Emission Spectrochemical Analysis of Vanadium and Iron in Titanium Tetrachloride Spark-in-Spray Excitation Method H. V. MALMSTADT and R. G. SCHOLZ Noyes Chemical Laboratory, University o f ///;nois, Urbana,
This investigation was undertaken to develop a simple solution excitation technique for emission spectroscopy which would be rapid, inexpensive, accurate, and applicable for the direct determination of vanadium and iron in hj-drolyzedtitanium tetrachloride solutions. In the spark-in-spray method, the solution is sprayed from an atomizer between two horizontal graphite electrodes across which a controlled high-voltage spark is applied. Source conditions were studied and working curves for vanadium and iron in titanium tetrachloride were plotted for the concentration ranges of 0.003 to 0.294 and 0.005 to O.lYc, respectively. Relative average deviations of 1.2% for vanadium and 4.8% for iron were obtained. The good results obtained for the specific determinations of vanadium and iron in titanium tetrachloride indicate the possible general application of the spark-in-spray excitation technique for the accurate emission spectrochemical analysis of many types of solution samples.
//I
Table I.
Spectrographic Conditions for Analysis
Electrodes Slit width, microns Analytical gap Gap-to-jet distance Gap-to-slit distance Wave-leneth reeion Exposuretime Emulsion Development Emulsion calibration Gas for atomization
National Carbon Co. high purity graphite electrodes ground t o a cone with 120' included angle 50 and 30 (fixed slits) 6 mm. 1.6 cm. 38 cm. (no optics b e h e e n analytical gap and slit) 2300 t o 2930 A. 40 seconds Kodak S . A . No. 1 plate 4 minutes a t 21' C. in Eastman D-19, 1 5 seconds with acid stop (570 acetic acid), 4 minutes Eastman acid fixer, 4 minutes wash Rotating step-sector, 1 to 1.5 ratio, 7 steps rotated a t approx. 1600 r.p.m. Oxygen (pressure controlled b y Beckman regulator)
APPARATUS AND SPECTROGRAPHIC CONDITIOYS
T
H E R E are several techniques for the direct emission spectrochemical analysis of solutions, and discussions and bibliogrnphies are included in several publications (2, 4). At present the porous cup technique ( I , 9) and rotating disk method (3,8 ) :ire most co:nmoiily used for spark arid direct, current arc excitation, and the direct atomization of solutions into gas is the most f:irored for flame excitation. -1few investigators have comhined atomization with spark twitation, but the methods have not generally been applied. I-zumasa and Okuno (10) employed a spark through mist technique for the determination of several elements. Lamb (4) used direct atomization into a vertical spark gap for the deter~nination of magnesium in blood. Lundegardh and Philipson (.i) sparked across a flame for the determination of several elements. Owen ( 7 )developed a gas transport apparatus for sparkiiig atomized solutions passed through a hollow electrode. Because of the commercial availability of atomizers which perform so excellently for the dirert atomization of solutions into gas for flame excitation, it was considered n-orth while t o tmild a spark stand which could utilize such an atomizer to spray solutions between two horizontal graphite electrodes across which :I spark discharge was applied. The method is hereafter referred t o as the spark-in-spray method. The good reproducibility of atornixation coupled with a controlled spark source should give precise analytical results and high sensitivity for most elements. The results obtained in this investigation shox the success of the method for a specific analysis and indicate the possibility of general application for the emission spectrochemical analysis of many types of. solutions, because the technique is rapid, precise, and inexpensive per determination. 1-anadium is an abundant impurity in titanium tetrachloride, niid it is important to have a precise and rapid method for its determination. Iron is another possible impurity in t,itanium tetrachloride. The spark-in-spray technique was therefore npplied t o the determination of vanadium and iron in titanium tetrachloride, and working curves were plotted for the concentration ranges of 0.003 to 0.2% and 0.005 to O . l % , respectively. 881
Spark excitation was obtained from two different units, a National Spectrographic Laboratories Spec-Power unit and an Applied Research Laboratories (ARL) Multisource. A Bausch & Lomb Large Littrow spectrograph and both ilRL and JarrellAsh comparator densitometers were used X Beckman RIodel 4030 atomizer was used to spray solutions between two horizontal graphite electrodes as schematically represented in Figure 1. A special electrode stand was constructed so that the small beakers filled with the sample solution could be seated in a holder and rapidly swung under the capillary for atomization by means of a rotating arm, similar t o the Beckman flame photometer attachment. I
,
ELECTRODE
ELECTRODE
I
iATOM1 ZER
02
CAPILLARY
SAMPLE CELL
m-1 1
Figure 1.
