Solid-phase Microextraction of Phenol Compounds Using a Fused-Silica Fiber Coated with β-Cyclodextrin-bonded Silica Particles

One-step in-situ growth of histidine-modified ZIF-90 on natural eggshell membrane for efficient extraction of p-nitrophenol and 3-methyl-4-nitrophenol in human urine and environmental water

Monitoring of p-nitrophenol (PNP) and 3-methyl-4-nitrophenol (PNMC) in human urine and environmental water is of great importance for human health assessment and environmental protection, as they are both urinary metabolites of some poisonous pesticides and priority environmental pollutants. However, efficient extraction of trace levels of PNP and PNMC from complex matrices remains challenging. This study presented the synthesis of histidine-modified ZIF-90 on natural eggshell membrane (ESM@His-ZIF-90) via a facile one-step in-situ growth strategy, and its application as an adsorbent for dispersive membrane extraction (DME) of PNP and PNMC in human urine and environmental water. The ESM@His-ZIF-90 exhibited extraordinary extraction efficiency due to the abundant adsorption activity of His-ZIF-90 and the rapid separation of ESM from sample solution. The adsorption behavior of ESM@His-ZIF-90 towards two nitrophenols followed Langmuir isotherm model and pseudo-second-order kinetic model. Notably, the ESM@His-ZIF-90 demonstrated fast adsorption kinetics with adsorption equilibrium achieved in only 10 min. The results of FT-IR, XPS and DFT calculations revealed that the rapid adsorption was attributed to the synergistic effect of π-π EDA, hydrophobic and hydrogen bonding interactions. By coupling ESM@His-ZIF-90-based DME with HPLC-UV, good linearity (R2 ≥ 0.9943) and low limits of detection of 0.25-0.65 μg L-1 were obtained. Finally, the method was successfully applied to the detection of PNP and PNMC in human urine and environmental water, and the method recoveries ranged from 83.0 to 106.1 % with RSDs lower than 7.2 %.

Cyclodextrins as a Key Piece in Nanostructured Materials: Quantitation and Remediation of Pollutants

Separation and pre-concentration of trace pollutants from their matrix by reversible formation of inclusion complexes has turned into a widely studied field, especially for the benefits provided to different areas. Cyclodextrins are non-toxic oligosaccharides that are well known for their host–guest chemistry, low prices, and negligible environmental impact. Therefore, they have been widely used as chiral selectors and delivery systems in the pharmaceutical and food industry over time. However, their use for extraction purposes is hampered by their high solubility in water. This difficulty is being overcome with a variety of investigations in materials science. The setting-up of novel solid sorbents with improved properties thanks to the presence of cyclodextrins at their structure is still an open research area. Some properties they can offer, such as an increased selectivity or a good distribution along the surface of a solid support, which provides better accessibility for guest molecules, are characteristics of great interest. This systematic review reports the most significant uses of cyclodextrins for the adsorption of pollutants in different-origin samples based on the works reported in the literature in the last years. The study has been carried out indistinctly for quantitation and remediation purposes.

Fabrication of a porous β-cyclodextrin-polymer-coated solid-phase microextraction fiber for the simultaneous determination of five contaminants in water using gas chromatography-mass spectrometry

A novel solid-phase microextraction fiber coated with a porous β-cyclodextrin polymer was developed. The porous β-cyclodextrin polymer cross-linked using tetrafluoroterephthalonitrile, possessed well-distributed pores and the largest surface area among current β-cyclodextrin polymers. Scanning electron microscopy revealed that the coating had a continuous wrinkled and folded structure, which guarantees a sufficient loading capacity for contaminants. The properties of the developed fiber were evaluated using headspace solid-phase microextraction of five contaminants as model analytes coupled with gas chromatography-mass spectrometry. Owing to the advantages of a large surface area and three-dimensional cavities, the novel fiber exhibited excellent operational stability and extraction ability. After optimisation of the extraction conditions, including extraction temperature, extraction time, salt effect, and desorption time, validation of the method with water samples achieved good linearity over a wide range (0.01–120 μg L⁻¹) and low detection limits (0.003–1.600 μg L⁻¹). The single-fiber and fiber-to-fiber repeatabilities were 1.7–11.0% and 1.9–11.0%, respectively. The method was applied to the simultaneous analysis of five analytes with satisfactory recoveries (76.6–106.0% for pond water and 89.0–105.9% for rainwater).

A novel solid-phase microextraction fiber coated with a porous β-cyclodextrin polymer was developed.

