Fast Screening of Diol Impurities in Methoxy Poly(Ethylene Glycol)s (mPEG)s by Liquid Chromatography on Monolithic Silica Rods

Abstract

The determination of diol impurities in methoxy poly(ethylene glycol)s (mPEG)s is of high importance, e.g., in the area of pharmaceutical applications, since mPEGs are considered the gold standard—based on properties of biocompatibility, stealth effect against the immune system, and well-established procedures used in PEGylation reactions. Herein, we communicate a straightforward and fast approach for the resolution of the PEGdiol impurities in mPEG products by liquid chromatography on reversed-phase monolithic silica-rods. Thus, we utilize fine, in-house prepared and narrow dispersity mPEGs (Ð ≤ 1.1) and commercial PEGdiol standards as a reference. Most efficient analysis of diol impurities becomes possible with reversed-phase liquid chromatography that results in selective elution of the PEGdiol from mPEG macromolecule populations in partition/adsorption mode. We do this by a minimum selectivity of the population of macromolecules characterizing the narrow molar mass distributions of mPEG. Control experiments with intentionally added water at the start of the well-controlled mPEG synthesis via the living anionic ring opening polymerization of ethylene oxide clearly reconciled the existence of PEGdiol impurity in chromatographed samples. The here-demonstrated methodology allows for the resolution of diol impurities of less than one percent in elution times of only a few minutes, confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) of the collected elution fractions. The unique combination of the open flow-through pore structure of the monolithic silica rods and resultant varying accessibility of C18-derivatized pore surfaces indicates beneficial properties for robust and end-group-specific adsorption/partition liquid chromatography of synthetic macromolecules.

Synthesis and characterization of poly(ethylene glycol) bottlebrush networks via ring‐opening metathesis polymerization

“…Unsurprisingly, polymerization under these conditions resulted in insoluble gels due to the presence of a commonly known diol impurity in commercial PEG. 8,[63][64][65] This impurity was small enough in our macromonomer to have no effect on peak integration ratios in its 1 H-NMR spectra, indicating its presence in low amounts (much lower than the 8% reported elsewhere). 65 While this diol impurity is known to exist in commercial PEG materials, to our knowledge there are no instances of directly addressing this issue as it pertains to bottlebrush synthesis.…”

“…8,[63][64][65] This impurity was small enough in our macromonomer to have no effect on peak integration ratios in its 1 H-NMR spectra, indicating its presence in low amounts (much lower than the 8% reported elsewhere). 65 While this diol impurity is known to exist in commercial PEG materials, to our knowledge there are no instances of directly addressing this issue as it pertains to bottlebrush synthesis. A common impurity among materials polymerized anionically, diol contaminants have been historically difficult to visualize, and challenging to remove due to having a polarity similar to that of their monofunctional counterparts.…”

Metal-Organic Frameworks for Macromolecular Recognition and Separation

“…70 LCCC has been recognized as an effective technique for polymer separation based on the terminal groups. 71,72 The use of the LCCC technique is, however, generally limited to analytical and laboratorial uses in a small working capacity because it requires careful optimization of conditions. 70 The MOF-based terminal recognition on the LC system uses a totally different separation mode based on the reversible polymer insertion into the MOF stationary phase, which enables large-scale preparative separations using much simpler conditions and apparatus.…”

Development and validation of LC–MS method for the determination of heptaethylene glycol monomethyl ether in benzonatate bulk drugs

“…There are other oligomers that can also be formed in the synthesis of BNZ drug substance and which can be determined as degradation impurities with the specified specification level by HPLC (Katakam et al, 2020d), and these components of interest are found by interference, co-elution and poor selectivity by this methodology owing to the consecutive elution of monomer units from n = 2 to n = 17. In the literature, the particular identification and characterization of poly(ethylene glycol) (PEG) and PEGylated products by LC-MS with post-column addition of amines (Huang et al, 2009) and by liquid chromatography on monolithic silica rods (Brunzel et al, 2018) with other spectroscopic techniques (Barman et al, 2009;Kimac et al, 2020;Sayers et al, 2014;Zhang et al, 2014) has been published. There is some published literature on the quantitative determination of the BNZ drug substance in human plasma and pharmacokinetic studies (Lin et al, 1996;Man et al, 2019), which is not specific to quantitation of the subject component of interest.…”