Host–guest interactions of 6-benzyladenine with normal and modified cucurbituril: 1H NMR,UV absorption spectroscopy and phase solubility methods

Guest–host inclusion complexes between 6-benzyladenine (6-BA), cucurbit[7]uril (Q[7]), symmetrical tetramethylcucurbit[6]uril (TMeQ[6]) and meta-hexamethyl-substituted cucurbit[6]uril (HMeQ[6]) in aqueous solution were investigated by ¹H NMR, UV absorption spectroscopy and phase solubility studies. The ¹H NMR spectra analysis revealed that the hosts selectively bound the phenyl moiety of the guests. Absorption spectroscopic analysis defined the stability of the host–guest inclusion complexes. A host:guest ratio of 1:1 was measured quantitatively as (5.63 ± 0.26) × 10⁴, (1.94 ± 0.17) × 10³ and (2.89 ± 0.23) × 10³ mol L^? 1 for the Q[7]-6-BA, TMeQ[6]-6-BA and HMeQ[6]-6-BA systems, respectively. Phase solubility diagrams were analysed through rigorous procedures to obtain estimates of the complex formation constants for Q[n]-6-BA complexation. The formation constants were (1.29 ± 0.24) × 10⁴ L mol^? 1 for Q[7]-6-BA, (3.20 ± 0.17) × 10³ L mol^? 1 for TMeQ[6]-6-BA and (3.52 ± 1.01) × 10³ L mol^? 1 for TMeQ[6]-6-BA. Furthermore, phase solubility studies showed that 6-BA solubility increased as a function of Q[7], TMeQ[6] and HMeQ[6] concentrations. The thermodynamic parameters of the complex formation were also determined. The formation of inclusion complexes between 6-BA and Q[7] was enthalpy controlled, suggesting that hydrophobic and van der Waals interactions were the main driving forces. Our results demonstrated that the complexation of 6-BA with Q[n] could be used to improve the solubility of 6-BA.     

Polymeric membrane coated graphite cesium selective electrode based on 4′,4″(5′) di–tert-butyl di-benzo-18-crown-6

A new PVC membrane coated graphite electrode for cesium ion based on 4′,4″(5′)di–tert-butyl di-benzo-18-crown-6 (DTBDB18C6) as ionophore was prepared. The electrode shows a near Nernstian response of 57.0 ± 1.8 mV decade^?1 over a wide activity range of 6.0 × 10^?6–1.0 × 10^?1 mol L^?1 with a limit of detection 4.0 × 10^?6 mol L^?1. The proposed electrode is suitable for use in aqueous solution in the pH range of 3.0–9.5. It has a fast response time of 10 s and can be used for at least 1 month without any considerable divergence in potential. The selectivity coefficients for Cs⁺ ion with respect to ammonium, alkali, alkaline earth and some selected transition metal ions were determined and showed a superior selectivity over Li⁺, Na⁺ and alkaline earth metal ions. The new electrode was applied for determination of Cs⁺ in spiked tap water. The electrode was also used as indicator electrode in potentiometric titration of Cs⁺ with sodium tetraphenyl borate.     

Flow Injection and Batch Spectrophotometric Determination of Ibuprofen Based on its Competitive Complexation Reaction with Phenolphthalein‐β‐Cyclodextrin Inclusion Complex

Abstract

Rapid, simple, and accurate spectrophotometric method is presented for the determination of ibuprofen by batch and flow injection analysis methods. The method is based on ibuprofen competitive complexation reaction with phenolphthalein‐β‐cyclodextrin (PHP‐β‐CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of ibuprofen was measured. Ibuprofen can be determined in the range 8.0×10^?6 ?3.2×10^?4 and 2.0×10^?5?5.0×10^?3 mol l^?1 by batch and flow methods, respectively. The limit of detection and limit of quantification were 6.19×10^?6 and 2.06×10^?5 mol l^?1 for batch and 1.77×10^?5 and 5.92×10^?5 mol l^?1 for flow method, respectively. The sampling rate in flow injection analysis method was 120±5 samples h^?1. The method was applied to the determination of pharmaceutical formulations.     

