Fabrication and Applications of Potentiometric Membrane Sensors Based on Specific Recognition Sites for the Measurement of the Quinolone Antibacterial Drug Gemifloxacin.

Supramolecular gemifloxacin (GF) sensors have been developed. Supramolecular chemistry is primarily concerned with noncovalent intermolecular and intramolecular interactions, which are far weaker than covalent connections, but they can be exploited to develop sensors with remarkable affinity for a target analyte. In order to determine the dose form of the quinolone antibacterial drug gemifloxacin, the current study's goal is to adapt three polyvinylchloride (PVC) membrane sensors into an electrochemical technique. Three new potentiometric membrane sensors with cylindric form and responsive to gemifloxacin (GF) were developed. The sensors' setup is based on the usage of o-nitrophenyl octyl ether (o-NPOE) as a plasticizer in a PVC matrix, ß-cyclodextrin (ß-CD) (sensor 1), γ-cyclodextrin (γ-CD) (sensor 2), and 4-tert-butylcalix[8]arene (calixarene) (sensor 3) as an ionophore, potassium tetrakis (4-chlorophenyl) borate (KTpClPB) as an ion additive for determination of GF. The developed method was verified according to IUPAC guidelines. The sensors under examination have good selectivity for GF, according to their selectivity coefficients. The constructed sensors demonstrated a significant response towards to GF over a concentration range of 2.4 × 10-6, 2.7 × 10-6, and 2.42 × 10-6 mol L-1 for sensors 1, 2, and 3, respectively. The sensors showed near-Nernstian cationic response for GF at 55 mV, 56 mV, and 60 mV per decade for sensors 1, 2, and 3, respectively. Good recovery and relative standard deviations during the day and between days are displayed by the sensors. They demonstrated good stability, quick response times, long lives, rapid recovery, and precision while also exhibiting good selectivity for GF in various matrices. To determine GF in bulk and dose form, the developed sensors have been successfully deployed. The sensors were also employed as end-point indicators for titrating GF with sodium tetraphenyl borate.

The 1,3-Dioctadecyl-1H-imidazol-3-ium Based Potentiometric Surfactant Sensor for Detecting Cationic Surfactants in Commercial Products.

A low-cost and fast potentiometric surfactant sensor for cationic surfactants, based on the new ion-pair 1,3-dioctadecyl-1H-imidazol-3-ium-tetraphenylborate (DODI-TPB), is presented. The new cationic surfactant DODI-Br was synthesized and characterized by NMR, LC-MS, and elemental analysis, and was used for synthesis of the DODI-TPB ionophore. The DODI-TPB surfactant sensor was obtained by implementation of the ionophore in PVC. The sensor showed excellent response characteristics with near-Nernstian slopes to the cationic surfactants DMIC, CPC, CTAB, and Hyamine 1622. The highest voltage responses were obtained for DMIC and CPC (58.7 mV/decade of activity). DMIC had the lowest detection limit (0.9 × 10-6 M) and the broadest useful linear concentration range (1.8 × 10-6 to 1.0 × 10-4 M). An interference study showed remarkable stability. Potentiometric titration curves for the titration of cationic surfactants (DMIC, CPC, CTAB, and Hyamine 1622), with DDS and TPB used as titrants, showed sigmoidal curves with well-defined inflexion points and a broad signal change. The standard addition method was successfully applied with recovery rates from 98.9 to 101.2 at two concentrations. The amount of cationic surfactant found in disinfectants and antiseptics was in good agreement with the referent two-phase titration method and the surfactant sensor on the market. This new surfactant sensor represents a low-cost alternative to existing methods for cationic surfactant detection.

Effect of Tetraphenylborate on Physicochemical Properties of Bovine Serum Albumin.