-
SoL"T'oN 1
Spark-in-spray apparatus
An exhaust hood should be used directly over the spark stand to prevent corrosive fumes from entering the laboratory. The general spectrographic conditions used for analysis are given in Table I. PREPARATION OF SOLUTIONS
Standard Stock Solutions of Titanium, Vanadium, and Iron. Stock solutions of hydrolyzed titanium tetrachloride were prepared by a procedure similar to that described by Malmstadt and Roberts (6). Forty milliliters of purified titanium tetrachloride were slowly added t o about 40 ml. of 3M hydrochloric acid in a two-necked round-bottomed flask immersed in an ice bath. The
ANALYTICAL CHEMISTRY
882
titanium tetrachloride was added through one neck of the flask from a pipet fitted with a stopper near the delivery end. The other neck was fitted with a reflux condenser topped with a water trap containing 20 ml. of water. After all of the titanium tetrachloride was added, the water in the trap was used to wash down the reflux condenser and to return any of the volatile materials caught in the trap back to the hydrolyzed solution. The contents of the round-bottomed flask were transferred to a 100-ml. volumetric flask and diluted to the mark with distilled water. The weight of purified titanium tetrachloride added to the hydrolysis flask was calculated from the density which was determined by weighing 10-ml. aliquots of the same solution. The resulting stock solution of titanium contained 0.676 gram of titanium tetrachloride per milliliter. A vanadium stock solution containing 6.76 mg. per ml. was prepared by dissolving 3.106 grams of ammonium vanadate in 1M hydrochloric acid and diluting with 1M hydrochloric acid to the mark in a 200-ml. volumetric flask. More dilute vanadium stock solutions containing 3.38, 1.35, 0.676, and 0.135 mg. per ml. were prepared by taking aliquots of the concentrated vanadium stock solution and diluting with 1.M hydrochloric acid to the mark in suitable volumetric flasks.
P
/
0.001
I
0.I
$
--
$
0.050-
4
> IL
0
z
0
-
0010=
-
U
z
0 U
0.005-
0
-
-
0'
0002
Figure 2.
I I I I I l l 5.0
I
Working curve for vanadium
NSL Spec-Power, 0.015 microfarad, residual inductance and resistance, 4 discharges per cycle, 12 amperes RF current
k-
z W
I
0.5 1.0 I N T E N S I T Y RATIO
Figure 3.
O.IOO=
a
I I II Ill1
I
1 1 11111 0.05
0.1
I
I I I I 1111 0.5
1.0
I 1
titanium internal standard line did not change significantly with relatively large changes in concentration. Unknown Samples of Titanium Tetrachloride. Samplee of titanium tetrachloride can be prepared for analysis in a similar manner to the preparation of the titanium stock solution. A 10ml. aliquot of titanium tetrachloride is added to 10 ml. of 3-11 hydrochloric acid, with the water trap containing 10 ml. of distilled water. -4fter washing down the reflux condenser and returning the solution in the water trap to the reaction flask, the solution is transferred to a graduated cylinder, diluted to about 40 ml. with water, and mixed. The resulting solution is ready for spectrographic analysis by the spark-in-spray method. The volume of the titanium tetrachloride sample can be scaled down by use of smaller apparatus. EXPERIMENTAL RESULTS
Working curves for vanadium and iron
ARL multisource, 10 microfarads, residual inductance, 2 ohms resistance
.4n iron stock solution containing 6.76 mg. per ml. was prepared by dissolving 32.70 grams of iron(II1) chloride hexahydrate with 1M hydrochloric acid in a 1-liter volumetric flask and diluting to the mark. More dilute iron stock solutions containing 3.38, 1.35, 0.676, and 0.338 mg. per ml. were prepared by taking aliquots of the concentrated iron stock solution and diluting with I J I hydrochloric acid to the mark in suitable volumetric flasks. Standard Solutions of Vanadium and Iron in Titanium Tetrachloride. Standard solutions containing approximately 0.1, 0.05, 0.02, 0.01, and 0.002% vanadium in titanium tetrachloride were prepared by adding 1-ml. aliquots of the proper vanadium stock solution to 10-ml. aliquots of the hydrolyzed titanium tetrachloride stock solution. These solutions were corrected for the small residual concentration of vanadium in the most purified titanium tetrachloride solutions available. The residual vanadium was determined by a chemical titration procedure (6) and was usually about 0.001 to 0.003% in specially purified titanium tetrachloride solutions. Titanium solutions containing 0.071, 0.091, and 0.171% vanadium in titanium tetrachloride were prepared by adding 1-ml. aliquots of the vanadium stock solutions to 10-ml. aliquots of a hydrolyzed technical grade titanium tetrachloride known to contain 0.071% vanadium. Standard solutions containing 0.1, 0.05, 0.02, 0.01, and 0.005% iron in titanium tetrachloride were prepared by adding 1-ml, aliquots of the proper iron stock solutions to 10-ml. aliquots of the hydrolyzed titanium tetrachloride stock solution. Each of the standard solutions prepared in the above manner was diluted with 5 ml. of distilled water in order to ensure good atomization. The intensity ratio of vanadium analysis line to
