Photografted fluoropolymers as novel chromatographic supports for polymeric monolithic stationary phases

Porous polymer monolithic columns to investigate the interaction of humic substances with herbicides and emerging pollutants by affinity chromatography

BACKGROUND

Understanding the interaction mechanisms and the relevant binding constants between humic acids and emerging or regulated pollutants is of utmost importance in predicting their geochemical mobility, bioavailability, and degradation. Fluorescence spectroscopy, UV-vis spectroscopy, equilibrium dialysis, and solid-phase extraction combined with liquid chromatography-mass spectrometry have been employed to elucidate interactions of humic acids with organic micropollutants, especially pharmaceutical drugs. These methods demand large sample volumes, long equilibration times, and laborious extraction steps which may imply analytical errors. Monolithic high-performance affinity chromatography is an alternative and simpler method to investigate these interactions and determine the binding constants.

RESULTS

Polymer monoliths based on aminated glycidyl methacrylate and ethylene glycol dimethacrylate served to immobilize Cu(II) and then humic acid to produce monolithic affinity chromatography columns with humic acid as the active interaction phase. About 86.5 mg of humic acid was immobilized per gram of polymer. The columns enabled a comparison of the binding strength of humic acid with herbicides and emerging pollutants at 25 °C and pH 6.0 ± 0.1. Paracetamol, acetylsalicylic acid, and salicylic acid did not retain. Among the compounds that interacted with humic acid, the order of increasing affinity, estimated by the global affinity constant (nKa) or partition coefficient (KD) was: caffeine < simazine < atrazine ∼ propazine < benzophenone. The nKa (L mol-1) values ranged from (4.9 ± 0.3) × 102 for caffeine to (1.9 ± 0.3) × 103 for benzophenone, whereas KD (L kg-1) varied from 14 ± 1 to 56 ± 8 for the same compounds.

SIGNIFICANCE AND NOVELTY

To our knowledge, this is the first paper demonstrating the use of a monolithic platform to immobilize supramolecular structures of humic acids exploiting immobilized metal affinity to comparatively evaluate their affinity towards emerging pollutants exploiting the concepts of high-performance affinity chromatography. The proposed approach needs only small amounts of humic acid, which is a relevant feature in preparing columns with humic substances isolated and purified from remote areas.

Multivariate surface self-assembly strategy to fabricate ionic covalent organic framework surface grafting monolithic sorbent for enrichment of aristolochic acids prior to high performance liquid chromatography analysis

Herein, an ionic covalent organic framework (iCOF) surface grafting monolithic sorbent was prepared by the multivariate surface self-assembly strategy for in-tube solid-phase microextraction (SPME) of trace aristolochic acids (AAs) in serum, traditional Chinese medicines (TCMs) and Chinese patent drug. Via adjusting the proportion of ionic COF building block during the self-assembly, the density of quaternary ammonium ions in the iCOF was modulated for the enhanced adsorption of AAs. The successful preparation of iCOF surface grafting monolithic sorbent was confirmed by different means. A multiple mode mechanism involving π-π stacking, hydrophobic, electrostatic and hydrogen-bonding interactions was primarily attributed to the adsorption. Several in-tube SPME operating conditions, such as the dosage of ionic COF building block, ACN percentage and TFA percentage in the sampling solution, ACN percentage and TFA percentage in eluent and the collection time span, were optimized to develop the online in-tube SPME-HPLC method for analysis of AAs. Under the optimized conditions, a good linearity was obtained in the concentration range of 20-1000 ng/mL for target AAs in serum samples, the limits of detection (LODs) were less than 10 ng/mL, while the recoveries ranged from 90.3 % to 98.7 % with RSDs (n = 5) below 7.9 %. This study developed a feasible approach to iCOF functionalized monolithic sorbent for SPME and further exhibited the vast potential for the application of COF based monolithic sorbent in sample preparation.

3D printing for the integration of porous materials into miniaturised fluidic devices: A review

Porous materials facilitate the efficient separation of chemicals and particulate matter by providing selectivity through structural and surface properties and are attractive as sorbent owing to their large surface area. This broad applicability of porous materials makes the integration of porous materials and microfluidic devices important in the development of more efficient, advanced separation platforms. Additive manufacturing approaches are fundamentally different to traditional manufacturing methods, providing unique opportunities in the fabrication of fluidic devices. The complementary 3D printing (3DP) methods are each accompanied by unique opportunities and limitations in terms of minimum channel size, scalability, functional integration and automation. This review focuses on the developments in the fabrication of 3DP miniaturised fluidic devices with integrated porous materials, focusing polymer-based methods including fused filament fabrication (FFF), inkjet 3D printing and digital light projection (DLP). The 3DP methods are compared based on resolution, scope for multimaterial printing and scalability for manufacturing. As opportunities for printing pores are limited by resolution, the focus is on approaches to incorporate materials with sub-micron pores to be used as membrane, sorbent or stationary phase in separation science using Post-Print, Print-Pause-Print and In-Print processes. Technical aspects analysing the efficiency of the fabrication process towards scalable manufacturing are combined with application aspects evaluating the separation and/or extraction performance. The review is concluded with an overview on achievements and opportunities for manufacturable 3D printed membrane/sorbent integrated fluidic devices.

