Resorcinol Concentration Research Articles

Mechanism of TMB Discoloration Catalyzed by Layered CoNi@CN Nanozymes: Application Based on Smart Phone for Resorcinol Detection

Comprehensive SummaryReal‐time on‐site monitoring of resorcinol (RS) concentrations is crucial for detecting hazardous levels, enabling prompt response measures to mitigate potential environmental and health risks. In this study, we developed an innovative method using CoNi@CN‐2 nanozymes to activate peroxymonosulfate (PMS) for oxidizing 3,3',5,5'‐tetramethylbenzidine (TMB). Our results show that the formation of Ni2+ through the oxidation of Ni0 on the CoNi@CN‐2 surface significantly enhances the electron‐donating capacity of Co0. The catalytic reaction of TMB is mediated by redox active species (SO4•−, •O2−, •OH and 1O2). RS drives colorimetry by transferring electrons to the benzene ring and specific nitrogen atoms in ox‐TMB, reducing ox‐TMB to TMB. Furthermore, the colorimetric assay shows a robust linear correlation between RS concentration and absorbance (Abs), described by Abs = –0.44[RS] + 0.886 (0—200 μmol/L, R2 = 0.983). Also, we introduce a novel smartphone‐integrated autonomous detection software that can analyze RS concentration and grayscale values (GSV), yielding GSV = 0.327[RS] + 63.601 (0—200 μmol/L, R2 = 0.990) with a detection limit of 5.29 μmol/L. Additionally, excess PMS leads to ROS attacking specific sites in ox‐TMB, forming secondary oxidation products. This study has enabled rapid and accurate detection of RS, making a significant contribution to environmental safety and protection.

High-Yield Preparation and Properties of Phenolic Resin-Based Carbon Microspheres.

This study aims to enhance the production efficiency of carbon microspheres (CS) and expand their potential applications. To this end, resorcinol-formaldehyde microspheres (RFS) were prepared in high yield through the modified Stöber method, utilizing resorcinol and formaldehyde as carbon sources, ammonia as a catalyst, and sodium dodecyl benzenesulfonate (SDBS) as a soft template. The resulting RFS were then carbonized to obtain high yield CS. This study examined the impact of key factors, namely, the concentration of resorcinol, ammonia, and the SDBS concentration, along with the temperature of carbonization, upon the properties of the resulting CS, which were observed with regard to microscopic morphology, average particle size, homogeneity, and yield. The findings demonstrated that the proclivity of RFS to agglomerate with one another at high carbon source concentrations was markedly diminished, while the yield of CS was notably enhanced through the introduction of the anionic surfactant SDBS. The particle size of RFS can be modified within the range 200-1000 nm by adjusting the resorcinol and ammonia concentration. The prepared RFS exhibited a regular spherical morphology and a smooth surface. Furthermore, the CS displayed a uniform spherical morphology following high-temperature carbonization, with no agglomeration or cross-linking observed between adjacent particles. It was observed that the yield of RFS reached a maximum of 93.2 g/L when the resorcinol concentration was 0.7 mol/L. Following carbonization at 800 °C, the yield of CS was found to be 41.9 g/L, with a diameter of 770 nm and good monodispersity.

Assessment of 5-Hydroxymethylfurfural in Food Matrix by an Innovative Spectrophotometric Assay.

Foods contaminants pose a challenge for food producers and consumers. Due to its spontaneous formation during heating and storage, hydroxymethylfurfural (HMF) is a prevalent contaminant in foods rich in carbohydrates and proteins. Colorimetric assays, such as the Seliwanoff test, offer a rapid and cost-effective method for HMF quantification but require careful optimization to ensure accuracy. We addressed potential interference in the Seliwanoff assay by systematically evaluating parameters like incubation time, temperature, and resorcinol or hydrochloric acid concentration, as well as the presence of interfering carbohydrates. Samples were analyzed using a UV-Vis spectrophotometer in scan mode, and data obtained were validated using HPLC, which also enabled quantification of unreacted HMF for assessing the protocol's accuracy. Incubation time and hydrochloric acid percentage positively influenced the colorimetric assay, while the opposite effect was observed with the increase in resorcinol concentration. Interference from carbohydrates was eliminated by reducing the acid content in the working reagent. HPLC analyses corroborated the spectrophotometer data and confirmed the efficacy of the proposed method. The average HMF content in balsamic vinegar samples was 1.97 ± 0.94 mg/mL. Spectrophotometric approaches demonstrated to efficiently determine HMF in complex food matrices. The HMF levels detected in balsamic vinegars significantly exceeded the maximum limits established for honey. This finding underscores the urgent need for regulations that restrict contaminant levels in various food products.