Amperometric Biosensor for Evaluation of Competitive Cholinesterase Inhibition by the Reactivator HI‐6

Abstract

Amperometric biosensors containing enzymes butyrylcholinesterase or acetylcholinesterase were prepared. The biosensors were employed for studying of cholinesterase reactivator: HI‐6. Competitions between HI‐6 and acetylthiocholine as enzyme substrate were used for determination of IC₅₀ value. Biosensors with butyrylcholinesterase from human serum determined IC₅₀ as (1.00±0.02)×10^?6 M; the biosensor with acetylcholinesterase from human erythrocytes performance provided IC₅₀ (3.31±0.13)×10^?6 M, the one with human recombinant acetylcholinesterase (2.00±0.06)×10^?6 M and finally biosensor with acetylcholinesterase from electric eel (6.17±0.17)×10^?6 M when 5 mM acetylthiocholine as substrate was used. We are encouraged to consider presented biosensors as a very useful for evaluation of newly prepared cholinesterase reactivators.     

Identification of MMP-1 and MMP-9 inhibitors from the roots of Eleutherococcus divaricatus,and the PAMPA test

The purpose of this study was the isolation of metalloproteinases MMP-1 and MMP-9 inhibitors from the chloroform extract of the Eleutherococcus divaricatus roots. Using GC-MS, ¹H and ¹³C NMR, HMQC, HMBC, COSY and DEPT, (+)-sesamin has been identified as a new anti-MMP inhibitor. We report for the first time that (+)-sesamin inhibited MMP-1 and MMP-9 activity in 40% and 17%, respectively. The high inhibitory potential has been shown by ursolic acid (90.9% and 89.8% for MMP-1 and MMP-9). In the PAMPA test, the Pe value for sesamin was established as 17.4 × 10^? 6 cm/s, that for ursolic acid as 30.0 × 10^? 6 cm/s. Verapamil and theophylline were used as a positive and negative control (Pe 42.1 and 2.9 × 10^? 6 cm/s). To our best knowledge, no information was available on this activity of sesamin and other compounds. These studies provide a biochemical basis for the regulation of MMP-1 and MMP-9 by E. divaricatus compounds.     

Selective Spectrofluorimetric Method and Uncertainty Calculation for the Determination of Camptothecin in the Presence of Irinotecan and Topotecan

A selective fluorimetric method was developed to quantify camptothecin (CPT) in irinotecan (CPT-11) and in topotecan (TPT) based anti-cancer drugs. Selectivity was achieved by experimental optimization and using synchronized scanning and second-order spectral derivatization. The limits of quantification for CPT were in the order of 1 × 10^?7 mol L^?1 with a linear response up to 1 × 10^?5 mol L^?1. The combined uncertainty associated with the CPT fluorescence measurement at a 5 × 10^?7 mol L^?1 level were 10.9% and 6% of the reference level, respectively, for TPT and CPT-11 based pharmaceutical formulations. The CPT recoveries of 95 ± 12% and 91 ± 5.6% (n = 3) were achieved, respectively, in samples containing CPT-11 and TPT.     

Evaluation of radon concentration and heavy metals in drinking water and their health implications to the population of Quetta,Balochistan, Pakistan

ABSTRACT

The purpose of this study is to estimate the concentrations of radon and heavy metals in drinking water and assess their health implications to the population of Quetta, Pakistan. The concentration of radon and heavy metals was measured in drinking water collected from tube wells of different depths of the Quetta, Balochistan, Pakistan, using RAD7 detector and Atomic Absorption Spectrometer, respectively. The results show that the concentration of radon ranged from 3.56 ± 0.98 to 8.56 ± 1.32Bq/L with an average of 5.67 ± 1.34Bq/L. The average value of contribution of radon in water to indoor air was found 2.02 ± 0.47mBq/L. In addition to concentration of radon in drinking water, physiochemical parameters like pH and electrical conductivity (EC), and annual effective doses for different age groups were also estimated. Positive correlation of (R² = 0.8471) was observed between depth of well and concentration of radon, however no such relations were found among pH and EC with concentration of radon. Average values of annual effective doses due to intake of radon for age groups 0–1 years (infants), 2–16 years (Children) and ≥17 years (adults) were found (3.00 ± 0.71)×10^?2, (1.1 ± 0.26)×10^?2 and (1.45 ± 0.34)×10^?2 mSv/y, respectively. Average values of heavy metals concentrations were found 1.85 ± 0.64, 3.21 ± 0.75, 5.06 ± 1.19, and 2.47 ± 0.77 and 5.58 ± 1.23 µg/L for As, Cr, Ni, Cd and Pb, respectively. The values of radon concentration and heavy metals in drinking water were found below the USEPA permissible limits, Thus we conclude that, the investigated waters are safe.     

