Flow injection chemiluminescence sensor based on core–shell magnetic molecularly imprinted nanoparticles for determination of sulfadiazine

A novel flow injection chemiluminescence (FI-CL) sensor for determination of sulfadiazine (SDZ) using core–shell magnetic molecularly imprinted polymers (MMIPs) as recognition element is developed. Briefly, a hydrophilic MMIPs layer was produced at the surface of Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. And it provided the MMIPs with excellent adsorption capacity and rapid adsorption rate due to the imprinted sites mostly situated on the surface of MMIPs. Then the prepared SDZ-MMIPs were packed into flow cell to establish a novel FI-CL sensor. The sensor provided a wide linear range for SDZ of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.54 × 10⁻⁷ mol L⁻¹. And the relative standard deviation (RSD) for the determination of 1.0 × 10⁻⁶ mol L⁻¹ SDZ was 2.56% (n = 11). The proposed method was applied to determine SDZ in urine samples and satisfactory results were obtained.     

A novel molecularly imprinted sensor for selectively probing imipramine created on ITO electrodes modified by Au nanoparticles

A sensitive molecularly imprinted electrochemical sensor was created for selective detection of a tricyclic antidepressant imipramine by combination of Au nanoparticles (Au-NPs) with a thin molecularly imprinted film. The sensor was fabricated onto the indium tin oxide (ITO) electrode via stepwise modification of Au-NPs by self-assembly and a thin film of molecularly imprinted polymers (MIPs) via sol-gel technology. It was observed that the molecularly imprinted film displayed excellent selectivity towards the target molecule imipramine. Meanwhile, the introduced Au-NPs exhibited noticeable catalytic activities towards imipramine oxidation, which remarkably enhanced the sensitivity of the imprinted film. Due to such combination, the as-prepared sensor responded quickly to imipramine, within only 1 min of incubation. The differential voltammetric anodic peak current was linear to the logarithm of imipramine concentration in the range from 5.0 × 10⁻⁶ to 1.0 × 10⁻³ mol L⁻¹, and the detection limits obtained was 1.0 × 10⁻⁹ mol L⁻¹. This method proposed was successfully applied to the determination of imipramine in drug tablets, and proven to be reliable compared with conventional UV method. These results reveal that such a sensor fulfills the selectivity, sensitivity, speed and simplicity requirements for imipramine detection, and provides possibilities of clinical application in physiological fluids.     

Electrochemical determination of L-phenylalanine at polyaniline modified carbon electrode based on β-cyclodextrin incorporated carbon nanotube composite material and imprinted sol-gel film

A sensitive and selective electrochemical sensor based on a polyaniline modified carbon electrode for the determination of l-phenylalanine has been proposed by utilizing β-cyclodextrin (β-CD) incorporated multi-walled carbon nanotube (MWNT) and imprinted sol-gel film. The electrochemical behavior of the sensor towards l-phenylalanine was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric i-t curve. The surface morphologies of layer-by-layer assembly electrodes were displayed by scanning electron microscope (SEM). The response mechanism of the imprinted sensor for l-phenylalanine was based on the inclusion interaction of β-CD and molecular recognition capacity of the imprinted film for l-phenylalanine. A linear calibration plot was obtained covering the concentration range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. With excellent sensitivity, selectivity, stability, reproducibility and recovery, the electrochemical imprinted sensor was used to detect l-phenylalanine in blood plasma samples successfully.     

Rapid simultaneous analysis of 1-hydroxypyrene, 2-hydroxyfluorene, 9-hydroxyphenanthrene, 1- and 2-naphthol in urine by first derivative synchronous fluorescence spectrometry using Tween-20 as a sensitizer