A novel colorimetric sensor through peroxymonosulfate activated by CoFe@CN nanozymes for on-site resorcinol detection

The presence of resorcinol (RS) in water contaminated with pollutants may engender environmental and ecosystem risks. In this study, we developed rapid and efficient colorimetric methods for the on-site quantitative determination of RS. Specifically, a synthetic nanozyme composed of nitrogen-doped carbon-coated cobalt-iron (CoFe@CN) was utilized to initiate the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) with the activator of peroxymonosulfate (PMS). Compared to the activator of hydrogen peroxide (H2O2), PMS demonstrated a sixfold enhancement in catalytic efficacy, markedly elevating the detection performance. Density Functional Theory calculations indicate that RS can serve as a reducing agent for oxTMB, confirming the theoretical feasibility of this process. A linear relationship between inhibition rate (IR %) of RS concentration and absorbance was established and the colorimetric analysis revealed a linear relationship between RS concentration and gray scale values over the range of 0–45 μM, with a detection limit of 3.39 μM. Furthermore, smartphone-based analysis of color images allows for on-site quantitative analysis of RS concentration, leveraging portability and real-time detection capabilities. This study provides pioneering analytical support for on-site water quality monitoring within the ecological environment.

Facile synthesis of sulfur quantum dots with red light emission: Implications for electrochemiluminescence analysis application

Sulfur quantum dots (SQDs) have been reported as a potential candidate due to their low toxicity and high luminescent performance. Here, SQDs with red light fluorescence (FL) emission were synthesized by a one-step hydrothermal method using Na2CO3 as an etching agent, using sublimed sulfur powder as a sulfur source, and using bovine serum albumin (BSA) as a stabilizer. The choice of etching agent (NaOH or Na2CO3) realized the tuning of SQDs’ FL emission with blue and red light. The synthesized SQDs showed good FL stability and high FL efficiency, with a quantum yield of 1.03 % in an aqueous solution at 575 nm. In addition, stable and efficient electrochemiluminescence (ECL) emission was achieved by employing SQDs as ECL emitters with K2S2O8 as the co-reactant. The resorcinol (RS) can enhance the ECL intensity of the SQDs-K2S2O8 system, and the ECL intensity had a good linear relationship with the concentration of RS in a range from 2.5 nM to 25 nM with a detection limit of 0.61 nM. This work provides an emerging red-light luminescent SQDs, which would open up a way for the development of new types of luminophor in FL or ECL analysis. It also provides convenience for bio-labeling of live cells, in vivo imaging and provide new materials for photoelectric devices.

The development of ternary and quaternary solid dispersion based hydrotropic blends of atorvastatin calcium

