Anastasios Economou

A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair

This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low mug l(-1) concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at -1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from -1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 mug l(-1) for Cd and for Pb and 0.7 mug l(-1) for Zn at a preconcentration time of 10 min. Finally, BFEs were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS).

Mercury film electrodes: developments, trends and potentialities for electroanalysis

In this article, the field of mercury film electrodes (MFEs) as electroanalytical devices is reviewed. Special emphasis is placed on the area of new materials as substrates for the mercury coating and the mercury plating process as well as on the developments related to the electrode modification used to achieve an increase in either the selectivity and/or the sensitivity of the analysis. Other topics discussed are microelectrodes, disposable electrodes and some novel, innovative or less well explored applications of electroanalytical methods using MFEs. The future prospects, potential uses and alternatives for MFEs in electroanalysis are finally discussed.

Determination of multi-class pesticides in wines by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

This work reports a new sensitive multi-residue liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detection, confirmation and quantification of forty-six pesticides and transformation products belonging to different chemical classes in wines. The proposed method makes use of a solid-phase extraction (SPE) procedure with Oasis HLB cartridges that combines isolation of the pesticides and sample clean-up in a single step. Analysis is performed by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-MS/MS) operated in the selected reaction monitoring (SRM) mode, acquiring two specific precursor-product ion transitions per target compound. An investigation of matrix effects has been performed during method validation showing medium to low effects for the majority of the compounds. Limits of detection (LODs) were in the range 0.0003-0.003 mg L(-1) and limits of quantification (LOQs) were in the range 0.001-0.01 mg L(-1). The average recoveries, measured at two concentration levels (0.010 and 0.050 mg L(-1)), were in the range 70-110% for most of the compounds tested with % relative standard deviations below 20%, while a value of 0.010 mg L(-1) has been established as the method limit of quantification (MLOQ) for all target species. Expanded uncertainty values were in the range 10-40% while the Horrat ratios were below 1. The method has been successfully applied to the analysis of 60 wine samples in the course of an annual monitoring study with carbendazim-benomyl, thiophanate-methyl and carbaryl being the most frequently determined pesticides.

A study of Nafion-coated bismuth-film electrodes for the determination of trace metals by anodic stripping voltammetry

This work reports on the fabrication, characterization and applications of Nafion-coated bismuth-film electrodes (NCBFEs) for the determination of trace metals by anodic stripping voltammetry (ASV). A NCBFE was typically prepared by first applying a 5 microl drop of a 1% Nafion solution onto the surface of a glassy-carbon rotating-disk electrode. After evaporation of the solvent, the Bi film was plated on the electrode in situ(i.e. by spiking the sample with 1000 microg l(-1) of Bi(iii) and simultaneous electrolytic deposition of the metal ions and bismuth film on the electrode surface at -1.4 V) or ex-situ(i.e. by electrolytic deposition of the bismuth film in a separate solution containing 1000 microg l(-1) of Bi(iii), followed by the ASV measurement step in the sample solution). Various fabrication and operational parameters were thoroughly investigated and discussed in terms of their effect on the ASV signals. It was found that this voltammetric sensor was suitable for the determination of metals at trace levels by square-wave ASV (SWASV) due to its multi-element detection potential, improved analytical sensitivity, high resistance to surfactants, low cost, ease of fabrication, robustness, speed of analysis and low toxicity (as compared to traditional mercury electrodes). In the presence of 4 mg l(-1) of Triton X-100, the NCBFE afforded a 10-fold peak height enhancement for the Pb peak and a 14-fold enhancement for the Cd peak over a bare BFE while the determination of Zn was feasible only on the NCBFE. The limits of detection (at a signal-to-noise ratio of 3) were 0.1 microg l(-1) for Cd and Pb and 0.4 microg l(-1) for Zn for a deposition time of 10 min. Finally, the electrode was applied to different real samples (tap-water, urine and wine) for the analysis of trace metals with satisfactory results.

Determination of trace aluminium by adsorptive stripping voltammetry on a preplated bismuth-film electrode in the presence of cupferron

This work reports the use of adsorptive stripping voltammetry (AdSV) for the determination of aluminium on a rotating-disc bismuth-film electrode (BiFE). Al(III) ions in the non-deoxygenated sample were complexed with cupferron and the complex was accumulated by adsorption on the surface of the preplated BiFE. The stripping step was carried out by using a square-wave (SW) potential-time voltammetric excitation signal. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3sigma limit of detection for aluminium was 0.5 microg l(-1) at a preconcentration time of 240 s and the relative standard deviation was 4.2% at the 5 microg 1(-1) level for a preconcentration time of 120 s (n=8). The accuracy of the method was established by analysing water and metallurgical samples.

On-line stripping voltammetry of trace metals at a flow-through bismuth-film electrode by means of a hybrid flow-injection/sequential-injection system.

