Two-dimensional liquid chromatography of PDMS–PS block copolymers

Towards early detection of the hydrolytic degradation of poly(bisphenol A)carbonate by hyphenated liquid chromatography and comprehensive two-dimensional liquid chromatography

Characterization of polyolefins by comprehensive high-temperature two-dimensional liquid chromatography (HT 2D-LC)

In this study, we evaluate the use of various two-dimensional liquid chromatographic methods to characterize water-soluble, synthetically grafted bio-polymers, consisting of long poly(acrylic acid) chains and short maltodextrin grafts. The confirmation of the presence of grafting and the estimation of its extent is challenging. It is complicated by the limited solubility of polymers, their structural dispersity and chemical heterogeneity. Moreover, the starting materials (and other reagents, reaction products and additives) may be present in the product. Reversed-phase liquid chromatography (RPLC), hydrophilic-interaction liquid chromatography (HILIC) and size-exclusion chromatography (SEC) were used to characterize the product, as well as the starting materials. Additionally, fractions were collected for off-line characterization by infrared spectroscopy and mass spectrometry. The one-dimensional separation methods were found to be inconclusive regarding the grafting question. Breakthrough (the early elution of polymer fractions due to strong injection solvents) is shown to be a perpetual problem. This issue is not solved by comprehensive two-dimensional liquid chromatography (LC × LC), but information demonstrating the success of the grafting reaction could be obtained. SEC × RPLC and HILIC × RPLC separations are presented and discussed.

With the combination of different mechanisms, two-dimensional liquid chromatography has brought revolutionary changes compared to the traditional one-dimensional separation, which dramatically improve the peak capacity in separation and meet the ever-increasing demand for the analysis of complex samples in different research fields, such as chemistry, medicine, etc. However, the incompatibilities between two columns due to the transport of the large sample volume and the solvent effect always limit the wide use of two-dimensional liquid chromatography. In order to resolve this problem an at-column dilution (ACD) modulator was established to overcome the solvent incompatibility in the orthogonal combination within the comprehensive two-dimensional liquid chromatography. This interface is modified from normal two-dimensional interfaces by an additional transfer pump, which realize the at-column dilution without a flow split during the transportation. Moreover, with the control of the transfer flow and the second-dimensional gradient flow, it is able to precisely regulate the at-column dilution factor and conveniently optimize the separation conditions in both dimensions. In this work, a systematic research has been done between the setups with/without the at-column interface in the combination of reversed-phase liquid chromatography and hydrophilic interaction chromatography (RPLC × HILIC) and HILIC × RPLC, which proved that the at-column interface is able to resolve the solvent conflict problem very well. Furthermore, red ginseng was chosen as a real sample to investigate the applicability of the at-column dilution modulator for comprehensive two-dimensional chromatography with high orthogonality.

Ordered surface patterning of biocompatible microdomain is potentially needed in many applications such as high sensitive biochips, biosensors, and nanobio devices for cell culturing. One of the efficient ways in the fabrication of patterned surface is using the microphase separation of well-defined block copolymers by controlling molecular weight and film formation process. Thus we synthesize several compositions of block copolymers containing 2-methacryloyloxyethyl phosphorylcholine (MPC) which is hydrophilic and shows excellent biocompatibility, and polydimethylsiloxane (PDMS) which has hydrophobic nature and usually used as soft lithography materials. All of the copolymers were synthesized by the atom transfer radical polymerization (ATRP) method at room temperature. The kinetics plot and molecular weight plot shows that the polymerizations of block copolymers were well controlled, thus the compositions of block copolymers were controllable. Two kinds of synthesized copolymers: the longest MPC segment and the shortest one, were cast on Si(100) substrate by spin casting or solvent casting. By using the IR-multichannel viewer and atom force microscope, we could conclude that the film formed by the longest MPC segment could not generate the well defined surface structure due to its long chain aggregation. By using the copolymer containing the shortest MPC segment, we could generate a nanoscale ordered surface patterning of phorsphorylcholine unit.

Characterization of ethoxylated fatty alcohols using liquid chromatography with density and refractive index detection II. Quantification in liquid chromatography under critical conditions

A multidimensional analytical approach based on time-decoupled online comprehensive two-dimensional liquid chromatography coupled with ion mobility quadrupole time-of-flight mass spectrometry for the analysis of ginsenosides from white and red ginsengs

A two-dimensional liquid chromatography (2D-LC) method, normal phase liquid chromatography (NPLC) for one dimension and reversed phase liquid chromatography (RPLC) for the other dimension, was employed to map the molecular weight distribution (MWD) of the individual blocks of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer. The first-dimension (1st-D) NPLC separates PS-b-PI according to the PS block length while the second-dimension (2nd-D) RPLC separates PS-b-PI according to the PI block length. For the first-dimension NPLC separation, the column temperature was controlled to improve the resolution while the 2nd-D RPLC was run isothermally to reduce the separation time. The MWD information of individual blocks provides equivalent information to MWD and chemical composition distribution of a block copolymer. In this analysis, the effluent from the 1st-D LC separation is concentrated before the injection to the 2nd-D LC by use of a trap column, which allows an efficient interface between the two LC separations. Over 200 different block copolymer species could be identified from the 2D-LC chromatogram.

