Separation and identification of polymeric dispersants in detergents by two-dimensional liquid chromatography

Mass spectrometry of polymers: A tutorial review

Ever since the inception of synthetic polymeric materials in the late 19th century, the number of studies on polymers as well as the complexity of their structures have only increased. The development and commercialization of new polymers with properties fine-tuned for specific technological, environmental, consumer, or biomedical applications requires powerful analytical techniques that permit the in-depth characterization of these materials. One such method with the ability to provide chemical composition and structure information with high sensitivity, selectivity, specificity, and speed is mass spectrometry (MS). This tutorial review presents and exemplifies the various MS techniques available for the elucidation of specific structural features in a synthetic polymer, including compositional complexity, primary structure, architecture, topology, and surface properties. Key to every MS analysis is sample conversion to gas-phase ions. This review describes the fundamentals of the most suitable ionization methods for synthetic materials and provides relevant sample preparation protocols. Most importantly, structural characterizations via one-step as well as hyphenated or multidimensional approaches are introduced and demonstrated with specific applications, including surface sensitive and imaging techniques. The aim of this tutorial review is to illustrate the capabilities of MS for the characterization of large, complex polymers and emphasize its potential as a powerful compositional and structural elucidation tool in polymer chemistry.

Two-dimensional separation of water-soluble polymers using size exclusion and reversed phase chromatography employing capillary-channeled polymer fiber columns

Polymeric materials are readily available, durable materials that have piqued the interest of many diverse fields, ranging from biomedical engineering to construction. The physiochemical properties of a polymer dictate the behavior and function, where large polydispersity among polymer properties can lead to problems; however, current polymer analysis methods often only report results for one particular property. Two-dimensional liquid chromatography (2DLC) applications have become increasingly popular due to the ability to implement two chromatographic modalities in one platform, meaning the ability to simultaneously address multiple physiochemical aspects of a polymer sample, such as functional group content and molar mass. The work presented employs size exclusion chromatography (SEC) and reversed-phase (RP) chromatography, through two coupling strategies: SEC x RP and RP x RP separations of the water-soluble polymers poly(methacrylic acid) (PMA) and polystyrene sulfonic acid (PSSA). Capillary-channeled polymer (C-CP) fiber (polyester and polypropylene) stationary phases were used for the RP separations. Particularly attractive is the fact that they are easily implemented as the second dimension in 2DLC workflows due to their low backpressure (<1000 psi at ∼70 mm sec-1) and fast separation times. In-line multi-angle light scattering (MALS) was also implemented for molecular weight determinations of the polymer samples, with the molecular weight of PMA ranging from 5 × 104 to 2 × 105 g mol-1, while PSSA ranges from 105 to 108 g mol-1. While the orthogonal pairing of SEC x RP addresses polymer sizing and chemistry, this approach is limited by long separation times (80 min), the need for high solute concentrations (PMA = 1.79 mg mL-1 and PSSA = 0.175 mg mL-1 to yield comparable absorbance responses) due to on-column dilution and subsequently limited resolution in the RP separation space. With RP x RP couplings, separation times were significantly reduced (40 min), with lower sample concentrations (0.595 mg mL-1 of PMA and 0.05 mg mL-1 of PSSA) required. The combined RP strategy provided better overall distinction in the chemical distribution of the polymers, yielding 7 distict species versus 3 for the SEC x RP coupling.

A fast stop-flow two-dimensional liquid chromatography tandem mass spectrometry and its application in food-derived protein hydrolysates

Food-derived bioactive peptides have many outstanding features like high safety, easy absorption, etc. However, explorations of the peptides are suffering from the limited knowledge of sample composition and low efficiency of separation techniques. In this work, a fast stop-flow two-dimensional liquid chromatography tandem mass spectrometry (2DLC-MS) was designed and constructed in-house. For chromatographic system optimization, the effects of column pairs and fraction transfer volumes on separation performance were studied. The pair of Protein BEH SEC and HSS T3 columns was found of high orthogonality. The peak capacity detected by the optimized 2DLC reached 1165 (for corn protein hydrolysates), indicating high resolving power. Moreover, the number of peptides identified from corn, soybean and casein protein hydrolysates reached as high as 8330, 8925 and 7215, respectively, demonstrating the high potential of the system. This would help reveal the peptide composition and facilitate the research on exploring bioactive peptides from food-derived protein hydrolysates.

Identification and quantification of polymeric impurity in block copolymer by one-dimensional and two-dimensional liquid chromatography coupled to high-resolution mass spectrometry and evaporative light scattering detector

Identifying and quantifying polymeric impurities in a polymeric material is critical for understanding material quality and performance, but it remains a challenge requiring developing new characterization methods. In this work, a comprehensive two-dimensional liquid chromatography method with simultaneous evaporative light scattering and high-resolution mass spectrometry detection was developed to separate and identify a polymeric impurity in alkyl alcohol-initiated polyethylene oxide/polybutylene oxide diblock copolymer. Size exclusion chromatography was implemented in the first dimension, and gradient reversed-phase liquid chromatography using a large-pore C4 column was applied in the second dimension using an active solvent modulation valve as the interface to minimize the polymer breakthrough. The two-dimensional separation significantly reduced the complexity of the mass spectra data compared to the one-dimensional separation, and the combination of retention time and mass spectral interpretation led to the successful identification of the water-initiated triblock copolymer impurity. This identification was confirmed by comparison with the synthesized triblock copolymer reference material. A one-dimensional LC method with evaporative light scattering detection was employed to quantify the triblock impurity. The impurity level in three samples made with the different processes was determined to be in the range of 9-18 wt% using the triblock reference material as the standard.

Gaining New Insights in Advanced Polymeric Materials Using Comprehensive Two-Dimensional Liquid Chromatography

Two-dimensional liquid chromatography (2D-LC) offers new insights into modern polymeric materials such as biodegradable polymers, polymers made from renewable feedstock, and complex formulated systems. Advances in instrumentation and the development of new modulation techniques enable more combinations of different separation modes. Hyphenation with universal and information-rich detectors further enhances the versatility and flexibility of the analytical strategy. Detailed characterization of copolymer composition heterogeneity and identification of polymeric ingredients in complex consumer products are key highlights of new applications.