Spectrophotometric Measurements Research Articles

HPTLC AND FIRST DERIVATIVE UV-SPECTROPHOTOMETRIC METHODS FOR ESTIMATION OF VILAZODONE IN PHARMACEUTICALS

A new HPTLC method and a sensitive UV spectrophotometric method were established for estimating vilazodone hydrochloride in its pharmaceutical formulations. An environment-friendly chromatographic mobile phase consisting of ethyl acetate: toluene: formic acid (5:4:1, V/V/V) along with ultraviolet densitometric detection at 240 nm using pre-coated silica gel plates was used. First derivative UV spectrophotometric determinations were performed using methanol as solvent, and amplitudes were measured for quantification purposes. Validation studies were compliant with ICH guidance. Vilazodone shows an optimum Rf value of 0.73 ± 0.02 by HPTLC method. First derivative spectrophotometric measurements were done at 230 nm (peak) and 247 nm (valley), respectively. Best method linearity was observed in the range of 100 - 600 ng band-1 and 100 - 600 ng mL-1 for the chromatographic and spectrophotometric methods, respectively. Method detection limits were 61.4 ng band-1 and 36.03 ng mL-1, for chromatography and spectrophotometry, respectively. Higher % recovery (> 99 %) of vilazodone from the in-house formulation satisfied study intent as well as instituted selectivity of both the methods. Both the newly developed methods have the potential of application in routine quantification of vilazodone in pharmaceuticals.

Colorimetric Probe for Mn2+ Using a Mixture of an Anionic Dye and a Cationic Polyelectrolyte in an Aqueous Solution.

A novel colorimetric probe for Mn2+ was easily prepared by mixing negatively charged alizarin complexone (ALC) with positively charged poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PQ-2) in aqueous solutions at pH 6.0. Upon adding Mn2+ to ALC alone, the solution underwent no distinct color change, while the mixture displayed selective detection of Mn2+ over different physiological and environmentally significant metal ions by an efficient naked-eye color change from red to purple. The detection of Mn2+ by the mixture was achieved from the electrostatic interactions between ALC and PQ-2. The quantitative determination of Mn2+ was obtained by spectrophotometric measurement and naked-eye observation. This sensing strategy can be an attractive approach for the development of new colorimetric probes due to the advantages such as no organic synthesis, facile fabrication, and simple visual detection.

Solvent induced selective response to metal ions of three HNBO-based chemosensors

The 2-(2-hydroxy-3-naphthyl)-4-methylbenzoxazole (HNBO) fluorophore has been linked to three different amine scaffolds obtaining three fluorescent chemosensors (L1–L3). The ESIPT (excited-state intramolecular proton transfer) behavior was investigated in ACN and DMSO by UV–Vis spectrophotometric and spectrofluorimetric measurements, revealing the occurrence of an ESIPT process only in ACN, in the case of L1 and L2, and in both aprotic solvents, besides protic solvents (water and EtOH-water mixture), in the case of L3. The emission of L1–L3 is related to the deprotonated form of the ligand. The binding properties of L1–L3 towards Alkali, Alkaline-earth and some transition metal ions were investigated in different solvents by UV–Vis absorption, fluorescence emission and NMR spectroscopies. The fluorescence switches-ON in the presence of selected metal ions, always showing a mechanism different from ESIPT. All L1–L3 show a selectivity for Mg2+ in DMSO, while in ACN the selectivity of L1 and L2 shifts towards Zn2+ and Cd2+. L3 is also able to respond to Mg2+ in other aprotic solvents (THF and dioxane). L1 and L3 also showed the ability to signal the presence of metal ions on a paper support (L1: Zn2+; L3: Zn2+, Cd2+ and Mg2+). Therefore, L3 revealed able to signal the presence of Mg2+ both in solution, in different solvents, as well as on a paper support.

Evaluation of hydrocortisone as a strain-dependent growth-regulator of Porphyromonasgingivalis

