Determination of dihydrozeatin and dihydrozeatin riboside in apples by anodic stripping voltammetry with a carbon fiber microelectrode

Analytical methods for determining both dihydrozeatin (DHZ) and dihydrozeatin riboside (DHZR) are optimized via voltammetric anodic stripping using a carbon fiber microelectrode, working in 0.05 M AcH/Ac^– buffer pH 4.0, previously accumulated at 0.00 V (vs. Ag/AgCl/ KCl 3 M) for 400 s, at a scan rate of 800 mV · s^–1. A detection limit of 40.0 ng · mL^–1 and a determination limit of 46.0 ng · mL^–1 for the DHZ are obtained. Using the same supporting electrolyte and accumulation potential conditions, but for periods of 70 s and carrying out a stripping scan rate of 900 mV s^–1, the detection limit calculated for the DHZR was 14.0 ng · mL^–1 and the determination limit obtained was 153 ng · mL^–1. The proposed methods were successfully applied to determine minute amounts of cytokinins in apples during their growth period. Received: 22 July 1998 / Revised: 9 December 1998 / Accepted: 14 December 1998     

Determination of linuron in soil by stripping voltammetry with a carbon fiber microelectrode

A carbon fiber microelectrode was used for the electroanalytical determination of Linuron (LIN) in soil extracts. The microelectrode was subjected to an electrochemical pretreatment in order to improve the herbicide adsorption on the electrode surface. With this preconcentration step, detection limits of 80 ng ml⁻¹ and determination limits of 260 ng ml⁻¹ were reached. Optimal conditions with respect to accumulation time and potential, scan rate and pH were established. The LIN was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC.     

Potentiometric stripping analysis and anodic stripping voltammetry with carbon fiber electrodes

High-modulus carbon fibers are used as working electrodes in differential-pulse stripping voltammetry and potentiometric stripping analysis. Different types of electrodes (particularly single-fiber and brush electrodes) are compared with regard to reproducibility, sensitivity, and practical aspects. Zinc, cadmium, and lead are determined in the 100 μg 1^?1 to 1 mg l^?1 range and optimum experimental parameters are described. The cut single-fiber electrode has the best general characteristics.     

Determination of carbendazim in soil samples by anodic stripping voltammetry using a carbon fiber ultramicroelectrode

A method for the determination of carbendazim (MBC) by anodic stripping voltammetry using a carbon fiber ultramicroelectrode was developed. The ultramicroelectrode was made in our laboratory and its electrochemical behavior was characterized by measuring the electrochemical response with a solution of potassium ferricyanide. The optimum parameters used for the determination of MBC are the following: 0.05 M phosphate buffer at pH 2.0 as supporting electrolyte; a scan rate of v = 10.00 V s(-1) and an accumulation potential of Eac = 0.00 V. The MBC was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC.     

Determination of carbendazim in soil samples by anodic stripping voltammetry using a carbon fiber ultramicroelectrode

A method for the determination of carbendazim (MBC) by anodic stripping voltammetry using a carbon fiber ultramicroelectrode was developed. The ultramicroelectrode was made in our laboratory and its electrochemical behavior was characterized by measuring the electrochemical response with a solution of potassium ferricyanide. The optimum parameters used for the determination of MBC are the following: 0.05 M phosphate buffer at pH 2.0 as supporting electrolyte; a scan rate of v = 10.00 V s^–1 and an accumulation potential of E_ac = 0.00 V. The MBC was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC.     

Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode

The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2 nM As(III) at pH 8 and 0.3 nM combined arsenic (III + V) at pH 1 with a 30 s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.     

Determination of nickel by anodic adsorptive stripping voltammetry with a cation exchanger-modified carbon paste electrode

The behavior of a modified carbon paste electrode (CPE) for nickel determination by anodic adsorptive stripping voltammetry (AAdsSV) was studied. The electrode was built incorporating the Dowex 50W x 12 (H(+) form) ion exchanger to a Nujol-graphite base paste. Ni(2+) was preconcentrated on the electrode surface in open circuit conditions, with the reduction (-1300 mV)/reoxidation step carried out in HCl solution (pH 3). During deposition time (5 min), the hydrogen evolution did not present obstacle in the quantification of nickel. For 12 min of accumulation and 5 min of deposition, nickel can be quantified up to 600 mug l(-1). The detection limit was 0.005 mug l(-1) at a linear potential scan rate of 200 mV s(-1). Interferences from Hg(2+) and Ag(2+) up to a concentration of 1 and 0.6 mg l(-1), respectively, were eliminated with the aid of the anion exchanger Dowex-2 (mesh 200-400) which was added to the sample in the preconcentration step. The tolerance for some metal ions such as Cu(2+), Cd(2+), Fe(3+), Zn(2+), Co(2+) and Pb(2+) was improved in the same way. The method was applied for the determination of nickel in samples of tap and mineral water. At the concentration level of 50 mug l(-1) of Ni (2+), the results were in good agreement with those obtained using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For a Ni(2+) concentration of 5 mug l(-1), the results obtained showed better accuracy than those obtained by ICP-AES.     

