A Fluorescence System Composed of Nitrogen-doped Graphene Quantum Dots and Gold Nanoparticles Coated With Phenylalanine for Selective and Sensitive Quantification of Piroxicam in Biological Samples

In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated with phenylalanine. The fluorescence emission of N-GQDs at 440 nm decreases with the increase of gold nanoparticles coated with phenylalanine. However, the addition of piroxicam causes the release of gold nanoparticles from the surface of quantum dots followed by the retrieval of the fluorescence emission of N-GQDs. Under the optimum conditions, the calibration graph was linear in the concentration range of 2.0-35.0 nmol L-1 for piroxicam with a limit of detection of 0.11 nmol L-1. The developed method was successfully applied for the determination of piroxicam in urine and serum samples.

Determination of uric acid in grain using HPLC

В данной статье показана возможность улучшения определения мочевой кислоты методом высокоэффективной жидкостной хроматографии (ВЭЖХ), с помощью увеличения растворимости ее в 1 %-ном растворе ацетата натрия, повышения удержания мочевой кислоты и тем самым изменения времени выхода, что позволяет повысить точность анализа. Проведено сравнение градуировочных растворов и опытных образцов зерна зараженных вредителями хлебных запасов. В процессе исследования был опробован метод для определения и идентификации мочевой кислоты как одного из загрязняющих зерно веществ с помощью ВЭЖХ в обращенной фазе. Экспериментально опробована и усовершенствована методика анализа мочевой кислоты в зерне с использованием жидкостного хроматографа «Стайер». Описаны оборудование и материалы для ВЭЖХ, условия хроматографического разделения и детектирования, построения калибровочного графика, экстракции, включая методику экстракции, сходимости результатов при экстракции и введении экстракта в хроматограф, а также порядок и расчет измерений. Экспериментально показано, что усовершенствованная методика с применением ВЭЖХ позволяет использовать ее для проведения дальнейших исследований зависимости содержания мочевой кислоты от величины загрязнения зерна насекомыми. This article shows the possibility of improving the determination of uric acid by high-performance liquid chromatography (HPLC), by increasing its solubility in a 1 % solution of sodium acetate, increasing the retention of uric acid, and thereby changing the yield time, which allow to improve the accuracy of the analysis, a comparison of calibration solutions and experimental grain samples of pest-infected bread stocks have been carried out. During the research course a method for the determination and identification of uric acid has been tested as one of the grain polluting substance using HPLC in the reversed phase. The method of uric acid in grain analysis using a liquid chromatograph «Stayer» has been experimentally tested and improved. The equipment and materials for HPLC, the conditions of chromatographic separation and detection, the construction of a calibration graph, extraction, including the extraction method, the convergence of the results during extraction and the introduction of the extract into the chromatograph, as well as the course and calculation of measurements have been described. It has been experimentally shown that the improved method with HPLC allows to use it for further research of the uric acid content dependence on the amount of grain contamination by insects.

Selective Voltammetric Detection of Ascorbic Acid from Rosa Canina on a Modified Graphene Oxide Paste Electrode by a Manganese(II) Complex

Voltammetric techniques have been considered as an important analytical tool applied to the determination of trace concentrations of many biological molecules including ascorbic acid. In this paper, ascorbic acid was detected by square wave voltammetry, using graphene oxide paste as a working electrode, modified by a film of a manganese(II) complex compound. Various factors, such as the effect of pH, affecting the response characteristics of the modified electrode were investigated. The relationship between the peak height and ascorbic acid concentration within the modified working electrode was investigated, using the calibration graph. The equation of the calibration graph was found to be: I = 0.0550γac + 0.155 with R2 = 0.9998, where I is the SWV current and γac is the mass concentration of ascorbic acid. The LOD and LOQ of the proposed method were determined to be 1.288 μg/L and 3.903 μg/L, respectively. Several compounds, such as riboflavin, biotin, and ions, such as Fe and Cu, were tested and it seemed that they did not interfere with the analytic signal. The proposed procedure was successfully applied in the determination of ascorbic acid in Rosa canina hips.

