Zhifen Deng

Simultaneous determination of six plant growth regulators in fruits using high performance liquid chromatography based on solid-phase extraction and cleanup with a novel mixed-mode functionalized calixarene sorbent

In this paper, a rapid and practical high performance liquid chromatography (HPLC) method, using home-made tetraazacalix[2]arene[2]triazine-modified silica gel (NCSi) as a solid-phase extraction (SPE) sorbent, was developed for the simultaneous determination of six plant growth regulators (PGRs) including thidiazuron (TDZ), naphthaleneacetic acid (NAA), p-chlorophenoxyacetic (PCPA), 2,4-dichlorophenoxyacetic acid (2,4-D), 6-benzylaminopurine (6-BA) and forchlorfenuron (KT-30) in fruits. NCSi is a novel multi-interaction and mixed mode functionalized calixarene sorbent, which can enrich different classes of PGRs. Prior to HPLC separation, the key factors influencing SPE performance were investigated in the sample pretreatment step, including the dosage of the NCSi sorbent, and the flow rate, volume and composition of the eluant. HPLC analysis was carried out on a Waters XBridge C18 column (250 × 4.6 mm i.d., 5 μm) with a mobile phase of methanol/0.1% H3PO4 (55 : 45,v/v). With a detection wavelength of 220 nm, the good linearities of the six PGRs were obtained in the concentration range of 0.03 to 200 mg kg−1 (R2 ≥ 0.999). The lower detection limits (4.3–20.4 μg kg−1) and quantitation limits (12.9–64.0 μg kg−1) of the six PGRs were also obtained, which can meet the trace analysis requirements. In addition, overall recoveries through the extraction and purification steps ranged from 72.4 to 94.9%, and RSDs were less than 4.84%. The proposed method was successfully used to determine residual PGRs in real samples. It is practical and promising for the study of plant physiology by the determination of trace PGR content in the plant or fruits with a complex matrix.

Determination of Trace Acrylamide in Starchy Foodstuffs by HPLC Using a Novel Mixed-Mode Functionalized Calixarene Sorbent for Solid-Phase Extraction Cleanup

In this paper, a rapid and effective HPLC method, using tetraazacalix[2]arene[2]triazine-modified silica gel (NCSi) as solid-phase extraction (SPE) sorbent, was developed for the purification and determination of trace acrylamide in starchy foodstuffs. The main influence factors of SPE including amount of NCSi sorbent, sample flow rate, and volume and composition of washing solution were investigated and evaluated in the sample pretreatment step. The optimized purification effect was achieved at the sample flow rate of 3 mL/min with 100 mg of NCSi and 2 mL of washing solution (water, 100%). The HPLC separation was carried out on a C18 column (250×4.6 mm i.d., 5 μm) with a mobile phase of methanol/water (10:90, v/v). The linear range of the calibration curve was 4-4000 ng/mL with s correlation coefficient of >0.9999. The intraday and interday RSDs (n=5) of peak areas of acrylamide were 0.22 and 0.90% and the intraday and interday RSDs (n=5) of retention times were 0.50 and 1.63%, respectively. In addition, overall recoveries through the extraction and NCSi-SPE purification ranged from 73.13 to 98%. Compared with the commercial SPE sorbents, NCSi featured excellent selectivity to retain polar and nonpolar interferences in the sample matrices. The improved method was simple, rapid, accurate, and promising for the determination of trace acrylamide in starchy foods with a complex matrix.

Development of a decaaza-cyclophane stationary phase for high-performance liquid chromatography

A new stationary phase for high-performance liquid chromatography was prepared by covalently bonding a heteroatom-bridged cyclophane onto silica gel using 3-aminopropyltriethoxysilane as the coupling reagent. The structure of the new material was characterized by infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The linear solvation energy relationship method was successfully employed to evaluate the new phase with a set of 25 solutes, and compared with octadecylsilyl and p-tert-butyl-calix[4]arene bonded stationary phases. The retention characteristics of the new phase are similar to the octadecylsilyl and conventional calixarene phases, and it also has distinctive features. In addition, the chromatographic behavior of the phase was illustrated by eluting alkylbenzenes and inorganic anions in the reversed-phase mode and anion-exchange mode, respectively. Thus, multi-interaction mechanisms and mixed-mode separation of the new phase can very likely guarantee its promising application in the analysis of complex samples. The column has been successfully employed for the analysis of triazines in milk, and it is demonstrated to be a competitive alternative analytical method for the determination of triazine herbicide residues.

