satisfactory for rapid reading. This can be largely corrected by using lampa having greater illumination intensitiea. Figure 5. calibration Pu(lll)
Colorimeter curve for
UTERATURE CITED
, A. H., U. 8. Atomic Energy C o r n . kept. HW-29599,pa25,October 12 1953. (Unclassified) (2) earson W.N., Jr., Michelson, C.E., Zbui., d-27744, April 30, 1963. (Uncladied) (3) Scott, F. A., Van Meter, W. P., Zbid., HW-39926, November 17, 1951. ( 1 ) Buehe
by an increase in the dark current of the cell. The cell is usually discarded when the dark current is 3'% of full scale on the meter. This dark current is checked occasionally in operation and zeroed using the Zero and the mcter adjustment screw.
The filter photometer can be used aa a photometric titrator by redesigning the sensing unit for a titration cell. No changes are necessary in the electronics chassis. The unit can also be used as a laboratory filter photonieter but the speed of response is not too
Declassified ) (4)'Stevenson 'C. E.,Zbid., IDO-14422, pp. 39-54, becember 31, 1957. (Confidential) ( 6 ) Van Meter, W. P., Michelson, C. E., Carson, W. N.,Jr., Zbid. y-29751, November 1, 1953. (Conbdential)
RECEIVEDfor review April 21, 1960. Accepted Janultr 9, 1961. Work performed under U. Atomic Energy Commission Contract AT(29-1)-1106.
8.
Spectrophotometric Determination of Boron in Steel and High Temperature Alloys WILLIAM 1. KARPEN Research laboratory, The Carpenter Steel Co., Reading, Pa.
B Small amounts of boron in high temperature alloys can be determined spectrophotometrically using the rosecolored boron tetrabromochrysazin complex. The metal is dissolved in a mixture of perchloric and phosphoric acids and the boron distilled as the trimethyl boron ester. In the presence of phosphoric acid, the perchloric acid does not esterify the methanol. The boron and reagent readily combine in 96% sulfuric acid in a 1 to 1 mole ratio. The colored complex reaches maximum intensity in 1 hour and the absorbance is measured at 540 mp. The combination of solvent, distilling apparatus, and reagent has proved satisfactory for determining boron in steels and high temperature alloys in the range of 0.0002 to 0.025%.
a
HE MOST accurate methods for the determination of boron in steel and high temperature alloys require the preliminary separation of boron from undesirable constituents. Of the various separative techniques employed, ion exchange, extraction, and distillation procedures have shown general applicability. Ion exchange methods, however, are not recommended for the separation of small amounts of boron
738
e
ANALYTICAL CHEMISTRY
(7). The recently developed solvent extraction method (4, 6) can only be applied to steels and high temperature alloys that are soluble in or H#OcH,PO( mixture. Although the distillation method is more time consuming than most other schemes, it is applicable to all ranges of boron and is to be preferred where best accuracy, freedom from interfering ions, and variable blanks are to be desired. Disadvantages have been listed for the more common boron reagents as quinalizarin, carmine, curcumin, and tumeric (9). The use of 1,ldianthramide is objectionable because of the rigid temperature control required over several hours in developing the maximum color with boron. The action of boric acid with several other hydroxy derivatives of anthraquinone is dependent on the reaction-time-and-volume factor (3). Tetrabromochrysazin, initially applied by Yoe and Grob for the determination of boron in plants @), waa buitable for this work. The stability of the reagent in 96% H2SO, eliminates the necessity of frequently preparing fresh reagent, as is the case with 1,1dianthramide and curcumin. The reagent has a high sensitivity to boron and readily unites in a 1 to 1 mole ratio.
