Determination of silver in solution with a piezoelectric detector after electrodeposition

Silver in solution is determined in situ by frequency change of a piezoelectric quartz crystal due to electrodeposition on the electrode of the crystal immersed in the solution. A test solution containing EDTA for masking other metal ions flows through a thermostated cell which contains the crystal with platinum-plated electrodes. The frequency change is proportional to the silver concentration in the range 10^?6?3 × 10^?5 M after electrodeposition for 10 min, and 2 × 10^?7?1 × 10^?6 M for 1 h.     

Single-drop method for determination of cyanide in solution with a piezoelectric quartz crystal

The change in frequency of a horizontal quartz crystal in contact with a single drop of solution is measured. When the gold electrode of the crystal is dissolved by reaction with cyanide in alkaline solution, the further change of frequency is linearly related to cyanide concentration in the range 10^-3–10^-4 M at pH 10.4. Only silver(I) and mercury(II) interfere if EDTA is added.     

Determination of micromolar concentrations of cyanide in solution with a piezoelectric detector

The silver plated electrodes of a piezoelectric quartz crystal are partly dissolved by cyanide in pH 9.6 solution during a 15-min immersion. The resulting frequency change of the crystal, measured in air, is proportional to cyanide concentration over the range 10^-7–10^-5 M.     

Determination of picomolar concentrations of bromide with a piezoelectric detector by catalysis of the permanganate/iodide reaction

The piezoelectric quartz crystal has been utilized to detect iodine produced by the bromide- catalyzed oxidation of iodine to iodate by permanganate in acidic solution. After extraction of iodine into toluene, the resulting frequency change caused by iodine adsorption on the crystal electrode is proportional to bromide concentration over the range 0.5–5 × 10^?12 M. Only silver (I), mercury(II) and large concentrations of chloride interfere significantly. The crystal detector is also used to indicate the end-point of a chloride titration with silver.     

Electrolytic determination of traces of iodide in solution with a piezoelectric quartz crystal

The frequency of a piezoelectric quartz crystal is decreased when iodide is electrodeposited on the silver electrode of the crystal at—0.05 V vs. Ag/AgCl. From 3 × lO^-7 M to 1 × 10^-5 M iodide can be determined with few interferences, and a procedure for removal of interfering species is given. Iodide is removed from the electrode by electrolysis at —0.4 V after each determination.     

Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave (E_{$\text{1}\text{2}$} = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10^-5 M but adsorptioncontrolled in 10^-4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10^-6—2 × 10^-5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i_p and BPA concentration is maintained.     

Design and Performance of a New Thin‐Layer Radial‐Flow Holder for a Quartz Crystal Resonator of an Electrochemical Quartz Crystal Microbalance

A new compact holder for either 5‐ or 10‐MHz AT‐cut quartz crystal resonator of an electrochemical quartz crystal microbalance was designed, fabricated and characterized. The holder is a hydrodynamically controlled thin‐layer radial‐flow microelectrochemical cell. Its unique feature consists of (i) a micrometer‐screw adjustable distance between the movable coaxial assembly of the Ag/Ag⁺ pseudoreference electrode and the inlet capillary nozzle with respect to the metal‐film working electrode of the quartz crystal resonator, and (ii) a U‐clamp mountable resonator, easily accessible for change without using any tools. The inlet solution stream is centered axially against the working electrode. The holder performance was tested under different flow conditions. These include hydrodynamic voltammetry measurements on the Fe(CN) /Fe(CN) couple, i.e., a redox system with no mass transfer across the solution–electrode interface, as well as simultaneous chronoamperometry and chronoelectrogravimetry measurements under flow injection analysis (FIA) conditions on the Ag/Ag⁺ couple, i.e., a system with electrodeposition of a rigid metallic film. Moreover, simultaneous changes of resonant frequency and dynamic resistance were measured under FIA conditions for a glycerol solution, i.e., an electroinactive viscous medium. For the 30<F_m<180 μL min^?1 volume flow rate of solution and 50<d<250 μm nozzle‐to‐resonator distance, the holder operates in a thin‐layer radial‐flow regime at a fully developed laminar flow. For F_m=30 μL min^?1 and d=100 μm, both mass and charge conversion accompanying silver electrodeposition is appreciably high and close to 35%. Simultaneous measurements of the resonant frequency change and current‐potential or current‐time transients allowed investigations of electrochemical processes involving mass changes of rigid deposits while those of the frequency change and dynamic resistance change involve changes of viscoelastic properties of medium.     