The binding interactions of bovine serum albumin (BSA) with tetraphenylborate ions ([B(Ph)4]-) have been investigated by a set of experimental methods (isothermal titration calorimetry, steady-state fluorescence spectroscopy, differential scanning calorimetry and circular dichroism spectroscopy) and molecular dynamics-based computational approaches. Two sets of structurally distinctive binding sites in BSA were found under the experimental conditions (10 mM cacodylate buffer, pH 7, 298.15 K). The obtained results, supported by the competitive interactions experiments of SDS with [B(Ph)4]- for BSA, enabled us to find the potential binding sites in BSA. The first site is located in the subdomain I A of the protein and binds two [B(Ph)4]- ions (logK(ITC)1 = 7.09 ± 0.10; ΔG(ITC)1 = -9.67 ± 0.14 kcal mol-1; ΔH(ITC)1 = -3.14 ± 0.12 kcal mol-1; TΔS(ITC)1 = -6.53 kcal mol-1), whereas the second site is localized in the subdomain III A and binds five ions (logK(ITC)2 = 5.39 ± 0.06; ΔG(ITC)2 = -7.35 ± 0.09 kcal mol-1; ΔH(ITC)2 = 4.00 ± 0.14 kcal mol-1; TΔS(ITC)2 = 11.3 kcal mol-1). The formation of the {[B(Ph)4]-}-BSA complex results in an increase in the thermal stability of the alfa-helical content, correlating with the saturation of the particular BSA binding sites, thus hindering its thermal unfolding.

Effect of methyl and halogen substituents on the transmembrane movement of lipophilic ions.

Penetrating cations are widely used for the design of bioactive mitochondria-targeted compounds. The introduction of various substituents into the phenyl rings of dodecyltriphenylphosphonium and the measurement of the flip-flop of the synthesized cations by the current relaxation method revealed that methyl groups accelerated significantly the cation penetration through the lipid membrane, depending on the number of groups introduced. However, halogenation slowed down the penetration of the analogues. This result is strictly opposite to the flip-flop acceleration observed for halogenated tetraphenylborate anions. Density functional theory and the polarizable continuum solvent model were used to calculate the solvation energies of methyltriphenylphosphonium and methyltriphenylborate analogues. A good agreement was demonstrated between the difference in the free energy of ion solvation in water and octane and the absolute value of the central free energy barrier estimated from experimental data. Our results reveal that increasing the size of the lipophilic ion can lead to both acceleration and deceleration of the transmembrane flip-flop rate depending on the substituent and sign of the ion. This finding also emphasizes the different nature of ion-water interactions for structurally similar substituted hydrophobic anions and cations.

Ecofriendly Long Life Nanocomposite Sensors for Determination of Carbachol in Presence of Choline: Application in Ophthalmic Solutions and Biological Fluids.

Several emerging nano scale forms of carbon are showing great promise in electrochemical sensing such as graphene and multi-walled carbon nanotubes (MWCNTs). Herein we present an ecofriendly method to fabricate long life and sensitive ion selective sensors based on graphene and MWCNTs nanocomposites with no need for volatile organic solvents. Both sensors were fabricated, for the analysis of carbachol in ophthalmic solutions, plasma and urine where ion- association complex was formed between cationic carbachol and anionic Sodium tetra phenyl borate (NaTBP) in a ratio 1:1. Both sensors were evaluated according to the IUPAC recommendation data, revealing linear response in the concentration range 10-7 M to 10-2 M with near Nernstian slopes 50.80 ± 5 and 58.14 ± 3 mV/decade and correlation coefficients 0.9992 and 0.9998 for graphene and MWCNTs based sensors, respectively. Both sensors were successfully applied as stability indicating method for the analysis of carbachol in presence of its metabolite choline, in ophthalmic preparations, in plasma and urine showing good recovery percentage values. MWCNTs based sensor showed some advantages over graphene sensor regarding lower limit of detection (LOD), longer life time and higher selectivity towards carbachol. Statistical comparison of the proposed sensors with the official method showed no significant difference for accuracy and precision.

Analytical Eco-Scale for Assessing the Greenness of a Developed Potentiometric Method for Lomefloxacin Hydrochloride Determination in its Different Dosage Forms, Plasma, and Dissolution Medium.

