Determination of paracetamol and its main impurity 4-aminophenol in analgesic preparations by micellar electrokinetic chromatography

Glassy carbon electrode modified with a film of tetraruthenated nickel(ii) porphyrin located in natural smectite clay's interlayer for the simultaneous sensing of dopamine, acetaminophen and tryptophan

A supramolecular complex μ-meso-tetra(4-pyridyl) porphyrinate nickel(ii)tetrakis[bis(bipyridine)(chloro)ruthenium(ii)] ([NiTPyP{Ru(bipy)2Cl}4]4+) was intercalated into the interlayer space of natural smectite clay (shortened as Ba) collected in a Cameroonian deposit at Bagba hill. Physicochemical characterization of the resulting material using ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) confirmed the intercalation of the porphyrin within the interlayer space of the clay. The intercalated clay was then used to form a stable thin film onto a glassy carbon electrode (GCE) by drop casting a suspension of the hybrid material. The GCE modified with the intercalated organoclay endowed the electrode with a larger electrochemically active surface area, good stability, high selectivity, and sensitivity toward dopamine (DA), acetaminophen (AC) and tryptophan (Trp). In addition, it was observed that the modified electrodes exhibited good and pH-dependent electrocatalytic properties toward these analytes. The simultaneous determination of DA, AC and Trp at [NiTPyP{Ru(bipy)2Cl}4]4+-Ba/GCE was thus possible without the interference of one analyte on the others, and the resulting calibration curve exhibits two segments for the three analytes. For DA, AC and Trp, the detection limits were found to be 0.8 μM, 0.3 μM and 0.3 μM, respectively. The [NiTPyP{Ru(bipy)2Cl}4]4+-Ba/GCE modified electrodes were successfully applied for the determination of AC in Paracetamol, a commercial product, and Trp in real pharmaceutical formulation samples.

An effective and stability-indicating method development and optimization utilizing the Box-Behnken design for the simultaneous determination of acetaminophen, caffeine, and aspirin in tablet formulation

Analytical techniques must be sensitive, specific, and accurate to assess the active pharmaceutical ingredients in pharmaceutical dosage forms. The quality-by-design (QbD) application has proven to be a practical method for magnifying HPLC operations. This article discusses the successfully developed QbD-based stability-indicative LC method for evaluating acetaminophen, caffeine, and aspirin (ASP) in tablet dosage form. To achieve the necessary chromatographic separation, Milli-Q water, methanol, and glacial acetic acid were employed in the following ratios: 63:35:2 (v/v/v) for mobile phase A and 18:80:2 (v/v/v) for mobile phase B. The flow rate, column temperature, and detecting wavelength were 1.0 ml/min, 40°C, and 275 nm, respectively, and an InertSustain C18 analytical column (150 × 4.6 mm, 3 μm) was used. Linearity was between 10.0 and 150.0 μg/ml for ASP and acetaminophen and between 2.6 and 39.0 μg/ml for caffeine. The accuracy findings were more than 97%, and the correlation coefficient for all three components was found to be greater than 0.999. The validated HPLC method yielded reliable and accurate results. ASP was shown to be vulnerable to both acid and alkaline hydrolysis in the forced degradation study. The described method is capable of separating the degradants produced during stress testing and is regarded as stability indicating. The proposed method can be used for a wider range of other formulations with an appropriate diluent selection and sample preparation procedure optimization.

MnO2-DNA nanomaterials toward the dual signal detection of P-aminophenol micropollutants

P-Aminophenol (PAP), a potentially toxic and mutagenic compound, is widely distributed in water and soil and has serious side effects on human health. This study presents a convenient, sensitive, and effective dual-signal assay for the detection of PAP in the environment. Two-dimensional manganese dioxide (MnO₂) nanosheets were used as the carrier and quencher for fluorophore-labelled DNA to form a dual-signal nanoprobe, MnO₂-DNA. Based on a specific redox reaction between the MnO₂ nanosheets and target PAP, the corresponding absorption intensity of the product and the fluorescence intensity were both "turn-on" and also exhibited excellent correlation with the concentration of PAP. This strategy not only remarkably simplifies the detection process but also improves the reliability of results due to the dual-signal response, which has promising applications in environmental, clinical, and industrial research fields.

