Cationic amine-bridged periodic mesoporous organosilica materials for off-line solid-phase extraction of phenoxy acid herbicides from water samples prior to their simultaneous enantiomeric determination by capillary electrophoresis

Mesoporous organosilicas with highly-content tyrosine framework as extractive phases for non-steroidal anti-inflammatory drugs in aquatic media

BACKGROUND

Attentions regarding ordered mesoporous silica materials (OMSs), with large specific surface areas and narrow pore size distribution, which are prepared via self-assembly techniques, have been raised in sorption, separation, and sample preparation. However, in order to extend and improve their applications, a functionalization step is required. Organic units can be anchored on the inner or outer surface as well as in the silica wall framework by co-condensation-, grafting-, and periodic mesoporous organosilica (PMO) preparation approaches. Apparently, by synthesizing PMO with extensive and flexible organic bridging groups within the mesoporous wall, an efficient extractive phase can be achieved.

RESULTS

We employed tyrosine amino acid to synthesize a PMO-based extractive phase. The FT-IR, 1H NMR, HR-ESI-MS, Low angle-XRD, TEM, FESEM, BET, and EDX-MAP analyses confirmed the successful synthesis of PMO within the salt-assisted templating method. A comprehensive study on sorption behavior of PMO was performed and its efficiency was evaluated against the grafting and co-condensation methods. Then, it was implemented to the pipette tip-micro solid phase extraction (PT-μ-SPE) of widely used non-steroidal anti-inflammatory drugs (NSAIDs) in water/wastewaters. Limits of detection and quantification were obtained in the range of 0.1-1.5 and 0.3-5 μg L-1, respectively. The calibration plots are linear in the 1-1000, 3-1000, 10-750, and 3-750 μg L-1, respectively. The intra-and inter-day precision at 50 and 200 μg L-1 levels are 2.9-7.1 % and 3.5-8%, while recoveries are between 84 and 111 %.

SIGNIFICANCE

High-capacity tyrosine functionalized PMO with 2D hexagonal symmetry silica mesoporous structures found to be highly efficient extractive media. Despite the bulkiness and flexibility of the bridging group within the mesoporous wall, the synthesis condition was optimized in order to load more organic content in the PMO structure. The PMO performance was superior over organically modified ordered mesoporous silica materials prepared by the grafting and co-condensation methods.

Two-step pressure injection-assisted online enrichment of herbicides from foods with affinity micelle sweeping by micellar electrokinetic chromatography

A novel online two-step pressure injection-assisted stacking preconcentration method, which involves sweeping and affinity micelles in micellar electrokinetic chromatography was developed to simultaneously measure various organic anions. The micellar solution was a mixed solution that contained 0.3 mM didodecyldimethylammonium bromide and 20 mM borax. After the micellar solution was injected for 60 s, the tested analytes prepared in 20 mM borax were introduced into the capillary for 150 s. The key experimental factors that influenced the separation and sensitivity were investigated and optimized, including the concentration and injection time of the micellar solution, the concentration of borax in the sample solution, the concentration of sodium dodecyl sulfate and borax in the background electrolyte (BGE), the content of acetonitrile in the BGE and the injection time of the sample solution. Compared with typical injection methods, this method achieved sensitivity enhancement factors ranging from 85 to 97 under optimized conditions. Good linearity for matrix-matched calibration was established for all analytes with R2 values of 0.9986-0.9996. The intraday (n = 6) and interday (n = 6) precisions of the method were less than 2.85% when expressed as relative standard deviations. When the method was applied to analyze rice and dried ginger samples, analyte recoveries ranged from 85.81% to 106.59%. Through sweeping and affinity micelles, stacking preconcentration method was successfully employed to analyze trace amounts of fenoprop and 2,4-dichlorophenoxyacetic acid in rice and dried ginger samples.

