Working Concentration Range Research Articles

Construction and performance characteristics of new ion selective electrodes based on carbon nanotubes for determination of meclofenoxate hydrochloride

This work offers construction and comparative evaluation the performance characteristics of conventional polymer (I), carbon paste (II) and carbon nanotubes chemically modified carbon paste ion selective electrodes (III) for meclofenoxate hydrochloride are described. These electrodes depend mainly on the incorporation of the ion pair of meclofenoxate hydrochloride with phosphomolybdic acid (PMA) or phosphotungestic acid (PTA). They showed near Nernestian responses over usable concentration range 1.0×10−5 to 1.0×10−2M with slopes in the range 55.15–59.74mV(concentrationdecade)−1. These developed electrodes were fully characterized in terms of their composition, response time, working concentration range, life span, usable pH and temperature range. The electrodes showed a very good selectivity for Meclo with respect to a large number of inorganic cations, sugars and in the presence of the degradation product of the drug (p-chloro phenoxy acetic acid). The standard additions method was applied to the determination of MecloCl in pure solution, pharmaceutical preparations and biological samples. Dissolution testing was also applied using the proposed sensors.

Determination of ethylene glycol dinitrate in dynamites using HPLC: Application to the plastic explosive Goma-2 ECO

In this study, a sequential extraction method using water and methanol to recover ethylene glycol dinitrate or nitroglycol (EGDN) contained in Goma-2 ECO dynamite was developed. After, an HPLC method was used for the determination of EGDN in the two extracted phases. The analytical method was validated by evaluating its selectivity, sensitivity, linearity, and linear working concentration range, limit of detection and quantitation, precision (as repeatability and intermediate precision), accuracy, and robustness, providing appropriate values (i.e. RSD values for precision about 6% and accuracy about 100%). Finally, the EGDN content of a sample of the Goma-2-ECO dynamite was determined obtaining a concentration of 30.29%, which is in accordance with the manufacturer's specifications for this dynamite (25.7-31.4%).

Polyvinyl chloride-based 18-crown-6, dibenzo18-crown-6 and calix-[6]-arene zinc(II)-potentiometric sensors

Polyvinyl chloride (PVC) based membranes of 18-crown-6 (18C6), dibenzo 18-crowen-6 (DB18C6) and calix[6]arene (CAX), as ionophores, with dioctylphenylphosphonate (DOPP), bis(ethylhexyl)sebacate (DOS) dioctyl phthalate (DOP), 2-nitrophenyloctylether (o-NPOE) and didecylphthalate (DDP) as plasticizing solvent mediators are prepared and constructed for the determination of Zn(II). Of the 15 membranes constructed, only the PVC based membranes of DB18C6 and 18C6 ionophores with DOPP, as plasticizer, in the ratio (w/w) PVC:ionophore:DOPP (60:2:120) give the best results in terms of working concentration range (1.0×10−5–1.0×10−1M) with a Nernstian slope of 29.0mV/decade of activity for membrane composed of DOPP+DB18C6(1a) and (1.0×10−5–1.0×10−1M) with a Nernstian slope of 30.0mV/decade of activity for membrane composed of DOPP+18C6(1b). The usable pH range of the sensors is 3.0–8.0, beyond which a drift in potential is observed. The response time of the sensors is ⩽15s with a lifetime of 2months during which they can be used without any measurable divergence. The selectivity coefficient values indicate that the electrode is highly selective for Zn2+ over a number of other cations except Pb2+ and Ag+. The electrodes have successfully been used to determine Zn(II) in real alloys and standard samples with a precision as relative standard deviation (RSD) <2% for each of the cited electrodes. The results obtained by the proposed ISEs are in good agreement with the results obtained by direct flame AAS method.

Glucose detection with surface plasmon resonance spectroscopy and molecularly imprinted hydrogel coatings

Molecularly imprinted hydrogel membranes were developed and evaluated for detection of small analytes via surface plasmon resonance spectroscopy. Imprinting of glucose phosphate barium salt into a poly(allylamine hydrochloride) network covalently bound to gold surfaces yielded a selective sensor for glucose. Optimization of relative amounts of chemicals used for preparation of the hydrogel was performed to obtain highest sensitivity. Addition of gold nanoparticles into the hydrogel matrix significantly amplified its response and sensitivity due to the impact of gold nanoparticles on the refractive index of the sensing layer. Evaluation of its selectivity showed that the sensor displayed preferential recognition to glucose compared to structurally related sugars in addition to being unaffected by phosphate as well as compounds containing amine groups, like creatinine. The detection limit of glucose in deionized water was calculated to be 0.02mg/mL. The developed sensor was finally exposed to human urine spiked with glucose illustrating the coating's ability to re-bind the analyte in complex matrices. While the working concentration range in water was determined to be suitable for glucose monitoring in diabetic individuals at physiological levels, the detection in urine was determined to be 0.12mg/mL. The decreased performance in urine provided an initial perspective on the difficulties associated with measurements in complex media.