Investigation of radical scavenging effects of acetaminophen, p-aminophenol and their O-sulfated conjugates

Acetaminophen (APAP) and p-aminophenol (p-AP) are the analogous simple phenolic compounds that undergo sulfate conjugation (sulfation) by cytosolic sulfotransferases. Sulfation is generally thought to lead to the inactivation and disposal of endogenous as well as xenobiotic compounds. This study aimed to investigate the antioxidative effects of O-sulfated form of APAP and p-AP, i.e., APAPS and p-APS, in comparison with their unsulfated counterparts. Using a 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay, the antioxidant capacity of APAPS was shown to be approximately 126-times lower than that of APAP. In contrast, p-APS displayed comparable activity as unsulfated p-AP. Similar trends concerning the suppressive effects of these chemicals on cellular O₂^- radical generation were found using an activated granulocytic neutrophil cell model. Collectively, these results indicated that, depending on the presence of an additional "active site", sulfation may not always decrease the antioxidant activities of phenolic compounds.

A novel electrochemical sensor based on TAPT-TFP-COF/COOH-MWCNT for simultaneous detection of dopamine and paracetamol

In this work, a covalent organic framework (COF) TAPT-TFP-COF containing a triazine ring was prepared by a typical Schiff base condensation reaction of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 1,3,5-triformyl phloroglucinol (TFP). The TAPT-TFP-COF and carboxyl-functionalized multi-wall carbon nanotubes (COOH-MWCNTs) were drip-coated on glassy carbon electrode respectively to develop a novel and simple electrochemical sensor in order to simultaneously detect dopamine (DA) and paracetamol (PA). COOH-MWCNTs interconnected the TAPT-TFP-COF and acted as bridges between the COF particles, which had a good synergistic effect and accelerated electron transfer. Under optimal conditions, linear responses were obtained over the concentration range 1-190 μM for DA and PA with limits of detection (LOD) of 0.14 μM and 0.19 μM, respectively. Furthermore, the fabricated sensor possesses outstanding repeatability and high selectivity, and can be applied for the determination of DA and PA in dopamine injection and acetaminophen drugs with satisfactory recoveries.

Dual-Mode Gradient HPLC and TLC Densitometry Methods for the Simultaneous Determination of Paracetamol and Methionine in the Presence of Paracetamol Impurities

Background

Paracetamol is one of the most widely analgesic and antipyretic drugs recently integrated into the supportive therapy of COVID-19. The pharmaceuticals containing methionine with paracetamol may contribute to avoid hepatotoxicity and eventual paracetamol overdose-dependent death.

Objective

The current work purposes to develop and validate two chromatographic methods for the simultaneous determination of methionine and paracetamol in presence of two paracetamol impurities (4-nitrophenol and 4-aminophenol).

Methods

Two chromatographic methods were established and validated according to the International Conference on Harmonization guidelines. The first one was a RP-HPLC/UV method based on applying a “dual-mode” gradient elution. The separation was realized via varying both the composition of the ternary mobile phase (acetonitrile–methanol–water) and its flow rate. This strategy enabled a relatively rapid analysis with a satisfactory resolution, although the investigated compounds exhibit a significant difference in lipophilicity. The second one relied on TLC- densitometry, where the optimum separation was realized using a quaternary mobile phase system composed of butanol–dioxane–toluene–methanol (8: 2.5: 3.5: 0.3, by volume). Both methods were monitored at 220 nm.

Results

The developed methods were proven to be robust, accurate, specific, and appropriate for the routine analysis of paracetamol in its pure form or in pharmaceutical formulations with methionine in quality control laboratories.

