Dilution Titration for Suppressors
Effects of contamination
Effects of chloride
Interpretation of "fingerprints"
Analysis of Inorganic Components
Other information
Literature references
Basic CVS
Voltammetry is an electrochemical measurment in which an applied potential
(voltage) is used to
cause the oxidation or reduction of a substance at the electrode surgace in
an electrolyte solution.
Oxidation, which can be defined as removing electrons from a molecule or ion,
is said to take place at the anode of an electrochemical cell, while reduction
(forcing electrons onto a molecule of ion) occurs
at the cathode. The electric current that results is measured at several
different applied potentials.
Usually, the current is plotted on the Y-axis, versus the applied potential,
which is plotted on the
X-axis.
In cyclic voltammetry, the applied potential is cycled back and forth. The
working electrode surface
alternately becomes the anode and the cathode. By definition, the electric
current is positive when the working electrode is the anode, and negative when
it is the cathode.
Cyclic Voltammetric Stripping (CVS) is cyclic voltammetry in which, during
the cycling, a solid is electrodeposited (electroplated) onto the electrode in
one part of the cycle, and electrochemically dissolved (stripped) in a different
part. In CVS, the total current that results from the stripping is integrated to
give the total charge used for stripping. The stripping charge ( in milicoulombs
) is essentially a tally of the number of electrons used to strip the deposited
chemical from the electrode.
Since the number of electrons is related directly to the number of atoms ( or
molecules ) stripped off, the stripping charge is directly related to the amount
of chemical deposited on the electrode.
Since a rotationg electrode is used by the QL-5, and since the integral of a
curve on a graph is equal to the area under the graph, we usually refer to the
stripping charge as Ar, Rotationg Area. The technique is quite sensitive - an Ar
value of 1.00mC ( easily measured with the QL-5 ) is equivalent to less than
0.66 micrograms of copper deposited on the electrode.
The area Ar can be related to the activity of organic additives through the
use of a response curve of
through the various techniques described in the Applications Notes. These
notes are provided for individual additive systems or can be found in the
published literature listed in the Literature References at the end of this
section.
Fig. 6 is an example of a CVS voltammogram, of " fingerprint " of an acid
copper plationg bath. The area
under the peak, referred to as Ar, referred to as Ar, repersents the charge (
in milicoulombs ) required to strip the plated copper from the platinum
electrode while the electrode is rotating. The amount of copper stripped off the
electrode is equal to the amount of copper deposited. This is of interest to the
electroplater, and is the basis of the CVS analysis.
The area Ar can be related to the activity of organic additives through the
use of a response curve or through the various techniques described in the
Applications Notes on page 35. These notes are provided for individual additive
systems or can be found in the published literature listed in the Literature
References, on page 181.
The voltage scanning takes the rotating platinum electrode ( see Fig. 6
above where numbers in parentheses refer to numbered sections of the CVS
trace in this figure )
1. From a high oxidizing voltage, which cleans the platinum surgace (2)
2. Through a voltage region where the surgace equilibrates
with solution components (3)
3. Into a plating voltage region where metal is deposited (4)
During Deposition, the voltage scan reaches its negative limit and reverses
(5), taking the rotationg electrode -
4. Through the negative voltage region where plating gradually decreases to zero
(6), at which time integration of the stripping current begins,
5. Through a stripping region (positive current) where the metal is stripped
off, at which time the positive current drops almost to zero (7) (integration of
stripping current ends shortly after that),
6. To a voltage where some oxidizable impurities cause a diffusion current,
which can be used to approximate their relative concentrations,
7. To a voltage where other oxidizable species (i.e. chloride) cause an
additional current.
8. Back to the cleaning potential (2)
When a steady state is achieved, the platinum plating surgace is
reproducible. This allows the electrode to be used repeatedly, and establishes a
reproducible basic for comparing the deposition from different solutions.
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