ObjectivePorphyromonas gingivalis is an oral key pathogen and known to be very diverse in geno- and phenotypes. It is a fastidious bacterium with low O2-tolerance and 3–7 days of incubation are necessary. With growing interest in the field of microbial endocrinology we explored the potential growth-stimulating effect of hydrocortisone (HC, synonym cortisol) on P. gingivalis cultures. Material and methodsSix different P. gingivalis strains were pre-incubated in supplemented Brain-Heart-Infusion broth under appropriate conditions for 24 h, diluted and transferred into microplates. A newly developed and semi-automated spectrophotometric measurement in triplicate, applying a SpectraMax i3x microplate reader at an optical density of 600 nm, was conducted to test growth differences between test group (exposed to a supplement of either 1.25, 2.5, 5, 10, or 20 μg/ml of hydrocortisone) and control group over 48 h of anaerobic incubation (O2 ≤ 1%). Furthermore, strains were also incubated on HC-supplemented blood agar to test for a possible growth-stimulating effect on solid media. ResultsHC significantly stimulated the lag-phase growth of four out of six P. gingivalis strains. Our data suggest a concentration-dependent growth stimulatory effect of HC between 2.5 and 5 μg/ml, while below 1.25 μg/ml and above 10 μg/ml HC either did not stimulate or inhibited growth. ConclusionsHC could reduce the incubation time when isolating P. gingivalis from clinical samples and could boost low biomass cultivations especially during their lag-phase. The growth-modulating effect might be via modulation of virulence factors/quorum sensing gene expression or by reactive oxygen species(ROS)-capturing during early stages of bacterial growth. Further experiments are necessary to explain the mechanism behind our observations.

Optical Characterization of Gadolinium Fluoride Films Using Universal Dispersion Model

The optical characterization of gadolinium fluoride (GdF3) films is performed in a wide spectral range using heterogeneous data-processing methods (the ellipsometric and spectrophotometric measurements for five samples with thicknesses ranging from 20 to 600 nm are processed simultaneously). The main result of the characterization is the optical constants of GdF3 in the range from far infrared to vacuum ultraviolet, both in the form of a table and in the form of dispersion parameters of the universal dispersion model (UDM). Such reliable data in such a broad spectral range have not been published so far. The GdF3 films exhibit several defects related to the porous polycrystalline structure, namely, surface roughness and a refractive index profile, which complicate the optical characterization. The main complication arises from the volatile adsorbed components, which can partially fill the pores. The presented optical method is based on the application of the UDM for the description of the optical response of GdF3 films with partially filled pores. Using this dispersion model, it is possible to effectively separate the optical response of the host material from the response of the adsorbed components. Several recently published structural and dispersion models are used for optical characterization for the first time. For example, a model of inhomogeneous rough films based on Rayleigh–Rice theory or asymmetric peak approximation with a Voigt profile for the phonon spectra of polycrystalline materials.

Silver films on glass with very thin chromium adherence interlayers; reflectance and adherence at film-glass interface

Silver (Ag) thin films deposited on glass are proficient in their visible range reflectance at both Ag/air and Ag/glass interfaces. However, the film adherence onto glass is feeble due to a surface free energy disparity between the materials. Issues such as peeling, pitting, and detaching of Ag films on glass used as mirrors and prisms in various optical instruments are common. Very thin and intermittent adherence interlayers of chromium (Cr), titanium (Ti), etc, between Ag and glass resolves the issues to a substantial level. With least possible net surface area of the interlayer and a sufficient adherence of the film system the reflectance at the film/glass interface may be affected only insignificantly. This study presents an adherence optimization of Ag thin films on glass using very thin Cr interlayer with an attempt to retain its Ag/glass interface reflectance at useful levels. Adherence layers of Cr at various thicknesses from 0.4 nm to 5.0 nm and overlayer Ag films around 120 nm on silica glass were deposited by thermal evaporation in vacuum. Then the adherence and reflectance of the film system at the glass interface were evaluated using Scratch and Scotch Tape Tests and UV–visible spectrophotometric measurements. Amount and distribution of the intermittent adherence layers have been evaluated by energy dispersive X-ray photoelectron spectroscopy. 0.7 nm thick intermittent chromium interlayer between the pure silver film and the glass were found to be useful as resolving the adherence issues with a loss about 4–5% in reflectance.

The Human Mercaptopyruvate Sulfurtransferase TUM1 Is Involved in Moco Biosynthesis, Cytosolic tRNA Thiolation and Cellular Bioenergetics in Human Embryonic Kidney Cells.

