Silica-Based Stationary Phase with Surface Bound N-Acetyl-glucosamine for Hydrophilic Interaction Liquid Chromatography.

A hydrophilic silica-based stationary phase with surface bound N-acetylglucosamine (GlcNAc-silica) was prepared in house and characterized physically via Fourier transform infrared (FTIR) analysis and thermogravimetric analysis (TGA) and chromatographically over a wide range of mobile phase compositions. While both FTIR and TGA confirmed the attachment of the GlcNAc ligands to the silica surface, the chromatographic evaluation of GlcNAc-silica with polar and slightly polar standard solutes (e.g., sugars, nucleic acid fragments, phenolic, and benzoic acid derivatives) yielded the typical hydrophilic interaction liquid chromatography (HILIC) behaviors in the sense that retention increased with increases in solute polarity and the organic content (i.e., acetonitrile) of the hydro-organic mobile phase (i.e., ACN-rich mobile phase). Sugars derivatized with 1-naphthylamine (1-NA) and 2-aminoanthrcene (2-AA) such as xylose, glucose, and short chains maltooligosaccharides constituted the most polar species for HILIC retention evaluation, and in addition, the maltooligosaccharides offered a polar homologous series for gauging the hydrophilicity of GlcNAc-silica in analogy with alkylbenzene homologous series and other nonpolar homologues for evaluating the hydrophobicity of non-polar stationary phases. On the other hand, the benzoic acid and phenolic acid derivatives were the probe solutes for evaluating the HILIC retention dependence of ionizable solutes on the pH of the mobile phase. Similarly, the nucleobase and nucleoside weak basic solutes as well as some typical cyclic nucleotide acidic solutes allowed for the examination of the dependence of solute retention on the pH of the mobile as well as the polarity of the species.

Nano-Liquid Chromatography with a New Monolithic Column for the Analysis of Coenzyme Q10 in Pistachio Samples.

Coenzyme Q10 (CoQ10) is a vital substance found throughout body. It helps convert food into energy and is eaten small amounts in foods. CoQ10 has gained great interest in recent years as a potential candidate for the treatment of various diseases. The content of CoQ10 in food samples is a crucial quality index for foods. Therefore, the development of sensitive separation and quantification method for determining the amount of CoQ10 in various samples, especially in foods, is an important issue, especially for food nutrition. In this study, a new, miniaturized monolithic column was developed and applied for the determination of CoQ10 in pistachio samples by nano-liquid chromatography (nano-LC). The monolithic column with a 50 µm i.d. was prepared by in situ polymerization using laurylmethacrylate (LMA) as the main monomer and ethylene dimethacrylate (EDMA) as the crosslinker. Methanol (MeOH) and polyethyleneglycol (PEG) were used as porogenic solvents. The final monolithic column was characterized by using scanning electron microscopy (SEM) and chromatographic analyses. The monolithic column with a 50 µm i.d. was applied to the analysis of CoQ10 in pistachio samples in nano-LC. This analytical method was validated by means of sensitivity, linearity, precision, recovery, and repeatability. The LOD and LOQ values were 0.05 and 0.48 µg/kg, respectively. The developed method using the monolithic column was optimized to achieve very sensitive analyses of CoQ10 content in the food samples. The applicability of the method was successfully demonstrated by the analysis of CoQ10 in pistachio samples.

Hydrophobic AEROSIL®R972 Fumed Silica Nanoparticles Incorporated Monolithic Nano-Columns for Small Molecule and Protein Separation by Nano-Liquid Chromatography.

