3D-printed stereolithographic fluidic devices for automatic nonsupported microelectromembrane extraction and clean-up of wastewater samples.

BACKGROUND: There is a quest of novel functional and reliable platforms for enhancing the efficiency of microextraction approaches in troublesome matrices, such as industrial wastewaters. 3D printing has been proven superb in the analytical field to act as the springboard of microscale extraction approaches. RESULTS: In this work, low-force stereolithography (SL) was exploited for 3D printing and prototyping bespoke fluidic devices for accommodating nonsupported microelectromembrane extraction (µEME). The analytical performance of 3D-printed µEME devices with distinct cross-sections, including square, circle, and obround, and various channel dimensions was explored against that of commonly used circular polytetrafluoroethylene (PTFE) tubing in flow injection systems. A computer-controlled millifluidic system was harnessed for the (i) automatic liquid-handling of minute volumes of donor, acceptor, and organic phases at the low µL level that spanned from 3 to 44 µL in this work, (ii) formation of three-phase µEME, (iii) in-line extraction, (iv) flow-through optical detection of the acceptor phase, and (v) solvent removal and regeneration of the µEME device and fluidic lines. Using methylene blue (MB) as a model analyte, experimental results evinced that the 3D-printed channels with an obround cross-section (2.5 mm × 2.5 mm) were the most efficient in terms of absolute extraction recovery (59%), as compared to PTFE tubing of 2.5 mm inner diameter (27%). This is attributed to the distinctive convex interface of the organic phase (1-octanol), with a more pronounced laminar pattern, in 3D-printed SL methacrylate-based fluidic channels against that of PTFE tubing on account of the enhanced 1-octanol wettability and lower contact angles for the 3D-printed devices. The devices with obround channels were leveraged for the automatic µEME and in-line clean-up of MB in high matrix textile dyeing wastewater samples with relative recoveries ≥81%, RSD% ≤ 17.1% and LOD of 1.3 mg L-1. The 3D-printed nonsupported µEME device was proven superb for the analysis of wastewater samples with an elevated ionic strength (0.7 mol L-1 NaCl, 5000 mg L-1 Na2CO3, and 0.013 mol L-1 NaOH) with recorded electric currents below 12 µA. NOVELTY: The coupling of 3D printing with nonsupported µEME in automatic flow-based systems is herein proposed for the first time and demonstrated for the clean-up of troublesome samples, such as wastewaters.

Biomimetic Dispersive Solid-Phase Microextraction: A Novel Concept for High-Throughput Estimation of Human Oral Absorption of Organic Compounds.

There is a quest for a novel in vitro analytical methodology that is properly validated for the prediction of human oral absorption and bioaccumulation of organic compounds with no need of animal models. The traditional log P parameter might not serve to predict bioparameters accurately inasmuch as it merely accounts for the hydrophobicity of the compound, but the actual interaction with the components of eukaryotic cells is neglected. This contribution proposes for the first time a novel biomimetic microextraction approach capitalized on immobilized phosphatidylcholine as a plasma membrane surrogate onto organic polymeric sorptive phases for the estimation of human intestinal effective permeability of a number of pharmaceuticals that are also deemed contaminants of emerging concern in environmental settings. A comprehensive exploration of the conformation of the lipid structure onto the surfaces is undertaken so as to discriminate the generation of either lipid monolayers or bilayers or the attachment of lipid nanovesicles. The experimentally obtained biomimetic extraction data is proven to be a superb parameter against other molecular descriptors for the development of reliable prediction models of human jejunum permeability with R2 = 0.76, but the incorporation of log D and the number of aromatic rings in multiple linear regression equations enabled improved correlations up to R2 = 0.88. This work is expected to open new avenues for expeditious in vitro screening methods for oral absorption of organic contaminants of emerging concern in human exposomics.

3D-printed chemiluminescence flow cells with customized cross-section geometry for enhanced analytical performance.

