Durie and D. J, Swaine, for helpful discussions. LITERATURE CITED
(1) Aleskovskii, V. B., Kalinina, T. I.,
Trudy Leningrad Tekhnol. Inst. im. Lensoveta No. 35, 178 (1956). (2) Belcher, R., Leonard, M. A., West, T.S., J. Chem. SOC.1959, 3577. (3) Brochmann-Hanssen, E., J . Am. Pharm. Assoc. 43, 307 (1954). (4) Brown, H. R., Durie, R. A., Schafer,
H. N. S., Fuel (London)38, 295 (1959). (5) Gee, A., Deita, V. R., ANAL. CHEM. 25, 1320 (1953). (6) Hillebrand, W. F., Lundell, G. E. F., Bright. H. A,. Hoffman, J. I., ‘LAmlied Inoyganic Analysis,” 2nd ed., Wiley, New York, 1953. (7) Honda, M., Yoshino, Y., Wabiko, T., J . Chem. SOC.Japan, Pure Chem. Sect.
(10) Osborn, G. H., Analyst 78, 220 (1953). (11) PiBce, R., Rev. Math-. Constr. Trav. Pub. No. 524, 107 (1959). (12) Samuelson, O., Svensk Kern. Tidskr. . 53, 60 (1941): ‘ (13) Zbid., 57, 158 (1945). (14) Scheffer, F., Kloke, A., Wittkopf,
G., Z. Pjlanzenernahr. Diing. Bodenk. 79, 232 (1957). 73, 348 (1952). (8) Johnson, C. A., Leonard, ?* A.,I. Analyst 86, 101 (1961). (9) Koblyanskir, A. G., J . Gen. Chem. RECEIVEDfor review July 23, 1962. Accepted October 18, 1962. USSR 24, 17 (1954).
Determination of Refractory Metals in Ferrous Alloys and High-Alloy Steel by the Borax Disk X-Ray Spectrochemical Method C. L. LUKE Bell Telephone Laborafories, Inc., Murray
b X-ray spectrochemical methods have been developed for the determination of Mol W, Nb, and Ta in heat-resisting and corrosion-resisting alloys and of Mo and W in high-alloy steel. The refractory metals are separated from the bulk of the alloy matrix b y conventional chemical separations, converted to oxides, fused in borax, and then determined by x-ray spectrochemical analysis. The methods are convenient, rapid, and yield excellent results.
T
of Mo, W,Nb, and T a in ferrous alloys and steel is a difficult and time-consuming analysis because of the similarity in the chemical behavior of these refractory metals. In recent years, matters have been greatly improved by the use of anion exchange techniques to effect the necessary separations. In the analysis of heat-resisting and corrosion-resisting alloys, Bandi et al. isolate the refractory metals from the bulk of the sample by conventional gravimetric separations, combine the precipitates, and convert the metals t,o oxides before proceeding to the anion exchange separations (4). Since the latter separations are rather time consuming, a more rapid method for the final determinations would be useful. It seemed probable that considerable time could be saved by fusing the isolated mixed oxides in borax and then determining the four metals in the cooled melt by the x-ray spectrochemical method (6, 6). This has proved to be true and, as a result, a new method is proposed which is rapid, convenient, and capable of yielding results which are comparable in accuracy to those obtained by other methods. The method has also been adapted to the analysis of
Hill, N . J . refractory metals in several other metals and alloys. The usefulness of the chemical separation x-ray analysis method for extending the sensitivity of x-ray methods in general or for facilitating the analysis of samples which are difficult to analyze by chemical or x-ray methods alone has been demonstrated previously (7, 8). In view of this, the present report will include, for the most part, only that material which has not appeared elsewhere. EXPERIMENTAL
HE DETERMINATION
56
ANALYTICAL CHEMISTRY
Apparatus. A General Electric x-ray spectrometer with a Pt target, a LiF crystal, a 10-mil Soller slit, a x 3/4-in~hA1 mask, and a scintillation counter was used. The gas-oxygen burner was supplied by Bethlehem Apparatus Co. of Hellertown, Pa. (Burner No. PMZC-L). Procedure. PREPARATION OF BORAXDISK STANDARDS.Transfer the following weighed portions of the dry, powdered, reagent grade oxides of the refractory metals from black glazed paper to 30-ml. Pt crucibles. KO,
Crucible Moo3 WOs SbzOs
Ta206
so. lJ 2, mg. mg.
No.
KO.
