Fast extraction of aflatoxins, ochratoxins and enniatins from maize with magnetic covalent organic framework prior to HPLC-MS/MS detection.

A simple, rapid and sensitive vortex-assisted magnetic solid phase extraction (MSPE) method using core-shell structured magnetic covalent organic frameworks (Fe3O4/COF-TpBD) as adsorbents was established for simultaneous determination of aflatoxins, ochratoxins and enniatins in maize before high-performance chromatography tandem spectrometry detection. Fe3O4/COF-TpBD was facilely fabricated, characterized, and applied for simultaneous extraction of ten mycotoxins from maize. Key parameters affecting MSPE efficiency were investigated. The method possessed good linearity (0.05-50 µg/kg), high sensitivity (0.02-1.67 µg/kg for limits of detection), and satisfactory recoveries (73.8-105.3 %), with relative standard deviations less than 8.5 %. The amount of adsorbent used (5 mg) and the time required (0.5 min each for adsorption and for desorption) for MSPE were greatly shortened in comparison with the previous reports. Therefore, the fabricated Fe3O4/COF-TpBD exhibited a great potential for rapid extraction of common mycotoxins in maize, which can be attributed to its multiple interactions with the target mycotoxins.

Polyelectrolyte-grafted anion exchangers with hydrophilic intermediate layers for ion chromatography.

The hydrophobicity of polymer-based anion exchangers is a persistent problem in suppressed anionic chromatography (SAC) due to its adverse effect on chromatographic performance. Herein we describe polyelectrolyte-grafted anion exchangers with modified hydrophilic intermediate layers. The anion exchangers were functionalized by successively grafting a linear cationic condensation polymer (LCCP), a preprepared polyelectrolyte. The carboxylic/hydroxylic intermediate layers formed during thiol-radical-mediated polymerization exert distinct effects on the phase capacity and hydrophobicity. The separation of typical inorganic anions, polarizable anions, and organic acids shows that the anion exchangers display good performance in SAC mode.

Facile synthesis and evaluation of three magnetic 1,3,5-triformylphloroglucinol based covalent organic polymers as adsorbents for high efficient extraction of phthalate esters from plastic packaged foods.

Three covalent organic polymers (COPs) were successfully fabricated by room-temperature solvent-free mechanochemical grinding method between 1,3,5-triformylphloroglucinol (TP) and p-phenyl enediamine (COP1), benzidine (COP2), 4, 4″-diamino-p-terphenyl (COP3), and followed by coprecipitation on the surface of Fe3O4 nanoparticles to form three corresponding magnetic Tp-series COPs. The fabricated magnetic COPs were evaluated and then applied for the extraction of phthalate esters from food samples before gas chromatography-tandem spectrometry analysis. Magnetic COP2 exhibited the highest extraction efficiency, which can be attributed to its larger pore size, and its strong hydrophobic and π-π interactions with phthalate esters. The method possessed good linearity (10-1000 µg·kg-1), high sensitivity (0.29-2.59 µg·kg-1 for LODs and 0.97-8.63 µg·kg-1 for LOQs), and satisfactory recoveries (70.2-108.1%) with relative standard deviations lower than 5.2%. This method has potentials for high efficient separation/preconcentration of hydrophobic phthalate esters from foods.

Covalently grafted anion exchangers with linear epoxy-amine functionalities for high-performance ion chromatography.

Chemical constitution and construction of functional sites play a crucial part in the chromatographic behavior of stationary phases. We present novel polymeric anion exchangers covalently grafted with linear quaternary ammonium polyelectrolytes via simple one-step epoxy-amine polymerization. In separation of various anionic analytes, the newly developed anion exchangers showed high efficiency (e.g., >30,000 plates m-1 for chloride with hydroxide elution) and peculiar chromatographic behavior as compared to previously reported hyperbranched phases. By adopting different amines as the building unite of linear polyelectrolytes, the two types of model anion exchangers displayed segregated selectivity which in our opinion is associated with charge density, hydrophilicity and low cross-linking of the functionalities.

[Simultaneous determination of eight phthalate ester plasticizers in sports beverages using supercritical fluid chromatography].