Conclusions

The corresponding methods are suitable to determine methionine and paracetamol in the presence of paracetamol impurities.

Highlights

The study achieves the analysis of methionine and paracetamol in the presence of paracetamol impurities via the application of HPLC and TLC- densitometry methods.

Simultaneous Determination of Paracetamol, Propyphenazone and Caffeine in Presence of Paracetamol Impurities Using Dual-Mode Gradient HPLC and TLC Densitometry Methods

Two chromatographic methods were validated for the determination of the widely prescribed analgesic and antipyretic drug combination of paracetamol (PC) (recently integrated into the supportive treatment of COVID-19), propyphenazone (PZ) and caffeine (CF) in the presence of two PC impurities, namely 4-aminophenol and 4-nitrophenol. A “dual-mode” gradient high-performance liquid chromatography method was developed, where the separation was achieved via “dual-mode” gradient by changing both the ternary mobile phase composition (acetonitrile: methanol: water) and the flow rate. This enables a good resolution within a relatively shorter analysis time. The analysis was realized using Zorbax Eclipse XDB column C18, 5 μm (250 × 4.6 mm) and the UV detector was set at 220 nm. The other method is a thin-layer chromatography densitometry method, where the separation was achieved using a mobile phase composed of chloroform: toluene: ethyl acetate: methanol: acetic acid (6: 6: 1: 2: 0.1, by volume). Densitometric detection was performed at 220 nm on silica gel 60 F254 plates. The developed methods were fully validated as per the ICH guidelines and proved to be accurate, robust, specific and suitable for application as purity indicating methods for routine analysis of PC in pure form or in pharmaceuticals with PZ and CF in quality control laboratories.

Validated specific HPLC-DAD method for simultaneous estimation of paracetamol and chlorzoxazone in the presence of five of their degradation products and toxic impurities

This work demonstrates a specific and reliable HPLC with diode array detection (DAD) method for the simultaneous estimation of paracetamol (PAR) and chlorzoxazone (CZ) in the presence of five of their degradation products and toxic impurities; namely; 4-aminophenol (AP), 4-nitrophenol (NP), acetanilide (AT), 4-chloroacetanilide (CA) and 2-amino-4-chlorophenol (ACP). Successful chromatographic separation was accomplished using Waters Symmetry C8 column (3.9 × 150 mm, 5 μm) with gradient elution of the mobile phase consisting of 0.05 M phosphate buffer pH 7.5 and methanol. The gradient elution started with 5% (by volume) methanol ramped up linearly to 50% in 10 min, and then maintained at this percentage afterward till the end of the run. The mobile phase was pumped at a flow rate of 1.0 mL/min. The multiple wavelength detector was adjusted at 244 and 285 nm to quantify PAR and CZ, respectively. Additionally, the wavelength 270 nm was found suitable for monitoring the separation of the entire mixture of PAR, CZ, and their impurities. Seven peaks eluted with excellent resolution at retention times 3.4, 5.7, 8.0, 10.1, 10.8, 13.5, and 14.4 min for AP, PAR, NP, AT, ACP, CZ, and CA, respectively. Performance of the proposed method was validated with respect to linearity, range, precision, accuracy, specificity, robustness, detection, and quantitation limits. Calibration curves were linear in the ranges of 10-75 and 10-100 µg/mL for PAR and CZ, respectively with correlation coefficients not less than 0.9998. The proposed method proved to be specific and stability indicating by the resolution of both drugs from their degradation products and toxic impurities. Validated HPLC method was successfully applied to the analysis of PAR and CZ in their combined capsules dosage form, and assay results were favorably compared with a published reference HPLC method. DAD served as an efficient tool for peak identity and purity verification.