Background: Traditional methods for Lomefloxacin hydrochloride (LOM) determination involve pretreatment steps, which extend analysis time and use hazardous chemicals. Objective: The ability to provide a rapid route without sample pretreatment for quantitative determination of compounds via a low-cost instrument is a challenging task. In this work, a simple potentiometric method was developed to determine the antibacterial LOM via in-house fabricated ion selective electrodes. Methods: Different sensors were fabricated using a poly vinyl chloride-based membrane, potassium tetrakis(4-chlorophenyl) borate as a cation exchanger, and 2-Nitrophenyl octyl ether as a plasticizer (sensor 1). To increase the selectivity of sensor 1, a selective molecular recognition component 2-hydroxypropyl-ß-cyclodextrin was used as ionophore (sensor 2). Results: The proposed method was validated according to International Union of Pure and Applied Chemistry recommendations, in which the proposed sensors show a linear dynamic range from 1 × 10-5 to 1 × 10-2 mol/L, with Nernstian slopes of 55.829 and 58.229 mV/decade for sensors 1 and 2, respectively. It was applied to determine LOM in bulk powder, in different dosage forms, and in plasma with no sample pretreatment. Also, the suggested method can be used as a green, in-line bench top real-time analyzer for in-process monitoring of LOM release from its tablets, under U.S. Food and Drug Administration dissolution regulations, with clear discrimination from common excipients. Results obtained by the proposed potentiometric method were compared with those obtained by a reported HPLC method. Conclusions: The proposed method is considered as a perfect alternative to traditional reported methods for LOM determination.

Colorimetric Microtiter Plate Assay of Polycationic Aminoglycoside Antibiotics in Culture Broth Using Amaranth.

We present a colorimetric method for the detection of aminoglycoside antibiotics such as neomycin (NEO) using a reddish anionic dye, amaranth (AR3-). Under acidic conditions, at which NEO exists in fully protonated form (NEOH6+), the AR3- anion associates with the NEOH6+ cation to form a precipitate, NEOH(AR)2. The precipitate was soluble in a buffer solution of pH 8.5, yielding a reddish solution with an absorption maximum at around 520 nm. Tobramycin and gentamycin, which exist as pentavalent cations under acidic conditions, gave almost the same results. On the other hand, kanamycin, amikacin and streptomycin, which would exist as tri- and tetravalent cations, were not precipitated. Thus, the AR3- anion could be considered to be an analytical reagent for specific aminoglycosides with polycationic functionality. However, since the precipitation reaction was considerably affected by other anions, a separation method using the tetraphenylborate anion was employed as a pretreatment. The separation method involves precipitating the polycationic aminoglycosides with the tetraphenylborate anion, washing the precipitate with acetonitrile, and re-precipitating the aminoglycosides as hydrochloride salts. Thus, the present method was applied to a microtiter plate assay of the products in an NEO-producing culture broth.

A new grading system for plant-available potassium using exhaustive cropping techniques combined with chemical analyses of soils.

A new grading system for plant-available potassium (K) in soils based on K release rate from soils and plant growth indices was established. In the study, fourteen different agricultural soils from the southern subtropical to the northern temperate zones in China were analyzed by both chemical extraction methods and exhaustive cropping techniques. Based on the change trends in plant growth indices, relative biomass yields of 70% and 50%, K-deficient coefficients of 35 and 22 under conventional exhaustive experiments, and tissue K concentrations of 40 g kg-1 and 15 g kg-1 under intensive exhaustive experiments were obtained as critical values that represent different change trends. In addition, the extraction method using 0.2 mol L-1 sodium tetraphenylboron (NaTPB) suggested soil K release rates of 12 mg kg-1 min-1 and 0.4 mg kg-1 min-1 as turning points that illustrated three different release trends. Thus, plant-available K in soils was classified into three categories: high available K, medium available K and low available K, and grading criteria and measurement methods were also proposed. This work has increased our understanding of soil K bioavailability and has direct application in terms of routine assessment of agriculture soils.

