Solid-contact Cu(II) ion-selective electrode based on 1,2-di-(<Emphasis Type="Italic">o</Emphasis>-salicylaldiminophenylthio)ethane

The development of Cu(II) solid-contact ion-selective electrodes, based on 1,2-di-(o-salicylaldiminophenylthio)ethane as a neutral carrier, is presented. For the electrodes construction, unmodified carbon ink (type 1 electrode) and polymer membrane-modified carbon ink (type 2 electrode) were used as solid support and transducer layer. Also, carbon ink composite polymer membrane electrode (type 3 electrode) was prepared. The analytical performance of the electrodes was evaluated with potentiometry, while bulk and interfacial electrode features were provided with electrochemical impedance spectroscopy. It is shown that modification of carbon ink with polymer membrane cocktail decreases the bulk contact resistance of the transducer layer and polymer membrane, thus enhancing the analytical performance of the electrode in terms of sensitivity, linear range, and stability of potential. The optimized electrodes of types 2 and 3 exhibit a wide linear range with detection limits of 1.8 × 10⁻⁶ and 1.6 × 10⁻⁶ M, respectively. They are suitable for determination of Cu²⁺ in analytical measurements by direct potentiometry and in potentiometric titrations, within pH between 2.3 and 6.5. The electrodes are selective for Cu²⁺ over a large number of tested transition and heavy metal ions.     

Results of the 16th proficiency test on the determination of pesticide residues in olive oil

Accreditation and Quality Assurance - The Italian National Reference Laboratory (NRL) for pesticide residues yearly organizes proficiency tests (PTs) on olive oil in cooperation with the...     

Determination of pyrethroid pesticide residues in fatty materials by solid-matrix dispersion partition, followed by mini-column size-exclusion chromatography

The method studied uses a combination of a solid-matrix dispersion partition (SMDP) followed by high-performance size-exclusion chromatography on a minicolumn (HPmSEC) of 7.8 mm I.D. for the separation of pyrethroid (PYR) residues from fatty material. The solid-matrix dispersion extraction is carried out by absorbing a fat solution onto an Extrelut-3 cartridge (filled with a macroporous diatomaceous material) and extracting the PYR residues with acetonitrile. Up to 1 g of fatty material can be extracted with 15 ml acetonitrile. The small amount (mean +/- S.D. = 12.4 +/- 5.9 mg) of fatty material which is eluted into the acetonitrile is further removed by HPmSEC. PYR pesticide residues are collected in a 2-ml fraction between 7 and 9 ml, the column being washed up to 24 ml. The two techniques used in series allow a better removal of fat, a greater input of sample and a lower consumption of solvent compared to the sole SEC on macrocolumns, and a lower limit of determination compared to the sole SEC on minicolumns. Recoveries of 9 PYR out of the 14 investigated residues from soya oil were in the range 66-83% at spiking levels ranging 0.49-2.57 mg/kg, while for 6 PYR residues tested at spiking levels in the range 0.13-0.53 mg/kg the recoveries were in the range 80-111%. Recovery of fluvalinate and permethrin could not be calculated due to interferences from soya oil, while lambda-cyhalothrin, esfenvalerate and tralomethrin gave low recovery. The final extract contains small amount (mean +/- S.D. = 2.4 +/- 0.9 mg) of lipid residue and is not completely free from interferences.     

Selective clean-up applicable to aqueous acetone extracts for the determination of carbendazim and thiabendazole in fruits and vegetables by high-performance liquid chromatography with UV detection

Fungicide residues in vegetables (benomyl, carbendazim, thiabendazole) are analyzed through a clean-up procedure that uses a portion of the aqueous acetone extract prepared for multiresidue methodology. A portion of the aqueous acetone extract (equivalent to 5 g of vegetables) is loaded onto an Extrelut-20 cartridge (the cartridge is filled with a coarse, large-pore diatomaceous material). Then, acetone is partially removed by an upward stream of nitrogen at 2l/min for 30 min. Benzimidazolic fungicides are recovered by percolating the cartridge with 100 ml of 0.1 M phosphoric acid solution, which also serves to convert benomyl to carbendazim. The percolating acid solution is drained on-line through a strong cation-exchange (SCX) solid-phase extraction cartridge with the aid of a slight vacuum. Benzimidazolic fungicides are retained on the SCX cartridge. The phosphoric acid solution is discarded together with the washings of the SCX cartridge, i.e., water followed by methanol-water (75:25), that remove unwanted coextractives. Finally, benzimidazolic fungicides are recovered by eluting the SCX cartridge with methanol-ammonium formate buffer (75:25). The final extract is then analyzed by reversed-phase HPLC with UV detection. Recoveries from crops such as apples, lettuce, strawberries and citrus fruits are generally greater than 80% and no interferences were observed. The clean-up is simple and straightforward, requires only disposable items, water solutions and a few milliliters of solvent and a minimum number of manipulations, and does not require concentration steps or electrical equipment.     

Organic light‐emitting transistors with voltage‐tunable lit area and full channel illumination

Organic light‐emitting transistors (OLETs) are multifunctional optoelectronic devices that hold great promise for a variety of applications, including flat panel displays, integrated light sources for sensing and optical communication systems. The narrow illumination area within the device channel is considered intrinsic to the device architecture and is a severe technological drawback for all those applications where a controlled, wide and homogeneous emission area is required. Here it is shown that not only the position but also the extension of the emission area is voltage‐tunable, and the entire channel of the transistor can be homogeneously illuminated. The modeling of the exciton distribution within the channel at the different bias conditions coupled to the modeling of the device emission profile highlights that excitons are spread through the entire channel width and across the bulk of the central emission layer of the p‐channel/emitter/n‐channel trilayer active heterostructure.     

Evaluation of the reproducibility standard deviation in the pesticide multi-residue methods on olive oil from past proficiency tests

Accreditation and Quality Assurance - The data reported in the frame of proficiency testing (PT) exercises organized from 2007 to 2016 have been statistically re-evaluated using Algorithm A of the...     

Fluoride electrode with LaF(3)-membrane and simple disjoining solid-state internal contact

Fluoride-selective electrode with LaF(3)-membrane and stainless steel internal contact has been prepared. The electrode has been tested in F(-) concentration range 10(-2)-10(-6) M and the results compared with those of commercial electrode and electrode with laboratory renewed internal electrolytic contact. The properties of simple disjoining solid-state contact have been investigated by means of electrochemical impedance spectroscopy (EIS). The impedance spectra show two time constants, which suggest that, at lower frequencies, proceed some Faradic reaction which probably stabilizes the potential between LaF(3)-membrane and stainless steel disk.     

Development of a flow manifold for Fe(III) ion determination with a fluoride ion-selective electrode

Continuous-flow (CF) and flow-injection (FI) analysis using the fluoride ion-selective electrode (FISE) as detector have been investigated. The measurements were performed in a home-made cell under appropriate flow conditions (2.86 or 3.45 ml min⁻¹, 0.2 ml samples, 10⁻⁶ M sodium fluoride). The calibration graph was obtained by plotting the signal height versus concentration of iron in the range of Fe(III) concentration from 10⁻⁵ to 10⁻¹ M in acetate buffer (pH 2.8 or 3.4). In all described procedures, the range of linear response extends to the Fe(III) concentration from 1×10⁻³ to 1×10⁻¹ M, with detection limit 9×10⁻⁵ M. The effect of double-line, two-line flow manifold and CF was investigated and discussed.