The color of the complex is stable for several weeks. EXPERIMENTAL
Apparatus and Reagents. Spectro-
photometer. Absorbance measurements were made with tt Beckman Model D U spectrophotometer, using l-em. matched Corex cells. Glassware. Corning No. 7280 boronfree glassware was employed for all operations requiring heat. The balance of the equipment was composed of borosilicate glass. Alkaline solutions boric acid, and the reagent were stored in Corning No. 7280 glass or polyethylene containers. Distilling Apparatus. The 300-ml. flask and connecting air condenser were Corning No. 7280. The reflux condenser and receiving flask were of borosilicate composition. All joints were 24/40. Standard Boron Stock Solution. . A solution was pre ared by dissolvtng 0.5720 gram of goric acid (Johnson Matthey Co., Ltd.,London) in distilled water to a volume of lo00 ml. Each milliliter contained 100 pg. of boron. Standard Boron Working Solution. Twenty milliliters of the standard boron stock solution waa diluted to lo00 ml. Each milliliter contained 2 pg. of boron. Tetrabromochrysazin Solution. A 1 x 1O-aM solution was prepared by dissolving 0.5560 gram of the reagent
in 9G% H,60, (by weight) to 1000 ml. The reagent can be obtained from the LaMottc Chemical Products Co., Ualtimore, Md. Calcium Hydroxide Suspcnsion. The suspension was prepared as outlined in ASTM Methods for Chemical Analvsis of Metals (I). Modified Phosfodant. A solution was prepared by mixing 500 ml. of HC10, (60 to 62%) with 1000 ml. of HnPOd (85%). -Recommended Procedure. CALIB R A T I O N CURVE. Transfer from 1.25 to 13.75 ml. of the standard boron working solution to 250-ml. beakers (Corning No. 7280). T o each sample and a blank add 5 ml. of 0.1N NaOH solution and 20 ml. of water. Evaporate the solution to dryness employing 250-watt infrared lamps. Continue heating the samples for an additional 20 minutw and cool to room temperature. Add sufficient 96% &SO4 to dissolve the residue and transfer the solution to 25ml. volumetric flasks containing exactly 2.50 ml. of the tetrabromochrysazin solution. Stopper each flask to prevent the absorption of moisture. Allow the color to develop for 1 hour, dilute to the mark with 96% H2S04, and mix the solutioii thoroughly. Measure the absorbance a t 540 mp using 96% &SO4 to zero the instrument. Subtract the blank value from the results obtained on the samples. Plot the micrograms of boron in 25 ml. of solution (2.5 to 27.5 pg.) against the absorbance value. Sample Analysis. ACID-SOLUBLE BORON. Weigh a sample containing from 2 to 25 pg. of boron into a 300-ml. Erlenmeyer flask (Corning No. 7280). Add 15 ml. of phosfodant (6) and connect the flask to a reflux condenser. Heat the flasks on hot plates a t moderate temperature until the metal is dissolved. Remove, cool to room temperature, and add 50 ml. of methanol to the sample. Place one end of the air condenser into the flask and the other end into the rtflux condenser. Attach a 500-ml. Florence flask containing 20 ml. of water and 5.0 ml. of a 0.1N NaOH solution to the reflux condenser. Fill the U-trap on the Florence flask with distilled water to trap any boron ester vapor that may pass into it. Immerse the flask in an ice bath. Distill the methyl borate ester by heating the solution to 70’ & 3’ C. Make a srronti distillation using 50 ml. of mrthnnol. ACIU-INSOLUBLE BORON.Remove all acid-insoluble material from the flask by filtration. Wash the residue on the pitper 7 or 8 times with distilled water. T r t a t the acid-insoluble sample in the mtmc manncr as describsrl (1). Distill the boron as described for the acidaolublc boron. Transfer thc solution Containing the total b o m i from the Florence flask to a 400-1111. lwiiker (Corning No. 7280). Evalwratc the solation to dryness using infrawd Iariips (92’ C.). Complete the dvtcrinin:ttion in the same manner desrribc d under Cnlibration Curve. Sovvn to 1 4 dcterniinations can be mndc in 2 to 3 working days by operat-
Table 1.
Boron in National Bureau of Standards 349 (Waspalloy).
No. of
Method HZSO, H0104 a
Detns.
+ HsPO,
17 18
Av. Per Cent of Boron Found 0,00545 0.0053
Provisional certificate of analysis:
Range of Per Cent Min. Max. O.OO50 0.0050
Std. Dev.,*
0.0059 0.0055
% O.OoO27 0.00016
Cr Ni Co Mo AI Ti B 19.50 57.15 13.95 4.04 1.23 3.05 0.0046
b Calculated by: Sigma = Where XI is a numerical result, Xis the mean value, and n is the number of determinations.
ing 7 to 14 distilling units simultaneously. DISCUSSION
The choice of a suitable solvent for samples of high temperature alloys is rather limited in a distillation-colorimetric procedure. Dilute &so4 readily dissolves many steels but the water must be disti:led prior to the addition of methanol to prevent hydrolyzation of the trimethyl borate ester. Some steels and high temperature alloys, however, are resistant to HsSO4 at any concentration. A suitable solvent for these metals is a mixture of IIclo4 and HsPO4 (6). I n this work, one part of 60 to 62% HCIO, with two parts of 85% HaPO, were effective in dissolving all teels and temperature alloys tested. The boron ester can be distilled from modified phosfodant without a violent reaction. This could readily occur if the strongly oxidizing clod- group were introduced into the methyl molecule. In the presence of HaPo,, the HClO4 will not esterify the methanol. Boron determinations have been successfully conducted in this laboratory for several years using modified phosfodant as the solvent. The amount of alkali used in evaporating the distillate to dryness is critical in procedures employing 96% H 8 0 4 as the medium for color development. Five milliliters of a 0.1N NaOH solution constitutes sufficient alkali to prevent the loss of boron during evaporation while producing a tolerable quantity of water on neutralization. To prevent variation in the sensitivity of the color reaction from this water, all samples are diluted to 25 ml. Variation in the water content of the H,SO4 should also be avoided by selecting acid having an assay of 96% by weight. Caution, of course, should be exercised in preparing the reagent and in neutralizing the evaporated sample to avoid or minimize moisture absorption by the acid.
