Wenfen Zhang

Calixarene ionic liquid modified silica gel: A novel stationary phase for mixed-mode chromatography.

A novel calixarene ionic liquid functionalized silica material was synthesized by the preparation of a new calixarene monomer and its grafting on mercaptopropyl modified silica gel. The material was characterized by infrared spectra, elemental analysis, and thermogravimetric analysis. To explore the retention mechanism of the stationary phase, linear solvation energy relationships (LSER) equation as an effective mathematical model was used. In addition to this, the distinct separation mechanisms were outlined by selected examples of chromatographic separations in the different modes. In reversed-phase liquid chromatography, this new stationary phase presented specific chromatographic performance when evaluated using alkylbenzenes, PAHs and phenols as solutes. Due to the existing polar functional groups, this stationary phase can also be used in hydrophilic interaction chromatography, six nucleosides and four ginsenosides were separated successfully in hydrophilic mode. Furthermore, anions can be separated on the column in anion exchange mode. Thus, this new material was can be applied as a new kind of mixed-mode stationary phase in liquid chromatography, which allows an exceptionally flexible adjustment of retention and selectivity by tuning the experimental conditions.

A new stationary phase for high performance liquid chromatography: Calix[4]arene derivatized chitosan bonded silica gel☆

In the present paper, a new calix[4]arene derivatized chitosan bonded stationary phase (CCS4) for high performance liquid chromatography (HPLC) was synthesized and characterized. Its chromatographic performance and retention mechanism were evaluated in reversed-phase mode compared with ODS using different solute probes including mono-substituted benzenes, phenols and nucleosides. The results showed that CCS4 stationary phase could provide various interactions with solutes, such as hydrophobic, hydrophilic, π-π, and inclusion interactions. It could perform the mixed-mode separation including RP and HILIC.

Sensitive determination of four tetracycline antibiotics in pig plasma by field-amplified sample stacking open-tubular capillary electrochromatography with dimethylethanolamine aminated polychloromethyl styrene nano-latex coated capillary column.

This paper described the preparation and application of a new dimethylethanolamine aminated polychloromethyl styrene nano-latex (DMEAPL) coated capillary column (ccc-DMEAPL) in the determination of four tetracycline antibiotics (TCA) including tetracycline (TC), oxytetracycline (OTC), doxycycline (DC) and chlorotetracycline (CTC) in pig plasma. The ccc-DMEAPL column was characterized with steady EOF values of ca. 1.5-5.2×10(-5)cm(2)/Vs at pH 1.8-6.3. The optimized conditions for field-amplified sample stacking open-tubular capillary electrochromatography (FASS-OT-CEC) were as following: background electrolyte, 10mmol/L Na2HPO4+15mmol/L citric acid (pH 3.2); ccc-DMEAPL, 50μm i.d.×50cm (effective length 41.5cm), separation voltage, 18kV; column temperature, 25°C; UV detection wavelength, 270nm; water-plug injection: 30mbar×10s; sample electrokinetic injection, 10kV×20s. The four TCA were extracted with the solution of 10mmol/L Na2HPO4+15mmol/L citric acid+4g/L EDTA-2Na (pH 3.2). The FASS-OT-CEC method was validated in terms of linearity, sensitivity, selectivity, precision and accuracy. The LODs ranged from 3 to 7ng/mL, the recoveries for the four TCA were all more than 80%. The developed method was successfully applied for the determination of TCs in the actual pig plasma samples.

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.

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).

Determination of trace nitrites and nitrates in human urine and plasma by field-amplified sample stacking open-tubular capillary electrochromatography in a nano-latex coated capillary

The associations of nitric oxide (NO) with many diseases are still being discovered, and sometimes, NO levels in the body fluids are too low to be detected. Thus, the determination methods for trace nitrites and nitrates in urine and plasma of healthy volunteers and rheumatoid arthritis (RA) patients are necessary. Using trimethylamine aminated polychloromethyl styrene nano-latex coated capillary column (ccc-TMAPL) and field-amplified sample stacking (FASS) injection, the sensitive open-tubular capillary electrochromatography (OT-CEC) methods for determining trace nitrites and nitrates in urine and plasma of healthy volunteers and RA patients were set up. The limits of detection for both nitrite and nitrate were 1 ng/mL. The intra- and inter-day relative standard deviations (RSDs) of the methods were less than 1.9%, and recoveries were between 89 and 96%. Plasma nitrate (diluted 10 times) levels were 93–301 ng/mL for healthy volunteers and 222–421 ng/mL for RA patients, respectively. Meanwhile, plasma nitrite levels were 7–18 and 40–82 ng/mL, respectively. The urinary nitrite levels were significantly elevated in RA patients. The proposed sensitive FASS-OT-CEC methods for trace nitrites and nitrates hold the promise of practical applications in a wide array of biological analyses, clinical and pathophysiology studies of the diseases related with NO hyperproduction and metabolites.

Sensitive analysis of trace caffeine in human serum by HPLC using tetraazacalix[2]arene[2]triazine-modified silica as SPE sorbent

In this paper, a rapid and effective SPE-HPLC method, using tetraazacalix[2]arene[2]triazine modified silica gel (NCSi) as solid-phase extraction (SPE) sorbent, was established to enrich and determine caffeine in human serum. All 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 limits of detection (LODs) and quantitation (LOQs) were 1 ng mL−1 and 5 ng mL−1, respectively, whereas the overall recoveries ranged from 90.3% to 93.5%, the relative standard deviation (RSD) of the method was less than 3.4%. In addition, the retention mechanism of caffeine on NCSi was investigated by quantum chemistry calculations. The optimized supramolecular structures showed that π–π and CH–π interactions exist between NCSi and caffeine. Thermodynamic results from quantum chemistry calculation (QCC) were consistent with the retention behaviors of caffeine on NCSi. The method of non-covalent interaction (NCI) 28 index developed by Yang and co-workers was used to distinguish strong interaction, van der Waals interaction and repulsive steric interactions. The QCC results further illustrated the stronger retention of caffeine on the tetraazacalix[2]arene[2]triazine-modified silica stationary phase. All of the results implied that NCSi was a promising SPE sorbent, and can be applied to the preconcentration and determination of trace caffeine in human serum.

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.

Determination of benzoic acid and sorbic acid in seasoning by capillary electrophoresis with a new triethylamine aminated polychloromethyl styrene nanolatex coated capillary column

In this work, a method for the determination of benzoic acid (BA) and sorbic acid (SA) in soy sauce and vinegar was developed by field-amplified sample stacking open-tubular capillary electrochromatography (FASS-OT-CEC) with a new triethylamine aminated polychloromethyl styrene nanolatex coated capillary column (ccc-TEAPL). The ccc-TEAPL was characterized with steady electroosmotic flow (EOF) values of ca. −16.7–19.8 × 10−5 cm2 V−1 s−1. Under the optimized conditions, BA and SA were well separated within 5 min (Rs > 1.5), and the limits of detection were 30 ng mL−1 and 5 ng mL−1, respectively. The recoveries were between 98.0 and 101.0%. These results demonstrate that the developed FASS-OT-CEC method is simple, rapid, sensitive and practical for the determination of BA and SA in the soy sauce and vinegar samples.