Electron Spectroscopy (ESCA) for Analysis of Cellulose Anion Exchangers Donald M. Soignet, Ralph J. Berni, and Ruth R. Benerito Southern Regional Research Center, P.O. Box 79687, New Orleans, La. 70179
Diethylaminoethyl (DEAE) cottons have been prepared in aqueous (1-4) and nonaqueous (5, 6) media. These modified celluloses have been used as anion exchangers (7, 8 ) , and as substrates (9-11) for further chemical reactions that are catalyzed by the in situ amino groups. Reacting such weak base anion exchange celluloses with either methyl iodide or ethyl bromide produces quaternization and strong base anion exchange properties ( 7 ) .Previously, elemental analyses and potentiometric titrimetry have been used to distinguish weak base anion exchangers from strong base anion exchangers. DEAE-cotton is usually prepared by reacting cotton with 2-chloroethyldiethylamineor its hydrochloride in the presence of base (1-6). With sodium cellulosate and the chloroalkylamine in nonaqueous media, the principal product (I) contains tertiary amino groups. Cello-Na+
-
+ C1CH2CH2N(C2H5)?
as a result of the bombardment. The E K E is dependent not only on EX-raybut also on the energy holding the electron in the atom. The latter energy, designated as the binding energy of the electron, EBEis characteristic of the element from which it is ejected. In addition, the E B de~ pends to a lesser extent on the energy level from which it was ejected and on any forces affecting the attractive force that holds an electron in an atom. The chemical environment of the atom in a molecule might affect the EBE of an electron of a given element and might be detectable by the ESCA technique. This paper reports on the use of ESCA for determining the relative amounts of quaternary ammonium and tertiary ammonium nitrogens present in samples of DEAEcotton. EXPERIMENTAL
Preparation of Anion Exchange Cottons. DEAE-cotton. Diethylaminoethylated (DEAE) cotton was prepared in the absence of water by reacting cotton with sodium methoxide in methanol (I) to form the sodium salt of cellulose. This was then reacted with In the presence of a proton donor, the tertiary amine hy2-chloroethyldiethylamine in tertiary butanol (5, 6). The product drosalt can be formed. A secondary product (11) might was washed in methanol and air-dried. The product contained 1.6 mequiv of N per gram of exchanger as determined by the Kjelalso be present if the original chloroalkylamine quaternidah1 method. Analyses showed nonaqueously prepared DEAEzes tertiary amino groups attached to the cellulose. cotton to be chlorine-free. (I) ClCH,CH,N(C,H,), Quaternized DEAE-cotton. The DEAE-cotton was refluxed in a 10% solution of freshly distilled methyl iodide in anhydrous ethyl C,H5 alcohol for 5 hours. Fabrics were washed in ethyl alcohol and air C ~ ~ ~ O C H ~ C H ~ + N - C H ~ C H , N ( C ~ H(2) ~ I ~ C dried. ~Spectra. Spectra were recorded on a Varian IEE spectrometer, model VIEE-15, with a Mg K a X-ray source. Samples were C2H5 ground to pass a 20-mesh screen and mounted on the probe with (11) tape. Binding energies for the nitrogen 1s electrons are reported Electron spectroscopy (ESCA) as developed by Siegwith reference t o the carbon 1s electrons of binding energy of 285 eV. bahn e t al. (12) is a useful tool for obtaining information
+ Na+Cl-
CellOCH,CHJ( C2H512
+
(1)
-
1I
relative to the chemical environment of atoms in solid samples. The technique involves bombardment of a speciand measuremen with X-rays of known energy, EX-ray, ment of the kinetic energy, EKE,of the electrons ejected (1) M . Hartmann. U.S.Patent1,777,970 (October 7, 1930). (2) D. M . Soignet and R . R . Benerito, Textile Res. J . 37, 1001 (1967) (3) D. M . Soignet, A . L . M u r p h y , and R . J . Bern), Amer. Dyest. Rep.. 58, (5), 38 (1969) ( 4 ) E . J. Roberts, C . P. Wade, and S. P. Rowland, Textile Res. J . , 41, 710 (1971). (5) R . J Berni, D. M . Soignet, and R . R. Benerito, Textile Res. J . , 40, 999 (1970) (6) D. M . Soignet, R J. Berni, and R . R . Benerito, J. Appl Polym. Sci.. 1 5 , 155 (1971). (7) R . R . Benerito. B . B. Woodward, and J D . Guthrie, Ana/. Chem.. 37, 1693 (1965). (8) D. M . Soignet, R J . Berni, and R. R. Benerito, Textile Res. J . . 36, 978 (1966). (9) D. M . Soignet, R . R . Benerito. and J . B McKelvey. J . Appi. Poiym. S o . . 1 1 , 1155 (1967) (10) D. M Soignet, R. R. Benerito, and M . W Pilkington, Textiie Res. J . , 39, 780 (1969) (11) R . J . Berni, R . R . Benerito, and D . M . Soignet, Textile Res. J . . 42, 667 (1972) (12) K . Siegbahn. C. Nordling, A . Faklman, R . Nordberg, K . Hamrin, J . Hedman, G Johansson. T. Bergmark, S.-E. Karlson, I . Lindgren.
and B. Lindberg, "ESCA, Atomic, Molecular and Solid State Structure Studied by Means of Electron Spectroscopy," Almquist & Wiksells A B , Stockholm, 1967.
RESULTS AND DISCUSSION The following three types of DEAE-cottons were examined by ESCA: (A) the original sample, (B) the original sample that had been treated in aqueous 0.5M NaOH, washed in deionized water, and then air dried, and (C) the NaOH-treated sample that had been exchanged with aqueous 0.5M HI, washed in deionized water, and then air dried. In Figure 1 are typical ESCA spectra of the N 1s electrons of these three exchangers. Each spectrum clearly shows a peak with maximum of 402.5 f 0.2 eV for the E B E . All but the DEAE-cotton that had been treated with HI showed another peak with maximum a t 399.5 eV. However, spectra of the HI-treated samples contained a shoulder at 400.0 eV. Using ESCA, Nordberg et al. (13) studied a variety of amines, amine hydrosalts, and quaternary ammonium salts. The authors found the E B E for N Is electron in the amine was about 2 eV lower than in the amine hydrosalt; in the amine hydrosalt, E R E was about 1 eV below that of the quaternary ammonium salt. Nordberg, R . G . Albridge, T. Bergmark, U. Ericson, J . Hedman, C. Nordling, H. Siegbahm, and B. J . Lindberg, A r k . Kemi. 28, 257
(13) R .
(1967)
ANALYTICAL CHEMISTRY, VOL. 46, NO. 7 , JUNE 1974
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i
Figu're 1. Nitrogein 1s ESCA spectra of ( A ) diethylaminoethyl ,..:** n".,