Sulfur is an important element that is incorporated into many biomolecules in humans. The incorporation and transfer of sulfur into biomolecules is, however, facilitated by a series of different sulfurtransferases. Among these sulfurtransferases is the human mercaptopyruvate sulfurtransferase (MPST) also designated as tRNA thiouridine modification protein (TUM1). The role of the human TUM1 protein has been suggested in a wide range of physiological processes in the cell among which are but not limited to involvement in Molybdenum cofactor (Moco) biosynthesis, cytosolic tRNA thiolation and generation of H2S as signaling molecule both in mitochondria and the cytosol. Previous interaction studies showed that TUM1 interacts with the L-cysteine desulfurase NFS1 and the Molybdenum cofactor biosynthesis protein 3 (MOCS3). Here, we show the roles of TUM1 in human cells using CRISPR/Cas9 genetically modified Human Embryonic Kidney cells. Here, we show that TUM1 is involved in the sulfur transfer for Molybdenum cofactor synthesis and tRNA thiomodification by spectrophotometric measurement of the activity of sulfite oxidase and liquid chromatography quantification of the level of sulfur-modified tRNA. Further, we show that TUM1 has a role in hydrogen sulfide production and cellular bioenergetics.

Characterization of chemically treated waste wood fiber and its potential application in cementitious composites

In recent years, the utilization of various fibers in cementitious composites gained remarkable popularity worldwide. Unlike well-known fibers, this study focused on examining the incorporation of waste wood fiber (WWF) assorted from construction and demolition sites into the cementitious matrix. In the first stage of the study, alkali-treatment of the WWF was carried out with different concentrations of sodium hydroxide (NaOH) solution (i.e., 1.0 M, 2.0 M, 2.5 M, 5.0 M, 10.0 M) and treatment durations (i.e., 2 h, 4 h, 6 h, 12 h) to eliminate impurities and enhance fiber properties and fiber-matrix compatibility through surface treatment. To investigate alkali-treatment efficiency, microstructural analyses were conducted on the untreated and alkali-treated WWFs by Scanning Electron Microscopy and Fourier Transform Infrared Spectrophotometer measurements. Afterward, physical and mechanical performance assessments were conducted by water absorption test, compressive and four-point bending tests on the WWF-incorporated cementitious composites to monitor the compatibility behaviour of the WWF-matrix interface. Microstructural examinations showed that after the alkali treatment, impurities (i.e., painting, hemicellulose, lignin, etc.) on the WWF surface were successfully removed; however, higher alkali concentrations (beyond 5.0 M) and longer treatment duration (after 6 h) lead to deterioration, fragmentation, and a more heterogeneous structure due to the degradation of long cellulosic chains of WWF. Four-point bending test results showed that the flexural strength capacity of 2.5M-2 h-WWF-composite was 7.9 MPa, which was higher than untreated WWF-composite and plain mortar by 34.7% and 39.8%, respectively. Furthermore, the 2.5M-2 h treated WWF composite had the highest compressive strength of 46.3 MPa, which was higher than plain mortar, and the untreated WWF composite by 6.4% and 21.5%, respectively. The elimination of impurities such as painting, lignin, hemicellulose, and other inorganic compounds at the optimal alkali treatment concentration and time increases the WWF surface area and strengthens the fiber-matrix interface adhesion, resulting in a stronger matrix-WWF interface connection and an increase in load-carrying capability. The study's findings are believed to encourage the usage of alkali-treated WWF in cementitious matrix with improved mechanical performance and high waste upcycling.

Wide pH Range Potentiometric and Spectrophotometric Investigation into the Acidic Constants of Quercetin, Luteolin and l-Ascorbic Acid in Aqueous Media

It is now well established that the dissociation constants of an organic compound are characteristic of the types of groups, or the combinations of groups, contained in it. Furthermore, the acid–base dissociation constants are important parameters to fully understand the properties of a molecule in biological systems. In this framework, the aim of the present study was to determine the acidic constants of three natural molecules with well-known antioxidant properties, namely quercetin, luteolin and l-ascorbic acid. The evaluation was carried out in aqueous media (i.e., 0.16 M NaCl) at 37 °C in a wide pH range by using a combined approach based on potentiometric and spectrophotometric measurements. The results underline the necessity to employ both experimental techniques to obtain accurate values for acidic constants, preventing uncertainties related to undesirable oxidation reactions.

Effect of Annealing Time on Structural and Optical Properties of ZnGa2O4: Cr3+ (2.0mol %) Nanostructure Prepared by Sol Gel Method

ZnGa2 O4 : Cr3+ (2.0mol %) nanopowders annealed at annealing times (AT) of = 1, 2, 3, and 4H (hour) were synthesized by the sol-gel method. X-ray diffraction (XRD) results confirmed that the prepared ZnGa2 O4 : Cr3+ samples were cubic structures. In this study we showed that the annealing time has no pronounced influence on the ZnGa2O4: Cr3+ crystallite size at annealing times in the range of 1H to 3H. A significant change in the crystallite size was observed for the sample annealed for a relatively long time (4H). Scanning electron microscopy (SEM) images show the morphology of the prepared nanopowders influenced by annealing time. UV-visible spectrophotometer measurements showed that the energy gap of the prepared nanoparticles could be tuned from 4.50 to 4.12 eV as the annealing time changed from 1H to 4H. Photoluminescence (PL) measurement showed that the annealing time increased, and the PL intensity also increased reaching the maximum value for the sample annealed at AT=3H. Energy dispersive X-ray spectroscopy (EDS) measurements confirmed the presence of Zn, Ga, O and Cr ions.

