Comprehensive two-dimensional liquid chromatography for the characterization of functional acrylate polymers

A comprehensive two-dimensional normal-phase x reversed-phase liquid chromatography based on the modification of mobile phases

A comprehensive orthogonal two-dimensional liquid chromatography (2D-LC) based on the modification of mobile phases was developed with a sample loop-valve interface. To improve the compatibility of mobile phases and analysis speed, some special solvents were chosen as the mobile phases, and the column temperature was elevated to decrease the viscosity of mobile phases of reversed-phase liquid chromatography (RPLC). Based on this principle, the first dimension was normal-phase liquid chromatography (NPLC) with a SiO2 column, and the second dimension was reversed-phase liquid chromatography containing two tandem C18 columns. 1,4-Dioxane was used in the NPLC mobile phase, and isopropyl alcohol was employed in the RPLC mobile phase. Moreover, the elevated column temperature enabled the reduction of the backpressure and using tandem C18 columns to improve the resolving power in RPLC. The new comprehensive 2D-LC system and applied strategy offered a novel idea for construction of 2D-LC system. A traditional Chinese medicine, Zhengtian pill, was used as the test sample to evaluate the constructed 2D-LC system. 876 peaks were detected, and the peak capacity reached 1740.

Approaches to comprehensive multidimensional liquid chromatography systems

This work compares the performance of the three different schemes implementing two-dimensional liquid chromatography (2D-LC) in terms of the peak capacity that they can generate and of the time that they need to complete a two-dimensional analysis. We discuss in detail how time is spent in these two-dimensional liquid chromatography x liquid chromatography (LC x LC) schemes and how to compare them. Keeping constant the characteristics of the first-dimension separation, we systematically varied those of the second-dimension separation and of its coupling to the first-dimension. In the process, five systems were created, based on the principles of the three known implementations of comprehensive 2D-LC. This work demonstrates an original method for the selection of the best comprehensive 2D-LC approach, depending on the desired peak capacity and on time constraints. The decision to use a 2D-LC method arises from the need to achieve a given resolution (i.e., a target peak capacity) within as short a time as possible or to reach the highest possible resolution in a given analysis time. Using the most appropriate schemes, we suggest how it is realistically possible to generate peak capacities ranging from 266 in just over 20 min or about 2800 in 2.3 h. When the time available for a two-dimensional separation is very short and the desired peak capacity cannot be achieved in 1D-LC, an on-line 2D-LC approach is unquestionably best. However, if a longer analysis time is acceptable, a 10-fold increase in the peak capacity can be obtained at the cost of a mere 7-fold increase in total analysis time.

Branched-polymer separations using comprehensive two-dimensional molecular-topology fractionation x size-exclusion chromatography

Branching has a strong influence on the processability and properties of polymers. However, the accurate characterization of branched polymers is genuinely difficult. Branched molecules of a certain molecular weight exhibit the same hydrodynamic volumes as linear molecules of substantially lower weights. Therefore, separation by size-exclusion chromatography (SEC), will result in the co-elution of molecules with different molecular weights and branching characteristics. Chromatographic separation of the polymer molecules in sub-microm channels, known as molecular-topology fractionation (MTF), may provide a better separation based on topological differences among sample molecules. MTF elution volumes depend on both the topology and molar mass. Therefore co-elution of branched molecules with linear molecules of lower molar mass may also occur in this separation. Because SEC and MTF exhibit significantly different selectivity, the best and clearest separations can be achieved by combining the two techniques in a comprehensive two-dimensional (MTFxSEC) separation system. In this work such a system has been used to demonstrate branching-selective separations of star branched polymers and of randomly long-chain-branched polymers. Star-shaped polymers were separated from linear polymers above a column-dependent molecular weight or size.

Comprehensive multidimensional liquid chromatography: Theory and applications

Comprehensive two-dimensional (2D) liquid chromatographic (LC x LC) techniques can be considered innovative methods only recently developed and adopted in many configurations. The revolutionary aspect of comprehensive two-dimensional techniques, with respect to classical multidimensional (MD) chromatography, is that the entire sample is subjected to the 2D advantage. The major benefit is that the separation capacities of each dimension are multiplied, offering a high peak capacity to resolve samples of great complexity. The first part of the present review briefly describes the theoretical and practical aspects related to the development of a multidimensional comprehensive liquid chromatographic method. Applicational experiences in comprehensive liquid chromatography are then described, divided into four groups, according to the HPLC modes used in the two dimensions and to the nature of the samples analyzed.

