Ultraviolet Spectrophotometric Determination of Zirconium RICHARD B. HAHN
and
LEON WEBER1
Chemistry Department, W a y n e University, D e t r o i t 7,
Mich.
quantity of 6M ammonia diluted to 50 ml. as reference. The amount of zirconium is determined by reference to the standard curve.
Zirconium tetramandelate dissolves in aqueous ammonia, forming a soluble, saltlike compound that exhibits maximum absorbance at a wave length of 258 mp. This is used as the basis of a spectrophotometric method for the determination of milligram amounts of zirconium in the presence of aluminum, iron, and titanium.
DISCUSSION
The amount of ammonia used to dissolve the zirconium tetramandelate is not critical; identical results were obtained in solutions 0.72M t o 2.16M in ammonia. The alcohol and ether wash ensures complete removal of any excess mandelic acid. The interference of diverse ions was studied by preparing samples containing a known amount of zirconium, adding known amounts of foreign ions, and analyzing the samples by the pro-
T
HE determination of zirconium using mandelic acid as pre-
cipitant was devised by Kumins (2). In this method the zirconium tetramandelate precipitate is ignited to the oxide, which is weighed. Iiumins observed that zirconium tetramandelate is completely soluble in aqueous solutions of ammonia, forming a clear colorless solution. Hahn and Weber showed that a soluble, saltlike compound is formed in this reaction (I). Spectrophotometric studies of solutions obtained by dissolving zirconium tetramandelate in ammonia (using I-cm. quartz cells in a Beckman Model DU spectrophotometer) showed absorption in the ultraviolet region. Maximum absorbance occurred a t a wave length of 258 mp. The absorbance curve is given in Figure 1. The absorbance is probably caused by the phenyl groups of the zirconium tetramandelate molecule, as ammonium mandelate solutions give an identical absorbance spectrum. The possibility of using this absorbance as an analytical method for the determination of zirconium was investigated.
* 7 * 0 0.6
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z a m c 0
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EXPERIMENTAL
U
Varying quantitiee of zirconyl ions were precipitated with mandelic acid and the precipitates were dissolved in about 20 ml. of 6 M ammonia. The resulting solutions were diluted to 50 ml. with distilled water. These solutions were stable for about 2 days. After this time hydrolysis occurred and zirconium hydroxide was precipitated. The absorbance was measured a t 258 mp. Results when plotted show that Beer's law is obeyed over the entire range. These data indicate that the method may be useful for the determination of small amounts of zirconium. After experimentation the following procedure was devised.
0.01 24 0
I
I
WAVELENGTH
,
260 IN
I
270
MILLIMICRONS
Figure 1. Ultraviolet absorption spectrum of ammonium zirconium tetramandelate
PROCEDURE
A solution containing 0.5 to 50 mg. of zirconium is placed in a 250-ml. beaker and diluted to about 20 ml. with distilled water. Twenty milliliters of 12M (concentrated) hydrochloric acid are added and the resulting solution is heated to about 85' C. Twenty-five milliliters of a l X (about 15%) solution of mandelic acid are added dropwise with stirring. The solution is maintained a t about 85" C. for 0.5 hour. The sample is allowed to cool, then to stand for about 24 hours. The precipitate is filtered by suction using a sintered-glass crucible of medium porosity. The preci itate is washed five times with a solution containing 5 % manfelic acid and 2% hydrochloric acid, three times with 95% ethyl alcohol, and twice with ethyl ether. The precipitate is treated with individual 5-ml. portions of 6M ammonia until it is completely dissolved. (Usually three or four treatments are necessary.) The crucible is finally washed three times with 5-ml. portions of distilled water and these washings are combined with the previous solution. The resulting solution is transferred to a 50-ml. volumetric flask and diluted to the mark with distilled water. The absorbance is measured a t 258 mp using the same 1
I
I
250
Table I. Determination of Zirconium in Presence of Aluminum, Ferric, and Titanium Chlorides Sample 1 2 3 4 5 6
7
8 9 10 11 12 13 14 15
Present address, Shell Development Co., Houston 25, Tex.
414
A1 20 20 10 10
10 20
.. ..
20 100
..
io0
io0
Ion Added, Mg. Ti Fe 20 20 10 10 10
..
..
20
20 10 10 10
..
..
20 20
..
.. loo
100 100 100
20
io0
..
loo
100
Zirconium, Mg. Taken Found 0.505 0.505 1.01 2.02 5.05 10.1 10.1
10.1 10.1 10.1 10.1 10.1
10.1 10.1 10.1
0.99 1.30 1.58 3.18 6 29 10.1 10.9 10.3 11.1 10.2 11.5 11.1 11.1 11.4 12.1
Error,
%
+96.0
>I00 +56.4
+57.4 +24.6
+5.9 +2.0 +9.9 +1.0 4-13.9 i9.9 +9.9 +12 9 +19.8
V O L U M E 28, NO. 3, M A R C H 1 9 5 6 cedure given previously. .4luminum(III), iron(III), and titanium(IV) were selected because they are frequently associated with zirconium in ores and alloys and are the most likely to cause interference. It was observed that the nitrate ion interferes by causing incomplete precipitation of the zirconium tetramandelate. The data given in Table I indicate that small amounts of zirconium can be determined by the above method in the presence of 100 mg. of aluminum(III), 10 mg. of iron(III), and 20 mg. of titanium(1V). Errors occur x-hen larger quantities of these ions are present. The accuracy is poor in samples containing less than 1 mg. of zirconium.
