Adsorptive stripping voltammetry for simultaneous determination of hydrochlorothiazide and triamterene in hemodialysis samples using a multi-walled carbon nanotube-modified glassy carbon electrode

Diuretics in Different Samples: Update on the Pretreatment and Analysis Techniques

Diuretics are drugs that promote the excretion of water and electrolytes in the body and produce diuretic effects. Clinically, they are often used in the treatment of edema caused by various reasons and hypertension. In sports, diuretics are banned by the World Anti-Doping Agency (WADA). Therefore, in order to monitor blood drug concentration, identify drug quality and maintain the fairness of sports competition, accurate, rapid, highly selective and sensitive detection methods are essential. This review provides a comprehensive summary of the pretreatment and detection of diuretics in various samples since 2015. Commonly used techniques to extract diuretics include liquid-liquid extraction, liquid-phase microextraction, solid-phase extraction, solid-phase microextraction, among others. Determination methods include methods based on liquid chromatography, fluorescent spectroscopy, electrochemical sensor method, capillary electrophoresis and so on. The advantages and disadvantages of various pretreatment and analytical techniques are elaborated. In addition, future development prospects of these techniques are discussed.

Using 3D printed magnetic platform as support for screen printed electrode applied for p-toluenediamine detection in biological fluid and water samples

The present work reports the development and application of a new electrochemical sensor for the determination of low concentration levels of p-toluenediamine (PTD) in biological fluids and surface water samples. The proposed sensor was developed using a 3D-printed magnetic device as platform for carbon screen printed electrode (CSPE) modified by magnetic nanoparticles functionalized with carboxylic groups and l-cysteine (MNP-CA-CYS). The results obtained from the morphological and electrochemical characterizations of the sensing platform enabled us to confirm the success of the sensor functionalization with l-cysteine and to have a better understanding of the electrochemical behavior and preconcentration of PTD on the electrode surface. PTD oxidation occurred at 0.24V on MNP-CA-CYS and the mechanism recorded an increase of 51.0% in anodic peak current. Under optimized conditions, the square wave voltammograms obtained for the electrode modified by 40.0 μL MNP-CA-CYS suspension at 1.0 mg mL^-1, with accumulation time of 3 min, presented an analytical curve with linear range of 8.00 × 10^-7 to 8.00 × 10^-5 mol L^-1, represented by the equation Iap = (0.383 ± 0.011)[PTD] - (8.112 ± 0.07) × 10^-8 (R² = 0.9994), and detection and quantification limits of 8.53 × 10^-8 and 2.56 × 10^-7 mol L^-1, respectively. Finally, the proposed method was validated through comparison with high performance liquid chromatography coupled to diode array detector (HPLC-DAD) technique and was successfully applied for PTD determination in samples of surface water, tap water, fetal bovine serum and artificial urine.

Electrochemical detection of triamterene in human urine using boron-doped diamond electrodes

Urine is one of the most used biological fluids for screening drug delivery and the resultant metabolites. In sports, the use of diuretics such as triamterene is considered a violation of anti-doping rules and is stipulated to be present at less than 79 nM in urine by the World Anti-Doping Agency (WADA). It is therefore important to develop effective rapid and low-cost tests for this diuretic. Here we apply electrochemical analysis using boron-doped diamond (BDD) electrodes, which have superior properties such as low background current, a wide potential window, and high resistance to deactivation. Since real urine samples show clear oxidation current peaks in the potential range more positive than 0.5 V (vs. Ag/AgCl) due to the presence of bio-components such as protein, uric acid, and ascorbic acid, to detect triamterene effectively, the electrochemical protocol was optimized towards a potential range where the other components have limited effect. Our results show that reduced triamterene exhibits an oxidation peak at 0.1 V (vs. Ag/AgCl) in 0.1 M phosphate buffer (PB) and at 0.2 V (vs. Ag/AgCl) in pooled human urine. The peak current value increased according to the triamterene concentration. The limit of detection (LOD) was 3.15 nM in the PB and 7.80 nM in pooled human urine. Finally, triamterene detection was attempted in individual urine samples. Triamterene was electrochemically detectable in individual urine samples, excluding urine samples containing an excess amount of ascorbic acid. The limit of detection (LOD) in individual urine samples was determined to be 20.8 nM.

