Table 111. Sensitivity of Reagent Quinalizarin Carminic acid Chromotropic acid Xethylene blue Curcumin Tetrabromochrvsazin Barium chloraLilate (tartaric acid) Barium chloranilate (saccharic acid)
Boron Methods
Absorptivity 28-650 190-600 480 7500 560-3400 790-1000 227, 355 mp 19, 530 mp 1207, pH 9.5, 346mp 165, pH 8.8, 355 mp
range over that of the tartaric acid method, sensitivity in the very low concentration range is not appreciably altered. However, a n investigation of the effect of pH indicated a maximum sensitivity at a p H of 9.5. At this p H the blank is also less strongly absorbing, and the opaque region caused by a reaction between the barium chloranilate and the buffer (1) extends only to about 346 mp. This permits making useful photometric measurements at this wavelength, closer to the wavelength of
maximum absorption than the 355 mp used previously. Table I1 shows the sensitivity which can be obtained through these modifications. I n effect, two useful modifications of the chloranilic acid method for the determination of boron have been devised. By substituting saccharic acid for tartaric, modifying the solvent system by the addition of methyl cellosolve, and carrying out the precipitation at a p H of 8.8, a method which is quite satisfactory for concentrations up to about 10 p.p.m. of boron is feasible. By simply altering the p H to a value of 9.5 and making photometric measurements a t 346 mfi, much less concentrated solutions can be readily analyzed. The principal precautions necessary are that the solutions must be agitated vigorously immediately after the addition of the barium chloranilate, and the latter must be thoroughly dry. -4 standard should be run together with each series of unknowns. Table I11 shows a comparison with other procedures. The data used were those compiled by Goward and Wiederkehr (3). The absorp-
tivity values for quinalizarin, carminic acid, and tetrabromochrysazin represent the high and low, corresponding to different reagent and sulfuric acid concentrations. The methylene blue methods as well as those based on other thionine derivatives offer extreme sensitivity, but are time consuming. The saccharic acid modification provides good sensitivity, while retaining the speed and simplicity inherent in chloranilate methods. LITERATURE CITED
(1) Bertolacini, R. J., Barney, J. E., 11, ANAL.CHEM.30, 202-5 (1958).
(2) Gautier, J. A., Pignard, P., Mzkrochem. Jfikroc. Acta 36-37, 793 (1951). (3) Goward, G. W., U'iederkehr, U. R., ANAL.CHEM.35, 1542-5 (1963). (4) Srivastava, R. D., Van Buren, P. R., Gesser, H., Ibid., 34, 209-10 (1962).
DONALD R. PETER SON^ JOHN R. HAYES The Pennsylvania State University University Park, Pa. 1 Present address, Fairway Spring Co., Inc., Elmira, N. Y.
Assay of Ammonium Perchlorate by Precipitation with Tetraphenylarsonium Chloride SIR: The most general method for determining perchlorates depends on determining the chloride ion produced by fusion of the perchlorate compound. Standard gravimetric or volumetric procedures are used for estimating the chloride ion. Perchlorates may also be determined by reduction in solution using titanous ion (2), titanium hydride ( I ) , ferrous or sulfuric ion ( 6 ) , stannous ion (4, acid (oleum) with starch (9). I n addition, perchlorate ion has been determined directly by precipitation as tetraphenylphosphonium perchlorate (5, 7). Although tetraphenylarsonium chloride is mentioned ( 8 ) , quantitative data is lacking except for trace analysis (3).
Table 1.
xH4ClO4 solns., aliquot NO.
1
2 3 4 5 6 7
8 9 10
306
As we were interested in assaying ammonium perchlorate, we decided to find the optimum conditions for the formation of tetraphenylarsonium perchlorate. EXPERIMENTAL
Reagents. All chemicals were C . P . or reagent grade. The ammonium perchlorate used was prepared by neutralizing reagent grade perchloric acid with the same quality ammonium hydroxide, after which the salt was recrystallized twice from water and dried in a desiccator over sulfuric acid. Solutions of tetraphenylarsonium chloride (Hach Chemical Co., Ames, Iowa) were filtered if necessary; otherwise the material was used as received.
Precipitation of Perchlorate Ion with Tetraphenylarsonium Chloride
0.05M Ph4AsC1, ml. diluted to 50 ml. 15 15 20 20 20 20 25 25 50 50
ANALYTICAL CHEMISTRY
Calcd. 0.2409 ... ... ... ...
...
... ... ... ...