Background and objective: Atorvastatin calcium (ATV) has a solubility in aqueous solutions of greater than 0.1 mg/ml to less than 1 mg/ml, which is very slightly soluble. When developing dosage forms for these medications, formulation scientists still face challenges. This study's goal was to use various hydrotropic agents in the formation of solid dispersion-based hydrotropic blends to improve the solubility properties of atorvastatin calcium. Methods: In this study, twenty-two distinct binary, ternary, and quaternary formulations of ATV were prepared by employing five different hydrotropic agents and combining at least two hydrotropic agents in concentrations of 10% and 20% (w/v). Moreover, solid dispersion by the solvent evaporation method and physical mixture-based hydrotropic blends in the ratio of (1:2) have been formulated. The produced formulations were characterized using an FTIR analysis. Results: According to the findings, binary formulations containing 20% (w/v) concentrations of sodium benzoate (SB), sodium salicylate (SS), and resorcinol (R) enhanced the solubility ratio of ATV by 439.31, 689.57, and 106.21 folds, respectively. Furthermore, ternary formulations (FT14) and quaternary formulations (FQ18) resulted in the enhancement of ATV solubility by 938.45 and 995.12 folds, respectively. Ternary solid dispersion demonstrated the highest enhancement in solubility ratio by 87.68 folds and resulted in a higher dissolution rate of ATV than pure samples of the drug. Finally, FTIR analyses excluded any interactions between medications and excipients by showing no noticeable shift in the peaks. Conclusion: Solid dispersion based hydrotropic blends can provide the production of the dosage forms of practically insoluble drugs with a favorable enhancement ratio in solubility.

Scalable Synthesis of Stable Electrocatalyst for Oxygen Reduction Reaction

Carbon-based materials have been widely recognized as support material of choice for the oxygen reduction reaction due to their intriguing properties, such as high electrical conductivity, structural flexibility, and low cost. Platinum and its alloys supported on carbon are currently considered the benchmark catalysts for the oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cells (PEMFCs). Confining platinum within the pore system of mesoporous carbon prepared by hard-templating has proven to be an effective way to mitigate catalyst degradation in PEMFCs.[1] However, the challenge of template removal and the limited yield have hindered its practical application in industry. As a remedy, we establish a simple synthesis of carbon gels through sol-gel polymerization of resorcinol (R) and formaldehyde (F), ultimately resulting in graphitic mesoporous carbons.The synthesis process involves mixing resorcinol and formaldehyde in the presence of a basic catalyst, followed by heating for a certain period of time to obtain crosslinked gels.[2] Specific metal salts can be incorporated into the reaction to synthesize mesoporous and highly graphitic carbon spheres (GRF-Sphere) in a straightforward manner, without the need for hydrothermal steps, solvent exchanges, supercritical drying, or post-activation techniques. While conventional carbonized RF spheres are typically non-graphitic and microporous (Fig. 1.), modification of the synthesis route allows for the production of mesoporous, highly graphitic carbon spheres (GRF-Sphere) by taking advantage of the porogenic and graphitization effect of Fe(acac)2. Platinum nanoparticles with an average size of ca. 3 nm were deposited into the pores of GRF-spheres by incipient wetness impregnation followed by annealing at 750 °C. The specific activity of the Pt/GRF-Sphere catalyst for the ORR was found to be greater than 0.45 mA cm-2 Pt at 0.9 V vs. RHE, which in comparison with the literature indicates high catalytic activity.[3] The confinement of the active phase within the pores of the GRF-Spheres contributed to enhancing the stability of the catalyst, as confirmed by an accelerated stress test performed within the typical operating range of a PEMFC (0.6 - 1.0 VRHE). The Pt/GRF-Sphere was found to retain a significantly higher proportion of active surface area when compared to a reference Pt/Vulcan catalyst with similar platinum particle size (Fig. 1.).Furthermore, increasing the concentrations of resorcinol and formaldehyde by 25-fold resulted in the synthesis of a mesoporous and highly graphitic gel, namely GRF-Gel, at a substantial volume yield of70 g L-1, which underlines the potential for this process to be scaled up for industrial application. The ORR activity and stability of GRF-Gel in RDE are currently being investigated. Moreover, the electrochemical performance of this material will be evaluated in a single-cell PEMFC in collaboration with the group of Prof. Hubert Gasteiger (TU Munich).Overall, this research provides a promising and straightforward approach to synthesize highly graphitic mesoporous carbon materials using iron acetylacetonate as a porogen and graphitization catalyst. The method is based on the established preparation of RF-gels but includes iron salts. We have demonstrated that Pt/GRF-Sphere, which is produced by depositing Pt nanoparticles into the pore system of the GRF-Sphere, exhibits high activity and stability for the ORR. Given the simplicity and scalability of our synthesis procedure and the tailored morphology of these carbon materials, we believe that Pt/GRF-Sphere and Pt/GRF-Gel have great potential for industrial applications. Acknowledgement: We acknowledge the financial support from the German Federal Ministry for Economic Affairs and Energy (BMWi) in the framework of POREForm (project number 03ETB027F).