KSEMAW: an open source software for the analysis of spectrophotometric, ellipsometric and photothermal deflection spectroscopy measurements.

The optical behavior of devices based on thin films is determined by complex refractive index and thickness of each slab composing the stack; these important parameters are usually evaluated from photometric and/or ellipsometric spectral measurements, given a model of the stack, by means of dedicated software. In the case of complex multilayer devices, generally a number of simpler specimens (like single-film on substrate) must be preliminarily characterized. This paper introduces the reader to a new open source software for thin film characterization finally released after about 30 years of development. The software has already been used in various fields of physics, such as thin film optical filters, architectural glazing, detectors for high energy physics, solar energy, and, last but not least, photovoltaic devices. Code source files, MS Windows executable, user manual as well as a sample of working directories populated with assorted files can be freely downloaded from the kSEMAW GitHub repository.

Evaluating The Role of Nila (indigo) Dye in Protection of Egyptian Linen Textiles from the Deterioration Factors

The indigo dyed linen textiles are one of the most popular textiles in most of historical periods in the Egyptian civilization. This study aims to investigate the role of indigo dye in preventing, reducing or inhibiting the deterioration of ancient Egyptian linen textiles. In this study linen textiles were experimentally dyed by indigo dye. Undyed and dyed linen were artificially aged by light, heat, soil and fungi. The change in the physical and chemical properties of the undyed and indigo-dyed linen textiles after being artificially aged were determined by various methods such as tensile strength and elongation, the crystallinity index (CrI) by using X-ray diffraction, the surface morphology by using Scanning Electron Microscope (SEM) and spectrophotometric measurements of the colour were calculated. The results confirm that indigo dye inhibits and reduces the deterioration of linen textiles. These results confirm that indigo dyed linen textiles are more durable than undyed ones. They may explain why archaeologists discover dyed linen textiles in better condition than undyed ones. Also, they explain why the Museums in Egypt have dyed linen textiles in better quality than undyed ones.

Evaluating The Role of Nila (indigo) Dye in Protection of Egyptian Linen Textiles from the Deterioration Factors

The indigo dyed linen textiles are one of the most popular textiles in most of historical periods in the Egyptian civilization. This study aims to investigate the role of indigo dye in preventing, reducing or inhibiting the deterioration of ancient Egyptian linen textiles. In this study linen textiles were experimentally dyed by indigo dye. Undyed and dyed linen were artificially aged by light, heat, soil and fungi. The change in the physical and chemical properties of the undyed and indigo-dyed linen textiles after being artificially aged were determined by various methods such as tensile strength and elongation, the crystallinity index (CrI) by using X-ray diffraction, the surface morphology by using Scanning Electron Microscope (SEM) and spectrophotometric measurements of the colour were calculated. The results confirm that indigo dye inhibits and reduces the deterioration of linen textiles. These results confirm that indigo dyed linen textiles are more durable than undyed ones. They may explain why archaeologists discover dyed linen textiles in better condition than undyed ones. Also, they explain why the Museums in Egypt have dyed linen textiles in better quality than undyed ones.

Modification of phycocyanin extraction from dry biomass of Spirulina by using ozone water

Phycocyanin is a water-soluble blue-green pigment from cyanobacteria such as Arthospira plantesis, widely known as Spirulina. The pigment is widely applied as a natural food colorant or consumed as a supplement due to its antioxidant activity. This study aimed to investigate the potential use of ozone water as an extraction solvent of phycocyanin from dry mass Spirulina. The yield, purity, and antioxidant capacity parameter measured the effectivity of ozone water as an extraction solvent. The phycocyanin was extracted by the cold maceration process preceded by the dissolving of the dry mass Spirulina in ozone water by the ratio 1:100. For the control, the dry mass Spirulina was dissolved in mineral water. The method was followed by centrifugation and spectrophotometer measurement. To check the antioxidant capacity, we measure the phycocyanin inhibition rate to DPPH. The data showed that using ozone water as an extraction solvent successfully resulted in a higher yield and purity of phycocyanin than the control. Besides, there is no negative effect on antioxidant capacity affected by ozone water. Therefore, ozone water is a potential solvent to enhance the extraction of phycocyanin from dry mass Spirulina.

