On-Fiber Derivatization of SPME Extracts of Phenol, Hydroquinone and Catechol with GC-MS Detection

Fabrication of Poly (Trans-3-(3-Pyridyl)Acrylic Acid)/Multi-Walled Carbon Nanotubes Membrane for Electrochemically Simultaneously Detecting Catechol and Hydroquinone

Herein, conductive polymer membrane with excellent performance was successfully fabricated by integrating carboxylated multi-walled carbon nanotubes (MWCNTs) and poly (trans-3-(3-pyridyl) acrylic acid) (PPAA) film. The drop-casting method was employed to coated MWCNTs on the glassy carbon electrode (GCE) surface, and PPAA was then electropolymerized onto the surface of the MWCNTs/GCE in order to form PPAA-MWCNTs membrane. This enables the verification of the excellent performances of proposed membrane by electrochemically determining catechol (CC) and hydroquinone (HQ) as the model. Cyclic voltammetry experiments showed that the proposed membrane exhibited an obvious electrocatalytic effect on CC and HQ, owing to the synergistic effect of PPAA and MWCNTs. Differential pulse voltammetry was adopted for simultaneous detection purposes, and an increased electrochemical responded to CC and HQ. A concentration increase was found in the range of 1.0 × 10^-6 mol/L~1.0 × 10^-4 mol/L, and it exhibited a good linear relationship with satisfactory detection limits of 3.17 × 10^-7 mol/L for CC and 2.03 × 10^-7 mol/L for HQ (S/N = 3). Additionally, this constructed membrane showed good reproducibility and stability. The final electrode was successfully applied to analyze CC and HQ in actual water samples, and it obtained robust recovery for CC with 95.2% and 98.5%, and for HQ with 97.0% and 97.3%. Overall, the constructed membrane can potentially be a good candidate for constructing electrochemical sensors in environmental analysis.

A voltammetry biosensor based on self-assembled layers of a heteroleptic tris(phthalocyaninato) europium triple-decker complex and tyrosinase for catechol detection

A highly efficient enzyme-based sensor was made from a heteroleptic tris(phthalocyaninato) europium triple-decker complex Eu₂(Pc)[Pc(OPh)₈]₂, for the first time. The ITO working electrode was modified by a mixture of hybrid multi-layers consisting of Eu₂(Pc)[Pc(OPh)₈]₂, stearic acid (SA) and tyrosinase (Tyr) (Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr-ITO) using the Langmuir-Blodgett (LB) technique. The microstructure and morphology of the resulting LB films can be characterized by their π-A isotherms, UV-vis absorption spectra, X-ray diffraction and atomic force microscopy (AFM) analysis. The experimental results revealed that the triple-decker molecules of Eu₂(Pc)[Pc(OPh)₈]₂ take a H-type molecular stacking mode in both pure and mixed LB film, and the microstructures of films were effectively improved by mixing SA within the triple-decker Eu₂(Pc)[Pc(OPh)₈]₂ molecules. The excellent electrocatalytic effect of the Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr LB films, leads to a good linear increase from 5.26 × 10^-7 to 2.1 × 10^-4 M for catechol. It also leads to an excellent sensitivity of 2.19 μA/μM, and a detection limits of 6.29 × 10^-8 M (S/N = 3) of catehol at the oxidation peak, achieving best catechol sensing performance among the phthalocyanine-based biosensing mediators. The reduction peak also showed a good linear increase from 5.26 × 10^-7 to 1.60 × 10^-4 M for catechol with a sensitivity of 0.615 μA/μM, and a detection limit of 1.69 × 10^-7 M (S/N = 3). Moreover, the Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr-ITO electrode are easy to reproduce, stable and resistant to interference when it comes to detection for catehol, and this indicates great potential of industrial application of tris(phthalocyaninato) rare earth complexes in ultrasensitive and specific biosensors.

Mass spectrometric detection of the Gibbs reaction for phenol analysis

This paper describes a new method for detecting phenols, by reaction with Gibbs reagent to form indophenols, followed by mass spectrometric detection. Unlike the standard Gibbs reaction, which uses a colorometric approach, the use of mass spectrometry allows for simultaneous detection of differently substituted phenols. The procedure is demonstrated to work for a large variety of phenols without para-substitution. With para-substituted phenols, Gibbs products are still often observed, but the specific product depends on the substituent. For para groups with high electronegativity, such as methoxy or halogens, the reaction proceeds by displacement of the substituent. For groups with lower electronegativity, such as amino or alkyl groups, Gibbs products are observed that retain the substituent, indicating that the reaction occurs at the ortho or meta position. In mixtures of phenols, the relative intensities of the Gibbs products are proportional to the relative concentrations, and concentrations as low as 1 μmol/L can be detected. The method is applied to the qualitative analysis of commercial liquid smoke, and it is found that hickory and mesquite flavors have significantly different phenolic composition.

Phenol-selective mass spectrometric analysis of jet fuel

A bromobenzyl charged tag selectively reacts with key contaminants in jet fuel to provide charged ethers that are readily detectable by ESI-MS.

Simultaneous electrochemical detection of catechol and hydroquinone based on gold nanoparticles@carbon nanocages modified electrode

Illustration of the synthesis of AuNPs@CNCs and the electrochemical oxidization of CC and HQ.

Microextraction in urine samples for gas chromatography: a review

Since the complexity origin of biological samples, the research trends have been directed to the development of new miniaturized sample preparation techniques. This review provides a comprehensive survey of past and present microextraction methods followed by GC analysis for preconcentration and determination of various analytes in urine samples. These techniques have been classified in three general groups, including liquid-, solid- and membrane-based techniques. The principal of different microextraction methods that are located in each general group as well as their various extraction modes and the recent developments introduced for them has been presented. Subsequently, a comparison survey has been carried out among different microextraction techniques and finally a future perspective has been predicted based on the existing literature.

Stable isotope dilution analysis of salicylic acid and hydroquinone in human skin samples by gas chromatography with mass spectrometric detection

A sensitive and accurate gas chromatographic-mass spectrometric (GC-MS) method has been developed for the quantitative determination of salicylic acid (SA) and hydroquinone (HQ) from human skin samples and cosmetic emulsions. Deuterium labeled SA-d(6) and HQ-d(6) were used as internal standards (IS). The samples were extracted with methanol, dried under nitrogen and derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)+1% trimethylchlorosilane (TMCS). Quantification was performed in SIM mode with a limit of quantification (LOQ) of 50 ng ml(-1) for SA and 10 ng ml(-1) for HQ. The inter-day variation (R.S.D.) was less than 5% and the accuracy was better than 13.3% for both compounds. The recoveries from the different matrices ranged between 93.1 and 103.3% for SA, and 97.3 and 100.8% for HQ.