Table I.
Comparison of Ratios Obtained by the Two Methods
Polymer
Methyl/Phenyl A 2.54 2 70 2 50 B 3.30 3 06 3 25 C 0.99 0 94 0 99 D i.is 1 25 1 20 E 2 78 2 55 2 36 F 1.96 1 87 1 95 G 0.90 0 99 0 89 IT 0 45 0 55 0 53 I 0.74 0 74 0 78 J 1.17 1 22 1 22 K 1 79 1 79 1 71 L 2 09 1 91 1 91 Standard deviat ion = 0.091.
Ratio 2.31
2.33
3.03
0 89 0:94 1.15 1.25 2.67 1 93 1:85 0.92 0.89
..
0.78 1.22 1.70
..
Value from C-H Analysis
Average 2.48 3.iS 0.95 1 20 2 59 1.91 0.90 0.51 0.76 1.21 1.75 1.97
2.5 3.47 0.68 1.50 2.09 0:82
..
..
smear of the polymer on a sodium chloride plate and allow about 5 minutes for the solvent to evaporate. The strong intensities of the absorption bands in silicone polymers require that the cast films be very thin; hence, solvent evaporation takes place very rapidly. The solvents generally used are toluene or xylene, which have no appreciable absorption at 8 microns and only slight absorption a t 7 microns due to a shoulder of a band near 6.8 microns; hence, traces of solvents do not interfere with the measurements. LITERATURE CITED
Table II.
Comparison of Experimental and Theoretical Values
Me/d Ratio by Infrared Method Individual Determination 0.99,0.91,0.93,0.93,0.94 Av. 0 94 1.43,1.43,1.40,1.33,1.36 Av. 1.39 2.69,2 80,3.04,2 95 Av. 2.87
Theoretical Me/$ Ratio
groups and not an absolute determination of the amount of either of these two groups. An absolute determination of each constituent individually n-odd in general be more dcsirable; however. practical limitations make such a determination difficult, if not impossible. The reason for this is as follows: Commercial silicone polymers are usually supplied in aromatic solvents such as xylenes, and an absolute de-
0 86 1.33 3.00 1.91
>le/+ from C-H Analysis Individual Determination 1 30,l 34 1 32 2 02;l 88 1.95 1.70,2.12
termination would necessitate the separation of the solvent from the solids. For many polymers, the solids become set up and insoluble when the solvent is removed; hence, redissolrinp the material in a solvent for infrared analysis becomes a problem. The method used herein does not require that the sample be weighed or the sample thickness be known. The technique used is simply to make a thin
(1) Fishl, Walter, Young, I. G., Appl. Spectroscopy 10, 213 (1956).
(2) h!urphy, C. M., Saunders, C. E., Smith. D. C.. Ind. Ena. Chem. 42, 2462 (1950j. (3)Rank, D. H.,Saksena, B. D., Shull, E. R., Discussions Faraday SOC.9, 187 (1950). (4) Richards, R. E., Thompson, H. W., J . Chem. Sac. 1949, 124. (5) Smith, D. C., French, J. >I., O’Neill, J. J., Naval Research Lab. Publ., 2746 (January 1946). (6) Wright, Norman, Hunter, M. J., J . Am. Chem. SOC.69, 803 (1947). (7) Toung, C. )I7.,Xoehler, J. S., McKinney, D. S., Ibid.. 69, 1410 (1947). (8) Young, C. W., Servals, P. C., Currie, C. C.. Hunter. RI. J.. Ibid.. 70, 3758 (1948j.
RECEIVEDfor review June 24, 1958. Accepted December 10, 1958. Division of Analytical Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
Colorimetric Determination of Boron with Victoria Violet CHARLES A. REYNOLDS Deparfmenf of Chemistry, Universify of Kansas, Lawrence, Kan.
b In the p H range of 7.7 to 10.0, the absorbance of the dye, Victoria Violet, is markedly lowered b y the presence of boric acid. A simple colorimetric method for boron in the range of 0.02 to 0.60 mg. of boron has been developed based on this decrease in absorbance. Measurements were made at 540 mp on solutions adjusted to pH 8.75.