A new feature of hydrophobic fumed silica nanoparticles (HFSNPs) when they apply to the preparation of monolithic nano-columns using narrow monolithic fused silica capillary columns (e.g., 50-µm inner diameter) was presented. The monolithic nano-columns were synthesized by an in-situ polymerization using butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) at various concentrations of AEROSIL®R972, called HFSNPs. Dimethyl formamide (DMF) and water were used as the porogenic solvents. These columns (referred to as HFSNP monoliths) were successfully characterized by using scanning electron microscopy (SEM) and reversed-phase nano-LC using alkylbenzenes and polyaromatic hydrocarbons as solute probes. The reproducibility values based on run-to-run, column-to-column and batch-to-batch were found as 2.3%, 2.48% and 2.99% (n = 3), respectively. The optimized column also indicated promising hydrophobic interactions under reversed-phase conditions, while the feasibility of the column allowed high efficiency and high throughput nano-LC separations. The potential of the final HFSNP monolith in relation to intact protein separation was successfully demonstrated using six intact proteins, including ribonuclease A, cytochrome C, carbonic anhydrase isozyme II, lysozyme, myoglobin, and α-chymotrypsinogen A in nano-LC. The results showed that HFSNP-based monolithic nanocolumns are promising materials and are powerful tools for sensitive separations.

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded octadecyl ligands for use in reversed-phase capillary electrochromatography.

A carboxy precursor monolithic column, namely poly(carboxy ethyl acrylate-co-ethylene glycol dimethacrylate) was first produced in a 100 µm i.d. fused-silica capillary and subsequently surface bonded with n-octadecyl (C18 ) ligands by a post-polymerization functionalization process with octadecylamine in the presence of N,N´-dicyclohexylcarbodiimide. The bonding of octadecyl ligands was achieved via an amide linkage between the carboxy functions of the precursor monolith and the amino group of the octadecylamine compound. The resulting C18 monolith exhibited a very low electroosmotic flow (EOF), a fact that required the incorporation of small amounts of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) in the polymerization solution to produce a precursor monolith with fixed negative charges of sulfonate groups. This may indicate that the conjugation of the carboxy functions with octadecylamine occurred to a large extent so that the amount of residual carboxy functions was sparsely dispersed and not enough to produce a desirable EOF. The EOF velocity of the C18 column having fixed negative charges provided by the incorporated AMPS increased with increasing ACN content of the mobile phase signaling an increased binding of mobile phase ions to the polar amide linkages near the monolithic surface, and a decreased viscosity of the mobile phase, both of which would result in increased EOF velocity. The C18 monolithic column constituted a novel nonpolar sorbent for reversed-phase capillary electrochromatography for nonpolar solutes, e.g., alkylbenzenes, alkylphenyl ketones, and polyaromatic hydrocarbons, and slightly polar compounds including phenol and chlorophenols. The C18 monolithic column exhibited relatively high selectivity toward chlorophenols differing by one chloro substituent.

Graphene oxide-octadecylsilane incorporated monolithic nano-columns with 50 µm id and 100 µm id for small molecule and protein separation by nano-liquid chromatography.

In this study, graphene oxide-octadecylsilane incorporated monolithic nano-columns were developed for protein analysis by nano liquid chromatography (nano LC). The monolithic column with 100 µm id was first prepared by an in situ polymerization using ethylene dimethacrylate (EDMA), 3-chloro-2-hydroxypropylmethacrylate (HPMA-Cl), and methacryloyl graphene oxide nanoparticles (MGONPs). MGONPs were synthesized by the treatment of 3-(trimethoxysilyl)propylmethacrylate (TMSPM) and GO. Tetrahydrofuran (THF) and dodecanol were used as the porogenic solvent. The resulting column was functionalized by dimethyloctadecylch lorosilane (DODCS) for the enhancement of hydrophobicity. The functionalization greatly improved the baseline separation of hydrophobic compounds such as polyaromatic hydrocarbons (PAHs). The optimized monolith with respect to total polymerization mixture was characterized by using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) X-ray diffraction (XRD) and chromatographic analyses. The blank monoliths without functionalization exhibited poor separation while a good separation performance of MGONPs functionalized monoliths was achieved. The monolith with 100 µm id was evaluated in protein separation in nano LC using RNase A, Cytochrome C, Lysozyme, Trypsin, and Ca isozyme II as the test proteins. It was shown that protein separation mechanism was based on large π-system of GO and hydrophobicity of the monolithic structure. Theoretical plates number up to 57 600 plates were achieved. The nano-column with 50 µm id was also prepared using the same polymerization mixture under the same chemical conditions. These nano-columns were employed for protein separation by nano LC, and the dependence of both nano-column performance on the internal diameter was also discussed.