hibit the full recovery of the boron as the ester. The water need not be distilled prior to adding the methanol. A comparison of the results obtained on a standard steel by the H2SOI and phosfodant methods indicates the percentages to be of the same order (Table I). The data do not prove that full recovery of the boron was obtained but only t h a t the two methods produced similar results when water was distilled from the &SO4 (30% by weight) and not from the phosfodant. Consequently, quantitative recovery has to be indicated in only one of the two methods. ‘ The H2S04 method was chosen to study the recovery of boron. Since a preliminary water distillation is required, a known amount of boron can be added to the acid as an aqueous synthetic solution. Since the calibration curve was derived from the results obtained on evaporated samples, rather than from samples that were distilled and evaporated, all of the boron was known to be present when complexed with the reagent. To check recovery on distilled samples, therefore, 5, 5, 10, 15, and 20 pg. of boron were added as an aqueous synthetic solution to I-gram samples of’a steel (0.0004% boron) dissolved in dilute HzSO~. The amounts recovered were 10, 11, 14,21, and 23 pg., respectively. The data indicate, therefore, that full recovery of the boron can be obtained from dilute H$04 and hence, from phosfodant as well. Table I shows that a better precision was exhibited with the use of phosfodant. Since a preliminary water separation is not required, the error associated with this step is eliminated. ACKNOWLEDGMENT
The author thanks The Carpenter Steel Co. for permission to publish this paper.
RESULTS
LITERATURE CITED
The amount of water present in 15 ml. of phosfodant is insufficient to in-
(1) “ASTM Methods of Chemical Analysis of Mctnls,” pp. 132-8, Am. Soa. VOL 33, NO. 6, MAY 1961
739
l’cnting Mntcrinls, l’hil:tdclpl~i:t, Pa., 1956.
Quintus, I b i d , 32,277 (1960). (6) Smith, C.F., “Mixcd Perchloric, Su1-
(2) Codcll, M., Norwitz, C., ANAL., phuric und Phosphoric Acids trnd Thcir CmM. 25, 1446 (3953). Applications in AnalysiN,” 2nd ed.,.p. (3) Cogbill, E. C., Yoe, .J. II., Jhid., 29, 55, The G . Frederick Smith Chemical 3253 ( 1957). Co., Columbus, Ohio 1042. (4) I’aaztor, Imdo, Bodc, J. D., ZM., (7) Woleaon J. D., dayca, ,I. R., Hill, 32, 1530 (1960). William k., ANAL. CHEM.29, 829 (5) l’:tsztOr, Lmzlo, node, J. D., Fernando, (1957).
(8) Yge, .J. II., Grol), It I,., /bid,, 26, 14G5 (1951).
ftk rcviow Scptcml)cr 28, 1960. Acceptctl I)wi:tnIwr 15, I!MO. I’ittslwrgh Conference oii Attnl.yt~ic:tl Chntriietry and Applied SpectroRcopy, I’ithhurgh, Pa., Febrrinry-AIarch, 1961. REcEIvEn
Rapid Spectrophotometric Determination of Vanadium and Molybdenum in Uranium Materials P. R. KUEHN, 0. H. HOWARD, and C. W. WEBER Technical Division, Oak Ridge Gaseous Diffusion Plant, Union Carbide Nuclear Co., Oak Ridge, Tenn.
b A rapid spectrophotometric procedure, which is a compatible adaptation of the benzohydroxamate procedure for vanadium and the thiocyanate method for molybdenum, provides a precise determination of these impurities in hydrolyzed uranium hexafluoride or dissolved uranium oxides after a single 1-hexanol extraction. Each element is determined with a precision of = t l pg. at the 95% confidence level in the range of 5 to 20 pg., and the lower limit of detection is 1 pg. The method is readily applied to process control; the complete analysis requires only 30 minutes. Common impurities are tolerated at reasonable levels; iron and uranium interference is eliminated by a simple phosphate wash of the 1-hexanol extract.
