A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3 mm × 5 mm) is immobilized on a wafer polyimide microchip (size 13.5 mm × 3.5 mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1 ± 0.1 mV decade⁻¹ over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, the lower detection limit is 0.05 μg mL⁻¹, the working pH is 2-9,and the output is 70-90 samples h⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.     

Comparison of a single-use pH test strip and a glass electrode for potentiometric titration

The potentiometric titration of a carbonate mixture or an acetate solution is a common experiment in analytical laboratories. Typically, a glass electrode combined with a calomel or Ag/AgCl reference electrode is used to locate the equivalence points in neutralization titrations. The dissociation constants of weak acids and bases can be calculated from the pH at the half-neutralization point. Recently, a new commercial product for measuring pH has been developed. This novel acid–base detection strip is a single-use sensor that requires neither storage in a preservation liquid nor calibration prior to use. This study examined its suitability for the continuous monitoring of pH changes in potentiometric titrations of carbonate mixtures, acetate solutions, or ammonia solutions. There were no significant differences in the concentrations of solutions tested using a glass electrode and a pH test strip. The pK_a, pK_b, and pH values determined using the two systems differed by less than 5%. The results confirmed that the pH strips are suitable for continuously monitoring pH changes during neutralization titrations. However, the strips can only be used once.     

H-point standard addition method for simultaneous determination of phenylephrine hydrochloride,chlorpheniramine maleate,and paracetamol as a ternary mixture in pharmaceutical formulations

The simultaneous analysis of a ternary mixture containing paracetamol (PAR), phenylephrine hydrochloride (PHE), and chlorpheniramine maleate (CPM) was conducted without prior separation and using an advanced spectrophotometric method. The H-point standard addition and absorbance correction methods were selected to determine the compounds, which are highly overlapped spectra in pharmaceutical formulations. The method is based on the use of three different wavelengths of 296, 272, and 227 nm for the ternary mixture. The concentration of PAR was calculated directly at 296 nm because no interferences existed. Absorbance correction method was used to remove the role of PAR at 272 and 227 nm. The concentrations of the PHE and CPM compounds in the mixture were determined by using the H-point standard addition method. The results showed that simultaneous determination of PAR, PHE, and CPM could be conducted within the range of 1–33 μg/mL, 1–23 μg/mL, and 1–36 μg/mL, respectively. The relative standard deviations for the simultaneous determination of PHE, CPM, and PAR were 0.617, 2.76, and 1.71, respectively. The proposed method was implemented successfully for the simultaneous determination of PAR, PHE, and CPM in pharmaceutical formulations.     

A new non-invasive, quantitative Raman technique for the determination of an active ingredient in pharmaceutical liquids by direct measurement through a plastic bottle

The concentration of an active pharmaceutical ingredient (povidone) in a commercial eyewash solution has been measured directly through a plastic (low-density polyethylene: LDPE) container using a wide area illumination (WAI) Raman scheme. The WAI scheme allows excitation using a 6 mm laser spot (focal length: 248 mm) that is designed to cover a wide sample area. As a result, it has the potential to improve the reliability Raman measurements by significantly enhancing representative sample interrogation, thus improving the reproducibility of sampling. It also decreases the sensitivity of sample placement with regard to the excitation focal plane. Simultaneously, isobutyric anhydride was placed in front of the bottles to use for a synchronous external standard configuration. This helps to correct the problematic variation of Raman intensity from the inherent fluctuation in laser power. Using the WAI Raman scheme combined with the synchronous standard method, the povidone concentration was successfully measured with spectral collection that was performed through a plastic barrier. The conventional Raman scheme was difficult to employ for the same purpose because of the degraded spectral reproducibility resulting from the smaller laser illumination area and the sensitivity of such an approach to the position of the sample bottle. The result from this study suggests that the WAI scheme exhibits a strong potential for the non-destructive quantitative analysis of pharmaceuticals measured directly in plastic containers. Preliminary work also shows that similar measurements can also be made in glass bottles. If implemented, this technique could be utilized as a simple and rugged method for quality assurance of final products in a manner consistent with Process analytical technology (PAT) requirements.     

