tion. At p H values 8 to 13, the spectrum of PCAM does not noticeably change; whereas the absorption maximum of PAM a t 292 mp shifts to 333 mp. The molar extinction coefficients of the oxime and the aldehyde a t the wave lengths of maximum and minimum absorption are given in Table I. PAM, in concentration of 2.5 y per ml., can be determined without interference from the acid hydrolytic products, PCAM and hydroxylamine, by reading in acid solution a t 292 mp or in alkaline solution a t 333 mp. The precision of the method can be seen from the values shown in Table 11, Ultraviolet absorption spectra of the syn configuration of PAM, in concentrations equivalent t o those shown in Figure 1, were obtained. It has the same absorption spectrum as pyridine2-carboxaldehyde methiodide. Thus, in acid or aqueous solution, the syn form has the same spectrum as its parent aldehyde, while the anti configuration displays not only greater absorbance, but also a significant wave length shift from 263 to 292 mp.
Table 11.
Analysis of Mixtures of Pyridine-2-aldoxime Methiodide (PAM) and Pyridine-2-carboxaldehyde Methiodide (PCAM)
PAM Taken,
PCAAI Taken,
Y/ML
Y/W.
5 10 10 5 .5
2.5 2.5 1 5 0
0 5 2.5 2.5 5 10 5 8 10 5
A
Absorbance
0.233 0.458 0.458 0.234 0.233 0.115 0.115 0.047 0.234 0.000
B
0.000 0.120 0.058 0.056 0.121 0.238 0.119 0.190 0.233 0.114
PAM Found, y/ML
PCAM Found, -//Ml.
5,1 10.0 10.0 5.1 ? .I1 2.5 2.5 1.0 5.1 0.0 ~~
0.0 5.1 2.5 2.4 5.1 10.0 5.0 8.0 10.0 4.8
A. Total absorbance at 292 mp in acid solution. B. Difference between total absorbance at 263 m p and that due to PAM at 263 nip.
LITERATURE CITED
(1) Czaky, T . Z., Acta Chem. Scand. 2,450 (1948). (2) Ginsburg, S., Kilson, I. B., J. Am. Chem. SOC.79,481 (1957). (3) Kewitz, H., Wilson, I. B., Sachmansohn, D., Arch. Biochem. Biophys. 64, 456 (1956). (4) Kondritzer, -4.A., Zvirblis, P. J., Am. Pharm. Assoc. 46, 531 (1957).
( 5 ) Lenart, G., Ber. deuf. chem. Ges. 47, 808 (1914). ( 6 ) Wills, J. IT., Kunkel, A. A 1 Bron-n, R. V., Groblewski, G. E., Sci&~ce125, 743 (1957). (7) Zvirblis, P., Socholitsky, I., Kondritzer, A. A, J . Am. Pharin. .4ssoc., Sci. Ed. 45, 450 (1956).
RECEIVEDfor review April 25, 1058. Accepted August 12, 1958.
Photometric Determination of Aluminum and Titanium in Polyethylene WlLLlAM T. BOLLETER Monsanto Chemical Co., Texas City, Tex.
b Wet- and dry-ashing procedures are used for the decomposition of polyethylene with the attendant dissolution of the metals in the polymer. Aluminum is determined photometrically after extraction of the aluminum 8-quinolinolate into trichloroethylene from an ammoniacal solution. The absorbance of the complex is measured a t 390 mp. Titanium is determined photometrically using chromotropic acid
(4,5 -dihydroxy-2,7-naphthalenedisulfonic acid) for the development of titanium-chromotropic acid complex. The maximum absorbance of the color produced occurs a t 420 mp when the p H is adjusted to about 5. Moderate to large amounts of foreign ions do not interfere. Amounts as low as 5 p.p.m. of both metals in a single 2gram polyethylene sample can b e readily determined.