Phthalate esters (PAEs) are a group of serious environmental pollutants that are carcinogenic or tumorigenic to humans. In this work, a green, rapid, and effective analytical method based on supercritical fluid chromatography (SFC) has been proposed for the simultaneous determination of the eight PAE plasticizers in sports beverage samples. They are dimethyl phthalate (DMP), diethyl phthalate (DEP), dipropyl phthalate (DPRP), dibutyl phthalate (DBP), dipentyl phthalate (DPP), benzyl butyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP), and di-n-octyl phthalate (DNOP). Liquid phase extraction (LPE) was employed to extract the PAE plasticizers before testing using SFC with ultraviolet (UV) detection. SFC parameters, including stationary phase screening, modifier composition and volume percentage, column temperature, flow rate, and backpressure, were optimized. Under the optimum conditions, all the eight PAE plasticizers could be determined simultaneously by SFC within 6 min at 225 nm. The optimized eluent was supercritical CO2 with 3% (v/v) methanol. The performance of the developed method was also evaluated. The eight PAE plasticizers exhibited satisfactory linearities with correlation coefficients (r) of 0.9991-0.9997 in the range of 0.05-25 mg/L. The limits of detection ranged from 7.5 to 15 µg/L (S/N=3, n=3). Recoveries of all the PAE plasticizers for the spiked samples ranged from 91.7%-100.2% with relative standard deviations of no more than 6.5% (n=3). This method is green, time-saving, simple, selective, robust, and convenient for the analysis of the eight PAE plasticizers in real sports beverage samples.

Graphene-coated polystyrene-divinylbenzene dispersive solid-phase extraction coupled with supercritical fluid chromatography for the rapid determination of 10 allergenic disperse dyes in industrial wastewater samples.

Allergenic disperse dyes are a group of environmental contaminants, which are toxic and mutagenic to human beings. In this work, a method of dispersive solid-phase extraction (d-SPE) using graphene-coated polystyrene-divinylbenzene (G@PS-DVB) microspheres coupled with supercritical fluid chromatography (SFC) was proposed for the rapid determination of 10 allergenic disperse dyes in industrial wastewater samples. G@PS-DVB microspheres were synthesized by coating graphene (G) sheets onto polystyrene-divinylbenzene (PS-DVB) polymers. Such novel sorbents were employed in d-SPE for the purification and concentration of allergenic disperse dyes in wastewater samples prior to the determination by SFC with UV detection. To achieve the maximum extraction efficiency for the target dyes, several parameters influencing d-SPE process such as sorbent dosage, extraction time, desorption conditions were investigated. SFC conditions including stationary phase, modifier composition and percentage, column temperature, backpressure and flow rate were optimized to well separate the allergenic disperse dyes. Under the optimum conditions, satisfactory linear relationship (R ≥ 0.9989) was observed with the concentration of dyes ranging from 0.02 to 10.0 µg/mL. The limits of detection (LOD, S/N = 3) for the ten dyes were in the range of 1.1-15.6 ng/mL. Recoveries for the spiked samples were between 89.1% and 99.7% with relative standard deviations (RSD) lower than 10.5% in all cases. The proposed method is time-saving, green, precise and repeatable for the analysis of the target dyes. Furthermore, the application of G@PS-DVB based d-SPE process can be potentially expanded to isolate and concentrate other aromatic compounds in various matrices and supercritical fluid chromatography methodology featuring rapidity, accuracy and green will be an ideal candidate for the analysis of these compounds.

Hyperbranched anion exchangers prepared from thiol-ene modified polymeric substrates for suppressed ion chromatography.

The covalent modification of polymeric particles has been a challenge due to their chemical inertness. Herein we describe a facile and neat method via thiol-ene reaction to immobilize cysteamine/cysteine onto allylmethacrylate-divinylbenzene (AMA-DVB) and ethylvinylbenzene-divinylbenzene (EVB-DVB). The introduced functionalities were verified by elementary analysis and scanning electron microscope coupled with energy dispersive spectroscopy. This modification enabled the further grafting of hyperbranched condensation polymers (HBCPs), which converted the particles into anion exchangers. The anion exchangers demonstrated good separation with carbonate/bicarbonate eluents and hydroxide eluents for suppressed anion exchange chromatography. In the case of a 3-layered anion exchanger, simultaneous separation of nine model anions was achieved by isocratic elution in 17 min with efficiencies up to 16,100 plates m-1. High stability and dependable durability was exhibited in long-term tests.

Simultaneous determination of 11 phthalate esters in bottled beverages by graphene oxide coated hollow fiber membrane extraction coupled with supercritical fluid chromatography.

