Carbon nanotube-based benzyl polymethacrylate composite monolith as a solid phase extraction adsorbent and a stationary phase material for simultaneous extraction and analysis of polycyclic aromatic hydrocarbon in water

Miniaturized liquid chromatography in environmental analysis. A review

The greater and more widespread use of chemicals, either from industry or daily use, is leading to an increase in the discharge of these substances into the environment. Some of these are known to be hazardous to humans and the environment and are regulated, but there is a large and increasing number of substances which pose a potential risk even at low concentration and are not controlled. In this context, new techniques and methodologies are being developed to deal with this concern. Miniaturized liquid chromatography (LC) emerges as a greener and more sensitive alternative to conventional LC. Furthermore, advances in instrument miniaturization have made possible the development of portable LC instrumentation which may become a promising tool for in-situ monitoring. This work reviews the environmental applications of miniaturized LC over the last 15 years and discusses the different instrumentation, including off- and on-line pretreatment techniques, chromatographic conditions, and contributions to the environmental knowledge.

Montmorillonite-based polymethacrylate composite monoliths as stationary phase materials for food and pharmaceutical analysis in capillary liquid and gas chromatography

This work relates to the preparation of novel and promising stationary phases containing inorganic-organic composites for capillary liquid and gas chromatography. A naturally occurring montmorillonite was introduced to polymethacrylate monoliths, then used under different conditions of GC and HPLC at the same time. The performance of the columns was evaluated for the separation of alkane and alkylbenzene series in GC and capillary HPLC, respectively. While the bare monoliths failed to separate the model analytes, montmorillonite-based polymethacrylate allowed a full separation of the mixtures with R_s≥1.42. The columns were applied for the determination of myrcene and limonene isomers in the peel extracts of some fruits using GC, and for the analysis of active ingredients including aspirin, vitamin-C, caffeine, and ibuprofen extracted from common drugs using capillary HPLC. In GC, fast separation was achieved in 1.0 min with R_s of 6.53. The columns exhibited the best efficiency for myrcene with 20,900 plates/m. Using the capillary HPLC columns, the active ingredients were resolved in 10 min with R_s≥5.72. The efficiency values located between 12,800-21,700 plates/m in all cases. The developed methods were found to be linear in the range of 0.10-10.0 and 0.20-180 μg/mL for GC and HPLC, respectively. In comparison with commercial columns, the results in GC methods reveal that, despite their much shorter length, the prepared columns proved a faster separation with higher efficiency and comparable detection limits and chromatographic resolution. The prepared HPLC capillaries exposed lower run times and detection limits with comparable efficiency and resolution, and consume fewer samples and mobile phase solvents. The results demonstrate that the montmorillonite-based polymethacrylate composites are applicable as stationary phases for routine analysis and quality control of important fields such as food and pharmaceutical samples.

Naturally Occurring Montmorillonite-Based Polymer Monolith Composites as Stationary Phases for Capillary Liquid and Gas Chromatography

This work is associated with the preparation of capillary chromatographic columns containing inorganic-organic composites comprised of naturally occurring montmorillonite (MMT) clay mineral and polymethacrylate monolithic material. The prepared composites combine the best qualities of both constituents, offering desirable properties for use under the disparate conditions of both GC and HPLC at the same time. The stationary phases were investigated by scanning electron microscopy (SEM), the specific surface area, and thermogravimetric analysis (TGA) and examined in terms of various conditions utilized for GC and HPLC methods. The prepared columns demonstrated an excellent permeability and stability against common chromatographic conditions, such as the eluent type, flow rate, pressure, and temperature. The results confirmed that the addition of small amounts of MMT into the monolith induced significant improvement in the specific surface area, which contributed to the formation of more active sites and enhanced the retention of analytes. The registered column backpressures did not exceed 980 kPa and 16,500 kPa for the prepared GC and HPLC columns, respectively. The prepared columns were subjected to the separation of various interesting compounds possessing different chemistries and polarities, including alkanes, alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), alcohols, ketones, phenols, some common organic solvents, and isomeric mixtures. Under the optimal conditions, the efficiency of the columns fell between 4900–38,500 plates m−1 for GC and 3400–58,800 plates m−1 for capillary HPLC applications. In all cases, the measured chromatographic resolution was more than 1.38, with excellent an peak symmetry and low tailing factors. In comparison with the most commonly used commercial columns, the polysiloxane open tubular column for GC and silica-based C18 packed column for HPLC, the prepared GC columns demonstrated a faster separation with a higher efficiency, comparable resolution and tailing factors, and lower consumption of carrier gas. Regarding the capillary columns prepared for HPLC, the chromatographic experiments exposed a much lower run time with a comparable efficiency and resolution and drastically lower consumption of mobile phase solvents and samples. The results demonstrate that the MMT-based polymethacrylate monolith composites are applicable as novel and promising separation media for analyzing various mixtures of interest in different fields, such as petrochemical and environmental samples.