A Facile One-Pot Synthetic Approach Towards CB@PCN-222(Fe) Composites for Simultaneous Electrochemical Detection of Dihydroxybenzene Isomers

A novel porphyrin-metal organic frameworks (MOFs) based hybrid composite was created by combining conductive carbon black (CB) and PCN-222(Fe) (PCN = porous coordination network) via a one-pot strategy. The proposed material unquestionably takes advantage of the high specific area from MOFs and the strong conductivity of CB, which contributes to the contact with analytes and detection sensitivity. A series of analyses showed that the proposed modified electrode could be an alternative candidate for electrochemical detection of dihydroxybenzene isomers. A good linear correlation occurred between the differential pulse voltammetry current and the concentration of hydroquinone (HQ), catechol (CC) and resorcinol (RC) under the optimized conditions. With low detection limits (0.122, 0.094 and 0.243 μM) at the ranges (0.5–280, 0.5–280 and 0.5–320 μM) of these isomers mentioned above, the sensor exhibited good cost-effectiveness, repeatability and stability. Our methodology drives us to directly analyze the dihydroxybenzene isomers in actual samples with dependable recovery, further broadening the electrochemical detection field for environmental pollutants based on porphyrin MOFs.

Towards sustainable water purification: MOFs as a promising solution to eliminate toxic water pollutant resorcinol

Abstract Water pollutants especially alcoholic based aromatic compounds are documented as emergent water pollutants and caused serious health problems for all living organisms. It is a major challenge for all researchers to synthesize effective adsorbents to eliminate these water pollutants. For this purpose, two MOFs were synthesized and characterized using SEM, FTIR, EDX and PXRD techniques. These MOFs exhibited excellent adsorption capacity for resorcinol and adsorption process was spontaneous, endothermic and proceeds with physiosorption as confirmed using thermodynamics data (∆H ads = 30.473 kJ/mol). Furthermore, separation-factor value was in the range of 0.0238–0.1312 for 30–100 ppm resorcinol concentration which represents that adsorption process was favorable. Langmuir and Pseudo 2nd order Models were best described which represented that chemisorption process also favored due to presence of –OH group and N-atom between adsorbent and adsorbate as well as monolayer adsorption-process is proceeded. Moreover, ion-exchange and electrostatic-interactions are the major interactions which are responsible for adsorption of resorcinol. Along with electrostatic-interactions, ion-exchange, hydrogen-bonding and π–π stacking/interactions are also accountable for adsorptive elimination of resorcinol. In summary we can conclude that MOFs are considered outstanding adsorbents for elimination of water pollutants to purify water, as water is very important for healthy life.

A comprehensive model of adsorption of resorcinol in rotating packed bed: Theoretical, isotherm, kinetics and thermodynamics

To study the feasibility of using rotating packed bed (RPB) as adsorption equipment to recover resorcinol from simulated wastewater, a comprehensive model was conducted, including theoretical model, adsorption isotherm model, adsorption kinetics model and thermodynamics model. The adsorption amount changing with high gravity factor, liquid spray density, pH, temperature and inlet resorcinol concentration were well simulated by theoretical model. The Freundlich model (R2 =0.9999, APE=0.0002793) showed the best performance among the other models with two parameters, three parameters, four parameters and five parameters, which indicated that the model performance was not much increased with more parameters introduced. Moreover, the rate constant of intraparticle diffusion model( R2 above 0.99, APE less than 0.35) in RPB could be increased 37 %. Finally, thermodynamics behaviors were also investigated, which had shown the adsorption process was an exothermic and spontaneous process. The above simulated results would be much useful for the design of the adsorber to remove harmful matter from wastewater.

