Capillary monolithic titania column for miniaturized liquid chromatography and extraction of organo-phosphorous compounds

Photocatalytic reactive liquid microjunction surface sampling-mass spectrometry for rapid and selective in-situ analysis of alpha-unsubstituted amine metabolites or drugs in brain tissue

In in-situ mass spectrometry (MS), different on-tissue derivatization methods have been developed to enhance the signals of poorly ionizable primary amines. However, those chemical derivatization methods are laborious and time-consuming, and are usually limited to detection of high-abundance amino acids which suppress the reaction of low-abundance monoamine neurotransmitters and drugs. Herein, A rapid and selective photocatalytic derivatization technique for alpha-unsubstituted primary amine was developed with 5-hydroxyindole as derivatization reagent and TiO₂ as photocatalyst, and was introduced into liquid microjunction surface sampling (LMJSS)-MS system as online derivatization. The results showed that the photocatalytic derivatization method largely enhanced the signals of primary amines by 5-300 fold, and were selective to alpha-unsubstituted primary amines. Thus, the suppression effects from high-abundance amino acids to the reaction of monoamine neurotransmitters and benzylamine drugs proved to be largely reduced in the new method (matrix effect>50%) comparing with those in chemical derivatization method (matrix effect<10%). In addition, the optimal pH of the derivatization reaction was measured to be 7, which indicates the mild and physiologically compatible reaction conditions. By in-situ synthesis of TiO₂ monolith in the transfer capillary of the LMJSS-MS system, rapid on-line photocatalytic derivatization was achieved and completed in 5 s during the transfer of sampling extract from the flow-probe to the MS inlet. With the new photocatalytic reactive LMJSS-MS method, detection limits of three primary amines on glass slides were in the range of 0.031-0.17 ng/mm² with acceptable linearity (r=0.9815-0.9998) and relatively high repeatability (relative standard deviations <22.1%). Finally, endogenous tyramine, serotonin, two dipeptides and one doped benzylamine drug were identified and in-situ analyzed in the mouse cerebrum by the new method with largely enhanced signals comparing with LMJSS-MS without online derivatization. The new method provides a more selective, rapid and automated way to analyze alpha-unsubstituted amine metabolites and drugs in-situ comparing with traditional methods.

Trends in monoliths: Packings, stationary phases and nanoparticles

Monoliths media are gaining interest as excellent substitutes to conventional particle-packed columns. Monolithic columns show higher permeability and lower flow resistance than conventional liquid chromatography columns, providing high-throughput performance, resolution and separation in short run times. Monolithic columns with longer length, smaller inner diameter and specific selectivity to peptides or enantiomers have been played important role in hyphenated system. Monolithic stationary phases possess great efficiency, resolution, selectivity and sensitivity in the separation of complex biological samples, such as the complex mixtures of peptides for proteome analysis. The development of monolithic stationary phases has opened the new avenue in chromatographic separation science and is in turn playing much more important roles in the wide application area. Monolithic stationary phases have been widely used in fast and high efficiency one- and multi-dimensional separation systems, miniaturized devices, and hyphenated system coupled with mass spectrometers. The developing technology for preparation of monolithic stationary phases is revolutionizing the column technology for the separation of complex biological samples. These techniques using porous monoliths offer several advantages, including miniaturization and on-line coupling with analytical instruments. Additionally, monoliths are ideal support media for imprinting template-specific sites, resulting in the so-called molecularly-imprinted monoliths, with ultra-high selectivity. In this review, the origin of the concept, the differences between their characteristics and those of traditional packings, their advantages and drawbacks, theory of separations, the methods for the monoliths preparation of different forms, nanoparticle monoliths and metal-organic framework are discussed. Two application areas of monolithic metal-organic framework and nanoparticle monoliths are provided. The review article discusses the results reported in a total of 218 references. Other older references were included to illustrate the historical development of monoliths, both in preparation and types, as well as separation mechanism.