Emulsification at the Liquid/Liquid Interface: Effects of Potential, Electrolytes and Surfactants.

Emulsification of oils at liquid/liquid interfaces is of fundamental importance across a range of applications, including detergency. Adsorption and partitioning of the anionic surface active ions at the interface between two immiscible solutions is known to cause predictable chaos at the transfer potential region of the surfactant. In this work, the phenomenon that leads to the chaotic behaviour shown by sodium dodecylbenzene sulfonate (SDBS) at the water/1,2-dichloroethane interface is applied to commercial surfactants and aqueous/glyceryl trioleate interface. Electrochemical methods, electrocapillary curves, optical microscopy and conductivity measurements demonstrated that at 1.5 mm of SDBS, surfactants are adsorbed at the interface and assemble into micelles, leading to interfacial instability. As the concentration of the anionic surfactant was enhanced to 8 and 13.4 mm, the Marangoni effect and the interfacial emulsification became more prominent. The chaotic behaviour was found to be dependent on the surfactant concentration and the electrolytes present.

Exploiting Fast Exciton Diffusion in Dye-Doped Polymer Nanoparticles to Engineer Efficient Photoswitching.

Photoswitching of bright fluorescent nanoparticles opens new possibilities for bioimaging with superior temporal and spatial resolution. However, efficient photoswitching of nanoparticles is hard to achieve using Förster resonance energy transfer (FRET) to a photochromic dye, because the particle size is usually larger than the Förster radius. Here, we propose to exploit the exciton diffusion within the FRET donor dyes to boost photoswitching efficiency in dye-doped polymer nanoparticles. To this end, we utilized bulky hydrophobic counterions that prevent self-quenching and favor communication of octadecyl rhodamine B dyes inside a polymer matrix of poly(D,L-lactide-co-glycolide). Among tested counterions, only perfluorinated tetraphenylborate that favors the exciton diffusion enables high photoswitching efficiency (on/off ratio ∼20). The switching improves with donor dye loading and requires only 0.1-0.3 wt % of a diphenylethene photochromic dye. Our nanoparticles were validated both in solution and at the single-particle level. The proposed concept paves the way to new efficient photoswitchable nanomaterials.

Organic nanoparticles of malachite green with enhanced far-red emission: size-dependence of particle rigidity.

In tracing the biological processes using fluorescent probes, it is desirable to shift the excitation/emission energy to a far-red/near-infrared (FR/NIR) region. In this study, we successfully synthesize FR fluorescent organic nanoparticles via ion-association between the malachite green (MG) cations and tetrakis(4-fluorophenyl)borate (TFPB) anions in the presence of a neutral stabilizing polymer. Binding of MG with TFPB results in the prominent appearance of an absorption band that can be assigned to an H-aggregate of MG. The fluorescence intensity as well as the fluorescence lifetime shows a significant increase with a decrease in the nanoparticle size. Since the MG dye is known as a local viscosity or environmental rigidity probe showing a rotational friction dependence of the excited state lifetime, we find that the rigidity of the organic nanoparticle is strongly size-dependent; that is, the smaller the size of the nanoparticle, the greater the rigidity of the nanoparticle. We also reveal that surface regions of the ion-based organic nanoparticles are more rigid than inner regions. The presence of H-aggregates that are almost non-fluorescent is the major origin of aggregation-caused quenching (ACQ) and still avoids the enhancement of the fluorescence quantum yield of the MG nanoparticles, so we develop a new approach to prevent H-aggregation inside the nanoparticle by incorporating photochemically inert, bulky phosphonium cations, which results in a 430-fold enhancement of its fluorescence yield. We believe that such a methodology will open up an avenue in the development of new types of fluorescent nanomaterials for many applications.

Surface morphology changes of polymer membrane and carbon paste sertraline sensors.