Size-Dependent Chlorinated Nitrogen-Doped Carbon Nanotubes: Their Use as Electrochemical Detectors for Catechol and Resorcinol

In this study, various-sized nitrogen-doped carbon nanotubes (NCNTs) were fabricated by varying the concentration of chlorine in the feed. The diameter of the NCNTs was found to influence the sensing ability of the nanomaterials when coated onto the glassy carbon electrode (GCE) and used for the detection of catechol (CC) and resorcinol (RS). Larger diameter NCNTs (denoted NCNTs (2 : 1)) were produced when a low concentration of chlorine was added into the acetonitrile feed, whereas smaller diameter NCNTs (denoted NCNTs (1 : 2)) were produced when a large concentration of chlorine was added. This investigation revealed that the addition of controllable amounts of chlorine during the fabrication of NCNTs led to the creation of nanostructures with different properties. The greatest current response which was evidenced by an enhanced anodic peak of CC and RS was obtained when GCE was coated with NCNTs (2 : 1), and this was attributed to their large diameter and high graphitic nature which facilitated electron transfer as evidenced by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis. A linear response was obtained when varying the concentration of both CC and RS, with the limits of detection of about 0.059 μM (CC) and 0.034 μM (RS) (3S/M) obtained.

Micellar enhanced chromatographic separation of selected hazardous chemical present in hair dye and their detection in formulations and swab, including assessment of damage caused to cuticle of hair shaft

Hydroquinone (HQ), resorcinol (RS), m-aminophenol (m-AMP) and p-phenylenediamine (p-PPD) are aromatic compounds which are generally used in hair dyes to provide different colours to hair. In European Union the concentrations of HQ, RS, m-AMP and p-PPD is regulated in hair dyes and other cosmetic products by EU commission regulation EU/2019/831. This legislation is generally exercised because all these compounds are toxic and may cause severe allergies when used regularly. However in India no such regulations exist to monitor these toxic compounds in hair dyes therefore in this study a simple, rapid, economical and ecofriendly micellar liquid chromatographic (MLC) technique has been developed which can monitor all the selected toxic compounds simultaneously. HQ and RS are positional isomers and are difficult to be separated by HPLC whereas with the developed MLC method it was well separated and detected. The developed MLC technique has been applied to detect and quantify selected analytes in oxidative and non-oxidative hair dyes and swab samples from the scalp. The simultaneous separation of selected analytes was performed in mobile phase 0.09 M SDS, 0.01 M NaH2PO4–2% v/v 1-butanol at pH 7 running through C18 column under isocratic mode at 1 mL/min. flow rate. All the analytes were eluted within 6 min. The present method has been validated following the EURCHEM Guideline, 2014 in terms of calibration range (0.08–15 µg/mL), limit of detection (0.01–0.09 µg/mL), limit of quantification (0.08–0.35 µg/mL), accuracy (<5.6%), precision (91–105%) and robustness (<5.8%). The selected compounds in hair dye formulation were found in the range of 0.06–12.2 µg/mL (when diluted 25 times). Hair dyes persistence study was conducted up to 10 days from the day of application on the scalp, suggesting that the dyes were not completely washed off and were retained on the scalp for more than one week. SEM analysis of dyed hair revealed that hair are severely damaged due to use of dyes. The advantage of the developed method is that it could easily be adopted by quality control and cosmetic laboratories for quality control and check for the simultaneous separation of positional isomers together with two other aromatic compounds.

Physicochemical parameters and modes of interaction associated with the micelle formation of a mixture of tetradecyltrimethylammonium bromide and cefixime trihydrate: effects of hydrotropes and temperature.