Low force stereolithography is exploited for the first time for one-step facile fabrication of chemiluminescence (CL) flow-through cells that bear unrivalled features as compared to those available through milling or blowing procedures or alternative 3D printing technologies. A variety of bespoke cross-section geometries with polyhedral features (namely, triangular, square, and five-side polygon) as well as semicircular cross-section are herein critically evaluated in terms of analytical performance against the standardcircular cross-section in a flat spirally-shape format. The idea behind is to maximize capture of elicited light by the new designs while leveraging 3D printing further for fabrication of (i) customized gaskets that enable reliable attaching of the active mixing zone of the CL cell to the detection window, (ii) in-line 3D-printed serpentine reactors, and (iii) flow confluences with tailorable shapes for enhancing mixing of samples with CL reagents. Up to twenty transparent functional cells were simultaneously fabricated without inner supports following post-curing and surface treatment protocols lasting less than 5 h. In fact, previous attempts to print spirally-shaped cells in one-step by resorting to less cost effective photopolymer inkjet printing technologies were unsuccessful because of the requirement of lengthy procedures (>15 days) for quantitative removal of the support material. By exploiting the phthalazinedione-hydrogen peroxide chemistry as a model reaction, the five-side irregular pentagon cell exhibited superior analytical figures of merit in terms of LOD, dynamic range and intermediate precision as compared to alternative designs. Computational fluid dynamic simulations for mapping velocities at the entry region of the spiral cell corroborated the fact that the 5-side polygon cross-section flow-cell with Y-type confluence permitted the most efficient mixing of reagents and sample while enabling larger flow velocities near the inlet that contribute to a more efficient capture of the photons from the flash-type reaction. The applicability of the 3D-printed 5-side polygon CL cell for automatic determination of hydrogen peroxide using a computerized hybrid flow system was demonstrated for the analysis of high matrix samples, viz., seawater and saliva, with relative recoveries ranging from 83 to 103%.

Skin absorption of inorganic nanoparticles and their toxicity: A review.

The role of inorganic nanoparticles in our society is increasing every day, from its use in sunscreens to their introduction in analytical laboratories, pharmacy, medicine, agricultural and other uses. Therefore, in order to establish precautions as well as correct handling of this type of material by operators, it is important to determine the ability of these compounds to travel through the different layers of the skin and to study their possible toxicological effects. In this sense, several authors have studied the ability of inorganic nanoparticles to penetrate the skin barrier by diverse methodologies in in vivo and in vitro modes. In the first case, most of the studies have been performed with animal skins that can imitate the human one (porcine, mouse and guinea pigs, among others), although human skin from surgery have been also explored. However, the use of animals is a common model that should be avoided in the following years due to ethical issues. In this sense, the use of in vitro methodologies is also usually selected to study the dermal absorption of nanoparticles through the skin. Nevertheless, most of the studies are performed with authentic animal skins, instead of the use of synthetic skins that imitate the permeability of our skin system, which has been scarcely studied. In addition, most of the literature is focused in achieving high-transdermal uptake to use nanoparticles (not only inorganic) as carriers for drugs, but little efforts have been done in the study of their inherent percutaneous absorption and toxicity. For these reasons, this review covers the current state-of-the-art of dermal absorption of inorganic nanoparticles in skin and their possible toxicity taking into account that people can be in contact with these nanomaterials in daily life, work or other places. In this sense, the observed results showed that the nanoparticles rarely reach the blood circulatory system, and no big toxicological effects were commonly found when in vivo and actual skin was used. In addition, similar results were found when synthetic skins were used, demonstrating the possibility of avoiding animals in these studies. In any case, more studies covering the dermal absorption of nanoparticles should be performed to have a better understanding of how nanoparticles can affect our health.

Reticular framework materials in miniaturized and emerging formats in analytical chemistry.

In recent years, important efforts have been put into miniaturization, coming on the scene formats such as chips, 3D-printed objects and paper-based devices. These systems have been applied to biological and chemical processes taking profit of their advantages such as waste reduction, low cost, portability, etc. Despite their benefits, there is a need to continue developing easier-to-use devices with enhanced performance addressed to face the current analytical challenges. In this sense, reticular porous materials such as metal- (MOFs) and covalent- (COFs) organic frameworks with unique features including tailorable porous architectures and tunable chemistry have attracted a lot of attention in various fields. Nevertheless, the combination of these materials with miniaturized and emerging formats has been scarcely investigated. This review is intended to bridge this gap and highlight the recent contributions of these materials in these analytical formats. Thus, this work aims to provide a comprehensive review of the field, highlighting incorporation strategies into the functional supports available to date, and the applications of the resulting systems in both off-site laboratory studies (mostly dedicated to (micro)extraction purposes) and on-site analysis. Finally, a discussion of challenges and future directions in this field is also given.

3D printed spinning cup-shaped device for immunoaffinity solid-phase extraction of diclofenac in wastewaters.