Novel monohydrogenphosphate ion-selective polymeric membrane sensor based on phenyl urea substituted calix[4]arene

A highly selective and sensitive PVC membrane, containing phenylurea substituted calix[4]arene was found to be a suitable ionophore for monohydrogen phosphate (HPO42−) ions that exhibited a Nernstian response (with a slope of −29.4±0.3mVdecade−1). The working concentration range of the electrode was 6.0×10−8–1.0×10−1molL−1 with a detection limit of 2.0×10−8molL−1. The response time of the sensor in the whole concentration range is very short (<8s), with a considerable lifetime of at least 15 weeks. The sensor possesses the advantages of short response time, low detection limit and a high selectivity towards a large number of inorganic anions. The developed sensor was used as an indicator electrode in potentiometric titration of monohydrogen phosphate ion with barium chloride. The proposed sensor was successfully applied for the direct determination of monohydrogen phosphate in real life samples.

Surfactant modified ZSM-5 zeolite as an active component of membrane electrode towards thiocyanate

A selective membrane electrode based on surfactant modified zeolite showed very good selectivity for thiocyanate anions over a wide variety of common inorganic and organic anions. The sensor displayed a near Nernstian slope of −58.9±0.9mV per decade of the thiocyanate concentration. The working concentration range of the electrode was 1.00×10−6 to 1.10×10−1M with a detection limit of 8.3×10−7M thiocyanate. The response of the sensor to thiocyanate remained constant in the pH range of 2.0–10.1. The best performance was obtained with a membrane composition in the ratio of 25.5% PVC, 64.5% dioctyl phthalate and 10% surfactant modified zeolite ZSM-5. The sensor was highly selective for thiocyanate over a wide variety of other anions and exhibited a rapid response time of <10s over a period of 2months with good reproducibility. Thus, this novel sensor may be applied as an indicator electrode in the argentometric titration of thiocyanate.

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd 2+ was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd 2+. The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg −1) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4 ± 0.6 mV decade −1 of activity for Cd 2+ ions and a working concentration range of 1.6 × 10 −6–1.0 × 10 −2 M. The sensor has a fast response time of 10 s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0–9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd 2+ from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.

Enhancement of sensitivity of glucose sensors from alizarin–boronic acid adducts in aqueous micelles

The sensitivity of glucose sensors fabricated from alizarin–boronic acid adducts was improved by an assistance of surfactants. Basically, Alizarin Red S (ARS) is not a fluorescence active compound. However, the fluorescence emission can be observed when forming an adduct with 2-formylphenyl boronic acid (2-FPBA). Using displacement strategy, the fluorescence intensity of the ARS/2-FPBA adduct decreased as a linear function of the glucose concentration. A simple and sensitive method was developed by incorporating the ARS/2-FPBA adduct in the hydrophobic core of micelles. Various parameters that could possibly affect the fluorescence quenching ability including solution pH, concentration of 2-FPBA, types of surfactants and concentrations of surfactants were investigated. The optimum condition for the determination of glucose by the proposed assay was 2 mM cetyltrimethylammonium bromide (CTAB) in 0.05 M phosphate buffer pH 7.0. The fluorescence intensity of the ARS/2-FPBA adduct in the presence of CTAB was remarkably 13 times higher than that in the buffer solution. Moreover, the linear working concentration range was found to be 1.2–80 mM, and the calibration sensitivity was 14 times higher than that from the system containing only buffer solution.

A novel Mg(II)-selective sensor based on 5,10,15,20-tetrakis(2-furyl)-21,23-dithiaporphyrin as an electroactive material

A novel poly(vinyl chloride) based membrane containing 5,10,15,20-tetrakis(2-furyl)-21,23-dithiaporphyrin (I) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and nitrophenyl octyl ether (NPOE) in the ratio 10:100:1:150 (I:NPOE:NaTPB:PVC) (w/w) was used to fabricate a Mg(II)-selective sensor. The developed sensor exhibits a wide working concentration range of 9.2×10−6–1.0×10−1M, with a Nernstian slope of 30.0±1.0mV/decade of activity and the response time of 15s. This sensor shows a detection limit of 8.0×10−6M. Its potential response remains unaffected of pH in the range 4.0–8.4, and the cell assembly can be successfully used in partially non-aqueous medium (up to 10% v/v) without any significant change in the slope or working concentration range. The sensor has a lifetime of about 8weeks and exhibits excellent selectivity over a number of mono-, bi-, and tri-valent cations including alkali, alkaline earth metal, heavy and transition metal ions. It has also been used for the determination of magnesium ion concentration in real samples.

