salt (in concentrations below 0.1%) caused low results. This interference was overcome by a large excess of neocuproine. In the case of butyl zymate the color faded rapidly (within 2 to 5 minutes) and no amount of excess neocuproine was of any assistance in overcoming the interference. Barium sulfonate and sodium sulfonate interfered in concentrations above 0.1%. This interference was more of a retarding nature, for after standing for about 4 hours, the color was completely developed. ADVANTAGES
The simplicity of the method described is not only due t o the use of neocuproine, but also to the novel approach used in the treatment of the sample. It is thus possible to determine the copper content directly without resorting to any prior treatment of the sample. The advantages may be listed as follows:
No ashing or acid extraction
KO acid dissolution of ash KObuffering or chelating
KOp H adjustments No extraction It is essential that the proper sized sample be used. As a time saving measure and to determine the proper size t o take, a simple spot test was employed. A drop of a standard solution of copper naphthenate was placed on a spot plate and the color developed by adding 1 drop of neocuproine and 1drop of chloroform. A drop of the unknown !vas treated in a similar manner. Comparison indicated the size of the sample to be taken for analysis. Using this simplified procedure it is possible to determine copper in fuel oil in a matter of a few minutes per sample. The copper in a single sample can be determined in less than 1 hour. The rapidity and simplicity of this method stand out when compared with the old ashing or acid extraction procedure. LITERATURE CITED
( 1 ) Andrus. S..dnalvst 80. 514 (1955). (2) Barney; J.' E., IT, A4xk~. CHEW'26, 567 (1954). (3) Breckenridge, J. G., Lewis, R. IT.>
Quick, L. A., Can. J . Reseurch B17, 258 (1939). (4) Elwell, W. T., Analyst 80,508 (1955). (.5 ,) Gahler. A. R.. ANAL. CHEM. 26. 577-9 (1954).' (6) Hackett. C. E. S.. Anal. Chim. Acta 12, 3k3-62 (1955). (7) Hague, J. L., Brovm, E. D., Bright, H. ii., J . Research h a t l . Bur. Standards 47, 380 (1951). (8) LaQue. F. L.. Corrosion 10. 391 (i954). (9) Luke, C. L., Campbell, bI. E., ANAL.CHEM.25, 1588 (1953). (10) Martens, R. I., Githens, R. E., Sr., Zbid.,24,991-3 (1952). (11) Melvin, E. H., Hawley, J. E., J . Am. Oil Chemists' SOC.2 8 , 346 (1951). (12) Michel, G. X, Maron, N., Anal. Chim. Acta 4, 542-50 (1950). (13) Pohl, Heinz, Zbid., 12, 54 (1955). (14) Rees, W. T., Analyst 75, 160-6 (1950). (15) Sinyakova, S. I., Borovaya, 11. S., Gavrikova. X. A . Zhur. Anal. Khim. 5, 330-8 (1950). (16) Rilkins, D. H., Smith, G. F., Anal. Chim. Acta 9, 538 (1953). RECEIVEDfor review May 17, 1956. Accepted September 6, 1956. Pittsburgh
Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., February 28, 1956. The opinions expressed in this paper are those of the authors and do not reflect the views of the Navy Department or of the Naval Service a t large.
Colorimetric Determination of Titanium in Polyethylene RICHARD A. ANDUZE Research and Engineering Division, Monsanfo Chemical Co., Dayton, Ohio
,Titanium can be determined colorimetrically in polyethylene by a method which involves ignition in an oxygen bomb, separation from interfering elements by coprecipitation with zirconium arsenate, and reaction of titanium with hydrogen peroxide in sulfuric acid solutions. The color produced is measured at 41 0 mp. Amounts as low as 3 p.p.m. can be determined.