Preparation and characterization of in situ carbon paste and screen-printed potentiometric sensors for determination of econazole nitrate: surface analysis using SEM and EDX

The construction and performance characteristics of new sensitive and selective in situ carbon paste (ICPE) and screen-printed (ISPE) potentiometric sensors modified with ion-pairing agents such as phosphotungstic acid, sodium tetraphenylborate, phosphomolybdic acid and ammonium reineckate for determination of econazole nitrate (ECN) have been developed. The reaction mechanism between ECN and ion-pairing agents at the electrode surface was studied through scanning electron microscope and energy-dispersive X-ray analysis. The electrodes under investigation showed potentiometric response for ECN in the concentration range from 1.0 × 10^?6 to 5.0 × 10^?3 mol L^?1 and from 1.0 × 10^?6 to 1.0 × 10^?2 mol L^?1 for ISPE (electrode I) and ICPE (electrode II) potentiometric sensors, respectively, at 25 °C. The electrode response was pH independent in the range 2.5–7.5 and 2.5–6.5 for electrodes I and II, respectively. These sensors have Nernstian slope values of 59.4 ± 0.2 and 59.10 ± 0.2 mV decade^?1 with detection limit of 1.0 × 10^?6 mol L^?1 for electrodes I and II, respectively. The electrodes showed fast response time of 4 and 9 s for electrodes I and II, respectively. The ISPE (electrode I) showed lifetime of 28 days, and this was considered as advantage over ICPE (electrode II). Selectivity for ECN with respect to a number of interfering materials was also investigated. The proposed electrodes were applied for determination of ECN in pure and pharmaceutical formulation using calibration, potentiometric titration and standard addition methods. The results showed good agreement with those obtained using official method. The t and F values indicated no significant difference between the suggested and reported methods. Method validation parameters were optimized according to ICH recommendations.     

Novel potentiometric sensors for pyrilamine maleate

The fabrication and electrochemical response characteristics of four novel potentiometric sensors for determination of pyrilamine maleate (PyraH) were described. The sensors include polymeric membrane electrodes (PME₁, PME₂) and carbon paste electrodes (CPE₁, CPE₂). The fabricated sensors were based on the ion-pair of pyrilamine with sodium tetraphenylborate (NaTPB) and ammonium reineckate (NH₄RN) using dibutyl phthalate (DBP) as plasticizing solvent. The sensors showed linear, stable and near-Nernstian slopes of 56.4 ± 0.4, 54.2 ± 0.2, 58.8 ± 0.3 and 57.9 ± 0.4 mV decade^?1 at 25 ± 0.1 °C and detection limits of 2.0 × 10^?5, 1.8 × 10^?5, 1.0 × 10^?5 and 9.5 × 10^?6 mol L^?1 for PME₁, PME₂, CPE₁ and CPE₂ sensors, respectively. The response time was less than 10 and 8 s for polymeric membrane and carbon paste sensors. The proposed sensors displayed good selectivity for pyrilamine with respect to a number of common inorganic and organic species. The thermal temperature coefficients of the investigated sensors were 0.9508, 0.7012, 0.9450 and 0.6497 mV °C^?1. Modified carbon paste sensors showed lower detection limits, higher thermal stability and faster response time than those of polymeric membrane sensors. The proposed sensors displayed useful analytical characteristics for determination of pyrilamine in pharmaceutical preparation and biological fluids (Human urine and plasma).     

Determination of ultratrace amounts of plutonium in high saline groundwater by inductively coupled plasma mass spectrometry

For determination of ultratrace amounts of plutonium in high saline groundwater, large-volume sampling and preconcentration are necessary. However, traditional co-precipitation methods, such as Fe(OH)₃, Ca(OH)₂–Mg(OH)₂ and hydroxide-carbonate co-precipitation, are unable to meet the requirements of preconcentration of the ultratrace plutonium in high saline groundwater. In this paper, the ultratrace plutonium in high saline groundwater was concentrated by sequential co-precipitation with MnO₂ and Fe(OH)₃, and purified by two-stage anion-exchange separation on Dowex1 × 4 resin column. Quadrupole ICP-MS was employed for the determination of ²³⁹Pu with ²⁴²Pu spiked. After co-precipitation and purification, the major matrix elements were significantly decreased to μg mL^?1 level and decontamination factor of uranium is better than 10⁶. The detection limit for ²³⁹Pu in 50 L high saline water is 2.1 × 10^?16 g L^?1. Three high saline fountain samples (total dissolved solids more than 20 g L^?1) from Dunhuang region of China were analyzed using this method. The concentrations of ²³⁹Pu in these samples were 0.48 ± 0.2 × 10^?15, 1.40 ± 0.10 × 10^?15 and 2.13 ± 0.21 × 10^?15 g L^?1 respectively. The recovery obtained for 7 pg of ²⁴²Pu spiked into real high saline-water samples was all above 70 %.     