C
sulfuric acid is required as the solvent for the majority of the colorimetric methods available for boron (1, 5 ) . I n this solvent a number of polyhydroxy compounds, including quinalizarin, carminic acid, and two new reagents introduced by Grob and Yoe ($), 5-benzamido-6-chloro-l,l’-bis (anthraquinONCENTRATED
1 102
ANALYTICAL CHEMISTRY
ony1)amine and 5-p-toluidine-1, 1’(anthraquinonyl)amine, give color changes in the presence of boric acid. Another commonly used reagent is curcumin, which forms a colored product with boric acid when a solution containing curcumin and boric and oxalic acids is evaporated to dryness. This colored product is subsequently taken up with 95% ethyl alcohol for absorbance measurements. Only one method for boron is available in which the absorbance of a n aqueous solution is a function of the boron content of that solution. This method, developed by Kuemmel and Mellon (4, involves the use of chromotropic acid, which forms a complex with boric acid in aqueous solution. However, neither chromatographic acid nor the complex formed between this
reagent and boric acid absorbs in the visible region of the spectrum; hence, an ultraviolet spectrophotometer is needed to utilize this method. Victoria Violet ((3.1. 53) is made by diazotizing p-nitroaniline, coupling it with chromotropic acid, and reducing the nitro group. It still has the adjacent hydroxy groups necessary for complexing with boric acid. I n addition i t absorbs in the visible region of the spectrum. This investigation was concerned with the development of a convenient and rapid procedure for the colorimetric determination of boron in aqueous solutions utilizing the colored complex formed between boric acid and Victoria Violet. REAGENTS AND APPARATUS
STANDARD BORICACID SOLUTIONS.
Table I. Reproducibility and Accuracy of Method
Boron Concn., Mg. of B/25 M1.
0.024 0.042 0.072 0.116 0.154
Figure 1 . Absorbance vs. wave length for Victoria Violet A. 4.96 X 10-5M d y e at pH 8.75 8. 4.96 X 10 %4 d y e plus 3 mg. of H&03 at pH 8.75
0.210
c I
10
L
0.450
-0 -0 -0 -0 -0 -0 -0 003-$0 -0 003-$0 -0 005-+O
002 0.280 003 0.357 004 0.454 -0 012-$0 012 0.547 15 separate determinations each boron concentration.
”’ 20
Deviations from Known Boron Concentrationo Range Average 003-$0 002 0 0017 004-+O 005 0 0024 005-+O 007 0 0035 005-+O 004 0 0026 009-+O 007 0 0052 003-+O 003 0 0028
478
WAVE LENGTH IN
All the standard boric acid solutions were prepared by direct weighing of Baker’s analyzed boric acid with subsequent dissolution in a buffer solution which was 0.1M in both sodium carbonate and sodium bicarbonate. STOCK SOLUTION OF VICTORIA VIOLET. A stock solution of Victoria Violet was prepared by weighing 3.00 grams of a product called Pontacyl Violet 4 BSN, given to the author by E. I. du Pont de Nemours & Co. This weight of the dye was dissolved in 1 liter of 0.1M sodium sulfite solution and stored in a black bottle. This stock solution should be prepared fresh about every 10 days, because air oxidation causes a brown precipitate to form after 2 weeks. BICARBONATE - CARBONATEBUFFER SOLUTION. A stock buffer solution of p H 8.75 was prepared by dissolving 80 grams of sodium bicarbonate and 8 grams of sodium carbonate in 1 liter of distilled water. Apparatus. Absorbance measurements were made both with a Beckman Model DK-1 recording spectrophotometer using 1.00-cm. Corex cells and with a Bausch & Lomb Spectronic 20 colorimeter, using the matched test tubes provided with the instrument. RESULTS
The effect of 3 nig. of boric acid on the absorption spectrum of a 4.96 X 10-6M solution of Victoria Violet buffered a t p H 8.75 is shown in Figure 1. The boric acid not only decreases the absorption maximum, but also shifts the absorption peak from a value of 545 mp to 535 mp. Although the absorbance difference a t 540 mp is only 0.21 absorbance unit with this dye concentration, if the dye concentration is increased to 6.5 X lO-3M or greater,
rnp
