Electrolytic determination of nanomolar concentrations of silver in solution with a piezoelectric quartz crystal

Silver in solution is determined in situ by the frequency change of a piezoelectric quartz crystal on electrodeposition on the electrode of the crystal. The electrolyte solution flows through a cell containing the platinum-plated electrode (cathode) of the quartz crystal, a coiled platinum-wire anode and a silver—silver(I) chloride reference electrode, and is electrolyzed at —0.2 V vs. $\text{Ag}\text{AgCl}$. The frequency change is proportional to the silver concentration in the range 10^-5–5 × 10^-7 M after electrodeposition for 5 min, and in the range 10^-8–10^-9 M by recycling 20 ml of the solution over the electrodes for 3 h.     

Determination Of Amino Acid Based On A Series Piezoelectric Quartz Crystal Sensor

ABSTRACT

A series piezoelectric quartz crystal (SPQC) sensor has been applied to detect L-glutamic acid and L-lysine acid. The effect of formaldehyde solution on the frequency shift was studied. Two methods were discussed. For the calibration curve method, in a neutralized formaldehyde medium, the linear ranges for determining L-glutamic acid and L-lysine acid were from 7.1×10^?6M to 6.5×10^?4M and from 6.9×10^?6 M to 7.4×10^?4 M, respectively, with the detection limit being 7.1×10^?6 M and 6.9×10^?6 M, the recoveries were 99.2% and 100.1%, the R.S.D were 1.63% (n=6) and 1.83%(n=6), respectively. Frequencimetric tiration method was also described and the lowest titratable concentrations were 8.3×10^?5M and 5.5×10^?5 M, respectively.     

Selective determination of silver in solution by adsorption on a piezoelectric quartz crystal

Electrodeposition of metal ions on the crystal is eliminated by using a specially constructed transistorized oscillator. When tartrate, citrate, EDTA or their mixtures are present, silver adsorption occurs. The frequency change is proportional to the silver concentration in the range 2 × 10^?7?1 × 10^?5 M after adsorption for 10 min from a 1 mM EDTA/3 mM tartrate solution. No significant interferences are caused by other metal ions. On the basis of cyclic voltammetric studies, it is suggested that silver is adsorbed as a silver (I) complex.     

Potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate film-modified electrode

A potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate(III) (CHCF) film-modified glassy carbon electrode is proposed. The electroactive film is introduced onto the glassy carbon electrode surface by electrodeposition of cobalt, which forms a thin CHCF film on subsequent anodic scanning in KClHCl solution (pH 5.0–5.5) containing K₃Fe(CN)₆. The thickness of the film on the electrode surface can be controlled by changing the electrodeposition time and the concentrations of cobalt(II) and Fe(CN)^3?₆ ions. The modified electrode exhibits a linear response in the concentration range 1 × 10^?1 ?3 × 10^?5 M potassium ion activity, with a near-Nernstian slope (48–54 mV per decade) at 25 ± 1°C. The detection limit is 1 × 10^?5 M. The stability, response time and selectivity were investigated. The electrode exhibits good selectivity for potassium ion with the twelve cations investigated. The relative standard deviation is 1.5% (n=10). The effects of the thickness of the electroactive film and the pH of the solution on the electrode response were also investigated.     

Effect of metal ions on a piezoelectric quartz crystal in aqueous solution and the adsorptive determination of iron(III) as phosphate

At 1.5 V applied between the electrodes on the piezoelectric crystal, many metals electrodeposit on an electrode so that the frequency changes. Iron(III) (1 × 10^?5-1 × 10^?4 M) can be determined by adsorption of iron(III) phosphate which also causes a frequency change. Electrodeposition can be prevented by covering one electrode with a thin glass plate.     

A nafion/crown ether film electrode and its application in the anodic stripping voltammetric determination of traces of silver

Glassy carbon electrodes are modified by coating with dicyclohexyl-18-crown-6 in Nafion-117. The electrode is used for a very sensitive anodic stripping voltammetric determination of silver. High sensitivity is obtained owing to the release of crown molecules from the silver-crown complex during the deposition. The detection limit is 2×10^?12 M after electrodeposition for 30 min. The recommended supporting electrolyte is 4×10^?3–7×10^?3 M potassium chloride in 0.01 M nitric acid with a deposition potential of ?0.30 V vs. SCE and a linear potential scan. Three typical calibration graphs were linear over the range 2×10^?11–1×10^?8 M for deposition times of 30, 20 and 8 min, respectively. The silver content of reagent-grade ammonium nitrate was found to be 0.48×10^?4% with a relative standard deviation of 3.7% (n=7) for parallel determinations.     