w
and dry-ashing-fusion procedures have been employed for the decomposition of polyethylene and dissolution of the metals in the polymer. The wet-ashing method is rapid and is ET-
not subject to the losses experienced in normal dry-ashing procedures for organic samples, nor to the tedious recovery and subsequent dissolution of metal oxides following combustion in an oxygen bomb. A 2- to 3-gram sample of polyethylene can be prepared for the determination of both titanium and aluminum in about 30 minutes, exclusive of the time required to cool the solution. With normal care the wetashing of polyethylene is not hazardous. Several hundred samples have been metashed in this laboratory without incident. The dry-ashing-fusion method of sample decomposition employs a niixture of potassium sulfate and nitrate to facilitate combustion of the polymer and recovery of the metals. A 5-gram sample of polyethylene can be ashed in about 15 minutes and the total time required to prepare a sample for analysis is the same as for the acid digestion procedure. The method for the spectrophotometric determination of aluminum by measurement of the intensity of the
yellow chloroform extract of the aluminum 8-quinolinolate has been reported (1, 8). A number of metal ions may interfere b u t procedures have been developed Tyhich eliminate (7, 1%’)or mask (5) this interference. The p H of the aqueous solution from TT hich the aluminum 8-quinolinolate is extracted is a n important factor in the determination (6). I n this investigation, a method for the determination of aluminum in polyethylene makes unnecessary the elimination of foreign ions and careful adjustment of the pH. Trichloroethylene has been substituted for chloroform as the extraction solvent because of its lower volatility. The determination of titanium in polyethylene reported by Anduze ( 2 ) requires the separation of titanium from interfering ions before development of the color with hydrogen peroxide. A method for the determination of titanium with 4,5-dihydroxy-2,7-naphthalenedisulfonic acid (chromotropic acid) which is more sensitive than the hydrogen peroxide method has been VOL 31, NO. 2, FEBRUARY 1959
201
reported by Ovenston, Parker, and Hatchard ( I O ) and by Rosotte and Jaudon (11). The reaction between chromotropic acid and titanium(1V) has been investigated by Brandt and Preiser (4) and OkBE and Sommer (9). Iron interferes when chromotropic acid is used and this ion must be removed, compensated for, or masked. I n this procedure, interference from iron is markedly reduced by the addition of (ethylenedinitrilo) tetraacetic acid (EDTA) to the color-developed solution. The decomposition and metal analysis methods can be easily used for the determination of as little as 5 p.p.m. of aluminum and 5 p.p.m. of titanium in a single 2-gram sample of polyethylene. APPARATUS AND REAGENTS
Beckman Model B spectrophotometer, 1-em. and 5-em. Corex cells. Fume eradicator with insealed dropping funnel and drip tip. Platinum crucible and cover. 8-Quinolinol, 2% in 9570 ethyl alcohol. Trichloroethylene, distilled technical grade. Chromotropic acid solution, 4% in
DRY-ASHING-FUSION. Weigh 5 grams of polyethylene pellets and about 2 grams of a 3 to 1 mixture of potassium sulfate and potassium nitrate into a platinum crucible (30 ml. or larger). Cover and heat gently Kith a n open flame until the polymer becomes molten. Increase the heating to ignite the polymer but control the rate so that the polymer burns with a flame not greater than 2 to 3 inches in height. After all the polymer has burned off, increase the rate of heating to burn the carbon off the sides and cover of the crucible. Cool the crucible for 2 to 3 minutes, then carefully add 1 ml. of concentrated sulfuric acid. Again heat the crucible until nitrogen dioxide ceases to be evolved. Replace the cover and continue heating until the melt boils quiescently. Cool the crucible, and add 10 ml. of 10% sulfuric acid. Heat the crucible to dissoke the solid. Transfer the solution to a 100-ml. volumetric flask and dilute to volume.
The analyses for aluminum and titanium are run on separate aliquots of the solutions from either of the decomposition procedures. If the concentrations of the metals in the polymer are less than 3 to 5 p.p.m., separate samples should be decomposed for each analysis. Each method of sample decomposition has its advantages. Wet-ashing can 4,5-dihydrosy-2,i-naphthalenedisulfonic be used on either polyethylene pori-der acid disodium salt, and 2% in sodium or pellets. I n the dry-ashing procebisulfite. dure, pellets must be uwd unless the Buffer-EDTA solution, 272 grams of sample size is very small. A large sodium acetate trihydrate, 64 ml. of (5-gram) sample of pellets can be deglacial acetic acid, and 10 grams of the composed more conveniently by the disodium salt of (ethylenedinitril0)dry-ashing method. tetraacetic acid per liter of solution. If necessary, the p H is adjusted to 5 with Aluminum Procedure. Pipet 50 ml. sodium hydroxide or acetic acid. of t h e solution from t h e ashing proAll other chemicals mere reagent cedure into a 125-1111. separatory fungrade. nel. Add 1 ml. of 10% thioglycolic acid, a few drops of