Haiyun Zhai

Molecularly imprinted coated graphene oxide solid-phase extraction monolithic capillary column for selective extraction and sensitive determination of phloxine B in coffee bean

A method was developed to sensitively determine phloxine B in coffee bean by molecularly imprinted polymers (MIPs) coated graphene oxide (GO) solid-phase extraction (GO-MISPE) coupled with high-performance liquid chromatography and laser-induced fluorescence detection (HPLC-LIF). The GO-MISPE capillary monolithic column was prepared by water-bath in situ polymerization, using GO as supporting material, phloxine B, methacrylic acid (MAA), and ethylene dimethacrylate (EDMA) as template, functional monomer, and cross-linker, respectively. The properties of the homemade GO-MISPE capillary monolithic column, including capacity and specificity, were investigated under optimized conditions. The GO-MIPs were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR). The mean recoveries of phloxine B in coffee bean ranged from 89.5% to 91.4% and the intra-day and inter-day relative standard deviation (RSD) values all ranged from 3.6% to 4.7%. Good linearity was obtained over 0.001-2.0 μg mL(-1) (r=0.9995) with the detection limit (S/N=3) of 0.075 ng mL(-1). Under the selected conditions, enrichment factors of over 90-fold were obtained and extraction on the monolithic column effectively cleaned up the coffee bean matrix. The results demonstrated that the proposed GO-MISPE HPLC-LIF method can be applied to sensitively determine phloxine B in coffee bean.

Preparation and evaluation of a novel molecularly imprinted SPE monolithic capillary column for the determination of auramine O in shrimp

A novel method combining molecular imprinting and SPE was developed in a capillary column for the determination of auramine O in shrimp. The capillary monolithic column was prepared by UV-initiated in situ polymerization, using auramine O as template and methacrylic acid and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The properties of the prepared capillary monolithic column were investigated under the optimized conditions coupled with HPLC, and then the morphologies of the inner polymers were characterized by SEM. The calibration curve was expressed as A = 103C + 19.8 (r = 0.9992) with a linear range of 0.25-25.0 μg/mL, and the recoveries of auramine O at different concentrations in shrimp ranged from 90.5 to 92.4% with RSDs ranging from 2.1 to 4.4%. The capacities of the molecularly imprinted polymer and nonimprinted polymer columns were 0.722 and 0.147 μg/mg, respectively, and the LOD (S/N = 3) of auramine O in shrimp was 17.85 μg/kg. Under the selected conditions, the enrichment factors obtained were higher than 70-fold. The results indicate that the prepared molecularly imprinted capillary monolithic column was reliable and applicable to the analysis of auramine O in shrimp.

Chip-based molecularly imprinted monolithic capillary array columns coated GO/SiO2 for selective extraction and sensitive determination of rhodamine B in chili powder

A novel solid-phase extraction chip embedded with array columns of molecularly imprinted polymer-coated silanized graphene oxide (GO/SiO2-MISPE) was established to detect trace rhodamine B (RB) in chili powder. GO/SiO2-MISPE monolithic columns for RB detection were prepared by optimizing the supporting substrate, template, and polymerizing monomer under mild water bath conditions. Adsorption capacity and specificity, which are critical properties for the application of the GO/SiO2-MISPE monolithic column, were investigated. GO/SiO2-MIP was examined by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy. The recovery and the intraday and interday relative standard deviations for RB ranged from 83.7% to 88.4% and 2.5% to 4.0% and the enrichment factors were higher than 110-fold. The chip-based array columns effectively eliminated impurities in chili powder, indicating that the chip-based GO/SiO2-MISPE method was reliable for RB detection in food samples using high-performance liquid chromatography. Accordingly, this method has direct applications for monitoring potentially harmful dyes in processed food.

