System peaks Sulfonation

Typical probes for the analysis of ionic solutes include 3-hydroxy-L-tyrosine (DOPA)24 and naphthalene-2-sulfonate,26 whereas those for use with uncharged solutes include nicotinamide,27 theophylline,28 and anthracene 29 Indirect detection is nonspecific and less suitable for the analysis of complex or impure samples, because unpurified biological samples, such as urine, contain a large number of hydrophilic solutes that will give problems such as extra system peaks. However, analyses of pharmaceutical products and quantification of impurities in substances are typical of applications.23... 

Figure 13.6 Indirect detection of anions and cations. Stationary phase //-Bondapak-Phenyl. Mobile phase naphthalene-2-sulfonate 4 x 10 M in 0.05 M phosphoric acid. Sample (1) butyl sulfate, (2) pentyl amine, (3) hexane sulfonate, (4) hep-tylamine (5) octane sulfonate (6) octyl sulfate (S) system peak. Reproduced with permission from J. Crommen, G. Schill, D. West-erlund and L. Hackzell, Chromatographia, 24 (1987) 252 (Fig. 1).

Figure 13.3 Separation of UV-inactive anionic and cationic compounds [reproduced with permission of Elsevier Science Publishers BV from M. Denkert eta ., J. Chromatogr., 218,31 (1981)]. Anions detected before the system peak produce positive peaks and cations produce negative peaks, whereas the reverse applies for compounds following the system peak. Conditions column, 10 cm x 3.2 mm i.d. stationary phase, ixBondapak Phenyl, 10 j,m mobile phase, 0.5ml min of 4x10 M naphthalene-2-sulfonate in 0.05M phosphoric acid UV detector, 254nm. Peaks 1 = butylsulfate 2 = pentylamine 3 —hexanesulfonate 4 — heptylamine 5 = octanesulfonate 6 = octylsulfate S = system peak.

A reversed response pattern, with positive solute peaks before the system peak and negative ones after, is obtained when the analytes have the same charge as the probe or are uncharged. The different directions of the peaks of anionic and cationic solutes are demonstrated in the chromatogram in Figure 9, where alkylamines and alkanesulfonates are separated with naphthalene-2-sulfonate in phosphoric acid as an anionic probe 156]. 

Figure 9. Separation of amines and sulfonates [56]. Stationary phase /iBondapak Phenyl (lOum). Mobile phase 4 x 10 M naphthalene-2-sulfonate in 0.05 M phosphoric acid. Detection 254 nm. Peaks 1, pentanesulfonate 2, diisopropylamine 3, hexanesulfonate 4, heptylamine 5, octanesulfonate. S, and Sj = system peaks. Reproduced from L. Hackzell and G. Schill, Chromatogmphia, 15, 439 (1982) by permission of Vieweg-Publishing.

Chromatographic System Use a liquid chromatograph equipped with a refractive index detector that is maintained at a constant temperature and a 9-mm x 30-cm column packed with a strong cation-exchange resin, about 9 pm in diameter, consisting of sulfonated cross-linked styrene-divinylbenzene copolymer in the calcium form (Aminex HPX-87c, or equivalent). Maintain the column temperature at 85° + 0.5°, and the flow rate of the Mobile Phase at about 0.5 mL/min. Chromatograph the Standard Preparation, and record the peak responses as directed under Procedure. Replicate injections show a relative standard deviation not greater than 2.0%. 

The peak shift due to aggregation is observed not only in LBK films containing azobenzene chromophores, but also for other chromophores with extended Ji-systems, such as viologen polymers. For monolayers of the poly(p-phenylene sulfonate) 9/ dioctadecyldimethylammonium bromide (DODA) complex, the peak shift due to aggregation results in a piezo-chromic effect—that is, upon compression of the monolayer, a significant shift of the poly(p-phenylene sulfate) A band is observed (see Figure 6.9). This photochromic effect has been shown to be based on the improved 7t-Jt interaction upon compression of the monolayer. ... 

Several SANS studies of ionomers have appeared on both deuterium labeled and unlabeled systems(8,12,18-20). The earlier work(14) showed that an ionic peak, similar to that observed by x-rays, could be discerned in some cases, especially when the sample was "decorated" by the incorporation of D20. It was also tentatively concluded(19) that the radius of gyration, R, of the individual chains is not altered when the acid 1s converted to the salt in the case of poly-styrene-methacrylic acid copolymers. Subsequent SANS experiments were performed on sulfonated polystyrene ionomers with up to 8.5% sul-fonation(12). The results of this study indicated that aggregation of the ionic groups is accompanied by considerable chain expansion, which is consistent with the theory of Forsman(ll). 

From Figure 10 it appears that a dipolar relaxation labeled a is superimposed on the phenomenon we have just discussed. The behavior of this a peak correlates well with the behavior of the dynamic mechanical a relaxation since it increases in magnitude and decreases in temperature with increasing sulfonation. The presence of this peak in the dielectric spectra of these materials and its behavior as a function of sulfonate concentration are consistent with the assignment of the mechanical a relaxation to an ionic-phase mechanism. However, it is not possible to cite this dielectric peak as proof of the mechanical assignment the known presence of ionic impurities in these systems and the unknown origin of the large increases in tan 8 and c dictate that the dielectric results be interpreted with caution. 

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