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.     

Oszillopolarographische mikroanalyse

In oscillographic polarography with alternating current, curves representing the functions $\text{casedE}\text{dt}$ = f(E), were employed for the purpose of quantitative analysis. A comparative titration was proposed, in which two curves were observed on the luminescent screen; one for the solution being analysed, the other for a comparison solution, which was titrated with a standard solution of the depolarizer being determined, until the two curves were identical.In the second method, the distance of the peak of the cut-in from the potential axis was measured with special equipment.For the determination of several metals in the concentration range from 10^-5 to 10^-9M a micro-analytical method was used, which is based on the previous separation of the ions to be determined at a stationary mercury electrode with subsequent oscillo-polarographic analysis of the amalgam formed.     

The automatic amperometric and potentiometric microtitration of pharmaceutically important sulfanilamide derivatives by diazotization with nitrite

The automatic amperometric and potentiometric microtitration of pharmaceutically important sulfanilamide derivatives by diazotization with nitrite is described. Optimal conditions for diazotization and amperometric indication are discussed. A new cathodic amperometric indication of nitrite in M hydrochloric acid-25% ($\text{w}\text{v}$) of potassium bromide medium is proposed; the electrode processes involved are interpreted on the basis of current-potential curves. The effects of the hydrochloric acid and bromide concentrations, and of temperature on the limiting current are described. Sulfamethazine, sulfadimethoxine, sulfamethoxypyridazine and sulfamethoxypyrazine were titrated amperometrically in the range 10^?3–10^?6 M. Potentiometric titrations of these sulfanilamides were possible in the range 10^?3–10^?4 M.     

Determination of trace amounts of silver with a chemically modified carbon paste electrode

A method for the determination of trace amounts of silver with a chemically modified carbon paste electrode is described. The modified electrode is prepared by simply mixing a chelating resin (a polythioether backbone and dioxymonosulphur polyethylene polyimines in the side-chain polymer) with graphite powder and Nujol oil. By immersing the electrode in a silver sample solution (pH = 6.5–7.5), silver can be adsorbed on the electrode surface and then determined by voltammetry in a separate blank solution. The response depends on the concentration of silver and the preconcentration time. For a preconcentration time of 5 min, the detection limit is about 3 × 10^?10 M and the linear range is from 5 × 10^?10 to 1 × 10^?7 M with a relative standard deviation of 4%. Many common metal ions have no or little effect on the determination of silver. The recommended procedure was applied to the determination of trace amounts of silver in waste water.     

The oscillation frequency of a quartz resonator in contact with liquid

A simple relationship is derived which expresses the change in oscillation frequency of a quartz crystal in contact with a fluid in terms of material parameters of the fluid and the quartz. The relationship is Δf = ?f^{$\text{3}\text{2}$}₀(η_L?_L/πμ_Q?_Q)^{$\text{1}\text{2}$}, where f₀ is the oscillation frequency of the free (dry) crystal, η_L and ?_L are the absolute viscosity and density of the liquid, respectively, and μ_Q and ?_Q are the elastic modulus and density of the quartz. This relation is obtained from a simple physical model which couples the shear wave in the quartz to a damped shear wave in the fluid. Quantitative comparisons with two test cases, aqueous solutions of glucose and ethanol at various concentrations, demonstrate the accuracy of this model.     

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.     

