Exploration of the Selectivity and Retention Behavior of Alternative Polyacrylamides in Temperature Responsive Liquid Chromatography

Abstract

Temperature responsive liquid chromatography (TRLC) allows for separation of organic solutes in purely aqueous mobile phases whereby retention is controlled through temperature. The vast majority of the work has thus far been performed on poly­[N-isopropylacrylamide] (PNIPAAm)-based columns, while the performance of other temperature responsive polymers has rarely been compared under identical conditions. Therefore, in this work, two novel TRLC phases based on poly­[N-n-propylacrylamide] (PNNPAAm) and poly­[N,N-diethylacrylamide] (PDEAAm) are reported and compared to the state of the art PNIPAAm based column. Optimal comparison is thereby obtained by the use of controlled radical polymerizations, identical molecular weights, and by maximizing carbon loads on the silica supporting material. Analysis of identical test mixtures of homologue series and pharmaceutical samples revealed that PNNPAAm performs in a similar way as PNIPAAm while offering enhanced retention and a shift of the useable temperature range toward lower temperatures. PDEAAm offers a range of novel possibilities as it depicts a different selectivity, allowing for enhanced resolution in TRLC in, for example, coupled column systems. Reduced plate heights of 3 could be obtained on the homemade columns, offering the promise for reasonable column efficiencies in TRLC despite the use of bulky polymers as stationary phases in HPLC.

Hydrogel Coating with Temperature Response Retention Behavior and Its Application in Selective Separation of Liquid Chromatography

“…That is to say, the stationary phase also shows certain temperature response characteristics to some hydrophilic analytes within a certain temperature range. This temperature-responsive retention behavior of the DL-hydrogel@SiO 2 column is consistent with the retention behavior of the reported temperature-responsive liquid chromatography . The possible reason is that with the change of temperature, the polarity inducing effect and hydrogen bonding ability of the amide bond in the polymer change, which leads to the change in the retention behavior of the analyte that has hydrogen bonding with the stationary phase.…”

“…This temperature-responsive retention behavior of the DL-hydrogel@SiO 2 column is consistent with the retention behavior of the reported temperature-responsive liquid chromatography. 34 The possible reason is that with the change of temperature, the polarity inducing effect and hydrogen bonding ability of the amide bond in the polymer change, which leads to the change in the retention behavior of the analyte that has hydrogen bonding with the stationary phase. In addition, the retention behavior of PAHs without hydrogen bonding with the stationary phase shows almost no temperature responsiveness.…”

Comprehensive two-dimensional temperature-responsive × reversed phase liquid chromatography for the analysis of wine phenolics

“…The test solutes were selected to cover analytes in the low, medium, and high retention range and different flavonoid and nonflavonoid compound classes. The data illustrates that at the optimal velocity plate heights of ~20 µm are obtained, which is 2x higher compared to what can be obtained on C18 based RPLC on the same particle size [24,25,27]. This lower efficiency is related to the slower mass transfer in the (thicker) stationary phase, the inhouse packing of the columns and due to the size dispersity of the aminopropyl silica used.…”

“…Retention is governed by changes in solubility of the polymer in water as a function of temperature. As a consequence, this offers a tunable separation and retention based on hydrophobicity in purely aqueous media [23,[25][26][27][28]. TRLC has thus far been mainly based on Poly (N-isopropylacrylamide) (PNIPAAm) immobilized on silica.…”

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

“…For example, thermoresponsive polymers have also been used for shape memory materials, [277][278][279] temperature and glucose sensors, 280,281 smart textiles, 282 and thermoresponsive chromatography and electrodes. [283][284][285] We anticipate that thermoresponsive molecules could be applied to more areas as smart materials and contribute a variety of interdisciplinary research.…”