Lipid oxidation is one of the major causes of food spoilage for lipid-rich foods. In particular, oil-in-water emulsions, like mayonnaises and spreads, are prone to oxidation due to the increased interfacial area that facilitates contact between the lipids and hydrophilic pro-oxidants present in the water phase. Polar, amphiphilic lipid species present at the oil/water interface, like the mono- (MAGs) and di-acylglycerols (DAGs), act as oxidation starters that initiate subsequent oxidation reactions of the non-polar lipids in the oil droplets. A comprehensive two-dimensional liquid chromatography (LC×LC) method with evaporative light-scattering detection (ELSD) was set up to study the composition of the complex mixture of oxidized polar and non-polar lipids. The LC×LC-ELSD method employs size exclusion chromatography (SEC) in the 1D (1st dimension) to separate the various lipid species according to size. In the 2D (2nd dimension), normal-phase liquid chromatography (NPLC) is used to separate the fractions according to their degree of oxidation. The coupling of SEC with NPLC yields a good separation of the oxidized triacylglycerols (TAGs) from the large excess of non-oxidized TAGs. In addition, it allows the isolation of non-oxidized DAGs and MAGs that usually interfere with the detection of a variety of oxidized products that have similar polarities. This method facilitates elucidating how lipid composition affects oxidation kinetics in emulsified foods and will aid in the development of more oxidation-stable products.

The separation of a mixture of three poly(styrene-block-t-butyl methacrylate) copolymers (PS-b-PtBMA), consisting of polystyrene (PS) blocks of similar length and t-butyl methacrylate (PtBMA) blocks of different lengths, was performed using various chromatographic techniques, that is, a gradient liquid chromatography on reversed-phase (C18 and C8) and normal-phase columns, a liquid chromatography under critical conditions for polystyrene as well as a fully automated two-dimensional liquid chromatography that separates block copolymers by chemical composition in the first dimension and by molar mass in the second dimension. The results show that a partial separation of the mixture of PS-b-PtBMA copolymers can be achieved only by gradient liquid chromatography on reversed-phase columns. The coelution of the two block copolymers is ascribed to a much shorter PtBMA block length, compared to the PS block, as well as a small difference in the length of the PtBMA block in two of these copolymers, which was confirmed by SEC-MALS and NMR spectroscopy.

Purity of double hydrophilic block copolymers revealed by capillary electrophoresis in the critical conditions

Comprehensive two-dimensional liquid chromatography (LC × LC) is a valuable and powerful tool for the analysis of complex real-world samples. The present review paper highlights the advantages, arising from the coupling of two different liquid chromatography separations in the sector of food analysis. The first part is devoted to both theoretical and practical considerations about method optimization; on the other hand, selected applications pertaining to polyphenol, triacylglycerol and carotenoid analysis where no sample preparation is needed (green approach) are reported and discussed. In this context, the LC × LC methodology become a promising greener and ecofriendly alternative that may reduce analysis time and solvent consumption.

Development of on-line comprehensive two-dimensional liquid chromatography method for the separation of biomass compounds

A total of 50 secondary metabolites were profiled in shea kernels and shells using two-dimensional liquid chromatography (RPLC × HILIC) coupled with electrospray cyclic ion mobility quadrupole time-of-flight mass spectrometry (ESI-Q-cIMS-qTOF) and data-independent acquisition (DIA). The 2D chromatograms revealed distinct regions occupied by specific chemical classes, facilitating compound annotation based on high-resolution mass spectra and collision cross-section (CCS) data. CCS values showed maximum deviation of 2.9 %, and equivalent to the inherent CCS calibration error, from experimental values from the AllCCS database, and deviation of 0.1-6.6 % (mean 3.4 %) from predicted values, confirming compound identities. Key findings included the first-time identification of epitaxifolin, procyanidins B1-B4, prodelphinidins B1-B4, isoorientin and isoquercitrin in shea. The flavone, flavanones and flavanonols were 1.3-9 times more abundant in shells, while flavone glycosides, flavan-3-ols and their dimers, including mono- and di-galloylated forms, were 1.9-50 times higher in kernels. Notably, quercetin-species levels in shells were 4-15 times higher than in kernels. The analytical platform demonstrated high spectral purity in DIA mode due to the arrival time separation of precursor ions prior to fragmentation. The single pass cIMS had, in certain cases, the potential to separate isobaric (isoorientin and quercitrin) and near-isobaric ions (ellagic acid and quercetin). However, accessing the fully resolved and structured 4D data required customized computing tools due to a lack of fit-for-purpose software, highlighting a barrier to broader adoption. These findings support the further valorization of both shea kernels and shells for nutraceutical and cosmetic applications.

An untargeted lipidomic strategy combining comprehensive two-dimensional liquid chromatography and chemometric analysis