Comprehensive two-dimensional liquid chromatography applying two parallel columns in the second dimension

The design of a new interface for comprehensive two-dimensional liquid chromatography (LC x LC) is described. To the conventionally used LC x LC system with the loop-type interface consisting of a two-position/ten-port switching valve equipped with two loops, an extra two-position/ten-port switching valve, a detector, a pump and a second column placed in parallel with the column in the second dimension, are added. The features of the interface are that the separation space in the second dimension is significantly enlarged and that the number of fractions transferred from the first to the second dimension can be increased, reducing the risk to lose resolution of the primary dimension. The potential of the system in NPLC x 2RPLC is illustrated with the analysis of a standard mixture and a lemon oil extract. For the lemon oil analysis, the effective peak capacity was increased from 437 using a conventional interface to 1095 with the new interface. RPLC x 2RPLC in combination with reduced modulation times was applied to the analysis of steroids and to the detection of impurities at the 0.05% relative concentration level in a sulfonamide drug sample.

Fast, comprehensive two-dimensional liquid chromatography

The absolute need to improve the separating power of liquid chromatography, especially for multi-constituent biological samples, is becoming increasingly evident. In response, over the past few years, there has been a great deal of interest in the development of two-dimensional liquid chromatography (2DLC). Just as 1DLC is preferred to 1DGC based on its compatibility with biological materials we believe that ultimately 2DLC will be preferred to the much more highly developed 2DGC for such samples. The huge advantage of 2D chromatographic techniques over 1D methods is inherent in the tremendous potential increase in peak capacity (resolving power). This is especially true of comprehensive 2D chromatography wherein it is possible, under ideal conditions, to obtain a total peak capacity equal to the product of the peak capacities of the first and second dimension separations. However, the very long timescale (typically several hours to tens of hours) of comprehensive 2DLC is clearly its chief drawback. Recent advances in the use of higher temperatures to speed up isocratic and gradient elution liquid chromatography have been used to decrease the time needed to do the second dimension LC separation of 2DLC to about 20s for a full gradient elution run. Thus, fast, high temperature LC is becoming a very promising technique. Peak capacities of over 2000 and rates of peak capacity production of nearly 1 peak/s have been achieved. In consequence, many real samples showing more than 200 peaks with signal to noise ratios of better than 10:1 have been run in total times of under 30 min. This report is not intended to be a comprehensive review of 2DLC, but is deliberately focused on the issues involved in doing fast 2DLC by means of elevating the column temperature; however, many issues of broader applicability will be discussed.

Comprehensive two-dimensional field-flow fractionation-liquid chromatography in the analysis of large molecules

A novel, comprehensive two-dimensional asymmetric field-flow fractionation-liquid chromatographic system is described (AsFlFFF-RPLC). The interface is based on a switching valve, and the whole sample is analyzed in both dimensions. The system proved to be repeatable and quantitative in the characterization of egg white proteins. Four peaks at 4, 5.5-6.0, 7.5-8.0, and 10.0-11.0 nm, and corresponding to lysozyme, ovalbumin, transferrin, and a dimer of transferrin, were obtained in the AsFlFFF first-dimension system. Lysozyme also produced an additional peak, which overlapped with ovalbumin. Twelve compounds were separated in the LC second-dimension system. Identifications were made with the help of standards (ovalbumin, ovotransferrin, lysozyme) and by comparison of the peak areas, particle sizes, and retention data with values given in the literature. The effect of heat on egg white denaturation was studied, and the unfolding of peptide bonds of the protein was found to be pronounced when the sample was heated in phosphate solution.

Comprehensive two-dimensional liquid chromatography in analysis of Lamiaceae herbs: Characterisation and quantification of antioxidant phenolic acids

A fast and effective dynamic sonication assisted ethanol extraction method was developed for extracting phenolic acids from basil, oregano, rosemary, sage, spearmint and thyme of the Lamiaceae family. The results were compared with results obtained by conventional solvent extraction techniques. A comprehensive two-dimensional liquid chromatography (LC x LC) system interfaced to electrospray ionisation time-of-flight (TOF) mass spectrometry was then optimised for analysis and quantification of the herb extracts. The optimised LC x LC system employed a combination of C18 and cyano columns. The relative standard deviations for the retention times were better than 0.05% (rosmarinic acid 0.1%) and those for the peak areas 2-14% (2 mg/l, n=3). Limits of detection were 18-90 ng/ml. The LC x LC-MS method was applied to the quantitative analysis of phenolic acids, and the results were compared with those obtained with conventional LC-MS.

