Amperometric and spectrophotometric determination of carbaryl in natural waters and commercial formulations

The work presented describes the development and evaluation of two flow-injection analysis (FIA) systems for the automated determination of carbaryl in spiked natural waters and commercial formulations. Samples are injected directly into the system where they are subjected to alkaline hydrolysis thus forming 1-naphthol. This product is readily oxidised at a glassy carbon electrode. The electrochemical behaviour of 1-naphthol allows the development of an FIA system with an amperometric detector in which 1-naphthol determination, and thus measurement of carbaryl concentration, can be performed. Linear response over the range 1.0×10^–7 to 1.0×10^–5 mol L^–1, with a sampling rate of 80 samples h^–1, was recorded. The detection limit was 1.0×10^–8 mol L^–1. Another FIA manifold was constructed but this used a colorimetric detector. The methodology was based on the coupling of 1-naphthol with phenylhydrazine hydrochloride to produce a red complex which has maximum absorbance at 495 nm. The response was linear from 1.0×10^–5 to 1.5×10^–3 mol L^–1 with a detection limit of 1.0×10^–6 mol L^–1. Sample-throughput was about 60 samples h^–1. Validation of the results provided by the two FIA methodologies was performed by comparing them with results from a standard HPLC–UV technique. The relative deviation was <5%. Recovery trials were also carried out and the values obtained ranged from 97.0 to 102.0% for both methods. The repeatability (RSD, %) of 12 consecutive injections of one sample was 0.8% and 1.6% for the amperometric and colorimetric systems, respectively.     

Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Simultaneous Determination of Aromatic Amines by Liquid Chromatography Coupled with Carbon Nanotubes/Poly (3-methylthiophene) Modified Dual-Electrode

Liquid chromatography with amperometric detection (LC-AD) is developed and applied to simultaneously determine five aromatic amines. In the LC-AD, a new carbon nanotubes/poly(3-methylthiophene) modified dual-electrode is fabricated and then used as the working electrode. It is found that this chemically modified electrode (CME) exhibits efficiently electrocatalytic oxidation for aromatic amines with relatively high sensitivity, stability and long-life. Thus, lower detection in LC-AD can be achieved, which are 4.0 × 10^–8 mol L^–1 for aniline, 1.6 ×10^–7 mol L^–1 for 4-nitroaniline, 1.0 × 10^–7 mol L^–1 for 4-chloroaniline, 1.5 × 10^–7 mol L^–1 for 1-naphthylamine, 1.7 × 10^–7 mol L^–1 for 2-bromoaniline. The recoveries of the five analytes are also determined, which range between 0.95 and 1.05 for drinking water, 0.86 and 1.10 for the LiWa River water.     

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO₃)₄], has a Nernstian potentiometric response from 2.0×10^–8 to 2.0×10^–2 mol L^–1 with a detection limit of 8.0×10^–9 mol L^–1 and a slope of –59.0±0.5 mV/decade in 0.01 mol L^–1 phosphate buffer solution (pH 3.0, 20°C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV–Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.     

Perchlorate-selective membrane electrode based on a new complex of uranil

A potentiometric ion-selective electrode based on new compound, as a carrier, has been successfully developed for detection of perchlorate anion in aqueous solution. Within the perchlorate ion concentration range 1.0×10^–6 to 1.0 mol L^–1 the electrode had a linear response with a Nernstian slope of 60.6±1.0 mV per decade . The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot was 8.0×10^–7 mol L^–1. The proposed electrode has fairly a good discriminating ability towards ClO₄^– ion in comparison to other anions. The sensor has a response time of 10 s and can be used for at least 2 months without substantial divergence in potential. It was successfully applied to direct determination of perchlorate in urine and water.     

Spectrophotometric determination of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3- H-indol-2-ylidene)propenyl]-3 H-indolium

A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of manganese in sewage. The method is based on the reaction of manganese with derivatives of 1,3,3-trimethyl-2-[3-(1,3,3-trimethyl-1,3-H-indol-2-ylidene)propenyl]-3H-indolium to form a colored ion associate with a sensitive absorption maximum at 560 nm. The appropriate reaction conditions have been established: pH 8.5–10.0, 1.25–2.3×10^–3 mol L^–1 1-nitroso-2-naphthol, and 1.6–2.4×10^–4 mol L^–1 dye reagent. Beer's law is obeyed for manganese concentrations up to 4.2 mg L^–1. The limit of detection is 0.01 mg L^–1 Mn²⁺; the molar absorptivity of the ion associate was 7.5×10⁴ L mol^–1 cm^–1. The effect of various foreign ions was examined. A reaction mechanism is suggested. The developed procedure was tested for determination of manganese in sewage with satisfactory precision and accuracy.     