Polymer monoliths for the concentration of viruses from environmental waters: A review

Even at low concentrations in environmental waters, some viruses are highly infective, making them a threat to human health. They are the leading cause of waterborne enteric diseases. In agriculture, plant viruses in irrigation and runoff water threat the crops. The low concentrations pose a challenge to early contamination detection. Thus, concentrating the virus particles into a small volume may be mandatory to achieve reliable detection in molecular techniques. This paper reviews the organic monoliths developments and their applications to concentrate virus particles from waters (waste, surface, tap, sea, and irrigation waters). Free-radical polymerization and polyaddition reactions are the most common strategies to prepare the monoliths currently used for virus concentration. Here, the routes for preparing and functionalizing both methacrylate and epoxy-based monoliths will be shortly described, following a revision of their retention mechanisms and applications in the concentration of enteric and plant viruses in several kinds of waters.

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.

Construction of polymer monolithic columns in polypropylene ink-pen tubes for separation of proteins by cation-exchange chromatography

We describe the synthesis of polymer monoliths inside polypropylene tubes from ink pens. These tubes are cheap, chemically stable, and resistant to pressure. UV-initiated grafting with 5 wt% benzophenone in methanol for 20 min activated the internal surface, thus enabling the covalent binding of ethylene glycol dimethacrylate, also via photografting. The pendant vinyl groups attached a poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith prepared via photopolymerization. These tubes measured 100-110 mm long, with 2 mm of internal diameter. The parent monoliths were functionalized with Na₂ SO₃ or iminodiacetate to produce strong and weak cation exchangers, respectively. The columns exhibited permeabilities varying from 2.7 to 3.3 × 10^-13  m² , which enabled the separation of proteins at 500 µL/min and back pressures <2.8 MPa. Neither structure collapse nor monolith detachment occurred at flow rates as high as 2.0 mL/min, which produced back pressures between 6.9 and 9.0 MPa. The retention times of ovalbumin, ribonuclease A, cytochrome C, and lysozyme in salt gradient at pH 7.0 followed the order of increasing isoelectric points, confirming the cation exchange mechanism. Separation and determination of lysozyme in egg white proved the applicability of the columns to the analysis of complex samples.

3D printed fluidic platform with in-situ covalently immobilized polymer monolithic column for automatic solid-phase extraction

In this work, 3D stereolithographic printing is proposed for the first time for the fabrication of fluidic devices aimed at in-situ covalent immobilization of polymer monolithic columns. Integration in advanced flow injection systems capitalized upon programmable flow was realized for fully automatic solid-phase extraction (SPE) and clean-up procedures as a 'front-end' to on-line liquid chromatography. The as-fabricated 3D-printed extraction column devices were designed to tolerate the pressure drop of forward-flow fluidic systems when handling large sample volumes as demonstrated by the determination of anti-microbial agents, plastic additives and monomers as models of emerging contaminants (4-hydroxybenzoic acid, methylparaben, phenylparaben, bisphenol A and triclosan). Decoration of the monolithic phase with gold nanoparticles (AuNPs) was proven most appropriate for the enrichment of phenolic-type target compounds. In particular, the absolute recoveries for the tested analytes ranged from 73 to 92% both in water and saliva samples. The 3D printed composite monolith showed remarkable analytical features in terms of loading capacity (2 mg g-1), breakthrough volume (10 mL), satisfactory batch-to-batch reproducibility (<9% RSD), and easy on-line coupling of the SPE device to HPLC systems. The fully automatic 3D-printed SPE-HPLC hyphenated system was also exploited for the on-line extraction, matrix clean-up and determination of triclosan in 200 μL of real saliva samples.

Influence of photo-initiators in the preparation of methacrylate monoliths into poly(ethylene-co-tetrafluoroethylene) tubing for microbore HPLC

In this study, poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) polymeric monoliths were in situ developed within 0.75 mm i.d. poly(ethylene-co-tetrafluoroethylene) (ETFE) tubing by UV polymerization via three different free-radical initiators (α,α'-azobisisobutyronitrile (AIBN), 2,2-dimethoxy-2-phenylacetophenone (DMPA) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMPP). The influence of the nature of each photo-initiator and irradiation time on the morphological features of the polymer was investigated by scanning electron microscopy, and the chromatographic properties of the resulting microbore columns were evaluated using alkyl benzenes as test substances. The beds photo-initiated with MTMPP gave the best performance (minimum plate heights of 38 μm for alkyl benzenes) and exhibited a satisfactory reproducibility in the chromatographic parameters (RSD < 11%). These monolithic columns were also successfully applied to the separation of phenylurea herbicides, proteins and a tryptic digest of β-casein.