Rapid synthesis of a hybrid of rGO/AuNPs/MWCNTs for sensitive sensing of 4-aminophenol and acetaminophen simultaneously

In this work, a hybrid of multiwalled carbon nanotubes, nanogold, and reduced graphene (rGO/AuNPs/MWCNTs) was synthesized rapidly with an easy method, and then combined with chitosan (CS), which was fixed on a glassy carbon electrode (GCE) to construct a new kind of electrochemical sensor to simultaneously determine 4-aminophenol (4-AP) and acetaminophen (AC). When detecting 4-AP and AC simultaneously, the linear range is 0.12~12 μM for acetaminophen and 0.05~25 μM for 4-aminophenol; the detection limit is 42 nM for acetaminophen and 2.95 nM for 4-aminophenol. Compared with previously related reports, the proposed sensor has an excellent electrocatalytic performance for the redox of 4-AP and AC, which can effectively determine 4-AP and AC simultaneously in actual samples and has potential application prospect. Graphical abstract.

Analysis of some pharmaceuticals in the presence of their synthetic impurities by applying hybrid micelle liquid chromatography

A stability-indicating hybrid micelle liquid chromatography accompanied by UV detection was developed for the simultaneous analysis of either paracetamol (PCA) or pseudoephedrine hydrochloride (PSU) with their synthetic impurities. Mixture I contains PCA with p-amino phenol and p-nitro phenol, while mixture II involves the estimation of PSU with benzaldehyde and benzoic acid. Both mixtures were separated using a C18 column that was thermostatically maintained at 40°C and operating under a flow rate of 1.5 mL/min, applying UV detection at 240 nm for mixture I and 220 nm for mixture II. In both cases, the mobile phase consisted of 0.1 M sodium dodecyl sulfate, acetonitrile, and triethylamine (90:10:0.3, v/v/v) and adjusted to pH 4 (mixture I) or pH 3.7 (mixture II) using 2.0 M O-phosphoric acid. The proposed method was validated and successfully applied to assay different pharmaceuticals containing PCA or PSU. Moreover, the stability-indicating nature of the proposed method was proved through applying photolytic degradation procedures for PCA.

Long-term stability of an infusion containing paracetamol, alizapride, ketorolac and tramadol in glass bottles at 5±3°C

Background and objective

Infusion containing paracetamol, alizapride, ketorolac and tramadol is used after a general anaesthesia in order to limit pain, fever and nausea. Currently, these infusions are prepared according to demand in the anaesthesia unit, but the preparation in advance could improve quality of preparation and time management. The aim of this study was to investigate the long-term stability of this infusion in glass bottles at 5°C ± 3 °C.

Method

Five bottles of infusion were stored at 5°C ± 3 °C for 60 days. A visual and microscope inspection were performed periodically to observe any particle appearance or colour change. pH and absorbance at three wavelengths were measured. The concentrations were measured by ultra-high performance liquid chromatography - diode array detection.

Results

Multiple verifications were performed during the first 35 days and no crystal, impurity or colour change were observed. At the next time point (42nd day), crystals were visible to the naked eye. pH and absorbance at 350 nm and 550 nm were stable. A slight increase in the absorbance at 410 nm was observed during the study, suggesting that a degradation product could be formed and absorb at this wavelength. The infusion was considered chemically stable while the lower one-sided prediction limit at 95% remains superior to 90% of the initial concentration. Concentration measurements demonstrated that ketorolac and alizapride remained stable in the infusion for 35 days. The stability of tramadol was 28 days. However, degradation of paracetamol was much faster given that concentration has fallen below 90% of the initial concentration after 7 days.

Conclusion

Infusion of paracetamol, alizapride, ketorolac and tramadol remains stable for 7 days in glass bottles at 5°C ± 3 °C and could be prepared in advance with these storage conditions.

