A method for sorption capacity determination of cellulose
matrices as trace metal sorbents has been studied. An analytical
method is based on infrared absorption band at 1725 cm-• featuring
C=O streching in a polymer molecule. Suitable samples are prepared
to construct a calibration curve. Samples are standardized
by the potentiometric method in terms of ion-exchange capacity.
Some features of the analytical procedure are discussed, particularly
with regard to the lower and upper limit of COOR-content
determination, the influence of sample structure and the precision
of the proposed method

S. Luterotti

V. Grdinić

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CROATICA CHEMICA ACTA CCACAA 52 (4) 391--396 (1979) CCA-1176 YU ISSN 0011-1643 544.62 Original Scientific Paper Sorption Capacity Determination of Cellulose Matrices by Infrared Absorption Spectrometry V. Grdinic and S. Luterotti Institute of Chemistry, Faculty of pharmacy and Biochemistry, University of Zagreb, 41000 Zagreb , Croatia, Yugoslavia Received October 23, 1978 A method for sorption capacity determination of cellulose matrices as trace metal sorbents has been studied. An analytical method is based on infrared absorption band at 1725 cm-• featuring C=O streching in a polymer molecule. Suitable samples are pre-pared to construct a calibration curve. Samples are standardized by the potentiometric method in terms of ion-exchange capacity. Some features of the analytical procedure are discussed, particu-larly with regard to the lower and upper limit of COOR-content determination, the influence of sample structure and the precision of the proposed method. INTRODUCTION The knowledge of sorption capacity of cellulose matrices is of great interest in various analytical aspects such as chromatography of inorganic systems1,2, spot test3•4, ring oven methods-7 and collection of trace metals from solutions8- 10. Cellulose matrices for sorption of trace metals can be characte-rized in terms of their capability for ion-exchange processes. Ion-exchange capacity of a cellulose polymer depends on a number of carboxylic and enolized carbonyl groups, as well as on lactone and ester groups which can be easily opened11 . These groups can be determined by chromatographic methods2•11- 1\ titrimetric methods15,16 , ring oven method17 and colorimetric methods18 • These methods are mostly based on a cation exchange process: m (Cell. R)Y Y n + yn (Me"' ')w ~ y {(Cell. R)111 Me,,} + mn (YY ' )w (l) where the solvated ions are characterized by subscvipt w. Further meanings of the symbols in eq. (1) are: Cell. R- = cellulose matrix with affixed groups of single negative charge, other symbols are self-explanatory. The methods for determination of ion-exchange capacity mentioned above, cannot be applied to any kind of cellulose matrices in a reliable manner, besides, they are taking too much time and chemicals for analysis. To test cellulose matrices which are suitable for sorption of trace metals, it is necessary to characterize them by infrared spectra. We have used spectral data from the 1700-1790 cm- 1 infrared region and made attempt to show how these data can be used for the quantitative determination of sorption (ion-exchange) capacity of cellulose matrices. 