Determination of thermodynamic parameters in reversed phase chromatography for polyethylene glycols and their methyl ethers in different mobile phases

Abstract

The thermodynamic parameters (entropy and enthalpy change) and their increment per repeat unit have been determined in RP chromatography of PEG and its mono- and dimethyl ethers in different mobile phases. The different approaches for their determination and the problems related to the characteristic volumes (void volume, interstitial volume, pore volume) of the column are discussed. Very different dependences or the thermodynamic parameters were observed in aqueous mobile phases containing ACN, acetone, or methanol as organic modifier. In the first two mobile phases a linear dependence on the number of repeat units n is found, and the additional entropy and enthalpy changes per repeat unit are positive. In methanol-water, the enthalpy change is negative with a non-linear dependence on n, and the entropy change is independent on n and close to zero. The contribution of the end groups is almost the same in the first two mobile phases, but much smaller in methanol-water.

Revisiting molecular adsorption: unconventional uptake of polymer chains from solution into sub-nanoporous media

“…Such terminal effect on the thermodynamic parameters is also observed in IC of polymers. 81 Further study on this intriguing column retention mechanism will be performed in our group with the aim of developing a new methodological framework for macromolecular recognition and separation. 44 …”

Striving for Uniformity: A Review on Advances and Challenges To Achieve Uniform Polyethylene Glycol

“…Furthermore, normal-phase HPLC showed better resolution for high molecular weight PEG oligomers than RP-HPLC. 103 , 104 Cho et al confirmed this finding, stating that NP-HPLC with an amino-bonded silica stationary phase provided ease in analyzing high molecular mass PEG samples. 105 …”

“…Furthermore, normal-phase HPLC showed better resolution for high molecular weight PEG oligomers than RP-HPLC. 103,104 Cho et al confirmed this finding, stating that NP-HPLC with an amino-bonded silica stationary phase provided ease in analyzing high molecular mass PEG samples. 105 Moreover, the temperature effect on the retention time was studied, and it showed that the separation of PEG polymers can be realized by using thermal gradients using an isocratic gradient; however, this was only verified for PEGs with MW < 2000 Da.…”

“…They discovered that the hydroxyl group of solvents in normal-phase HPLC played a crucial role in resolving and retaining PEG oligomers. Furthermore, normal-phase HPLC showed better resolution for high molecular weight PEG oligomers than RP-HPLC. , Cho et al confirmed this finding, stating that NP-HPLC with an amino-bonded silica stationary phase provided ease in analyzing high molecular mass PEG samples …”

Separation of Molar Weight-Distributed Polyethylene Glycols by Reversed-Phase Chromatography—Analysis and Modeling Based on Isocratic Analytical-Scale Investigations

“…As concerns analytical chromatography, also, the accurate determination of the MWD of PEGs is of interest, in particular for medium and large MWs. Analysis of PEGs by high-performance liquid chromatography (HPLC) has been studied using reversedphase (RP-HPLC) and normal phase (NP-HPLC) [3,[10][11][12][13][14][15][16][17][18][19][20]. Alternatively, supercritical fluid chromatography (SFC) can be applied [21,22].…”