Phthalate esters (PAEs) are a group of serious environmental pollutants, which lead to carcinogenicity or tumorigenicity in human body. In this study, a rapid, sensitive and green method by graphene oxide coated hollow fiber membrane extraction (GO-HFME) coupled with supercritical fluid chromatography (SFC) was proposed for the determination of 11 phthalate esters in bottled beverages. Graphene oxide (GO) was prepared and coated onto a porous hollow fiber membrane (HFM) to reinforce the efficiency of membrane extraction. The modified hollow fiber membrane was employed for the extraction of phthalate esters from bottled beverages prior to the determination by the supercritical fluid chromatography with UV detection. To achieve the maximum extraction efficiency, several parameters were investigated including GO concentration, extraction time, desorption solution and desorption time. SFC variables including stationary phase, modifier composition and percentage, column temperature, flow rate and backpressure were studied to improve the separation conditions. Under these optimized conditions, all the studied 11 phthalate esters were well separated and simultaneously determined in 7 min by SFC. The performance of the developed method was evaluated. Good linearity was observed (R ≥ 0.999) in the range of 0.02-10.0 µg/mL with limit of detection (LOD, S/N = 3) ranging from 1.5 to 3.0 ng/mL. Recoveries of all the PAEs for the spiked samples were between 92.1% and 99.3% with satisfactory relative standard deviations (RSD) less than 5.9%. The proposed method is time-saving, green, simple and robust, which will be an alternative way to the analysis of PAEs in real samples.

Simultaneous determination of two plant growth regulators in ten food samples using ion chromatography combined with QuEChERS extraction method (IC-QuEChERS) and coupled with fluorescence detector.

A new simple, isocratic, selective and highly sensitive method has been developed for the simultaneous separation and determination of two plant growth regulators (PGRs): 2-(1-Naphthyl)acetic acid (NAA) and 2-(Naphthalen-1-yl)acetamide (NAD). Both PGRs were extracted by modified and miniaturized ion chromatography-Quick, Easy, Cheap, Effective, Rugged and Safe (IC-QuEChERS) method from ten food samples. The separation and sensitive determination were carried out by using ion chromatography coupled with fluorescence and ultraviolet (IC-FLD/UV) detector. The proposed analytical and extraction methods were validated by using blank samples, fortified with a standard solution of these two PGRs at three concentration levels 5, 15 and 25µg/kg. The method showed good linearity (r2≥0.980), satisfactory recoveries (76.3-112) with tolerable precision having relative standard deviations less than 15.4% (RSDs, n=3). The limit of detection and limit of quantification were also in the range of 0.08-6.6ng/kg and 2.2-20ng/kg, respectively.

Graphene-coated polymeric anion exchangers for ion chromatography.

Carbonaceous stationary phases have gained much attention for their peculiar selectivity and robustness. Herein we report the fabrication and application of a graphene-coated polymeric stationary phase for anion exchange chromatography. The graphene-coated particles were fabricated by a facile evaporation-reduction method. These hydrophilic particles were proven appropriate substrates for grafting of hyperbranched condensation polymers (HBCPs) to make pellicular anion exchangers. The new phase was characterized by zeta potentials, Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscope. Frontal displacement chromatography showed that the capacities of the anion exchangers were tuned by both graphene amount and HBCPs layer count. The chromatographic performance of graphene-coated anion exchangers was demonstrated with separation of inorganic anions, organic acids, carbohydrates and amino acids. Good reproducibility was obtained by consecutive injections, indicating high chemical stability of the coating.

Detection of trace fluoride in serum and urine by online membrane-based distillation coupled with ion chromatography.

An online membrane-based distillation (MBD) coupled with ion chromatography (IC) method was proposed for automatic detection of trace fluoride (F-) in serum and urine samples. The system consisted of a sample vessel, a lab-made membrane module and an ion chromatograph. Hydrophobic polytetrafluoroethylene (PTFE) hollow fiber membrane was used in MBD which was directly performed in serum and urine samples to eliminate the matrix interferences and enrich fluoride, while enabling automation. The determination of fluoride in biological samples was carried out by IC with suppressed conductometric detection. The proposed method feasibly determined trace fluoride in serum and urine matrices with the optimized parameters, such as acid concentration, distillation temperature, and distillation time, etc. Fluoride exhibited satisfactory linearity in the range of 0.01-5.0mg/L with a correlation coefficient of 0.9992. The limit of detection (LOD, S/N=3) and limit of quantification (LOQ, S/N=10) were 0.78µg/L and 2.61µg/L, respectively. The relative standard deviations of peak area and peak height were all less than 5.15%. The developed method was validated for the determination of fluoride in serum and urine with good spiked recoveries ranging between 97.1-101.9%. This method also can be proposed as a suitable alternative for the analysis of fluoride in other complex biological samples.

