A comparative study of first-derivative spectrophotometry and high-performance liquid chromatography applied to the determination of losartan potassium in tablets

All-solid-state paper-based potentiometric combined sensor modified with reduced graphene oxide (rGO) and molecularly imprinted polymer for monitoring losartan drug in pharmaceuticals and biological samples

A cost-effective, highly selective and sensitive paper-based potentiometric combined sensor for losartan potassium drug (LOS) is fabricated, characterized and used for the drug monitoring. The sensor consists of 2 strips of filter paper (20 × 5 mm each) as platform, each imprinted with 4 mm diameter circular spot of carbon. One carbon spot is covered by a reduced graphene oxide (rGO) for use as a substrate for the recognition sensor and the other without rGO is used for the reference electrode. LOS molecularly imprinted drug polymer (MIP) is applied onto the graphene oxide containing strip to act as a drug recognition sensing material and a solid-state polyvinyl butyral (PVB) is applied onto the second carbon spot to act as a reference electrode. Performance characteristics of the combined sensor are examined with chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Increase effect of rGO on the interfacial double-layer capacitance of the sensing membrane and consequently on the potential stability is confirmed. The developed combined sensor (strip cell) displays a Nernstian slope of -58.2 ± 0.3 mV/decade (R² = 0.9994) over the linear range 8.5 × 10^-7 - 6.9 × 10^-2 M with a detection limit of 2.7 ± 0.3 × 10^-7 M. The sensor shows remarkable selectivity toward various related compounds especially those commonly used by the COVID-19 patients such as paracetamol, ascorbic acid and dextromethorphan. The assay method is validated and proved to be satisfactory for direct potentiometric determination of LOS-K in some pharmaceutical formulations and in spiked human urine samples. An average recovery of 96.3 ± 0.3-98.7 ± 0.6% of the nominal or spiked concentration and a mean relative standard deviation of ±0.6% are obtained. The use of an indicating and a reference electrodes combined into a single flexible disposable paper platform enables applications to a minimum sample volume due to the close proximity of the responsive membrane and the liquid junction. The efficiency of the proposed sensor in complex urine matrix suggests its application in hospitals for rapid diagnosis of overdose patients and for quality control/quality assurance tests in pharmaceutical industry.

Development of a Novel Nanocomposite Based on Reduced Graphene Oxide/Chitosan/Au/ZnO and Electrochemical Sensor for Determination of Losartan

Background:

Hypertension is a major risk for morbidity and mortality, while hypertension is associated with cardiovascular disease and organ damage. Recent research efforts have focused on the development of highly selective angiotensin receptor blockers. In which losartan (LOS) is considered as a new generation of an effective oral drug product against arterial hypertension. Therefore, the determination of drugs in biological fluids, pharmaceuticals (tablets), and wastewater is of critical importance for clinical applications, forensics, quality control, and environmental protection that call for the development of analytical methods. Many ranges of methods such as spectroscopic methods and chromatographic techniques have been developed to determine LOS in pharmaceutical formulations and biological fluids. However, there are crucial interference problems in these methods. For these reasons, more sensitive, desirable, portable, low-cost, simple, and selective nanocomposite-based sensors are needed in terms of health safety. Nanomaterials such as reduced graphene oxide, chitosan, and metal nanoparticles are used to improve the sensitivity in the development of electrochemical sensors.

Objective:

In this study, a novel reduced graphene oxide (RGO), chitosan (Chit), gold (Au), and zinc oxide (ZnO) nanocomposite (RGO/Chitosan/Au/ZnO) was synthesized and used to develop a sensitive and efficient electrochemical sensor for LOS detection.

Methods:

Modification of electrode by RGO/Chit/Au/ZnO nanocomposite was performed in four stages with GO (at -2.0 V for 150 s), Chitosan (at -3.0 V for 300 s), Au nanoparticles (at -0.4 V for 400 s), and Zn nanoflowers like (at -0.7 V for 1200 s). The RGO/Chitosan/Au/ZnO nanocomposite was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR). Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were used to detect LOS, and the influence of pH value, scan rate, accumulation potential, and time also losartan concentration on the performance of ZnO/Au/Chitosan/RGO/GCE were investigated. In order to investigate the selectivity of the modified electrode for the determination of LOS, the effect of possible interfering species was evaluated and showed that these species are not interferences. Also, the reproducibility of the modified electrode was investigated and implying that the RGO/Chit/Au/ZnO nanocomposite was highly reproducible.