A novel method for Ion Exchange Capacity characterization applied to Anion Exchange Membranes for Water Electrolysers

Hydrogen production from water electrolysis, hydrogen fuel cells and redox flow batteries are the right approach for the renewable energy sector because the electricity generated by solar, wind, photovoltaic, hydroelectric can be managed with a carbon-free approach. These technologies all have in common one fundamental component: the membrane. Different types of membranes have been developed for both cationic and anionic exchange, and recently, research activity focalized on improving their performances is very fervent. One fundamental characteristic of a membrane is its Ion Exchange Capacity (IEC), i.e. the density of charged functionalizing groups. Within our research project NEMESI, funded by EU-PNRR (ID: RSH2B_000002), and dedicated to Anion Exchange Membrane Water Electrolysis, we studied and validated a novel alternative method to measure IEC. The present titration methods have limitations for the need of dedicated hardware or qualitative inspection of their color-turning endpoint. The proposed method, based on the redox titration of potassium ferricyanide with ascorbic acid, allows a quantitative and independent assessment based on both potentiometric and spectrophotometric measurements, along with the usually adopted visual observation, as the yellow-colored ferricyanide is reduced to colorless ferrocyanide. Moreover, if compared to the classical Mohr titration with silver nitrate, the new method can be carried out at variable ferricyanide concentrations during the addition of the ascorbic acid, so a complete curve of the redox reaction can be constructed: the initial ferricyanide ion load of the membrane (IEC) can thus be derived in a more precise way than with a single-point evaluation. Only one Ag/AgCl reference electrode and a platinum working electrode are required without any power supply/potentiostat. The proposed method was validated using Anion Exchange Membranes with known IEC.

LOW-COST AND EASY ACCESS MATERIALS FOR A LABORATORY CLASS: A PROPOSAL OF LIQUID CHROMATOGRAPHY FOR FOOD COLORING SEPARATION AS AN EXPERIENCE OF MEANINGFUL LEARNING

The experimental activities for undergraduate chemistry students play an important role to develop skills and expertise in that science thus, the practice-experimental classes are so important to achieve this purpose. This work deals with a demonstrative experience for dye separation from food coloring sample using liquid column chromatography. Beyond the experimental practice and the facility in visualizing the separation, this demonstration shows how a simple experiment involving alternative and easy access materials can promote a meaningful learning once it is possible to handle the acquired data, trace and analyze the results themselves, thus developing skills rather than the operational procedure. This proposal could be implemented in initial chemistry classes in Brazilian universities. Sea and river sands were used as stationary phases and aqueous ethanolic solutions were used as mobile phases. A food coloring (a mixture of 3 dyes) was chosen as sample to be studied. Chromatographic separation was followed by spectrophotometric measurements. A set of analyses were carried out to discuss the solubility of the food coloring, granulometric studies of the stationary phases used and electronic microscopy images of the sands studied here. As alternative materials were used in this work, a chromatographic column was also constructed with low-cost materials.

Salivary Oxidative Stress Biomarkers in Thai Adolescents and Young Adults with Type 1 Diabetes Mellitus: A Cross-Sectional Study.

The primary objectives of this study were to compare salivary oxidative stress (OS) biomarker levels in patients with type 1 diabetes mellitus (T1DM) and without T1DM (non-T1DM) and evaluate the relationships between diabetes, periodontal status, and OS biomarker levels. Twenty patients with T1DM and 20 age-matched patients without T1DM were enrolled. All participants were 15-23 years of age and had permanent dentition. Unstimulated whole saliva was collected in a sterile test tube before examination of clinical periodontal parameters, including bleeding on probing (BOP). Salivary levels of OS biomarkers-malondialdehyde, protein carbonyl, total oxidant status (TOS), and total antioxidant capacity-were determined using oxidative and antioxidative assays followed by spectrophotometric measurement at 375-532 nm. The relationships between diabetes, periodontal status, and OS biomarkers were analyzed using multiple linear regression. TOS was significantly lower in the T1DM group compared with the non-T1DM group (5.06 ± 0.39 vs. 6.44 ± 0.51 µmol H2O2 Eq/l, P = 0.035). After adjusting for confounding factors (age, gender, BMI, clinical periodontal parameters, BOP, or diabetes status accordingly), the multiple linear regression showed that T1DM was significantly associated with a reduction of TOS level (P = 0.008). The BOP > 30% group showed a significant correlation with increased TOS levels compared with the BOP ≤ 30% group (P = 0.002). No relationship was found between OS biomarkers and HbA1c levels. Salivary TOS levels were related to both diabetes status and the extent of gingival inflammation. Further studies to elucidate the role of OS in relation of periodontal disease and T1DM are required.