Determination of subnanomolar concentrations of cobalt by adsorptive stripping voltammetry at a bismuth film electrode

Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10^–10 to 2 × 10^–8 mol L^–1. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10^–9 mol L^–1 was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10^–11 mol L^–1. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples.     

A novel amperometric sensor and chromatographic detector for determination of parathion

A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10^–9–2.0×10^–5 mol L^–1. The detection limit was 1.0×10^–9 mol L^–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10^–9 mol L^–1. Application of the method for determination of parathion in rice was satisfactory.     

Micro-pumping flow system for spectrophotometric determination of anionic surfactants in water

A novel procedure has been developed for spectrophotometric determination of anionic surfactants in water using a solenoid micro-pump as fluid-propulsion device. The proposed method is based on substitution of methyl orange (MO) by anionic surfactants in the formation of an ion-pair with the cetyl pyridine ion (CPC⁺) at pH 5.0. The flow network comprised four solenoid micro-pumps which, under microcomputer control, enabled sample and reagent introduction, and homogenisation in the reaction zone. The system is flexible and simple to operate and control, and sensitive and precise. The analytical plot for the anionic surfactant was linear between 1.43×10^–6 and 1.43×10^–5 mol L^–1 (0.5 to 5.0 mg L^–1; R=0.997, n=5). The relative standard deviation was 0.8% (n=11) for a sample containing 5.74×10^–6 mol L^–1 (2 mg L^–1) surfactant. The limit of detection was 9.76×10^–8 mol L^–1 (0.034 mg L^–1) and the sampling throughput was 60 determinations per hour. The results obtained for washing-water samples were comparable with those obtained by use of the reference method, and no significant differences at the 95% confidence level were observed.     

Voltammetric study of glibenclamide at carbon paste and Sephadex-modified carbon paste electrodes

The oxidative behaviour of the antidiabetic agent glibenclamide on a bare carbon paste electrode (CPE) and a Sephadex-modified carbon paste electrode (SMCPE) was explored by cyclic and differential pulse voltammetry (DPV). The analysis procedure consisted of an open circuit accumulation step in stirred sample solution of Britton-Robinson buffer (0.04 mol L^–1, pH 2.0). This was followed by medium exchange to a clean solution of Britton-Robinson buffer (0.04 mol L^–1, pH 5.0), and subsequently an anodic potential scan was effected to obtain the voltammetric peak. The glibenclamide oxidation peak current obtained by DPV was proportional to the concentration of the glibenclamide in the range of 1.0×10^–9 mol L^–1 to 5.0×10^–8 mol L^–1 for 180 s accumulation time, with a detection limit of 4.0×10^–10 mol L^–1. A method was developed for the determination of glibenclamide in formulation and spiked human serum. Moreover, the proposed procedure was used to estimate the serum concentrations after oral administration of a 5 mg tablet of glibenclamide to three diabetic subjects.     

Reproterol plastic membrane ion-selective electrodes based on its individual and mixed ion-exchangers with phosphotungstic and/or phosphomolybdic acids

Reproterol hydrochloride (RpCl), selective PVC membranes based on ion associates of reproterolium-phosphotungstate (Rp-PTA); reproterolium-phospho-molybdate (Rp-PMA) or a mixture of both (Rp-PTA/PMA) were prepared. The electrodes displayed a linear response over the concentration range of 6.3×10⁻⁶–1.0×10⁻¹ mol dm⁻³ RpCl. The working pH ranges of the above electrodes were 2.5–9.0, 2.5–8.5 and 2.0–9.0 and their isothermal temperature coefficients were 0.00014, 0.00090 and 0.00103 V/°C, respectively. The electrodes showed good selectivity to the reproterolium ion with respect to many inorganic cations, sugars and amino acids. The standard additions and potentiometric titration methods were used to determine RpCl in pure solutions and in its pharmaceutical preparations with high accuracy and precision.     