Sensitive determination of rose bengal in brown sugar by a molecularly imprinted solid-phase extraction monolithic capillary column coupled with capillary electrophoresis

A method employing molecularly imprinted solid-phase extraction (MISPE) coupled with capillary electrophoresis laser-induced fluorescence detection (CE-LIF) was developed for the determination of rose bengal in brown sugar. The rose bengal imprinted monolithic column was prepared by in situ polymerization, utilizing rose bengal as a template, methacrylic acid as a functional monomer and ethylene dimethacrylate as a cross-linker. The capacity and specificity of this column were evaluated by CE-LIF, and the morphology was characterized by scanning electron microscopy. The recoveries ranged from 89.7% to 90.3% (relative standard deviation 3.6–4.5%, n = 5). The capacities of the molecularly imprinted polymer and non-imprinted polymer columns were 1.314 μg mg−1 and 0.531 μg mg−1, respectively. The detection limit (S/N = 3) was 3 ng mL−1. The enrichment factor was higher than 63-fold and the MISPE column managed to remove rose bengal from the matrix of brown sugar effectively. This method can be applied to sensitively and effectively determine rose bengal in brown sugar.

A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis

A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y‐style optical fiber was used to transmit the excitation light and a four‐branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low‐cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis.

Synthesis of carbon quantum dots-doped dummy molecularly imprinted polymer monolithic column for selective enrichment and analysis of aflatoxin B 1 in peanut

Graphical abstract Figure. No caption available. HighlightsA novel CDs‐DMIP monolithic capillary column coupled with HPLC‐FLD was prepared.The column showed ability of impurities removal and excellent selectivity.Template elution process of CDs‐DMIP was easier than that of DMIP.Aflatoxin B1 existed in peanut sample was enriched more than 71 times.The method was prospered to analyze Aflatoxin B1 and LOD achieved 0.118 ng mL−1. ABSTRACT In this study, a novel method was proposed to sensitively determine aflatoxin B1 (AFB1) in peanut sample by using a carbon quantum dots‐coated dummy molecularly imprinted polymer (CDs‐DMIP) monolithic column for pretreatment coupled with high performance liquid chromatography‐fluorescence detection (HPLC‐FLD). The CDs‐DMIP monolithic column was prepared by in‐situ polymerization in a water bath using 5,7‐dimethoxycoumarin as dummy template molecule. The CDs‐DMIP monolithic column was applied to determine AFB1 by HPLC‐FLD. Satisfactory linearity was obtained over 0.5–2000 ng mL−1, with a high correlation coefficient of 0.9999. The recoveries of AFB1 in peanut sample ranged from 79.5% to 91.2%, and the intraday and interday relative standard deviation ranged from 1.2% to 4.9%. Limit of detection (S/N = 3) and limit of quantitation (S/N = 10) were 0.118 ng mL−1 and 0.393 ng mL−1, respectively. Under the optimized conditions, the enrichment factor was over 71‐fold. AFB1 in peanut sample and even some other samples could be sensitively determined by CDs‐DMIP‐HPLC‐FLD method.

The electrochemical behaviors of tetrahydropalmatine at a nickel nanoparticles/sulfonated graphene sheets modified glassy carbon electrode

A novel electrochemical sensor was designed to determine tetrahydropalmatine (THP) by using a nickel nanoparticles deposited on sulfonated graphene sheets-modified glassy carbon electrode (NiNPs/SGS/GCE). The components and morphological properties of the NiNPs/SGS nanocomposites were investigated by scanning electron microscopy. The anodic peak current (Ipa) of THP at the GCE modified with NiNPs/SGS was much higher than those at the bare GCE and SGS/GCE due to the enhanced effect of the modified nanomaterials. Differential pulse voltammetry (DPV) disclosed a good linear relationship between Ipa and concentrations of THP (0.50–20.0 μM), with a limit of detection of 0.17 μM. Finally, the modified electrode was successfully applied for the determination of THP in Yuanhu Zhitong capsules.