Determination of polycyclic aromatic hydrocarbons in surface waters by high performance liquid chromatography previous to preconcentration through solid-phase extraction by using polymeric monoliths

A simple, sensitive and reproducible solid-phase extraction method using plastic cartridges containing a monolithic sorbent (m-SPE), coupled to reverse phase liquid chromatography analysis, aiming to determine fifteen polycyclic aromatic hydrocarbons in surface water samples, was developed. The sorbent was easily prepared through a thermal polymerization reaction by using a mixture of n-butyl methacrylate as non-polar monomer and ethylene glycol dimethacrylate as crosslinker contained in a typical Polypropylene syringe cartridge. The effect of different parameters (type of hydrophobic monomer, elution solvent, sample volume, sorbent amount and sorbent load capacity) on the extraction efficiency was optimized. The optimal conditions were achieved by using n-butyl methacrylate as monomer, tetrahydrofurane (THF) as solvent for sorbent cleaning, THF:acetone (1:1) as elution solvent, 25.00 mL of sample volume, 600 µL of the polymerization mixture and 60 µg L^-1 as sample loading capacity. Finally, the sorbent charge capacity, the reusability of the cartridges and the extraction efficiency of the m-SPE monolith, as compared with a typical C8 cartridge, were evaluated. Under the optimized experimental conditions, enrichment factors were between 76 and 103, relative recovery factors from 78 to 103%, accuracy values in the range of 58 to 98%, and inter-batch reproducibility values from between 2 and 10%, were obtained. The limits of detection and quantification were obtained by two different procedures: the signal to noise (S/N) ratios (3 and 10, respectively) and the IUPAC convention. The lowest LOD and LOQ values, obtained with the S/N ratios, were between 0.02 and 1.00 µg L^-1, respectively whereas with the IUPAC convention the values were between 0.07 and 5 µg L^-1. Using this procedure, several PAHs could be detected in the surface water sample taken from a river stream located in La Plata city (Buenos Aires Province, Argentina).

[Fabrication of nanomaterials incorporated polymeric monoliths and application in sample pretreatment]

Polymeric monolithic columns are fabricated by in situ polymerization of the corresponding monomer, crosslinkers, porogenic solvents and radical initiators within a mold. Compared with the conventional packed solid phase extraction adsorbents, polymeric monolithic columns with a continuous porous structure process distinctive advantages of rapid mass transfer and excellent permeability, which facilitates the extraction of trace amounts of the target from the matrix even at high flow velocities. Besides, these materials can be easily fabricated in situ within various cartridges, avoiding a further packing step associated with packed particulate adsorbents. Additionally, the abundant monomer availability, flexible porous structure, and wide applicable pH range make monoliths versatile for use in separation science. Thus, polymeric monolithic columns have been increasingly applied as efficient and promising extraction media for sample pretreatment food, pharmaceutical, biological and environmental analyses. However, these materials usually have the difficulty in morphology control and their interconnected porous micro-globular structure, which may result in low porosity, limited specific surface area and poor efficiency. In addition, polymeric monoliths suffer from the swelling in organic solvents, thus decreasing the service life and precision while increasing the cost consumption. Recently, the development of nanomaterial-incorporated polymeric monoliths with an improved ordered structure, enhanced adsorption efficiency and outstanding selectivity has attracted considerable attention. Nanoparticles are considered as particulates within the size range of 1-100 nm in at least one dimension, which endows them with unique optical, electrical and magnetic properties. These materials have a large surface area, excellent thermal and chemical stabilities, remarkable versatility, as well as a wide variety of active functional groups on their surface. With the aim of exploiting these advantages, researchers have shown great interest in applying nanomaterial-incorporated polymeric monoliths to separation science. Accordingly, significant progress has been achieved in this field. Nanomaterials can be entrapped via the direct synthesis of a polymerization solution that contains well dispersed nanomaterials in porogens. In addition, nanoparticles can be incorporated into the monolithic matrix by copolymerization and post-polymerization modification via specific interactions. Therefore, nanomaterial-incorporated polymeric monoliths combined the different shapes, chemical properties, and physical properties of the polymers with those of the nanoparticles. The presence of nanoparticles can improve the structural rigidity as well as the thermal and chemical stabilities of monolithic adsorbents. Besides, nanoparticles are capable of increasing the specific surface area and providing multiple active sites, which leads to enhanced extraction performance and selectivity of polymeric monolithic materials. In recent years, diverse types of nanomaterials, such as carbonaceous nanoparticles, metallic materials and metal oxides, metal-organic frameworks, covalent organic frameworks and inorganic nanoparticles have been extensively explored as hybrid adsorbents in the modes of solid phase extraction, solid phase microextraction, stir bar sorption extraction and on-line solid phase extraction. This review specifically summarizes the fabrication methods for nanomaterial incorporated polymeric monoliths and their application to the field of sample pretreatment. The existing challenges and future possible perspectives in the field are also discussed.