Polymer membrane and chemically modified carbon paste (CMCP) sensors for determination of sertraline HCl (Ser-Cl) incorporating sertraline tetraphenylborate (Ser-TPB) as an electro-active material were constructed. They showed a rapid and linear response for Ser-ion over the concentration range 0.01-10.00 mmol L(-1). The limits of detection were 2.80 and 9.55 µmol L(-1), and Nernastian slopes were 56.60, 59.60 mV decade(-1) for membrane and CMCP sensors for batch method. In flow injection analysis (FIA), the electrodes revealed comparatively good selectivity for Ser-ion with regard to a wide variety of different cations, sugars, and amino acids. The addition of different anionic additives, namely sodium tetraphenylborate (NaTPB), potassium tetraphenylborate (KTPB), potassium tetrakis[3,5-bis-(triflouromethyl)phenyl]borate (KTFMPB), and sodium tetrakis[3,5-bis(trifluoro-methyl)phenyl]borate (NaTFMPB), to the prepared mixture improved their response characteristics. The surface morphologies of membrane films containing PVC only (blank), plasticizer+PVC, Ser-TPB+plasticizer+PVC, and Ser-TPB +plasticizer+PVC+additive were studied using scanning and atomic force electron microscopes. These sensors had been used in the potentiometric titration of Ser-ion against NaTPB. Standard addition method for the pure raw material and some of its pharmaceutical tablets was used for Ser-Cl determination. The obtained results were tested for their repeatability and reproducibility and were statistically treated by F- and t- tests.

A simple approach for fabricating solid-contact ion-selective electrodes using nanomaterials as transducers.

A simple and robust approach for the development of solid-state ion-selective electrodes (ISEs) using nanomaterials as solid contacts is described. The electrodes are fabricated by using the mixture of an ionic liquid (IL) and a nanomaterial as intermediate layer, formed by melting the IL. Tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500) is chosen as an model of IL to provide strong adhesion between the inner glassy carbon electrode and the intermediate layer. Nanomaterials including single-walled carbon nanotubes (SWCNTs) and graphene were used as active ion-to-electron transducers between the glassy carbon electrode and the ionophore-doped ISE membrane. By using the proposed approach, the solid-contact Cu(2+)- and Pb(2+)-selective electrodes based on ETH 500/SWCNTs and ETH 500/graphene as transducers, respectively, have been fabricated. The proposed electrodes show detection limits in the nanomolar range and exhibit a good response time and excellent stability.

Interfacial processes studied by coupling electrochemistry at the polarised liquid-liquid interface with in situ confocal Raman spectroscopy.

Interfacial processes controlled by ion transfer voltammetry at the interface between two immiscible electrolyte solutions were studied by in situ Raman spectroscopy. Raman spectra of the interface between a 5 mM NaCl aqueous solution and 10 mM bis(triphenyl-phosphoranydieneammonium) tetrakis(4-chlorophenyl)borate in 1,2-dichloroethane were recorded at open circuit potential and at various interfacial potential differences. At open-circuit potential, Raman peaks assigned to vibrational modes of 1,2-dichloroethane are clearly visible and peaks of weak intensity are measured for the organic electrolyte ions. When a negative interfacial potential difference is applied, the intensity of the peaks of the cation of the organic electrolyte increases, confirming its transfer induced by the interfacial potential difference applied. The electrochemically assisted generation of mesoporous silica deposits was then followed by in situ confocal Raman spectroscopy. The condensation of mesoporous silica was controlled by the transfer of cetyltrimethylammonium (CTA(+)) ions to an aqueous phase containing hydrolysed silanes. The transfer of CTA(+) at the interface was monitored in situ by confocal Raman spectroscopy, and formation of silica was observed.

Collective fluorescence switching of counterion-assembled dyes in polymer nanoparticles.