This article reports current research efforts towards designing bespoke microscale extraction approaches exploiting the versatility of 3D printing for fast prototyping of novel geometries of sorptive devices. This is demonstrated via the so-called 3D printed spinning cup-based platform for immunoextraction of emerging contaminants using diclofenac as a model analyte. A new format of rotating cylindrical scaffold (containing a semispherical upper cavity) with enhanced coverage of biorecognition elements, and providing elevated enhancement factors with no need of eluate processing as compared with other microextraction stirring units is proposed. Two distinct synthetic routes capitalized upon modification of the acrylate surface of stereolithographic 3D printed parts with hexamethylenediamine or branched polyethyleneimine chemistries were assayed for covalent binding of monoclonal diclofenac antibody.Under the optimized experimental conditions, a LOD of 108 ng L-1 diclofenac, dynamic linear range of 0.4-1,500 µg L-1, and enrichment factors > 83 (for near-exhaustive extraction) were obtained using liquid chromatography coupled with UV-Vis detection. The feasibility of the antibody-laden device for handling of complex samples was demonstrated with the analysis of raw influent wastewaters with relative recoveries ranging from 102 to 109%. By exploiting stereolithographic 3D printing, up to 36 midget devices were fabricated in a single run with an estimated cost of mere 0.68 euros per 3D print and up to 16 €/device after the incorporation of the monoclonal antibody.

An automatic flow-through system for exploration of the human bioaccessibility of endocrine disrupting compounds from microplastics.

This article reports on the first attempt towards investigating the leaching rates in the human gastrointestinal (GI) tract of plastic-borne contaminants that can be ingested accidentally using physiologically relevant body fluids. Oral bioaccessibility under fasted and fed states was determined in dynamic mode exploiting an automatic flow setup. The flow system is able to mimic the fast uptake of the released species from the polymeric matrix by absorption in the human digestive system by the in-line removal of the leached species. Complex GI extractants based on the Unified Bioaccessibility Method (UBM, fasted state) and Versantvoort test (fed-state) were brought through a microplastic-loaded metal microcolumn for semi-continuous leaching of plasticizers (phthalic acid ester congeners) and monomer/antioxidant species (bisphenol A, BPA) followed by in-line solid-phase extraction and clean-up of GI extracts prior to liquid chromatography analysis. The temporal extraction profiles were fitted to a first-order kinetic model for the estimation of maximum bioaccessibility pools and apparent leaching rates. Among all studied contaminants, only BPA, dimethylphthalate and diethylphthalate were appreciably released under dynamic GI conditions from high-density polyethylene pellets (average size of 110 µm), with average bioaccessibility values spanning from 51 to 84% and 48 to 87% for UBM and Versantvoort methods, respectively. No statistically significant differences in oral bioaccessibility pools were found under fed- and fasted-state dynamic extractions. The apparent kinetic constants under the fed state were greater by ≥30% as a consequence of the effect of the larger amounts of bile salts and digestive enzymes in the Versantvoort test on the leaching rates. The estimated average daily intake, in which bioaccessibility data are contemplated, indicated that plastic materials exceeding 0.3% (w/w) BPA might pose real risks to human health.

Determination of antibiotics in meat samples using analytical methodologies: A review.

Antibiotics are widely used to prevent or treat some diseases in human and veterinary medicine and also as animal growth promoters. The presence of these compounds in foods derived from food-producing animals can be a risk for human health. Consequently, regulatory agencies have set maximum residue limits for antibiotics in food samples. Therefore, the development of novel methodologies for its determination in food samples is required. Specifically, the analysis and quantification of these substances in meat tissues is a challenge for the analytical chemistry research community. This is due to the complexity of the matrix and the low detection limits required by the regulatory agencies. In this sense, a comprehensive review on the development of new sample preparation treatments involving extraction, cleanup, and enrichment steps of antibiotics in meat samples in combination with sensitive and sophisticated determination techniques that have been carry out in the last years is necessary. Therefore, the aim of this work is to summarize the published methodologies for the determination of antibiotics from 2016 until the beginning of the second semester of 2020. The first part of this review includes an introduction about antibiotic families, followed by sample preparation and determination techniques applied to the different families. Finally, a detailed discussion of the current trends and the future possible perspectives in this field are also included.

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.

Hybrid monoliths with metal-organic frameworks in spin columns for extraction of non-steroidal drugs prior to their quantitation by reversed-phase HPLC.

