Correction to: Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone.

The published version of this article, unfortunately, contains error. The author found out that Chart 1 image was wrongly incorporated in the online paper.

Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone.

Graphene oxide (GO) was modified with the cobalt(II) and zinc(II) complexes (CoTFPP and ZnTFPP) of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin in order to improve the electrocatalytic activity of GO towards catechol (CC) and hydroquinone (HQ). It is found that the CoTFPP-modified GO on a glassy carbon electrode (GCE) displays the highest electrocatalytic activity. The response to CC (at 0.14 V vs. SCE) is linear in the 1-220 µM concentration range. The response to HQ (at 0.04 V vs. SCE) extends from 1 µM to 200 µM. The sensitivity and detection limits are 10.40 µA∙µM-1∙cm-2 and 0.17 µM for CC, and 8.40 µA∙µM-1∙cm-2 and 0.21 µM for HQ. Experimental results indicate that the Co(II) and Zn(II) ions in the porphyrins positively affect the electron transfer rate in the hybrid materials. The GCE modified with CoTFPP/GO was successfully applied to the simultaneous determination of CC and HQ in spiked samples of tap and lake water. Graphical abstract Schematic presentation of a voltammetric method for simultaneous determination of catechol (CC) and hydroquinone (HQ). It is based on the use of a cobalt (II) fluoroporphyrin (CoTFPP) functionalized graphene oxide (GO) hybrid.

Determination of Phenolic Compounds in Environmental Water by HPLC Combination with On-Line Solid-Phase Extraction Using Molecularly Imprinted Polymers.

A novel molecularly imprinted polymer (MIP) was synthesized using halloysite nanotubes (HNT) as matrix, ß-cyclodextrin (ß-CD) and methyl propyl acid (MAA) as functional monomers, and 2,4,6-TCP as template molecule by graft copolymerization. Infrared spectroscopy and transmission electron microscopy (TEM) were used to characterize the as-synthesized imprinted polymer. The selective recognizability of the MIP towards four phenolic analogs were determined and the recognition coefficients for 2,4,6-TCP, 2,6-DCP, 4-CP and phenol were found to be 2.17, 1.85, 2.02 and 1.36, respectively. Using as the packing material of solid-phase extraction, the imprinted polymer has been applied to on-line extraction of the four phenolic compounds in environmental water. The corresponding analytical methods to determine these four phenolic compounds have been developed. Good linear relationships were obtained over the range of 0.05-5.0 mg x L(-1). The average recoveries for spiked samples were in the range of 74.8-97.2%, and the detection limits for 2,4,6-TCP, 2,6-DCP, p-chlorophenol, phenol were 0.19, 0.20, 0.75, 0.73 mg x L(-1), respectively. The method is rapid, accurate and high selectivity. It was feasible for the determination of trace level phenolic compounds in environmental samples.

Simultaneous determination of five flavonoids components in different parts of Callistephus chinensis by HPLC / 中草药

Objective: To establish an HPLC method for the simultaneous determination of five flavonnid components in different parts of Callistephus chinensis. Methods: The chromatographic separation was performed on an XUnion C18 column (250 mm × 4.6 mm, 5 μm) with a gradient of acetonitrile and water, at a flow rate of 1 mL/min, and detected at 210 nm. Results: The calibration curve was linear within 2.5-200 mg/L for hyperoside, apigenin-7-O-β-D-glucopyranoside, luteolin, apigenin, and kaempferol, respectively, with the correlation r > 0.999 0. The extraction recoveries varied from 95% to 105%. Conclusion: The method is accurate and selective, and can be used for the quality control of different parts of C. chinensis.

Self-assembly of L-cysteine for chiral recognition of mandelic acid in gas phase.

