
on sample 220 (melt H-1400) by eight different laboratories, using photometric, spectrochemical, and gravimetric methods, was 0.040% magnesium.
Table 11. 220,
Determination of Magnesium in Electronic Nickel Samples 220 Melt H-1400,
%
%
0.038 0.038
0.041 0.041 0.041
0.040 0.039
225,
%
0.066 0.066 0.064
999 None detected
Cathaloy A-30,
Cathaloy A-3 1,
0.028 0.025 0.027 0.028
0.038
%
%
0.038 0.038
0.039
LITERATURE CITED
(1) Luke, C. L., and Campbell, 11.E., ANAL.CHEW,25, 1592 (1953). RECEIVED for review March 27, 1964. Accepted July 29, 1954,
Recent Developments in White Sugar Colorimetry T. R. GILLETT and W. D. HEATH California and Hawaiian Sugar Refining Corp., Ltd., Crockett, Calif,
Color is especially important in the sugar industry, where color removal is one of the primary objectives of the refining process. Color measurement is required in the research laboratory, and in the plant for control of operations and for maintenance of product quality. Many procedures for sugar color measurement have been developed, but no one method has yet received general acceptance in the industry. Today, most laboratories use methods and instruments which they have devised or adapted. This lack of uniformity has led to considerable confusion in units and terminology, which has made it nearl? impossible to formulate uniform quality standards in the sugar and sugar-consuming industries. These difficulties have been recognized for some time and considerable work has been done in an effort to correct the situation. Some recent developments in this field are outlined in this paper, and a proposed method and instrument for measuring the color of white sugar solutions are discussed.
S
UGAR colors, in general, range from the brown of raw sugars
to the slight yellowish or white color of refined products. While it would be extremely desirable to utilize a single method and instrument for both light and dark sugars, it is not yet possible to do this in a simple manner. Therefore, separate methods are generally utilized for light and dark colored products. I n early years, color determinations were generally made by visual methods which involved comparisons of sugar solutions with various color standards of glass or solutions of mineral salts. Some of these methods are still in use ( 1 , 11). Since the photocell has been developed, photoelectric procedures have gained general acceptance. These procedures are now widely used because of their better reproducibility as compared to visual observations. Most photoelectric methods are based on a measurement of the amount of light which can be transmitted through the sugar solution as compared to that which can be transmitted through a reference standard, such as distilled water. Colorimeters, which employ glass color filters, are usually used for this measurement. In recent years, spectrophotometers have also received considerable application due to their greater accurkcy and ability to iso-
late relatively narrow wave bands of light. However, because of their more complicated nature and higher cost, spectrophotometers are primarily employed for research work, and are not too generally used for routine measurements. Although photoelectric color instruments and methods offer numerous advantages over visual methods, various problems are involved in obtaining accurate and uniform procedures. Small amounts of light-scattering particles are sometimes present in sugar solutions, and this turbid material has a pronounced effect on the transmittancy reading. For dark sugars, filtration can usually be used for its removal. I n white sugars, however, filtration is difficult ( S ) , and can effect some color removal. Filtration procedures previously recommended for white sugars (10) are too slow and cumbersome for routine use. To overcome these difficulties, turbidity compensation has been advocated by several investigators (3, 6, 8, 9) as a substitite for filtration. Turbidity compensation usually requires measurements a t two points in the spectrum and the application of an empirically determined corrective factor, based on the relationship between the two readings. This correction is valid only where the character and size distribution of the turbid particles remain relatively constant. Fortunately, the turbidity of most adequately refined white sugars is uniform enough to permit this simplification, and turbidity compensation has been used for control analyses for these products by many laboratories in the sugar and allied industries. Various other problems exist in the preparation of solutions prior to color determination, the establishment of suitable and uniform terminology, and the development of a simple but arcurate photoelectric instrument. RECENT DEVELOPMENTS
I n the past 2 to 3 years, many investigators have been working to solve some of these problems in sugar color measurement (4). Considerable attention has also been devoted to developing standardized methods and terminology which, if generally adopted, would eliminate some of the present confusion in this field. Zerban (IS) recently proposed a standard color method for raw sugars as a result of his work with the Association of Official Agricultural Chemists. Broeg and Walton (1)have developed visual color standards for cane sirups and edible molasses.