A novel method of first derivative synchronous fluorescence was developed for the rapid simultaneous analysis of trace 1-hydroxypyrene (1-OHP), 1-naphthol (1-NAP), 2-naphthol (2-NAP), 9-hydroxyphenanthrene (9-OHPe) and 2-hydroxyfluorene (2-OHFlu) in human urine. Only one single scan was needed for quantitative determination of five compounds simultaneously when Δλ = 10 nm was chosen. In the optimal experimental conditions, there was a linear relationship between the fluorescence intensity and the concentration of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in the range of 1.75 × 10⁻⁹ to 4.50 × 10⁻⁶ mol L⁻¹, 3.64 × 10⁻⁸ to 2.20 × 10⁻⁴ mol L⁻¹, 8.18 × 10⁻⁹ to 1.20 × 10⁻⁴ mol L⁻¹, 3.26 × 10⁻⁹ to 8.50 × 10⁻⁵ mol L⁻¹ and 4.88 × 10⁻⁹ to 5.50 × 10⁻⁶ mol L⁻¹, respectively. The limits of detection (LOD) were found to be 5.25 × 10⁻¹⁰ mol L⁻¹ for 1-OHP, 1.10 × 10⁻⁸ mol L⁻¹ for 1-NAP, 2.46 × 10⁻⁹ mol L⁻¹ for 2-NAP, 9.77 × 10⁻¹⁰ mol L⁻¹ for 9-OHPe and 1.46 × 10⁻⁹ mol L⁻¹ for 2-OHFlu. The proposed method is reliable, selective and sensitive, and has been used successfully in the determination of traces of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in human urine samples, whose results were in good agreement with those gained by the HPLC method.     

Determination of brominated phenols in water samples by on-line coupled isotachophoresis with capillary zone electrophoresis

A method for determination of nine brominated phenols as environmental risk compounds was developed by on-line coupled capillary isotachophoresis and capillary zone electrophoresis (ITP–CZE). For ITP step, 1 × 10⁻² mol L⁻¹ hydrochloric acid with 3 × 10⁻² mol L⁻¹ ammediol pH 9.1 was used as the leading electrolyte, and 3 × 10⁻² mol L⁻¹ β-alanine with 2 × 10⁻² mol L⁻¹ sodium hydroxide pH 10.05 was used as the terminating electrolyte. As the background electrolyte for CZE separation, 2.5 × 10⁻² mol L⁻¹ β-alanine with 2.5 × 10⁻² mol L⁻¹ lysine pH 9.6 was used. All electrolytes contained 0.05% or 0.1% (m/v) hydroxyethylcellulose to suppress the electroosmotic flow. UV detection at wavelength 220 nm was used. Detection limits in order of tens of nmol L⁻¹ were achieved. Good repeatability of migration times (less than 0.33% RSD) and good repeatability of peak areas (less than 7.19% RSD) at concentration level 5 × 10⁻⁸ mol L⁻¹ were observed. Developed ITP–CZE method was applied to determination of brominated phenols in spiked tap and river water samples.     

A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

Localized surface plasmon resonance sensor for simultaneous kinetic determination of peroxyacetic acid and hydrogen peroxide

A new sensor for simultaneous determination of peroxyacetic acid and hydrogen peroxide using silver nanoparticles (Ag-NPs) as a chromogenic reagent is introduced. The silver nanoparticles have the catalytic ability for the decomposition of peroxyacetic acid and hydrogen peroxide; then the decomposition of them induces the degradation of silver nanoparticles. Hence, a remarkable change in the localized surface plasmon resonance absorbance strength could be observed. Spectra-kinetic approach and artificial neural network was applied for the simultaneous determination of peroxyacetic acid and hydrogen peroxide. Linear calibration graphs were obtained in the concentration range of (8.20 × 10⁻⁵ to 2.00 × 10⁻³ mol L⁻¹) for peroxyacetic acid and (2.00 × 10⁻⁵ to 4.80 × 10⁻³ mol L⁻¹) for hydrogen peroxide. The analytical performance of this sensor has been evaluated for the detection of simultaneous determination of peroxyacetic acid and hydrogen peroxide in real samples.     