Results:

The modified electrode was used as a sensor for the selective and sensitive determination of LOS with a detection limit of 0.073 μM over the dynamic linear range of 0.5μM to 18.0 μM. In addition, electrochemical oxidation of LOS was well recovered in pharmaceutical formulations.

Conclusion:

LOS is used to treat high blood pressure, taking into account the oxidation of this compound, the use of electrochemical based sensors, ideally suited to a specific chemical species, can be fully selectable and High-sensitivity answer is very important. In this study, the electrodes with RGO/Chit/Au/ZnO nanocomposite were modified by the electrochemical method. Nanocomposites were characterized by various methods such as FE-SEM, FT-IR, XRD, Raman, and XPS. The electrocatalytic activity of the modified electrode was then investigated for measuring LOS. According to the results of the modified electrode, high sensitivity, reproducibility, and selectivity have been shown to oxidize this composition.

Computational study of influence of diffuse basis functions on geometry optimization and spectroscopic properties of losartan potassium

The work was aimed at investigating the influence of diffusion of basis functions on the geometry optimization of molecule of losartan in acidic and salt form. Spectroscopic properties of losartan potassium were also calculated and compared with experiment. Density functional theory method with various basis sets: 6-31G(d,p) and its diffused variations 6-31G(d,p)+ and 6-31G(d,p)++ was used. Application of diffuse basis functions in geometry optimization resulted in significant change of total molecule energy. Total molecule energy of losartan potassium decreased by 112.91kJ/mol and 114.32kJ/mol for 6-31G(d,p)+ and 6-31G(d,p)++ basis sets, respectively. Almost the same decrease was observed for losartan: 114.99kJ/mol and 117.08kJ/mol respectively for 6-31G(d,p)+ and 6-31G(d,p)++ basis sets. Further investigation showed significant difference within geometries of losartan potassium optimized with investigated basis sets. Application of diffused basis functions resulted in average 1.29Å difference in relative position between corresponding atoms of three obtained geometries. Similar study taken on losartan resulted in only average 0.22Å of dislocation. Extensive analysis of geometry changes in molecules obtained with diffused and non-diffuse basis functions was carried out in order to elucidate observed changes. The analysis was supported by electrostatic potential maps and calculation of natural atomic charges. UV, FT-IR and Raman spectra of losartan potassium were calculated and compared with experimental results. No crucial differences between Raman spectra obtained with different basis sets were observed. However, FT-IR spectra of geometry of losartan potassium optimized with 6-31G(d,p)++ basis set resulted in 40% better correlation with experimental FT-IR spectra than FT-IR calculated with geometry optimized with 6-31G(d,p) basis set. Therefore, it is highly advisable to optimize geometry of molecules with ionic interactions using diffuse basis functions when accuracy of results is a priority.

Optimization of a spectrofluorimetric method based on a central composite design for the determination of potassium losartan in pharmaceutical products

Here, a spectrofluorimetric method for the determination of potassium losartan (PL) in pharmaceutical products is described. The effects of critical parameters, pH, acid molarity, and temperature, on the fluorescence intensity of PL were analyzed, and these parameters were optimized using a central composite design (CCD). The highest fluorescent intensity at excitation (λex) and emission (λem) wavelengths of 248 nm and 410 nm, respectively, was achieved using 0.01 M sulfurous acid (pH 2) at 21.6 °C. Under optimum conditions, the method was linear from 0.025-0.5 µg/mL, with a reasonably high correlation coefficient (0.9993). Furthermore, the method was very sensitive (LOQ, 0.006), accurate (RE, ≤7.06), and precise (%RSD, ≤6.51). After development and validation of the method, samples containing PL were analyzed with this method, and the obtained data were statistically compared with those obtained with a previously published reference method using a two one-sided equivalence test (TOST). According to the data, the results from the proposed and reference assays were equivalent.