Multisyringe flow injection analysis hyphenated with liquid core waveguides for the development of cleaner spectroscopic analytical methods: improved determination of chloride in waters

In this work, the hyphenation of the multisyringe flow injection analysis technique with a 100-cm-long pathlength liquid core waveguide has been accomplished. The Cl⁻/Hg(SCN)₂/Fe³⁺ reaction system for the spectrophotometric determination of chloride (Cl⁻) in waters was used as chemical model. As a result, this classic analytical methodology has been improved, minimizing dramatically the consumption of reagents, in particular, that of the highly biotoxic chemical Hg(SCN)₂. The proposed method features a linear dynamic range composed of two steps between (1) 0.2–2 and (2) 2–8 mg Cl⁻ L⁻¹, thus extended applicability due to on-line sample dilution (up to 400 mg Cl⁻ L⁻¹). It also presents improved limits of detection and quantification of 0.06 and 0.20 mg Cl⁻ L⁻¹, respectively. The coefficient of variation and the injection throughput were 1.3% (n = 10, 2 mg Cl⁻ L⁻¹) and 21 h⁻¹. Furthermore, a very low consumption of reagents per Cl⁻ determination of 0.2 μg Hg(II) and 28 μg Fe³⁺ has been achieved. The method was successfully applied to the determination of Cl⁻ in different types of water samples. Finally, the proposed system is critically compared from a green analytical chemistry point of view against other flow systems for the same purpose.     

Potassium permanganate-glyoxal chemiluminescence system for flow injection analysis of cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium in pharmaceutical preparations

A sensitive flow injection chemiluminescence (FL-CL) method for the determination of cephalosporin antibiotics, was developed. The method was based on that cephalosporin antibiotics could enhance the CL reaction of glyoxal and KMnO₄ in sulfuric acid. Method development included the optimization of reagent concentrations and flow-rate. Under the optimized conditions, three cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium, were determined. The detection limits of the method are 10 ng ml⁻¹ cefalexin, 2 ng ml⁻¹ cefadroxil, and 2 ng ml⁻¹ cefazolin sodium. The method was successfully applied to the determination of three cephalosporin antibiotics in pharmaceutical preparations.     

Water-acetic acid mediated an efficient and eco-friendly protocol for the one-pot synthesis of bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones under mild reaction conditions

A cost-effective and eco-friendly straightforward synthesis of new bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones is successfully achieved via one-pot three-component reaction of N-isoxazolyl enaminone, aryl glyoxal monohydrates and 4-amino-3-methyl-5-styrylisoxazoles by using water as a reaction medium and acetic acid (AcOH) as cheap and green promoter. The protocol proves to be an efficient and environmentally benign in terms of high yields, low reaction time, operational simplicity, metal-free and wide substrates scope. Most important of all, this reaction process is green.     

A simple and green analytical method for determination of iron based on micro flow analysis

A simple, inexpensive and reagent-less colorimetric micro flow analysis (μFA) system was implemented in a polymethyl methacrylate (PMMA) micro fluidic manifold. A T-shaped micro channel on a PMMA chip was fabricated by laser ablation and topped with molded polydimethylsiloxane (PDMS). The fabricated μFA system was integrated with the optical components as detector and applied to the determination of iron in water samples. It is based on the measurement of Fe(III)-nitroso-R salt complex at 720 nm formed by the reaction between Fe(III) and nitroso-R salt in an acetate buffer solution pH 5. The proposed μFA consumed very small amount of reagent and sample, it released waste of less than 2.0 mL h⁻¹. The relative standard deviation (R.S.D.) was less than 2% (n = 11) with the recovery of 98.7 ± 0.12 (n = 5). The linear range for the determination of iron in water samples was over the range of 0.05-4.0 μg mL⁻¹ with a correlation coefficient (r²) of 0.9994. The limit of detection (3σ) and limit of quantitation (10σ) were 0.021 μg mL⁻¹ and 0.081 μg mL⁻¹, respectively with a sample throughput of 40 h⁻¹.     