V
colorimetric determinations of small amounts of titanium have been described in the literature (3, 6-7). Of the many color reagents proposed, hydrogen peroxide is the most readily available and needs no further purification. I n suIfuric acid-titanium solutions, hydrogen peroxide causes a yellow color to develop. This color is due to the formation of the complex peroxidic ion furnished by the peroxodisulfatotitanic acid freed by the reaction between titanium, peroxide, and sulfuric acid. This colored ion has been considered an anion, but recent work indicates that it is a cation (2). The 90
ARIOUS
ANALYTICAL CHEMISTRY
color is stable for oyer 2 years ( 1 ) . However, the necessary separation of interfering cations is often tedious and may lead to losses of titanium (5). For the determination of titanium in polyethylene or other organic materials, a method based on the formation of the complex titanium-peroxide ion has been developed. It differs from methods heretofore published in the method of decomposing the sample, and in that the sensitivity of the method has been extended. This method will detect 3 p.p.m. of titanium in a 1.5-gram sample. Vanadium, nickel, chromium, manganese, molybdenum, copper, silicon, and iron do not interfere, because titanium is separated from them by coprecipitation with zirconium arsenate (8). The mixed titanium and zirconium arsenate are dissolved in hydrochloric acid, and the color of the complex peroxidic cation is developed by hydrogen peroxide in sulfuric acid and measured spectrophotometrically. APPARATUS AND REAGENTS
Parr oxygen bomb, self-sealing type,
with 5-ml. Vitreosil crucibles, wide-form. International clinical centrifuge, Model CL . Beckman spectrophotometer, Model B, with blue-sensitive phototube, 23-mm. vertical and 50-mm. horizontal cylindrical cells. Zirconium sulfate solution, 0.1M. Dissolve 2.83 grams of zirconium sulfate in 100 ml. of 2.4N hydrochloric acid. Warm if necessary to effect solution. Filter before use if not perfectly clear. Arsenic acid solution, 1 . 5 X . Dissolve 21.3 grams of arsenic acid in 100 ml. of water, heating to effect solution. Filter before use if not perfectly clear. Rash solution. Dilute 1 ml. of arsenic acid solution to 100 ml. Kith 2.4N hydrochloric acid. Hydrogen peroxide, 3% analytical reagent grade. Sulfuric acid, 36N and 3.6,!*. Hydrochloric acid, 2 . 4 5 and 1.2.\-. RECOMMENDED PROCEDURE
Sample Preparation. Weigh 1.5 grams of sample in a 5-ml., form Vitreosil crucible. R u n a concurrently, using 2 ml. of
about wideblank ethyl
alcohol as sample. If t h e sample is powdered, pellet before weighing. Ignite the sample and the blank in the Parr oxygen bomb. Transfer the aqueous residue to a small beaker, using water to effect quantitative transfer. Filter the mixture, reserving the filtrate. Char and ignite the filter paper in a platinum crucible. Fuse the ash with not more than 0.30 gram of potassium bisulfate adding a few drops of concentrated sulfuric acid to aid in the fusion of any titanium dioxide present. Dissolve the melt in water and filter the solution into the reserved filtrate. Acidify the combined filtrates with 0.5 ml. of concentrated sulfuric acid and evaporate the solution to about 10 ml. Separation of Interfering Ions. Transfer the solution to a 30-ml. centrifuge tube, dilute t o 20 ml., and pipet in 1 ml. of zirconium sulfate solution followed by 1 ml. of arsenic acid solution. Allow the mixture to stand for 3 minutes and centrifuge. Decant the supernatant liquid into a second tube containing 1 ml. of zirconium sulfate solution, allow t o stand for 3 minutes, and centrifuge. Discard the supernatant liquid. Wash the precipitates with 10 ml. of wash solution and centrifuge. Discard the supernatant liquid. Dissolve the precipitate in one tube with 2.5 ml. of concentrated sulfuric acid, then transfer the solution to the second tube. After the second precipitate has dissolved, transfer the solution to a 25-ml. volumetric flask, rinsing the tubes mith a total of not more than 15 ml. of water. If the sample is high in titanium, before transferring to the centrifuge tube add 1 ml. of concentrated sulfuric acid and evaporate on a hot plate to incipient dryness. Dissolve the cooled residue with a little water, and then transfer to the centrifuge tube, diluting to 30 ml. with water. Transfer to a 100nil. volumetric flask. Color Development. Allow the solution t o come t o room temperature. Add 5 ml. of 3y0 hydrogen peroxide, shake, and dilute t o volume. Transfer the solution t o a 50-mm. colorimeter cell. Measure the absorbances of the sample and the blank a t 410 mp, using water as the reference solution. Subtract the absorbance of the blank from that of the sample. From the calibration curve determine the weight of titanium present in the sample. Calibration Curves. Weigh replicate samples of National Bureau of Standards’ titanium dioxide. Fuse with potassium bisulfate, dissolve the melt in 3 . 6 5 sulfuric acid, and dilute to a predetermined volume. Treat suitable aliquots nith 37, hydrogen peroxide and measure the peroxodisulfatotitanic acid color a t 410 mp. Curves should be prepared for use with either the 23mm. cells or the 50- mm. cells.