SOLID PHASE EXTRACTION BASED ON Mn3O4-TIO2 NANOCOMPOSITE FOR THE DETERMINATION OF MOLYBDENUM IN WATER SAMPLES

The Mn3O4-TiO2 nanocomposite was applied as a new solid phase adsorbent for preconcentration of Molybdenum before determination by an UV-Vis spectrophotometer. The solid-phase extraction conditions as pH, the mass of sorbent, contact time, stirring speed, and the elution condition were investigated. Under optimized conditions, the adsorption capacity of adsorbent was 20.69 mg/g, and the elution condition was 0.2M NaOH solution. Molybdenum ions were determined based on its catalytic effect on the oxidation of 1-amino-2- naphthol-4-sulfonic acid (ANSA) with H2O2. The linear calibration graph was in the range of 0.2–2.5 µg/L (r2 = 0.995) with a detection limit of 0.0502 µg/L. The relative standard deviation for five measurements of 2 µg/L of Mo (VI) was 3,37%. The method was applied to the determination of Molybdenum in water samples.

Point-of-Care Detection of Salivary Nitrite Based on the Surface Plasmon-Assisted Catalytic Coupling Reaction of Aromatic Amines

Rapid quantification of nitrite (NO2−) in food, drink and body fluids is of significant importance for both food safety and point-of-care (POA) applications. However, conventional nitrite analytical methods are complicated, constrained to sample content, and time-consuming. Inspired by a nitrite-triggered surface plasmon-assisted catalysis (SPAC) reaction, a rapid point-of-care detection salivary nitrate was developed in this work. NO2− ions can trigger the rapid conversion of p-aminothiophenol (PATP) to p,p′-dimercaptozaobenzene (DMAB) on gold nanoparticles (GNPs) under light illumination, and the emerged new bands at ca. 1140, 1390, 1432 cm−1 originating from DMAB can be used to the quantification of nitrite. Meanwhile, to make the method entirely suitable for on-site fast screen or point-of-care application, the technique is needed to be further optimized. The calibration graph for nitrates was linear in the range of 1–100 µM with a correlation coefficient of 0.9579. The limit of detection was 1 µM. The facile method could lead to a further understanding of the progression and treatment of periodontitis and to guide professionals in planning on-site campaigns to effectively control periodontal diseases.

Green spectrofluorimetric assay of dantrolene sodium via reduction method: application to content uniformity testing

Green analysis has turned out to be of a great value in all areas, including pharmaceutical analysis. Thus, it is extremely important to consider the environmental influence of each step in developing any analysis technique. The present work illustrates a validated, simple and green spectrofluorimetric method for the analysis of dantrolene sodium (DAN). The developed process is characterized by being of high sensitivity as well as being relatively inexpensive. The suggested technique based on the formation of a highly fluorescent product of DAN via its reduction by the aid of Zn/HCl system. The resulting fluorophore showed a powerful fluorescence at λ em 344 nm after excitation at λ ex 279 nm. Calibration graph revealed a great linear regression ( r = 0.9998) within concentration ranging from 0.05 to 2.0 µg ml −1 . The suggested method had very low detection and quantification limits of 0.010 and 0.031 µg ml −1 , respectively. The applied technique was effectively used in the determination of DAN in its pharmaceutical preparations. The results were compared with those from using the official United States Pharmacopeia (USP) method and they were in a good agreement. Moreover, content uniformity testing of DAN in capsules was performed adopting the investigated technique with satisfying results. The greenness of the suggested technique was confirmed by the three standard assessment tools. Therefore, the developed technique can be used in the routine quality control analysis of DAN with minimum harmful impact on nature or individuals.

Determination of fenthion in environmental water samples by dispersive liquid–liquid microextraction coupled with spectrofluorimetric and chemometrics methods

In the present study, a simple, rapid and efficient dispersive liquid–liquid microextraction (DLLME) coupled with spectrofluorimetry and chemometrics methods have been proposed for the preconcentration and determination of fenthion in water samples. Box–Behnken design was applied for multivariate optimization of the extraction conditions (sample pH, the volume of dispersive solvent and volume of extraction solvent). Analysis of variance was performed to study the statistical significance of the variables, their interactions and the model. Under the optimum conditions, the calibration graph was linear in the range of 5.0–110.0 ng mL-1 with the detection limit of 1.23 ng mL-1 (3Sb/m). Parallel factor analysis (PARAFAC) and partial least square (PLS) modelling were applied for the multivariate calibration of the spectrofluorimetric data. The orthogonal signal correction (OSC) was applied for preprocessing of data matrices and the prediction results of model, and the analysis results were statistically compared. The accuracy of the methods, evaluated by the root mean square error of prediction (RMSEP) for fenthion by OSC-PARAFAC and OSC-PLS models were 0.37 and 0.78, respectively. The proposed procedure could be successfully applied for the determination of fenthion in water samples.