Analysis of Sartans: a review

The risk of cardiovascular diseases is closely related to hypertension, high cholesterol levels, and diabetes. When these risk factors appear together they are referred to as a metabolic syndrome. In the treatment of cardiovascular diseases, a combination of antihypertensive, hypolipemiant, and antidiabetic drugs is often applied. Diuretics (chlortalidone, hydrochlorothiazide, etc.) and angiotensin II receptors antagonist (sartans) are used to control hypertension, whereas statins (fluvastatin, simvastatin, etc.) are used to reduce cholesterol levels. This review is concerned with methods for the analysis of sartans in various matrices, such as pharmaceutical formulations, environmental and biological samples, and discusses the current status of stability studies of sartans . It also presents analytical methods for the simultaneous determination of sartans, diuretics, and statins.

A simple and precise conductometric method for the determination of losartan in pharmaceutical products

Losartan is an antihypertensive agent that lost its patent protection in 2010, and, consequently, it has been available in generic form. The latter motivated the search for a rapid and precise alternative method. Here, a simple conductometric titration in aqueous medium is described for the losartan analysis in pharmaceutical formulations. The first step of the titration occurs with the protonation of losartan producing a white precipitate and resulting in a slow increase in conductivity. When the protonation stage is complete, a sharp increase in conductivity occurs which was determined to be due to the presence of excess of acid. The titrimetric method was applied to the determination of losartan in pharmaceutical products and the results are comparable with values obtained using a chromatographic method recommended by the United States Pharmacopoeia. The relative standard deviation for successive measurements of a 125 mg L−1 (2.71×10−4 mol L−1) losartan solution was approximately 2%. Recovery study in tablet samples ranged between 99 and 102.4%. The procedure is fast, simple, and represents an attractive alternative for losartan quantification in routine analysis. In addition, it avoids organic solvents, minimizes the risk of exposure to the operator, and the waste treatment is easier compared to classical chromatographic methods.

Spectrofluorimetric method for determination of some angiotensin II receptor antagonists

A simple, rapid, accurate and highly sensitive spectrofluorimetric method has been developed for determination of some angiotensin II receptor antagonists (AIIRA's), namely Losartan potassium (Los-K), Irbesartan (Irb), Valsartan (Val) and Candesartan cilexetil (Cand) in pure forms as well as in their pharmaceutical dosage forms. All the variables affecting the relative fluorescence intensity (RFI) were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9982-0.9991) were obtained over the concentration range from 0.006 μg/mL to 1.7 μg/mL. Good accuracy and precision were successfully obtained for the analysis of tablets containing each drug alone or combined with hydrochlorothiazide (HCTZ) without interferences from the co-formulated HCTZ or the additives commonly present in tablets.

Sensitive and accurate estimation of losartan potassium formulation by high-performance thin-layer chromatography

AIM AND OBJECTIVES

To develop a simple, sensitive, cost-effective and reproducible UV-spectrophotometric method and validate for the estimation of disodium edetate in topical gel formulations.

MATERIALS AND METHODS

Solution of disodium edetate reacts with ferric chloride to form complex in 0.1 N HCl giving λmax at 270 nm. Beer's law was obeyed in the concentration range of 5-50 μg/mL (r (2) = 0.9997).

RESULTS

The limit of detection and limit of quantitation were found to be 1.190 and 3.608 μg/mL, respectively. The results show that the procedure is accurate, precise, and reproducible (relative standard deviation < 1%), while being simple and less time consuming.

CONCLUSIONS

The study concluded that the UV-spectrophotometric method could be used for the quantification of disodium edetate in pure form as well as in pharmaceutical formulations.

Comparative study of analytical methods by direct and first-derivative UV spectrophotometry for evaluation of losartan potassium in capsules

Losartan potassium is an antihypertensive non-peptide agent, which exerts its action by specific blockade of angiotensin II receptors. The aim of the present study was the validation and application of analytical methods for the quality control of losartan potassium 50 mg in pharmaceutical capsules, using direct and first-derivative UV spectrophotometry. Based on losartan potassium spectrophotometric characteristics, a signal at 205 nm of the zero-order spectrum and a signal at 234 nm of the first-derivative spectrum, were found adequate for quantification. The results were used to compare these instrumental techniques. The linearity between the signals and concentrations of losartan potassium in the ranges of 3.0-7.0 mg L-1 and 6.0-14.0 mg L-1 for direct and first-derivative spectrophotometry in aqueous solutions, respectively, presented a correlation coefficient (r) of 0.9999 in both cases. The methods were applied for losartan potassium in capsule dosage obtained from local pharmacies, and were shown to be efficient, easy to apply and low cost. These methods do not use polluting reagents and require relatively inexpensive equipment.