Ph4AsC104, g. Found 0.2398 0.2396 0.2400 0.2412 0,2406 0.2404 0.2406 0.2400 0.2436 0.2431
Recovery,
%
99.5 99.5 99.6 100.1 99.9 99.8 99.9 99.6 101.1 100.9
Procedure. Weigh accurately a 2to 2.5-gram sample of ammonium perchlorate into a 1-liter volumetric flask, dissolve in water, and dilute to volume with water. To a 25-ml. aliquot of the above solution in a 100-ml. beaker, add 5 ml. of concentrated hydrochloric acid and mix. To this stirred solution, add 50 ml. of 0.02.V tetraphenylarsonium chloride and allow 15 to 20 minutes for coagulation. Filter the solution through a previously weighed medium porosity, sintered glass crucible, using a wash solution of water saturated with tetraphenylarsonium perchlorate to transfer the precipitate into the crucible. Dry the crucible containing the precipitate at 100' C. for 1 hour, cool, and weigh. RESULTS A N D DISCUSSION
I n exploratory experiments, the perchlorate ion could be recovered nearly quantitatively as the insoluble tetraphenylarsonium salt (Ph4AsC10a) from 0.02121 aqueous solutions using about 100% excess of the reagent. I n the absence of hydrochloric acid, coagulation was slow. The precipitate was not completely filtered in 3 hours. With 0.5, 1.0, and 5.0 ml. of concentrated hydrochloric acid as coagulant, the precipitate required more than 1 hour, more than 0.5 hour, and 10 to 15 minutes for settling, respectively. After each of these solutions was filtered and the precipitate dried at 100" for 40
minutes, the per cent recovery in the order given was 99.7, 99.5, and 99.7. Next, a series of experiments was run in which the mole ratio of Ph4AsCl to perchlorate was varied. l-sing 25 ml. of 0.02M ammonium perchlorate mixed with 5 ml. of concentrated hydrochloric acid, the volume of 0.02M Ph4AsC1 added was varied from 30 to 50 ml. (mole ratio of 1.2-2.0 to 1). Ten to 15 minutes were allowed for coagulation and the precipitate was filtered, washed with water saturated with Ph4AsC104, and dried as before. The per cent recovery ranged from 99.3 to 99.8. Because the final volume of the solution containing the precipitate was different in each of these experiments, another series was set up using various volumes of 0.05.11 Ph4hsC1, each of which was diluted to 50 ml. before being added to the ammonium perchlorate-hydrochloric acid solution. The results of these experiments are given in Table I. Table I shows that, with 0.006M perchlorate ion and 0.8M hydrogen ion,
the optimum concentration of Ph4AsC1 is 0.012 to 0.016M (molar ratio of 2.02.5 to 1). With less than a 2 : l ratio, slightly low results were obtained, which were probably caused by incomplete precipitation. With a ratio of 5 : 1 , high results were obtained, probably because of absorption of the reagent. The data from Table I using the optimum mole ratio (aliquots 3 through 8 ) , combined with the results from two other experiments using 50 ml. of 0.02M Ph4AsC1, give an average recovery of 99.80/, with a standard deviation of 0.18. ?;either chlorate nor bromate interfere in the analysis when present up to O.4yGin ammonium perchlorate. The interference of other ions was not determined. However, Willard and Smith (8) found that the reagent would precipitate perrhenate, permanganate, periodate, tungstate, molybdate, chromate, iodide, bromide, and the chloride complexes of mercuric, stannic, cadmium, and zinc ions.
LITERATURE CITED
( 1 ) Alley, B. J., Dykes, H. W. H.,
ANAL.CHEM.36, 1124 (1964). ( 2 ) Burns, E. A,, Muraca, R. F., Zbid., 32, 1316 (1960). ( 3 ) Greenhalgh, It., Riley, J. P., J . Marine Biol. Assoc. United Kingdom 41, 175 (1961). C.A. 55, 27714b (1961). ( 4 ) Haight, G. P., ANAL.CHEM.25, 642 (1953). ( 5 ) Ribaudo, C., "Methods of Analyzing
Polysulfide-Perchlorate Propellants," Tech. Rept. 2334, Samuel Feltman Ammunition Laboratories, Picatinny Arsenal, Dover, N. J., September 19.56. (6) Sjolemma, B., Z . dnorg. Chem. 42,
127 11904). ( 7 ) Willard,'H. H., Perkins, L. R., ANAL. CHEM.25, 1634 (1953). (8) Willard, H . H., Smith, G. M., IND. ENG.CHEM.,ANAL.ED. 11, 186 (1939). ( 9 ) Willard, H. H., ThomDson. J. J., Ibid., 2, 272 (1930).
DONALD J. GLOVER J. M. ROSEN Organic Chemistry Division Chemistry Research Department U. S. Naval Ordnance Laboratory White Oak, Silver Spring, Md. 20910
An Improved Portable Fluorescent X-Ray Instrument Using Radioisotope Excitation Sources SIR: Karttunen et al. (2) recently described a portable fluorescent x-ray instrument utilizing the radioisotope tritium absorbed in zirconium to excite the K-x radiation of elements 2 = 16 to 35. This particular radioisotope was chosen because it most efficiently excited the elements of most interest to them, the components of meteorites. This paper demonstrates that the radioisotope promethium-147 in a n aluminum matrix and emitting bremsstrahlung radiation is a more universal excitation source for fluorescent x-rays covering the elemental range 2 = 19 through 92. A krypton-methane sealed proportional counter is used for detection and resolution. The apparatus weighs approximately 10 Ib. and occupies a volume of 1/2 cubic foot.
and it is a n excellent excitation source for t h e generation of fluorescent x-rays in elements requiring 3 to 12 k.e.v. This radioactive source is used to excite the characteristic fluorescent x-rays of elements in the range 2 = 16 to 35 and 2 = 45 to 82. I n the lighter
L
16000
14000
E,
(Pm"'/AI
F
elements the K-x radiation is generated while in the heavier elements the L-x radiation is excited. The bremsstrahlung emitted from the radioisotope promethium-147 when in an aluminum matrix is an excellent excitation source for fluorescent x-rays
SOURCE)
I O O O O ~
c w
c
EXPERIMENTAL
Apparatus. T h e portable fluorescent x-ray instrument mentioned above is used for t h e collection of data. The apparatus consists of only two major pieces, a nickel-cadmium battery powered transistorized power supplgrecorder, and a sealed proportional counter for detection and resolution, plus the small radioisotope excitation source. Sources. T h e tritium/zirconium bremsstrahlung sourcp has been fully described in the previous publication,
4000
2 000
1 Au I i Bi 2 20 2223
U
2
VOL. 37, NO. 2, FEBRUARY 1965
307