A thin-layer solid-phase extraction-liquid film elution technique used for the enrichment of polycyclic aromatic hydrocarbons in water

In this article, we propose a novel microsolid-phase extraction and elution technique, which we called the thin-layer solid-phase extraction-liquid film elution technique. The thin-layer solid-phase extraction phase is an octadecylsilylated sol gel- coated porous silica thin film prepared on the outer wall of a test tube, which has a larger surface area for the extraction of the target compounds compared to a conventional solid-phase microextraction phase. After optimization of the extraction procedure for five types of polycyclic aromatic hydrocarbons, the liquid film elution technique was investigated. Liquid film elution is an elution technique wherein the compounds extracted into the thin-layer solid-phase extraction phase are eluted using a small volume of solvent film formed around the extraction phase. The results show that the elution can be carried out using 150 μL of eluent. Enrichment factors between 20 and 34 were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings in 10 mL aliquots of aqueous samples. Finally, recoveries of 85-112% were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings from spiked natural water samples using the thin-layer solid-phase extraction-liquid film elution technique.

Trace detection of polycyclic aromatic hydrocarbons in environmental waters by SERS

Polycyclic aromatic hydrocarbons (PAHs) are among the most hazardous pollutants and have attracted significant attention in the last decades. Up to now, rapid and on-site trace detection of PAHs remains a challenging issue. Here, taking advantage of the high sensitivity and reliable qualification of Surface-enhanced Raman Spectroscopy (SERS), we firstly carried out trace analyses of 16 typical PAHs in water at concentrations as low as 100-0.1 μg/L, depending on the number of aromatic rings of the molecule. Furthermore, owing to the simplicity of the liquid-liquid extraction (LLE) step, the sensitivity was further improved 2-3 orders of magnitude, and the lowest detectable concentrations were 100, 50, and 5 ng/L for anthracene, pyrene, and benzo[a]pyrene (the three PAHs typically found in heavily polluted waters), respectively. The LLE-SERS approach was successfully applied to the qualitative and quantitative analyses of different (ocean and coast) water samples being spiked by these three PAHs, which showed great promise as a trace detection tool of PAHs under water environments having different contaminant matrices.

Determination of Monoaromatic Hydrocarbons in Water Samples by Nano-Liquid Chromatography using a Composite Carbon Nanotubes- Lauryl Polymethacrylate Capillary Monolithic Column

Background:

This work reports a green analytical method for the determination of organic environmental pollutants using nano-liquid chromatography with a self-made column for rapid, sensitive, inexpensive and efficient analysis of BTX pollutants in water. The applications of monolithic nanoscale columns for quantitative analysis of environmental real samples are very limited in the literature.

Methods:

A capillary column containing a composite of multi-walled carbon nanotubes incorporated into a lauryl methacrylate-co-ethylene dimethacrylate porous monolithic polymer was fabricated for the determination of BTX pollutants in real water samples.

