Adsorption solvent, rinsing from

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

Figure 17. The effect of cyclohexane (A) and dichloromethane (B) solvents on the desorption of cinchonidine (abbreviated as CD) from platinum [66], In both cases, a clean platinum surface was first exposed to a cinchonidine solution in CC14 to allow for the adsorption of cinchonidine, and the platinum disk was then exposed to either cyclohexane or dichloromethane. In the case of cyclohexane, a total rinsing with 180 mL in several sequential flushings did not lead to significant change of the infrared spectra. On the other hand, with dichloromethane (B), one flush was sufficient to remove most of the adsorbate. [Reproduced by permission of the American Chemical Society from Ma, Z. Zaera, F. J. Phys. Chem. B 2005,109, 406-414.]...

Although DMVES reacts on silica surfaces [37], we have found it to adsorb on oxidized A1 only under specific conditions [4]. When spin cast on plasma alumina from solutions of either H20, acetone, or ethanol at concentrations 2.0 vol.% or greater, prohibitively thick films were obtained which adhered poorly to the alumina surface, evidenced by the fact they could be easily rinsed off with the above solvents. Lower solution concentrations resulted in no detectable adsorption. From these results we concluded that for DMVES to adsorb on alumina, the solutions must be dilute (<2.0 vol.%) and the exposure time increased. 

Neutral organic compounds that cannot exist as cations may be retained by physical adsorption but can be washed off the cation exchange colunm by a brief rinse with an organic solvent. The amine cation can then be eluted from the column with a 1 M solution of trimethylamine in methanol. The trimethylamine converts the amine cation to the free amine which is no longer retained by the cation exchanger. Because of its volatility, trimethylamine is easily removed from the eluate. After acidification, the sample amines can be separated by cation chromatography. 

Figure 7 The adsorption of sodium n-dodecylsulphate (SDS), /3-lacto-globulin, and /3-lactoglobulin from a mixture of 0.1% w/v protein plus 0.5% w/v SDS onto methylated silica as a function of degree of dilution. 0, pure SDS Q, pure /3-lactoglobulin O, SDS + /3 lactoglobulin. The open symbols are adsorption after 30 minutes, and the closed symbols are adsorption after 30 minutes of rinsing. Solvent 0.01 M phosphate buffer, pH 7 plus 0.15 M sodium chloride. (Reproduced from Wahlgren and Amebrant [65] with permission from Academic Press.)...

Glass vessels may also contribute to loss of an analyte, especially from aqueous solution, through adsorption on the vessel surface. This can be largely prevented by silanization of active sites on the glass. Alternatively, the vessel should be rinsed with solvent after removal of the sample, with the rinse solution then added to the sample itself [147]. 

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