Hexagonal boron nitride nanosheets based magnetic solid phase extraction for the extraction of phenoxy carboxylic acid herbicides from water samples followed by high-performance liquid chromatography-tandem mass spectrometry

High-efficiency caption of pesticide residue is of vital significance for environmental safety monitoring. Herein, a hexagonal boron nitride nanosheets-based magnetic composite (Fe₃O₄@h-BNNSs) was synthesized and applied for the magnetic solid phase extraction (MSPE) of five phenoxy carboxylic acid (PCA) herbicides from water samples. Based on the π-π interaction, hydrogen bond and halogen bond, the Fe₃O₄@h-BNNSs composite showed excellent adsorption ability towards PCA herbicides. Several main variables that influenced the extraction efficiencies of PCA herbicides were investigated and optimized via single-factor experiment. Combining this Fe₃O₄@h-BNNSs composite-based MSPE with high-performance liquid chromatography-tandem mass spectrometry, a novel sensitive method for the analysis of PCA herbicides was developed. Under the most favorable conditions, the proposed method displayed good linear ranges (20.0-10000.0 ng L^-1), low limits of detection (5.6-10.3 ng L^-1), satisfactory precisions (1.1-6.8%) and recoveries (76.6-107.2%). Overall, the present work can be a versatile and worthy utility for the determination of PCA herbicides from different water samples.

Synthesis of CoFe2O4/Peanut Shell Powder Composites and the Associated Magnetic Solid Phase Extraction of Phenoxy Carboxylic Acid Herbicides in Water

The magnetic biochar material CoFe₂O₄/PCPS (peanut shell powder) was prepared based on the hybrid calcination method. The properties of prepared composites and the extraction effect of magnetic solid phase extraction on phenoxy carboxylic acid herbicides were assessed. The morphology, crystal structure, specific surface area, and pore size distribution of the material were analysed using a transmission electron microscope (TEM), infrared Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and N₂ absorption surface analysis (BET). The results of the magnetic solid phase extraction of a variety of phenoxy carboxylic acid herbicides in water using CoFe₂O₄/PCPS composites showed that, when the mass ratio of CoFe₂O₄ and PCPS was 1:1, 40 mg of the composite was used, and the adsorption time was 10 min at pH 8.50. Methanol was used as the eluent, and the recovery rates of the three phenoxy carboxylic acid herbicides were maintained at 81.95–99.07%. Furthermore, the actual water sample analysis results showed that the established method had good accuracy, stability, and reliability.

Plugged bifunctional periodic mesoporous organosilica as a high-performance solid phase microextraction coating for improving extraction efficiency of chlorophenols in different matrices

In this study, a sensitive solid phase microextraction (SPME) coating was developed based on two kinds of plugged and non-plugged bifunctional periodic mesoporous organosilicas (BFPMO) with ionic liquid and ethyl units. The extraction efficiency of all plugged and unplugged sorbents was investigated for the extraction of chlorophenols (CPs) in water and honey samples by emphasizing the effect of different physicochemical properties. The separation and determination of the CPs was performed by gas chromatography-mass spectrometry (GC-MS). The extraction results showed that plugged BFPMO coating exhibited outstanding enrichment ability for the extraction of CPs as model analytes with different polarities. This can be attributed to a valuable hydrophobic-hydrophilic balance in the mesochanels of the plugged BFPMO, which is the result of the combination of plug technology and bridged organic groups. Low limits of detection in the range of 5-70 ng L^-1, wide linearity, and good reproducibility (RSD = 8.1-10.1 % for n = 6) under the optimized extraction conditions were achieved. Finally, the BFPMOs coated fiber was successfully used for determination of CPs in real water samples. The relative recoveries for the five CPs were in the range of 92.3-104.0 %, which proved the applicability of the method.

Hypercrosslinked polymer microspheres decorated with anion- and cation-exchange groups for the simultaneous solid-phase extraction of acidic and basic analytes from environmental waters

