fluoride plates. The spectrum run using sodium chloride plates clearly shows the spectrum of ammonium chloride superimposed on that of the ammonium fluoride. An attempt t o run the reverse exchange, using ammonium chloride mull on the calcium fluoride plate, gave no indication of en ammonium fluoride spectrum. There was also no etching of the calcium fluoride plate although the mull was in contact with it for over an hour. No care was taken to exclude moisture, and the ammonium chloride was used directly from a stock bottle.
All spectra were run using a Beckman I-R5 spectrophotometer. The x-ray powder photograph of the surface scrapings from NaCl plates was taken using CuK, radiation. LITERATURE CITED
( 1 ) Bovey, L. F. H., J. O p t . SOC.Am. 41, 866 (1951). (2) Crocket, D. S., Haendler, H. M., ANAL.CHEM.31, 626 (1959). (3) Ketelaar, J. A. A., Haas, C., van der Elshen, J., J . Chem. Phys., 24, 624 (1956). (4) Kutaelnigg, W., Nonnenmttcher, G., Mecke, R., Chem. Ber. 93, 1279 (1960). \ - - - - I .
(5) Meloche, V. W., Kalbus, G. E., J . Inoro. Nucl. Chem. 6. 104 (1956). (6) PlGmb, R. C., Hornig, D.'F., J. Chem. Phys. 23, 947 (1955). (7) Wagner, E. L., Hornig, D. F., Zbid., 18, 296 (1950). DAVIDS. CROCKET A. GROSSMAN ROBERT Department of Chemistry
Lafayette College Easton, Pa. THISwork waa supported part by the National Science Foundation Grant No. G14180, by the National Science Foundation Undergraduate Research Participation Program, and by the Lafayette College Research Fund.
A General Microqualitative Technique.
Combination of Ring Oven, Cation Exchange Paper, and Emission Spectrograph
SIR: The emission spectrograph is an excellent qualitative tool for very small samples; however, with conventional spectrochemical techniques the nonmetals 0, N, C, S, F, C1, Br, I, and the inert gases are not detected. Frequently the entire sample is consumed and none of the above elements can be identified. Many of the nonmetals exist in solution as anions, whereas the spectrographically detectable elements are cations, with some exceptions such as the permanganate ion. A combination of the Weisz ring oven (6) and cation exchange paper (4is useful in running a complete qualitative analysis on a single drop of solution. EXPERIMENTAL
Apparatus and Procedure. Ring oven, Il'ational Appliance Co., Portland, Ore. Whatman CbI50, carboxymethylcellulose cation exchange paper. Nine-mm. disks cut with a No. 4 cork borer. Whatman 41H filter ~. paper, 5.5-em. circles. Spectrograph, ARL 1.5-meter Quantograph, 2400-4600 A. Kodak S.A. 2 film. The sample is placed on a disk and
Figure 1 .
The filter paper circles were cut in half, and a silver nitrate ring test for chloride on one semicircle was positive in every case. T h e other semicircle and the disk were tested for nickel with dimethylglyoxime and are shown aa A , B, C, and D of Figure 1. The faint nickel ring in C shows that breakthrough had occurred, although the disk is not saturated. The capacity of CM50 as listed by the manufacturer is 0.5 meq. per gram. Sample C contained 0.4 pmole of nickel, which is about 25y0 of theoretical capacity for the 6-mg. disk. When the sample was transferred to the disk on the ring oven without prior drymg, breakthrough occurred a t a much lower level. Elution of Nickel. A sample identical to B in Figure 1 was eluted by washing with 3 N nitric. The resultant dimethylglyoxime test on t h e disk and semicircle, E of Figure 1, shows complete transfer t o the ring.
Separation and elution of nickel chloride A.
0.04 p o l e
B
0.08 pmole C. 0.4 pnole D. 0.8 pmole E. 0.08 pmole (eluted)
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air-dried. The disk is then placed in the center of a filter paper circle, and the anions are washed to the ring with distilled water. The disk and a portion of the ring zone are analyzed spectrographically by placing the paper directly in a graphite electrode for the d.c. arc method. Alternatively, the disk and ring zone may be leached with 6N nitric acid and the solution analyzed by the copper (3) or graphite (2) spark technique. The remaining portion of the ring is sectioned and tested for anions ( 5 )' The cations can be identified with the ring oven also. The cation exchange paper disk is transferred to a fresh filter paper circle and the cations are washed out to the ring with 3N nitric, where ring oven qualitative tests are made. Cation Capacity. Aliquots of a nickel chloride solution were dried on disks and washed on the ring oven.