On-line hyphenation of supercritical fluid extraction and two-dimensional high performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometer for the analysis ofGanoderma lucidum

A novel on-line system combining supercritical fluid extraction (SFE) and two-dimensional high performance liquid chromatography (2D-HPLC) was developed. A trap column and two three-port valves were employed to couple SFE and 2D-HPLC system, which was composed of a CN column and a monolithic silica column, connected by a 10-port dual-position valve. The analytes extracted by supercritical CO2 were completely transferred to the 2D-HPLC system. After separation in two orthogonal modes, the eluents were delivered to APCI-tandem-MS for identification of the samples. In this way, sample preparation, separation, detection, and identification were integrated into an on-line system permitting analysis of the fruiting bodies of Ganoderma lucidum, and at least 73 components in the extract were resolved with calculated peak capacity of up to 1643.

Hyphenation of infrared spectroscopy to liquid chromatography for qualitative and quantitative polymer analysis: Degradation of poly(bisphenol A)carbonate

Hyphenation of infrared spectroscopy (IR) to liquid chromatography (LC) has been applied to study chemical changes in poly(bisphenol A)carbonate (PC) as a result of degradation. Especially coupling of LC to FTIR through solvent elimination is a sensitive approach to identify changes in functionality observed in the LC chromatograms as has been demonstrated by coupling of liquid chromatography under critical conditions (LCCC) to IR. Furthermore, an example is shown in which two-dimensional liquid chromatography, i.e. LCCC x SEC, was coupled to IR by means of a flow cell. This resulted in data sets containing most probably valuable data, but extracting relevant information from these large data sets is not straightforward at all. Therefore, multivariate data analysis (MVDA) of SEC-FTIR data was used to extract relevant data from large data sets. This approach revealed chemical differences due to degradation that could not be detected by other means. Spectral features could be identified that allowed to quantitatively predict the degradation of poly(bisphenol A)carbonate as a function of degradation conditions.

Comprehensive two-dimensional liquid chromatography–time-of-flight mass spectrometry in the analysis of acidic compounds in atmospheric aerosols

A novel method utilising comprehensive two-dimensional liquid chromatography interfaced to electrospray ionisation time-of-flight mass spectrometry was developed for the determination of organic acids in atmospheric aerosols. The system was applied to the analysis of methanolic extracts of filters from a high volume sampler. The enhanced separation power of two-dimensional separation was demonstrated in the analysis of both rural and urban samples. Quantification was performed for compounds for which standards were available. Limit of detection was 2-200 ng/ml. Average reproducibility of retention times in each dimensions was 0.1%, and average reproducibility of peak areas was 8% (10 microg/ml, n=3).

Off-line comprehensive two-dimensional high-performance liquid chromatography system with size exclusion column and reverse phase column for separation of complex traditional Chinese medicine Qingkailing injection

A comprehensive two-dimensional liquid chromatography system was constructed on the combination of size exclusion chromatography (SEC) and reverse phase liquid chromatography (RPLC). The first dimension used a SEC column with 300 mm x 8mm i.d., packed with Toyopearl HW-40S. The column was eluted with 0.05 mol/l Tris-HCl (pH 6.9) at a flow rate of 0.4 ml/min. The second dimension used a RPLC column with 100 mm x 4.6mm i.d., which was operated in gradient form at a flow rate of 1.0 ml/min. An automatic switching valve was used to collect the effluent of the SEC column every 3 min, and the effluent was automatically injected into the RPLC column. Mass spectrometer was used for peak identification. This system was used to separate Qingkailing injection, a traditional Chinese medicine (TCM). The result showed that the total peak capacity of this system could reach 1134 and the qualitative analysis of seven chemical components of the Qingkailing injection was accomplished by this system. The results show that comprehensive two-dimensional liquid chromatography system is of great importance and high value in the separation of complex TCM.

Separation and identification of compounds in Adinandra nitida by comprehensive two-dimensional liquid chromatography coupled to atmospheric pressure chemical ionization source ion trap tandem mass spectrometry

A comprehensive two-dimensional liquid chromatographic (2D-LC) separation system based on the combination of a CN column and a Merck Chromolith Flash reversed-phase column was developed for the separation of components in Adinandra nitida, one type of traditional Chinese medicine (TCM). The two dimensions were connected by a ten-port, dual-position valve controlled automatically by software written in-house. The effluents were detected by both ultraviolet and atmospheric pressure chemical ionization source ion trap tandem mass spectrometry (MS). The calculated peak capacity of the 2D-LC-MS/MS system was above 1240. More than 57 components were resolved in the methanol extract from Adinandra nitida leaves, and five of these were identified based on their relative retention times, molecular weights and MS/MS spectra.