Heterogenization of a molybdenum Schiff base complex as a magnetic nanocatalyst: An eco-friendly,efficient, selective and recyclable nanocatalyst for the oxidation of alkenes

A Schiff base ligand derived from 5-bromo-2-hydroxybenzaldehyde and 2,2′-dimethylpropylenediamine (H₂L) and its corresponding dioxomolybdenum(VI) complex (Mo(O)₂L) has been synthesized and characterized by spectroscopic methods. The adsorption of Mo(O)₂L on the surface of silica-coated magnetite nanoparticles via hydrogen bonding led to the formation of (α-Fe₂O₃)–MCM-41–Mo(O)₂L as a heterogeneous catalyst. FT-IR and atomic absorption spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize and investigate the new nanocatalyst. A practical catalytic method for the efficient and highly selective oxidation of a wide range of olefins with hydrogen peroxide and tert-butyl hydroperoxide in ethanol over the prepared molybdenum nanocatalyst was investigated. Under reflux conditions, the oxidation of cyclooctene with tert-butyl hydroperoxide or hydrogen peroxide led to the formation of epoxide as the sole product. The catalyst was reused at least six times without a significant decrease in catalytic activity or selectivity, and without detectable leaching of the catalyst.     

Mechanoenzymatic resolution of racemic chiral amines,a green technique for the synthesis of pharmaceutical building blocks

Very recently, several successful biocatalytic processes using mechanical activation to carry out enantioselective reactions have been reported. The present work describes the use of Candida antarctica Lipase B (CALB) in the kinetic resolution of racemic chiral amines by means of High-Speed Ball Milling (HSBM), minimizing the use of solvent and reducing reaction times. This approach provides an efficient and easily scalable strategy that was used for the green synthesis of enantiopure Rasagiline, as an illustrative example.     

Application of a new method for data analysis of isothermal titration calorimetry in the interaction between human serum albumin and Ni

The interaction of human serum albumin (HAS) with divalent nickel ion was studied by isothermal titration calorimetry (ITC) in 30 mM Tris buffer, pH 7.0. There is a set of eight identical and independent binding sites for nickel ions on the protein at the temperature of 300 K. A new calorimetric data analysis allows the determination of the complete set of thermodynamic parameters. The binding isotherm for nickel-HSA interaction is easily obtained by carrying out two different ITC experiments. In the first experiment, the enthalpy of binding for one mole of nickel ion to one mole of binding site on HSA (ΔH=−36.5 kJ) is obtained, and is used in a second experiment to determine the binding isotherm and to find the number of binding sites (g=8) and the equilibrium constant (K=0.57 μM⁻¹).     

New,simple and validated kinetics spectrophotometric method for determination of moxifloxacine in its pharmaceutical formulations

The objective of this research was to develop a kinetic spectrophotometric method for determination of moxifloxacine (MOXF) in pure form and pharmaceutical formulations. The method was based on the formation of a colored N-vinyl chlorobenzoquinone derivative of MOXF by its reaction with 2,3,5,6-tetrachloro-1,4-benzoquinone in presence of acetaldehyde.The formation of the colored product was monitored spectrophotometrically by measuring the absorbance at 652 nm. Factors affecting the reaction were studied and optimized. The stoichiometry of the reaction was determined, and the reaction pathway was postulated. The activation energy of the reaction was calculated and found to be 6.65 kJ mol^?1. Under the optimized conditions, the initial rate and fixed time (at 5 min) methods were utilized for constructing the calibration graphs. The graphs were linear in concentration ranges 5–100 and 15–150 μg ml^?1 with limit of detection of 2.0 and 5.0 μg ml^?1 for the initial rate and fixed time methods, respectively. The analytical performance for both methods was fully validated, and the results were satisfactory. No interference was observed from the excipients that are commonly present in the pharmaceutical formulations. The proposed method was successfully applied to the determination of MOXF in its pharmaceutical formulations. The label claim percentages were 101.25 ± 0.73% and 100.92 ± 0.65% for the initial rate and fixed time method, respectively. Statistical comparison of the results with those obtained by a reference spectrophotometric method showed excellent agreement between the accuracy and precision of the two methods. The proposed method has great value in its application to the analysis of MOXF in quality control laboratories.     