DETERMINATION OF GLUCOSE OXIDASE ACTIVITY BY SPECTROPHOTOMETRIC METHOD

В статье рассматривается универсальная, чувствительная, быстрая и воспроизводимая методика определения активности глюкозооксидазы, основанная на окислении пероксидом водорода йодида калия в присутствии молибдата аммония и фотометрировании образующегося синего комплекса «йод-крахмал». Построен калибровочный график для определения концентрации пероксида водорода в реакционной смеси. Проведен анализ образования пероксида водорода в реакции окисления глюкозы глюкозооксидазой при варьировании начальной концентрации глюкозы. The article developed a universal, sensitive, fast and reproducible method for determining glucose oxidase activity, based on the oxidation of potassium iodide by hydrogen peroxide in the presence of ammonium molybdate and photometry of the resulting blue iodine-starch complex. A calibration graph is constructed to determine the concentration of hydrogen peroxide in the reaction mixture. Analysis of hydrogen peroxide formation in glucose oxidation reaction with glucose oxidase at variation of initial glucose concentration was performed.

State of collagenolysis in experimental periodontitis of bacterial-immune genesis and its correction with flavonol

The article presents an assessment of the dynamics of changes in the content of the marker of collagenolysis – free oxyproline in the homogeniate of soft tissues and bone in experimental bacterial-immune periodontitis and elucidation of the effect of flavonol quercetin on these indicators. The aim of this study was to determine the role of cytokinogenesis and the effect of flavonol on it in the pathogenesis, development and course of experimental periodontitis. During the experiment, a fragment of the mandible was taken from the animals, from which the soft tissues and bone were carefully separated. The state of collagen was determined by the content of free oxyproline in the soft and bone tissues. The concentration was determined according to the calibration graph and expressed in μmol/g. The results of studies of the indicators of the state of biopolymers of connective tissue structures of periodontium on the 7th, 14th and 30th day of experimental bacterial-immune periodontitis and after its correction with flavonol (from the 7th to the 14th day of the experiment) are presented. The data on the nature of changes in the content of collagen monomers in the process of formation of the inflammatory focus in the periodontal complex are given. During the acute phase of the inflammatory process in rats there was revealed a slight increase in blood free oxyproline in bone homogenate and homogenate of soft periodontal tissues, on the 14th day the dynamics continued to increase, at a later stage of the experiment, namely on the 30th day, increase in bone resorption continued as compared to the 7th and 14th day. During the correction of disorders resulted from the development of this pathological process there was a decrease in the level of free oxyproline in the bone homogenate and homogenate of soft tissues of mandibular periodontium, as compared to the same indicators of animals who did not receive quercetin on the 14th day. The use of flavonol quercetin, which, by affecting immune processes, limited the inflammatory response in periodontal tissues and stabilized collagenolysis processes in periodontal tissues was manifested by a decrease in free oxyproline in bone and soft tissue homogenates of experimental animals.

Determination of levofloxacin by HPLC with fluorescence detection in human breast milk

Aim: A new HPLC method with fluorescence detection has been developed and validated for the determination of levofloxacin, one of the fluoroquinolone class antibiotics, in breast milk. Materials & methods: Chromatographic separation was carried out on a reversed phase C18 column with acetonitrile and 10 mM o-phosphoric acid (25:75,v/v) mobile phase composition. Moxifloxacin was used as internal standard and the peaks were detected by fluorescence detection. Results & conclusion: Calibration graph was found linearly within the range of 2.5–500 ng/ml. Limit of detection and limit of quantification were found to be 0.63 and 2.11 ng/ml, respectively. Mean absolute recovery was 96.18%. The developed method has been successfully applied to the determination of levofloxacin in human breast milk taken from two healthy volunteers.