The interaction between an antibiotic drug (cefixime trihydrate (CMT)) and a cationic surfactant (tetradecyltrimethylammonium bromide (TTAB)) was examined in the presence of both ionic and non-ionic hydrotropes (HTs) over the temperature range of 300.55 to 320.55 K. The values of the critical micelle concentration (CMC) of the TTAB + CMT mixture were experienced to have dwindled with an enhancement of the concentrations of resorcinol (ReSC), sodium benzoate (NaBz), sodium salicylate (NaS), while for the same system, a monotonically augmentation of CMC was observed in aq. 4-aminobenzoic acid (PABA) solution. A gradual increase in CMC, as a function of temperature, was also observed. The values of the degree of counterion binding (β) for the TTAB + CMT mixture were experienced to be influenced by the concentrations of ReSC/NaBz/NaS/PABA and a change in temperature. The micellization process of TTAB + CMT was observed to be spontaneous (negative standard Gibbs free energy change (ΔG0m)) at all conditions studied. Also, the values of standard enthalpy change (ΔH0m) and entropy change (ΔS0m) were found negative and positive, respectively (with a few exceptions), for the test cases indicating an exothermic and enthalpy-entropy directed micellization process. The recommended interaction forces between the components in the micellar system are electrostatic and hydrophobic interactions. In this study, the values of ΔC0m were negative in aqueous NaBz, ReSC, and PABA media, and positive in case of NaS. An excellent compensation scenario between the enthalpy and entropy for the CMT + TTAB mixed system in the investigated HTs solutions is well defined in the current work.

Development of periodic colored bands via frontal polymerization

The development of periodic brown-white colored structural patterns during the frontal polymerization process has been studied in Methacrylic acid (MAA), Resorcinol, Benzoyl peroxide (BP), and N, N Dimethyl aniline (DMA) reaction system. The reaction has been carried out in a thin glass test tube under ambient conditions. Pattern formation and their dependency on the concentration of MAA monomer, Resorcinol, and DMA initiator have largely been observed. Methanol has also been used as a solvent to optimize the effect of dilution levels on the periodicity of colored structural patterns. The materials characterization is carried out using NMR, SEM, IR, CHNS, and UV–visible analyses to show the possible reaction mechanisms and elemental composition of the polymerization reaction. It has been observed that white and brown colored polymeric phases are formed during FP reactions and polymerized simultaneously. In this context, a possible chemical mechanism has been proposed which shows the formation of white colored polymethacrylic acid and brown phase poly (2–hydroxy, 1, 4 napthaquinone methacrylic acid). The analytical data observed during the study has a good agreement with the proposed chemical mechanism. The characteristics of colored patterns found depending on the concentration of resorcinol, BP, and EtOH have been studied and properly discussed.

A Rapid Fluorescence Sensor for the Direct Quantification of Rongalite in Foodstuffs.

Rongalite was reported illegally used as a food additive for bleaching purposes and improving the tenderness of foodstuffs, which may endanger public health. At present, rongalite was mostly detected by indirect methods via derivatization or determining its decomposition products. In this study, we developed a new fluorescence sensor for the direct quantification of rongalite based on the principles: (1) dopamine reacts with resorcinol and generates strong fluorophore (azamonardine); (2) rongalite could inhibit the production of fluorophores and then result in lower fluorescence intensity. Hence, the rongalite concentration was inversely proportional to fluorescence intensity of fluorophore. Several crucial reaction conditions of fluorescence sensor were further optimized, such as dopamine and resorcinol concentration, pH values, and reaction time. Under the optimal conditions, the limit of detection of fluorescence sensor was 0.28–0.38 μg/g in vermicelli, wheat and rice powder samples, exhibiting almost 3.5-fold improvement compared to that of lateral flow immunoassay. Moreover, the detection time was substantially decreased to 20 min. The recoveries in spiked samples were 80.7–102.1% with a coefficient of variation of less than 12.6%. In summary, we developed a direct, high throughput, selective and accurate fluorescence sensor that poses a promising application for the rapid detection of rongalite in foodstuffs.