3,
4, mg. 10.0 20.0 40.0 30.0
mg. 30.0 20.0 40.0 40.0 10.0 30.0 20.0 30.0 10.0 10.0 40.0 20.0
To each crucible add 2.0 grams of dry, powdered, reagent grade BaO followed by 10.0 grams of pure, dry, powdered borax (Na2B407). Heat on a gas-oxygen flame to fuse the mixture and then swirl vigorously for about 30 seconds or until the oxides have dissolved completely. Pour the melt onto a smooth, bare, ‘/*-inch A1 plate which
is maintained a t a temperature of about 180’ C. Remove the A1 plate from the hot plate and allow t o cool. Keep the disks in a desiccator when not in use. DISSOLUTION OF S A m L E . To analyze heat-resisting alloys such as KBS 167 and 168, transfer 0.50 gram of the subdivided sample to a 100-ml. Pt dish. Add 10 ml. of HF-HN03 solution (2 I) and cover with a flat, round polyethylene bottle rest. Heat gently until dissolution of the sample is complete. Wash and remove the cover and evaporate the solution just to moist dryness. Add 5 ml. of water, heat, and swirl to dissolve soluble salts. K i t h the aid of a steel reinforced polyethylene stirring rod, wash the solution and precipitate into a 400-ml. beaker containing 10 ml. of HClO,. Evaporate rapidly to expel volatile acids. R hen fumes of KC104 begin to be evolved, flame the sides of the beaker t o expel all traces of HF and then take to copious fumes t o destroy carbides and to oxidize Cr and V. When the HClO4 condenses about two thirds of the way up the mall of the beaker, cool, add 10 ml. of HC1, cover, and heat to boiling to dissolve soluble salts and to reduce Cr and V. Avoid excessive loss of HCl. When most of the oxidizing fumes have been expelled, add 180 ml. of water. To analyze corrosion-resisting alloys such as NBS 123a and 123b, dissolve 4.00 grams as completely as possible in a covered 400-ml. beaker in 50 ml. of HCl by heating gently. Carefully add 5 ml. of HN03 in small portions to oxidize the Fe. Then add 1 ml. of H F and 25 ml. of HClO4. Evaporate rapidly to copious fumes. Cool, add 20 ml. of HC1, cover, heat t o boiling, and add 250 ml. of water. T o analyze high-alloy steel, dissolve 0.15 to 0.30 gram of the sample in 5 ml. of HN03 plus 5.0 ml. of niobium solution (dissolve 1.00 gram of hTbz06 in 25 ml. of HF and dilute to 100 ml.) in a 400-ml. beaker. Add 10 ml. of HC104,
+
evaporate to copious fumes, and dilute Chemical Separations. Preliminary with HC1 and water as in the analysis dissolution of most ferrous alloys of heat-resisting alloys. and steels can be effected in HC1 and, THE CY-BENZOIKOXIME SEPARATION. in fact, where large samples are inPrecipitate the M o in the solution with volved, this means of attack should a-benzoinoxime (1) and collect the always be used. It is possible to isolate niised precipitate on coarse textured W from steel, with relatively little conpaper-e.g. Whatman KO. 41-contamination from matrix metals, after taining some paper pulp. Wash the dissolution of the sample in HCl followed paper and precipitate until the washings show little or 1.0 ferric iron by the by "03. On the other hand, when KSCK test. It is essential that most analyzing Nb- and Ta-bearing samples of the HClOd be removed to prevent such as NBS 167 and 168, dissolution of popping and spitting during the subsethe sample in HCl and HNO, leaves the quent combustion. [W. R. Eandi has separated oxides of W, Nb, and Ta suggested that the popping and spitting heavily contaminated with matrix can be eliminated by adding several metals. In view of the need for redrops of H&04 to the sample in the moval of almost all of the Ni, it is Pt crucible before the combustion (3) .] necessary, when analyzing these samHeat the paper and precipitate slowly in a 30-ml. Pt crucible to destroy the ples, to use a method of dissolution in organic matter and then ignite a t 500" which the carbides can be decomposed to 525' C. (1). Add 2.0 grams of BaO more thoroughly. By dissolving the followed by 10.0 grams of boras and samples in HF-HN03 solution followed prepare the disk. X-RAY AKALYSISOF THE SAMPLE by fuming with HClO4, the carbides can be completely destroyed. AXD STANDARDS. Measure the fluoresI n the proposed method, the sepcent radiation of the sample and standaration of the refractory metals from the ards for 100 seconds a t 50 kv. and a tube matrix metals is accomplished, in the current which will give adequate counts in the analysis. Using the data obusual manner, by hydrolysis and tained from the standards, plot the a-benzoinoxime precipitations. When milligrams of each oxide us. the counts ferrous alloys containing Nb and T a are obtained. Then, using the appropriate or HNO, plus HCl dissolved in "08, graph, determine the weight of oxide and then taken to fumes with HC104, present in the sample being analyzed. it is necessary, to obtain complete precipitation of the refractory metals, to DISCUSSION dilute and boil the solution to