Effect Of Reagent Concentration Research Articles

SONOCHEMICAL SYNTHESIS OF SILVER NANOPARTICLES FOR GAS-DIFFUSION ELECTRODES APPLICATION

The aim of the current study is to explore the application of silver nanoparticles (AgNPs) as a catalyst in air gas-diffusion electrodes (AGDE). AgNPs have been successfully synthesized through an original sonochemical method. The effects of reagent concentrations, temperature and reaction time were studied as well. Composites of AgNPs and activated carbon (Norit NK) were prepared by using two adsorption methods to demonstrate the catalytic activity. Method 1 involves homogenizing preliminary prepared AgNPs colloid solution and Norit NK followed by evaporation of the suspension. One-step route was used for Method 2, i.e. all components were mixed altogether and sonicated, resulting in the AgNPs formation directly on the surface and inside the pores of Norit NK. Additionally,some of the samples were thermally treated at 300°C for 1h under air and argon. The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-Ray analysis (SEM/EDX) and transmission electron microscopy (TEM). The catalytic activity of the obtained composites regarding oxygen reduction reaction (ORR) was investigated in AGDE using an aqueous 4M NaCl electrolyte. The thermally treated composite obtained via Method 2 appears to show improved electrochemical catalytic activity regarding ORR in comparison to the Method 1 samples.

Spectrophotometric Determination of Atorvastatin Based on Charge Transfer Reaction with Quinalizarin

An easy and economical spectrophotometric method has been developed for the determination of atorvastatin from tablet formulation. This method is based on the formation of a blue-colored charge transfer complex of Atorvastatin with quinalizarin in methanol medium. The blue colored complex gives maximum absorbance at 573 nm. In order to develop the quantitative analysis method of atorvastatin, several parameters such as the type of solvent, the effect of reagent concentration, and the reaction time and temperature on absorbance of complex were investigated. It was determined that the optimum Quinz solution (0.5x10-³ M) was 3mL and the optimum temperature of the reaction was room temperature. Beer’s law range of proposed method is found 10-100 µg.mL-1. LOD and LOQ of the proposed method were found as 1.49 µg.mL-1 and 4.98 µg.mL-1, respectively. As a result, this proposed method can be used in the quantitative analysis of atorvastatin in tablet formulations

Characterisation of products from EDC-mediated PEG substitution of chitosan allows optimisation of reaction conditions

PEGylation is a common method use to modify the physiochemical properties and increase the solubility of chitosan (CHI). Knowledge of optimal reaction conditions for PEGylation of CHI underpins its ongoing use in nanomedicine. This study synthesised methoxy polyethyleneglycol grafted CHI (mPEG-CHI) using carbodiimide-mediated coupling. The effect of reagent concentrations and pH on the degree of substitution (DS) and the PEGylation yield (conversion of free PEG to conjugated PEG) was evaluated through detailed chemical characterisation. Within the parameter space investigated, optimised reaction conditions (NH2: COOH:NHS:EDC of 3.5:1:1:10, pH = 5) resulted in a DS of 24 % and a PEGylation yield of 84 %. An EDC-derived adduct formed at pH ≥ 5.5 and at a 15-fold excess of EDC relative to COOH. The adduct was evaluated to be a guanidine derivative formed by the reaction of the amine group of CHI directly with EDC. DS ≥ 12 % imparted water solubility to CHI at physiological pH and mPEG-CHI (0.2–1.0 mg/mL) was not cytotoxic against the breast cancer cell lines MCF-7 and MDA-MB-231, indicating its suitability for medical applications.

Spectrophotometric determination of Ciprofloxacin Hydrochloride, Moxifloxacin Hydrochloride and Roxithromycin Hydrochloride in Pure Form

A straightforward, sensitive, and quick spectrophotometric approach was created and validated for the detection of Ciprofloxacin hydrochloride, Moxifloxacin hydrochloride, and Roxithromycin hydrochloride in pure form. These techniques were based upon the fact that these antibiotics produced dark yellow ion pairs when combined with bromophenol blue. The binary complex in universal buffer solution of the optimum pH values was demonstrated at absorption maxima at 633 nm, 632 nm, and 633 nm for the three drugs, respectively, with bromophenol blue. Various parameters, such as the effect of time and the effect of reagent concentration, were optimized. Beer’s law plots were obeyed in the concentration ranges 2– 8 µg ml-1, 1– 4 µg ml-1, and 1– 6 µg ml-1, for the three drugs, respectively, with bromophenol blue. The detection limits were found to be 1.65, 0.83 and 0.79 μg mL-1, respectively, for Ciprofloxacin hydrochloride, Moxifloxacin hydrochloride, and Roxithromycin hydrochloride with bromophenol blue. The correlation coefficient value suggests that all three systems are linearly consistent.