Solid-state ion selective electrode based on polypyrrole conducting polymer nanofilm as a new potentiometric sensor for Zn2+ ion

A pencil graphite electrode (PGE) electrodeposited by a polypyrrole conducting polymer doped with tartrazine (termed as PGE/PPy/Tar) was prepared and used as a zinc (II) solid-state ion-selective electrode. For the preparation of the zinc sensor electrode, electrodeposition of a polypyrrole nanofilm was carried out potentiostatically (E _app?=?0.75 V vs SCE) in a solution containing 0.010 M pyrrole and 0.001 M tartrazine trisodium salt. A pencil graphite and Pt wire were used as working and auxiliary electrodes, respectively. The introduced electrode in the current paper can be fabricated simply and was found to possess high selectivity, exhibited wide working concentration range, sufficiently rapid response, potential stability, and very good sensitivity to Zn (II) ion. The sensor electrode showed a linear Nernstian response over the range of 1.0?×?10^?5 to 1.0?×?10^?1 M with a slope of 28.23 mV per decade change in zinc ion concentration. A detection limit of 8.0?×?10^?6 M was obtained. The optimum pH working of the electrode was found to be 5.0.     

Kinetic determination of some inorganic and organic compounds by oxidation with iodate

Sulphite (5.0 × 10^?1?5.0 × 10^?3 M), ascorbic acid and other compounds are oxidized by potassium iodate in dilute sulphuric acid; the production of iodide is monitored by an iodide-selective electrode. The time needed for a 40-mV potential change is inversely proportional to concentration. For sulphite (1.0 × 10^?5?1.0 × 10^?4 M), selectivity is improved by sweeping the sulphur dioxide formed in acidic EDTA-containing solution into the iodate solution.     

Simultaneous spectrofluorimetric determination of terbium,samarium and europium with hexafluoroacetylacetone-trioctylphosphine oxide and Triton X-100

In aqueous solution, the fluorescence intensity is a linear function of concentration in the ranges 1.0 × 10^?4-1.0 × 1.0^?6 M Sm and 1.0 × 10^?6-1.0 × 10^?8 M Tb and Eu. The optimum conditions are 1 × 10^?3 M hexafluoroacetylacetone, 1 × 10^?4 M trioctylphosphine oxide and 0.05% Triton X-100 at pH 3.0.     

Determination of lead by adsorption of the extracted 8-quinolinolate on the electrodes of a piezoelectric quartz crystal

Lead 8-quinolinolate extracted into chloroform is adsorbed on the electrodes of a piezoelectric quartz crystal. The change in frequency of the crystal is used to measure the lead concentration over the range 3 × 10^-6–5 × 10^-5 M in aqueous solution. The interferences of Fe(III), Ni, Co(II), Zn, Cd and Ag(I) can be masked byl-ascorbic acid and cyanide.     

Gold nanoparticles-carbon nanotubes modified sensor for electrochemical determination of organophosphate pesticides

An electrochemical sensor was developed for the detection of organophosphate pesticides based on electrodeposition of gold nanoparticles on a multi-walled carbon nanotubes modified glassy carbon electrode. Cyclic voltammetry was employed in the process of electrodeposition. Field emission scanning electron microscope and X-ray diffraction techniques were used for characterization of the composite. Organophosphate pesticides (e.g. parathion) were determined using linear scan voltammetry. A highly linear response to parathion in the concentration range from 6.0?×?10^?5 to 5.0?×?10^?7 M was observed, with a detection limit of 1.0?×?10^?7 M estimated at a signal-to-noise ratio of 3. The method has been applied to the analysis of parathion in real samples.     

Characterization and Electrocatalytic Property of Cobalt Hexacyanoferrate Film on Carbon Nanotubes Modified Gold Electrode

Abstract

Cobalt hexacyanoferrate (CoHCF) film was formed on multiwalled carbon nanotubes (MWNTs) modified gold electrode by electrodeposition from 0.5 M KCl solution containing CoCl₂ and K₃Fe(CN)₆. The electrochemical behavior and the electrocatalytic property of the modified electrode were investigated. Compared with CoHCF/gold electrode, the CoHCF/MWNTs/gold electrode exhibits greatly improved stability and enhanced electrocatalytic activity toward the oxidation of thiosulfate. A linear range from 5.0×10^?5 to 6.5×10^?3 M (r=0.9990) for thiosulfate detection at the CoHCF/MWNTs/gold electrode was obtained, with a detection limit of 2.0×10^?5 M (S/N=3).     

One‐Step Electrodeposited Carbon Nanotube/Zirconia/Myoglobin Film for Direct Electron Transfer and Electrocatalysis

A nanobiocomposite film consisted of zirconia, multiwalled carbon nanotubes (MWNTs) and Myoglobin (Mb) was electrochemically deposited on the electrode. Direct electron transfer for the immobilized Mb was realized and high electrocatalytic efficiency toward H₂O₂ was observed. The proposed biosensor via a simple one‐step electrodeposition method displayed a broader linear range and a lower detection limit for H₂O₂, as compared with those CNT or ZrO₂ based biosensor. The linear range is from 2 × 10^?6 M to 1 × 10^?3 M with the detection limit of 6 × 10^?7 M. The present strategy provides a simple and effective method to assemble CNT, ZrO₂ and enzyme nanohybrid on the electrode and expands the scope of CNT‐based electrochemical devices.     