392 V. GRDINIC ANDS. LUTEROTTI EXPERIMENTAL Preparation of the Cellulose Samples Microcrystalline cellulose (E. Merck, A. G. Darmstadt, Germany) and medical cotton (Ph. Jug. III) are utilized as starting materials. Three different procedures are applied. (i) Sodium Hypochlorite Oxycelluloses19 The oxidant is prepared by dissolving 29.780 g of sodium hypochlorite, 11.803 g of sodium hydroxide and 60.005 g of sodium dihydrogen phosphate in distilled water and adjusting to 1 litre. By treating 20 g of medical cotton with 1 litre of this diluted solution for 20 and 40 hours at 20 °C, the samples C-Cell 1 and C-Cell 2, respectively, are formed. This diluted solution is 0.04 mol dm-3 with respect to hypo-chlorite, 0.0295 mol dm-3 to sodium hydroxide and 0.05 mol dm-3 to phosphate. After oxidation the product is washed thoroughly with distilled water, left standing for 1 to 2 hours in 0.1 mol dm-3 hydrochloric acid and again washed very thoroughly with distilled water. (ii) Sodium Hypobromite OxyceUuloses10 The oxidant is prepared by dissolving 13.92 g of sodium bromate and 60 g of sodium bromide in distilled water and adjusting to 1 litre. A quantity of 200 cm" of this solution is pipetted into a 1 litre measuring flask and 200 cm3 of 1 mol dm -'1 sulphuric acid is added very quickly. After 30 minutes, the solution is chilled to 10-15 °c and 250 cm3 of 2 mol dm-3 sodium hydroxide is added. The temperature of the solution is regulated to 20 °c and the measuring flask filled to the mark with distilled water. The solution is 0.1 mol dm-3 with respect to the hypobromite and sodium hydroxide. It is stored protected from light. The oxidation is effected in a dark flask at 20 °C for about 20 (sample micro-crystalline cellulose C-Cell 3, sample medical cotton C-Cell 5) and 40 (sample micro-crystalline cellulose C-Cell 4, sample medical cotton C-Cell 6) hours, with 20 g of cellulose and 1 litre of the oxidant. The flask is shaken occasionally. The powder or fibre is washed free from hypobromite in a dark room equipped with red light, shaken with 0.1 mol dm-3 hydrochloric acid for 2 hours and finally washed very thoroughly with distilled water and dried in air. The dry sample C-Cell 6 treated several times alternatively with 0.1 mol dm-:i sodium hydrooide and 0.1 mol dm-3 hydrochloric acid is marked as a sample C-Cell 7. (iii) Chelating Cellulose with a.(~)-Alanine-N,N-diacetic Acid Anchor Groups20 Alkaline cellulose is prepared by treating 10 g of microcrystalline cellulose with 44.80/o sodium hydroxide and macerating it for 4 hours .The cellulose sample is then pressed to remove the liquid and to lower the weight to 1/4 of the starting weight. After standing for 6 hours in air-free atmosphere the alkaline cellulose is mixed with 8.4 g of the disodium salt of iminodiacetic acid and suspended in 20 cm3 of acetone. 50 cm3 of acetone solution containing 4.1 g of 1,2-dibromo methyl propionate is added into the suspension with stirring. The mixture is vigorously stirred and refluxed at 70 °c for 3 hours. After cooling, solid particles are suspended into the 255 cm3 of ethanol-water-glacial acetic acid (25 : 25 : 1) mixture. Chelating cellulose is washed several times with distilled water, ethanol and acetone and dried in air. Three series of samples prepared by this procedure are marked as IDA-Cell 1, IDA--Cell 2 and IDA-Cell 3. Commercial sorbents e.g. microcrystalline cellulose, m-Cell; carboxymethyl cel-lulose, CM-Cell (Macherey-Nagel, Duren, Germany) and oxidized regenerated cel·-lulose, Surgicel 1-3 (Johnson & Johnson, New Jersey, USA) are also used as experimental materials. Apparatus (i) Perkin Elmer Model 457 double beam grating infrared spectrophotometer is used for analysis. The recordings are performed using slit setting »3« and speed setting »slow«. (ii) Orion research digital pH Meter Model 701 with combination pH electrode is used. SORPTION CAPACITY OF CELLULOSE MATRICES Exchange Capacity Measurements (i) Calcium Acetate Method21 393 The capacity of cellulose matrix is obtained from the volume of t itrant at the inflection point of the titration curve by the potentiometric method. About 0.5 g of acid form cellulose sample is equilibrated in a ir an d weighed accurately