RP-HPLC and UV Spectrophotometric Analysis of Paracetamol, Ibuprofen, and Caffeine in Solid Pharmaceutical Dosage Forms by Derivative, Fourier, and Wavelet Transforms: A Comparison Study

Different signal-transforming algorithms were applied for UV spectrophotometric analysis of paracetamol, ibuprofen, and caffeine in ternary mixtures. Phosphate buffer pH 7.2 was used as the spectrophotometric solvent. Severe overlapping spectra could be resolved into individual bands in the range of wavelengths 200-300 nm by using Savitzky-Golay smoothing and differentiation, trigonometric Fourier series, and mother wavelet functions (i.e., sym6, haar, coif3, and mexh). To optimize spectral recoveries, the concentration of various types of divisors (single, double, and successive) was tested. The developed spectrophotometric methods showed linearity over the ranges 20-40 mg/L for paracetamol, 12-32 mg/L for ibuprofen, and 1-3.5 mg/L for caffeine (R ² > 0.990). They could be successfully applied to the assay and dissolution test of paracetamol, ibuprofen, and caffeine in their combined tablets and capsules, with accuracy (99.1-101.5% recovery) and precision (RSD < 2%). For comparison, an isocratic RP-HPLC analysis was also developed and validated on an Agilent ZORBAX Eclipse XDB-C18 (150 × 4.6 mm, 5 µm) at an ambient temperature. A mixture of methanol : phosphate buffer 0.01 M pH 3 (30 : 70 v/v) was used as the mobile phase delivered at 2 mL/min, and the effluent was monitored at 225 nm. It was shown that spectrophotometric data were statistically comparable to HPLC (p > 0.05), suggesting possible interchange between UV spectrophotometric and HPLC methods for routine analysis of paracetamol, ibuprofen, and caffeine in their solid pharmaceutical dosage forms.

Simultaneous detection of paracetamol and 4-aminophenol at nanomolar levels using biocompatible cysteine-substituted phthalocyanine

Extension of the conjugation and biocompatibility of the phthalocyanine molecule is expected to improve its stability and interaction with bio-molecules without any fouling.

Platinized agarose microspheres as a new modifier in graphite paste electrodes for the electrochemical determination of 4-aminophenol

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant. In this study, platinized agarose microspheres (PtAM) were used for the first time, for the preparation of a novel, modified graphite paste electrode (GPE/PtAM) for the electrochemical determination of 4-AP. PtAM was characterized using transmission electron microscopy, field emission scanning electron microscopy and energy dispersive X-ray analysis. The electrochemical response characteristics of GPE/PtAM towards 4-AP were investigated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The value of the charge transfer resistance obtained for GPE/PtAM was 27.3 Ω. Microscopic surface areas and the surface concentration of the electroactive species for GPE/PtAM were calculated to be 0.077 cm² and 1.13 × 10⁻³ mol cm⁻², respectively. The electron transfer coefficient, diffusion coefficient and standard heterogeneous rate constants of 4-AP were calculated as 0.274, 4.56 × 10⁻⁴ cm² s⁻¹, and 3.32 × 10⁻¹ cm s⁻¹, respectively. The influence of pH on the oxidation of 4-AP was investigated and a pH value of 2.0 (using a phosphate buffer solution) was selected as the optimum pH. Under optimum conditions, the calibration was linear between 0.8 and 87 μM with a detection limit of 45 nM. Moreover, GPE/PtAM was applied to determine the concentrations of 4-AP in water samples with satisfactory results.

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant.

Different stability-indicating chromatographic methods for specific determination of paracetamol, dantrolene sodium, their toxic impurities and degradation products