Fabrication of novel coated graphite electrodes for the selective nano-level determination of Cd 2+ ions in biological and environmental samples

Novel cadmium selective coated graphite electrodes were prepared using three different ionophores N 1, N 2-dicyanoethyl-N 1, N 2-bis(pyridin-2-ylmethyl)benzene-1, 2-diamine [L 1], N 1, N 2-dicyanoethyl-N 1, N 2-bis(thiophen-2-ylmethyl) benzene-1, 2-diamine [L 2] and N 1, N 2-dicyanoethyl-N 1, N 2-bis(furan-2-ylmethyl)benzene-1, 2-diamine [L 3], and their potentiometric characteristics were determined. Membranes having different compositions of poly(vinylchloride) (PVC), the plasticizer o-nitrophenyloctylether ( o-NPOE), sodium tetraphenylborate (NaTPB) as an anionic additive and ionophores were coated onto the graphite surface. The potential response measurements showed that the best performance was exhibited by the electrodes with membranes having the composition L 1: o-NPOE:NaTPB:PVC as 4:51:2.5:42.5 (wt.%), L 2: o-NPOE:NaTPB:PVC as 3:52.5:1.5:43 (wt.%) and L 3: o-NPOE:NaTPB:PVC as 7:49:3.5:40.5 (wt.%). These electrodes had the widest working concentration range, Nernstian slope and fast response times of 12 s, 7 s and 17 s for L 1, L 2 and L 3, respectively. The selectivity studies showed that these electrodes have higher selectivity towards Cd 2+ over a large number of cations and could tolerate up to 20 vol.% non-aqueous impurities. Furthermore, the electrodes generated constant potentials in the pH range 2.0–8.0, with a shelf life of approximately four to six weeks. The high selectivity of these electrodes permits their use in the detection of the Cd 2+ content in some medicinal plants, soil and industrial wastewater samples. The electrodes could also be used as an indicator electrode in the potentiometric titration of Cd 2+ with EDTA.

Solid-state Cu (II) ion-selective electrode based on polyaniline-conducting polymer film doped with copper carmoisine dye complex

A pencil graphite electrode coated by copper (II)–carmoisine dye complex in polyaniline (emeraldine base form) matrix (termed as PGE/PA/Cu-Car) was prepared and used as copper ion-selective electrode. The introduced electrode was found to have high selectivity toward copper ion (II) and exhibited wide working concentration range, low response time, and good shelf life. The sensor electrode showed a linear Nernstian response over the range of 5.0 × 10−6 to 1.0 × 10−1 M with a slope of 29.7 ± 1 mV per decade change in concentration. A detection limit of 2.0 × 10−6 M was obtained. The optimum pH working range of the electrode was found to be 4.0–7.0.

Stress degradation studies on cefpodoxime proxetil and development of a validated stability-indicating HPLC method

Summary A simple, sensitive, specific, precise, and stability-indicating high-performance liquid chromatographic (HPLC) method for determination of cefpodoxime proxetil as bulk drug and as pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. An isocratic separation was achieved using a Phenomenex Luna C18 (250 mm × 4.6 mm i.d., 5 μm particle size) column with a flow rate of 1 mL min−1 and a UV detector to monitor the eluate at 254 nm. The mobile phase consisted of acetonitrile and 50 mM ammonium acetate pH 6 (pH was adjusted with o-phosphoric acid) in the ratio of 45:55 (υ/υ). The linear regression analysis data for the calibration plots showed good linear relationship with r2 = 0.9998 in the working concentration range of 1–80 μg mL−1. The LOD and LOQ were 0.17 and 0.5 μg mL−1, respectively. The drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment, and photodegradation. The standard drug peaks we...