Poly (styrene-divinyl benzene-glycidylmethacrylate) stationary phase grafted with poly amidoamine (PAMAM) dendrimers for rapid determination of phenylene diamine isomers in HPLC.

A novel high performance liquid stationary phase was prepared by grafting poly amidoamine (PAMAM) dendrimers to poly (styrene-divinyl benzene-glycidylmethacrylate) matrix in this work. Different generations of PAMAM dendrimers grafted to polymer matrices containing different glycidylmethacrylate amounts by reacting with epoxy groups in glycidylmethacrylate molecules. The synthesized PAMAM dendrimers and stationary phase were characterized by fourier transform infrared spectroscopy, scanning electron microscope, N2 adsorption/desorption, elemental analysis and thermo gravimetric analyzer. The proposed stationary phase was suitable for rapid separation of phenylene diamine isomers and aminobenzene. The separation mechanism of benzene rings attraction and amino repulsion was verified by retention behaviors of methylamine, phenylamine, phenylene diamine, naphthylamine and toluene. The reliability of the stationary phase was demonstrated by separation and determination of phenylene diamine isomers including m-phenylene diamine, o-phenylene diamine and p-phenylene diamine in hair dye precursors within 10min. Satisfactory resolution and short analysis time make the columns promising for determination of aniline compounds in various fields.

Hydrothermal carbon nanosphere-based agglomerated anion exchanger for ion chromatography.

This work reports the application of hydrothermal carbon nanospheres (HCNSs) as stationary phases in ion chromatography. HCNSs were facilely quaternized through polycondensation of methylamine and 1,4-butanediol diglycidyl ether. The quaternization was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Owing to the electrostatic interaction, quaternized HCNSs were equably attached onto the surface of sulfonated polystyrene-divinylbenzene (PS-DVB) beads to construct the anion exchangers. The aggregation was verified by scanning electron microscopy and elemental analysis. Common anions, aliphatic monocarboxylic acids, polarizable anions, and aromatic acids were well separated on the stationary phases with good stability and symmetry. The prepared column was further applied to detect phosphate content in Cola drink samples. The limit of detection (S/N=3) was 0.09mg/L, and the relative standard deviation (n=10) of retention time was 0.31%. The average recovery was 99.58%.

Polystyrene-divinylbenzene-glycidyl methacrylate stationary phase grafted with poly (amidoamine) dendrimers for ion chromatography.

In this work, a novel ion exchange stationary phase based on different generations of poly (amidoamine) dendrimers (PAMAM) was developed for the determination of inorganic anions and carbohydrates. Synthesis of the PAMAM was carried out with the polymerization reaction of ethylenediamine and methyl acrylate. The synthesized PAMAM was then grafted to the polystyrene-divinylbenzene-glycidyl methacrylate (PS-GMA) to form PAMAM-based beads. These beads were finally modified with 1,4-butanediol diglycidyl ether (BDDE) to generate the anion exchanger, which were characterized by scanning electron microscopy (SEM), brunauer-emmett-teller (BET), fourier transform infrared spectroscopy (FTIR), and elemental analysis. Elemental analysis, breakthrough curves and capacity factors showed that more epoxy groups and higher PAMAM generations in stationary phase could result in higher anion exchange capacity. The efficiency, durability and stability of the proposed anion exchanger were investigated by using six inorganic anions (fluoride, chloride, nitrite, bromide, nitrate and sulfate) and four carbohydrates (trehalose, glucose, maltotriose and galacturonic acid) as analytes, respectively. The reliability of the proposed ion chromatographic stationary phase was demonstrated by determining the content of galacturonic acid in polysaccharides from Poria cocos and Atractylodes macrocephala. The relative standard deviations of retention time, peak height, and peak area for galacturonic acid were 0.39%, 1.22%, and 2.02%, respectively. The spiked recoveries were in the range of 88.29%-100.51% for plant polysaccharides. Due to the good structural homogeneity, intense internal porosity, biological compatibility and high density of active groups in PAMAM, this grafted stationary phase showed good ion-exchange characteristics, especially in biological charged molecules.