Quantitative determination of zinc in milkvetch by anodic stripping voltammetry with bismuth film electrodes

Bismuth film electrode (BiFE) was shown to be an attractive alternative to common mercury film electrode (MFE) for anodic stripping voltammetric measurements. In this study, bismuth film, that was in situ deposited onto glassy carbon electrode, was used to detect zinc content of milkvetch, used in traditional Chinese medicine. Variables affecting the response have been evaluated and optimized. Experimental results showed a high response, with a good linearity (between 0.5 × 10⁻⁶ mol L⁻¹ and 3 × 10⁻⁶ mol L⁻¹) a good precision (R.S.D. = 3.58%) and a low detection limit (9.6 × 10⁻⁹ mol L⁻¹ with a 120 s anodic). The anodic stripping performance makes the bismuth film electrode very desirable for measurements of trace nutritive element zinc in milkvetch and should impart possible restrictions on the use of mercury electrode.     

A novel high selective and sensitive para-nitrophenol voltammetric sensor, based on a molecularly imprinted polymer-carbon paste electrode

By using a molecularly imprinted polymer (MIP) as a recognition element, the design and construction of a high selective voltammetric sensor for para-nitrophenol was formed. Para-nitrophenol selective MIP and a non-imprinted polymer (NIP) were synthesized, and then used for carbon paste (CP) electrode preparation. The MIP-CP electrode showed greater recognition ability in comparison to the NIP-CP. It was shown that electrode washing after para-nitrophenol extraction led to enhanced selectivity, without noticeably decreasing the sensitivity. Some parameters affecting sensor response were optimized and a calibration curve was plotted. A dynamic linear range of 8 × 10⁻⁹ to 5 × 10⁻⁶ mol L⁻¹ was obtained. The detection limit of the sensor was calculated as 3 × 10⁻⁹ mol L⁻¹. Thus, this sensor was used successfully for the para-nitrophenol determination in different water samples.     

Preliminary evaluation of monolithic column high-performance liquid chromatography with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection for the determination of quetiapine in human body fluids

High-performance liquid chromatography (HPLC) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection methodology is reported for the determination of the atypical antipsychotic drug quetiapine and the observation of its major active and inactive metabolites in human urine and serum. The method uses a monolithic chromatographic column allowing high flow rates of 3 mL min⁻¹ enabling rapid quantification. Flow injection analysis (FIA) with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection and HPLC time of flight mass spectrometry (TOF-MS) were used for the determination of quetiapine in a pharmaceutical preparation to establish its suitability as a calibration standard. The limit of detection achieved with FIA was 2 × 10⁻¹¹ mol L⁻¹ in simple aqueous solution. The limits of detection achieved with HPLC were 7 × 10⁻⁸ and 2 × 10⁻¹⁰ mol L⁻¹ in urine and serum, respectively. The calibration range for FIA was between 5 × 10⁻⁹ and 1 × 10⁻⁶ mol L⁻¹. The calibration ranges for HPLC were between 1 × 10⁻⁷-1 × 10⁻⁴ and 1 × 10⁻⁸-1 × 10⁻⁴ mol L⁻¹ in urine and serum, respectively. The quetiapine concentrations in patient samples were found to be 3 × 10⁻⁶ mol L⁻¹ in urine and 7 × 10⁻⁷ mol L⁻¹ in serum. Without the need for preconcentration, the HPLC detection limits compared favourably with those in previously published methodologies. The metabolites were identified using HPLC-TOF-MS.     

An emphatic orthogonal signal correction-support vector machine method for the classification of tissue sections of endometrial carcinoma by near infrared spectroscopy