Spectrophotometric quantification of paracetamol and tramadol hydrochloride by chemometric calibration methods.

The results of UV spectrophotometric analysis were analysed using partial least squares (PLS) and principal component regression (PCR) techniques to allow simultaneous evaluation of tramadol hydrochloride (TRA) and p-acetaminophen (PAR) in tablets. A calibration set of 16 mixtures, each containing PAR and TRA in various amounts, was created using a 24-full fractional design. The absorbance data set for the calibration set were obtained between 215-280 nm (Δλ = 0.1 nm). Subsequently, the concentration and absorbance sets were used to generate PCR and PLS calibrations. The ratio spectra- first derivative method was devised as a solution to the same problem to compare the outcomes of the chemometric methods used for the same experiment. After the proposed methods were shown to be accurate in the testing of validation samples, they were used in analysing commercial tablet samples. The analytical results showed that PCR and PLS methods can be used as alternative methods to high-performance liquid chromatography (HPLC). Correlation coefficients were determined for the working concentration range of 6-36 g.mL-1 for PAR and 4-22 g.mL-1 for TRA. The limits of detection and quantification were calculated as 0.9104 μg.mL-1 and 3.0347 μg.mL-1, respectively. The test results of the chemometric analyses and ratio spectra- first derivative method of the commercial tablet form are in agreement with the results of the one-way ANOVA with a confidence interval of 95%. This study shows that the ratio spectra- first derivative method, PCR and PLS models based on spectrophotometric measurements are very useful and straightforward techniques for the quantitative resolution of a two-component pharmaceutical preparation, requiring little sample preparation and little time for analysis.

A comparative analysis of ten milk samples with differential scanning calorimetry and Fourier transform infrared spectroscopy

Milk proteins occupy a prominent place in the nutrition of adults and children. Generally, some commercial dairy contains proteins, lactose, other sugar derivatives, and additives. The proportions of the components that make up the milk are different in commercial milk. For this reason, analyzing milk correctly is essential for determining these contents. In this research, analyses of the milk were made by taking differential scanning calorimetry measurements (DSC), and Fourier transform infrared spectrophotometer (FTIR) measurements. Specific heat values and specific values of temperature peaks were examined for ten kinds of milk. DSC curves revealed triacylglycerol dissolution, lactose crystallization, and protein denaturation peaks. Wide variations were observed with the same fat content from 10 milk powders. Most characteristic peaks were not observed when the samples were re-measured after a year at -20°C. The powder samples were compared in terms of protein, fat, lactose content, whey protein casein, and caseinate contents according to differences in FTIR spectra. The FTIR results confirm the DSC curves for most of the analyzed milk types.

Analysis of Some Phenothiazine Drugs and Their S-Oxides using Enzymatic Method of Cholinesterase Inhibition

In this work, a highly sensitive spectrophotometric method was developed for the determination of cholinesterase (AChE) inhibitors - phenothiazine derivatives (PhTs). The assay involves spectrophotometric measurement of a mixture of buffer, solutions of acetylcholine (Ach), a sample containing AChE, H2O2, and PhTs. The rate of the enzymatic hydrolysis of Ach reaction was determined by the tangent method of the linear part of the kinetic curve in the A (358 nm) – t-coordinate. Results from the determination of PhTs and S-oxide PhTs with the AChE regulated spectrophotometric system showed the limit of quantitation of 5 ng/mL (IE20) and a linear dynamic range from 5 to 30 ng/mL for Chlorpromazine, Promethazine and from 0.5 to 10 ng/mL for Chlorpromazine S-oxide, from 1 to 10 ng/mL for Promethazine S-oxide, 12 to 40 ng/mL for Thioridazine 2,5-disulfoxide respectively. RSD for concentrations of PhTs as low as 1.5·10-8 mol/L did not exceed 6.7 %, while their corresponding sulfoxides at 1.50·10-9 didn’t exceed +6.5 %. δ < +3.8 %. Findings in this work demonstrate that this method may be used for the determination of phenothiazine based drugs, and sensitive tests for rapid PhT monitoring without the addition of other exogenous catalysts