Copper determination in ethanol fuel samples by anodic stripping voltammetry at a gold microelectrode

A linear sweep anodic stripping voltammetric method was developed for copper determination in commercial ethanol fuel samples by using a gold microelectrode. Under the optimized conditions, a linear range from 0.05 to 1.0 μM was obtained, with detection limit of 22 nM. The method was employed to determine copper ions in six commercial ethanol fuel samples and the results were compared with those obtained by FAAS. This study showed that for most samples both methods produced concordant results. However, for two samples, copper is distributed in its labile and complexed forms leading to copper contents contrasting with those obtained by flame atomic absorption spectroscopy (FAAS). It was observed that acidification of the samples is a very efficient way to recover copper from its complexed forms. After acidification, the copper contents obtained were concordant with those obtained by FAAS. Thus, the method can be employed to the reliable copper determination in commercial ethanol fuel samples. Moreover, this is the first work providing some insights about copper speciation in commercial ethanol fuel samples.     

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

Determination of trace metoclopramide by anodic stripping voltammetry with nafion modified glassy carbon electrode

A novel method is described for determination of metoclopramide (MCP) by second-derivative adsorptive anodic stripping voltammetry with a nafion-modified electrode. The stripping peak current is proportional to the concentration of MCP over the range 1.2×10⁻⁹–4.6×10⁻⁷ M. The detection limit is 8.0×10⁻¹¹ M with 4-min accumulation. The method has been successfully applied to the determination of MCP in human serum.     

掺杂硒碳糊电极阳极溶出法测定铋

建立了一种测定痕量铋的新方法,即利用掺杂硒碳糊电极作为工作电极的阳极溶出法.在0.1 mol/L的HCl底液中,Bi3+于+0.05V(vs.Ag/AgCl)出现灵敏的氧化溶出峰,铋离子的浓度在1.0×10-5～1.0×10-9 mol/L范围内其对数值lgc与铋的氧化峰电流值呈线性关系,检出限达1.0×10 -10 ...     

Determination of zinc in sea-water by anodic stripping voltammetry

The horizontal distribution of zinc in surface waters from Guanabara Bay has been studied by use of optimized voltammetric techniques and ultraclean working procedures. The non-linearity observed between the peak current for zinc and the electrolysis time, as well as the appearance of a peak at −1.16 V, are discussed. The values found for total zinc in the samples range between 0.3 and 22 μg/l.     

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.     

Determination of thallium in natural waters by anodic stripping voltammetry

Thallium was determined in natural waters by anodic stripping voltammetry at a hanging mercury drop electrode, in acetate buffer pH 4.6+EDTA, after preconcentration and separation on an anion exhange resin. For Pacific Ocean surface waters a mean value of 13.0±1.4 ng Tl l^?1 was found, while for freshwater samples the value was 3.7±1.0 ng Tl l^?1. Thermodynamic considerations of thallium speciation predict that both in seawater and freshwater thallium exists primarily in the trivalent state. This was confirmed by experiment.     

Square-wave anodic stripping voltammetry with a mercury-plated reticulated vitreous carbon electrode

A rotating mercury-plated reticulated vitreous carbon (RVC) electrode is tested for square-wave anodic stripping voltammetry; RVC provides very large surface areas which are easily plated with mercury. Despite the ill-defined geometry of the electrode, the square-wave stripping peaks are very well defined; their behaviour conforms partly to known theory for square-wave stripping from mercury film electrodes. Fast analytical determinations of lead and cadmium in the μg l^?1 range are facilitated by the high efficiency of the preconcentration step and the high sensitivity given by the stripping waveform.     

Determination of copper and lead in schist by anodic stripping voltammetry

Samples were decomposed in HClO₄/HF mixture in a Teflon beaker to avoid electrochemical interference from platinum ions. The residue remaining after evaporation to dryness was taken up in nitric acid and examined by anodic stripping voltammetry. Both the hanging mercury drop electrode and the rotating glassy carbon electrode, mercury-plated in situ, were used with success. Copper at 120 ppm and lead at 40 ppm were determined with a relative standard deviation of 6%. The schist was the Nordic reference sample ASK-2.     

Determination of gallium traces by differential pulse anodic stripping voltammetry

Summary The determination of gallium traces is carried out on the hanging drop mercury electrode in solutions of low ionic strength and in absence of complexing agents. At pH=3.2, where stable solutions are obtained, concentrations of 0.2 g Ga l^–1 are determinated with a standard deviation of 0.96% and a detection limit of 4 ng Ga l^–1.The effect of various instrumental parameters is investigated and optimized conditions established. The theory of differential pulse anodic stripping voltammetry is verified with the results obtained experimentally. The use of salicylate as base electrolyte is also considered.

---

Bestimmung von Galliumspuren durch Differentialpuls-Anodic Stripping-Voltammetrie

     

Determination of levofloxacin in human urine by adsorptive square-wave anodic stripping voltammetry on a glassy carbon electrode

The adsorption behavior of levofloxacin on a glassy carbon electrode was explored by cyclic and square-wave voltammetry. The drug was accumulated on a glassy carbon electrode and a well-defined oxidation peak was obtained in acetate buffer pH 5.0. Using square-wave anodic stripping voltammetry and accumulation at +0.4 V versus Ag/AgCl (saturated KCl) for 300 s, linear calibration graph was obtained from 6.0x10(-9) to 5.0x10(-7) M levofloxacin. The detection limit was calculated to be 5.0x10(-9) M. The R.S.D. determined from ten determinations at the 1.0x10(-7) M level was 1.7%. The method was applied for the direct determination of levofloxacin in diluted urine samples. It was validated using high-performance liquid chromatography (HPLC) as a reference method.