On-line monitoring amplification of bromate in bottled ozonated water by flow injection analysis and spectrophotometry

A simple and sensitive online monitoring amplification method coupled with the flow injection spectrophotometric approach (OMAFIA) was used to determine bromate in ozonated bottled water samples. The method relies on the use of two mini-anion exchange columns to amplify bromate anions. The method involves the passage of a sample solution containing BrO3-through OH−- from a column to release an equivalent amount of OH−, which is then passed through a BrO3−form column, and then the released BrO3− is passed back through the first column. A suitable eluent is used to elute the collected amount of bromate anions after a specific amplification period, and the reaction between BrO3−chlorpromazine hydrochloride in an acidic medium produces an intense pink colour detected spectrophotometrically at 528 nm. The method optimized the conditions of an analyte, such as the effects of reagent concentration, bed volume, length of columns, and flow rate. Prior to injection, real samples underwent significant sample pretreatment by using OnGuard Ba/Ag/H cartridge. The concentration range, obeying Beer’s law, was 0.9–200 µg/L with a method limit of detection of 0.56 µg/L and a limit of quantification of 1.72 µg/L. The repeatability was satisfactory, with relative standard deviations of 3.27% and 1.24% for 10 and 100 µg/L, respectively, through 10 injections. The amplification method is exceptionally effective for ozonated bottled mineral waters containing bromate compared with ion chromatography as the standard method, which is below the standard level of 10 µg/L.

Graphical Application to Assist Students Understand the Basic Concepts in Acid–Base Titrations

During the 1960s, Edgar Dale published the concept that learners are likely to retain more information if they see and hear information rather than just listen. Therefore, many educational applications have been created for students to learn theoretical concepts through visuals and in an interactive manner. Microsoft (MS) Excel has been used in many of these applications due to ease of use and widespread applicability. The main objective of this research is to introduce an MS Excel application to study the theoretical concepts associated with acid–base titrations. This application allows the user to select the type of titration, Ka/Kb values where applicable, concentrations of the reagents, titration volume, commonly used indicators, and follow the variation in the titration curve. With the use of the application, students can clearly visualize the change in pH during the titration, buffer region, and the effect of reagent concentrations and Ka/Kb values on the titration curves. It further allows the user to determine the end point of the titration via a first derivative plot, observe the variation in fractional composition of the reactive species with pH, and identify the indicator best suited for the titration. The application was proven successful when used to teach the concepts of acid–base titrations to a group of high school students.

The Synthesis of Hydroxyapatite by Hydrothermal Process with Calcium Lactate Pentahydrate: The Effect of Reagent Concentrations, pH, Temperature, and Pressure.

Hydroxyapatite and other calcium phosphates in the form of whiskers are lately widely considered as fillers for biocomposites due to their special biological and reinforcing properties. Depending on the method of synthesis, apatite whiskers of various sizes and phase composition can be obtained. In our work, hydroxyapatite (HAp) whiskers were successfully prepared in reaction between calcium lactate pentahydrate and orthophosphoric acid. The advantage of the proposed technique is the simple but precise control of the HAp crystal morphology and high product purity which is necessary for biomedical applications. The effect of reagent concentrations, pH, reaction temperature, and pressure on HAp whiskers' morphology and composition was investigated. In the result, we obtained hydroxyapatite of different morphology such as whiskers, hexagonal rods, and nanorods. The products were characterized by SEM, XRD, and FTIR. In this work, the synthesis of HAp whiskers by direct decomposition of calcium lactate pentahydrate chelates under hydrothermal conditions was showed for the first time.

A Novel Chromogenic Scheme for the Determination of Cu(II) in Water Samples

In the present study, a novel chromogenic scheme for the determination of copper(II) using thiocyanate and variamine blue has been proposed. The proposed spectrophotometric method is based on the reaction of copper(II) with potassium thiocyanate which leads to the formation of thiocyanogen. The thiocyanogen formed subsequently oxidizes variamine blue to violet coloured dye cation which gives maximum absorbance at 550 nm. Beer’s law was obeyed in the concentration range 0.05-7.0 µg mL-1. The detection limit and quantification limit were found to be 7.8×10-3 μg mL-1 and 2.3×10-2 μg mL-1 respectively, for the coloured system. The molar absorptivity and Sandell’s sensitivity were found to be 6.646×103 L mol-1cm-1 and 9.5×10-3 μg cm-2, respectively. The effect of reagent concentration, pH, time, temperature on the color reaction were investigated and the required conditions for the method were optimized. The effect of various interfering species were also studied, and it was found that most of the ions did not interfere. The method is simple, rapid, cost-effective, comparably sensitive, highly selective, non-extractive, does not involve any tedious synthetic step and the recommended procedure has good accuracy and precision. The method was successfully applied for the determination of copper in different water sample and recovery percentage was found to be between 97.0 % to 99.4 % for different environmental matrices.

