ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 3, pp. 420!422. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + S.S. Ermakov, A.A. Sheremet, L.N. Moskvin, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 3, pp. 434!436.
AND CORROSION PROTECTION OF METALS
Determination of Zinc in Aqueous Solutions by a Combined
No-Standard Electrochemical Method with Preliminary
Electrolytic Separation of Copper
S. S. Ermakov, A. A. Sheremet, and L. N. Moskvin
St. Petersburg State University, St. Petersburg, Russia
Received September 20, 2007
Abstract-A combined method for no-standard determination of zinc in aqueous solutions (calibration of
the device against standard solutions or use of standard additions is not required) is suggested. The method is
based on principles of stripping voltammetry and potentiostatic coulometry.
Stripping voltammetry (SVA) is a commonly used
method for determination of copper, cadmium, lead,
and zinc in various aqueous media and food products.
One of drawbacks of the method is the necessity of
calibration against reference samples, i.e., it requires
time-consuming construction of calibration plots.
Several versions of no-standard electrochemical
methods without references, allowing determination
of metals in aqueous solution, have been suggested
[1!5]. Companys et al. [1, 2] used the potentiometric
analytical procedure: they deposited on the surface
of an electrode by pre-electrolysis an amalgam with
a known concentration of a metal being determined
and then used the quasi-equilibrium potential of the
system to calculate the concentration of
a substance being analyzed in solution. A stripping
chronopotentiometric version of the no-standard elec-
trochemical method has been suggested . This
method is based on multiple-cycle dissolution of
a metal from an amalgam obtained in the pre-electro-
lysis stage and subsequent finding of a charge Q
responding to complete deposition of the substance
from solution. A technique termed dynamic coulome-
try was suggested in [4, 5]. This method is based on
multiple-cycle scanning of the potential. A combined
electrochemical method based on principles of SVA
and potentiostatic coulometry was developed in [6!8].
The possibility of using it for the determination of
lead ions , of copper and cadmium ions in the
absence and in the presence of lead ions , and of
mercury ions  was demonstrated previously. One of
the main drawbacks of SVA in the case of simultane-
ous presence of ions of several metals is manifestation
of the effects associated with formation of intermet-
allic compounds (IMC) in the amalgam of the work-
ing electrode. This phenomenon results in the shift
of the peaks of the analyzed substances or leads to
the appearance of new peaks .
This study is concerned with the development of
a combined no-standard electrochemical method for
zinc determination in the presence of copper, which
includes preliminary electrolytic separation of copper
to prevent formation of IMCs.
The stripping-voltammetric measurements were
performed on a PU-1 polarograph (ZIP, Gomel, Be-
larus) with an AKV-07 sensor (Akvilon NPKF, Mos-
cow) and on an AKV-07MK voltammetric analyzer
(Akvilon) with Polar-4.1 software in the dc and ac
modes. Solutions with various concentrations of zinc
and copper ions were prepared from solutions of
state reference samples (GSO 6742 and
GSO 7255, respectively) using chemicals of chemical-
ly pure or analytically pure grade and double-distilled
water. The measurements were carried out on a mer-
cury!graphite film electrode rotating at a speed of
1000 rpm in the accumulation stage. A solution of
composition (M) 1 10
was used as supporting electrolyte.
The pre-electrolysis in SVA measurements was per-
formed at a potential of about !1.3 V, with a silver
chloride reference electrode. The design of the elec-
trochemical cell and electrodes has been described
previously [6, 7]. To satisfy the conditions of com-
plete dissolution of the metal from the amalgam, slow
) potential sweep rates were used .