Chemically‐reduced Graphene Oxide Sensor for Dipyrone Quantification in Pharmaceutical Samples Using Amperometric Detection

Dipyrone (metamizole sodium) is one of the most consumed drugs in the world. In this work a novel analytical method was developed for dipyrone sensing. This method involves the amperometric detection on a chemically‐reduced graphene‐oxide (CRGO)‐modified glassy carbon electrode. Raman spectroscopy and scanning electron microscopy revealed the presence of multilayer graphene layers that contributed to the electrocatalytic oxidation of dipyrone and increase in the electroactive area. Advantages of this sensor include elimination of previous separations, solvent extraction, or sample filtration, low detection limit (0.13 μmol L^?1) with a linear range from 48 to 246 μmol L^?1 and adequate recovery values (97–103 %). Applied to commercial pharmaceutical samples, this method showed results ranging from 451 to 541 mg of dipyrone per tablet, which agreed with the expected values. The results obtained by amperometry were compared statistically with the official method recommended by the Brazilian Pharmacopoeia (iodometric method), with no significant differences between them at 95 % confidence level. The proposed method is accurate for the monitoring of sodium dipyrone in pharmaceutical formulations, highlighting the lower reagent consumption and interferences in the analytical process.     

Novel clorsulon voltammetric sensors based on zinc oxide nanostructure

Herein, the fabrication and electrochemical characterization of a novel clorsulon (CLO) sensor were evaluated. Among the different tested metal oxides nanostructures, bulk modification of the carbon paste working electrode with zinc oxide exhibited the proper electrocatalytic activity towards CLO with irreversible anodic oxidation peak at 1.02 in universal buffer pH 7.0. Clorsulon molecule showed diffusion–reaction mechanism through the involvement of one-electron and one proton as illustrated by the sweep rate, pH studies, and sustained by the molecular orbital calculations. The fabricated sensors showed linear calibration curves within the CLO concentration range from 0.45 to 10.13 × 10^?9 mol L^?1 with LOD value of 0.14 × 10^?9 mol L^?1. Enhanced sensitivity with good measurement reproducibility and long operational lifetime were cited as shining futures of the fabricated sensor. The constructed sensors were utilized for clorsulon quantification in veterinary formulations and milk samples with high accuracy and precision compared with the traditional methods.     

Spectrofluorimetric Assay of Temafloxacin in Pharmaceutical Formulations and in Serum

A simple and rapid assay is described for the determination of temafloxacin, 1-(2,4-difluorophenyl)-6-fluoro-7-(3-methylpiperazin-1-yl) 1,4- dihydro-4-oxoquinolin-3-carboxylic acid hydrochloride, in pharmaceutical formulations and in serum, based on the fluorescence emission of the drug. The assay of pharmaceuticals involves the measurement of fluorescence at 460 nm of the sample diluted in 0.1 H₂SO₄ with an excitation wavelenght of 276 nm and the assay of serum involves the use of the synchronous spectrofluorimetric method. An appropriate selection of the difference between the wavelengts of both monochromators (ΔΛ) allowed the direct and rapid determination of temafloxacin in serum samples without previous extraction. The procedure, which has been shown to be accurate, precise and sensitive requires only 0.25–0.4 ml of serum depending on the drug concentration.     

Simultaneous Differential Pulse Voltammetric Determination of Sulfamethoxazole and Trimethoprim on a Boron‐Doped Diamond Electrode

The performance of hydrogen‐ (HT) and oxygen‐terminated (OT) boron‐doped diamond (BDD) electrodes (electrochemically pretreated) on the simultaneous differential pulse voltammetric determination of sulfamethoxazole and trimethoprim in pharmaceutical products is presented. Under the optimum analytical experimental conditions, the HT‐BDD electrode presented two well‐defined oxidation peaks at 920 and 1100 mV vs. Ag/AgCl for sulfamethoxazole and trimethoprim, respectively. On the other hand, when the OT‐BDD electrode was used, the sulfamethoxazole oxidation current peak was decreased twenty fold. The calculated LOD values for sulfamethoxazole and trimethoprim using the HT‐BDD electrode were 3.65 μg L^?1 and 3.92 μg L^?1, respectively. The results obtained in the simultaneous determination of sulfamethoxazole and trimethoprim in three different commercial formulations were similar to those obtained using a standard HPLC method at 95% confidence level.     