Superhydrophobic modification of nanocellulose based on an octadecylamine/dopamine system

We prepared super-hydrophobic nanocellulose films using a non-toxic octadecylamine/polydopamine system. Octadecylamine, a low surface energy material, was used to provide hydrophobic alkyl long chains. Polydopamine was produced by dopamine under alkaline conditions, creating an adhesive substance, which reinforced the hydrophobic long chains and increased the surface roughness of nanocellulose. The effects of reagent concentration, reaction temperature, and reaction time on hydrophobicity were then investigated. The results showed that with a 1:1 mass ratio of nanocellulose to octadecylamine, and reacting at 60 °C for 4 h, the contact angle of the obtained composite membrane reached 168.2°. Scanning electron microscope images revealed that the modified nanocellulose had a smaller particle size and more uniform distribution, which effectively improved the hydrophobicity of the nanocellulose. Thus, the green preparation of superhydrophobic films with high-temperature resistance and wear resistance was realized, which contributed to the high-value utilization of nanocellulose.

Deciphering the Kinetic Study of Sodium Dodecyl Sulfate on Ag Nanoparticle Synthesis Using Cassia siamea Flower Extract as a Reducing Agent.

Silver nanoparticles (Ag NPs) were synthesized using Cassia siamea flower petal extract (CSFE) as a reducing agent for the first time. In its presence and absence, the correlative effects of the anionic surface-active agent sodium dodecyl sulfate (SDS) were studied with respect to the development and texture of Ag NPs. Under different reagent compositions, the Ag NPs were inferred by localized surface plasmon resonance peaks between 419 and 455 nm. In the absence of SDS, there was a small eminence at 290 and around 350 nm, pointing toward the possibility of irregular polytope Ag NPs, which was confirmed in the transmission electron microscopy images. This elevation vanished beyond the cmc of [SDS], resulting in spherical and oval shaped Ag NPs. The effects of reagent concentrations were studied at 25 °C and around 7 and 9 pH in the absence and presence of SDS, respectively. Also, kinetic studies were performed by UV–visible spectrophotometry. Prodigious effects on shape and size were found under different synthesis conditions in terms of hexagonal, rod-, irregular-, and spherical shaped Ag NPs. Furthermore, the antimycotic activity of the synthesized Ag NPs was established on different Candida strains, and best results were found pertaining Candida tropicalis. The ensuing study impels the control of texture and dispersity for Ag NPs by CSFE and SDS, and the resultant polytope Ag NPs could be a future solution for drug-resistant pathogenic fungi.

Synthesis, Characterization and Theoretical Study of Azoimine and Using for Analysis of Palladium (II) Ion by Turbidimetric Method in Environmental Samples

Simple and rapid efficiency using the turbidity method acting for the pre-concentration and estimating of Pd (II) in environmental samples by using turbidity meter device detection. In the proposed approach, 2-(((2-(((E)-2-hydroxy-4-((E)-o-tolyldiazenyl)benzylidene)amino)benzyl)imino)methyl-5-(o-tolyldiazenyl) phenol] (A3) was synthesized and characterized by UV-visible, FT-IR, 1H-NMR and Mass spectra. Additionally, the structure of chemical compound (A3) was studied the Frontier Molecular Orbitals (FMOs) of (A3) were computed at the B3LYP/6-31G(d,p) level of theory, and the synthesized compound used as a complexing agent with as a surfactant (SDS). Parameters, which provided optimum reaction conditions, were studied such as the effect of order addition, the effect of reagent concentrations, the effect of surfactant concentration (SDS), the effect of pH solution, the effects of equilibrium measure temperature, and time. A linear calibration curve where the linearity range was found to lie between 0-60μg.L-1 with a correlation coefficient of 0.999, the limit of quantification (LOQ) 0.40μgL-1, and the detection limit (LOD) 0.12μg.L-1. Precision and accuracy of the method were found to be RSD 2.80% and the method was applied successfully to determine palladium ion concentration in various environmental samples, was found the recovery in the range 99.0-102.44%.