Column selectivity for two-dimensional liquid chromatography

Selectivity of phase system is of primary concern when designing a 2-D separation, as it affects the 2-D system orthogonality and consequently the peak capacity controlling the number of peaks that can be separated in the available 2-D retention space limited by the time of analysis. Possibilities for characterization of LC phase system selectivity with respect to different polar and nonpolar structural units are compared, with special attention to multidimensional samples with various types of repeat groups, such as homopolymers, (co)polymers, fatty acid esters with various acyl lengths and number and position of double bonds, etc. Possibilities of the 2-D LC separations of these and other sample types, including pharmaceuticals, natural phenolic compounds, biopolymers, etc., using various combinations of separation modes are reviewed. Rules for design of comprehensive 2-D LC x LC systems are discussed, with respect to mobile phase compatibility in the two systems and modulation techniques suppressing band broadening connected with the sample fraction transfer from the first to the second dimension. Pitfalls connected with online connection of normal-phase and RP LC systems and their possible practical solutions are addressed and illustrated by practical examples.

Chemical variance, a useful tool for the interpretation and analysis of two-dimensional chromatograms

A new method is presented for the analysis of comprehensive two-dimensional data. The approach complements existing chemometric methods for analysing these kinds of data (e.g. multivariate-curve-resolution methods, MCR), and is especially suited for the analysis of families of compounds. The method is based on finding a new pair of axes (replacing the retention time axes) to represent the data. A drop in the matrix rank is observed when one of the axes collects all the variance for a certain family of compounds. This is achieved by introducing retention models (in both chromatographic dimensions) that describe the behaviour of a family of compounds as a function of the property that varies between the members. After this transformation, a single family of compounds gives rise to a single source of variance. This suggests the application of MCR techniques in a second step to separate the contributions of different (overlapped) families of compounds. For the latter application, more research has to be performed. The approach is illustrated using the separation of families of functional poly(methyl-methacrylate) polymers with different numbers of hydroxyl end groups and degrees of polymerisation or, equivalently, with the molecular weight as the key descriptive property within one family.

A protocol for designing comprehensive two-dimensional liquid chromatography separation systems

In this paper a protocol is proposed for establishing suitable column dimensions (length and diameters), particle sizes, flow rates, and second-dimension injection volumes (i.e. loop sizes) in comprehensive two-dimensional liquid chromatography (LC x LC). The chromatographer should select the maximum allowable first-dimension retention time, which is approximately equal to the overall analysis time. Also, (s)he should define the maximum allowable pressure in both dimensions and the (minimum) diameter of the first-dimension column. The proposed protocol provides design parameters corresponding to the ideal (theoretically optimal) conditions or to realistic practical conditions. The protocol also allowed us to study the implications of contemporary developments in LC, such as the use of high temperatures (implying reduced viscosities and increased diffusion coefficients), monolithic columns (implying smaller flow-resistance factors), and ultra-high-pressure LC. The combination of (reversed-phase or normal-phase) liquid chromatography with size-exclusion chromatography (LC x SEC) is frequently employed for analysing complex polymers. The proposed protocol is used to design a suitable LC x SEC system under realistic conditions. The results resemble the systems that have been designed and implemented by expert chromatographers, but they also indicate how current practice can be improved.

Two-dimensional liquid chromatography normal-phase and reversed-phase separation of (co)oligomers