A sequential injection analysis (SIA) spectrophotometric method for determining tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC) in different sample matrices were described. The method was based on the reaction between tetracyclines and yttrium (III) in weak basic micellar medium, yielding the light yellow complexes, which were monitored at 390, 392 and 395 nm, respectively. A cationic surfactant, cetyltrimethylammonium bromide (CTAB) was used to obtain the micellar system. The linear ranges of calibration graphs were between 1.0 × 10⁻⁵ and 4 × 10⁻⁴ mol L⁻¹, respectively. The molar absorptivities were 5.24 × 10⁵, 4.98 × 10⁴ and 4.78 × 10⁴ L mol⁻¹ cm⁻¹. The detection limits (3σ) were between 4.9 × 10⁻⁶ and 7.8 × 10⁻⁶ mol L⁻¹ whereas the limit of quantitations (10σ) were between 1.63 × 10⁻⁵ and 2.60 × 10⁻⁵ mol L⁻¹ the interday and intraday precisions within a weak revealed as the relative standard deviations (R.S.D., n = 11) were less than 4%. The method was rapid with a sampling rate of over 60 samples h⁻¹ for the three drugs. The proposed method has been satisfactorily applied for the determination of tetracycline and its derivatives in pharmaceutical preparations together with their residues in milk and honey samples collected in Chiang Mai Province. The accuracy was found to be high as the Student's t-values were found to be less than the theoretical ones. The results were compared favorably with those obtained by the conventional spectrophotometric method.     

A novel dual-function molecularly imprinted polymer on CdTe/ZnS quantum dots for highly selective and sensitive determination of ractopamine

A novel dual-function material was synthesized by anchoring a molecularly imprinted polymer (MIP) layer on CdTe/ZnS quantum dots (QDs) using a sol–gel with surface imprinting. The material exhibited highly selective and sensitive determination of ractopamine (RAC) through spectrofluorometry and solid-phase extraction (SPE) coupled with high performance liquid chromatography (HPLC). A series of adsorption experiments revealed that the material showed high selectivity, good adsorption capacity and a fast mass transfer rate. Fluorescence from the MIP-coated QDs was more strongly quenched by RAC than that of the non-imprinted polymer, which indicated that the MIP-coated QDs acted as a fluorescence sensing material could recognize RAC. In addition, the MIP-coated QDs as a sorbent was also shown to be promising for SPE coupled with HPLC for the determination of trace RAC in feeding stuffs and pork samples. Under optimal conditions, the spectrofluorometry and SPE-HPLC methods using the MIP-coated QDs had linear ranges of 5.00 × 10⁻¹⁰–3.55 × 10⁻⁷ and 1.50 × 10⁻¹⁰–8.90 × 10⁻⁸ mol L⁻¹, respectively, with limits of detection of 1.47 × 10⁻¹⁰ and 8.30 × 10⁻¹¹ mol L⁻¹, the relative standard deviations for six repeat experiments of RAC (2.90 × 10⁻⁹ mol L⁻¹) were below 2.83% and 7.11%.     

Linear polyamines as carriers in thiocyanate-selective membrane electrodes

The polyamines, octyl-[2-(2-octylamino-ethylamino)-ethyl]-amine (L¹) and octyl-{2-[2-(2-octylamino-ethylamino)-ethylamino]-ethyl}-amine (L²), have been used as anion ionophores in PVC-based membrane ion-selective electrodes. Different electrodes were prepared containing L¹, or L², and o-nitrophenyl octyl ether (NPOE) or bis(2-ethylhexyl)sebacate (DOS) as plasticizers. The response of the electrodes was tested in two different buffers, HEPES-KOH (pH 7) and MES-KOH (pH 5.6). Electrodes containing L¹ and L² with NPOE (E1 and E2, respectively) showed a Nernstian response for thiocyanate with a good response time. The detection limit, linear range and slope for electrode E1 were 3.8 × 10⁻⁶ mol dm⁻³, 1 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −57.2 mV decade⁻¹ at pH 5.6 and 4.47 × 10⁻⁶ mol dm⁻³, 1.95 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −58.1 mV decade⁻¹ at pH 7.0. For electrode E2 the detection limit, linear range and slope found were 2.63 × 10⁻⁶ mol dm⁻³, 7.94 × 10⁻⁶ to 1 × 10⁻¹ mol dm⁻³ and −58.5 mV decade⁻¹ at pH 5.6 and 1.23 × 10⁻⁵ mol dm⁻³, 7.95 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³ and −46.0 mV decade⁻¹ at pH 7. In contrast, electrodes containing DOS as plasticizers gave only response at pH 5.6 (detection limit, linear range and slope at pH 5.6 were 3.16 × 10⁻⁵ mol dm⁻³, 1 × 10⁻⁴ to 1 × 10⁻¹ mol dm⁻³ and −52.6 mV decade⁻¹). Selectivity coefficients for different anions with respect to thiocyanate were calculated. The electrode E2 at pH 5.6 was also used for the determination of SCN⁻ by potentiometric titrations with Ag⁺ ions with good results. The electrode E2 was also used to determine concentrations of thiocyanate in biological samples.     