Fabrication of a new nanocomposite modified carbon paste Al<Superscript>3+</Superscript>-ion selective electrode based on <Emphasis Type="Italic">N,N</Emphasis>′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as an active material

Construction and feature of a nanocomposite modified carbon paste electrode for aluminum(III) ion determination based on N,N′-dipyridoxyl (1,2-cyclohexanediamine) (PYCA) as a novel selector material will be covered by this paper. The optimum composition, Nernstian slope/linear range/detection limit in the forms of calibration graph, response time, utilizable pH range, repeatability and precision of measurements of the aluminum(III) ion using the new fabricated Al³⁺-CPE was evaluated. The optimal composition which performed over Al⁺³ ion concentration range 1.0 × 10^?8 mol L^?1–1.0 × 10^?1 mol L^?1 with near-Nernstian slope equal 20.9 ± 0.2 mV decade^?1 and low detection limit about 5.0 × 10^?9 mol L^?1, was formed of ionophore (PYCA 3 %), binder (paraffin oil 30 %), modifier [multi-wall carbon nanotubes (MWCNTs) 1 %] & [Nanosilica (NS) 0.5 %], and inert matrix (graphite powder 65.5). The request time to give rise Nernstian response of electrode for concentrations from 1.0 × 10^?8 mol L^?1 to 1.0 × 10^?1 mol L^?1 of Al³⁺ ion solution was estimated about ~6 s. The new Al³⁺-CPE was applied in pH range 2.0–5.0 with no consequential change in potential response. To verify the selectivity of electrode toward aluminum(III) ion in the presence of different metallic cations, matched potential method was used. The obtain results in analytical applications reflect the excellent ability of this electrode to play the role as endpoint indicator electrode in both titration and direct potentiometric measurements.     

Modified Screen-Printed Electrode for Potentiometric Determination of Copper(II) in Water Samples

Modified screen printed (SPE) and carbon paste electrodes (CPE) with phenanthroline–tetraphenyl borate ionophore [Phen:TPB] were fabricated for the determination of copper(II). The modified electrodes have linear responses over a wide concentration range (1 × 10^?6–1 × 10^?2 mol·L^?1) of copper(II) ion at 25 °C with divalent cationic slopes of 29.85 ± 0.58 and 29.45 ± 0.81 mV·decade^?1 and exhibit a detection limit of 1 × 10^?6 mol·L^?1 for SPE and CPE. The selectivity coefficient was measured using the match potential method in acetate buffer of pH = 4.2. The modified SPE and CPE sensors show high selectivity and sensitivity for determination of copper(II) and also show stable and reproducible response over a period of five and three months for SPE and CPE sensors, respectively. This method can be used for determination of copper(II) in water, soil, plant and fish tissue samples and the results obtained agreed with those obtained with atomic absorption spectrometer (AAS).     

Uranium in groundwater from Western Haryana,India

This study was undertaken to assess uranium in groundwater and radiological and chemical risks associated with its ingestion in rural habitats in the vicinity of proposed nuclear power project in Western Haryana, India. Uranium concentration in the groundwater of the study area varied from 0.3 to 256.4 μg L^?1. Radiological risk calculated in the form of average life time dose was found 5.1 × 10^?2 mSv to the residents of the area from the ingestion of groundwater. The average cancer mortality and average cancer morbidity risk were calculated to be 4.9 × 10^?6 and 7.7 × 10^?6 respectively indicating the absence of carcinogenic risks. Chemical risk was in the range of 0.02–18.8 µg kg^?1 day^?1. Hazard quotient for 72 % samples was greater than unity which indicates health risk due to chemical toxicity of uranium in groundwater. The results indicate that uranium concentrations in the groundwater of the study area are important due to chemical risk than radiological risk.     

New Copper(II) Ion-Selective Membrane Electrode Based on Erythromycin Ethyl Succinate as a Neutral Ionophore

Abstract

The potentiometric response characteristics of a new copper(II) ion-selective PVC membrane electrode based on erythromycin ethyl succinate (EES) as ionophore were investigated. The electrode exhibited a Nernstian response to Cu²⁺ ions over the activity range of 1.5 × 10^?2 to 2.0 × 10^?6 mol L^?1 with a limit of detection of 6.3 × 10^?7 mol L^?1. Stable potentials were obtained in the pH range of 5.5–6.5. The potentiometric selectivity coefficients were calculated by using fixed interference method and revealed no important interferences except for Ag⁺. This electrode was successfully applied as an indicator electrode in determination of copper ions in real water samples.     