complete the hydrolysis ( 2 ) . On the other hand, To determine refractory metals in if H F is present a t the time of the ferrous alloys and high-alloy steels, it is fuming with HC104, quantitative prewually best t o isolate the metals to be cipitation of the two metals occurs determined before attempting the x-ray during the fuming, provided that a t analysis. In this way it is possible to least 10 mg. of Nb plus T a is present. amid difficulties due to lack of control Moreover, if the W present is not in of line or absorption interference, lack of excess of that which can be carried down suitable solid standards, undesirable by the Nb plus Ta it will accompany the physical form, or nonhoniogeneity. The latter metals quantitatively (3). metals that may cause line interference In the absence of Nb and Ta, the i n the determination of Mo, W,Nb, and separation of W as WOa is incomplete, Ta, if chemical separations are not especially in the presence of Mo, unless emplojed, are Xi and Zr. Since the Zr the usual digestion with cinchonine is content is usually small and since most made. Since the latter is a time conof this metal as well as the Ni can be suming operation, it has appeared prefrcmoved by suitable separations, no erable, when analyzing steels, to add difficulty due to line interference is endeliberately enough S b to the sample to countered in the proposed method. ensure the complete precipitation of the
Sample
a
W during the HClO4 fuming operation. The addition of Nb has the further advantage that it makes the heavy metal matrix of the sample disk more nearly match that of the composite standards. Mo does not influence the completeness of precipitation of W, Yb, and T a and it is advantageous to combine the hydrolysis and a-benzoinoxime precipitation so that all four refractory metals can be recovered by a single filtration (9). Mutual Absorption of the Refractory Metals in a Borax Disk. I n the proposed method, isolation of the refractory metals eliminates line and absorption interference by the matrix metals. Nevertheless, severe negative errors due to mutual absorption of the refractory metals must be dealt mith. (Since no attempt is made to evaluate the true background, the observed mutual absorption is greatly enhanced because it represents the sum of the absorption of the metal and scattered background radiation). The mutual absorption of Mo and Nb is negligible because of the low mass absorption coefficients of these metals in the region of their Ka lines but appreciable absorption is encountered with any other combination of the four metals. Because of this it is necessary to load the borax disks with a heavy metal to reduce this error (5, 6). Of the several heavy metals tested, Bi appeared a t first to be the best one to use in the present work because of its exceptionally high mass absorption coefficient a t the wavelengths of the four refractory metals. However, the use of Biz08 (or PbO) presents difficulties because of the ease with which it can be reduced to the metal. In the present investigation certain batches of borax were encountered which contained reducing material. Moreover, it is not always possible to destroy all of the carbonaceous material during the combustion of the a-benzoinoxime precipitate. While small amounts of precipitated Bi do not appear to influence the analytical results, severe damage t o the Pt crucible may occur if appreciable re-
Table I. Analysis of NBS Samples Containing Niobium and Tantalum l\lolybdenum Tungsten Siobium Present, % Found, % ' Present, % Found, % Present, % Found, % 0 75
0 75
0.75
0.76
4.50
4.6 4.5
3.15
3.2
3.95
3.9 3.9
2.95
123a
0 12
0 11
0 11
0 10
123b
0.17
0.18 0 . 17'
0.18
0.17
167
3.90
3.9 3.9
168
3.95
4.0
3.9
4.0a
0.184
4.0"
Tantalum Present, % Found, % 0 02
0 00
0.20
0.19
3.2
0.08
0.04 0.06
3.0 3.0
0.95
0.75"
3.04
0.19Q
0.93
0.89 0.906
20 mg. of ZrOl added to the sample before analysis.
VOL. 35, NO. 1, JANUARY 1963
a
57
Table II.
Analysis of NBS Samples of High-Alloy Steel
Tungsten Molybdenum. PresPresent, Found, ent, Found, Sample % % % % 18.05 18 50b 0.401 0.40 6.29 6.2 132 7.07 7 . 2 6.3 7.1 6.20 6.1 132a 4.51 4.5 6.0 4.5 1.82 1.8 134 8.68 8.7 1.8 8.8 2.00 1.9 134a 8.35 8 . 3 2.0 8.3 2.0 8.4 1.4 1.58 153 8.38 8 . 3 1.5 8.5 1.4 8.3 155 0.039 0.035" 0.517 0.51" 0.50" 0,040" a Analyzed as a corrosion-resisting alloy but 5 ml. of niobium solution added in place of 1 ml. of HF. duction of the Biz03 occurs. I n attempting to overcome this difficulty it was reasoned that if the Biz03 is added on top of the borax, the carbon in the bottom of the crucible will have been air-oxidized by the time the Biz03begins to fuse. This proved to be true but unfortunately the method had to be abandoned because a n appreciable amount of the Bi was lost by volatilization. It is evident that if Biz03 is t o be used it must be covered by the borax.