A well-known analgesic (paracetamol, PAR) and skeletal muscle relaxant [dantrolene sodium (DNS)] have been analyzed without interference from their toxic impurities and degradation products. The studied PAR impurities are the genotoxic and nephrotoxic p-amino phenol (PAP) and the hepatotoxic and nephrotoxic chloroacetanilide, while 5-(4-nitrophenyl)-2-furaldehyde is reported to be a mutagenic and carcinogenic degradation product of DNS. The five studied components were determined and quantified by TLC-densitometric and RP-HPLC methods. TLC-densitometry (method 1) used TLC silica gel and chloroform-ethyl acetate-acetic acid-triethylamine (7:3:0.5:0.05, by volume) as the mobile phase with UV scanning at 230 nm, while RP-HPLC (method 2) was based on separation on a C₁₈ column using methanol-water (55:45, v/v pH 3 with aqueous formic acid) as mobile phase at 1 mL/min and detection at 230 nm. The developed methods were used for determination and quantification of the five studied components in different laboratory-prepared mixtures. The were also applied for analysis of Dantrelax^® compound capsules where no interference among the studied components with each other or from excipients was observed. The methods were validated as per International Conference on Harmonization guidelines, and they compared favorably with the reported ones.

Simultaneous detection of acetaminophen and 4-aminophenol with an electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide

Simultaneous detection of acetaminophen and 4-aminophenol with a highly sensitive electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide.

A hybrid nanocomposite of CeO2–ZnO–chitosan as an enhanced sensing platform for highly sensitive voltammetric determination of paracetamol and its degradation product p-aminophenol

A highly selective electrochemical sensor was fabricated based on CeO₂–ZnO–chitosan hybrid nanocomposite modified electrode and was successfully applied for the determination of PAR in pharmaceutical formulations.

Electrochemical Sensor for the Determination of Paracetamol at Carbamazepine Film Coated Carbon Paste Electrode

The electrochemical behavior of paracetamol (PC) was investigated at carbamazepine (CBZ) film coated carbon paste electrode in 0.2 M PBS of pH 7.4 by cyclic voltammetric technique. The modified electrode was exhibited a good electrochemical activity towards the oxidation of paracetamol, which results in a noticeable improvement of the peak currents and feasible oxidation as compared to the bare carbon paste electrode. Under optimal experimental conditions the electrochemical response to PC was linear in the concentration range from 1.0×10−4 M to 3.94×10−4 M with a detection limit of 0.24 μM by cyclic voltammetric technique. The sensitivity, long-term stability, reproducibility was shown by the modified electrode. Finally, the proposed method was successfully applied to determine PC in pharmaceutical samples.

Different applications of isosbestic points, normalized spectra and dual wavelength as powerful tools for resolution of multicomponent mixtures with severely overlapping spectra

Background

Analysis of complex mixture containing three or more components represented a challenge for analysts. New smart spectrophotometric methods have been recently evolved with no limitation. A study of different novel and smart spectrophotometric techniques for resolution of severely overlapping spectra were presented in this work utilizing isosbestic points present in different absorption spectra, normalized spectra as a divisor and dual wavelengths. A quaternary mixture of drotaverine (DRO), caffeine (CAF), paracetamol (PCT) and para-aminophenol (PAP) was taken as an example for application of the proposed techniques without any separation steps. The adopted techniques adopted of successive and progressive steps manipulating zero /or ratio /or derivative spectra. The proposed techniques includes eight novel and simple methods namely direct spectrophotometry after applying derivative transformation (DT) via multiplying by a decoding spectrum, spectrum subtraction (SS), advanced absorbance subtraction (AAS), advanced amplitude modulation (AAM), simultaneous derivative ratio (S¹DD), advanced ratio difference (ARD), induced ratio difference (IRD) and finally double divisor–ratio difference-dual wavelength (DD-RD-DW) methods.

Results

The proposed methods were assessed by analyzing synthetic mixtures of the studied drugs. They were also successfully applied to commercial pharmaceutical formulations without interference from other dosage form additives. The methods were validated according to the ICH guidelines, accuracy, precision, repeatability, were found to be within the acceptable limits.

Conclusion

The proposed procedures are accurate, simple and reproducible and yet economic. They are also sensitive and selective and could be used for routine analysis of complex most of the binary, ternary and quaternary mixtures and even more complex mixtures.