phenolphthalein, EXPERIMENTAL and 25 ml. of concentrated ammonium hydroxide. Afore or less ammonium Sample Preparation. ACID-DIGES- hydroxide may be added, depending TION. Weigh about 2 grams of polyupon the acidity of the aluminum soluethylene (powder or pellet) in a 250tion, but use about 10 ml. in excess of ml. Erlenmeyer flask a n d add 20 ml. that required for neutralization. ildd of concentrated sulfuric acid. P u t 1 ml. of 1M sodium cyanide, 5 ml. of a drip tip in t h e top of t h e flask and 2% 8-quinolinol, and 10 ml. of triplace t h e flask on a hot plate under a chloroethylene. Stopper the separafume eradicator, attached to a water tory funnel and shake for about 1 aspirator through a scrubbing flask. minute. Run the lower layer through Heat the flask and contents to decoma No. 31 filter paper (to drv the organic pose the polymer and when the sample phase) into a I-em. cell and measure the is completely charred, slowly add, absorbance at 390 mp against a reagent through the dropping funnel, 20 ml. of blank. The stability of the colored concentrated nitric acid to oxidize all extract is limited only by the volatility carbonaceous materials. If any black of the solvent. Determine the weight carbon particles remain, add more nitric of aluminum in the sample aliquot by acid. Add 5 ml. of 70 to 72% perreferring to a calibration curve prepared chloric dropwise to the amber solution. by subjpcting aliquots of a standard Continue heating for several minutes aluminum solution to the given proto ensure volatilization of all acids excedure. cept sulfuric. The volume of the colorEFFECTOF FOREIGN IONSON DEless solution should be about 5 ml. SulTERMINATION OF ALUMINUM. The furic acid may be added at any time amount of foreign ions equivalent to 1 y during the acid digestion to prevent the of aluminum was determined by using solution from going to dryness. After aliquots of a standard solution of the adequate cooling, add 50 ml. of water ion under investigation in the deterand heat for several minutes. Cool, mination of aluminum. One microgram transfer to a 100-ml. volumetric flask, of aluminum is equivalent to 100 of and dilute to volume. titanium, vanadium, and zirconium; 202
ANALYTICAL CHEMISTRY
500 of iron; 5000 of molybdenum; and 10,000 of nickel, copper, zinc, and chromium. OPTIMUM RANGEFOR ALUMIKUM. The optimum concentration range (3) for aluminum is 5 to 30 y per 10 ml. of extracting solvent for measurements a t a 1-em. optical path. The system conforms to Beer’s law over this range. Aluminum can be determined in this range within h 0 . 2 y. Titanium Procedure. Pipet 25 ml. of the solution from t h e ashing procedure into a 100-ml. volumetric flask. Add 2 ml. of chromotropic acid solution. Adjust the p H t o about 4 by adding 6J4 sodium hydroxide until the amber solution becomes yellow. Add 10 ml. of the buffer-EDTA solution and dilute to volume. Transfer the solution to a 5-cm. (or 1-cm.) absorption cell. Measure the absorbance a t 420 mp against a reagent blank. The colordeveloped solution is stable for a t least 24 hours. Determine the rreight of titanium in the sample aliquot by reference to a calibration curve prepared by taking aliquots of a standard titanium solution through the given procedure. Prepare calibration curves for 1-cm. and 5-cm. cells. EFFECT OF PH. A study was made as to the effect of pH on the determination of titanium. Absorbance of the color-developed solutions increased R ith a n increase in pH up to 4.75. Constant absorbance readings were obtained over the p H range 4.75 to 5.50. EFFECT OF FOREIGN 10x-s. I n testing for interference by foreign ions, aliquots of a standard titanium solution and the ion under investigation n ere subjected to the procedure for the determination of titanium. Interference \yas taken as the largest amount of foreign ion that could be present n i t h 1 p.p.m. of titanium and give a n absorbance difference of not more than 0.004 from that of titanium solution alone IT hen measured a t a 1-cm. optical path. This absorbance difference corresponds to a 1% error in the determination of 1 p.p.m. of titanium. The tolerance for foreign ions was found to be 4 p.p.m. for zirconium and chromium; 10 for iron; 25 for vanadium and copper; 75 for molybdenum; and greater than 100 for nickel, zinc, and aluminum. Interference from chromium(III), copper, and iron is due to the color of the metal ion-EDTA chelates. If EDTA is not added, iron forms a green product with chromotropic acid which interferes much more than the yellow iron-EDTA complex. The tolerance for vanadium in the absence of EDTA is 2 p.p.m. Zirconium consumed the chromotropic acid without imparting color and was unique in that it caused low results for titanium. The ratio of chromotropic acid to zirconium and the time required for full color development affect the amount of zirconium which
causes a 1% error. Higher ratios and longer times increase the tolerance for this metal. Chloride, nitrate, or perchlorate in concentrations u p to 0.5M did not interfere. Higher concentrations were not tried. Ammonium. ions interfere by causing erratic absorbance readings and rapid fading of the y e l l o ~ . OPTIRlUhl
RAKGE FOR
TIT.4NUM.