Effect of Reagent Concentrations on Equilibria in Water-Soluble Complexes

Effect of Reagent Concentrations on Equilibria in Water-Soluble Complexes

Automated syringe-pump-based flow-batch analysis for spectrophotometric determination of trace hexavalent chromium in water samples

In this work, we established an automated spectrophotometric method for determining hexavalent chromium in water samples using an integrated syringe pump-based environmental water analyzer (iSEA) based on the classic 1,5‑diphenylcarbazide chemistry. The device was computer-controlled with programs written by LabVIEW. The effects of reagent concentration, sample salinity and foreign ion interferences were investigated. Standard solutions (GBW(E)081584-1) were used to test the accuracy of the method. When equipped with a 5 cm Z-shaped flow cell, the detection limit was 0.024 μM with sample throughput of >30 h−1. In order to meet the requirements for trace Cr(VI) determination, the system was modified with a 2.5 m liquid waveguide capillary cell (internal diameter of 0.55 mm). The sample consumption was <2.1 mL. The detection limit was 0.54 nM with sample throughput of 20 h−1 and good linearity with R2 = 0.9985 (n = 110, obtained over 14 days). The two methods were successfully applied to determine Cr(VI) level in different water samples including tap water, river water, industrial wastewater and 37 brands of bottled water with spiked recovery in the range of 89.5%–117%.

High-frequency underway analysis of ammonium in coastal waters using an integrated syringe-pump-based environmental-water analyzer (iSEA)

Accurate methods and related robust analytical instruments for sensitive shipboard determination of ammonium in coastal waters are highly desirable for both oceanographers and environmental scientists. In this study, a multipurpose integrated syringe-pump-based environmental-water analyzer (iSEA) was combined with an on-line filtration system for underway analysis of ammonium in coastal areas. The chemistry is based on a modified indophenol method using o-phenylphenol. The effects of reagent concentrations and sample temperatures were evaluated. The detection limit was 0.15 μM with a 3-cm Z-flow cell, and the linearity was as high as 200 μM. The relative standard deviations at different concentrations (2, 10, and 20 μM) were 2.2%, 0.33%, 0.32% (n = 11). For n = 288 and without any stoppage during repeated analysis for 24 h, the relative standard deviation was 0.85%. The sample throughput was 12 h−1. The effects of salinity and five organic nitrogen compounds were evaluated and showed no interference using the proposed protocol for ammonium analysis. Between results obtained by reference and the present methods, there were no significant differences in the measurements of reference materials and different aqueous samples (n = 51). The analyzers worked well in the transect of 420 km during 7 cruises. A total of 716 analyses were performed automatically on board, demonstrating the capability of iSEA in automated real-time mapping of ammonium distribution in a shipboard laboratory.

Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer ( iSEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water.

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer ( iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using o-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h-1. Relative standard deviations at different concentrations (0-20 μM) were 0.23-3.36% ( n = 3-11) and 1.0% ( n = 144, in 24 h of continuous measurement, ∼5 μM). Calibration curves were linear ( R2 = 0.9998) over the range of 0-20 and 0-70 μM for the detection at 700 and 600 nm, respectively. The iSEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples ( n = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20-30 μL/run) and sample/standards (2.9 mL/run).

Synchrotron X-ray absorption of iron oxide (Fe2O3) nanoparticles: Effects of reagent concentration and sonication in co-precipitation synthesis

Synchrotron X-ray absorption spectroscopy was used to complement X-ray diffraction in the characterization of iron oxide nanoparticles synthesized by ultrasonic-assisted co-precipitation. We studied the effects of ultrasonication on the nanoparticle synthesis and used X-ray diffraction to show that impurity phases were present in samples synthesized without ultrasonication. The hematite phase was shown to be absent from our X-ray diffraction results, and X-ray absorption spectroscopy revealed a preference for the maghemite phase over magnetite. Our results showed that maghemite nanoparticles formed with larger crystallite sizes and lower structural distortion when higher reagent concentrations and longer sonication/reaction times were used. Moreover, the synthesis at low reagent concentration gave rise to materials with an amorphous maghemite phase.