In the proposed method BaO has been recommended since it cannot be reduced under the conditions of the borax fusion. The addition of the B a 0 t o the standard and sample disks markedly reduces the error due t o radiation absorption in the analyses but does not entirely eliminate it. However, the small negative error that remains can be largely compensated for by the use of composite calibration samples in which the refractory metal environment approximates that existing in the samples t o be analyzed. This makes it possible t o obtain good straight line calibration graphs and excellent accuracy in the analysis of the refractory metals (Tables I and 11). Other Analyses. Excellent chemical separation-borax disk methods have been developed for the determination of M o in low-alloy steel and ferromagnetic alloys and of W or Zr in cathode nickel. Moreover, in certain instances, where the refractory metal content is sufficiently high, where no line interference is encountered, and where the composition of the alloy does not vary too much, it has been possible t o determine Mo, W, Nb, Ta, Zr, or V by the borax disk method without resorting to chemical separations. To do this a 0.2-gram sample is dissolved in 2 ml. of "03 (1 1) plus a drop of HF in a covered Pt crucible. After evaporation, ignition a t 500" C., and
+
fusion with 10 grams of borax, the disk is analyzed. The standard disks required are prepared by fusing appropriate amounts of oxides of the matrix metals and of the metal in question with 10 grams of borax. ACKNOWLEDGMENT
The author expresses his appreciation t o Herbert Schreiber and Shirley AT.. Vincent for helpful discussions and suggestions in the x-ray work of the present investigation. LITERATURE CITED
1) Am. SOC. Testing Materials, Philadelphia, Pa., "ASTM Methods of Chemical Analysis of Metals," p. 137,
(1960).
(21 Ibid., pa 176. (3) Bandi, W. R:, United States Steel Corp., Monroeville, Pa., private communication, August 1962.
(4) Bandi, W.R., Buyok, E. G., Lewis, L. L Melnick, L. AI., ANAL. CHEM. 33, 1275 (1961). (5) Bruch, J., Arch. Eisenhiittenw. 33, 5 (1962). (6) Claisse, F., Norelco Reporter 4, 3 (1957). (7) Rothmann, H., Schneider, H., S i e buhr, J., Pothmann, C., Arch. Eisenhtdfenw. 33, 17 (1962). (8) Tomkins, bl. L., Borun, G. A , , Fahlbusch, W. A., ANAL.CHEM.34, 1260 (1962). (9) Yagoda, H., Fales, A. A , , J.Ani. Cheni. SOC.60, 640 (1938). RECEIVEDfor review June 12, 1962. Accepted October 31, 1962.
The Amperometric Determination of Amines Titration of Sympathomimetic Amines with Sodium Tetra phenylborate EDWARD SMITH,' LEE F. WORRELLt2 and JOSEPH E. SINSHEIMER College of Pharmacy, University o f Michigan, Ann Arbor, Mich. In order to investigate the amperometric titration of amines with sodium tetraphenylborate (TPB) a series of sympathomimetic amines was analyzed. Two general techniques were used. The first was based upon anodic depolarization a t a dropping mercury electrode by excess TPB titrant, while the second procedure was based upon electrochemical oxidation of the TPB ion a t a graphite electrode. The ability to determine sympathomimetic amines b y these techniques can b e correlated to the structure of the amines and solubilities of amine-TPB salts. Amperometric titrations can b e applied directly to amines even in complex mixtures provided their TPB salts have a solubility in the order of
58
ANALYTICAL CHEMISTRY
6 X 10-4M or less. These titrations were found to b e more convenient, rapid, and precise than other procedures currently in use.
I
of this investigation t o study the quantitative analytical application of sodium tetraphenylborate (TPB) to the determination of pharmacologically active amines. A general method was sought for the determination of amines in aqueous solutions and in complex mixtures, without tedious prior separations. Sympathomimetic amines were chosen for study because of their widespread use per se and in combination with T WAS THE PURPOSE
other pharmaceutical agents and because of the range of structures available. A summary of the extensive literature on the application of sodium T P B for chemical analysis has been included in a comprehensive review by Flaschka and Barnard (6) and in the bibliographies of Barnard and Buechl ( 3 ) . Precipitation of amines by T P B has been described by Crane (2) and by Howick and Pflaum (IO). Work in these laboratories (16) indicated ap1 Present address, Division of Pharmaceutical Chemistry, Food and Drug Administration, Washington, D. C. * Present address, College of Pharmacy, University of Texas, Austin, Tex.