This study demonstrates a new approach for the selective recognition of chiral mandelic acid by quartz crystal microbalance (QCM) using L-cysteine as the selector. The modification of L-cysteine on the QCM sensor was identified using resonant frequency detection, the contact angle, cyclic voltammetry, and X-ray photoelectron spectroscopy measurements. The chiral recognizability of L- and D-MA on the L-cysteine-modified surface was examined using QCM detection integrated with a vapor diffused molecular assembly reaction technique. The present chiral recognition results suggest that the L-cysteine is a good resolving agent for detecting chiral mandelic acid.

Chiral recognition of mandelic acid on quartz crystal microbalance by vapor diffused molecular assembly method.

This study presents a new approach for the highly selective recognition of chiral L/D-mandelic acid (MA) using a quartz crystal microbalance (QCM) with L-phenylalanine (L-Phe) as the selector. The immobilization of L-Phe on the gold surface of the QCM sensor was performed using a four steps layer-by-layer assembling procedure. The modification of the gold surface of the QCM sensor after each modification step was verified by the cyclic voltammetry, contact angle, FTIR, and QCM detection. The chiral recognition ability of L- and D-MA on the chiral surface was checked by sensing using the vapor diffused molecular assembly (VDMA) method with the QCM. The chiral discrimination factor between L- and D-MA, aplha(L-MA/D-MA), was found to be about 9. The L-Phe-modified QCM gold sensor also showed good stability and reusability. The high chiral discrimination ability of the modified surface might be the result of the different hydrogen bonding force between L- or D-MA and L-Phe.

Chiral recognition of mandelic acid by L-phenylalanine-modified sensor using quartz crystal microbalance.

This study presents a new method for the highly selective recognition of chiral mandelic acid (MA) using L-phenylalanine (L-Phe) as the selector. The proposed method is based on quartz crystal microbalance (QCM) detection, integrated with a vapor diffused molecular assembly (VDMA) reaction technique. The construction of the L-Phe-modified QCM sensor involved a two-step assembly procedure. The chiral recognizability of L- and D-MA on the L-Phe-modified surface was then examined using the VDMA method and QCM. The chiral discrimination factor between L- and D-MA detected by QCM, alpha(L-MA/D-MA), was found to be about 8. The VDMA selective sensing of L-MA on the L-Phe-modified surface was also confirmed by the contact angle measurements. The L-Phe-modified QCM sensor showed good stability and reusability. The present chiral recognition results suggest that L-phe is an excellent resolving agent for the resolution of chiral mandelic acid.

Versatile method for chiral recognition by the quartz crystal microbalance: chiral mandelic acid as the detection model.

Chiral recognition is considered to be the most important, fundamental basis in the development of separation technology for chiral isomers in the pharmaceutical and biotechnology fields. However, the selective detection of individual enantiomers is still one of the most difficult analytical tasks because of the close similarity of the molecular configurations between chiral isomers. This study presents a versatile vapor-diffused molecular assembly (VDMA) reaction approach for chiral recognition by the quartz crystal microbalance (QCM). Chiral L/D-mandelic acid (MA) was used as the detection model, and L-phenylalanine (L-Phe) was used as the selector. The construction of the L-Phe-modified QCM sensor involved a four-step layer-by-layer assembly procedure. Each modification step was analyzed by cyclic voltammetry, the contact angle, and a resonance frequency measurement. The chiral recognizability of the L-Phe-modified QCM sensor to L-mandelic acid was then examined by resonance frequency measurement using the novel VDMA technique and also investigated by atomic force microscope (AFM) measurements. A chiral discrimination factor of up to approximately 9 between L- and d-MA on the L-Phe-modified QCM sensor was obtained by using this gaseous-phase reaction technique. AFM results also showed obvious selective aggregation of L-MA on the L-Phe-modified surface but no noticeable aggregation of D-MA during the VDMA reaction. Both of the QCM and AFM results confirmed the usefulness of this proposed VDMA technique for the study of chiral recognition. The main advantage of the proposed method is that it offers a universal simple application scheme for the QCM detection of small resonance frequency changes due to chiral molecular recognition by a chiral selector immobilized on the QCM sensor surface.