Tris(2,2'-bipyridyl)ruthenium(II)-Zirconia-Nafion composite modified electrode applied as solid-state electrochemiluminescence detector on electrophoretic microchip for detection of pharmaceuticals of tramadol, lidocaine and ofloxacin

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-Zirconia-Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)-ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy)₃²⁺ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy)₃²⁺ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N = 3) were 2.5 × 10⁻⁵ mol L⁻¹ for tramadol, 5.0 × 10⁻⁶ mol L⁻¹ for lidocaine, 1.0 × 10⁻⁵ mol L⁻¹ for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for tramadol, 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹ for lidocaine, and 1.0 × 10⁻⁵ to 2.5 × 10⁻³ mol L⁻¹ for ofloxacin, respectively.     

Ultrasensitive determination of silver ion based on synchronous fluorescence spectroscopy with nanoparticles

Based on the characteristics of synchronous fluorescence spectroscopy (SFS), a new method with high sensitivity and selectivity was developed for rapid determination of silver ion with functional cadmium sulphide (CdS) nanoparticles as a fluorescence probe. When Δλ (λ_em − λ_ex) = 215 nm, maximum synchronous fluorescence is produced at 304 nm. Under optimal conditions, functional cadmium sulphide displayed a calibration response for silver ion over a wide concentration range from 0.8 × 10⁻¹⁰ to 1.5 × 10⁻⁸ mol L⁻¹. The limit of detection was 0.4 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of seven replicate measurements for the lowest concentration (0.8 × 10⁻¹⁰ mol L⁻¹) was 2.8%. Compared with several fluorescence methods, the proposed method had a wider linear range and improved the sensitivity. Furthermore, the concentration dependence of the synchronous fluorescence intensity is effectively described by a Langmuir-type binding isotherm.     

Determination of uranium by adsorptive stripping voltammetry at a lead film electrode

An adsorptive stripping voltammetric procedure for the determination of U(VI) at an in situ plated lead film electrode is described. The U(VI) complex with cupferron was accumulated from an acetate buffer solution of pH 4.2 at the potential −0.65 V. The measurements were carried out from undeaerated solutions. The calibration graph for an accumulation time of 180 s was linear from 5 × 10⁻¹⁰ to 2 × 10⁻⁸ mol L⁻¹. The detection limit was 2 × 10⁻¹⁰ mol L⁻¹, the relative standard deviation for 2 × 10⁻⁸ mol L⁻¹ U(VI) was 4.3%. The proposed procedure was validated in the course of U(VI) determination in water certified reference materials.     

Study of the influence of silver nanoparticles on the second-order scattering and the fluorescence of the complexes of Tb(III) with quinolones and determination of the quinolones

Quinolones (Qs) can form the complex with Tb(III) ion, and the intramolecular energy transfer from Qs to Tb(III) takes place when excited. And thus the characteristic fluorescence of Tb(III) ion was enhanced and the maximum fluorescence peak locates at 545 nm. The second-order scattering (SOS) peak at 545 nm also appears for the Tb(III)-Qs complexes with the exciting wavelength of 274 nm. When the silver nanoparticles were added to the Tb(III)-Qs system, the luminescence intensity at 545 nm greatly increased. And the relative intensity is proportional to the amount of Qs. Based on this phenomenon, a novel method for determination of quinolones has been developed by using a common spectrofluorometer to measure the intensity of fluorescence and SOS. The luminescence intensity is greatly enhanced by silver nanoparticles in the pH range 5.5-6.2. The calibration graphs for pipemidic acid (PPA) and lomefloxacin (LMFX) are linear in the range 2.0 × 10⁻¹⁰ to 1.0 × 10⁻⁵ and 1.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹, respectively. The limits of detection are 4.7 × 10⁻¹¹ mol L⁻¹ for PPA and 1.1 × 10⁻¹⁰ mol L⁻¹ for LMFX. The method was applied satisfactorily to the determination of the two quinolones (Qs) in tablet, capsule, urine and serum samples. The experimental results showed that it is the certain size and certain concentration of silver nanoparticles that can greatly enhance the fluorescence -SOS intensity.     

