No abstract

Adsorption properties of zeolites were investigated for the removal of p-cresol from aqueous solutions at 37°C within the context of studying alternative methods to dialysis for removing uremic toxin from blood. MFIframework type zeolites with different degrees of hydrophobicity and charge compensating cations were prepared: one pure silica MFI and four alumino-silicate MFIs (Si/Al = 30), with H + , Na + , K + and Mg 2+ as charge compensating cations. Adsorption isotherms and microcalorimetric measurements show a high affinity of p-cresol for all MFI type zeolites. The best capacity is obtained for the pure silica MFI, whereas the alumino-silicate samples show a higher affinity in the low concentration range. In the case of pure silica sample, the microscopic adsorption mechanism including the role of confined water is elucidated with the help of NMR, X-ray analysis (including Rietveld refinement) and Monte Carlo simulations. For all samples the high affinity is preserved in physiological serum solution, even in the presence of other toxin molecules such as urea. It is also shown that the compensating cation state of the samples is imposed by the physiological medium.

An analytical methodology with mass spectrometry as the core technique was developed for precise characterization of end groups, size, and comonomeric composition of poly(lactic-co-glycolic acid) (PLGA) copolymers, as a preliminary step to qualify their biodegradability. Four PLGA samples were studied, with GA molar content varying from 0 to 50% and M w ranging from 18 to 75 kg mol −1 according to the supplier. Size exclusion chromatography (SEC) and liquid state nuclear magnetic resonance (NMR) were used as either complementary or validation techniques. As confirmed by tandem mass spectrometry (MS/MS) experiments, macrocycles were most prominent in the low mass range. Nevertheless, elemental compositions derived from high resolution (HR) mass measurements of linear species were consistent with chain terminations revealed by NMR. Off-line coupling of SEC with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) permitted calibration curves to be built based on absolute molecular weights and, although slightly overestimated, so-obtained M n and M w values compared well with SEC and NMR results. Homogeneity of the co-monomeric content of all chains within each PLGA sample was demonstrated using surface-assisted laser desorption/ionization in a reactive mode (reactive-SALDI), a newly developed technique that takes advantage of residual acid on desorption ionization using through-hole alumina membrane (DIUTHAME) chips to induce dissociation of highmolecular-weight polymers containing cleavable C−O bonds. All HRMS data were best handled with Kendrick analysis, which helped reveal minor species and allowed automated computation of congested mass spectra.