the absorbance difference caused by 3 nig. of boric acid is greater than 1.50 absorbance units. The presence of boric acid causes a decrease in the absorbance peak of Victoria Violet in the p H range of 7.7 to 10.0, but the difference is greatest in the p H range of 8.5 to 9.0. The actual value of the absorbance difference is critically dependent upon the p H of the solution, and the pH of the solutions being measured should not be different by more than 0.1 p H unit. Standard analyses were run by pipetting exactly 2 ml. each of the standard boric acid solutions into a 25-ml. volumetric flask, followed by exactly 2 ml. of the stock dye solution, and diluting to volume with the bicarbonate-carbonate buffer solution of p H 8.75. I n all cases, the p H of the final solution was 8.75 I 0.05 units. A blank solution was prepared a t the same time by pipetting exactly 2 ml. of the stock dye solution into a 25-ml. volumetric flask, followed by dilution to the mark with the same buffer solution. A calibration curve was prepared by plotting absorbancy differences which were obtained by placing the blank solution in the sample side of the Beckman DK-1 instrument and the solution containing boric acid in the reference beam. I n this manner a differential curve was obtained in the form of a sharp peak: the peak heights were plotted vs. milligrams of boron to obtain a Beer’s law plot. Beer’s law was obeyed over the range of 25 to 550 y of boron per 25 ml. of solution. The average differential molar absorbance index over this range was 791. Tn each run the instrument was
0 0 0 0
0028
0031 0042
010 run for
zeroed a t SO0 mg, a t which point the black solution and the solution containing the boric acid have the same absorbance, followed by scanning do\%nscale to 450 mp. The tungsten filament light source and the photomultiplier detector unit of the instrument were employed a t all times. All absorbance measurements R ere made 30 minutes after mixing was conipleted. However, no difference in the absorbance decreases was noticed if the solutions m-ere allowed to stand for 24 hours. The only stability problem encountered involved the air oxidation of the stock dye solution. If the stock solution of Victoria Violet n a s allowed to stand more than 2 n-eeks after preparation, the differential absorbance curves obtained with boric acid had lower peak heights, and a light brown precipitate was evident in the dye solution itself. Table I shows the results of 15 runs made over a period of 6 neeks on each of 10 standard boric acid solutions. Four different stock dye solutions were employed in the determinations. The reproducibility of the method is about 275 \Then samples larger than 200 y of boron are used. Similar results should be obtained when a single-beam instrument having a multiplier phototube detector is employed. Howerer, when an instrument which has only an ordinary phototube is used, the sensitivity of the method is decreased, even though the reproducibility remains constant. DISCUSSION
S o attempt u-as made to ascertain the nature of the complex formed between borax acid and the dye, Victoria, Yiolet. However, it is evident that the reaction between these two reagents is an equilibrium reaction, because the reaction is shifted toward formation of the complex by the addition of greater amounts of either boric acid or Tictoria Violet. The possible interference of many common anions was investigated, and VOL. 31, NO. 6, JUNE 1959
1103
no one of these anions was found to produce any interference. One hundred milligrams of fluoride, chloride, iodide, monohydrogen phosphate, perchlorate, oxalate, nitrite, nitrate, and sulfate ions were added separately to a standard solution containing 0.210 mg. of boron, buffered at p H 8.75; in no case did the differential peak height differ from that of the pure boron solution of the same concentration. Cations which are known to react with chromotropic acid and its derivatives, such as ferric ion. aluminum ion, and chromium ion, precipitated as the hydrous oxides a t the p H a t ivhich absorbance measurements were made, and therefore, a separation of these substances was required before a boron analysis was attempted. This procedure m-as used in the analysis of several rare earth borides for boron content (2). After the boride had been brought into solution with nitric acid, the p H of the solution was adjusted to about 8.5 with a solution of sodium hydroside, and the rare earth hydrous oxides were then allowed to settle. An
aliquot of the supernatant liquid was taken for boron analysis with Victoria Violet using the Bausch &. Lomb Spectronic 20. Strong oxidizing agents such as permanganate, ceric ion, and dichromate cannot be present, because of their effect upon the dye itself.