Development and validation of a capillary electrophoresis method with ultraviolet detection for the determination of the related substances in a pharmaceutical compound

A capillary electrophoresis (CE) method was successfully developed to quantify the impurity profile of a new substance of pharmacological interest: LAS 35917. CE method was developed in order to separate the chloromethylated, monomethylated and hydroxylated impurities (molecules with very similar chemical structures) having the three coelution in the reversed-phase LC method initially established. Taking into account the structure of the impurities of LAS 35917, separation by conventional liquid chromatography (LC) methods would be longer and tedious than separation by CE, which is an appropriate and versatile technique giving easier and quicker methods. Among the three potential impurities mentioned of LAS 35917, two are due to the synthesis route of this drug, and the third arises from degradation. These drug-related impurities were separated using a capillary of 56 cm of effective length and 50 microm I.D., a 60 mM tetraborate buffer, at pH 9.2, and a positive voltage of 20 kV. The optimised CE method was preliminary validated with regard to specificity, linearity, limits of detection and quantitation, repeatability and solution stability. The method allows the detection and quantitation of impurities above 0.04 and 0.08% level, respectively. All three related substances were separated, detected and quantified from their parent drug in the analysis of real samples of LAS 35917, stressed or not stressed, with this simple and fast CE method.     

Validation of HPLC stability-indicating method for Vitamin C in semisolid pharmaceutical/cosmetic preparations with glutathione and sodium metabisulfite, as antioxidants

HPLC stability-indicating method was validated for Vitamin C (ascorbic acid) in semisolid pharmaceutical/cosmetic formulations containing glutathione and sodium metabisulfite, as antioxidants. The described procedure included a reliable, precise, accurate and specific method determination employing a 250 mm × 4.6 mm C₁₈ column, 0.2% metaphosphoric acid/methanol/acetonitrile (90:8:2, v/v/v) as the mobile phase and detection at 254 nm. Nicotinic and ascorbic acids were employed as standards, both presenting purity of 99.0%. Linearity was established for the ascorbic acid concentrations ranging form 1.0 to 12 μg mL⁻¹, accuracy/recovery percentage was 95.46-101.54%, precision values were 0.38 (intra-day) and 1.22% (inter-days), and LOD and LOQ were found to be 0.05 and 0.17 μg mL⁻¹, respectively. The working mobile phase elevated the ascorbic acid retention time to ≈3.5 min at a flow rate of 1.0 mL min⁻¹ and provided resolution of the active from the nicotinic acid (internal standard), degradation product (oxalic acid) and other excipients from the pharmaceutical/cosmetic preparations.     

Development of a single-run liquid chromatography-mass spectrometry analysis for the detection of 11 multiclass contaminants of emerging concern using a direct filtration method

In toxicological analysis, the analytical validation method is important to assess the exact risk of contaminants of emerging concern in the environment. Syringe filters are mainly used to remove impurities from sample solutions. However, the loss of analyte to the syringe filter could be considerable, causing an underestimate of the analyte concentrations. The current study develops and validates simultaneous liquid chromatography-mass spectrometry analysis using a direct filtration method to detect four groups of contaminants of emerging concern. The adsorption of the analyte onto three different matrices and six types of syringe filters is reported. The lowest adsorption of analytes was observed in methanol (16.72%), followed by deionized water (48.19%) and filtered surface lake water (48.94%). Irrespective of the type of the matrices, the lowest average adsorption by the syringe filter was observed in the 0.45 μm polypropylene membrane (15.15%), followed by the 0.20 μm polypropylene membrane (16.10%), the 0.20 μm regenerated cellulose (16.15%), the 0.20 μm polytetrafluoroethylene membrane (47.38%), the 0.45 μm nylon membrane (64.87%) and the 0.20 μm nylon membrane (71.30%). In conclusion, the recommended syringe filter membranes for contaminants of emerging concern analysis are polypropylene membranes and regenerated cellulose, regardless of the matrix used.     

Direct analysis of bottom sediments by a microcoulometric titration method for determination of total organic halide pollutants

Up to now the content of the organic halides in sediments was measured as extractable organic halides compounds by different methods including microcoulometric titration one. We describe a procedure for microcoulometric determination of total organic halide pollutants by using a direct combustion of the sediments into the microcoulometric system furnace. An accelerated removal of the inorganic chlorides by reaction with potassium nitrate using ultrasonic radiation was attained. The procedure was validated for analysis of bottom sediments from natural and anthropogenic sources. The repeatability RSD = 8.5%, the expanded relative uncertainty U (n = 7, P = 95%, k = 2) = 6.4%, the reproducibility RSD was within the range 10.0–7.3%, the average recovery R = 97.6% and method LOD = 11 mg kg⁻¹ Cl. Correspondence: Zara V. Aneva, Analytical Department, University “Prof. Dr. Assen Zlatarov”, Nr. 1 Prof. Yakimov street, 8010 Bourgas, Bulgaria     

