Zr(IV)-based metal-organic framework nanocomposites with enhanced peroxidase-like activity as a colorimetric sensing platform for sensitive detection of hydrogen peroxide and phenol

Recently, metal-organic frameworks (MOFs) have great potential as an emerging peroxide-mimicking enzyme, and the improvement of its enzyme-like activity is desired. There are few studies on improving the peroxidase-like activity of MOFs by using the strategy of size reduction. Moreover, it is challenging to enhance the activity of Zr-based MOFs with peroxidase-mimicking activity by size reduction strategy. In this work, the synthesis of Zr-based MOFs capped with polyvinylpyrrolidone (Zr-MOF-PVP) was firstly reported to reduce crystal size of peroxidase-mimicking enzyme for enhanced catalytic activity. Using the 3,3',5,5'-Tetramethylbenzidine (TMB) as substrate, the synthesized Zr-MOF-PVP nanocomposites with nanosize (about 45 nm) possessed obviously enhanced peroxidase-like activity compared with the pristine Zr-MOF. Based on the above, the Zr-MOF-PVP was also successfully applied in constructing colorimetric detection. By using hydrogen peroxide (H₂O₂) and phenol as the model analytes, the satisfactory detection performance was obtained, indicating that the proposed method had an attractive application prospect in the field of peroxidase-related detection. Besides, this work also provided a new perspective for improving the catalytic activity of nanozymes.

Simultaneous determination of 11 preservatives in cosmetics and pharmaceuticals by matrix solid-phase dispersion coupled with gas chromatography

A convenient method was developed for simultaneous determination of 11 preservatives in cosmetics and pharmaceuticals. Matrix solid-phase dispersion had been optimized as the sample pretreatment technology, using Florisil as a dispersant, anhydrous sodium sulfate as a dehydrant, formic acid as an additive, and n-hexane and ethyl acetate as eluents successively, and followed by gas chromatography–flame ionization detection on a TR-5 capillary column. Experimental results showed that 11 preservatives were baseline separated within 22 min. Good linearities were observed in the concentration range of 0.53–250 μg/mL for all analytes, and there were also minor differences. All correlation coefficients (r) were more than 0.995. The average recoveries at 3 levels of spiked samples ranged from 80% to 124% with 0.9–12% intra-day RSD and 1.8–12% inter-day RSD. The limits of detection were less than 0.18 μg/mL for all analytes. Besides, there was no obvious matrix effect on the analytes. The conclusion was that the developed method was simple, cheap, accurate, precise, and environment-friendly, in addition to existing little matrix effects. It could be recommended to determine 11 preservatives individually or in any their combinations to not only in liquid and gel cosmetics but also in liquid medicine and ointment.

Analysis of methylparaben in cosmetics based on a chemiluminescence H2 O2 -NaIO4 -CNQDs system

In this article, a simple, effective chemiluminescence (CL) method for the detection of methylparaben (MP) in cosmetic samples was developed based on an IO₄ ^- -H₂ O₂ -carbon nitrogen quantum dots (CNQDs) system without a separation process. The results indicated that the redox reaction between periodate and hydrogen peroxide released hydroxide radicals and superoxide radical anions in the presence of bicarbonate. These two radicals were responsible for the formation of excited luminophor CNQD* with a maximum wavelength at 480 nm. Due to the competitive reaction with hydroxide radicals, CL intensity was markedly diminished in the presence of MP. The relative standard deviation in the intraday assay was below 5.5% (n = 9), and the detection limit was as low as 0.50 μmol/L. The proposed method allowed for the successful, selective determination of MP in cosmetics.

Positive lists of cosmetic ingredients: Analytical methodology for regulatory and safety controls - A review

Cosmetic products placed on the market and their ingredients, must be safe under reasonable conditions of use, in accordance to the current legislation. Therefore, regulated and allowed chemical substances must meet the regulatory criteria to be used as ingredients in cosmetics and personal care products, and adequate analytical methodology is needed to evaluate the degree of compliance. This article reviews the most recent methods (2005-2015) used for the extraction and the analytical determination of the ingredients included in the positive lists of the European Regulation of Cosmetic Products (EC 1223/2009): comprising colorants, preservatives and UV filters. It summarizes the analytical properties of the most relevant analytical methods along with the possibilities of fulfilment of the current regulatory issues. The cosmetic legislation is frequently being updated; consequently, the analytical methodology must be constantly revised and improved to meet safety requirements. The article highlights the most important advances in analytical methodology for cosmetics control, both in relation to the sample pretreatment and extraction and the different instrumental approaches developed to solve this challenge. Cosmetics are complex samples, and most of them require a sample pretreatment before analysis. In the last times, the research conducted covering this aspect, tended to the use of green extraction and microextraction techniques. Analytical methods were generally based on liquid chromatography with UV detection, and gas and liquid chromatographic techniques hyphenated with single or tandem mass spectrometry; but some interesting proposals based on electrophoresis have also been reported, together with some electroanalytical approaches. Regarding the number of ingredients considered for analytical control, single analyte methods have been proposed, although the most useful ones in the real life cosmetic analysis are the multianalyte approaches.

Preparation of magnetic core–shell nanoflower Fe3O4@MnO2 as reusable oxidase mimetics for colorimetric detection of phenol

In this paper, magnetic core–shell nanoflower Fe₃O₄@MnO₂ were fabricated via a solvothermal method.

Determination of anions using monolithic capillary column ion chromatography with end-to-end differential contactless conductometric detectors under resonance approach

An end-to-end differential measurement approach with capacitively coupled contactless conductivity detection (C(4)D) was applied to anion-exchange monolithic capillary column ion chromatography. The column was prepared by thermally initiated radical polymerization of poly(glycidyl methacrylate) in a fused-silica capillary of 320 μm i.d. and modified by quaternary ammonium latex surface coating. Two C(4)Ds were placed near both ends of the capillary column and the output difference between them was measured. With 15 mM potassium hydrogen phthalate used as the eluent, good separation of a mixture of inorganic anions (F(-), Cl(-), NO(2)(-), NO(3)(-)) was achieved. The detection limits of conventional C(4)D are 1.6, 0.28, 0.53, and 0.47 mg L(-1) for F(-), Cl(-), NO(2)(-), and NO(3)(-), respectively. To further enhance the sensitivity, the capacitive impedance from C(4)D was neutralized by an inductive impedance from a piezoelectric resonator. An increase in sensitivity by a factor of 7-8 was achieved in the resonating C(4)D in comparison with the conventional C(4)D. The detection limits of the resonating C(4)D are 0.23, 0.041, 0.065, and 0.059 mg L(-1) for F(-), Cl(-), NO(2)(-), and NO(3)(-), respectively. The response of the resonating C(4)D was analyzed based on an equivalent circuit model.