Evaluation of the efficiency of continuous wavelet transform as processing and preprocessing algorithm for resolution of overlapped signals in univariate and multivariate regression analyses; an application to ternary and quaternary mixtures

Wavelets have been adapted for a vast number of signal-processing applications due to the amount of information that can be extracted from a signal. In this work, a comparative study on the efficiency of continuous wavelet transform (CWT) as a signal processing tool in univariate regression and a pre-processing tool in multivariate analysis using partial least square (CWT-PLS) was conducted. These were applied to complex spectral signals of ternary and quaternary mixtures. CWT-PLS method succeeded in the simultaneous determination of a quaternary mixture of drotaverine (DRO), caffeine (CAF), paracetamol (PAR) and p-aminophenol (PAP, the major impurity of paracetamol). While, the univariate CWT failed to simultaneously determine the quaternary mixture components and was able to determine only PAR and PAP, the ternary mixtures of DRO, CAF, and PAR and CAF, PAR, and PAP. During the calculations of CWT, different wavelet families were tested. The univariate CWT method was validated according to the ICH guidelines. While for the development of the CWT-PLS model a calibration set was prepared by means of an orthogonal experimental design and their absorption spectra were recorded and processed by CWT. The CWT-PLS model was constructed by regression between the wavelet coefficients and concentration matrices and validation was performed by both cross validation and external validation sets. Both methods were successfully applied for determination of the studied drugs in pharmaceutical formulations.

Graphene-polyaniline modified electrochemical droplet-based microfluidic sensor for high-throughput determination of 4-aminophenol

We report herein the first development of graphene-polyaniline modified carbon paste electrode (G-PANI/CPE) coupled with droplet-based microfluidic sensor for high-throughput detection of 4-aminophenol (4-AP) in pharmaceutical paracetamol (PA) formulations. A simple T-junction microfluidic platform using an oil flow rate of 1.8 μL/min and an aqueous flow rate of 0.8 μL/min was used to produce aqueous testing microdroplets continuously. The microchannel was designed to extend the aqueous droplet to cover all 3 electrodes, allowing for electrochemical measurements in a single droplet. Parameters including flow rate, water fraction, and applied detection potential (Edet) were investigated to obtain optimal conditions. Using G-PANI/CPE significantly increased the current response for both cyclic voltammetric detections of ferri/ferrocyanide [Fe(CN)6](3-/4-) (10 times) and 4-AP (2 times), compared to an unmodified electrode. Using the optimized conditions in the droplet system, 4-AP in the presence of PA was selectively determined. The linear range of 4-AP was 50-500 μM (R(2) = 0.99), limit of detection (LOD, S/N = 3) was 15.68 μM, and limit of quantification (LOQ, S/N = 10) was 52.28 μM. Finally, the system was used to determine 4-AP spiked in commercial PA liquid samples and the amounts of 4-AP were found in good agreement with those obtained from the conventional capillary zone electrophoresis/UV-Visible spectrophotometry (CZE/UV-Vis). The proposed microfluidic device could be employed for a high-throughput screening (at least 60 samples h(-1)) of pharmaceutical purity requiring low sample and reagent consumption.

In situ reduction of well-dispersed nickel nanoparticles on hierarchical nickel silicate hollow nanofibers as a highly efficient transition metal catalyst

Ni nanoparticles were immobilized on the hierarchically double-shell nickel silicate hollow nanofibers, the composites exhibited an excellent catalytic activity.

Novel hydrothermal synthesis of MoS2nanocluster structure for sensitive electrochemical detection of human and environmental hazardous pollutant 4-aminophenol

A trace level electrochemical detection platform for the determination of environmentally hazardous pollutant 4-aminophenol at MoS₂nanoclusters is reported.

Electrochemical sensors based on carbon nanomaterials for acetaminophen detection: A review

This study describes the advancements made over the last five years in the development of electrochemical sensors and biosensors for acetaminophen detection. This study reviews the different configurations based on unmodified and chemically modified carbon nanotubes and graphene. The influence of various modifiers on the two types of materials is presented along with their role on the enhancement of the selectivity and sensitivity of (bio)sensors. The review is focused on a comparative description of the applications of carbon-based nanomaterials towards acetaminophen detection and presents the results in a critical manner.