Electrochemistry of sinapine and its detection in medicinal plants

Sinapine (O-sinapoyl choline) is a crucial component, with much medicinal value, of many dietary and medicinal plants. It has been found that sinapine gives an electrochemical response at a pyrolytic graphite electrode. The electrochemical properties of sinapine have been investigated. The peak current in the cyclic voltammogram is linear in the concentration range 1.9×10^–6–2.5×10^–4 mol L^–1 and the limit of detection is 9.9×10^–7 mol L^–1. These properties can be applied to the determination of sinapine in extracts from three kinds of medicinal plant. The electrochemical method reported here is highly selective, sensitive, and stable.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

Construction and Performance Characterization of Ion‐Selective Electrodes for Potentiometric Determination of Paroxetine Hydrochloride in Pharmaceutical Preparations and Biological Fluids

Three types of ion‐selective electrodes: PVC membrane, modified carbon paste (CPE), and coated graphite electrodes (CGE) have been constructed for determining paroxetine hydrochloride (Prx). The electrodes are based on the ion pair of paroxetine with sodium tetraphenylborate (NaTPB) using dibutyl phthalate as plasticizing solvent. Fast, stable and potentiometric response was obtained over the concentration range of 1.1×10^?5–1×10^?2 mol L^?1 with low detection limit of 6.9×10^?6 mol L^?1 and slope of a 56.7±0.3mV decade^?1 for PVC membrane electrode, the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 1.2×10^?5 mol L^?1 and slope of a 57.7±0.6 mV decade^?1 for CPE, and the concentration range of 2×10^?5–1×10^?2 mol L^?1 with low detection limit of 8.9×10^?6 mol L^?1 and slope of a 56.1±0.1 mV decade^?1 for CGE. The proposed electrodes display good selectivity for paroxetine with respect to a number of common inorganic and organic species. The electrodes were successfully applied to the potentiometric determination of paroxetine hydrochloride in its pure state, its pharmaceutical preparation, human urine and plasma.     

Rapid determination of telmisartan in pharmaceuticals and serum by the parallel catalytic hydrogen wave method

The polarographic characteristics of telmisartan have been investigated in 0.8 mol L^–1 NH₃.H₂O–NH₄Cl (pH 8.9)–0.01 mol L^–1 H₂O₂ as supporting electrolyte. The results demonstrate that the polarographic reduction wave at ca. –1.30 V in the absence of H₂O₂ is a catalytic hydrogen wave, and the reduction wave enhanced by H₂O₂ is a so-called parallel catalytic hydrogen wave. The analytical sensitivity of the parallel catalytic hydrogen wave is ca. 60 times higher than that of the corresponding catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave a novel method has been developed for determination of telmisartan by linear sweep polarography. The calibration curve is linear in the range 2.0×10^–8–2.0×10^–6 mol L^–1 and the detection limit is 1.0×10^–8 mol L^–1. The precision is excellent with relative standard deviations of 2.6% at a concentration of 1.0×10^–7 mol L^–1 telmisartan. The proposed method has been applied to the direct determination of the telmisartan in capsule forms and biological samples. The proposed method has been proved to be advantageous over existing CZE and MEKC methods in simplicity, rapidity, and reproducibility.     

Anodic stripping voltammetric determination of mercury using multi-walled carbon nanotubes film coated glassy carbon electrode

An electrochemical method for the determination of trace levels of mercury based on a multi-walled carbon nanotubes (MWNT) film coated glassy carbon electrode (GCE) is described. In 0.1 mol L^–1 HCl solution containing 0.02 mol L^–1 KI, Hg²⁺ was firstly preconcentrated at the MWNT film and then reduced at –0.60 V. During the anodic potential sweep, reduced mercury was oxidized, and then a sensitive and well-defined stripping peak at about –0.20 V appeared. Under identical conditions, a MWNT film coated GCE greatly enhances the stripping peak current of mercury in contrast to a bare GCE. Low concentrations of I^– remarkably improve the determining sensitivity, since this increases the accumulation efficiency of Hg²⁺ at the MWNT film coated GCE. The stripping peak current is proportional to the concentration of Hg²⁺ over the range 8×10^–10–5×10^–7 mol L^–1. The lowest detectable concentration of Hg²⁺ is 2×10^–10 mol L^–1 at 5 min accumulation. The relative standard deviation (RSD) at 1×10^–8 mol L^–1 Hg²⁺ was about 6% (n=10). By using this proposed method, Hg²⁺ in some water samples was determined, and the results were compared with those obtained by atomic absorption spectrometry (AAS). The two results are similar, suggesting that the MWNT-film coated GCE has great potential in practical analysis.     