An optical redox chemical sensor for determination of iodide

A novel optical sensor based on a redox reaction for the determination of iodide has been developed. The optode membrane is constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of chloride as counter ion with iodate in the membrane changes the color to yellow, when it is placed in acidic solution of iodide. The sensor can readily be regenerated by 0.1 mol L⁻¹ NaOH in less than 15 s. The optode has a linear range of 3.94 × 10⁻⁶ to 5.51 × 10⁻⁵ mol L⁻¹ of iodide ions with a limit of detection 7.44 × 10⁻⁷ mol L⁻¹. The relative standard deviation for eight replicate measurements of 3.94 × 10⁻⁶ and 1.57 × 10⁻⁵ mol L⁻¹ of iodide was 2.83 and 1.38%, respectively. The sensor was successfully applied to the determination of iodide in tablet, powdered milk and urine samples.     

A new method for electrocatalytic oxidation of ascorbic acid at the Cu(II) zeolite-modified electrode

A new method is developed for the catalytic oxidation of ascorbic acid at graphite zeolite-modified electrode, doped with copper(II) (Cu²⁺A/ZCME). Copper(II) exchanged in zeolite type A acts as catalyst to oxidize ascorbic acid. The modified electrode lowered the overpotential of the reaction by ∼400 mV. First, the electrochemical behavior of copper(II), incorporated in the zeolite type A modified electrode, was studied. The results illustrate that diffusion can control the copper(II)/copper(0) redox process at the Cu²⁺A/ZCME. Then, the behavior of electrocatalytic oxidation reaction for ascorbic acid was researched. The electrode was employed to study electrocatalytic oxidation of ascorbic acid, using cyclic voltammetry and chronoamperometry as diagnostic techniques. The diffusion coefficient of ascorbic acid was equal to 1.028 × 10⁻⁵ cm² s⁻¹. A linear calibration graph was obtained over the ascorbic acid with a concentration range of 0.003-6.00 mmol L⁻¹. The detection limit (DL) of ascorbic acid was estimated as 2.76 × 10⁻⁷ mol L⁻¹. The relative standard deviations of 10 replicate measurements (performed on a single electrode at several ascorbic acid concentrations between 3.0 and 200 μmol L⁻¹) were measured between 1.0 and 2.4%.     

Preparation of silver hexacyanoferrate nanoparticles and its application for the simultaneous determination of ascorbic acid, dopamine and uric acid

A silver hexacyanoferrate nanoparticles/carbon nanotubes modified glassy carbon electrode was fabricated and then successfully used for the simultaneous determination of ascorbic acid, dopamine and uric acid by cyclic voltammetry. A detailed investigation by transmission electron microscopy (TEM) and electrochemistry was performed in order to elucidate the preparation process and properties of the nanocomposites. The size of silver hexacyanoferrate nanoparticles was examined by TEM around 27 nm. Linear calibration plots were obtained over the range of 4.0 × 10⁻⁶-7.8 × 10⁻⁵, 2.4 × 10⁻⁶-1.3 × 10⁻⁴ and 2.0 × 10⁻⁶-1.5 × 10⁻⁴ mol L⁻¹ with detection limits of 4.2 × 10⁻⁷,1.4 × 10⁻⁷ and 6.0 × 10⁻⁸ mol L⁻¹ for ascorbic acid, dopamine and uric acid, respectively. The practical analytical utilities of the modified electrode were demonstrated by the determination of ascorbic acid, dopamine and uric acid in urine and human blood serum samples.