The standard solutions of vanadium afid iron in titanium tetrachloride were used to prepare working curves, and two different commercial sources of spark excitation were used. Figure 2 shows vanadium and iron working curves obtained from an ilpplied Research Laboratories Multisource using 10-microfarad capacitance, residual inductance, and 2-ohm resistance. Many other source conditions were tried, but none proved so sensitive for the determination of vanadium. Figure 3 shows a vanadium working curve obtained with a Sational Spectrographic Laboratories Spec Poaer Unit using 0,015-microfarad capacitance,
T a b l e 11. Reproducibility of Spark-in-Spyay Method for Determination of V a n a d i u m and Iron in T i t a n i u m Tetrachloride" Determination 1
2 3 4
5 6
7 8 9
a
T'anadium Concn. determined, Devia% tion 0 0 0 0 0 0 0 0 0 0
100 102 098 099 099 099
101
099 101
Iron Concn. determined,
%
Deviation
0.000
0.048
0.005
0,002 0,002
0.048
0,002 0.004 0.000 0.004 0.003 0.000 0.000 0.002
0,001 0.001 0.001 0.001 0.001 0.001
0.046 0.050 0.054 0.053 0.050
0.050 0.052
0,002 0,004 102 0.054 10 0.100 0.0012 0.050 0.0024 Average Source, A R L Multisource. Oxygen pressure 20 lb./sq. inch.
V O L U M E 2 7 , N O . 6, J U N E 1 9 5 5 residual inductance, residual resistance, and four discharges per cycle. The reproducibility for the determination of 0.100% vanadium and 0.050% iron in titanium tetrachloride is shown in Table 11. The relative average deviation for vanadium is 1.2% and for iron 4.8y0. I t was found best to use an oxygen pressure of 20 pounds per square inch for atomization because of the high viscosity of the hydrolyzed titanium tetrachloride solutions. An oxygen pressure of 10 pounds per square inch was suitable for less viscous solutions. hpprosimately 1 nil. of solution was atomized during the exposure period. .4 small deposit of titanium dioxide accumulated on the electrode tips during the 40-second exposure. However, it was found that the intensity ratio of analys’s line to internal standard line remained nearly constant for five consecutive 10-second exposures over a total time of 50 seconds. About l t ’ ~ inch was ground off the graphite electrodes to ensure the removal of any depofiit before the succeeding exposure. Betneen determinations, and before the electrodes were set in position, the atomizer was washed by spraying with distilled water for about 30 seconds. The spark source was started immediately after,swinging the sample cell into position for atomization. The 2687.96-.4. line was found to be the most sensitive line for vanadium and the 2382.01--4. line the most sensitive for iron. The sensitivities for vanadium and iron in titanium tetrachloride nere about 0.001 and 0.004%, respectively. The 30-micron slit is suggested for highest sensitivity. Two different titanium internal standard lines were used and
883 both gave good results. Parallel working curves were obtained using the tn-o internal standard lines under the same excitation conditions. The titanium 2695.g.4. line is not listed in the Massachusetts Institute of Technology tables. There is some danger of vanadium interference on the 2688.82-A. titanium line, but there was no apparent interference up to 0.2’70 vanadium. If higher concentrations of vanadium were determined it would be wise to check for interference before using the 2688.82--4. titanium internal standard line. ACKNOWLEDGMENT
The authors are indebted t o Cramet, Inc., Chattanooga, Tenn., for grants-in-aid for this project. LITERATURE CITED
(1) Feldman, C., ANAL. CHEM.,21, 1041 (1949). (2) Harvey, C. E., “Spectrochemical Procedures,” Applied Research Laboratories, Glendale, Calif., 1950. (3) Heller, H. 4 . , and Lewis, R. W., ANAL.CHEM.,25, 1038 (1953). ( 4 ) Lamb, F. m‘.,IND. ENG.CHEM.,A N A L . ED., 13, 185 (1941). (5) Lundegardh, H., and Philipson, T., Lantbruks-Hdgskol. B n n . , 5, 249 (1938). (6) Malmstadt, H. V., and Roberts, C., ANAL. CHEM.,27, 741 (1955). (7) Owen, L. E., J . O p t . SOC.Amer., 41, 709 (1951). (8) Pagliassotti, J. P., and Porsche, F. mi.,ANAL.CHEM.,23, 198 (1951). (9) Peterson, RI. J., Ibid., 22, 1398 (1950). (10) Uzumasa, Y., and Okuno, H., J. Chem. SOC.Japan, 54, 631 (1933); 55, 622 (1934); 56, 1174 (1935).