In this work, we describe an automated stripping analyzer operating on a hybrid flow-injection/sequential-injection (FIA/SIA) mode and utilizing a bismuth-film electrode (BiFE) as a flow-through sensor for on-line stripping voltammetry of trace metals. The instrument combines the advantages of FIA and SIA and is characterised by simplicity, low-cost, rapidity, versatility and low consumption of solutions. The proposed analytical flow methodology was applied to the determination of Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) and of Ni(II) and Co(II) by adsorptive stripping voltammetry (AdSV). The steps of the rather complex experimental sequence (i.e. the bismuth-film formation, the analyte accumulation, the voltammetric stripping and the electrode cleaning/regeneration) were conducted on-line and the critical parameters related to the respective analytical procedures were investigated. In ASV, for a accumulation time of 180s the limits of detection for Cd(II) and Pb(II) were 2 and 1microg l(-1), respectively (S/N=3) and the relative standard deviations were 5.3% and 4.7%, respectively (n=8). In AdSV, for a total sample volume of 1000microl, the limits of detection for Ni(II) and Co(II) were 1microg l(-1) (S/N=3) and the relative standard deviations were 5.5% and 6.2%, respectively (n=8). The measurement frequency ranged between 15 and 20 stripping cycles h(-1). The results indicate that the BiFE is well suited as a flow-through detector for on-line stripping analysis and, by virtue of its low toxicity, can serve as a viable alternative to mercury-based flow-through electrodes.

Sensitive determination of captopril by flow injection analysis with chemiluminescence detection based on the enhancement of the luminol reaction

This work reports a novel flow injection (FI) method for the determination of captopril, 1-[(2 S)-3-mercapto-2-methylpropionyl]-l-proline (CPL), based on the enhancement CPL affords on the chemiluminescence (CL) reaction between luminol and hydrogen peroxide. For this purpose alkaline luminol and hydrogen peroxide solutions were mixed online, the sample containing CPL was injected into an aqueous carrier stream, mixed with the luminol-hydrogen peroxide stream and pumped into a glass flow cell positioned in front of a photomultiplier tube (PMT). The increase in the CL intensity was recorded in the form of FI peaks, the height of which was related to the CPL mass concentration in the sample. Different chemical and instrumental parameters affecting the CL response were investigated. Under the selected conditions, the log–log calibration curve was linear in the range 5–5000 gl −1 of CPL, the limit of detection was 2 gl −1 (at the 3σ level), the R.S.D., sr was 3.1% at the 100 gl −1 level (n = 8) and the sampling rate was 180 injections h −1 . The method was applied to the determination of CPL in pharmaceutical formulations with recoveries in the range 100 ± 3%.

Disposable screen-printed sensors modified with bismuth precursor compounds for the rapid voltammetric screening of trace Pb(II) and Cd(II).

In this article, a study of novel screen-printed electrodes bulk-modified with five potential bismuth precursor compounds (bismuth citrate, bismuth titanate, bismuth oxide, bismuth aluminate and bismuth zirconate) is presented for the determination of Cd(II) and Pb(II) by anodic stripping voltammetry. During the electrolytic deposition step, the precursor was reduced and served as the source of bismuth. Different key parameters were investigated in detail such as the nature of the bismuth precursor compound, the precursor content in the carbon ink, the polarisation range of the sensors, the supporting electrolyte, the stripping waveform, the deposition time, the deposition potential and the long-term stability of the sensors under continuous use. Using bismuth citrate as the precursor, the limit of detection was 0.9 μg L(-1) for Pb(II) and 1.1 μg L(-1) for Cd(II). The reproducibility on the same sensor (expressed as % relative standard deviation, (n=8)) was 5.4% for Pb(II) and 7.2% for Cd(II) at the 20 μg L(-1) level. Finally, the sensors were applied to the determination of Cd(II) and Pb(II) in water samples.

Recent developments in on-line electrochemical stripping analysis--an overview of the last 12 years.

This paper presents an overview of the field of electrochemical stripping analysis in flow systems covering developments in the last 12 years (since 1998). The review discusses the flow schemes utilized in stripping analysis, techniques for on-line sample pre-treatment, the main pre-concentration and stripping/detection modes, the most important flow-through cell configurations used and the different types of working electrodes. Finally, applications in inorganic and organic analysis are discussed. Special emphasis is given to different novel approaches developed over the last few years that hold some promise for the future such as the use of the lab-on-a valve (LOV) configuration, microfluidic manifolds, flow-probes for remote sensing, environmentally friendly electrode materials and hyphenation with spectroscopic techniques.

Disposable mercury-free cell-on-a-chip devices with integrated microfabricated electrodes for the determination of trace nickel(II) by adsorptive stripping voltammetry.

This work reports the fabrication of disposable three-electrode cells with integrated sputtered metal-film electrodes. The working electrode was a bismuth-film electrode (BiFE) while the reference and counter electrodes were made of Ag and Pt, respectively. The deposition of the metal layers was carried out by sputtering of the respective metals on a silicon substrate while the exact geometry of the electrodes was defined via a metal mask placed on the substrate during the deposition process. Initially, the electrodes were characterised by cyclic voltammetry. The utility of these devices was tested for the trace determination of Ni(II) by square wave adsorptive stripping voltammetry (SWAdSV) after complexation with dimethylglyoxime (DMG). The experimental variables (the presence of oxygen, the DMG concentration, the preconcentration potential, the accumulation time and the SW parameters), as well as potential interferences, were investigated. Using the selected conditions, the 3sigma limit of detection was 100 ng L(-1) for Ni(II) (for 90 s of preconcentration) and the relative standard deviation for Ni(II) was 2.3% at the 10 microg L(-1) level (n=8). Finally, the method was applied to the determination of Ni(II) in a certified river water sample.