Voltammetric Determination of Methylparaban in Cosmetics Using a Multi-Wall Carbon Nanotubes/Nafion Composite Modified Glassy Carbon Electrode

A novel voltammetric sensor using multi-wall carbon nanotubes (MWNTs) coupled with Nafion modified glassy carbon electrode (GCE) was developed for the detection of methylparaben (MP). The sensor exhibited good electrocatalytic activity toward the oxidation of MP in the phosphate buffer solution (PBS, pH 6.5). It displayed good sensitivity, repeatability, reproducibility, and long-term stability. Under the optimized conditions, the anodic peak current was linear with the concentration of MP in the range of 3 × 10^?6 mol L^?1 to 1 × 10^?4 mol L^?1. The detection limit was 1 × 10^?6 mol L^?1. The proposed method was successfully applied to determine MP in cosmetics with satisfactory results.     

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s^?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10^?11?mol?cm^?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10^?4 to 5.6?×?10^?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM^?1?cm^?2 and a detection limit of 2.5?×?10^?5?M (S/N=3).     

Lanthanum-selective sensors based on 3-amino-2-mercapto-3H-quinazolin-4-one in PVC matrix

A new solvent polymeric membrane (PME) and coated graphite (CGE) electrodes based on 3-amino-2-mercapto-3H-quinazolin-4-one as a suitable carrier for La(III) ion are described. The sensors exhibited a Nernstian response for La(III) ion over a wide concentration range (3.0 × 10^?7 to 1.0 × 10^?1 M for PME and 1.0 × 10^?7 to 1.0 × 10^?1 M for CGE) with a slope of 20.1 ± 0.3 (PME) and 23.4 ± 0.4 (CGE) mV decade^?1. The lower detection limits by PME and CGE were 2.0 × 10^?7 and 7.1 × 10^?8 M, respectively. The potentiometric response of the proposed electrodes was independent of the pH of the test solution in the pH range 3.0–9.0 with a fast response time (<10 s). The applications of prepared sensors were demonstrated in the determination of lanthanum ions in spiked water sample and also utilized for indirect determination of fluoride content of two mouth wash preparation samples.     

Human Saliva-Based Quantitative Monitoring of Clarithromycin by Flow Injection Chemiluminescence Analysis: A Pharmacokinetic Study

Human saliva quantitative monitoring of clarithromycin (CLA) by chemiluminescence (CL) with flow injection analysis was proposed for the first time, which was based on the quenching effect of CLA on luminol–bovine serum albumin (BSA) CL system with a linear range from 7.5?×?10^?4 to 2.0 ng/ml. This proposed approach, offering a maximum sample throughput of 100 h^?1, was successfully applied to the quantitative monitoring of CLA levels in human saliva during 24 h after a single oral dose of 250 mg intake, with recoveries of 95.2～109.0 % and relative standard deviations lower than 6.5 % (N?=?7). Results showed that CLA reached maximum concentration of 2.28?±?0.02 μg/ml at approximately 3 h, and the total elimination ratio was 99.6 % in 24 h. The pharmacokinetic parameters including absorption rate constant (0.058?±?0.006 h^?1), elimination rate constant (0.149?±?0.009 h^?1) and elimination half-life time (4.66?±?0.08 h) were obtained. A comparison of human saliva and urine monitoring was also given. The mechanism study of BSA–CLA interaction revealed the binding of CLA to BSA is an entropy driven and spontaneous process through hydrophobic interaction, with binding constant K _BSA–CLA of 4.78?×?10⁶ l/mol and the number of binding sites n of 0.82 by flow injection–chemiluminescence model. Molecular docking analysis further showed CLA might be in subdomain IIA of BSA, with K _BSA–CLA of 6.82?×?10⁵ l/mol and ΔG of ?33.28 kJ/mol.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Direct Electroanalytical Determination of Fluvastatin in a Pharmaceutical Dosage Form: Batch and Flow Analysis

Abstract

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately ?1.26 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 × 10^?8 and 2.7 × 10^?6 mol L^?1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 × 10^?9 mol L^?1 and 3.3 × 10^?8 mol L^?1, respectively.

Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 × 10^?6 to 1.0 × 10^?5 mol L^?1, with an LOD of 2.4 × 10^?7 mol L^?1 and an LOQ of 8.0 × 10^?7 mol L^?1. A sample rate of 50 injections per hour was achieved.

Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.