providing the necessary calibration is carried out. Different ratios of internal standard to material being measured were tested but the correction factors did not change. The last peak to emerge on the chromatograms obtained from styrenated alkyds was established as phthalic anhydride by injecting phthalic anhydride onto the column and observing the retention time. Attempts to estimate the phthalate content of resins by pyrolysis were not successful. The total area method was used for comparison because it is the simplest and one of the most widely used methods for quantitative estimates. Another technique (IO), utilizing a calibration curve obtained from a series of samples of known composition would be more accurate than the total area method but its general application to organic coating systems has not been illustrated. Injection port temperature was found to be a critical variable and erratic results were produced by higher settings. The pyrolysis probes used were calibrated by the manufacturer and the maximum temperature used in this study exceeded 1000° C. A thermal degradation study (6) of poly(methy1 methacrylate) and polystyrene has shown that temperatures as high as 1000" C. produce low monomer yields. The high yields of monomer obtained in this investigation have been credited to the geometry of the filament used, with the transition temperatures during degradation being near optimum. The proposed method is rapid, relatively simple, and should be applicable
Table I.
Semiquantitative Analysis of Methacrylate and Styrene Polymers in Organic Coatings
Bystem Poly(butyl methacrylate) Poly(viny1 chloride) Dioctyl phthalate Poly( butyl methacrylate) Nitrocellulose Butyl phthalate Poly( methyl methacrylate) Butyl benzyl phthalate
Present 45.8%
Found Internal standard 43.0; 44.8; 43.3
Total area 76.9
64.3
62 7 ; 5 9 . 7 ; 6 2 . 9
74.1
68.8
69.6; 69.2
95.7
Polystyrene 33.8 36.0; 36.3 Rosin ester Tricresyl phosphate Styrenated alkyd 44. Oa 44.8; 43.2; 43.7 Styrenated alkyd 35.14 33.1; 31.0; 33.9 Polystyrene content determined by chemical method (11).
to a broad range of vinyl-type coating materials currently in use. ACKNOWLEDGMENT
The advisory assistance of C. F. Pickett, director of the laboratory, and M. H. Swann of the analytical section is acknowledged and appreciated. LITERATURE CITED
(1) Barlow, A,, Lehrle, R. S., Robb, J. C., "Techniques of Polymer Science," Plastics and Polymer Group, Society of
Chemical Industry, London, September 1962. (2) Cobler, J . G.7 SamSel, E. p., SOC. Plastics Engrs. Trans. 2 , 145 (1962). (3) Cox, B. C., Ellis, B., ANAL.CHEM.36, 90 (1964).
85.7 61.3 59.7
(4) Ettre, K., Varadi, P. F., Ibid., 34, 752 (1962). (5) Hewitt, G. C., Whitham, B. T., Analyst 86, 643 (1961). (6) Lehmann. F. A,. Brauer. G. hf.. ANAL. CHEM.33, 673 (1961). ' (7) Nelson, D. F., Yee, J. L., Kirk, P. L., Microchem. J . 6 , 225 (1962). (8) Pariss, W. H., Holland, P. I)., Brit. PZastics 33, 372 (1960). (9) Sadowski, F., Kuhn, E., Farbe u. Luck 69, 267 (1963). ( l o ) .Strassburger, J., Brauer, G. M., Tryon, M.,Forziati, A. F., ANAL. CHEM.32, 454 (1960). (11) Swann, M. H., Ibid., 25, 1735 (1953). G. G. ESPOSITO Coating and Chemical Laboratory Aberdeen Proving Ground, Md. RECEIVEDfor review June 8, 1964. Accepted July 14, 1964.
Column Chromatography with a Polynitrostyrene Resin Stationary Phase SIR: This is a report of the preliminary evaluation of a polynitrostyrene resin as a chromatographic adsorbent for electron donor molecules such as polycyclic aromatic hydrocarbons, aromatic amines, and phenols. The stationary phase, which has the structure
I
will be referred to as tetranitrobenzylpolystyrene (TXI3P) resin. T K B P resin was prepared by conventional Friedel-Crafts benzylation of 2%
divinylbenzene-polystyrene resin using benzyl chloride in nitrobenzene solvent, followed by nitration with a mixture of fuming nitric and fuming sulfuric acids. T N 3 P is thermally stable to a t least 160" C. and displays the chemical inertness typical of nitroaromatics. The structure was assigned from infrared and NMR spectra and from elemental analysis. The resin was converted to the desired chromatographic form by grinding, screening to a suitable mesh range, and washing with acetone. I t was stored overnight in the eluting solvent to ensure equilibration, after which the column was wet-packed in the conventional manner. Samples were introduced to the column in half-milliter volumes of solvent; elution was carried out by gravity
flow. For the experiment shown in Figure 1 the positions of the bands on the column were followed by observing the fluorescence of the sorbates. Fractions of elutriant were collected automatically and were analyzed for anthracene and pyrene by measuring absorbances a t 377 and 273 mM, respectively. The number of theoretical plates were calculated by the method of James and Martin ( 2 ) ; the Rs value was obtained according to the suggestion of De Ligny et al. ( I ) . Pi charge-transfer complexation is proposed as the mode of chromatographic adsorption, with the resin acting as the acceptor and the sorbate as the donor. This is based on the known complexation between polynitroaromatics and electron donors, on the spectra of the charge-transfer complexes of VOL. 36, N O . 1 1 , OCTOBER 1964
2185
0.4001
the cross-linked resin is useful as a chromatographic stationary phase for fractionation of mixtures of these compounds. A detailed report is being prepared.