Liquid chromatographic behavior of two alanine-substituted calix[4]arene-bonded silica gel stationary phases.

Two new kinds of alanine-substituted calix[4]arene stationary phases of 5,11,17,23-p-tert-butyl-25,27-bis(l-alanine-methylester-N-carbonyl-methoxy)-26,28-dihyroxycalix[4]arene-bonded silica gel stationary phase (BABS4) and 5, 11, 17, 23-p-tert-butyl-25,26,27,28-tetra(l-alanine-methylester-N-carbonyl-methoxy)-calix[4]arene-bonded silica gel stationary phase (TABS4) were prepared and characterized in the present study. They were compared with each other and investigated in terms of their chromatographic performance by using polycyclic aromatic hydrocarbons, disubstituted benzene isomers, and mono-substituted benzenes as solute probes. The results indicated that both BABS4 and TABS4 exhibited multiple interactions with analytes. In addition, the commonly used Tanaka characterization protocol for the evaluation of commercially available stationary phases was applied to evaluate the properties of these two new functionalized calixarene stationary phases. The Tanaka test results were compared with Zorbax Eclipse XDB C18 and Kromasil phenyl columns, respectively. BABS4 has stronger hydrogen-bonding capacity and ion-exchange capacity than TABS4, and features weaker hydrophobicity and hydrophobic selectivity. Both of them behave similarly in stereoselectivity. Both BABS4 and TABS4 are weaker than C18 and phenyl stationary phases in hydrophobicity and hydrophobic selectivity.

Analysis of nitrites and nitrates in hams and sausages by open-tubular capillary electrochromatography with a nanolatex-coated capillary column.

In this work, a new open-tubular capillary electrochromatography (OT-CEC) method with the nanolatex-coated column was proposed for the determination of nitrites and nitrates in foodstuffs. The method was simple and repeatable as a result of avoiding the introduction of an electroosmotic flow reverse additive (such as cetyltrimethylammonium chloride) in electrophoretic buffer. The limits of quantitation were 0.89 and 1.05 mg kg⁻¹ for nitrate and nitrite, respectively, whereas the overall recoveries ranged from 94 to 103%. The developed OT-CEC method was successfully applied for 12 samples, and the residue profiles of nitrites and nitrates in hams and sausages were obtained and evaluated.

On-cartridge derivatisation using a calixarene solid-phase extraction sorbent for facile, sensitive and fast determination of formaldehyde in beer

This work demonstrates the successful application of an on-cartridge derivatisation procedure for facile, fast and sensitive determination of formaldehyde in beer by HPLC-UV. The derivatisation and solid-phase extraction (SPE) were integrated into a novel calixarene SPE sorbent: tetraazacalix[2]arene[2]triazine bonded silica gel. Specifically, 2,4-dinitrophenylhydrazine was adsorbed onto the sorbent in advance, based on the charge-transfer interaction between the macrocyclic molecule and nitrobenzenes. The method was optimised and validated: under the optimal conditions of derivatisation, SPE and HPLC separation, good linearity was obtained in the range of 0.080-3.2μgmL(-1) with a correlation coefficient of 0.9939, the limit of detection was 3.0ngmL(-1) (S/N=3), the limit of quantification was 10ngmL(-1) (S/N=10), and the recovery level using this method was desirable at 75-84%. The developed method was successfully applied to determine formaldehyde content in real beer samples; the results were in the range of 0.11-1.1μgmL(-1).

SPE-UHPLC-FLD Method for the Simultaneous Determination of Five Anthraquinones in Human Urine Using Mixed-Mode Bis(tetraoxacalix[2]arene[2]triazine) Modified Silica as Sorbent

The five anthraquinones compounds (including aloe-emodin, emodin, physcion, chrysophanol, and rhein) are regarded as the main effective ingredients in rhubarb (Dahuang in Chinese, one of the commonly used Chinese herbal medicines). In this work, a simple and effective solid phase extraction (SPE) method based on bis(tetraoxacalix[2]arene[2]triazine) modified silica gel as adsorbent was developed. Coupled with UHPLC-FLD, the developed method was successfully applied for the measuring of main anthraquinones in human urine after oral administration of the extracts of rhubarb. To obtain the highest recoveries of the five anthraquinones in the SPE process, the main parameters which may affect extraction efficiency were optimized. The optimized sorbent amount, sample loading pH, sample loading rate, washing solution, and eluent condition were obtained. The developed method showed good linearity in 0.012–1.800 μg mL−1 for the five anthraquinones with correlation coefficients more than 0.9993. The investigated LOD values ranged from 3.9 to 5.7 ng mL−1, while the LOQs were between 12.0 and 18.2 ng mL−1. The recoveries of the method were also investigated, which were in the range of 94.8–106.6%. The application of the mixed-mode SPE materials in the proposed method was feasible and simple, and suitable for the enrichment of anthraquinones in urine samples.