Basic principles,recent trends and future directions of microextraction techniques for the analysis of aqueous environmental samples

Microextraction-based sample preparation techniques have exhibited remarkable importance in analytical chemistry since they were first developed in the 1980s. The application of these techniques involves efficient and, at the same time, environmentally-friendly analytical methodologies. They are also generally faster when compared with classical sample preparation techniques, requiring low solvent and sample volumes, and also allowing for automated or semi-automated procedures. This paper provides an overview of the basic principles of sample preparation techniques and the important applications and developments that have taken place in this area over the past five years. These procedures include solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), bar adsorptive microextraction (BAμE), rotating disk sorptive extraction (RDSE), micro solid-phase extraction (μ-SPE) and liquid-phase microextraction (LPME). The main variations are discussed with a focus on recent applications in the analysis of environmental water samples. Lastly, some of the trends and perspectives associated with these outstanding microextraction sample preparation approaches are highlighted.     

Applying green analytical chemistry (GAC) for development of stability indicating HPLC method for determining clonazepam and its related substances in pharmaceutical formulations and calculating uncertainty

Clonazepam contains one benzodiazepine ring in its chemical structure which makes it vulnerable to degradation. In this study, green analytical chemistry approach was applied in attempts for the development of validated stability indicating RP-HPLC method for determining clonazepam and its related substances in pharmaceutical formulation. Validation has been performed according to ICH guidelines. Assay was capable of simultaneous monitoring of the intact drug in the presence of its related substances within the same run. HPLC assay involved an ODS column and a mobile phase composed of 2% sodium dodecyl sulfate, 0.05 M sodium acetate buffer pH 3.5 and isopropanol in ratio (25:55:20) at a flow rate of 1.5 mL/min and detection was carried out at 254 nm. HPLC method allowed good resolution between the peaks that corresponded to the active pharmaceutical ingredients and its degradation products with good linearity, precision, accuracy, specificity, LOD and LOQ. The expanded uncertainty (0.33%) of the method was also estimated from method validation data. This analytical technique is not only ecofriendly but also faster than the conventional liquid chromatographic system official in the USP-36.     

Aqueous two-phase systems: An efficient,environmentally safe and economically viable method for purification of natural dye carmine

Partition of the natural dye carmine has been studied in aqueous two-phase systems prepared by mixing aqueous solutions of polymer or copolymer with aqueous salt solutions (Na₂SO₄ and Li₂SO₄). The carmine dye partition coefficient was investigated as a function of system pH, polymer molar mass, hydrophobicity, system tie-line length and nature of the electrolyte. It has been observed that the carmine partition coefficient is highly dependent on the electrolyte nature and pH of the system, reaching values as high as 300, indicating the high potential of the two-phase extraction with ATPS in the purification of carmine dye. The partition relative order was Li₂SO₄ ? Na₂SO₄. Carmine molecules were concentrated in the polymer-rich phase, indicating an enthalpic specific interaction between carmine and the pseudopolycation, which is formed by cation adsorption along the macromolecule chain. When the enthalpic carmine–pseudopolycation interaction decreases, entropic forces dominate the natural dye-transfer process, and the carmine partitioning coefficient decreases. The optimization of the extraction process was obtained by a central composite face-centered (CCF) design. The CCF design was used to evaluate the influence of Li₂SO₄ and PEO 1500 concentration and of the pH on the partition coefficient of carmine. The conditions that maximize the partition of carmine into the top phase were determined to be high concentrations of PEO and Li₂SO₄ and low pH values within the ranges studied.     

Room-temperature,phosphorimetric determination of the beta-blocking agent pindolol in pharmaceutical tablets,urine and blood serum

It is already recognised that heavy-atom-induced, room-temperature phosphorescence can be used to determine pindolol in pharmaceutical samples and biological fluids. We describe here a new, simple, rapid and selective development of this technique. The phosphorescence signals derive from the interaction of pindolol with a relatively high concentration of heavy-atom salts in the presence of sodium sulphite as oxygen scavenger. Phosphorescence was registered in the presence of 1.2 M potassium iodide, 15 mM sodium sulphite and 30% v/v methanol at 450 nm, exciting at 285 nm. The detection limit was 21.1 ng mL⁻¹. The method has been successfully applied to the determination of pindolol in commercial pharmaceutical tablets, urine and blood serum.