Precursor carboxy-silica for functionalization with interactive ligands. I. Carbodiimide-assisted preparation of silica-bonded stationary phases with octadecyl, naphthyl, and anthracenyl ligands: Comparison of their selectivity and retentivity.

A precursor carboxy-silica support was introduced for grafting retentive ligands for use in high-performance liquid chromatography. This support was prepared by sequentially reacting 5 µm silica particles with vinyltrimethoxysilane and then thioglycolic acid. The carboxy-silica thus obtained was subsequently functionalized with octadecylamine, 2-naphthylamine, or 2-aminoanthracene by on-column reactions via a carbodiimide conjugation reaction. The carbodiimide with its zero-length carboxyl-to-amine coupling ability works by activating the surface carboxyl groups of the precursor support for direct reaction with the primary amines of octadecylamine, 2-naphthylamine, or 2-aminoanthracene via amide bond formation. These reactions series, which are applied for the first time in high-performance liquid chromatography column fabrication, yielded the octadecyl-, naphthyl-, and anthracenyl-silica columns. The three columns were evaluated for their reversed-phase chromatography retention properties with alkylbenzenes, alkylphenyl ketones, nitroalkanes, benzene and toluene derivatives, polyaromatic hydrocarbons, and nitro-substituted amino acids. The naphthyl- and anthracenyl-silica exhibited a good selectivity and efficiency toward most of the aromatic analytes when compared to the octadecyl-silica. Nitro-substituted amino acids containing electron withdrawing groups showed greater selectivity than other analytes on the aromatic-based columns than the C18 column. This is because of the ability of the π electron system of the analyte to accept electrons from the aromatic-based stationary phase (a Lewis base).

Platelet-to-lymphocyte ratio is correlated with a delay in feeding resumption following a transhiatal esophagectomy with cervical anastomosis.

INTRODUCTION: The lymphocytic population, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) are prognostic tools predictive of adverse outcomes for several solid tumors and oncologic surgeries, one of which is esophageal adenocarcinoma. Furthermore, delayed resumption of oral feeding postoperatively is associated with significant morbidity. Given the controversies regarding post-op nutritional support in these patients, this study investigates the prognostic role of the lymphocytic percentage, the NLR, and the PLR in predicting prolonged length of hospital stay (LOHS) and ICU stay (LOICUS) as well as delayed oral feeding following transhiatal esophagectomy (THE) for adenocarcinoma of the esophagogastric junction (AEG). METHODS: Forty consecutive patients who underwent transhiatal esophagectomy performed by a single surgeon for Siewert type II and type III adenocarcinoma of the esophagogastric junction at a tertiary referral center were selected. Retrospective data collection was performed from the patients' medical records, and statistical analysis was performed using Pearson correlation and Student's t test and Chi-square testing. RESULTS: An increased LOHS was correlated with a lower preoperative lymphocyte percentage (p = 0.043), higher NLR (p = 0.010) and PLR (p = 0.015), and an increased number of packed red blood cell (PRBC) transfusions perioperatively (p = 0.030). An increased LOICUS was correlated with a lower preoperative lymphocyte percentage (p = 0.033), higher NLR (p = 0.018) and PLR (p = 0.044), an increased number of PRBC transfusions (p = 0.001), and patients' comorbidities (p < 0.05). A delay in feeding resumption was correlated with a lower preoperative lymphocyte percentage (p = 0.022), higher NLR (p = 0.004) and PLR (p = 0.001), an increased PRBC transfusions (p = 0.001), and diabetes mellitus (p = 0.033). Multivariate analysis with automatic linear modeling showed that only the preoperative PLR was a powerful predictor for the delay of feeding resumption (p < 0.01). CONCLUSION: The lymphocyte percentage, PLR, and NLR are found to be associated with prolonged hospitalization and ICU stay and delayed oral feeding following THE for Siewert types II and III AEG. We hope by this series, to have set, at least one preliminary cornerstone, in the creation of a prognostic model, capable of assessing the need for an intraoperative jejunostomy placement, in patients undergoing esophagectomy for distal esophageal carcinoma.