Extraction and Separation Study of Mo(VI) and W(VI) Using Organophosphorous Extractant

Organophosphorous extractant, Cyanex-923, has been used for the extraction and separation of Mo(VI) and W(VI) is described. The extraction of the metal ions is studied as the function of several parameters such as effect of pH, effect of reagent concentration, stripping agents, diluents study and effect of diverse ion. It was observed that Cyanex-923 extracts Mo(VI) at pH 2.5-4.5 while W(VI) was extracted at pH 0.5-1.5. The extracted Mo(VI) was stripped back using 0.1M NaOH, while W(VI) was stripped back using 1.0 M (NH4)2CO3. The stoichiometry of the extracted species of Mo(VI) and W(VI) was determined on the basis of slope analysis method. Based on the results sequential methods of separation of both the metals were developed.

Extraction and Separation Study of Mo(VI) and W(VI) Using Organophosphorous Extractant

Organophosphorous extractant, Cyanex-923, has been used for the extraction and separation of Mo(VI) and W(VI) is described. The extraction of the metal ions is studied as the function of several parameters such as effect of pH, effect of reagent concentration, stripping agents, diluents study and effect of diverse ion. It was observed that Cyanex-923 extracts Mo(VI) at pH 2.5-4.5 while W(VI) was extracted at pH 0.5-1.5. The extracted Mo(VI) was stripped back using 0.1M NaOH, while W(VI) was stripped back using 1.0 M (NH4)2CO3. The stoichiometry of the extracted species of Mo(VI) and W(VI) was determined on the basis of slope analysis method. Based on the results sequential methods of separation of both the metals were developed.

Spectrophotometric Determination of Some Antibiotics Using Bromophenol Blue as Ion Pair Reagent

Objective: Simple and rapid methods have been developed for the determination of azithromycin, sparfloxacin and cephalexin monohydrate in bulk and pharmaceutical formulations. Method: These methods were based on the formation of bluish-green ion pair complexes of these antibiotics with bromophenol blue (BPB). Acetonitrile was used as a solvent for azithromycin and sparfloxacin whereas methanolacetonitrile medium for cephalexin monohydrate. Results: 2:1 complexes were formed between the drug and reagent almost instantaneously with absorption maxima 595 nm, 620 nm, 600 nm for the three drugs respectively. Different parameters such as effect of time, effect of reagent concentration were optimised. Under optimum conditions, calibration curves were found to be linear over the range of 0-50 μg mL-1 for azithromycin, 10-80 μg mL-1 for sparfloxacin and 10-170 μg mL-1 for cephalexin monohydrate respectively. The detection limits were found to be 0.10 μg mL-1, 0.21 μg mL-1 and 1.69 μg mL-1 with Sandell’s sensitivity 0.0559 μg cm-2, 0.1034 μg cm-2 and 1.3920 μg cm-2 respectively for the three drugs. Stability constant (log K) was found to be 6.19 ± 0.04, 5.00 ± 0.07 and 4.05 ± 0.05 showing high stability of the complexes. Molar absorptivity was found to be 1.369×104 L mol-1 cm-1, 3.774×103 L mol-1 cm-1 and 2.620×102 L mol-1 cm-1 with Gibb’s free energy change -2.725×103 kJ mol-1, -2.393×103 kJ mol-1 and -1.938×103 kJ mol-1. These methods were subjected to analytical quality control. Accuracy, precision, recovery and interference studies have been carried out. Conclusion: The proposed methods were successfully applied to the determination of these drugs in their pharmaceutical formulations and human urine samples.

Preparation and Characterization of Homopolymer Polyacrylonitrile-Based Fibrous Sorbents for Arsenic Removal

This research investigated the modification of homopolymer polyacrylonitrile (PAN) fibers for use as an adsorbent for removing arsenic from drinking water. Fibers were chemically modified and cross-linked using combinations of hydrazine hydrate and sodium hydroxide (NaOH) before being loaded with ferric hydroxide using two different iron loading procedures. Effects of reagent concentrations and reaction times on degree of chemical modification and fiber properties were investigated using Fourier transform infrared spectroscopy and ion-exchange measurements. Arsenate adsorption was a function of both the iron loading and the properties of the underlying fiber. For fibers treated with only a single reagent, both Fe3+ and arsenate adsorption could be understood in terms of ion-exchange properties of the fiber surfaces. However, for fibers treated with both hydrazine and NaOH, the ion-exchange properties of the surface could not explain the Fe3+ and arsenate adsorption behavior. The best arsenate removal performance was obtained using the simplest pretreatment procedure of soaking in 10% NaOH at 95°C for 90 min, followed by precipitation coating of ferric hydroxide. This simple preparation procedure involves only two commonly available and inexpensive reagents and can be carried out without any specialized equipment. This suggests that adsorbents based on inexpensive homopolymer PAN fabric may be produced in developing areas of the world where commercial products may not be available.