Figure 6. Effect of iron on molybdenum thiocyanate color development
in 30 minutes. For process monitoriag, the other methods considered do not provide an acceptable conibination of speed specificity, scnsitivity, nrid rangc. LITERATURE CITED
(1) Blake, C. A. Lowrir,
I
0 0
20
I
I
40 60 MOLYBOENUH, p Q
I
eo
H. S.,Brown, K. B., Oak Ridgr National Laboratory, Y-12 Area, Rept. AECD-3212, p. 41, Ma 24, 1951. (2) BYatt, A. H., “Organic Syntheses,” Vol. 11, p. 67, Wiley, New York, 1944. (3) Daa Cupta, A. K., Singh, M. hl., J. Sei. Ind. Research (Zndta) 11B, 268-73 ( 1952). (4) “Encyclopedia
100
of Chemical Technology,” R. E. Kirk, D. F. Othmer, eds., Vol. XIV, p. 446, Interscience, New
Table V.
Precision of Method for Vanadium and Molybdenum in Uranium Hexafluoride [All sainp1i.s cont,ained 2 to 7 grams of UFn, 1000 pg. of Fe, and 500 pg. t w h of Cit, Ni, W (as
Vanadiiini,
tringatnte), Cr (as chromatc)]
Molybdenum, pg.
pg.
Prcscnt
Found
Present
Found-
5.0 20 0 60.0
5 . 1 f 0.2 21.3 f 0 . 9 59, 60
5.0 20.0
5.5 f 0.9 1D.G f 1 . 2
I
(2-analyses)
molylirleniim in the prrsrnre of 2 to 7 granis of hydrolyztd uranium hexafliioride. 7‘he r t w l t s presented in Tnble V were obtltined on samples cortt:iiriing iron(IJI), copper, nickel, cltromium (rhromntc), and tungsten (tungstate) imprtriticis. Independent tests with moderate levrls of tin and tihtiiitm impurities showed that they would not intrrferc with the analyses. Other poknti:il intcrfcrentm were not invrstigrtted; however, Wise and Brandt (I.?) havc chnractcrizcd many ions in
the vanadium-bcnzohydroxamate extraction. In t h r analysis of routine process contml samples, the BHASCN method has been compared with the ferrous titration for vanadium, thc conventional thiocyanate method for molybdenum, and a spectrographic mtithod for both elements. Agreement is within 5% of the values for coinparisons with the two other chemical mcthotls, and within 10% of the less prerisr spectrographic results. The procedrirr is completed
York 1955. (5) Hulcher, F. H., ANAL. CHEM.32, 1183-5 (1960). (6) Jones, G. B., Watkinson, J. H., Ibtd., 31, 1344-7 (1959),., ( 7 ) Mellor, J. W., Inorganic and Theo-
retical Chemistry,” Suppl. 11, Part I,
p. 462, Longmans, Green, New York, 1956. (8) Meloan, C. E., Brandt, W. W., ANAL. CHEM.33, 102-4 (1961). (9) Meloan, C. E., Holkehoer, P., Brandt, W. W., Ibid., 32,791-3 (1960). (10) Priyadarshini, U., Tandon, S. G., Zbid., 33, 436 (1961). (11) Snell, F. T., Snell, C. T., “Colori-
metric Methods of Analysis,” 3rd ed., Vol. 11, pp. 482-3, Van Nostrand, New
York, 1949. (12) Scott, W. W., “Standard Methods of
Chemical Analysis,” 5th ed., Vol. I, p. 607, Van Nostrand, New York, 1050. (13) Wise, W. M., Brandt, W. W., ANAL. CHEM.27, 1392-5 (1955).
RECEIVED for review Ortober 31, 1060. Acccpted February 1, 1961. Analytical Section, Southeastern Rrpional ACR Mecting, Birmingham, Ala., Novemher 1060. Work performed at the Oak Ridge Caseous Diffusion Plant o crated by Union Cnrhide Corp. for the S. Atomic Energy Commission.
8
Direct Spectrophotometric Determination of Niobium, Titanium, and Tungsten with Hydroquinone Using Background Correction Technique J. P. ,McKAVENEY Crucible Sfeel Co. o f America, Pittsburgh, 7 3, Pa.
,The background correction technique with hydroquinone was developed to permit a direct determination of niobium, tungsten, or titanium in high temperature alloys and thus eliminate a lengthy hydrolysis separation. The technique permits the individual determination of the elements when present singly in an alloy as well as combinations of niobium and tungsten or niobium and titanium.