Preparation of monolithic polymer-magnetite nanoparticle composites into poly(ethylene-co-tetrafluoroethylene) tubes for uses in micro-bore HPLC separation and extraction of phosphorylated compounds

This paper describes the fabrication of a novel microbore monolithic column modified with magnetite nanoparticles (MNPs) prepared in a poly(ethylene-co-tetrafluoroethylene) (EFTE) tubing, and its application as stationary phase for the chromatographic separation of phosphorylated compounds. In order to obtain the composite column, a two-step procedure was performed. The formation of a glycidyl methacrylate-based monolith inside the activated ETFE tube was firstly carried out. Then, two incorporation approaches of MNPs in monoliths were investigated. The generic polymer was modified with 3-aminopropyltrimethoxysilane (APTMS) to be subsequently attached to MNP surfaces. Alternatively, APTMS-coated MNPs were firstly prepared and subsequently used for attachment onto the monolith surface through reaction of epoxy groups present in the generic monolith. This last strategy gave a reproducible layer of MNPs coated onto the polymer monolith as well as robust and permeable chromatographic columns. The retention behaviour of this MNP-based composite monolithic column was studied by using small phosphorylated compounds (adenosine phosphates). It was found that the retention of model analytes was ruled by partitioning and adsorption HILIC mechanisms. The columns also exhibited satisfactory performance in the separation of these target compounds, showing good chromatographic behaviour after two months of continued use. These composite monolithic columns were also successfully applied to the extraction of a tryptic digest of β-casein.

Modified nucleoside triphosphates exist in mammals

By establishing a chemical labeling method in combination with liquid chromatography-mass spectrometry analysis, we reported the widespread existence of various modified nucleoside triphosphates in eukaryotes.

DNA and RNA contain diverse chemical modifications that exert important influences in a variety of cellular processes. In addition to enzyme-mediated modifications of DNA and RNA, previous in vitro studies showed that pre-modified nucleoside triphosphates (NTPs) can be incorporated into DNA and RNA during replication and transcription. Herein, we established a chemical labeling method in combination with liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analysis for the determination of endogenous NTPs in the mammalian cells and tissues. We synthesized 8-(diazomethyl)quinoline (8-DMQ) that could efficiently react with the phosphate group under mild condition to label NTPs. The developed method allowed sensitive detection of NTPs, with the detection limits improved by 56–137 folds. The results showed that 12 types of endogenous modified NTPs were distinctly determined in the mammalian cells and tissues. In addition, the majority of these modified NTPs exhibited significantly decreased contents in human hepatocellular carcinoma (HCC) tissues compared to tumor-adjacent normal tissues. Taken together, our study revealed the widespread existence of various modified NTPs in eukaryotes.

Sol-gel niobia sorbent with a positively charged octadecyl ligand providing enhanced enrichment of nucleotides and organophosphorus pesticides in capillary microextraction for online HPLC analysis

A niobia-based sol-gel organic-inorganic hybrid sorbent carrying a positively charged C₁₈ ligand (Nb₂ O₅ -C₁₈ (+ve)) was synthesized to achieve enhanced enrichment capability in capillary microextraction of organophosphorus compounds (which include organophosphorus pesticides and nucleotides) before their online analysis by high-performance liquid chromatography. The sorbent was designed to simultaneously provide three different types of molecular level interactions: electrostatic, Lewis acid-base, and van der Waals interactions. To understand relative contributions of various molecular level analyte-sorbent interactions in the extraction process, two other sol-gel niobia sorbents were also created: (a) a purely inorganic sol-gel niobia sorbent (Nb₂ O₅ ) and (b) an organic-inorganic hybrid sol-gel niobia sorbent carrying an electrically neutral-bonded octadecyl ligand (Nb₂ O₅ -C₁₈ ). The extraction efficiency of the created sol-gel niobia sorbent (Nb₂ O₅ -C₁₈ (+ve)) was compared with that of analogously designed and synthesized titania-based sol-gel sorbent (TiO₂ -C₁₈ (+ve)), taking into consideration that titania-based sorbents present state-of-the-art extraction media for organophosphorus compounds. In capillary microextraction with high-performance liquid chromatography analysis, Nb₂ O₅ -C₁₈ (+ve) had shown 40-50% higher specific extraction values (a measure of extraction efficiency) over that of TiO₂ -C₁₈ (+ve). Compared to TiO₂ -C₁₈ (+ve), Nb₂ O₅ -C₁₈ (+ve) also provided superior analyte desorption efficiency (96 vs. 90%) during the online release of the extracted organophosphorus pesticides from the sorbent coating in the capillary microextraction capillary to the chromatographic column using reversed-phase high-performance liquid chromatography mobile phase.