Artificial neural network assisted kinetic spectrophotometric technique for simultaneous determination of paracetamol and p-aminophenol in pharmaceutical samples using localized surface plasmon resonance band of silver nanoparticles

Spectrophotometric analysis method based on the combination of the principal component analysis (PCA) with the feed-forward neural network (FFNN) and the radial basis function network (RBFN) was proposed for the simultaneous determination of paracetamol (PAC) and p-aminophenol (PAP). This technique relies on the difference between the kinetic rates of the reactions between analytes and silver nitrate as the oxidizing agent in the presence of polyvinylpyrrolidone (PVP) which is the stabilizer. The reactions are monitored at the analytical wavelength of 420nm of the localized surface plasmon resonance (LSPR) band of the formed silver nanoparticles (Ag-NPs). Under the optimized conditions, the linear calibration graphs were obtained in the concentration range of 0.122-2.425μgmL(-1) for PAC and 0.021-5.245μgmL(-1) for PAP. The limit of detection in terms of standard approach (LODSA) and upper limit approach (LODULA) were calculated to be 0.027 and 0.032μgmL(-1) for PAC and 0.006 and 0.009μgmL(-1) for PAP. The important parameters were optimized for the artificial neural network (ANN) models. Statistical parameters indicated that the ability of the both methods is comparable. The proposed method was successfully applied to the simultaneous determination of PAC and PAP in pharmaceutical preparations.

p-Aminophenol sensor based on tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube hybrid

The hybrid tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube was designed and synthesized, which can serve as an efficient catalyst for sensitive p-aminophenol detection due to synergistic effects between phthalocyanine and the carbon.

A new strategy for simultaneous determination of 4-aminophenol, uric acid and nitrite based on a graphene/hydroxyapatite composite modified glassy carbon electrode

A novel electrochemical sensor has been fabricated based on a graphene/hydroxyapatite composite modified GCE for the selective and simultaneous detection of 4-aminophenol, uric acid and nitrite ions (NO²⁻) by voltammetric method for the first time.

Copper phthalocyanine modified SiO2/C electrode as a biomimetic electrocatalyst for 4-aminophenol in the development of an amperometric sensor

SiO₂/C/CuPc sensor response for 4-aminophenol oxidation.

Separation and determination of impurities in paracetamol, codeine and pitophenone in the presence of fenpiverinium in combined suppository dosage form

A new HPLC method for separation and determination of impurities in paracetamol, codeine phosphate hemihydrate and pitophenone hydrochloride in the presence of fenpiverinium bromide in combined suppository dosage form was developed and validated. The separation of paracetamol and its impurities 4-aminophenol, 4-nitrophenol, 4-chloracetanilid; codeine and its impurities methylcodeine, morphine, codeine dimer and 10-hydroxycodeine; pitophenone and its impurities 2-[4-[2-(1-piperidinyl)ethoxy]benzoyl] benzoic acid, 2-[4-[2-(1-piperidinyl)ethoxy]benzoyl]benzoic acid 2-(1-piperidinyl)-ethyl ester, methyl ester of 2-(4-hydroxybenzoyl) benzoic acid and fenpiverinium was achieved by using ion-pair reversed phase liquid chromatography with UV detection. Validation parameters such as the precision, accuracy, linearity, limit of detection (LOD), limit of quantification (LOQ) and robustness were verified for all the mentioned impurities of codeine phosphate hemihydrate and 4-aminophenol and 2-[4-[2-(1-piperidinyl)ethoxy]benzoyl] benzoic acid as the main degradation products of paracetamol and pitophenone hydrochloride, respectively. The described method was found to be useful for analysis of the stability samples and therefore suitable for routine purity testing of the drug product.