415
This method should prove useful for the rapid determination of small amounts of zirconium, as it requires no final ignitions and weighings. LITERATURE CITED
(1) Hahn, R. B., Weber, L., J . A m . Chem. SOC.77, 4777 (1955). (2) Kumins, C. A,, i l ~ a CHEM. ~ . 19, 1861 (1947). RECEIVED for review August 1, 1955. Accepted December 1. 1955. Sub. mitted as a thesis b y Leon Weber in partial fulfillment of the requirements f o r t h e M.S. degree in chemistry, Wayne Cniversity.
Oscillometric Determination of FIuoride CLARENCE L. GRANT and HELMUT M. HAENDLER Department of Chemistry, University of N e w Hampshire, Durham,
A procedure is described for the determination of macro quantities of fluoride. The method employs a modification of the Willard and Winter steam-distillation procedure, followed by accurate adjustment of the pH, and subsequent titration with thorium nitrate using a high frequency oscillometer for end point detection. For the range of 3 to 8 mg. of fluoride per 100 ml. of solution, the average accuracy is within 0.2%. The method is rapid and has the particular advantage of being easily adaptable to automatic recording.
T
HE determination of macro quantities of fluoride is a problem
of major analytical concern. Considerable work has been published on techniques of decomposition and separation, the latter commonly using a modification of the Willard and Winter steam-distillation procedure (26). The separated fluosilicic acid can be analyzed gravimetrically or volumetrically. Gravimetric procedures, such as precipitation of calcium fluoride (do), lead chlorofluoride ( d l ) , lead bromofluoride (Y), lanthanum fluoride (14, 18), triphenyltin fluoride ( I ) , and bismuth(II1) fluoride (61, are tedious. The precipitates are often of variable composition and have appreciable solubilities. Volumetric methods, such as the titrations with thorium nitrate (25), aluminum chloride (IS), cerous chloride (b), ferric chloride (8) or hydroxide (17 , 2 2 ) , are subject to many difficulties. In general, the indicator color changes are extremely subtle, making the method unsatisfactory for the inexperienced analyst or technician. Rickson (1.9) states that the widely used thorium nitrate titration and its modifications “appear to be based more on personal choice than on any fundamental reasoning.” For these reasons, recent interest has centered around the possibility of adapting a titration procedure to a recording instrument. It was the purpose of this investigation to determine the applicability of a high frequency oscillometer to one of the fluoride reactions. High frequency automatic titrators are adaptable to a variety of reactions including precipitation, acid-base, complex formation, a few oxidation-reduction reactions, and reactions in organic solvents; therefore, they seemed to have promise. Good end point detection has been found by this method for such inorganic ions as thorium (4),chloride (S), beryllium (8), calcium (ft?), magnesium ( I d ) , and sulfate (16). Blaedel and Malmstadt (4)have stated that the reaction of fluoride with thorium is definitely not useful for high frequency titrations because of excess curvature in the instrument response curve in the region of the equivalence point. This curvature was not eliminated by varying conditions such as acidity and thorium concentration. Harley and Revinson ( I O ) reported encouraging
N. H.
results in the titration of micro quantities of fluoride with thorium, using a high frequency oscillator to detect the end point. The analytical results, however, have never been published. The advantages of the high frequency method are not due to increased accuracy or sensitivity over conventional electrometric procedures, but lie in the convenience of operation, the ability to show the end points for reactions which are masked when other indicators are used, and the absence of physical contact of electrodes with the solution. This eliminates the influence of electrode potentials as well as the possibility of electrode contamination and electrolytic alteration of the concentration. An additional advantage is the ease with which high frequency titrators may be adapted for use with automatic recorders. A disadvantage is the uncertain relationship between the indicated end point for a reaction and the stoichiometric equivalence point. APPARATUS AND R E 4 G E Y T S
The distillation apparatus is that described by Huckabay, Welch, and Metler (11). A , specially constructed Glaa-Col heater was used to heat the distillation chamber. The high frequency measurements were made with a Sargent Model V chemical oscillometer, operating at a frequency of approximately 5 megacycles (24). The instrument operates on a capacitive retune principle. The sample cell is in parallel with calibrated capacitors, and because capacitance in parallel is additive, it is necessary simply to adjust these capacitors to bring the instrument back into resonance after the addition of each titration increment. Readings are made in scale units having the dimensions of capacitance. Two types of cells mrere used during the course of the work. Because of the possibility of corrosion, tests were made on a polyethylene cell similar to the glass cell of Hall and Gibson ( 9 ) , and employed in conjunction with the Sargent oscillometric cell compensator (24). Satisfactory operation was obtained but the stability and sensitivity were not so good as with the 150-ml. glass titration cell supplied with the unit. The major portion of the work, including all analytical results reported here, was performed in the glass cell, v.-hich showed onlj minor corrosion over a 2-year period. Solutions were stirred continuously with a motor stirrer during the titrations. Timed increments of titrant were added from a 10ml. microburet. All glassware was calibrated. A Beckman Model H-2 p H meter, with glass and saturated calomel electrodes, was used for the pH measurements. Sodium fluoride, analytical reagent grade, was used m the standard. From a consideration of the stated analysis, the fluoride content was calculated to be equivalent to that of a sodium fluoride 100.0% pure. Consequently, no further purification waa attempted. A solution containing 1 mg. of fluoride per milliliter was prepared by dissolving 2.2100 grams of the material, dried overnight a t 140’ C., to make 1 liter of solution, which waa stored in a polyethylene bottle.