Determination of thiocyanate ions at nanolevel in real samples using coated graphite electrode based on synthesised macrocyclic Zn(II) complex

The electrode characteristics and selectivities of PVC-based thiocyanate selective polymeric membrane electrode (PME) incorporating the newly synthesized zinc complex of 6,7:14,15-Bzo(2)-10,11-(4-methylbenzene)-[15]-6,8,12,14-tetraene-9,12-N(2)-1,5-O(2) (I(1)) and zinc complex of 6,7:14,15-Bzo(2)-10,11-(4-methylbenzene)-[15]-6,14-diene-9,12-dimethylacrylate-9,12-N(2)-1,5-O(2) (I(2)) are reported here. The best response was observed with the membrane having a composition of I(2):PVC:o-NPOE:HTAB in the ratio of 6:33:59:2 (w/w; milligram). This electrode exhibited Nernstian slope for thiocyanate ions over working concentration range of 4.4 × 10(-7) to 1.0 × 10(-2) mol L(-1) with detection limit of 2.2 × 10(-7) mol L(-1). The performance of this electrode was compared with coated graphite electrode (CGE), which showed better response characteristics w.r.t Nernstian slope 59.0 ± 0.2 mV decade(-1) activity, wide concentration range of 8.9 × 10(-8) to 1.0 × 10(-2) mol L(-1) and detection limit of 6.7 × 10(-8) mol L(-1). The response time for CGE and PME was found to be 8 and 10 s, respectively. The proposed electrode (CGE) was successfully applied to direct determination of thiocyanate in biological and environmental samples and also as indicator electrode in potentiometric titration of SCN(-) ion.

Simultaneous quantification of diterpenoids in Premna integrifolia using a validated HPTLC method

A sensitive, selective and robust densitometric high-performance thin layer chromatographic method was developed and validated for the determination of diterpenoids in the root bark of Premna integrifolia. Diterpenoids 1β,3α,8β-trihydroxy-pimara-15-ene (A), 6α,11,12,16-tetrahydroxy-7-oxo-abieta-8,11,13-triene (B) and 2α,19-dihydroxy-pimara-7,15-diene (C) were used as chemical markers for the standardization of P. integrifolia plant extracts. The separation was performed on silica gel 60F(254) high-performance thin layer chromatography plates using hexane/acetone/ethylacetate (60:20:20 v/v) as mobile phase. The quantitation of diterpenoids was carried out using densitometric reflection/absorption mode at 475 nm after post-chromatographic derivatization using vanillin-sulfuric acid reagent. A precise and accurate quantification can be performed for compounds A, B and C in the linear working concentration range of 1-10 μg/spot with good correlations (r(2) =0.9985, 0.9996 and 0.9992, respectively). The method was validated for peak purity, precision, robustness, limit of detection (LOD) and quantitation (LOQ) etc., as per the International Conference on Harmonization (ICH) guidelines. Specificity of quantitation was confirmed using retention factor (R(f)) and spectra correlation of markers in standard and sample tracks. The method reported here is simple and reproducible which may be applied for quantitative analysis of above diterpenoids in the root bark of P. integrifolia.

Pico molar assay of riboflavin in human urine using voltammetry

Using a new type of DNA and carbon nano tube (CNT) mixed paste electrode using cyclic and square wave anodic stripping voltammetric (SWASV) methods, this study presents an assay of riboflavin (RF) under optimum conditions. Results of the experiment yielded a low working concentration range of nanograms with 1–10 and 10–170ngL−1 and 5–105μgL−1, at an accumulation time of 80s in a 0.1M H3PO4 electrolyte solution. A relative standard deviation of 30μgL−1 was observed at an accuracy level of 0.1164% (n=15) under optimum conditions. The detection limit (S/N) was pegged at 0.2ngL−1 (5.31×10−13molL−1 RF). The proposed method was successfully applied to an actual human urine and drug sample, and can be applied to assays of other biological samples.

Patterning of Quantum Dot Bioconjugates via Particle Lithography

We present a simple technique to fabricate hexagonally ordered quantum dot bioconjugate (QDBC) dot arrays on glass coverslips. We used particle lithography to create periodic holes in a layer of methoxy-poly(ethylene glycol)-silane and then adsorbed QDBCs into the holes. To demonstrate the versatility of this technique, we made separate periodic arrays of quantum dots (QDs) conjugated to three different biologically important molecules: biotin, streptavidin, and anti-mouse IgG. The diameters of the regions where the QDBCs adsorbed were 500-600 nm and independent of the QDBC patterned. The site density of the QDBCs in the patterned holes could be varied by simply adjusting the coating concentration of the QDBC solution. We demonstrate the applicability of these substrates by designing a QDBC-based binding assay with a working concentration range of several orders of magnitude and a sub-picomolar detection limit.