tion in the sample beam, and zero the instrument a t 800 mfi. Scan downscale to 450 mp and measure the height of the differential absorbance peak. Compare with a calibration curve previously prepared by running standard solutions of boric acid in exactly the same manner. ACKNOWLEDGMENT
RECOMMENDED PROCEDURE
An aqueous aliquot containing from 0.02 to 0.60 mg. of boron (0.1 to 3.5 mg. of boric acid) should be adjusted to p H 8.5 to 9.0. The volume of the solution a t this point should be 10 to 15 ml. To this solution add 2 ml. of a 6.5 X 10-3M solution of Victoria Violet and dilute to 25 ml. with the stock bicarbonate-carbonate buffer solution. The p H of the final solution 0.05 units. Prepare should be 8.75 a blank solution a t the same time b y pipetting 2 ml. of the 6.5 X 10-3M solution of Victoria Violet into a 25 ml. volumetric flask and diluting to the mark with the same buffer. After 30 minutes of development time, place the sample in the reference beam of the Beckman DK-1 and the blank solu-
*
The author acknowledges the support of the United States Atomic Energy Commission for this n-ork. LITERATURE CITED
(1) Cogbill, E. C., Yoe, J. H., Anal. Chim. Acta 12, 455-63 (1955). (2) Eick, H. A., Gilles, P. W., Abstracts, 134th Meeting, ACS, p. lS, September
1958. (3) Grob, R. L., Yoe, J. H., Anal. Chim. Acta 14, 253 (1956). (4) Kuemmel, D. P., Mellon, M. S., ANAL. C H E ~ 29,378-82 I. (1957). (5) Snell, J. D., Snell, C. T., “Colorimetric Methods of Bnalysis,” Vol. 2, pp. 703-4, Van Nostrand, New York, 1949. RECEIVED for review October 31, 1958. Accepted January 26, 1959.
Direct Determination of Oxygen and Nitrogen in Titanium and Titanium Alloys Use of Bromine Trifluoride WILLIAM A. DUPRAW’ and HUGH J. O’NEILL Armour Research Foundafion o f lllinois lnsfitufe of Technology, Technology Center, Chicago 7 6,
b This investigation was undertaken to expand the usefulness of the bromine trifluoride technique. Low levels of the gaseous impurities, oxygen and nitrogen, in titanium and titanium alloys can b e determined. The relative deviation for oxygen over the entire range of oxygen values (0.05 to 1.0%) averThe presence of iron or ages 4.8%. aluminum in the alloy reduces the total nitrogen recovery but does not effect oxygen recovery. The method offers a new approach for determining oxygen and nitrogen levels in other metals which would b e almost impossible to analyze by more common procedures.
T
accurate determination of oxygen, nitrogen, and hydrogen in titanium metal and alloys is essential to the metallurgical evaluation of the metal in terms of physical performance. Loss of ductility, increased hardness, increased notch sensitivity, and emHE
1 Present address, Columbia-National Corp., P. 0. Box 1247, Pensacola, Fla.
1 104 *
ANALYTICAL CHEMISTRY
brittlement are associated Fvith these impurities. Current analytical methods are based on techniques of vacuum fusion (1, 3, 6, 13, 14, 17), chlorination (2, 6), bromination (4), and, more recently, emission spectroscopy (9). The vacuum fusion and bromination techniques h a r e been used more extensively. The use of bromine trifluoride as a reagent was first suggested by Emelbus and Woolf (8, 15), who reported its action on 28 metal oxides. Hoekstra and Katz (IO) studied its application to determination of combined oxygen in many metal osides. The literature does not cite any investigation on the applicability of this reagent to the determination of low amounts of oxygen. Bromine trifluoride liberates all combined oxygen, as molecular gas, from those metal oxides which form volatile fluorides or fluorides TT hich are soluble in bromine trifluoride. The reaction for titanium is quantitative a t approximately 75’ C., and for oxides analogous to titanium dioside it is:
3MOr
Ill.
+ 4BrF3
-.f
3MF4
+ 2Br2 + 302
A similar reaction, resulting in quantitative liberation of molecular nitrogen, has been assumed for metal nitrides. Metals forming reactive oxides are indicated by Emelkus and Woolf (8, 15) and further elucidated by Hoekstra and Katz (10). However, when oxygen and nitrogen are present in residual amounts in titanium, the gases are not in combination as oxides and nitrides. Titanium has a single phase with oxygen and nitrogen dissolved in solid solution and dispersed in the hexagonal lattice of the titanium metal. This single phase exists up to approximately 14 weight % oxygen and 3 weight yonitrogen (16). Titanium reacts with bromine trifluoride as follows: 3Ti 4BrF3 43TiF4 2Br2 It was assumed that this reaction could provide the basis of a method for determining residual levels of oxygen and nitrogen in titanium metal and alloys. The so-called interstitial gases would be released as molecular oxygen and nitro-
+
+