Preparation of GO-COOH/AuNPs/ZnAPTPP nanocomposites based on the π-π conjugation: Efficient interface for low-potential photoelectrochemical sensing of 4-nitrophenol

The GO-COOH/AuNPs/ZnAPTPP nanocomposites were constructed using zinc monoamino porphyrin (ZnAPTPP) through π-π conjugation with carboxylated graphene oxide (GO-COOH) loaded with Au nanoparticles (AuNPs). Prepared materials were characterized by ¹H NMR spectra, UV-vis absorption spectroscopy and electrochemical impedance spectroscopy. ITO electrode surface was modified with the prepared nanocomposites showed a good photocurrent response when the bias potential, -0.1V was applied. Nanocomposites modified ITO electrode exhibited good photo-response to the 4-nitrophenol (4-NP). ZnAPTPP were excited from HOMO to LUMO under light irradiation, the photoexcited electrons injected into the conduction band of GO-COOH, and then transferred to AuNPs further to the ITO. The presence of GO-COOH and AuNPs improved the separation of photogenerated charges due to their synergetic effect and excellent conductivity. Externally added 4-NP scavenges the photogenerated holes i.e. it acts as a sacrificial electron donor thereby it enhances the photocurrent of the system. Based on this interaction, a novel method for photoelectrochemical detection of 4-NP was developed with a linear range from 0.1 to 15nmol/L (r = 0.996) and detection limit of 0.04nmol/L (S/N = 3). Proposed method is simple and sensitive and this was successfully applied for the quantification 4-NP in river water sample matrices.

Periodic mesoporous organosilica with ionic liquid framework as a novel fiber coating for headspace solid-phase microextraction of polycyclic aromatic hydrocarbons

Periodic mesoporous organosilica based on alkylimidazolium ionic liquid (PMO-IL) was prepared and used as a highly porous fiber coating material for solid-phase microextraction (SPME). The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography-mass spectrometry (GC-MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, stirring rate, and desorption temperature and time. In optimum conditions, the repeatability for one fiber (n=3), expressed as relative standard deviation (R.S.D.%), was between 4.3% and 9.7% for the test compounds. The detection limits for the studied compounds were between 4 and 9 pg mL(-1). The developed method offers the advantage of being simple to use, with shorter analysis time, lower cost of equipment, thermal stability of fiber and high relative recovery in comparison to conventional methods of analysis.

Preparative separation and purification of epigallocatechin gallate from green tea extracts using a silica adsorbent containing β-cyclodextrin

A silica adsorbent containing β-cyclodextrin (β-CD) has been developed and used for the separation and purification of epigallocatechin gallate (EGCG) from the green tea extracts. The batch adsorption experiments demonstrated that, the β-CD bonded silica adsorbent possessed excellent adsorption equilibrium capacity (> 55 mg/g adsorbent) and adsorption ratio (>95%) for EGCG compared to the other tea catechins and caffeine. The excellent adsorption capacity and selectivity for EGCG are attributed to the specific interactions between β-CD and EGCG. The preparative separation and purification performance of EGCG on the β-CD bonded silica column (220 mm L × 15 mm i.d., 40-63 μm) was then evaluated. The column was operated in the polar organic mode using methanol/acetonitrile/acetic acid as the mobile phase and eluted under a three-step gradient elution program. The sample was dissolved in acetonitrile and loaded on a preparative scale of about 0.8 mg/g adsorbent. Under the optimal chromatographic conditions, the target compound, EGCG, being the most retained species, was obtained at a purity of about 90% with a recovery of about 90%. The productivity of EGCG was about 6 mg per injection, which can be further increased by scaling-up the chromatographic system.

Optimization of headspace solid phase microextraction procedure for trace analysis of toluene

This study describes optimization of headspace solid phase microextraction followed by gas chromatography equipped with a flame ionization detector for toluene at trace level in spiked urine. The parameters affecting the extraction and gas chromatographic determination of analytes were studied: extraction time and temperature; desorption time and temperature; addition of NaCl; and pH, volume and agitation of the sample. Optimized headspace extraction was carried out at 30 degrees C for 6 min in the presence of 0.2 g.m(-1)of NaCl in the sample solution. Also, sample volume and sample pH were optimized at 5 ml and 7 (neutral pH), respectively. Desorption of the analytes was carried out at 250 degrees C for 60 s. The optimized procedure was validated with 3 different pools of spiked urine; it showed good reproducibility over 6 consecutive days and 6 within-day experiments. The study also determined the accuracy, linearity and detection limits of this method.

Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO(2)) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO(2) in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO(2) for phenol is 2.4 mg g(-1) with distribution coefficients up to 3.4 x 10(4) mL g(-1); corresponding data for 1-naphthol are 1.5 mg g(-1) and 3 x 10(3) mL g(-1). The distribution coefficient does not change significantly for solution volumes of 0.025-0.5 L and adsorbent mass less than 0.03 g; 1-90 microg analyte can be easily eluted by 1-3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A(540)) and phenol concentration (C) in water was found according to the equation A(540) = (6 +/- 1) x 10(-2) + (0.9 +/- 0.1) C (micromol L(-1)) with a detection range from 1 x 10(-8) mol L(-1) (0.9 microL g(-1)) to 2 x 10(-7) mol L(-1) (19 microL g(-1)), a limit of quantification of 1 microL g(-1) (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 microL g(-1) while the quantification limit is 20 microL g(-1). A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08-3.2 mL g(-1).

Sol–gel coated polydimethylsiloxane/β-cyclodextrin as novel stationary phase for stir bar sorptive extraction and its application to analysis of estrogens and bisphenol A

A sol-gel technique was used for the preparation of a stir bar coated with a composite composed of polydimethysiloxane and beta-cyclodextrin (PDMS/beta-CD). The sol-gel mechanism during coating procedure was discussed and successful binding of beta-CD to the sol-gel network was confirmed by the IR spectra. Scanning electron micrographs of the stir bars revealed a homogeneous surface with a film thickness of 30-150 microm attributing to different coating times. Good thermal stability and solvent-resistance of the stir bar were found thanks to chemical binding formed between the stationary phase and the glass substrate. The PDMS/beta-CD coated stir bar was proved to have better selectivity to polar compounds compared to the PDMS coated stir bar, and higher extraction capacity compared to the corresponding PDMS/beta-CD coated fiber. Methods for the determinations of estrogens in environmental water, bisphenol A in drinking water and in leachate of one-off dishware by the PDMS/beta-CD coated stir bar coupled with high-performance liquid chromatography (HPLC) were developed. The limits of detection were within the range of 0.04-0.11 microg l(-1) for estrogens using UV detection and 8 ngl(-1) for bisphenol A using fluorescence detection. Reproducibility with RSD less than 9.7% for extractions of real water samples at microg l(-1) or ngl(-1) level was obtained.

Preparation and application of poly(dimethylsiloxane)/β-cyclodextrin solid-phase microextraction fibers

A novel poly(dimethylsiloxane)/beta-cyclodextrin (PDMS/beta-CD) coating was prepared for solid-phase microextraction (SPME). The PDMS/beta-CD coating proved to have a porous structure, providing high surface areas and allowing for high extraction efficiency. The coating had a high thermal stability (340 degrees C) and a long lifetime due to its chemical binding to the fiber surface. Polar phenols and amines were used to evaluate the character of the coating fiber by headspace (HS) extraction and thermal desorption, followed by GC-FID analysis. Parameters that affected the extraction process were investigated; these include extraction time and temperature, desorption time, pH, and ionic strength of the solution. For phenols, the range of linearity of the method was 4-500 microg/L and the LOD was 1.3-2.1 microg/L. For amines, the range of linearity was 1-1000 microg/L and the LOD was 1.2-2.8 microg/L. The presence of beta-CD not only increases the thermal stability of the fiber coating, but also enhances its selectivity. Compared with commercially available SPME fibers, the new phases show better selectivity and sensitivity towards polar compounds.

β-Cyclodextrin-bonded silica particles as the solid-phase extraction medium for the determination of phenol compounds in water samples followed by gas chromatography with flame ionization and mass spectrometry detection

A new absorbent for solid-phase extraction (SPE) was prepared by a beta-cyclodextrin bonded silica stationary phase (CDS) has been applied to determine the concentrations of phenol compounds in water samples. SPE of selected phenolic compounds from aqueous samples were performed using 250 mg CDS. The determination was subsequently carried out by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Compared with available SPE, the CDS showed high sensitivity and fast velocity of mass transfer for phenolic compound because of its porous structure of beta-cyclodextrin. The relative standard deviation (RSD) for river water sample spiked with phenolic compounds at sub-ppb level was lower than 10% and limit of detection (LOD) for these compounds were between 10 and 100 ng l(-1).