Various Strategies in Post-Polymerization Functionalization of Organic Polymer-Based Monoliths Used in Liquid Phase Separation Techniques.

This review article is aimed at summarizing the various strategies that have been developed so far for post-polymerization functionalization (PPF) of organic polymer-based monoliths used in liquid phase separation techniques, namely HPLC at all scales and capillary electrochromatography (CEC). The reader will find the organic reactions performed on monolithic columns for grafting the chromatographic ligands needed for solving the separation problems on hand. This process involves therefore the fabrication of template monoliths that carry reactive functional groups to which chromatographic ligands can be covalently attached in a post-polymerization kind of approach. That is, the template monolith that has been optimized in terms of pore structure and other morphology can be readily modified and tailor made on column to fit a particular separation. The review article will not only cover the various strategies developed so far but also describe their separation applications. To the best of our knowledge, this review article will be the first of its kind.

Organic polymer-based monolithic capillary columns and their applications in food analysis.

In recent years, the use of organic polymer monolithic capillary columns in separation science has gained popularity due to the fact that they are easy to fabricate and do not require retaining frits. These materials have been applied in different fields including foods, proteomics, and pharmaceuticals. The interest in food analysis still needs to develop in order to increase the sensitivity towards micro/nano-scale food applications for food samples of < 5 µg (e.g., foodomics). In this regard, polymer monolithic capillary columns offer great separation capability in the food analytical separation science. We review the most important applications in food analysis using polymer monolithic capillary columns. In addition, several examples of the use of capillary separation methods combined with mass spectrometry detection in food analysis are summarized.

Organic polymer-based monolithic stationary phases with incorporated nanostructured materials for HPLC and CEC.

This review article is concerned with the recent advances made in the field of organic polymer-based monoliths with incorporated nanostructured materials (NSMs) for use in liquid chromatography and capillary electrochromatography. It covers the pertinent literature published over the last 7-8 years with a total of 56 references. The present article has two distinct parts: one major part encompassing "traditional" organic polymer-based monoliths modified with NSMs and a minor part on cryogels modified with NSMs.

Liquid-phase based separation systems for depletion, prefractionation, and enrichment of proteins in biological fluids and matrices for in-depth proteomics analysis-An update covering the period 2014-2016.

This review article is an update of our previous one by C. Puangpila, E. Mayadunne, and Z. El Rassi, Electrophoresis 2015, 36, 238-252. Similarly to the previous article, this review has two main topics, including (i) proteomic sample preparation (e.g., depletion of high-abundance proteins, reduction of the protein dynamic concentration range, and enrichment of a particular subproteome), and (ii) the subsequent chromatographic and/or electrophoretic prefractionation prior to protein separation and identification by LC-MS/MS. More than 70 papers published in the period extending from mid-2014 to the present have been reviewed. Although an effort was made to yield a comprehensive review article, one may safely state that this review article is by no means thorough, and the aim was to rather provide a concise description of the latest developments in the field.

Polar silica-based stationary phases. Part I - Singly and doubly layered sorbents consisting of TRIS-silica and chondroitin sulfate A-TRIS-silica for hydrophilic interaction liquid chromatography.