DISCUSSION
The data shown in Table I were obtained by adding weighed amounts of YBS titanium dioxide to samples of
commercial polyethylene containing no titanium, and applying the procedure given above. Interference with the colorimetric measurement by chromium and nickel from the bomb wire was shorn-n by titanium recoveries ranging from 0.011 t o 0.037 mg. greater than the amount added. Horrever, separation of the titanium by coprecipitation with zirconium arsenate resulted in recoveries of better than 98%, as shown in Table I. That excess zirconium and arsenate do not affect the complex peroxidic cation color measurement TTas evidenced by full recovery of titanium in samples to which zirconium and arsenate had been added in great excess. Duplicate analyses !yere made on five different samples of pilot plant polyethylene. The following results \yere obtained:
Sample Run A Run B Run C Run D Run E
Titanium Found, P.P.M , 109 105 19.0 16.0 330 320 440 380 504 531
Alkali metal sulfates lower the recovery of titanium by bleaching the color slightly and inhibiting the coprecipitation of titanium m-ith zirconium arsenate. The bleaching action is more pronounced in solutions of lower sulfuric acid concentration (4). It was established that the optimum acidity for the complete precipitation of titanium with arsenate is l to 57, in sulfuric acid. Therefore, the separation was done in 501, sulfuric acid and the color developed in 10% sulfuric acid.
Table 1. Recovery of Titanium after Coprecipitation with Zirconium Arsenate Titanium, Mg. Added Found 0.285 0.281 0.215 0.213 0.182 0.180
Recovery,
%
98.6 99.1 98.9
desired range for precipitation with arsenate. Results were erratic when polyethylene samples were decomposed by acid digestion with sulfuric acid-nitric acid mixtures, or by ashing in an open platinum crucible follorred by solution in sulfuric acid. Therefore, ignition in a Parr oxygen bomb is recommended.
Table 11.
Effect of Alkali Metal Salts
(In 5% sulfuric acid solutions) Titanium, h k . Recovery, $’& Added Found 0.154 0.154 100.0 99.6 0.256 0.255 98.9 0.410 0.405 91.1 0.256 0.233 93.5 0.154 0.144 90.2 0.410 0.370 100.0 0.154 0.154 100.8 0.256 0.258 98.9 0.410 0.405
Potassium Added, Grams None None Sone 0.31” 0.31° 0.31” 0.09* 0.09* 0.09b
About 1 gram of potassium pyrosulfate. About 0.3 gram of potassium bisulfate.
The absorbance a t 410 nip is a linear function of the titanium concentration within the range of 0 to 5 mg. of titanium. Higher concentrations were not studied. ACKNOWLEDGMENT
The author is grateful to E d m r d hl. Hubbard for his advice and suggestions throughout the course of the investigation, and to Kathryn O’Keeffe for her help in editing the paper. LITERATURE CITED
(1) Ayres, G. H., Vienneau, E. M.,IND. EKG.CHEM.,ANAL. ED. 12, 96 (1940). (2) Calkns, R . C., Stenger, V. A., ANAL. CHEM.28, 400 (1956),; (3) Feigl, F., “Spot Tests, 4th ed., Vol. 11, D. 186, Elsevier, Kew York, 1954. 14’1 Hall. R. D.. J. Am. Chem. SOC.26. 1241 (1904). Hillebrand, W. F., Lundell, G. E.!F., Bright, H. A., Hoffman,. J. I., “Applied Inorganic Analysis,” 2nd ed., pp. 581-4, Wiley, Sew York, 1953. Sandell, E. B., “Colorimetric Determination of Traces of Metals,’’ 2nd ed., pp. 571-5, Interscience, New York, ..~ 1950. Schonr1, J. L., 2. anal. Chem. 9, 330 (1 ,- 87 - . ni - ,. (8) Simmler, J. R., Roberts, K. H., Tuthill, S. M., ANAL.CHEX.26, 1902 (1954). ~
Table I1 shows the importance of keeping the amount of potassium bisulfate, used to fuse the ashed residue in the preparation of the sample, at a maximum of 0.3 gram. This reduces the bleaching effect of alkali salts and keeps the acidity of the sample in the
RECEIVED for review July 26, 1956. Accepted September 24, 1956. VOL. 2 9 , NO. I , JANUARY 1957
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