A (glycidyl methacrylate)-co-(ethylene glycol dimethacrylate) polymer (poly(GMA-co-EDMA)) was functionalized with metal-organic frameworks (MOF) and used as a sorbent for solid-phase extraction (SPE). The polymeric sorbent was prepared in-situ by photopolymerization in a previously wall-modified spin column, and then modified with an amino-modified MOF of type NH2-MIL-101(Cr). The sorbents were used for the extraction of nonsteroidal anti-inflammatory drugs (NSAIDs) from human urine samples. The sorbent was compared with the parent monolith and embedded approach, where the MOF particles are admixed in the polymerization mixture before the in-situ polymerization in the modified spin column. SPE is performed by percolating the sample solutions in a centrifuge, which streamlines the SPE steps. The hybrid composites were characterized by scanning electron microscopy and nitrogen intrusion porosimetry. Three NSAIDs (ketoprofen, flurbiprofen, and ibuprofen) were tested. They were eluted from the sorbent with acidified water-acetonitrile mixtures and subsequently analyzed by reversed-phase HPLC with UV detection. The detection limits varied in the range from 0.1 to 7 µg·L-1, and the precisions (relative standard deviation) were <14% in all the cases. The recoveries were between 71.0 and 78.0% in spiked urine samples. Graphical abstractA hybrid monolith modified with amino-modified MOF [named NH2-MIL-101(Cr)] in wall-modified spin columns was prepared. The resulting micro-extraction device was applied to the extraction and preconcentration of non-steroidal anti-inflammatory drugs.

Current trends in affinity-based monoliths in microextraction approaches: A review.

This article reviews the research contributions along the past five years concerning to monolithic materials for the development of affinity-based sorbents in the field of microextraction techniques. The first part of this paper includes an introduction regarding monolithic affinity media and information of different binding agents (such as immunoglobulin-binding proteins, enzymes, lectins, antibodies, aptamers, dyes and immobilized metal ions and nanoparticles, among others) that can act as affinity ligands. Then, the preparation of monoliths and ligand immobilization strategies as well as the different available formats (syringes, pipette tips, spin columns, capillaries, disks and microfluidic devices) for their use in micro-solid phase extraction are mentioned. On the basis of the binding agents used to prepare affinity monolithic-based sorbents, the last part of manuscript includes several analytical and preparative applications of these monoliths for sample preparation covering different fields (analytical chemistry, biotechnology, proteomics, etc.). Current trends and possible future directions of these affinity-based sorbents in sample preparation are also given.

Incorporation of metal-organic framework amino-modified MIL-101 into glycidyl methacrylate monoliths for nano LC separation.

Metal-organic frameworks consisting of amino-modified MIL-101(M: Cr, Al, and Fe) crystals have been synthesized and subsequently incorporated to glycidyl methacrylate monoliths to develop novel stationary phases for nano-liquid chromatography. Two incorporation approaches of these materials in monoliths were explored. The metal-organic framework materials were firstly attached to the pore surface through reaction of epoxy groups present in the parent glycidyl methacrylate-based monolith. Alternatively, NH2 -MIL-101(M) were admixed in the polymerization mixture. Using short time UV-initiated polymerization, monolithic beds with homogenously dispersed metal-organic frameworks were obtained. The chromatographic performance of embedded UV-initiated composites was demonstrated with separations of polycyclic aromatic hydrocarbons and non-steroidal anti-inflammatory drugs as test solutes. In particular, the incorporation of the NH2 -MIL-101(Al) into the organic polymer monoliths led to an increase in the retention of all the analytes compared to the parent monolith. The hybrid monolithic columns also exhibited satisfactory run-to-run and column-to-column reproducibility.

Zwitterionic codeine-derived methacrylate monoliths for enantioselective capillary electrochromatography of chiral acids and chiral bases.

Thiol-ene click reaction of N-acetyl-L-cysteine methyl ester to codeine, followed by reaction with allyl isocyanate and hydrolysis to the corresponding zwitterionic chiral selector and its subsequent bonding to the surface of a methacrylate monolith provided a new chiral capillary column for enantiomer separation of chiral acids and chiral bases. First, the epoxy groups of a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith were converted into amine residues, followed by reaction with allylglycidyl ether. In this way, a spacer arm was bonded to the surface before coating and cross-linking poly(3-mercaptopropyl methylsiloxane) (PMPMS) via radical addition (thiol-ene click reaction) to the surface. In order to improve the performance of the monolithic chiral stationary phase, thio ether and residual thiol groups were oxidized to sulfonyl and sulphonate groups, respectively. This novel chiral stationary phase (CSP) was evaluated by capillary electrochromatography (CEC) using two chiral model compounds, namely N-3,5-dinitrobenzoyl-R,S-leucine (retained by anion-exchange mechanism) and mefloquine (by cation-exchange process). The ion-exchange retention mechanism on the CSP was characterized for these two counterionic model solutes by varying the mobile phase composition, including the nature of solvents, the concentration of counter-ions and co-ions, and the acid-to-base ratio. A series of chiral ß-blockers and amino acid derivatives was used to further check the performance of the modified monolith under the optimal conditions. Several enantiomers were baseline resolved with reasonable peak efficiencies (up to 60,000 theoretical plates per meter for the second eluted enantiomer).