M
OLYBDENUM
ANI>
VANADIUM
occur in uraniuin-lwaring orrs; rapid and sensitive determinations of these elements are therefore necessary in the production of high purity liraniiim oxides and fluorides. The control of a purification process for uranium hcsafluoride needed a mcthod which had a sensitivity of 1 pg. for each clement, was applicable to a broad concentration range, and required only readily available laboratory equipment. A conipatible adaptation of the colorimetric method of Wise and Brandt (IS)for vanadium in steel and oil, and the thiocyanate method for molybdenum (11) waa devised for detemlining these elements in uranium solutions, and especially in hydrolyzed uranium hexafluoride. The method provides the desired sensitivity, scope, speed, and simplicity. Since completion of this work, Priyadarshini and Tandon (IO) have reported on the use of N-benzoylN-phenylhydroxylamine for detcrmin740
ANALYTICAL CHEMISTRY
FERROUS SULFATESOLIJTION.Dissolve 1 gram of ferrotis ammonium sulfate, FeS04,(NH&SO4.6H@, and 1 ml. of sulfuric acid in 100 ml. of water. Vanadium Determination. Hydrolyze 1 t,o 7 grams of uranium hexafluoride in 50 ml. of distilled EXPERIMENTAL water or take a suitable aliquot of a Reagents. POTAMUM RENZOHY- u raniu m-beari iig solution and transfer to a 250-ml. lwskcr. Add 1 ml. of DROXAMATE. Prepared by a published 0.2y0 potassium dicliromate solution. proccdure (2). The rragmt Can be obThree grams of boric acid is added tained from Aldrich Chemical Co., when fluoride is prcscnt. Adjust the Milwaukee, Wts. BENZOHY DROXAMIC ACID SOLUTION pfI to 2 f 0.3 with hydrochloric acid and ammonium hydroxide. (BHA), 0.2M aqueous. Dimolve 35 Trsnsfcr the solution to a 250-ml. grams of potassium benaohydroxaniate separatory funnel and dilute to approxiin water. Adjust p H to 5 with hydromately 100 nil. Pipet 20.0 ml. of 1chloric acid and ammonium hydroxide. hexanol into the funnel and shake for Dilute to 1 liter. The solution is 5 to 10 seconds. Add 2 ml. of 13HA stable for at least 30 days. solution nnd shake for 1 minute. Allow PHOSPHATE SOLUTION. Contains 20 2 minutes for the phases to separate weight % of diammonium hydrogen and discard thc aqueous phase. Add phosphate in water; p€I adjusted to 1.5 2 ml. of H I M solution and shake for 5 with hydrochloric acid and ammonium to 10 seconds. Add 10 ml. of phoshydroxide. phate solution, shake for 1 minute, STANNOUS CHLORILIE SOLUTION.Disallow 2 minutes for phase separation, solve 112 grams of stannous chloride and discard the aqueous phase. in 100 ml. of concentrated hydrochloric Transfer the I-hexanol extract to a acid and dilute to 1 liter. STANDARD VANADIUM SOLUTION. 50-ml.centrifuge tribe and centrifuge for 2 minutes. Measure the absorbance Dissolve 0.1785 gram of vanadium of the 1-hcxanol extract a t 450 mp pentovide in 10 ml. of 5% sodium hyagainst 1-hexanol. Read the vanadium droxide and 1 ml. of 30% hydrogen content from an established calibration peroxide. Boil until colorless. Dilute curve. Save the 1-hexanol ext’ract, for to 100 ml. Dilute 10 ml. of this determination of molybdenum. solution to 1 liter to obtain a solution Molybdenum Determination. Aftcr having a concentration of 10 pg. of the absorbance measurement for vavanadium pcr ml. Ammonium vannadium has becn made, transfer the adatc used by some investigators (5, 1-hexanol extract to a 125-ml. IS) as a vanadium standard was not separatory funnel. Add 50 ml. of considered reliable; titrations of both 14 weight % sulfuric acid, 1 ml. of ammonium vanadate and sodium ferrous sulfate solution, and 10 ml. of vanadate supplies indicated nonconstannous cliloride solution. Shake formance with formula weights, probthe funnel for a few seconds. Add ably as a result of hydration effects. STANDARD MOLYBDENUM SOLUTION. 5 ml. of 5% ammonium thiocyanate solution and shake the funnel for i Dissolve 0.184 gram of ammonium minute. Allow 2 minutes for phase in 10 molybdate, (NH4),M070u. 4H20, separation; discard the aqueous phase. ml. of 5y0 sodium hydroxide and dilute Centrifuge the 1-hexsnol extract in a to 100 ml. Dilute 10 ml. of this solu50-ml. tube for 2 minutes. Measure the tion to 1 liter for the standard which absorbance of the 1-hexanol extract a t mill contain 10 pg. of molybdenum per 460 mp against 1-hexanoi. Read the ml. ing vanadium. A slight gain in sensitivity over bciiaohydroxamic acid is indicated, although their reagent is evidently less stable than benzohydroxamic acid.