Photocatalytic degradation of rhodamine B catalyzed by TiO2films on a capillary column

TiO₂ films on a capillary column were prepared using tetrabutoxytitanium as a source of TiO₂via the sol–gel method. The film thickness showed a linear increase with tetrabutoxytitanium concentration. The specific surface area of the film was improved by adding polyethylene glycol with different molecular weights. Under optimal conditions, the prepared film had a good mesoporous structure with specific surface area of 47.72 m² g⁻¹, and showed nearly spherical nanoparticles with a 10 nm diameter and anatase phase. Influences of the thickness, specific surface area, and initial solution concentration on photodegradation of rhodamine B using TiO₂ films as a catalyst were investigated. The results showed that the photodegradation efficiency increased with an increasing thickness and specific surface area of TiO₂ films. For a rhodamine B solution of 15 mg L⁻¹, the photodegradation efficiency was 98.33% in 30 min under the optimal conditions. The catalysts could be reused up to eight times with almost the same efficiency, indicating a firm immobilization of films on the inner wall of the capillary. Therefore, TiO₂ films are promising for the treatment of wastewater.

TiO₂ films on a capillary column were prepared using tetrabutoxytitanium as a source of TiO₂via the sol–gel method.

3-Dimensional X-ray microtomography methodology for characterization of monolithic stationary phases and columns for capillary liquid chromatography - A tutorial

In this tutorial we describe a fast, nondestructive, three-dimensional (3-D) view approach to be used in morphology characterization of capillary monoliths and columns by reconstruction from X-ray microtomography (XMT) obtained by acquiring projection images of the sample from a number of different directions. The method comprises imaging acquisition, imaging reconstruction using specific algorithms and imaging analysis by generation of a 3-D image of the sample from radiographic images. The 3-D images show the morphological data for bulk macropore space and skeleton connectivity of the monoliths and were compared with other images from imaging techniques such as scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and with chromatographic performance. The 3-D XMT methodology is applicable for organic and inorganic capillary chromatographic monolithic materials and it allows the acquisition of many hundreds (in our case 1001 projections) of longitudinal and cross-sectional images in a single session, resolving morphological details with a 3D-view of the monolithic structure, inclusive inside the column in a sectional structure with volume (three dimensions) when compared to the sectional structure area (with only two dimensions) when using SEM and FESEM techniques.

Zirconia--a stationary phase capable of the separation of polar markers of myocardial metabolism in hydrophilic interaction chromatography

Creatine, phosphocreatine, and adenine nucleotides are highly polar markers of myocardial metabolism that are poorly retained on RP silica sorbents. Zirconia represents an alternative material to silica with high promise to be used in hydrophilic interaction chromatography (HILIC). This study describes a first systematic investigation of the ability of ZrO2 to separate creatine, phosphocreatine, adenosine 5'-monophosphate, adenosine 5'-diphosphate, and adenosine 5'-triphosphate and compares the results with those obtained on TiO2 . All analytes showed a HILIC-like retention pattern when mobile phases of different strengths were tested. Stronger retention and better column performance were achieved in organic-rich mobile phases as compared to aqueous conditions, where poor retention and insufficient column performance were observed. The effect of mobile phase pH and ionic strength was evaluated as well. The analysis of myocardial tissue demonstrated that all compounds were separated in a relevant biological material and thus proved ZrO2 as a promising phase for HILIC of biological samples that deserves further investigation.