Mixed-mode ion-exchange sorbents were introduced to improve the selectivity and retention of solid-phase extraction (SPE) sorbents. Mixed-mode ion-exchange sorbents integrate reversed-phase chemistry with ion-exchange groups to promote favourable interactions with ionic species. Nevertheless, a need to extract analytes with acidic and basic properties simultaneously within the same SPE cartridge led to the introduction of novel amphoteric/zwitterionic sorbents, which incorporate cation- and anion-exchange moieties within the same functional group attached to the polymeric network. In the present study, the development, preparation and SPE evaluation of two novel hypercrosslinked zwitterionic polymeric sorbents, functionalised with either strong anion-exchange (SAX) and weak cation-exchange (WCX) or weak anion-exchange (WAX) and strong cation-exchange (SCX) groups (namely HXLPP-SAX/WCX and the HXLPP-WAX/SCX), is presented for the simultaneous retention of acidic and basic compounds. The sorbents were prepared by a precipitation polymerisation route which yielded poly(divinylbenzene-co-vinylbenzylchloride) as a precursor polymer; subsequently, the precursor polymer was hypercrosslinked, to increase the specific surface areas and capacities of the sorbents, and then functionalised to impart the zwitterionic character. The HXLPP-SAX/WCX sorbent was decorated with quaternised sarcosine groups and the HXLPP-WAX/SCX sorbent was decorated with taurine moieties. The SPE parameters were optimised to exploit the ionic interactions between compounds and the functional groups. The optimal conditions involve a washing step to remove the compounds retained by hydrophobic interactions, thus increasing the selectivity. The optimised SPE protocol used the quaternised sarcosine-based sorbent followed by liquid chromatography and tandem mass spectrometry, and was applied to determine compounds with acidic and basic properties from environmental samples, such as river water and effluent wastewater samples, with excellent selectivity and matrix effect values below -30% and apparent recovery results ranging from 52% to 105% for most of the compounds. The analytical method was validated for environmental water samples and used in the analysis of samples in which some of the target compounds were found at ng L^-1 concentration levels.

Magnetic molecularly imprinted polymer for the simultaneous selective extraction of phenoxy acid herbicides from environmental water samples

A selective magnetic molecularly imprinted polymer (MMIP) was synthetized with 4-chloro-2-methylphenoxyacetic acid as template and 4-vinylpiridine as monomer in presence of vinylized magnetite nanoparticles. Scanning electron microscopy, nitrogen adsorption-desorption isotherms, Fourier transform infrared spectrometry and vibrating sample magnetometry were applied to characterize the resulting material. The synthesized MMIP was applied as sorbent in magnetic molecularly imprinted solid-phase extraction (MMISPE) for selective extraction of a mixture of the five herbicides 4-chloro-2-methylphenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB), mecoprop (MCPP), fenoxaprop (FEN) and haloxyfop (HAL). Several parameters affecting the extraction conditions were optimized to achieve the best extraction performance. The best MMISPE combined with HPLC-DAD gave detection and quantification limits between 0.33 and 0.71 μg L^-1 and 1.1-2.4 μg L^-1, respectively, were obtained. The precision of the whole method provided RSD values below 7.3%, and the accuracy was demonstrated by the analysis of several water samples of different origins, with recoveries ranged from 77 to 98%. Moreover, a remarkable re-usability of the MMIP sorbent, more than 65 uses without losses in extraction capacity, was obtained.

A magnetic multi-walled carbon nanotube preparative method for analyzing asymmetric carbon, phosphorus and sulfur atoms of chiral pesticide residues in Chinese herbals by chiral liquid chromatography-quadrupole/linear ion trap mass spectrometry determination

An analytical method for the determination of asymmetric carbon, phosphorus and sulfur atoms in chiral pesticide residues by magnetic multi-walled carbon nanotube sample pretreatment combined with chiral ultra-performance liquid chromatography/quadrupole/linear ion trap mass spectrometry (UPLC-MS/Qtrap) was developed and applied to chiral pesticide residues analysis in Chinese herbals. Eleven different chiral pesticides were found, and 36.4% were positive in Chinese herbals. Three plants containing detectable pesticide residues were observed in Dendrobium nobile, Panax notoginseng flowers and honeysuckle, in the order of decreasing detected concentration. High detection frequencies of 26.1% for (R/S)-(±)-difenoconazole and 14.5% for (R/S)-(±)-metalaxyl and (R/S)-(±)-propiconazole were observed, the residual amount for (R/S)-(±)-difenoconazole, (R/S)-(±)-metalaxyl and (R/S)-(±)-propiconazole were 0.32 ~ 2.5 mg/kg, 0.022 ~ 0.23 mg/kg, 0.62 ~ 3.21 mg/kg respectively. The EF value of (R/S)-(±)-difenoconazole was 0.506 ± 0.046. The EF value of (R/S)-(±)-metalaxyl was lower than 0.5 in Dendrobium nobile, Panax notoginseng flowers, Panax notoginseng roots and hawthorn. The EF of (R/S)-(±)-propiconazole was not significantly enantioselective in honeysuckle and Panax notoginseng flowers. The enantioselectivity of various pesticide residues in different plants cannot be predicted from our existing knowledge and may closely depend on plant growth, environmental conditions or molecular structure.