RECEIVED f a r review September 27, 1954.
Accepted February 8 , 1955.
Identification of Frozen liquid Samples with the X-Ray Diff ractometer H. N. SMITH and H. H. HEADY Petroleum and O i l - S h a l e Experiment Station, Bureau o f M i n e s , Laramie, W y o .
The x-ray diffractometer unit can be used to identify components of frozen liquid samples. The low-temperature apparatus consists of a special sample holder with an attached cooling chamber, a Pliofilm cover to prevent frost formation on the sample, and an aircooling system. Identifications are made by comparing the x-ray chart obtained for the powdered frozen sample with x-ray charts of known frozen liquids. This lowtemperature technique has been successfully applied to identifying and making percentage estimates of the components of the liquid shale-oil distillate fractions of high boiling point.
T
H E x-ray diffractometer unit can be used to identify components of frozen liquid samples. The liquid sample is frozen, ground into a fine powder, and loaded into a standard-size sample holder that is modified to include a small cooling chamber on the underside. Cold air is drawn through this chamber to retain the sample in frozen condition. Frost formation on the sample is prevented by a thin Pliofilm material placed over the semicircular opening in the radiation shield that slides over the goniometer shaft and completely surrounds the sample holder. Identifications are made by comparing the x-ray powder pattern thus obtained with standard x-ray charts of known frozen liquids. This low-temperature technique has been successfully applied to identifying and making percentage estimates of the components of liquid shale-oil distillate fractions of high boiling point. The literature reveals that considerable work has been done in developing and improving the technique of low-temperature
x-ray analysis. In 1923 Broom6 ( 4 ) and Eastman (8) obtained x-ray powder patterns of benzene. The technique employed by Eastman involved flowing liquid air into a special camera and over a centrally located capillary tube containing the sample. In 1928 and 1932 Cox (6, 7 ) made single crystal studies of benzene. The apparatus consisted of a camera which permitted circulating cooled alcohol to produce temperatures as low as minus 40’ C. within the camera. The benzene sample was placed in a thin gelatin capsule and mounted inside the camera. In 1935 Barnes and Hampton (2) developed a camera wherein the specimen to be analyzed was mounted on a copper block cooled by circulating a liquid coolant internally. In 1936 Vonnegut and Warren ( I S ) made a single crystal analysis of bromine. The bromine crystal was kept frozen by flowing a coal stream of dry air over the entire sample. The technique used by Lonsdale and Smith ( I O ) in 1941 involved freezing a liquid sample placed in a thin-walled cellophane holder by bloq-ing a cold stream of dry air over the container. Perhaps the most suitable technique for low-temperature singlecrystal work was developed in 1949 by Kaufmrtn and Fankuchen ( 9 ) and modified in 1951 by Post, Schwartz, and Fankuchen (11). Abrahams ( I ) and others also contributed to the development of this technique. Briefly, the method involved placing a sample in a thin-walled glass capillary, accurately mounting this capillary, then freezing the sample to a crystalline state with a cold, dry air stream. Snother stream of warm, dry air surrounded the cold air jet to prevent condensation on the capillary, and a thermocouple was incorporated to measure the sample temperature. Tombs ( 1 2 ) and \J700d ( 1 4 ) also contributed to