Acclimatization of resorcinol results in microbial community dynamics and physicochemical characteristics of aerobic activated sludge

Several studies have demonstrated that the biodegradation of resorcinol as a major pollutant in domestic coal gas wastewater can vary greatly with respect to its physicochemical properties and the structure of the bacterial flora induced during acclimation. The primary objective of this study is to investigate the degradation of resorcinol by aerobic activated sludge at different stages of domestication, changes in the toxicity of the sludge and the resultant dynamic changes in the structure of the dominant bacterial population. During the 40-day domestication process, we show that as the influent resorcinol concentration increased from 0 mg/L to 50 mg/L to 100 mg/L, the effluent resorcinol concentration and chemical oxygen demand concentration tended to increase then decrease. Organic matter in the sludge, ranging in size from 5 to 10 kDa, gradually accumulated to a concentration of 94.8 ± 1.8 mg/L (0 mg/L), 141.3 ± 2.1 mg/L (50 mg/L) and 192.4 ± 2.3 mg/L (100 mg/L), which constitutes the majority of its organic toxicity. Moreover, our study reveals that the total number of major degrading enzyme genes in the sludge samples during the domestication and stabilization period were 27322 (0 mg/L), 46076 (50 mg/L) and 32472 (100 mg/L). The results of the experiment indicate that Methylotenera, Methylophilus, and Azoarcus gradually took on the role of dominant resorcinol degraders. This contribution is fruitful in explaining the shift in sludge organic toxicity as the result of changes in the enzyme system of microflora in the sludge, which then resulted in an increase in the population of functional bacteria with enzymes that can degrade resorcinol, and in turn, stimulated the increase of the microbial enzyme system.

Estimating the Analytical Performance of Raman Spectroscopy for Quantification of Active Ingredients in Human Stratum Corneum.

Confocal Raman microscopy (CRM) has become a versatile technique that can be applied routinely to monitor skin penetration of active molecules. In the present study, CRM coupled to multivariate analysis (namely PLSR—partial least squares regression) is used for the quantitative measurement of an active ingredient (AI) applied to isolated (ex vivo) human stratum corneum (SC), using systematically varied doses of resorcinol, as model compound, and the performance is quantified according to key figures of merit defined by regulatory bodies (ICH, FDA, and EMA). A methodology is thus demonstrated to establish the limit of detection (LOD), precision, accuracy, sensitivity (SEN), and selectivity (SEL) of the technique, and the performance according to these key figures of merit is compared to that of similar established methodologies, based on studies available in literature. First, principal components analysis (PCA) was used to examine the variability within the spectral data set collected. Second, ratios calculated from the area under the curve (AUC) of characteristic resorcinol and proteins/lipids bands (1400–1500 cm−1) were used to perform linear regression analysis of the Raman spectra. Third, cross-validated PLSR analysis was applied to perform quantitative analysis in the fingerprint region. The AUC results show clearly that the intensities of Raman features in the spectra collected are linearly correlated to resorcinol concentrations in the SC (R2 = 0.999) despite a heterogeneity in the distribution of the active molecule in the samples. The Root Mean Square Error of Cross-Validation (RMSECV) (0.017 mg resorcinol/mg SC), The Root Mean Square of Prediction (RMSEP) (0.015 mg resorcinol/mg SC), and R2 (0.971) demonstrate the reliability of the linear regression constructed, enabling accurate quantification of resorcinol. Furthermore, the results have enabled the determination, for the first time, of numerical criteria to estimate analytical performances of CRM, including LOD, precision using bias corrected mean square error prediction (BCMSEP), sensitivity, and selectivity, for quantification of the performance of the analytical technique. This is one step further towards demonstrating that Raman spectroscopy complies with international guidelines and to establishing the technique as a reference and approved tool for permeation studies.