The current challenge in the field of fluorescent nanoparticles (NPs) for bioimaging is to achieve extreme brightness and external control of their emission using biodegradable materials. Here we propose a new concept of fluorescent polymer NPs, doped with ionic liquid-like salts of a cationic dye (octadecyl rhodamine B) with a bulky hydrophobic counterion (fluorinated tetraphenylborate) that serves as spacer minimizing dye aggregation and self-quenching. The obtained 40-nm poly(D,L-lactide-co-glycolide) NPs containing up to 500 dyes are brighter than quantum dots and exhibit photo-induced reversible on/off fluorescence switching, never reported for dye-doped NPs. We show that this collective switching of hundreds of dyes is due to ultrafast excitation energy transfer and can be used for super-resolution imaging. These NPs, being spontaneously endocytosed by living cells, feature high signal-to-noise ratio and absence of toxicity. The counterion-based concept opens the way to a new class of nanomaterials for sensing, imaging and light harvesting.

Autocatalytic formation of an iron(IV)-oxo complex via scandium ion-promoted radical chain autoxidation of an iron(II) complex with dioxygen and tetraphenylborate.

A non-heme iron(IV)-oxo complex, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was formed by oxidation of an iron(II) complex ([(TMC)Fe(II)](2+)) with dioxygen (O2) and tetraphenylborate (BPh4(-)) in the presence of scandium triflate (Sc(OTf)3) in acetonitrile at 298 K via autocatalytic radical chain reactions rather than by a direct O2 activation pathway. The autocatalytic radical chain reaction is initiated by scandium ion-promoted electron transfer from BPh4(-) to [(TMC)Fe(IV)(O)](2+) to produce phenyl radical (Ph(•)). The chain propagation step is composed of the addition of O2 to Ph(•) and the reduction of the resulting phenylperoxyl radical (PhOO(•)) by scandium ion-promoted electron transfer from BPh4(-) to PhOO(•) to produce phenyl hydroperoxide (PhOOH), accompanied by regeneration of phenyl radical. PhOOH reacts with [(TMC)Fe(II)](2+) to yield phenol (PhOH) and [(TMC)Fe(IV)(O)](2+). Biphenyl (Ph-Ph) was formed via the radical chain autoxidation of BPh3 by O2. The induction period of the autocatalytic radical chain reactions was shortened by addition of a catalytic amount of [(TMC)Fe(IV)(O)](2+), whereas addition of a catalytic amount of ferrocene that can reduce [(TMC)Fe(IV)(O)](2+) resulted in elongation of the induction period. Radical chain autoxidation of BPh4(-) by O2 also occurred in the presence of Sc(OTf)3 without [(TMC)Fe(IV)(O)](2+), initiating the autocatalytic oxidation of [(TMC)Fe(II)](2+) with O2 and BPh4(-) to yield [(TMC)Fe(IV)(O)](2+). Thus, the general view for formation of non-heme iron(IV)-oxo complexes via O2-binding iron species (e.g., Fe(III)(O2(•-))) without contribution of autocatalytic radical chain reactions should be viewed with caution.

Isolation and stable nitrogen isotope analysis of ammonium ions in ammonium nitrate prills using sodium tetraphenylborate.

RATIONALE: Because of the threat of bombings using improvised explosives containing ammonium nitrate (AN), law enforcement and intelligence communities have been interested in stable isotope techniques for tracking and discriminating AN sources. Separate analysis of the AN component ions ammonium and nitrate would add discriminatory power to these techniques. METHODS: Ammonium ions in dissolved AN solution were isolated from samples by precipitation using sodium tetraphenylborate solution. We tested the isolation of ammonium from nitrates using solutions of ammonium and nitrate salts with different (15)N/(14)N isotope ratios. Ammonium tetraphenylborate and AN were separately analyzed for their (15)N/(14)N isotope ratios using EA-ConFlo-IRMS, and the (15)N/(14)N isotope ratios of the nitrate ions were calculated using mass balance. Ammonium and nitrate nitrogen isotope ratios were plotted as two separate variables. RESULTS: Isolation of ammonium precipitate from solutions containing dissolved nitrates did not influence the nitrogen isotope ratios of test ammonium salts. A survey set of 42 AN samples showed that the ammonium and nitrate (15)N/(14)N isotope ratios were not significantly correlated, and the paired mean differences were not statistically significant. Both ammonium and nitrate were depleted in (15)N relative to their theoretical atmospheric sources. CONCLUSIONS: Isolation of the ammonium ion from AN adds another dimension for the discrimination of forensic AN samples. This technique using sodium tetraphenylborate is robust and does not require specialized equipment. Our observations indicated that ammonium nitrogen and nitrate nitrogen have independent sources of isotopic variation.

