Direct determination of free Zn concentration in samples of biological interest

Absence of Gradients and Nernstian Equilibrium Stripping (AGNES): An Electroanalytical Technique for Chemical Speciation: A Tutorial Review

“…The thin film of mercury was electroplated on this electrode from a solution of 0.24 mmol L −1 Hg(NO 3 ) 2 (Merck, Certipur ® ) and 0.15 mol L −1 HNO 3 (adjusted to pH 1.9). The step by step modification of the working electrode can be seen in [22]. The cleaning solution of the rotating electrode and the reoxidation solution of the mercury film contained 1 mol L −1 CH 3 COONH 4 and 0.1 mol L −1 NH 4 SCN (both from Merck, Emsure ® ), respectively, in 0.5 mol L −1 HCl (FisherScientific, Darmstadt, Germany, Trace Metal Grade).…”

“…We kept the variant 2P (see Section 2.1.3) for the first stage, but we used the rotating disk electrode due to advantages such as: (i) an enhanced mass transport and (ii) a large surface-to-volume ratio. To avoid the possible interference of particularly strong adsorption or particle adhesion: (a) we used the variant SCP for the second stage (which provides a charge to be processed with the fundamental Equation ( 6) and there is no need of blank), and (b) we covered the mercury film with Nafion [22]. The procedure AGNES-SCP_2P.nox is provided in the Supplementary Materials.…”

“…For moderate gains (e.g., free concentrations above 0.1 µmol L −1 ), the renewal of the HMDE is usually efficient. For large gains, the covering of the RDE with Nafion [22,42,43] can be a good option.…”

“…Our lab has been working with AGNES since the internal presentation of the seminal idea in May 1999. In the first publications [8,9], the basic principles were described and applied to solutions with Cd and Zn, but many other developments (also by other research groups) followed, such as the tackling of other elements [10][11][12], validations of AGNES against other techniques [13], measurements in a variety of media and systems [14][15][16][17][18][19][20], new variants [21], other electrodes [22], etc. So, there is a wealth of sources in the literature about successful implementations of AGNES that were reviewed a short time ago [23].…”