Results:

Baseline separation was accomplished at 0.4 µL/min flow rate with UV-detection set at 208 nm. Under the optimum conditions, the calibration curves were validated over the range of 1.0-500 µg/L with R2 more than 0.9992. The detection limits of benzene, toluene, o-xylene and m/p-xylene were 0.25, 0.05, 0.075 and 0.05 µg/L, respectively. After a simple extraction process with a theoretical preconcentration factor equal to 200, the recovery values in Milli-Q, tap and sea water samples were found to be ranged from 84.85 to 97.84% with %RSD less than 7.5. Furthermore, we reported a comparison between our prepared composite column with a commercial C18 silica based column which is the most used in such analytical field. Each column demonstrated its advantages from different analytical aspects.

Conclusion:

The application of monolithic columns and nano-scale LC for routine analysis of environmental samples is very promising as the use of monolithic capillary columns offers several advantages over conventional scale particulate packed columns.

The determination of pesticides in tea samples followed by magnetic multiwalled carbon nanotube-based magnetic solid-phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry

A simple and efficient method regarding ultrasound-assisted extraction combined with magnetic solid-phase extraction (UA-MSPE) by UHPLC-MS/MS was set up for the determination of three pesticides in tea leaf samples.

Micro-solid phase extraction of some polycyclic aromatic hydrocarbons from environmental water samples using magnetic β-cyclodextrin-carbon nano-tube composite as a sorbent

Previous studies have demonstrated the excellent capability of the cyclodextrins in pre-concentration of the organic pollutants from the aqueous solutions. In this work, β-cyclodextrin- multiwalled carbon nano-tube composite was produced from the reaction of oxidized carbon nano-tube with cyclodextrin in the presence of the hydrazine hydrate, and subsequently attaching this composite to the iron oxide nano-particles. Prepared magnetic nano-composite was characterized by the attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), the thermogravimetric analysis (TGA), the field emission scanning electron microscopy (FESEM), and the X-ray diffraction (XRD). This composite was applied to extract seven polycyclic aromatic hydrocarbons (PAHs) from the environmental water samples as follows: naphthalene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene and benzo[a]pyrene. Analytes analysis was performed using the gas chromatography (GC) followed by the flame ionization detection (FID), and the predominant parameters influencing the extraction efficiency were investigated thoroughly. Under the optimized extraction conditions, the enrichment factor (EF) was ranging from 41.3 to 49.3 (EF_max = 50.0), and a suitable linearity was obtained (R² = 0.992-0.997) within the range of 2.0-1000 ng/mL. The limits of the quantification and detection were 2.0-10.0 and 0.6-3.0 ng/mL, respectively. Finally, the synthesized magnetic sorbent and method were successfully utilized for the analysis of rain, well and agricultural water samples. The relative recoveries were ranging from 75.3-107.0% with an acceptable precision (5.5-8.3%) for PAHs extraction.

Fabric-phase sorptive extraction coupled with ion mobility spectrometry for on-site rapid detection of PAHs in aquatic environment

The contamination of water is a high risk to human health, so there is an urgent need to rapidly detect water pollution in the field. Ion mobility spectrometry (IMS) is suitable for on-site analysis with the merit of rapid analysis and compact size. In this study, we developed a new method which coupled fabric phase sorptive extraction (FPSE) with IMS for rapid detection of polycyclic aromatic hydrocarbons (PAHs) in water present in the field. Polydimethylsiloxane (PDMS) was coated on the glass fiber cloth through a sol-gel reaction. After extracting the PAHs in water, the fabric coated PDMS could be directly put into the inlet of IMS instrument for thermal desorption. The PAHs were analyzed by the IMS instrument operated in the positive ion mode with a corona discharge (CD) ionization source. The primary parameters affecting extraction efficiency such as extraction time, extraction temperature, and ionic strength were investigated and optimized by using phenanthrene (Phe), benzo[a]anthracene (BaA) and benzo[a]pyrene (BaP) as model compounds. Under the optimal conditions, the FPSE-IMS detection limits were 5 ng ml^-1,8 ng ml^-1 and 10 ng ml^-1 respectively. Satisfactory recoveries were obtained in the range from 80.5% to 100.5% by testing the spiked real water samples and validated by the standard method（HJ487-2009）. Based on the results, the method of FPSE-IMS could be feasibly applied for monitoring the water quality on-site and providing early warning in the field.