Simultaneous determination of hydrochlorothiazide, amlodipine, and telmisartan with spectrophotometric and HPLC green chemistry applications

For the quantifiable amounts of Telmisartan (TLM) and Hydrochlorothiazide (HYD) in the presence of Amlodipine (AML) in a ternary mixture of synthetic laboratory mixture, a novel, sensitive, quick, and practical reversed-phase high-performance liquid chromatography (RP-HPLC) method was given. In order to separate, a Waters Spherisorb ODS-2 C18 column was used. For HYD, TLM, and AML, these techniques were viable over linearity ranges of 4-12 μg/mL, 4-25 μg/mL, and 5-40 μg/mL, respectively. The mobile phase system was acetonitrile:methanol: phosphate buffer at pH 2.5 (65:5:30 v/v/v), and the flow rate was 1.5 mL/min. Novel spectrophotometric methods were applied for active substances to determine simultaneously. The first method is absorptivity centering using factorized spectrum, and the second method is dual amplitude difference coupled with absorbance subtraction. These approaches have been effectively applied to bulk, laboratory synthetic mixtures to employ active components quantitatively. Correlation coefficients were found to be higher than 0.99 and the limit of detection values lower than 0.49 μg/mL in both spectrophotometric methods. The methodologies were validated following ICH recommendations. In the developed HPLC method, the limit of detection values was found to be 0.01 μg/mL for HYD and 0.02 μg/mL for AML and TLM. The correlation coefficients for the HPLC method were found to be 0.9971 for HYD, 0.9990 for AML, and 0.9983 for TLM. The suggested HPLC technique is a simple, effective, sensitive, environmentally friendly, and time-saving approach for determining TLM and HYD in the presence of AML.

Understanding Carbon Nanotube Voltammetry: Distinguishing Adsorptive and Thin Layer Effects via "Single-Entity" Electrochemistry

Cyclic voltammetry of ensembles of nanotube-modified electrodes fails to distinguish between signals from electroactive material adsorbed on the tubes from those due to a thin-layer response of analyte material occluded in the pores of the ensemble. We demonstrate that the distinction can be clearly made by combining cyclic voltammetry with single-entity measurements and provide proof of concept for the case of b-MWCNTs and the oxidation of 4-hexylresorcinol (HR), where the increased signals seen at the modified electrode are concluded to arise from thin-layer diffusion and not adsorptive effects. The physical insights are generic to porous, conductive composites.

Ultra-Performance Liquid Chromatographic and Densitometric Methods for Sensitive Determination of Xipamide and Triamterene in Pure and Pharmaceutical Dosage Forms

BACKGROUND

Validated UPLC method and TLC densitometric method were prescribed for determination of antihypertensive components. Objectives: To establish and validate rapid and accurate Ultra performance liquid chromatographic (UPLC) and TLC densitometric methods for determination of Xipamide and Triamterene in pure and dosage forms.

METHODS

The first method; UPLC method, depended on using Agilent Zorbax Eclipse Plus C8 (50 mm × 2.1 mm, 1.8 μm), as the column, mobile phase composed of (acetonitrile-water) (70 + 30, v/v) adjusted by acetic acid to obtain (pH 3), 0.2 mL/min flow rate and UV detection at 231.4 nm. The second method was a thin layer chromatography (TLC) densitometric method, separation was achieved by using toluene-methanol-ethyl chloride-acetic acid (7 + 2 + 1 + 0.2, v/v/v) as the mobile phase, pre coated silica gel plates as the stationary phase and UV detection at 300.0 nm.

RESULTS

The obtained results were validated and statistically compared with official and reported methods. The obtained results showed high accuracy and reproducible results with excellent mean recoveries for both drugs.