Three-dimensional chitosan/graphene oxide aerogel for high-efficiency solid-phase extraction of acidic herbicides in vegetables

A simple, facile method was adopted to synthesize three-dimensional chitosan grafted graphene oxide aerogel modified silica (3D CS/GOA@Sil) as an eco-friendly, sustainable extraction material for the preconcentration of phenoxy acid herbicides.

Analytical methods to analyze pesticides and herbicides

Presented in this paper is an annual review of literatures published in 2018 on topics relating to analytical methods for pesticides and herbicides. According to the different techniques, this review is divided into six sections, including extraction methods; chromatographic or mass spectrometric techniques; electrochemical techniques; spectrophotometric techniques; chemiluminescence and fluorescence methods; and biochemical assays. PRACTITIONER POINTS: Totally 134 relevant research articles are summarized. The review is divided into six parts according to the techniques. Chromatographic and mass spectrometric methods are the most widely used.

Modeling-based optimization of the simultaneous enantiomeric separation of multicomponent mixtures of phenoxy acid herbicides using dual cyclodextrin systems by Capillary Electrophoresis

In this work, the Dubsky's model proposed for Capillary Electrophoresis (CE) enantioseparation systems with a mixture of chiral selectors was applied to the rapid optimization of the simultaneous enantiomeric separation of a multicomponent mixture of six phenoxy acid herbicides using a dual system of two cyclodextrins (CDs), (2-hydroxypropyl)-β-CD (HP-β-CD) and heptakis(2,3,6-tri-O-methyl)-β-CD (TM-β-CD). Simply by carrying out a small number of individual experiments separately with each CD, the Dubsky's model enabled to foresee the results that could be obtained for any possible combination of concentrations and relative proportion of both CDs in the mixture. Results obtained in this work demonstrated that the model was successful by improving the previous results experimentally obtained by the trial and error method for the simultaneous enantiomeric separation of the six phenoxy acid herbicides studied in this work. In fact, the separation was improved in terms of enantiomeric resolutions obtained (from 1.2 to 4.2 for concentrations of CDs of 4 mM HP-β-CD and 16 mM TM-β-CD) and by considerably reducing the time to optimize the separation conditions enabling to find, in a faster and efficient way, the most adequate proportion of both CDs and the concentration of each CD in the mixture to obtain baseline separation of the twelve enantiomers. Additionally, the apparent complexation constants between enantiomers and each CD were calculated. This is the first time that the above-mentioned model was applied to a multicomponent mixture of chiral compounds.

Chiral Selectors in Capillary Electrophoresis: Trends During 2017⁻2018

Chiral separation is an important process in the chemical and pharmaceutical industries. From the analytical chemistry perspective, chiral separation is required for assessing the fit-for-purpose and the safety of chemical products. Capillary electrophoresis, in the electrokinetic chromatography mode is an established analytical technique for chiral separations. A water-soluble chiral selector is typically used. This review therefore examines the use of various chiral selectors in electrokinetic chromatography during 2017–2018. The chiral selectors were both low and high (macromolecules) molecular mass molecules as well as molecular aggregates (supramolecules). There were 58 papers found by search in Scopus, indicating continuous and active activity in this research area. The macromolecules were sugar-, amino acid-, and nucleic acid-based polymers. The supramolecules were bile salt micelles. The low molecular mass selectors were mainly ionic liquids and complexes with a central ion. A majority of the papers were on the use or preparation of sugar-based macromolecules, e.g., native or derivatised cyclodextrins. Studies to explain chiral recognition of macromolecular and supramolecular chiral selectors were mainly done by molecular modelling and nuclear magnetic resonance spectroscopy. Demonstrations were predominantly on drug analysis for the separation of racemates.