Photografted methacrylate-based monolithic columns coated with cellulose tris(3,5-dimethylphenylcarbamate) for chiral separation in CEC.

A chiral capillary monolithic column for enantiomer separation in capillary electrochromatography was prepared by coating cellulose tris(3,5-dimethylphenylcarbamate) on porous glycidyl methacrylate-co-ethylene dimethacrylate monolith in capillary format grafted with chains of [2(methacryloyloxy)ethyl] trimethylammonium chloride. The surface modification of the monolith by the photografting of [2(methacryloyloxy)ethyl] trimethylammonium chloride monomer as well as the coating conditions of cellulose tris(3,5-dimethylphenylcarbamate) onto the grafted monolithic scaffold were optimized to obtain a stable and reproducible chiral stationary phase for capillary electrochromatography. The effect of organic modifier (acetonitrile) in aqueous mobile phase for the enantiomer separation by capillary electrochromatography was also investigated. Several pairs of enantiomers including acidic, neutral, and basic analytes were tested and most of them were partially or completely resolved under aqueous mobile phases. The prepared monolithic chiral stationary phases exhibited a good stability, repeatability, and column-to-column reproducibility, with relative standard deviations below 11% in the studied electrochromatographic parameters.

Incorporation of zeolitic imidazolate framework (ZIF-8)-derived nanoporous carbons in methacrylate polymeric monoliths for capillary electrochromatography.

A series of metal organic frameworks-derived nanoporous carbons originating from zeolitic imidazolate framework-8 (ZIF-8) crystals as precursors have been prepared via varying the preparation conditions. The ZIF-8-derived carbons were subsequently admixed in the methacrylate monomers containing polymerization mixtures and polymerized to obtain monolithic columns for capillary electrochromatography (CEC). The effect of particle size and content of the ZIF-8-derived carbon materials in the polymerization mixture on the performance of the hybrid monolithic columns was investigated in detail. The resulting composites were characterized using scanning electron microscopy. Using short time UV-initiated polymerization, monolithic beds with homogenously dispersed ZIF-8-derived carbons were obtained. The chromatographic performance of these composites was demonstrated with separations of polycyclic aromatic hydrocarbons and non-steroidal anti-inflammatory drugs as test solutes. The incorporation of the ZIF-8-derived carbons into the organic polymer monoliths led to an increase in the retention of all the analytes compared to the parent monolith. Finally, the hybrid monolithic columns exhibited satisfactory run-to-run and batch-to-batch reproducibility.

Application of Organic Monolithic Materials to Enantioseparation in Capillary Separation Techniques.

This review article is primarily focused on the state-of-the-art of enantioseparations on organic monolithic materials. The article gives an overview of the chiral stationary phases and its application in capillary electrochromatography (CEC), and capillary- and nano-liquid chromatography (cLC and nLC). Since thousands of publications have been emerged from 2000's and citing all these papers would extend the scope of this review; then, recent developments from last 10 years (2006 to 2016) will be mentioned. Mostly, stationary phases based on copolymers obtained from chiral functional monomers and surface modifications of organic monoliths with chiral ligands will be discussed. The effective application of these chiral separation methodologies in several analysis areas will be also included.

Phosphatidylcholine covalently linked to a methacrylate-based monolith as a biomimetic stationary phase for capillary liquid chromatography.

In this study a strategy to immobilize phospholipids onto a polymer-based stationary phase is described. Methacrylate-based monoliths in capillary format (150×0.1mm) were modified by soybean phosphatidylcholine through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide coupling to obtain stationary phases suitable to mimic cell surface membranes. The covalent coupling reaction involves the phosphate group in phospholipids; therefore, the described methodology is suitable for all types of phospholipids. Immobilization of soy bean phosphatidylcholine on the monolith was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry of the fatty alcohol profile, generated upon reductive cleavage of the fatty acyl side chains of the phospholipid on the monolith surface with lithium aluminium hydride. The prepared stationary phases were evaluated through studies on the retention of low-molar mass model analytes including neutral, acidic, and basic compounds. Liquid chromatographic studies confirmed predominant hydrophobic interactions between the analytes and the synthesized stationary phase; however, electrostatic interactions contributed to the retention as well. The synthesized columns showed high stability even with fully aqueous mobile phases such as Dulbecco's phosphate-buffered saline solution.