to four points. The sample is then stir red for 30 minutes in 50.00 cm3 of calcium acetate aq. solution (1 : 50). The released protons are titrated with 0.01 mol dm-3 sodium hydroxide. The used volume of standard sodium hydroxide solution is corrected by the titration of 50.00 cm3 of calcium acetate aq. solution (1 : 50). It is necessary to use freshly prepared solution of calcium acetate. (ii) Infrared Spectrophotometric Procedure The method of sorption capacity determination of cellulose matrices is based upon the characteristic streching band at 1725 cm-1 (5.8 ,,tm) belonging to the carbo-xylic and carbonyl group. Infrared spectra of cellulose -samples are recorded by KBr-disks m ade from KBr of appropriate purity and reduced amount of water . A blank pellet containing 300 mg of KBr is recorded in the 1900-1500 cm· 1 infrared region to show degree of purity and amount of present water. All weighings are done on an analytical b alance. 2 mg of cellulose sample and 300 mg of KBr are homogenized in agate mortar. The obtained mixture is then subjected to a load of 2.4 · 10" kg m-2 for 5 minutes to make the pellet. The measurement of the height (in mm) of the absorption peak at 1725 cm-1 , is performed in a way shown in Figure 1. Wave length /J.Jm 5-0TT I I I TTI 16!0111 I E E - -==i 0-0 7·0 0 ·1 I ...-,0 ·2 - J Cl! 03 -1 l '-0 0 ·4 - (/) .D 0 ·5 -1 I <( I ::::.'J 2000 1800 1600 1-0 -j UuuJW.UI ULW 1lu I ULI llllJ 11 11111I 1111u1_ .... J Wave number/cm·1 Fig ure 1. Graphic determination of the effect of C = O s tre ching. RESULTS AND DISCUSSION Potentiometric determination of sorption capacity of 15 cellulose matrices for collection of trace metal ions have shown that the cellulose sorbents ranging i1n capacity from 0.02 to 4.10 mval g-1 can b e prepared. Table I contains 394 V . GRDINIC AND S. LUTEROTTI TABLE I Results of potentiometric sorption capacity determination of ceHulose matrices as an ion-exchange capacity (IEC) and related values of specific analytical signal obtained by infrared spectroscopy Potentiometric method Average value of infrared Samples specific signal (mm) at 0/o of COOR IEC/mval g-1 1725 cm-1 m-Cell 0.08 0.017 0.0 C-Cell 1 0.15 0.033 1.0 C-Cell 2 0.13 0.028 2.0 C-Cell 3 1.10 0.244 9.5 C-Cell 4 1.19 0.263 14.0 C-Cell 5 0.66 0.147 5.0 C-Cell 6 1.90 0.422 23.0 C-Cell 7 1.47 0.326 19.0 CM-Cell 2.80 0.622 34.0 IDA-Cell 1.93 0.429 15.0 IDA-Cell 2 4.59 1.019 34.0 IDA-Cell 3 8.51 1.890 40.5 Surgicel 1 15.21 3.379 43.5 Surgicel 2 16.72 3.713 40.0 Surgicel 3 18.43 4.093 39.5 results. The obtained results are used for construction of the calibration curve, x = g (C), and for the determination of the range obeying Lambert-Beer's law. The results also indicate that the absorption intensity of C= 0 streching band at 1725 cm- 1 (x) depends on sorption capacity or on percentage of COOR groups in a sample (C). Characteristics of calibration curve are shown in Figure 2. x/rn rn 40 30 20 1--9 T ,·· ' - - -:_~.:--: ~- - - -0 - - - - - - - - - - - - - - - - ~- - -~ -,o l )--'----"- ~~~~_L__,[ - - -10 15 C/ %COOH 5 Figure 2. Calibration curve. SORPTION CAPACITY OF CELLULOSE MATRICES 395 It may be concluded that calibration curve, x = g (C), is not the same for all cellulose sorbent types containing C=O group in a polymer molecule, since the different percentage of COOR groups in a polymer can exhibit the same values of specific analytical signal. For example, 2 mg of CM-Cell and IDA--Cell 2 in KBr-pellet produce under given conditions the absorption peak with the same height, x = 34 mm. It means that the structure of sorbent will influence the formation of analytical signal. A shown formula of basic unit of cellulose sorbent (Figure 3) can contain, for example, at position R different