Many samples contain compounds with various numbers of two or more regular structural groups. Such "multidimensional" samples (according to the Giddings' notation) are best separated in orthogonal chromatographic systems with different selectivities for the individual repeat structural groups, described by separation factors. Correlations between the repeat group selectivities characterize the degree of orthogonality and suitability of chromatographic systems for two-dimensional (2D) separations of two-dimensional samples. The range of the structural units in that can be resolved in a given time can be predicted on the basis of a model describing the repeat group selectivity in the first- and second-dimension systems. Two-dimensional liquid chromatographic system combining reversed-phase (RP) mode in the first dimension and normal-phase (NP) mode in the second dimension were studied with respect to the possibilities of in-line fraction transfer between the two modes. Hydrophilic interaction liquid chromatography (HILIC) with an aminopropyl silica column (APS) is more resistant than classical non-aqueous NP systems against adsorbent desactivation with aqueous solvents transferred in the fractions from the first, RP dimension to the second dimension. Hence, HILIC is useful as a second-dimension separation system for comprehensive RP-NP LCxLC. A comprehensive 2D RP-NP HPLC method was developed for comprehensive 2D separation of ethylene oxide-propylene oxide (EO-PO) (co)oligomers. The first-dimension RP system employed a 120 min gradient of acetonitrile in water on a C18 microbore column at the flow-rate of 10 microL/min. In the second dimension, isocratic HILIC NP with ethanol-dichloromethane-water mobile phase on an aminopropyl silica column at 0.5 mL/min was used. Ten microliter fractions were transferred from the RP to the HILIC NP system at 1 min switching valve cycle frequency.

Considerations on the possibilities and limitations of comprehensive normal phase–reversed phase liquid chromatography (NPLC×RPLC)

A comprehensive normal phase system LC-reversed phase LC (NPLC x RPLC) was evaluated for the separation of a pharmaceutical mixture and citrus oil extracts. NPLC was performed on a 25 cm x 1 mm ID x 5 microm dp diol phase. In the second dimension, an RP 18 monolithic column (10 cm L x 4.6 mm ID x 2 microm macropore size) and an octadecyl silicagel-packed column (5 cm L x 4.6 mm ID x 3.5 microm dp) were applied for the analyses of the pharmaceutical sample and the citrus oil extracts, respectively. A two-position/ten-port switching valve was used as interface. Under optimised LC conditions, the high degree of orthogonality between NP and RP resulted in peak capacities of 300 for the pharmaceutical sample and of 450 for the citrus oil extract composed of lemon and orange oil. Despite the features of NPLC x RPLC, several shortcomings related with the solvent incompatibility between the two LC modes were identified and the practical consequences were discussed.

Living Radical Polymerization by the RAFT Process—A First Update

This paper provides a first update to the review of living radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of Reversible Addition–Fragmentation chain Transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymerization ranging over reagent synthesis and properties, kinetics, and mechanism of polymerization, novel polymer syntheses, and diverse applications.

Comprehensive multi-dimensional liquid chromatographic separation in biomedical and pharmaceutical analysis: a review

'Multi-dimensional' liquid separations have a history almost as long as chromatography. In multi-dimensional chromatography the sample is subjected to more than one separation mechanism; each mechanism is considered an independent separation dimension. The separations can be carried out either offline via fraction collection, or directly coupled online. Early multi-dimensional separations using combinations of paper chromatography, electrophoresis and gels, in both planar and columnar modes are reviewed. Developments in HPLC have increased the number of measurable analytes in ever more complex matrices, and this has led to the concept of 'global metabolite profiling'. This review focuses on the theory and practice of modern 'comprehensive' multi-dimensional liquid chromatography when applied to biomedical and pharmaceutical analysis.

Separation of branched polystyrene by comprehensive two-dimensional liquid chromatography

Branched polystyrenes (PS) featuring a bivariate distribution in the molecular weight and in the number of branches were characterized by comprehensive two-dimensional liquid chromatography (2D-LC). The branched PS were prepared by anionic polymerization using n-butyl Li as an initiator and a subsequent linking reaction with p-(chlorodimethylsilyl)styrene (CDMSS). The n-butyl Li initiator yields polystyryl anions with broad molecular weight distribution (MWD) and the linking reaction with CDMSS yields branched PS with different number of branches. For the first dimension (1st-D) separation, reversed-phase temperature gradient interaction chromatography (RP-TGIC) was employed to separate the branched polymer according to mainly the molecular weight. In the second dimension (2nd-D) separation, the effluents from the RP-TGIC separation are subjected to liquid chromatography at chromatographic critical conditions (LCCC), in which the separation was carried out at the critical condition of linear homo-PS to separate the branched PS in terms of the number of branches. The 2D-LC resolution of RP-TGICxLCCC combination worked better than the common LCCCxsize-exclusion chromatography (SEC) configuration due to the higher resolution of RP-TGIC in molecular weight than SEC. Furthermore, by virtue of using the same eluent in RP-TGIC and LCCC (only the column temperature is different), RP-TGICxLCCC separation is free from possible 'break through' and large system peak problems. This type of 2D-LC separation could be utilized efficiently for the analysis of branched polymers with branching units distinguishable by LC separation.