The optimum concentration range ( 3 ) for titanium in the color-developed solution is 0.4 to 2.5 p.p.m. when using 1-cm. cells, and 0.08 to 0.5 p.p.m. for a 5-cm. optical path. The system conforms to Beer’s law over these ranges. The relative error in these concentration ranges is about lye, RECOVERY AND PRECISION
From 10 to 200 y of aluminum and,’or titanium in the presence of polyethylene which contained neither of these metals were subjected to the procedures for
the decomposition of the polymer and the analysis for the metals. Recovery of the titanium and aluminum was within 2 and 37,, respectively, of the amounts added. The precision of the methods was evaluated from replicate analyses of polyethylene samples decomposed by both procedures. The standard deviation for the analysis of each metal is 1 1 in the range of 5 to 50 p.p.m. The two decomposition procedures ryere shon n statistically to give the same results. ACKNOWLEDGMENT
The author is grateful to J. L. Slate, B. 11. Eldred, and E. F. Dougherty for the assistance in obtaining the data reported. LITERATURE CITED
rllesander, J. \I*., in “Summaries of Doctoral Dissertations, University of
(1)
Wsconsin,” Vol. 6, p. 205, Univ. of Kisconsin Press, Madison, 1942. (2) Anduze, R. A., ANAL. CHEW 29, 90 (1057). (3) Ayres, G. H., Zbzd., 21, 652 (1949). (4) Brandt, W. It7.,Preiser, -4.E., Zbzd., 25,567 (1953). (5) Claassen, A,, Bastings, L., Visser, J., Anal. Chinz. Acta 10, 373 (1954). (6) Gentry, C. H. R., Sherrington, L. G , Analysf 71, 432 (1946) ( 7 ) Margerum, D. W , Sprain, Wilbur, Banks, C. V., AKAL. C H E X 25, 249 (1953). (8) Moeller, Therald, IXD.EXG.CEIEhf., ASAL.ED. 15, 346 (1043). (9) OkitE, Arnost, Sommer, L. S i ColZectzon Czechosloz . Chem. Ccnimzin. 22, 433 (1057). (10) Ovenston, T. C. J., Parker, C. A . Hatchard, C. G., Anul Chzni. Acta 6 , 7 ( 1952). (11) Fosotte, R. Jaudon, E., Zbzd , 6, 149 (1902). (12) Sprain, Wilbur, Banks, C. V., Ibzd., 6, 363 (1952).
RECEIVEDfor review September 7, 1957. Accepted September 22, 1958. Division of Analytical Chemistry, 132nd Meeting, ACS, Kew Yorlr, September 1957.
Spectrophotometric Determination of Styrene in a Sty re ne-Methyl Metha cry1ate Cop o Iyme r A. V..TOBOLSKY, A. EISENBERG, and K. F. O’DRISCOLL Frick Chemica! laboratory, Princefon University, Princeton, N. J.
b A rapid method for the determination of the styrene content of a styrenemethyl methacrylate copolymer was developed by determining the absorbance of a sample containing 1 mg. of copolymer per ml. of chloroform a t 269 mp.
with stirring. One purification was found sufficient, as two additional reprecipitations of samples of high styrene content did not lower the absorbance of
the polymer. The compositions of four samples of the copolymer were determined by carbon analysis, and were found to be in excellent agreement n itli
A
s poly(methy1 methacrylate) does
not absorb above 250 mp, and the absorption of polystyrene in t h a t region of the ultraviolet spectrum is pronounced, a method was developed for the quantitative determination of the styrene content of a copolymer of styrene and methyl methacrylate by determining its absorbance a t 269 mp. EXPERIMENTAL
~
0
The monomers used in this experiment were purified by the usual methods. Ten-milliliter samples of 0, 10, 20, 30, etc., volume % styrene were polymerized with twice recrystallized 2,2’-azobisisobutyronitrile as an initiator at 62” C. Conversion of 5 to 10% was achieved in 40 minutes. The polymer solution was precipitated in methanol, filtered, dried, and then purified by dissolving in chloroform and reprecipitating in methanol by dropwise addition
‘
0
‘ 50
%STYRENE
IN
~
~
~
100
COPOLYMER
Figure 1 . Polymer composition composition of solution
P vs.
d
1
~
’
0 Experimental points 0 By initial and final monomer quantities ( I ) By carbon analysis ( I )
A
Figure 2. sorbance
Polymer composition vs. ab-
I
0
I
I
0
1
l
/
/
l
10
% STYRENE
VOL. 31, NO. 2,
I
/ 100
IN C O P O L Y M E R
FEBRUARY 1959
203