Figure 3. Basic unit of cellulose matrix. groups such as COOR and CR00CR"COOR (samples C-Cell, Surgicel and CM-Cell) or CR"OCR"CR[N(CR"COORL]COOCR0 (samples IDA-Cell). This is, probably the reason why it is not possible to construct a general calibration curve. Therefore, the equation of regression line will not hold for samples IDA-Cell. Figure 2 also shows that linearity of calibration function is observed up to about 30/o of COOR in a sample, which includes the maj-ority of cellulose derivatives prepared by oxidation. The lower limit of carboxyl content determination by the proposed method is about 0.20/o of COOR which means 0.044 mval g-1 . The equation of regression line of calibration curve which holds for C < 30/o, is specific analytical signal (x) = 14.701 C - 3.515 (2) On the other hand, the amount of carboxylic groups (e.g. for celluronic acid, pectinic acid and alginic acid) or related lactones can be calculated from the inverted equation of regression line: 0/o of COOR (C) = 0.068 x + 0.239 (mval g-1) = (O/o of COOR) · 0.2221 (3) (4) This simple and fast method for the determination of sorption capacity of cellulose matrices does not appear to be highly precise. F·or example, standard deviation of CM-Cell samples is 3.17, for n = 12 and£;= 34.0. REFERENCES 1. G. Ackermann and G. Kruger, Z. Anal. Chem. 191 (1962) 17. 2. G. Ackermann and R.-P. Frey, Z. Anal. Chem. 233 (1968) 321. 3. P. W. West and R. C. Ram i 1 ton, Mikrochemie 38 (1951) 100. 4. G. Ackermann, Mikrocchim. Acta (Wien) 1959, 358. 5. V. Gr din i c, Mikrovhim. Acta (Wien) 1975 I, 253. 6. V. Gr din i c and A. Gertner, Acta Pharm. Jugoslav. 25 (1975) o5. 7. V. Gr din i c, Acta Pharm. Jugoslav. 25 (1975) 195. 8. R. A. A. Mu z z are 11 i , Natural Chelating Polymers, Pergamon Press, Oxford, 1973. 9. E. S ch u 1 e k, Z s. Rem p o rt - Ro r v a th, A. La s z t it y, and E. K i:i r i:i s, TaLanta 16 (1969) 323. 396 V . GRDINIC ANDS. LUTEROTTI 10. K. H. Lieser, M. F 6 rs t er and P. Burb a, Z. AnaL. Chem. 284 (1977) 199. 11. A. J. U 1 tee and J. Harte 1, .4.naL Chem. 27 {1955) 557. 12. K. H . S ch r 6 d er, Chem.-Ztg. 81 (1957) 558. 13. G. Knudson, L. R am a 1 e y and R. A. K e 11 er, J. Chromatogr. Sci. 7 (1969) 500. 14. K. Mos k a 1 i u k and M. 0 gr i z e k - G y i k e t t a, Mikrochim. Acta (Wien) 1974, 179. 15. T . S ch 6 n f e 1 d and E. B r o d a, Mikrochemie ver. Mikrochi m. Acta 36/37 (1951) 537. 16. G. M. Nab a r and V. A. Shen a i, J. AppL. Polymer Sci. 11 (1970) 1215. 17. V. Gr din i c, in preparation. 18. 0. H . Weber, J. Prakt. Chemie 158 (1941) 33. 19. 0. Ant - Wuori n en and A. Vis pa a, Paperi Puu 50 (1968) 677 . 20. I. Ko j d 1, J. Prakt. Chemie 38 (1969) 851. 21. U. S. Pharmacopeia XVIII, p. 103. SAZETAK Odredivanje kapaciteta sorpcije celuloznih matrica infracrvenom apsorpcijskom spektrometrijom V. Grdinic i S. Luterotti Proucavana je metoda odredivanja sorpcijskog kapaciteta celuloznih matrica koj e se koriste za skupljanje tragova iona iz otopina. Analiticka metoda t emelji se na infracrvenoj apsorpcijskoj spektrometriji kod 1725 cm-1 sto je karakteristicno za iste-zanje skupine C=O u molekuli polimera. Za izradu kalibracijske krivulje pripre-mljeni su pogodni u zorci, standardizirani odredivanjem ionsko-izmjenjivackog kapa-citeta potenciometrijskom metodom. Diskut irane su neke osobine analitickog pos-tupka, posebno s obzirom na donju i gor n ju granicu odredivanja sadrfaja COOH, utjecaj strukture uzorka i preciznost predlozene metode. ZA VOD ZA KEMIJU FARMACEUTSKO-BIOKEMIJSKI FAKULTET SVEUCILISTA U ZAGREBU 41000 ZAGREB Prispjelo · 23 . listopada 1978. 

Sorption Capacity Determination of Cellulose Matrices by Infrared Absorption Spectrometry

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