Hybrid methacrylate monolithic columns containing magnetic nanoparticles for capillary electrochromatography.

Vinylized iron oxide magnetic nanoparticles (VMNPs) were incorporated into polymethacrylate monolithic columns to develop novel stationary phases with enhanced separation performance. The VMNPs were dispersed in a polymerization mixture containing gycidyl methacrylate and ethylene glycol dimethacrylate as monomers, cyclohexanol and 1-dodecanol as porogens and azobisisobutyronitrile as initiator. The stability of the VMNPs in the polymerization mixture was investigated at several VMNP contents. Using short UV-polymerization times, polymeric beds with homogenously dispersed VMNPs were obtained. The novel stationary phases were characterized by scanning electron microscopy. The chromatographic performance of these hybrid monoliths was evaluated using alkyl benzenes and organophosphorous pesticides as test solutes. Using capillary electrochromatography, efficiencies up to 130,000 plates/m were achieved. The increase of the specific surface area of hybrid monoliths led to an increase in the retention of all the test analytes, and an enhancement of efficiency. The resulting hybrid monolithic columns exhibited satisfactory column to-column and batch-to-batch reproducibilities with RSDs values below 6%.

Sensitive determination of parabens in human urine and serum using methacrylate monoliths and reversed-phase capillary liquid chromatography-mass spectrometry.

A method for the determination of parabens in human urine and serum by capillary liquid chromatography (cLC) with UV-Vis and mass spectrometry (MS) detection using methacrylate ester-based monolithic columns has been developed. The influence of composition of polymerization mixture was studied. The optimum monolith was obtained with butyl methacrylate monomer at 60/40% (wt/wt) butyl methacrylate/ethylene dimethacrylate ratio and 50wt% porogens (composed of 36wt% of 1,4-butanediol, 54wt% 1-propanol and 10wt% water). Baseline resolution of analytes was achieved through a mobile phase of acetonitrile/water in gradient elution mode. Additionally, dispersive liquid-liquid microextraction (DLLME) was combined with both cLC-UV-Vis and cLC-MS to achieve the determination of parabens in human urine and serum samples with very low limits of detection. Satisfactory intra- and inter-day repeatabilities were obtained in UV-Vis and MS detection, although the latter provided lower detection limits (up to 300-fold) than the UV-Vis detection. Recoveries for the target analytes from spiked biological samples ranged from 95.2% to 106.7%. The proposed methodology for the ultra-low determination of parabens in human urine and serum samples is simple and fast, the consumption of reagents is very low, and very small samples can be analyzed.

Evaluation of 2,3-epoxypropyl groups and functionalization yield in glycidyl methacrylate monoliths using gas chromatography.

Poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) is most frequently used as parent monolith to obtain stationary phases with a variety of surface chemistries for liquid chromatography and capillary electrochromatography. Functionalization is performed by opening the accessible 2,3-epoxypropyl groups of the monolith with a suitable reagent. The number of 2,3-epoxypropyl groups which are accessible before and after the functionalization reaction, and the grafting yield, are important parameters, required both to optimize functionalization and to interpret the chromatographic performance of functionalized monoliths. In this work, a method capable of providing this information for parent and functionalized poly(GMA-co-EDMA) monoliths prepared both in silica capillaries and in other supports is proposed. First, sulfuric acid and lithium aluminium hydride (LiAlH4) are sequentially used to release the 2,3-epoxypropyl groups as glycerol, which is subsequently determined by GC. About 6.0mmol of 2,3-epoxypropyl groups per gram of monolith was found in this work for the parent monoliths prepared in silica capillaries using UV-initiation. The monoliths were also functionalized using ammonia (NH3), diethylamine (DEA) and epinephrine, and the amount of residual 2,3-epoxypropyl groups, and hence the functionalization yield, were established by also measuring the GC peak of glycerol. The amounts of 2,3-epoxypropyl groups and the derivatization yields were established with RSDs of 1.7 and 3.4%, respectively. The proposed method was also applied to the characterization of poly(GMA-co-EDMA) monoliths prepared in glass vials. Significant differences with respect to those prepared in 100µm I.D. silica capillaries were evidenced.