CONCLUSIONS

The UPLC method showed shorter retention time for both Xipamide (0.88 min) and Triamterene (0.63 min), lower detection limit less than 0.055 µg/mL for both drugs with high selectivity, decreased injection volume (1 µL) and lower flow rate other than any HPLC method. Both proposed methods were sensitive, selective, and effectively applied to pure and dosage forms (Epitens®).

HIGHLIGHTS

Unprecedented sensitive, rapid, and reproducible UPLC and TLC methods were developed for selective determination of mixture of Xipamide and Triamterene with LOD less than 0.076 µg/mL for both drugs.

HPTLC Method for the Ultrasensitive Detection of Triamterene in Plasma

A high-performance thin-layer chromatographic (HPTLC) method has developed for the selective detection of a diuretic drug, triamterene (TRIAM), in pure form, tablets and human plasma. The method was based on chromatographic separation of TRIAM using HPTLC plates, precoated with silica gel, and a mobile phase consisted of ethyl acetate: dimethylformamide: ammonia (7.0: 2.7: 0.3, by volume). The native fluorescence signal of TRIAM was detected at 440 nm and used to quantify TRIAM using the proposed method, improving the method sensitivity to ~250-folds in comparison to that reported in previous HPTLC studies. The developed method enabled the detection of TRIAM in pure drug and biological samples (human plasma) within linear concentrations ranged from 0.8 to 60 ng/band or 1.0 to 60 ng/band for pure drug and plasma samples, respectively. Furthermore, the method was validated according to the official guidelines to permit its applicability in quality control and clinical laboratories.

Assessment of the autoxidation mechanism of p-toluenediamine by air and hydrogen peroxide and determination of mutagenic environmental contaminant in beauty salon effluent

The present work investigated the autoxidation reaction of p-toluenediamine (PTD) - a precursor - widely used in permanent hair dyeing formulation, under experimental conditions close to the hair dyeing process (oxygen and/or peroxide in ammoniacal medium), by chromatographic and spectroscopic techniques. In additional, evaluated the mutagenicity of the PTD oxidation products and the presence of PTD and this products in wastewater from beauty salon, as well as in surface water and drinking water using HPLC coupled to a diode array detector and linear scan voltammetry. Through this study, it was possible the identification of semi-quinonediimine, quinonediimine, dimers (derived from toluenediamine), and trimer radical identified as Bandrowski's Base derivative (BBD) formed during autoxidation of PTD. Salmonella Typhimurium YG1041 assay with and without metabolic activation induced rat-liver (S9) indicated mutagenic activity for BBD. Levels of PTD were determined by the standard addition method in samples collected from the wastewater of a beauty salon, as well as from the water before and after treatment in a drinking water treatment plant (DWTP) reached concentrations of 2.08 ± 0.21, 2.36 ± 0.10 × 10^-3, and 1.77 ± 0.13 × 10^-3 mg L^-1, respectively. In addition, linear sweep voltammetry was used to monitor the BBD found at the concentration of 1.59 ± 0.35 mg L^-1 in wastewater collected from the beauty salon.

New Generation of Electrochemical Sensors Based on Multi-Walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWCNT) have provided unprecedented advances in the design of electrochemical sensors. They are composed by sp2 carbon units oriented as multiple concentric tubes of rolled-up graphene, and present remarkable active surface area, chemical inertness, high strength, and low charge-transfer resistance in both aqueous and non-aqueous solutions. MWCNT are very versatile and have been boosting the development of a new generation of electrochemical sensors with application in medicine, pharmacology, food industry, forensic chemistry, and environmental fields. This work highlights the most important synthesis methods and relevant electrochemical properties of MWCNT for the construction of electrochemical sensors, and the numerous configurations and successful applications of these devices. Thousands of studies have been attesting to the exceptional electroanalytical performance of these devices, but there are still questions in MWCNT electrochemistry that deserve more investigation, aiming to provide new outlooks and advances in this field. Additionally, MWCNT-based sensors should be further explored for real industrial applications including for on-line quality control.