Resorcinol - determination method in the workplace air

Resorcinol (1,3-dihydroxybenzene) is a white solid used in rubber, pharmaceuticals, cosmetics, paints and varnishes and other industries. Resorcinol is a harmful, irritant, methemoglobin-forming and hemolytic substance. It can cause kidney and liver damage. The aim of the study was to develop a method for the determination of resorcinol in the workplace air, which would enable the determination of its concentrations in the range 0.1-2 of the MAC (maximum allowable concentration) value. The method relies on passing the test air containing resorcinol through a cellulose filter, extraction with aqueous methanol solution and chromatographic analysis of the obtained solution. The tests were performed using a liquid chromatograph (HPLC) 1200 series of Agilent Technologies with a diode array detector (DAD). The determinations were carried out using an Allure Basix column (250 × 4.6 mm, 5 μm granulation). The procedure was validated according to European Standard PN-EN 482. The developed method allows the determination of resorcinol in the workplace air in the concentration range of 4.5-90 mg/m3. The limit of detection is 0.087 μg/ml, the precision 5.16% and the relative expanded uncertainty 22.6%. The method described enables selective determination of resorcinol in workplace air in the presence of 1,2-dihydroxybenzene, 1,4-dihydroxybenzene, benzene and phenol. The method is characterized by good precision and accuracy; it meets the requirements of the European Standard PN-EN 482, and can be used by occupational hygiene laboratories to measure concentrations of resorcinol in workplace air to assess workers' exposure to this substance. Med Pr. 2022;73(2):135-42.

Development and characterization of La2O3 nanoparticles@snowflake-like Cu2S nanostructure composite modified electrode and application for simultaneous detection of catechol, hydroquinone and resorcinol as an electrochemical sensor

We could successfully fabricate a new composite of La2O3 nanoparticles@snowflake-like Cu2S nanostructure (La2O3 NP@SF-L Cu2S NS composite) for simultaneous detection of hydroquinone (HQ), catechol (CT), and resorcinol (RS). Field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscope (EDX) and X-ray diffraction (XRD) were used to characterize the constructed La2O3 NP@SF-L Cu2S NS composites. The presence of HQ, CT and RS was simultaneously detected on the surface of modified La2O3 NP@SF-L Cu2S NS composites because of unique properties such as large surface area, high electrical conductivity and potent catalytic activity, with the appearance of three distinctive peaks. Moreover, differential pulse voltammetric (DPV), chronoamperometry (CHA) and cyclic voltammetric (CV) were also employed to determine the electrocatalytic profile of CT, HQ and RS on electrode modified with the nanocomposite (La2O3 NP@SF-L Cu2S NS/GCE). There was a significant elevation in the HQ, CT and RS oxidation currents when compared to those on both bare and modified electrodes. The peak of the catalytic current was directly variable based on the concentrations of HQ, CT and RS (0.66 to 266.6 μM), respectively. Further, the limit of detection (LOD) was calculated to be 0.056 μM, 0.058 μM and 0.059 μM for all HQ, CT and RS, respectively. Acceptable outcomes were achieved for the applicability of La2O3 NP@SF-L Cu2S NS/GCE in detecting HQ, CT and RS present in real specimens.

In situ crosslinked weak gels with ultralong and tunable gelation times for improving oil recovery

Polymer-based in situ cross-linked gels have been widely used in improving the oil recovery process; however, the insufficient and uncontrollable gelation time still deteriorates the successful in-depth water shutoff and conformance control for oil reservoirs due to the short and uncertain moving distance underground. Herein, we report weak gels formed by in situ crosslinking of partially hydrolyzed polyacrylamide with hexamethylenetetramine and resorcinol as binary crosslinker pairs. These gels exhibit ultralong and adjustable gelation times between 3 and 47 days at 45 ℃. The chemical principles of controllable gelation time and microstructure evolution during gel formation are well elaborated using nuclear magnetic resonance spectroscopy and scanning electron microscopy. The crosslinker pairs and temperature greatly affect gelation kinetics, and polymer molecular weight and concentration as well as salinity also affect the gelation process. Fine-tuning the hexamethylenetetramine and resorcinol concentrations affords a series of gels with gelation times in a large range. The activation energy for the system with the longest gelation time was calculated to be 95.33 kJ/mol, much higher than similar gel systems reported previously, accounting for the ultralong gelation time. Core plugging and flooding tests showed that this gel system can be easily injected into porous media and form in situ gels that selectively block highly permeable layers and force subsequent injected water to pass through low permeability zones, improving sweep efficiency and oil recovery. These in situ cross-linked gels could find wide applications for water shutoff and conformance control in heterogeneous oil reservoirs, and the knowledge obtained provides new insight into gelling process control and would help in developing novel systems with desirable gelation time under various conditions.