Two polar silica bonded stationary phases were prepared by first functionalizing the silica surface with γ-glycidoxypropyltrimethoxysilane, which was then reacted with TRIS to yield a polyhydroxy surface that also has secondary amine functionalities. This step produced the singly layered TRIS-silica column, a cationic hydrophilic column. The TRIS-silica surface was further coated with a layer of chondroitin sulfate A (CSA) yielding the doubly layered hydrophilic CSA-TRIS-silica column. The adsorbed CSA layer provided enhanced hydrophilicity and multi-mode interactions with polar solutes leading to different retention behavior and selectivity compared to the singly layered TRIS-silica column. The anionic sulfate and carboxylate groups in the CSA coating are electrostatically attracted by the cationic TRIS-silica surface yielding a relatively stable physically anchored CSA layer under HILIC elution conditions. The CSA-TRIS-silica column exhibited dual cationic and anionic character with mobile phases at pH ∼3.0 and pH > 4.5, respectively. When comparing solute retention observed on both columns under identical elution conditions, the k values of neutral and cationic solutes were significantly higher on the more hydrophilic doubly layered CSA-TRIS-silica column whereas anionic solutes showed lower k values due to the electrostatic repulsion from the CSA layer.

Poly (N-acryloxysuccinimide-co-ethylene glycol dimethacrylate) precursor monolith and its post polymerization modification with alkyl ligands, trypsin and lectins for reversed-phase chromatography, miniaturized enzyme reactors and lectin affinity chromatography, respectively.

This investigation was aimed at introducing a monolithic precursor that can be conveniently grafted with the desired chromatographic ligand via the process of post polymerization modification (PPM). The precursor was obtained by the in-situ polymerization of N-acryloxysuccinimide (NAS) and ethylene glycol dimethacrylate (EDMA) in a narrow bore stainless steel column of 1 mm i.d. yielding a poly(NAS-co-EDMA) monolithic column designated as the poly(NAS-co-EDMA) monolith (NASM) column. In a first PPM, the NASM column was bonded with octadecyl (OD) ligands yielding a nonpolar NASM-OD column that proved useful for reversed phase chromatography (RPC) of proteins in gradient elution at increasing %ACN in the mobile phase. NASM-OD resulted from the reaction between the N-hydroxysuccinimide of NASM with octadecyl amine. In a second PPM, NASM was surface immobilized with trypsin generating a proteolytic narrow bore enzyme reactor called NASM-trypsin immobilized enzyme reactor (IMER) that permitted the online digestion of proteins in a 20-min single pass through the IMER incorporated in a setup equipped with a short RPC column to achieve simultaneously a peptide tryptic map. This constituted a rapid turnover whereby ∼95% of the protein was hydrolyzed by the immobilized trypsin. In a third PPM, the NASM column was surface immobilized with three different lectins (LCA, Con A and RCA) having complementary affinities toward serum glycoproteins thus permitting the capture of a wide range of glycoproteins/glycoforms. The three NASM-lectin columns when operated in a tandem format led to assessing the level of the various glycoforms in human serum via LC-MS/MS analysis of the captured protein fractions by each NASM-lectin column.

Selective precolumn derivatization of fatty acids with the fluorescent tag 6-aminoquinoline and their determination in some food samples by reversed-phase chromatography.

Fatty acids (FAs) have been selectively derivatized with a fluorescent tag, 6-aminoquinoline (6AQ), which yielded fluorescent FA-6AQ derivatives that have excitation (λexc = 270 nm) and emission (λemi = 495 nm) wavelengths that are farther apart. This precolumn derivatization is characterized by its simplicity occurring at room temperature between the carboxylic acid group of the FA and the amino group of 6AQ in the presence of a nonaqueous soluble carbodiimide coupling agent such as the N,N´-dicyclohexylcarbodiimide. The FAs extracts are readily derivatized in chloroform and can be analyzed without any further sample cleanup that minimizes sample loss. The FA-6AQ derivatives derived from standard FAs as well as from extracted FAs from food samples were separated by reversed phase chromatography on a homemade naphthyl methacrylate monolithic (NMM) column and C4 silica-based column. While the NMM column provided excellent separation for saturated FA-6AQ derivatives, the C4 silica column was able to separate simultaneously saturated and unsaturated FA-6AQ derivatives. The MNN column permitted the analysis and quantitation of the saturated FA-6AQ derivatives extracted from coconut oil. The C4 column provided the selectivity needed to analyze and quantify saturated and unsaturated derivatized with 6AQ and extracted from meat. The limits of detection and quantitation were 5 and 20 nM, respectively, with a linear dynamic range extending from 20 nM to 40 µM. The 40 µM upper limit was due to the limited solubility of the FA-6AQ derivatives in the diluting mobile phase, which is the initial mobile phase used in gradient runs.

