Flow based determination of Cr(VI) by adsorptive cathodic stripping voltammetry on an immobilized magnetic poly(ionic liquid) modified electrode.

In this work an electrochemical procedure for Cr(VI) flow based determination in tap water is presented. An AdCSV method was developed using a screen printed electrode modified with magnetic poly(1-allyl-3-methylimidazolium) chloride and the procedure does not require the addition of complexing agents in the solution unlike the methodologies reported so far for Cr(VI) determination. The flow based system is described and the control variables were studied in detail and optimized using a Taguchi parameters design. Under optimal conditions, the electrochemical sensor offered an excellent response to Cr(VI) and the limit of detection estimated from 3σ was 0.5 µg L-1 (n = 3) allowing the analysis of tap water samples. The effect of interfering ions was also investigated below the maximum permissible limits for tap water according to Mexican standards. The presence of the magnetic particles on the sorbent allowed its easy modification on the electrode surface between each determination when removing the magnetic field placed in the wall-jet cell. Finally, the precision of the method was tested with tap water samples using standard addition method for Cr(VI) quantification and the accuracy was evaluated comparing the results with the dyphenylcarbazide method and by analyzing a certified water sample. The method shows good repeatability and reproducibility (%RSD less than 5%) making it feasible for Cr(VI) flow based determination and no significant difference is observed in the results obtained by both methods.

Ferreira TA ，Rodríguez JA ，Galán-Vidal CA ，Castrillejo Y ，Barrado E ... -  《-》

Electrochemical Sensor Based on Glassy Carbon Electrode Modified with Carbon Nanohorns (SWCNH) for Determination of Cr(VI) via Adsorptive Cathodic Stripping Voltammetry (AdCSV) in Tap Water.

Liendo F ，Pichún B ，Vega AP ，Penagos J ，Serrano N ，Díaz-Cruz JM ，Pizarro J ，Segura R ，Aguirre MJ ... -  《Nanomaterials》

A highly sensitive and selective electrochemical sensor for determination of Cr(VI) in the presence of Cr(III) using modified multi-walled carbon nanotubes/quercetin screen-printed electrode.

A novel screen-printed carbon electrode modified with quercetin/multi-walled carbon nanotubes was fabricated for determination of Cr(VI) in the presence of excess of Cr(III) without any pretreatment. The method is based on accumulation of the quercetin-Cr(III) complex generated in situ from Cr(VI) at the modified electrode surface in an open circuit followed by differential pulse voltammetry detection. The new method allowed selective determination of Cr(VI) in the presence of Cr(III). The influence of various parameters affecting the adsorptive stripping voltammetry performance was investigated. Under the optimum conditions, the calibration plot was found to be linear in the Cr(VI) concentration range from 1.0 to 200 μmol(-1) with a limit of detection(S/N=3) of 0.3 μmol L(-1). The relative standard deviation (RSD%) of seven replicates of the current measurements for a 50 μmol(-1) of Cr(VI) solution was 3.0%. The developed electrode displayed a very low or no sensitivity to alkali, alkali-earth and transition metal cations and was successfully applied for the determination of Cr(VI) in drinking water samples.

Sadeghi S ，Garmroodi A 《-》

Chitosan coated magnetite nanoparticle as a working electrode for determination of Cr(VI) using square wave adsorptive cathodic stripping voltammetry.

The application of chitosan coated magnetite nanoparticle modified carbon paste electrode as a working electrode (chitosan@Fe3O4/CPE) for Cr(VI) analysis is presented. The electrochemical detection mode of square wave adsorptive cathodic stripping voltammetry (SWAdCSV) was selected for determination of Cr(VI) due to the high sensitivity and selectivity. The optimal conditions for electrode preparation and the electrode behavior including parameters affecting the SWAdCSV signal were investigated. Two linear ranges of Cr(VI) determination were observed 0.01-0.3 μg L-1 and 0.5-30 μg L-1 with limits of detection of 0.0061 and 0.078 μg L-1, respectively. The precision of the electrode output in terms of %RSD was 11.4% (n = 30). The method was successfully applied to determine Cr(VI) in drinking water and sea water samples with recovery percentages in range 87-110%. Moreover, the results obtained agree with a paired t-test at the 95% confidence level which were comparable to the standard UV-visible spectrophotometric method.

Sanchayanukun P ，Muncharoen S 《-》

Determination of chromium in estuarine waters by catalytic cathodic stripping voltammetry using a vibrating silver amalgam microwire electrode.

Chromium (Cr(VI)) in water can be determined by adsorptive catalytic cathodic stripping voltammetry in the presence of diethylenetriaminepentaacetic acid (DTPA) and nitrate on the hanging mercury drop electrode (HMDE). Predominately Cr(VI) is detected and the water is UV-digested to convert all Cr to Cr(VI) prior to analysis. We develop here an alternative to the HMDE by using a silver amalgam electrode based on a vibrating microwire. The microwire electrodes were 12.5 μm in diameter and electrochemically coated with mercury, and were stable for a week. Conditions were re-optimised, and we used a DTPA concentration of 5mM, 30 mM acetate pH buffer (pH 5.5 in seawater and pH 5.8 in pure water), and 1.5M nitrate solution. The microwire was reactivated prior to each scan by applying a negative potential (-3V) for 2s which removed all deposited Cr. The detection limit for chromium in pH buffer was found to be 0.2 nM Cr(VI) and in seawater 0.3 nM Cr(VI) at a deposition time of 30s. The response increased linearly with the concentration of Cr(VI) up to 60 nM Cr(VI) in seawater. The limit of detection is less good than using the HMDE, but the linear range is good and the microwire electrode could form the basis of apparatus for flow-analysis. The method was successfully tested on water samples from the estuary of the river Mersey (Liverpool Bay) giving chromium concentrations between 1.48 nM and 2.29 nM.

Espada-Bellido E ，Bi Z ，van den Berg CM 《-》