ANALYTICAL CHEMISTRY
0 1
1
1
1 1 1
Spectrographic Sensitivities. Figure 2 shoivs the results of an evperiment t h a t was designed to determine the spectrographic sensitivity for a number of elements, two of which were present as anions. The nitrates of Pb, Al, Co, Xi, Ca, and Mg; and (NH4)6M07024. H 2 0 and K2CrOP were transferred to disks. Four disks mere prepared, with the first as a blank, and all elements a t 0.25, 2.5, and 25 pg. levels, respectively, on the others. After development, the dry disk and a portion of the ring were folded into a United lOlL spectrographic electrode, and arced a t 13 amperes d.c. for 30 seconds. The densitometric readings were converted to a function of line-tobackground intensity ratios and are plotted against micrograms of the elements in Figure 2 . In a separate experiment the cations of Cd, Sn, Mn, Zn, and Hg were tested in a similar manner a t the 2.5- and 25pg. ler-el. Sn and Mn were detected a t 2.5 pg., and Cd, Zn, and Hg were not detected. Anion Tests. S o systematic qualitative scheme for anions using the ring oven has been published; however, a number of individual tests have been suggested by Weisz ( 5 ) . In this work the following anions were detected in the ring zone after cation s e w ration: I-, CL< CN-, cro4-2, SO;-^, r\.100~-~, si03-', Br-, Br03-3, PO,-3, and KO3-. Cyanide is lost during the separation, apparently as a consequence of the volatility of hydrocyanic acid. This difficulty was overcome by drying a drop of 0.01-V sodium hydroxide on the edge of the filter paper before the ring is developed; then the cyanide test
is run in the alkaline section of the ring. This fact can be used to advantage in eliminating interferences. DISCUSSION
The choice of Whatman CM5O and Whatman 41H was based upon the chloride blank levels after washing. A small cation exchange paper disk in the center of a filter paper circle is used rather than a circle of the ion exchange paper because the latter interferes with some of the qualitative tests. Also, loading and transfer operations are simplified. There is a discrepancy between the cation capacity and the spectrographic sensitivity tests. Twenty-five micrograms each of 7 cations far exceed the capacity of the disk, but Figure 2 shows that line intensity is proportional to element content. For the above reasons the results cannot be considered quantitative, although they do show that there is a blank for three elements. The failure to detect Cd, Zn, Hg, and K is due to the poor spectrographic sensitivity and/or high volatility of these elements. Elution and ring oven tests (5) would be much more sensitive for some elements. It might be best to divide the disk and use both techniques. The time required to make the separation and tests is not materially greater khan that required for the usual ring oven separations ( 5 ) , which are rapid for microchemical techniques.
The separation of cations and test for a single anion can usually be completed in 10 minutes. A general qualitative anion scheme that fits this system is being investigated for specificity and sensitivity. A detailed report will be presented later. Other applications of ion exchange papers and the ring oven are possible through the various separation techniques of ion exchange chromatography, such as the separation of metal chloride complexes on strong anion exchange resins (1). ACKNOWLEDGMENT
The author is indebted to R. T. DeMuth, who has conducted much of the experimental work. LITERATURE CITED
(1) Kraus, K. A., Nelson, F., Proc. Intern.
Conf. Peaceful Uses Atomic Energy, Geneva, 1955 7, 113-25 (pub. 1956). ( 2 ) Morris, J. M., Pink, F. X., Am. SOC. Testing Mater. Spec. Tech. Publ. NO.
221, pp. 39-46 (1957). (3) Nachtrieb, N. H. "Principles a n i Practice of Spectrochemical Analysis pp. 264-77, McGraw-Hill, New Yo& 1950. m. (4) Peterson, E. A., Sober, H. A., J . A Chem. SOC.78, 751.(1956). (5) Weisz, H., L'Microanalysis by the Ring Oven Technique," p. 56, Pergamon Press, New York, 1961. (6) Weisz, H., Mikrochim. Acta. 1954, 140-7. JOHN B. MOONEY Varian Associates 611 Hansen Way Palo Alto, Calif.
Rapid Determination of Aluminum in Minerals and Rocks by Thermal Neutron Activation Analysis SIR: -4ctivation analysis with thermal neutrons from a Van de Graaff accelerator photoneutron source (2-4) is a convenient nondestructive method for routine determination of aluminum in minerals and rocks. The method is very attractive because it makes possible the analysis of 30 to 40 samples per hour and, unlike the technique described by Caldwell and Mills (I), there is no possibility of interference from fast neutron activation of the many other elements commonly found in rocks. EXPERIMENTAL
Apparatus. The neutrons are ated by magnetically scanning electron beam from a 3-m.e.v. de Graaff accelerator a length of
crethe Van
0.75
inch over a 40-mil thick, water-cooled gold target. A portion of the energy in the beam is converted to bremsstrahlung which in t u r n produces neutrons by the Be9 ( y , n)Be8 reaction in beryllium rods located directly below the gold. The beryllium assembly is surrounded by a paraffi moderator in which sample ports are located. In the port b e d for aluminum activations the thermal flux is 2 X 108 neutrons/sq. cm. per sec. a t an electron beam current of 1.0 ma. A block diagram of the sample transfer, irradiation, and counting system is shown in Figure 1. A sample is put in the irradiation position by inserting in a sample loader located near the counter end of a 60-foot polyethylene transfer tube and pressing a button which opens solenoid valves 1 and 2. Air a t a pressure of approximately 40 p s i . is used for propulsion. When the sample enters
the neutron source, it actuates a switch starting an irradiation timer. This timer closes valves 1 and 2 and opens valves 3 and 4 to eject automatically the sample a t a preselected time. With the departure of the sample, the source switch opens, causing a delay timer to start, and subsequently turning on the counting equipment. Two 3-inch diameter X 3-inch thick NaI(T1) scintillation counters are used to detect the 1.78-m.e.v. gamma rays from the 2.3-minute Ala induced in the sample by .the A I 2 7 (n,y ) A I 2 8 reaction. The outputs of the two counters are fed in parallel through an amplifier and a single channel pulse height analyzer to a scaler and a multichannel analyzer. Normally the multichannel analyzer is used only as an aid in selecting and checking on the base line and window width settings of the single channel analyzer. V O L 34, NO. 1 1 , OCTOBER 1962
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