A novel coated platinum electrode for oseltamivir determination in pharmaceuticals.

New coated platinum selective electrodes have been prepared and used for the determination of oseltamivir phosphate (OSL) in bulk drug solutions and in pharmaceutical preparations. Electrodes were using plasticized PVC membranes doped with ion-pair complexes based on drug-phosphomolybdate and drug-tetraphenylborate as electroactive materials. The influence of membrane composition (plasticizers and ion-pair complexes) has been investigated. Optimum performance was obtained for two polymeric membranes: PVC:o-NPPE:OSL-TPB in the ratio of 30:68:2 (%, w:w:w) and PVC:DPP:OSL-PMA in the ratio of 30:68:2 (%, w:w:w). The electrodes exhibited linear responses over large concentration ranges (1.0×10(-5)-1.0×10(-2) and 5.0×10(-5)-5.0×10(-2)M, respectively) with near-Nernstian responses (58.9 and 57.3mV/decade, respectively). The selectivity coefficients indicated good selectivity for OSL drug over a large number of organic compounds and some inorganic cations. The proposed electrodes were successfully applied to the determination of OSL in raw material and in pharmaceutical formulations. The results were validated by comparison with a capillary electrophoresis method.

Determination of ultra trace amounts of copper by a multi-injection technique of electrothermal atomic absorption spectrometry after using solid-phase extraction.

A new method using a multi-injection technique combined with SPE was developed for the determination of copper (Cu) in environmental samples. The method is based on SPE of copper ions on naphthalene as its 2-(5-bromo-2-pyridylazo)- 5-diethylaminophenol (5-Br-PADAP)-ammonium tetraphenylborate complex, in the pH range 6.0-9.5, and determined by electrothermal atomic absorption spectrometry. No chemical modifier is required in the graphite furnace. The detection limit can be reduced to 1.5 ng/L using an injection volume of 25.0 µL (five 5.0 µL) without interference by the matrixes. The optimum pyrolysis and atomization temperatures were 500 and 2200°C, respectively, for the concentrated solution of Cu. The sensitivity for 1% absorption was 2.6 pg Cu. Eight replicate determinations for 0.1 µg Cu in 5.0mL dimethylformamide gave an RSD of 2.3% for a single injection and 2.7% for a multi-injection. The procedure was validated with certified reference materials and successfully applied to the determination of copper in water and plant samples.

Reduction of thrombogenicity of PVC-based sodium selective membrane electrodes using heparin-modified chitosan.

Heparin-modified chitosan (H-chitosan) membrane was utilized to enhance biocompatibility of sodium selective membrane electrode based on the highly thrombogenic polyvinyl chloride (PVC). Sodium ion sensing film was prepared using PVC, sodium ionophore-X, potassium tetrakis(chlorophenyl)-borate, and o-nitrophenyloctylether. The PVC-based sensing film was sandwiched to chitosan or H-chitosan to prevent platelet adhesion on the surface of PVC. Potentiometric response characteristics of PVC-chitosan and PVC-H-chitosan membrane electrodes were found to be comparable to that of a control PVC based sodium-selective electrode. This indicates that chitosan and H-chitosan layers do not alter the response behaviour of the PVC-based sensing film. Biocompatibility of H-chitosan was confirmed by in vitro platelet adhesion study. The platelet adhesion investigations indicated that H-chitosan film is less thrombogenic compared to PVC, which could result in enhancement of biocompatibility of sodium selective membrane electrodes based on PVC, while maintaining the overall electrochemical performance of the PVC-based sensing film.