Use of ICP and XAS to determine the enhancement of gold phytoextraction by <Emphasis Type="Italic">Chilopsis linearis</Emphasis> using thiocyanate as a complexing agent

Under natural conditions gold has low solubility that reduces its bioavailability, a critical factor for phytoextraction. Researchers have found that phytoextraction can be improved by using synthetic chelating agents. Preliminary studies have shown that desert willow (Chilopsis linearis), a common inhabitant of the Chihuahuan Desert, is able to extract gold from a gold-enriched medium. The objective of the present study was to determine the ability of thiocyanate to enhance the gold-uptake capacity of C. linearis. Seedlings of this plant were exposed to the following hydroponics treatment: (1) 5 mg Au L^–1 (2.5×10^–5 mol L^–1), (2) 5 mg Au L^–1+10^–5 mol L^–1 NH₄SCN, (3) 5 mg Au L^–1+5×10^–5 mol L^–1 NH₄SCN, and (4) 5 mg Au L^–1+10^–4 mol L^–1 NH₄SCN. Each treatment had its respective control. After 2 weeks we determined the effect of the treatment on plant growth and gold content by inductively coupled plasma–optical emission spectroscopy (ICP–OES). No signs of shoot-growth inhibition were observed at any NH₄SCN treatment level. The ICP–OES analysis showed that addition of 10^–4 mol L^–1 NH₄SCN increased the concentration of gold by about 595, 396, and 467% in roots, stems, and leaves, respectively. X-ray absorption spectroscopy (XAS) studies showed that the oxidation state of gold was Au(0) and that gold nanoparticles were formed inside the plants.     

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite–polyurethane composite electrode

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L^–1; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s^–1, E_a=50 mV, E_I=2 mV) and detection and quantification limits of 6.4×10^–8 mol L^–1 (12.1 g L^–1) and 5.2×10^–6 mol L^–1 (0.9 mg L^–1), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10^–6 mol L^–1 dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.     

Determination of thiol compounds in rat striatum microdialysate by HPLC with a nanosized CoHCF-modified electrode

A cobalt hexacyanoferrate (CoHCF) nanoparticle (size ca. 60 nm) chemically modified electrode (CME) was fabricated and the electrochemical behavior of thiols at this nanosized CoHCF CME was studied. In comparison with a bare glassy carbon (GC) electrode and with a general CoHCF CME which was electrodeposited in the traditional manner, the present nanosized CoHCF CME efficiently performed electrocatalytic oxidation for glutathione (GSH) and L-Cysteine (L-Cys) with relatively high sensitivity, outstanding stability, and long-life. Combined with high-performance liquid chromatography (HPLC), the nanosized CoHCF CME was used for electrochemical determination (ECD) of GSH and L-Cys. The peak currents were a linear function of concentrations in the range 2.0×10^–7 to 2.0×10^–4 mol L^–1 for both GSH and L-Cys, with detection limits of 1.2×10^–7 and 1.0×10^–7 mol L^–1, respectively. Coupled with microdialysis sampling, the HPLC–ECD system has been successfully used to assess the GSH and L-Cys content of rat striatum.     

Determination of trace europium by use of the new fluorescence system europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate

A new lanthanide-sensitized luminescence system: europium–sparfloxacin–1,10-phenanthroline–sodium dodecyl sulfate has been discovered. The spectrofluorimetric properties of the system were studied. The effect of experimental conditions on the fluorescence intensity was defined. Under the optimum conditions, the fluorescence intensity of the system is a linear function of the concentration of europium in the range 5.0×10^–9–1.0×10^–6 mol L^–1 and the detection limit is 1.0×10^–10 mol L^–1. The system was used for the determination of trace amounts of europium in rare earth samples with satisfactory results.