Biotransformation and biomonitoring of phenylurea herbicide diuron

A Gram-positive, Micrococcus sp. strain PS-1 isolated from diuron storage site was studied for its capability of biotransformation of phenylurea herbicide diuron to a secondary metabolite, 1-(3,4-dichlorophenyl)urea (DCPU) for bioconjugation and antibody development applications. The metabolite formed associated with profound changes in bacterial cell morphology demonstrated increase in the degradation kinetics of diuron in presence of small quantity of a surfactant. The synthesized metabolite identified by chromatographic and mass spectrometry techniques was conjugated with carrier protein, and used as an immunogen for antibodies production. The generated antibody was highly specific, demonstrating excellent sensitivity against diuron. The antibody was used as receptor molecules in standard fluorescence immunoassay (FIA) format showing detection limit of 0.01 ng/mL in the optimum working concentration range of diuron with good signal precision (∼2%). The study presented first time the degradation pathway of herbicide by specific microorganism to synthesize hapten for bioconjugation and immunoassay development.

A novel ion selective sensor for promethium determination

This is a first promethium 145 ion-selective sensor based on the comparative study of two Schiff base ligands (X 1 and X 2) as neutral ionophores. Effect of various plasticizers: 2-nitrophenyloctylether ( o-NPOE), dibutyl phosphonate (DBP), dioctylphthalate (DOP), tri-(2-ethylhexyl) phosphate (TEHP), dibutyl butylphosphonate (DBBP), chloronaphthalene (CN) and anion excluders: potassium tetrakis (p-chloropheny1) borate (KTpClPB), sodiumtetraphenylborate (NaTPB) and oleic acid (OA) have been studied. The membrane with a composition of ionophore (X 1/X 2):KTpClPB:PVC: o-NPOE (w/w, %) in the ratio of 5:5:30:60 exhibited best performance. The best responsive membrane sensors (8 and 21) exhibited working concentration range of 4.5 × 10 −7–1.0 × 10 −2 M and 3.5 × 10 −6–1.0 × 10 −2 M with a detection limits of 3.2 × 10 −7 M and 2.3 × 10 −6 M and Nernstian slopes of 20.0 ± 0.5, 19.5 ± 0.5 mV decade −1 of activity, respectively. The sensor no. 8 works satisfactorily in partially non-aqueous media up to 10% (v/v) content of methanol, ethanol and acetonitrile. Analytical application of the proposed sensor has been demonstrated in determination of promethium (III) ions in spiked water samples.

Optimization of tramadol–PVC membrane electrodes using miscellaneous plasticizers and ion-pair complexes

Effect of the ISE membrane composition on the characteristics of the tramadol–PVC-electrodes has been investigated. The parameters studied include the effect of the plasticizer and the effect of the ion-pair complex. The plasticizers used were 2-nitrophenyl octyl ether (2-NPOE), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tris(2-ethylhexyl) phosphate (TEPh), dioctyl sebacate (DOS), tributyl phosphate (TBPh) and dibutyl butyl phosphonate (DBBPh) and the ion-pair complexes were tramadolium–silicotungstate (TD–ST), silicomolybdate (TD–SM). These electrodes were fully characterized in terms of composition, life span, usable pH range and working concentration range. The results showed that the best combination was TD–ST as the ion-pair complex and DBP as the plasticizer that produced the electrode with favorable characteristics. Another electrode using TD–SM was tested and produced close results. The present electrodes show clear discrimination of tramadol hydrochloride from several inorganic, organic ions, sugars and some common drug excipients. The sensors were applied for determination of tramadol hydrochloride in urine, milk and pharmaceutical preparations using potentiometric determination, standard addition and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay.

Fluoroimmunoassay based on suppression of fluorescence self-quenching for ultra-sensitive detection of herbicide diuron

A highly sensitive heterogeneous fluoroimmunoassay has been developed for monitoring phenylurea herbicide diuron on the basis of suppression of fluorescence self-quenching. Specific antibody against diuron was produced and labeled with rhodamine isothiocyanate at different molar ratios and used as tracer in the developed immunoassay. The analytical sensitivity of immunoassay was enhanced by changing the microenvironment of fluorescence label with glycerin solution after the completion of immunoassay. Enhancer treatment on developed immunoassay showed improvement of fluorescence signal intensity by approximately 4-folds with higher stability compared with the signal determined without enhancer treatment of the wells. The immunoassay has a detection limit of 0.1 ng mL −1 with good signal precision (∼2%) in the optimum working concentration range between 0.01 and 100 ng mL −1 of diuron. In addition, the use of enhancer improved the stability of fluorescence signal by suppression of self-quenching of fluorescence signal. The proposed method has been applied satisfactorily for the ultra-sensitive detection of herbicide diuron in samples.