Chip-based dual-molecularly imprinted monolithic capillary array columns coated Ag/GO for selective extraction and simultaneous determination of bisphenol A and nonyl phenol in fish samples

An analytical technique for selective, simultaneous determination of bisphenol A (BPA) and nonyl phenol (NP) in fish samples was established by a solid-phase extraction chip integrated with array columns of dual-molecularly imprinted polymer-coated silver-modified graphene oxide (Ag/GO-dual-MISPE-chip). Ag/GO dual-molecularly imprinted polymers (Ag/GO-dual-MIPs) were synthesized by in situ polymerization using Ag/GO as the supporting matrix which extracted templates easily. The affinity and specificity on the Ag/GO-dual-MISPE monolithic column were also investigated. The array extraction chip showed high binding capacity and selectivity to BPA and NP, with the imprinting factors of BPA and NP reaching 2.6 and 2.9, respectively. Ag/GO-dual-MIPs were characterized by scanning electron microscopy and Fourier transform-infrared (FT-IR) spectroscopy. As Low as 2.4ngL-1 BPA and 4.7ngL-1 NP were detected by high performance liquid chromatography coupled with fluorescence detection. The enrichment factor was 113-fold for BPA and 92-fold for NP. Therefore, the chip-based array columns are feasibly applicable to facile extraction of BPA and NP and effective clean-up of impurities in fish samples.

Preparation and characterization of molecularly imprinted solid-phase extraction column coupled with high-performance liquid chromatography for selective determination of melamine

We synthesized a selective molecularly imprinted solid-phase extraction (MIP-SPE) column and established an extraction and enrichment method using this MIP-SPE column. By coupling with HPLC, we developed a new method to detect trace amounts of melamine in eggs. The MIP-SPE column was synthesized by in situ thermal-initiated polymerization using melamine as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and azodiisobutyronitrile as the initiator. HPLC was used to evaluate the identification and enrichment capability of the MIP-SPE column and for the measurement of melamine in the sample. The melamine concentration exhibited an excellent linear relationship in the range of 0.1–25.0 µg ml−1 (r = 0.9983). The identification capability of the MIP-SPE column was apparently superior to that of the non-imprinted polymer solid-phase extraction column; an average enrichment factor of 46.8-fold (RSD = 3.5%) was obtained for 0.4 µg ml−1 melamine by the MIP-SPE column. When the MIP-SPE HPLC method was applied to the detection of melamine in eggs, an average recovery rate of 93.5–102.0% (RSD = 3.6–4.9%) and a limit of detection of 0.05 µg kg−1 were obtained. This method is simple, fast and cost-effective; thus, it can greatly simplify the pre-treatment of complex samples and can be used in the detection of residual melamine in eggs and other products.

A simple and sensitive sensor based on a molecularly imprinted polymer-modified carbon paste electrode for the determination of curcumin in foods

A highly sensitive and selective molecularly imprinted polymer-modified carbon paste electrode (MIP-CPE) was designed. The curcumin molecularly imprinted polymer (CUR-MIP) was prepared by thermally induced precipitation polymerization, using curcumin (CUR) as the template molecule, methacrylic acid (MAA) as the functional monomer, 2,2′-azodiisobutyronitrile (AIBN) as the initiator, and ethylene glycol dimethacrylate (EDGMA) as the cross-linker. The modified electrode was prepared by mixing the polymer, graphite powder, and paraffin oil in specific proportions. The electrochemical behaviour of CUR on this electrode was studied, and a method for direct CUR determination using this electrode was established. The results showed that CUR exhibited a distinct oxidation peak (Epa) at 0.434 V (vs. SCE) in the mixed phosphate buffer solution (PBS) at pH 3.06. The optimum addition ratio of the polymer in the modified electrode was 20%, and the peak current (Ipa) was 4.5-fold higher than that of the bare CPE. The Ipa showed a good linear relationship with concentration in the range 0.1–50 μM, and the detection limit was 10.1 nM. The method was applied to determine CUR contents in food, giving recovery rates of 90.77–105.7%.