Enzymatic determination of vitamin A in pharmaceutical formulations with spectrophotometric detection

An enzymatic method for the determination vitamin A (retinol) is reported using soluble and immobilized alcohol dehydrogenase, isolated from rabbit liver. The reaction is based on the oxidation of retinol and simultaneous reduction of NAD⁺ to NADH followed by spectrophotometric detection at 340 nm. The calibration graph was linear over the range of 2.0–10 μM with correlation coefficients of 0.9967 and 0.9992 (n = 5) for soluble and immobilized alcohol dehydrogenase respectively, with relative standard deviations (n = 3) in the range of 0.5–1.2%. The limit of detection was lower than 1.0 μM. The proposed method was applied to determine vitamin A in pharmaceuticals, and the results obtained were in reasonable agreement with the amount labeled. The results were compared using spectrophotometric reference method, and no significant difference was found between the results of the both methods.     

Determination of nitrogen in hydrolyzed protein formulations by continuous vapour phase FTIR

An on-line system with vapour generation (VG) and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of free ammonium and organic nitrogen in agrochemical formulations containing hydrolyzed proteins. Commercial samples were digested, in batch mode, with sulphuric acid and the obtained solution was alkalinized on-line to transform the NH₄⁺ to NH₃ that was continuously monitored by FTIR. Free ammonium was determined in the same system after simple dilution of undigested samples with water. Different gas phase separators were assayed in order to introduce gaseous NH₃ into a home made IR gas cell of 10 cm pathlength, where the corresponding FTIR spectra were acquired by accumulating 10 scans per spectrum. The 967.0 cm⁻¹ band was used for the quantification of ammonia. The figures of merit of the proposed method involve a linear range up to 100 mg L⁻¹, a limit of detection (3σ) of 1.4 mg L⁻¹ of N, a limit of quantification (10σ) of 4.8 mg L⁻¹ of N, a precision (R.S.D.) of 3.0% for 10 replicate determinations of a 10.0 mg L⁻¹ of N and a sample measurement frequency of 60 h⁻¹. The method was successfully applied to the determination of free ammonium and total N in commercial amino acid formulations and results compare well with those obtained by the Kjeldhal method.     

Optimization of transmission near infrared spectrometry procedures for quality control of pesticide formulations

The use of different response functions to be optimized in the frame of the use of near infrared spectrometry for quality control of active principles in agrochemical formulations has been evaluated. Both, simple functions, based on parameters like sensitivity, repeatability, accuracy, signal to noise ratio, limit of detection or sample throughput, and a complex function, considering all the aforementioned aspects, were employed in the development of a new method for Iprodione determination in agrochemicals. Optimization strategies were based on the previous screening of the most important instrumental factors like number of cumulated scans, nominal resolution, mirror velocity and zero filling factor, based on a two-level full factorial design and on the search for the optimum conditions using central composite designs. Data found evidenced the influence of the response function on the optimum values of experimental conditions and could be employed as a general guide to evaluate the experimental factors in routine use of near infrared spectrometry. Finally the optimized method for Iprodione has been applied to the determination of Diuron and results found compared with those obtained by a conventional approach.     

Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream

We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream.     

Method development and validation for the simultaneous determination of five selective serotonin reuptake inhibitors by capillary zone electrophoresis

Summary A capillary zone electrophoresis method is proposed for the separation of five antidepressants. Optimum conditions for the separation were investigated. A background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.5, hydrodynamic injection, and a 28 kV separation voltage were used. Relative standard deviations (RSD) were <0.9% and <1.7% for migration time and corrected peak area (n=21), respectively. The detection limits for the five antidepressants ranged from 0.3 to 0.7 mg L⁻¹. The stability of the solutions, linearity, accuracy, and precision were examined during validation of the method. The method is rapid and sensitive, when it was tested for the analysis of pharmaceutical formulations the recoveries obtained were between 98 and 103% of the nominal content.     

Optimisation and validation of a generic method for the LC assay of six corticosteroids and salicylic acid in dermopharmaceutical forms

Summary A generic method was developed for the liquid chromatographic (LC) assay of six corticosteraids and salicylic acid in different dermatological formulations containing methylparaben and propylparaben or sorbic acid as preservatives. An adequate separation was obtained using octadecylsilica as stationary phase and a mixture of acetonitrile (MeCN) and 25 mM phosphate buffer of pH 3.5 as mobile phase. Segmented gradient elution was applied from 30 to 45% of MeCN in 9.9 minutes, then from 45 to 96% in 19.0 minutes. UV detection was performed at 240 nm. The method was validated. Very good results were obtained with respect to linearity, selectivity, precision and accuracy.