In situ preparation of core–shell magnetic porous aromatic framework nanoparticles for mixed–mode solid–phase extraction and adsorption of trace multitarget analytes

This study reports a novel strategy for the preparation of porous aromatic framework (PAF-6) coated magnetic nanoparticles (PAF-6 MNPs) using cyanuric chloride as a planar trigonal basis upon which to build a linear piperazine linker unit. The PAF-6 MNPs were examined as an efficient solid-phase extraction (SPE) sorbent for enrichment of trace organic pollutants including phenol, 2,4,6-trinitrophenol, naphthalene, naphthol, bisphenol A, 2,4-dichlorophenol and 3-nitrochlorobenzene in water. The high-performance liquid chromatography detection limits of such analytes were in the range of 0.08-5.02 ng/mL and recoveries were found to be 84.0-94.0% in well water, tap water, river water and wastewater. The main toxic components of cigarette smoke, including phenolic compounds and benzo[a]pyrene, are efficiently adsorbed by PAF-6 MNPs, and over 50% of such toxins are removed. Theoretical computations were performed to understand the molecular interaction mechanism between PAF-6 and such analytes. The results demonstrate that the PAF-6 MNPs sorbents show excellent adsorption of phenols, polycyclic aromatic hydrocarbons and nitroaromatics based on multiple π-π stacking and hydrogen-bond interactions. These results suggest that the PAF-6 MNPs can be applied to extraction, removal and determination of diverse trace multi-target analytes from complex media.

Selective removal of IgG from the urine of patients with proteinuria using a polymer coated core–shell magnetic nanoparticle

Selective removal of highly abundant proteins prior to analysis is an important issue in proteomics. In this study, a core–shell structured magnetic nanocomposite of Fe3O4@SiO2@MAsp-HEMA was found to be an effective and selective adsorbent to remove highly abundant IgG from the urine of patients with proteinuria. This novel magnetic adsorbent was prepared by coating a poly(N-methacryloyl-L-aspartic acid-hydroxyethyl methacrylate) shell on Fe3O4@SiO2 nanoparticles via a coupling agent of KH-570 using the mini-emulsion polymerization method. The as-synthesized nanoparticle was characterized by X-ray diffraction, elemental analysis, thermal gravimetric analysis, infrared spectroscopy, magnetic hysteresis loop curves, scanning electronic microscopy and transmission electron microscopy. A kinetic adsorption experiment was performed to investigate the speed of adsorption and the time to reach the adsorption balance. 1D SDS-PAGE analysis and capillary electrophoresis were used to validate its selective adsorption ability. The resulting Fe3O4@SiO2@MAsp-HEMA showed a uniform spherical shape at nanoscale dimensions of about 200–300 nm, removing efficiency above 80%, and maximum adsorption capacity of 18.08 μg mg−1 at 15 ± 0.5 °C. The binding between IgG and the ligand was confirmed by isothermal titration calorimetry. The hydrogen bonding force was demonstrated as one of the major interactions between the functional groups of the as-synthesized magnetic nanoparticles and IgG by a molecular docking experiment.

Tetra-proline modified calix[4]arene bonded silica gel: A novel stationary phase for hydrophilic interaction liquid chromatography

Calixarenes and their derivatives have been widely used in chromatographic studies due to unique host-guest recognition properties. However, stationary phases in hydrophilic interaction chromatography associated with them have yet to be studied because of their general hydrophobicity. In this paper, a tetra-proline modified calix[4]arene bonded stationary phase (DTPCSP) was prepared and characterized by FT-IR spectra, elemental analysis, solid state 13C NMR, SEM, EDS and thermogravimetric analysis. The chromatographic performance and retention mechanism of the developed stationary phase were validated in hydrophilic interaction mode and compared with a commercial column using a variety of hydrophilic or hydrophobic compounds including phenols, nucleosides and sulfonamides. The developed stationary phase exhibited better selectivity than conventional calixarene phases, and the retention behaviors of phenols on DTPCSP column were elucidated by the calculation of quantum chemistry using ODS as contrast. All the results indicate that the developed DTPCSP stationary phase can be beneficial for simultaneously separating complex hydrophilic samples with high selectivity.