Polar and nonpolar organic polymer-based monolithic columns for capillary electrochromatography and high-performance liquid chromatography.

This review article is a continuation of the previous reviews on the area of monolithic columns covering the progress made in the field over the last couple of years from the beginning of the second half of 2014 until the end of the first half of 2016. It summarizes and evaluates the evolvement of both polar and nonpolar organic monolithic columns and their use in hydrophilic interaction LC and CEC and reversed-phase chromatography and RP-CEC. The review article discusses the results reported in a total of 62 references.

Monolithic capillary columns consisting of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) and their diol derivatives with incorporated hydroxyl functionalized multiwalled carbon nanotubes for reversed-phase capillary electrochromatography.

Two types of monolithic stationary phases with incorporated hydroxyl functionalized multiwalled carbon nanotubes (OH-MWCNTs) were introduced and evaluated, namely, the poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith, denoted as poly(GMA-co-EDMA), and a diol derivative of the poly(GMA-co-EDMA) monolith. The diol derivative monolith was obtained by subjecting the poly(GMA-co-EDMA) monolith with physically incorporated OH-MWCNTs to an acid treatment with 0.1 M sulfuric acid at a moderate temperature of 50 °C for a total of 7.5 h. Also, the poly(GMA-co-EDMA) monolith with both physically and covalently incorporated OH-MWCNTs was prepared by subjecting the physically incorporated monolithic column to a Lewis acid catalyzed reaction in the presence of BF3 in order to react some of the OH-MWCNTs with the epoxy rings of the poly(GMA-co-EDMA) monolith. In all cases, the OH-MWCNTs were subjected to high power sonication at an output power of 10 W for 15 min with the aim of better dispersing the incorporated nanotubes into the monoliths under investigation. In fact, high power sonication yielded columns with a relatively higher plate count (∼2 fold increase) when compared to low power sonication. While the incorporation of OH-MWCNTs into the poly(GMA-co-EDMA) monolith acted as an amendment boosting the nonpolar character of the monolith and providing additional π-π interactions, the diol derivative monolith with its polar backbone character acted nearly as a support for the OH-MWCNT stationary phase giving rise to a carbon nanotube sorbent providing hydrophobic and π-π interactions via the incorporated OH-MWCNTs. These two kinds of columns were evaluated using alkylbenzenes, toluene derivatives, aniline compounds, phenols and polyaromatic hydrocarbons.

Postpolymerization modification of a hydroxy monolith precursor. Part III. Activation of poly(hydroxyethyl methacrylate-co-pentaerythritol triacrylate) monolith with epoxy functionalities followed by bonding of glycerol, polyamines, and hydroxypropyl-ß-cyclodextrin for hydrophilic interaction and chiral capillary electrochromatography.

In this last part of the series of investigations involving the postpolymerization modification of a hydroxy monolith (OHM) capillary column, the surface hydroxyl groups were first reacted with glycerol diglycidyl ether in the presence of boron trifluoride (BF3 ) to convert the surface into epoxy activated OHM. The column thus activated with epoxy functions was further functionalized with polar compounds such as glycerol and polyamines to yield polyol OHM and polyamine OHM columns, respectively, for use in hydrophilic interaction electrochromatography. In another postpolymerization functionalization of the epoxy-activated OHM, hydroxypropyl-ß-CD (HP-ß-CD) was grafted onto the epoxy OHM surface to produce HP-ß-CD OHM for enantioseparation by CEC (chiral CEC). The polyol OHM capillary column and polyamine OHM capillary columns exhibited the typical hydrophilic interactions columns vis-à-vis polar solutes such as phenolic compounds and nucleobases. The HP-ß-CD OHM column was able to resolve some racemic compounds as well as positional isomers. All the columns exhibited good reproducibility from run to run, day to day, and column to column.