ANTHRACENE
a300
0.100 0.1000 0
43
b,,
LITERATURE CITED
$020/]
I
45
,
47
Figure 1.
,
49
(1) De Ligny, C. L., Schmidt, H. M., De Vries, W., Rec. Trav. Chim. 82, 1061 11963). ( 2 ) James, A. T., Martin, A. J. P., Bzochem. J . 50, 679 (1952). ( 3 ) Smets, G., Balogh, V., Castrille, Y., J . Polymer Scz., Pt. C , S o . 4, 1467 (1964).
‘-%+
51
53 55 57 ml. SOLVENT
59
61
63
,
65 6 5
Elution curve for anthracene and pyrene
Bed depth, 4 8 cm.; bed diameter, 1.2 cm.; particle size, 2 5 0 - 2 7 0 mesh; solvent, 3 :1 by volume acetone-n-hexane (Spectrograde); flow rate, 3.03.5 ml./hr.; fraction size, 0.38-0.42 ml.; sample size, 3 . 0 6 mg. of anthrocene, 3 . 1 5 mg. of pyrene; R,, 0.72 far anthracene, 0.60 far pyrene; H E T P , 0.39 cm.; R, value, 2.45
linear T N B P with various donors obtained by us, and on the work of Smets et al. ( 3 ) related to the study of electron acceptor polymers. The charge-transfer spectra associated with T N B P exhibit absorption maxima in the ultraviolet
and visible between 350 and 500 mp. Our observations indicate that T N B P forms complexes with such molecules as naphthalene, anthracene, pyrene, carbazole, naphthylamine, aniline, transstilbene and dimethylphenol and that
Department of Chemistry Florida State University Tallahassee. Fla. 32306 RECEIVEDfor review July 6, 1964. Accepted Auguat 4, 1964. Work supported by Research Grant 536-A from the Petroleum Research Fund and by Research Grant Gbl 10064 from the United States Public Health Service.
Coulometric Diffusion Layer Titrations Using the Ring-Disk Electrode with Amperometric End Point Detection SIR: A rapid, simple, and sensitive electrochemical technique has been developed which is based upon the titration of a species present in the diffusion layer of a rotating ring-disk electrode. This method has been applied to the analysis of arsenious solutions over the Concentration range 1 x 10-~J1to 1 x l O - 3 M and utilizes the unique hydrodynamic features of a ring-disk electrode, the simplicity of a constant-current coulometric titration with internally generated reagent, and the sensitivity of an amperometric end point detection. Thiq technique is described below in terms of reaction between bromine and arsenious ion. Bromine can be generatpd a t a 100% current efficiency from an acid bromide supporting electrolyte by anodic oxidation a t a platinum disk electrode. If the supporting electrolyte also contains arsenious ion (which is not electroactive a t the potential bromide is oxidized to bromine), and the reaction Brz
+ As(III)+
.\s(V)
+ 2 Br-
is fast compared to convective diffusion, the surface concentration of bromine a t the disk electrode will remain zero until the anodic current flowing through the disk electrode (iajD exceeds the maximum flux of arsenious to the electrode, 2 186
ANALYTICAL CHEMISTRY
f4a(III))
by the amount shown in Equa-
tion l : cia)D
2 2 Ff4s(III) A
(1)
where d is the electrode area and F is Faraday’s constant. If the disk electrode is surrounded by a closely spaced, but electrically insulated, ring electrode, and the potential of the ring electrode is adjusted so as to reduce any bromine which reaches the ring electrode, the excess bromine generated a t the disk electrode will produce a cathodic ring current ( i J R . I t is not necessary to solve this boundary value problem analytically to arrive a t the form of the ( Q R us. (i.)D curve. Excess bromine generated at the disk electrode will diffuse into the solution normal to the disk electrode and will reach the ring by convective radial flow of supporting electrolyte and diffusion. Before any free bromine can reach the ring electrode, the bromine muqt react with additional As(II1) over and above that given by the minimum current in Equation 1. First, excess bromine will penetrate into the diffusion layer normal to the disk electrode, producing a zero As(II1) concentration for some distance away from the disk electrode and thereby consuming s o r e of the excess bromine. Second, the As(II1) present in the cylindrical shell normal to
the annulus between the ring and disk will react with excess bromine before any bromine can be reduced a t the ring electrode. Ring current will be observed initially when the bromine reaches is the inner edge of the ring; as (ia)D increased, the ring current will increase nonlinearly until the concentration in the region normal to the ring surface has been reduced to zero for some distance away from the ring electrode. Further increase in ( i J Dwill then produce a linear increase in (iJR. Extrapolation of this linear portion back to the ring electrode residual current will give a value of ( i , j D proportional to the concentration of As(II1) in the supporting electrolyte. EXPERIMENTAL
Apparatus and Reagents.
CHEMAnalytical Reagent Grade chemicals and conductivity water were used. Sulfuric acid should be freshly fumed for best results. The supporting electrolyte was 0.2M KBr and 1, O M
ICALS.
HzSOI. RING-DISKELECTRODE. An electrode with a disk diameter of 0.7772 cm., inner ring diameter of 0.7973 cm., and outer ring diameter of 0.8886 cm. was used. The disk and ring were constructed of platinum. A detailed description of the construction of such electrodes will be published in the near future.