Analytical application of triethylenetetraaminehexa- acetic acid: Part 2. Polarographic Investigation of the reactions of TTHA at the dropping mercury electrode

TTHA gives an anodic d.c. wave and s.w. peak corresponding to oxidation of mercury at the d.m.e. surface with formation of a Hg(II)—TTHA complex. Similar processes are known for other ligands, e.g. EDTA and DCTA, but the greater stability of the Hg(II)—TTHA complex gives a significant improvement in the shapes of the anodic wave and s.w. peak. An increase in pH shifts the E_{$\text{1}\text{2}$} and E_p values towards more negative values because the conditional stability constant of the Hg(II)—TTHA complex is increased. Although the half–wave potentials of the reduction wave of Hg(II)—TTHA and of the anodic wave of TTHA, are the same, other criteria for the reversibility of polarographic reactions suggest that the anodic TTHA process at the d.m.e. is not completely reversible. The temperature coefficient of the wave and s.w. peak as well as the dependence of the wave height on the square root of the mercury head prove that the process is diffusion–controlled. Supporting electrolytes are given for which the d.c. wave and the s.w. peak of TTHA are well-shaped, with linear dependence between the wave or peak height and the concentration of TTHA in the ranges 5 × 10^-5–5 × 10^-4 M (d.c.) and 1 0^-5–1 × 10^-4 M (s.w.).     

Rapid determination of nicotinic acid by immobilized lactobacillus arabinosus

A rapid determination of aicotinic acid by using immobilized Lactobacillus arabinosus and a combined glass electrode is reported. L. arabinosus is immobilized in agar gel. The optimum agar concentration is from 2–2.5% ($\text{w}\text{v}$) and the optimum bacterial concentration in the agar gel matrix is 10 mg wet cells ml^-1. The relationship between the potential difference and the logarithm of the nicotinic acid concentration is linear over the range 5 X 10^-8–5 X 10^-6 g ml^-1. The assay requires only 1 h; potentials are reproducible with an average relative error of 5%. The growth of L. arabinosus in agar gel matrix is observed in the medium containing nicotinic acid. Immobilized L. arabinosus is stable for 30 days.     

A thallium(I)-selective electrode based on a liquid ion-exchanger containing 0,0'-didecyldithiophosphoric acid

A liquid ion-exchange electrode containing thallium(I) 0,0'-didecyldithiophosphate in chlorocyclohexane is described. Nernstian behaviour is obtained in the pTI range 1–5.5, the slope of the calibration graph being 57.6 mV/decade change in activity at ionic strength 0.1, Alkali and alkaline earth metal cations do not interfere (K_{$\text{TI}\text{M}$} < 10^?5). Potentials are established rapidly, and are unaffected by pH in the range 5–12. In analytical applications direct potentiometry and potentiometric precipitation titrations with iodide or tetraphenylborate solutions are satisfactory. Various interfering ions can be masked with EDTA.     

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.     

A new coated-wire cobalt(II)-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair

A cobalt-selective electrode based on the benzalkonium tetrathiocyanatocobaltate(II) ion pair is described. The response is Nemstian (slope 29.3 $\text{mV}\text{pCo}$) in the cobalt concentration range 10^-1–10^-4 M in solutions with a constant ionic strength of 3.0 M made up with KSCN at 25°C. The electrode is suitable for end-point detection in titrations of cobalt(II) with EDTA as well as for direct potentiometric determinations of cobalt(II), even in the presence of large amounts of several metal ions (Ni²⁺, Fe²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Ba²⁺) and anions (HCO₃^-, Br^-, I^-, NO₃^-, SO₄^2-).     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Effect of the diffuse double layer on the interpretation of EQCM results in dilute NaClO4 solutions

The response of the electrochemical quartz crystal microbalance (EQCM) in dilute NaClO₄ solutions was studied with gold and iron electrodes during a stepwise increase of the perchlorate concentration. In the range from 10⁻⁴ M to 7.8×10⁻² M, the quartz resonant frequency of the 10 MHz AT cut crystals increased by about 700 Hz, indicating a mass loss on the electrode. A model was developed in which the diffuse double layer and the oscillating bulk electrolyte layer, characterised by the velocity decay length of the damped shear wave in solution, are treated as two independent, superimposed sheets. By assuming a characteristic thickness of the diffuse double layer according to the Gouy–Chapman theory and by treating the diffuse double layer as a rigid sheet, the measured mass loss could be simulated qualitatively. The viscosity changes in the diffuse double layer as well as in the sensed electrolyte bulk layer were found to be negligible in the concentration range investigated. In dilute solutions, the frequency shift following a concentration change is entirely due to thinning of the diffuse double layer with increasing concentration. The results demonstrate the importance of diffuse double layer effects for EQCM measurements in dilute electrolytes.