Characterization of complex polyether polyols using comprehensive two-dimensional liquid chromatography hyphenated to high-resolution mass spectrometry.

Polyether polyols are often used in formulated systems, but their complete characterization is challenging, because of simultaneous heterogeneities in chemical composition, molecular weight and functionality. One-dimensional liquid chromatography-mass spectrometry is commonly used to characterize polyether polyols. However, the separation power of this technique is not sufficient to resolve the complexity of such samples entirely. In this study, comprehensive two-dimensional liquid chromatography hyphenated with high-resolution mass spectrometry (LC × LC-HRMS) was used for the characterization of (i) castor oil ethoxylates (COEs) reacted with different mole equivalents of ethylene oxide and (ii) a blended formulation consisting of glycerol ethoxylate, glycerol propoxylate and glycerol ethoxylate-random-propoxylate copolymers. Retention in the first (hydrophilic-interaction-chromatography) dimension was mainly governed by degree of ethoxylation, while the second reversed-phase dimension resolved the samples based on degree of propoxylation (blended formulation) or alkyl chain length (COEs). For different COE samples, we observed the separation of isomer distributions of various di-, tri- and tetra-esters, and such positional isomers were studied by tandem mass spectrometry (LC-MS/MS). This revealed characteristic fragmentation patterns, which allowed discrimination of the isomers based on terminal or internal positioning of the fatty-acid moieties and provided insight in the LC × LC retention behavior of such species.

Critical investigation of the substituent distribution in the polymer chains of hydroxypropyl methylcelluloses by (LC-)ESI-MS.

Three hydroxypropyl methylcellulose samples (HPMC1-3, DS(Me) = 1.45, 1.29, and 1.36; MS(HP) = 0.28, 0.46, and 0.84) were analyzed with respect to their methyl and hydroxypropyl substitution pattern in the polymer chains. Ionization yield of HPMC oligomers in electrospray ionization ion trap mass spectrometry (ESI-IT-MS) is strongly influenced by the hydroxypropyl pattern. Therefore, a sample derivatization procedure, as well as suitable measurement conditions that enable relative quantification were elaborated. Analysis was performed by negative ESI-IT-MS after per(deutero)methylation, partial depolymerization, and reductive amination with m-aminobenzoic acid. Measurement parameters like solvent, trap drive, and voltages of the ion transportation unit were studied with regard to the suitability for quantitative evaluation. Using direct infusion of the samples, strong influence of trap drive and octopole settings was observed. Optimized measurement conditions were used for the determination of the HP pattern of the permethylated samples by direct infusion. The methyl pattern was determined from the perdeuteromethylated samples by high-performance liquid chromatography-electrospray tandem mass spectrometry. For HPMC1, substituents were both found to fit the random distribution model. The other two samples showed pronounced heterogeneity which could be interpreted in more detail by extracting methyl subpatterns depending on the number of HP groups.

Simultaneous determination of substituent patterns in partially acid hydrolyzed O-Me/O-Me-d(3)-cellulose and quantification of the obtained oligomers by HPLC-ESI-MS.

Substituent patterns in oligosaccharide derivatives obtained from methyl cellulose were determined up to DP10 by electrospray ionization mass spectrometry employing separation of the oligomer fractions by HPLC. Oligosaccharides were labeled with meta-aminobenzoic acid after perdeuteromethylation and partial hydrolysis of methyl cellulose, enabling simultaneous quantification according to DP by HPLC/UV. Control of the HPLC-method was performed with a defined oligomer mixture obtained from ß-cyclodextrin. Results from LC-ESI-MS are discussed in comparison with those from syringe pump injection and compared to a calculated pattern for a random distribution. Programing of instrumental parameters optimized for each DP and avoidance of competition of successively eluting analytes in the electrospray process allowed extension of the established method for determination of the substitution pattern of cellulose derivatives along the polymer chain from DP5 to DP10 and thus a significant gain of information.

A novel software tool for copolymer characterization by coupling of liquid chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

The results of copolymer characterization by coupling of chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) techniques and subsequent calculation of copolymer composition using a novel software tool 'MassChrom2D' are presented. For high-resolution mass analysis copolymer samples were fractionated by means of liquid adsorption chromatography (LAC). These fractions were investigated off-line by MALDI-TOF MS. Various mono-n-butyl ethers of polyethylene oxide-polypropylene oxide copolymers (PEO-co-PPO) were investigated. As well as the copolymer composition presented in two-dimensional plots, the applied approach can give additional hints on specific structure-dependent separation conditions in chromatography.