Indirect Differential Pulse Voltammetric Determination of Aluminum Biological Samples in the Presence of 3, 4-Dihydroxyphenylalanine

ABSTRACT

Indirect differential pulse voltammetric (DPV) determination of aluminum in the presence of 3, 4-dihydroxyphenylalanine (L-dopa) with glass carbon electrode as working electrode has been described. The method relies on the decrease of DPV anodic peak current of L-dopa with the addition of Al^III The decreasing value of the peak current is linear with the increase of Al^III concentration. Under the optimum experimental conditions (pH 4.8, 6×10^?4 M L-dopa, 0.06M NaAc - HAc ¹buffer solution), the linear ranges are 4.0×10^?7 - 5.2×10^?6 M and 7.2×10^?6 - 4.5×10^?5 M. The relative standard deviation for 8×10^?6 M aluminum is 1.0% (n = 8) and the detection limit is 3.5×10^?7 M. A number of foreign species for interference have been studied. The method has been applied to determine aluminum in drinking water, synthetic renal dialysate and urine samples.     

Direct determination of pesticides in vegetable samples using gold nanoelectrode ensembles

Gold nanowires were produced by electrodeposition in polycarbonate membrane, with an average diameter of 200 nm and a height of about 2 μm. The nanowire array prepared by the proposed method can be considered as nanoelectrode ensembles (NEEs). An amperometric pesticides sensor based on gold NEEs has been developed and used for determination of phoxim and dimethoate in vegetable samples. The electrochemical performance of the gold NEEs has also been studied by the amperometric method. The electrode provided a linear response over a concentration range of 5.9 × 10^?5 to 1.2 × 10^?2 M for phoxim with a detection limit of 4.8 × 10^?6 M and 6.3 × 10^?5 to 1.1 × 10^?2 M for dimethoate. This sensor displayed high sensitivity and selectivity, long-term stability and wide linear range. In addition, the ellipsis of enzyme and the reactivation of enzyme make the operation simple. This sensor has been used to determine pesticides in a real vegetable sample.     

Kinetics of silver electrodeposition from thiocarbamide solutions at a regular surface coverage with sulfide ions

Kinetics of silver electrodeposition in the presence of sulfide ions is studied on electrodes renewed by cutting off a thin surface layer, at a controlled time of contact of the “fresh” surface with the electrolyte. Solutions containing 10^?2 M AgNO₃, 0.1 M thiocarbamide, 0.5 M HClO₄, and from 2 × 10^?6 to 1.5 × 10^?5 M Na₂S are studied. It is shown that under the studied conditions, the effect of silver electrodeposition on the surface concentration of sulfide ions is insignificant. As the concentration of sulfide ions in solution and their coverage on the electrode surface θ increase, the cathodic polarization decreases. Tafel curves plotted for θ = const are used in estimating the exchange current i ₀ and the transfer coefficient α. It is shown that α ≈ 0.5 and weakly depends on θ, whereas the exchange current increases with the increase in θ by an approximately linear law from 10^?5 A/cm² at θ ? 0 to 10^?4 A/cm² at θ = 0.43. The obtained data are compared with the results of kinetic studies of silver anodic dissolution in similar solutions.     

Flow-Injection Spectrophotometric Determination of Oxalate,Citrate and Tartrate Based on Photochemical Reactions

Abstract

A flow-injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochemical reactions was detected by measuring the absorbance after complexation with ferrozine (λ_max=562 nm). Linear calibration graphs were obtained over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?4 M, 8 × 10^?6 - 1.8 × 10^?4 M and 1.0 × 10^?6 - 2 × 10^?5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1x10^?5 M concentration level were within the range 1.29 - 1.47 %. The sampling frequency was about 40 samples h^?1. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.     

Spectrophotometric determination of iodate,iodide and acids by flow injection analysis

The production of iodine by reaction of iodate and iodide in acidic solution is used for the spectrophotometric determination of 1–6 × 10^?5 M iodate, 2–8 × 10^?3 M iodide, and ca. 10^?3 M acids. The sample is injected into a carrier stream containing the other two ions. The injection rate is ca. 100 h^?1.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

Effect of biogenic photochromic electron acceptors on chlorophyll fluorescence

It is shown that the photophysical properties of chlorophyll a (Chl) depend on the nature and relative amounts of 2-methyl-1,4-naphthoquinone (MNQ) and nicotinamide adenine dinucleotide phosphate (NADP). Photoinduced charge separation occurs in aqueous ethanol solutions of Chl (1 × 10^?5 M) and NADP (5 × 10^?6–5 × 10^?4 M), resulting in the dynamic quenching of Chl fluorescence. Coordination interaction between Chl and NADP is established at an NADP concentration of ≥5 × 10^?4 M. The nonlinear Stern-Volmer dependence in this range is due to the input from static quenching. It is shown that the quenching of Chl fluorescence in an MNQ solution at Chl and MNQ concentrations of 1 × 10^?5 M and 6.7 × 10^?5–1 × 10^?4 M, respectively, is described by a linear dependence in the Stern-Volmer coordinates; no complex formation is observed for Chl and MNQ under these conditions, and electron transfer is of the dynamic type. Static or mixed-type energy transfer from MNQ to Chl dominates at elevated MNQ concentrations.