Postpolymerization modification of a hydroxy monolith precursor. Part II. Epoxy biphenyl modified poly (hydroxyethyl methacrylate-co-pentaerythritol triacrylate) monolithic capillary columns for reversed-phase capillary electrochromatography based on π-π and hydrophobic interactions.

In this second part of the series of investigations involving the postpolymerization modification of a hydroxy monolith (OHM) capillary column, the surface hydroxyl groups were reacted with epoxy biphenyl thus yielding the so-called Biphenyl OHM capillary column. The modification involved the epoxy ring opening of the 2-biphenylyl glycidyl ether catalyzed by BF3 and its subsequent reaction with the hydroxyl groups on the OHM precursor surface. The Biphenyl OHM capillary column thus obtained exhibited the typical reversed phase behavior by primarily hydrophobic interactions vis-à-vis the homologous series of alkyl benzenes and in addition by π-π interactions toward nitroalkane homologous series via their π-electron rich nitro groups. This dual retention mechanism was very distinctly observed with a set of PAH solutes in the sense that the k values of the PAH solutes were comparable to those obtained on a more non polar stationary phase, namely the Epoxy OHM C-16 reported in the preceding article. Other aromatic solutes showed the dual retention mechanism on the Biphenyl OHM capillary including phenols, anilines derivatives, and phenoxy acid herbicides. The Biphenyl OHM capillary exhibited good reproducibility from run-to-run, day-to-day, and column-to-column.

Postpolymerization modification of a hydroxy monolith precursor. Part I. Epoxy alkane and octadecyl isocyanate modified poly (hydroxyethyl methacrylate-co-pentaerythritol triacrylate) monolithic capillary columns for reversed-phase capillary electrochromatography.

A novel precursor monolithic capillary column referred to as "hydroxy monolith" or OHM was prepared by the in situ copolymerization of hydroxyethylmethacrylate (HEMA) with pentaerythritol triacrylate (PETA) yielding the neutral poly(HEMA-co-PETA) monolith. The neutral precursor OHM capillary thus obtained was subjected to postpolymerization modifications of the hydroxyl functional groups present on its surface with 1,2-epoxyalkanes catalyzed by boron trifluoride (BF3 ) ultimately providing Epoxy OHM C-m capillary column at varying alkyl chain lengths where m = 8, 12, 14, and 16 for RP-CEC. Also, the same precursor OHM was grafted with octadecyl isocyanate yielding Isocyanato OHM C-18 column to provide an insight into the effect of the nature of the linkage to the surface hydroxyl groups of the OHM precursor. While the epoxide reaction leaves on the surface of the OHM precursor hydroxy-ether linkages, the isocyanato reaction leaves carbamate linkages on the same surface of the OHM precursor. This study revealed that changing the alkyl chain length resulted in changing the column phase ratio (ϕ) and also the solute distribution constant (K). While increasing the surface alkyl chain length increased steeply the solute hydrophobic selectivity, i.e. methylene group selectivity, the nature of the ligand linkage produced different retention for the same solutes and affected the selectivity of slightly polar solutes. The various monoliths proved very useful for RP-CEC of different small solutes at varying polarity over a wide range of mobile phase composition.

Recent advances in nonpolar and polar organic monoliths for HPLC and CEC.

This article is aimed at providing a review of the progress made in the field over the period 2011 to present in order to expand in parts on two previous reviews (S. Karenga and Z. El Rassi, Electrophoresis, 2011, 32, 90-104; D. Gunasena and Z. El Rassi, Electrophoresis, 2012, 33, 251-261). In brief, this review article describes progress made in nonpolar and polar monoliths used in RP HPLC and CEC and in hydrophilic interaction LC/CEC, respectively. This article is by no means an exhaustive review of the literature; it is rather a survey of the recent progress made in the field with 69 references published on nonpolar and polar polymeric monoliths.