Espinozasalomonsen4410

Traditional polymer-separation methods, such as size-exclusion chromatography and (gradient) liquid adsorption chromatography, cannot provide separations exclusively based on the number of deprotonated carboxylic-acid groups along the backbone chain of polymers. A novel separation method, based on non-aqueous ion-exchange chromatography (NAIEX), was developed, which allows such a separation of acid-functional polymers that are soluble in organic solvents. The polar, aprotic N-methyl-2-pyrrolidone was found to be a suitable solvent. It features a high relative permittivity (favouring dissociation of ion pairs into free ions) and it is a good solvent for polymers and organic salts, such as triethyl-ammonium formate. A negative charge is established on these polymers by deprotonation of the carboxylic-acid groups in the presence of an organic superbase (tetramethyl guanidine). Traditional potent organic bases, such as triethylamine, do not possess the base strength to compensate for the increase in pKa of polymeric carboxylic acid groups in non-aqueous conditions. Triethyl-ammonium formate is proposed as an alternative to traditional salts used for elution in aqueous ion-exchange chromatography. Separation was performed on an industry-standard strong-anion-exchange column and (near-)universal detection of the polymers was performed by high-temperature evaporative-light-scattering detection. The NAIEX method yielded a separation based on the acid-functionality distribution of the polymer. NAIEX was compared with traditional normal- and reversed-phase liquid-chromatography approaches for the separation of acid-functional copolymers.In ionexchange chromatography, the pH gradient mode becomes more and more popular today for the analysis of therapeutic proteins as this mode can provide higher or alternative selectivity to the commonly used salt gradient mode. Ideally, a linear pH response is expected when performing linear gradients. However up to now, only a very few buffer systems have been developed and are commercially available which can perform nearly linear pH responses when flowing through a given column. It is also known that a selected buffer system (mobile phase) can work well on one column but can fail on other column. The goal of this study was to practically evaluate the effects that ionexchange columns (weak and strong exchangers) might have on effluent pH, when performing linear pH gradient separations of therapeutic monoclonal antibodies. To attain this objective, the pH was monitored on-line at the column outlet using a specific setup. To make comprehensive observations of the phenomenon, four different mobile phase conditions and five cation exchange columns (weak and strong exchangers) were employed. The obtained pH responses were systematically compared to responses measured in the absence of the columns. From this work, it has become clear that both the column and mobile phase can have significant effects on pH gradient chromatography and that their combination must be considered when developing a new method. Phase systems (column + mobile phase) providing linear pH responses are indeed the most suitable for separating mAbs with different isoelectric points and, with them, it is possible to elute mAbs across wide retention time ranges and with high selectivity.In the present work, a very sensitive and fully automated direct immersion PAL SPME Arrow procedure, coupled with GC-MS, has been developed and validated for determination of nine phosphorus flame retardants in different types of water samples (river, drinking and rainwater). PDMS/DVB was selected among three commercially available SPME Arrows (PDMS/DVB, DVB/PDMS/CWR and PDMS/CWR), since it resulted in the best sensitivity. The important experimental parameters were optimized via a central composite design response surface methodology and as result, extraction time of 65 min, extraction temperature of 80 °C and added salt concentration of 19% (w/v), were selected as the optimum values. The optimized method showed linear response over the calibration range (2 - 500 ng L-1), with R2-values higher than 0.9937. The precision (RSD%) measured by replicate analyses (n = 7) was estimated at 2 and 100 ng L-1 and was less than 29% and 21%, respectively. The LOQ of PAL SPME Arrow, calculated as S/N = 10, was between 0.2 and 1.2 ng L-1 (for triphenyl phosphate and tris-(1‑chloro‑2-propyl) phosphate, respectively) with extraction efficiencies between 5.9 and 31% (for tris-(1,3-dichloro-2-propyl) phosphate and tri-n‑butyl phosphate, respectively). To assess the performance of the developed technique for real samples, two river water samples, tap water from two regions and a rainwater sample were analyzed. Most of the target analytes were observed in the river samples with concentrations of 1.0 - 250 ng L-1 and the obtained recoveries at 50 ng L-1 ranged between 60 and 107%. Considering the figures of merit of the optimized method, PAL SPME Arrow-GC-MS showed to be the most sensitive analytical approach for determination of phosphorus flame retardants in water, with satisfying precision and accuracy, compared with conventional SPME-NPD, LLE-GC-MS and SPE-LC-MS/MS.Solid-phase extraction (SPE) is a widely-used and very well-established sample preparation technique for liquid samples. An area of on-going focus for innovation in this field concerns the development of new and improved SPE sorbents that can enhance the sensitivity and/or the selectivity of SPE processes. In this context, mixed-mode ion-exchange sorbents have been developed and commercialised, thereby allowing enhanced capacity and selectivity to be offered by one single material. GSK1120212 The ion-selectivity of these materials is such that either anion-exchange or cation-exchange is possible, however one limitation to their use is that more than one sorbent type is required to capture both anions and cations. In this paper, we disclose the design, synthesis and exploitation of a novel SPE sorbent based on microporous polymer microspheres with amphoteric character. We show that it is possible to switch the ion-exchange retention mechanism of the sorbent simply by changing the pH of the loading solution; anion-exchange dominates at low pH, cation-exchange dominates at high pH, and both mechanisms can contribute to retention when the polymer-bound amphoteric species, which are based on the α-amino acid sarcosine (N-methylglycine), are in a zwitterionic state.