causes a 1% error. Higher ratios and longer times increase the tolerance for this metal. Chloride, nitrate, or perchlorate in concentrations up 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 rene-Methyl Methacry1ate 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 at 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 that 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
P
Figure 1 . Polymer composition vs. composition of solution
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
those obtained by Lewis et al. (I), both by carbon analysis and by the determination of the initial and final monomer quantities in the polymerization mixture. The compositions of the other samples were determined by interpolation of the graph of volume per cent styrene in the monomer solution us. mole per cent of styrene in the polymer as determined experimentally. This graph is shown in Figure 1. Samples of 100.0 mg. were weighed out, dissolved in chloroform, and diluted
to a concentration of 1.000 mg. per ml. The slope of this line is 0.0157, sugThe absorbance of each sample was degesting the following relationship : termined a t 269 mp in a Beckman DU Absorbance = 0.0157 X per cent styrene spectrophotometer and the data are shown in Figure 2. The value for pure LITFATURE CITED polystyrene obtained here may be compared with that obtained by Newel1 (I) . (1) Lewis, F. hI., Walling, C., Cummings, T.,Briggs, E. R.,Mayo, F. R., J. A m . Chem. SOC.70, 1519 (1948). DISCUSSION ( 2 ) Keivell, J.1 E.;_ A N A L . CHEX 23, 445 (1951). The relationship of per cent styrene to absorbance a t 269 mp is linear only R E C E I ~ Efor D review February 11, 1958. Accepted June 17, 1958. up to about 40% styrene (Figure 2).
Spectrophotometric Determination of Stabilized Diazonium Compounds HELEN M. ROSENBERGER and CLARENCE J. SHOEMAKER Chemical Research and Engineering Department, A. B. Dick Co., Chicago 37, 111.
b A simple, accurate spectrophotometric method for the determination of stabilized diazonium compounds utilizes the maximum absorbance of an aqueous solution at 380 mp. The method is rapid, requires no pretreatment of the sample, and represents a satisfactory control method for determining the rate of decomposition of the diazo salts. Results compare favorably with those obtained by the nitrometer method.
The absorption spectra (Figure 1) of the diazonium compounds investigated exhibit a strong absorption band in the 350- to 400-mp region attributed chromophore group. to the -N=NThe 380-mfi absorption peak obeyed Beer’s law in the concentration investigated from 1 to 10 p.p.m. It showed a continuous decrease in absorbancv as the s a m d e was irradiated. Diazonium compbunds decompose according to the equation: R
T
use of stabilized diazonium salts as paper coating materials for diazotype reproduction papers has increased rapidly during the past several years. The paper coating industry uses these salts as the zinc chloride-stabilized compounds, but even these salts undergo decomposition with time and temperature. The need for a rapid and accurate method for the determination of the decomposition rate of stabilized diazonium compounds has led to the development of this spectrophotometric method of analysis. The conventional methods for determining the diazonium group in organic compounds are: the nitrometer (6-7)’ titration with standard coupling agents (8, 6), or standard reducing agents (2, 4). These methods all require strict adherence to an established technique and the end points of the titrations are often obscure to inexperienced technicians. However, from a manufacturing control standpoint, the most serious disadvantage is the length of time involved in completing each analysis.
A-
HE
204
ANALYTICAL CHEMISTRY
R
\/
- ()+ OH
+ HC1
+ NZ + ZnCh + HzO
The absorbance a t 380 mp can be used as a quantitative measure of the diazo nitrogen, because none of the decomposition products or impurities attendant to the manufacture of the salts absorb a t this wave length. Baril ( I ) reported the use of this absorption range to select the wave length for irradiating a diazonium compound to determine the quantum yield of the diazonium salt. A literature search indicated that the spectrophotometric determination of diazo nitrogen had not been explored in the analytical application to diazonium compounds. Experiments were performed to correlate the ultraviolet absorbance a t 380 mp with the nitrometer values. EXPERIMENTAL
Nitrometer Procedure.
The pow-
dered material or an aliquot of a stock solution containing 0.3 t o 0.4 gram of sample was introduced into the reaction flask and the flask was attached t o the apparatus (Figure 2) using silicone grease. The threeway stopcock was opened to the atmosphere and the air in the system was displaced with carbon dioxide. Two grams of cuprous chloride dissolved in 10 ml. of concentrated hydrochloric acid were placed in the separatory funnel and the three-way stopcock was opened to the nitrometer. Microbubbles were obtained after a short period and the flow of carbon dioxide was regulated through the bubble counter at the rate of 1 bubble per second. Residual gas was removed from the nitrometer by raising the leveling bulb and opening the stopcock to the air. The leveling bulb was lowered and the time recorded. The cuprous chloride was added to the reaction flask followed by sufficient distilled water to bring the total volume of water to 20 ml. The burner was adjusted so that a steady flow of gas passed into the nitrometer. The solution was kept just boiling until the reaction was completed, as evidenced by the reappearance of microbubbles. The leveling bulb was raised to the height of the meniscus of the liquid in the nitrometer and the volume of gas was recorded. The temperature a t the nitrometer, the barometric pressure, and the time were also recorded. A blank was determined on an equal volume of reagents in exactly the same manner and for an identical time period. CALCULATIONS. V = volume of gas corrected for carbon dioxide blank P = pressure - vapor pressure of 50Yo potassium hydroxide solution T = temperature at analysis