744
ANALYTICAL CHEMISTRY
T
HE DIRECT indiviciunl di*t,wmixi:Ltion of niobium, t,itwiiiini, and tungsten with hydroquinonc W:IS introduced to thc metals indristry by Johnson (3, 4). Iktmhrrry, M:irt,in, and Royer (2) improvrd Johnsoii’s method when they devrloprd the siiniiltaneous equation, doublc wavr-lrngth procedure. They detc:r~:iiurd niohiiim and tungsten, when prrc,v?t, together in nn alloy, with hydroquinonc nftrr a
double hydrolysis separation. Johnson’s and 1kenI)crry’s methods were not univrrsnlly nrrcptcd bcrnusc of difirulties with the niobium determination. Recently, Wntrrbury nnd Bric8lic.r (6) usrd hydroquinonc to determine niobiiim in urnniiim alloys. Thrir work holpcd explnin some of thc ditfirultirs resulting from the r e g e n t preparation :rnd stnbility which had previously affrctrd t h r niohirtm determination.
‘l‘his invcstigatioii was unrltbrtnken to ronibine the modified aJohnson ( I ) dirrct solution color devclopmcnt method with the simultaneous cquation, double wavelength procrrliirr of I k c n h r r y et d. The nrw proccrlure worilrl rlirniniite t h e doirhlr prrvipitntion nnd ignition required t o remove niobium, tungstrn, or titmiiim wlicn c~ombincrli n an alloy, from the othw constituents. Also, it, would d i m i n a k the LISP of Ioca.1 standards to correct for the natural color interfrrcnce in the direct nwthod when analyziiig singly for niohiiim! titanium, or tungsten. To accomplish this, it ~ ~ 1 necrssary . s to correct for thc absorhaners of the varioiis colored ions :IS well as that of the hydroquinonr ren.gent. These valiics were determinrd easily by using 95% sulfuric acid as the reference solvent in both methods. The method of reagent preparation, reagent age, and thc effects of sunlight and color development time were studied carefully in a n effort to rninimizc the hydroquinone reagent blank and to incrcasc the rrproducibility of the method. APPARATUS A N D REAGENTS
A Beckman Model DTJspectrophotometer was used to obtain all absorbance me:isurements in thc ultraviolet and visible regions. A 5 0-ml. microburet with 0.01-ml. subdivisions was used to dispense sample a l i q u o k Solvent Mixture. To 300 ml. of watrr, carefully add 400 ml. of 85% phosphoric acid plus 120 ml. of 95% sulfuric acid, and dilute to 1 liter with water. Stannous Chloride. Dissolve 88 grams of stannous chloride (SnCIt. 2H20, reagent grade, J. T. Baker Chemical Co.) in 60 ml. of concentrated hydrochloric acid; diesolve 50 grams of tartaric acid in 100 ml. of water. Then combine the stannous chloride and tartaric acid solutions and dilute to 250 ml. with water. Dilution Mixturr. Carefully add 350 ml. of concentrated sulfuric acid to 600 ml. of water. After the solution haa coolrd dilute it to 1 1itr.r with water. Hydroquinone Sulfuric Reagent. Transfer exactly 15.00 grams of hydroquinone (Mallinckrodt photo-purified) to 8 1-liter dry amber reagent bottle. Carefully add 500 ml. of 95% sulfuric acid from a volumetric flask. Insert the glass stopper and periodically shake ge?tly to obtain solution of the hydroquinone. Allow to stand 16 to 24 hours before use. Use a 50-ml. amber buret for delivering this solution. Standard Niobium Solution. Trantrfer 1.0050 grnms of niobium metal powder (99.5% pure, A. D. Mackay, Inc., i 9 8 Broadway, Ncw York, N. Y,) to a platinum dish. Add 30 ml. of water 20 ml. of concentrated nitrir acid, and about 5 ml. of 4801, hydrofluoric acid to the niobium and maintain at a below miling temprrature to obtain solution. Cool, transfer to a I-liter volumetric flask, and dilute with wnwr to 1 liter.
After mixing, immrdiritrly transfer to a dry polyrtliylrne bottle for storage. This solution iwntains 1.00 mg. of niobium prr niillilitrr. Stnndard Tantaliim Soliition. ‘Transfer 1.0010 grams of tant:tlum metal powder (99.9% pure, A. I). Mackay, Inc ) to a platinum dish and Iirepare in :he same way as the niobium solution. V+
