Analytica Chimica Acta 522 (2004) 35–44
Metal ion analysis in contaminated water samples using
anodic stripping voltammetry and a nanocrystalline
diamond thin-film electrode
Prerna Sonthalia, Elizabeth McGaw, Yoshiyuki Show, Greg M. Swain∗
Department of Chemistry, Michigan State University, 320 Chemistry Building, East Lansing, MI48824, USA
Abstract
Boron-doped nanocrystalline diamond thin-film electrodes were employed for the detection and quantification of Ag (I), Cu (II), Pb (II),
Cd (II), and Zn (II) in several contaminated water samples using anodic stripping voltammetric (ASV). Diamond is an alternate electrode
that possesses many of the same attributes as Hg and, therefore, appears to be a viable material for this electroanalytical measurement.
The nanocrystalline form has been found to perform slightly better than the more conventional microcrystalline form of diamond in this
application. Differential pulse voltammetry (DPASV) was used to detect these metal ions in lake water, well water, tap water, wastewater
treatment sludge, and soil. The electrochemical results were compared with data from inductively coupled plasma mass spectrometric
(ICP-MS) and or atomic absorption spectrometric (AAS) measurements of the same samples. Diamond is shown to function well in this
electroanalytical application, providing a wide linear dynamic range, a low limit of quantitation, excellent response precision, and good
response accuracy. For the analysis of Pb (II), bare diamond provided a response nearly identical to that obtained with a Hg-coated glassy
carbon electrode.
The method, when coupled with an appropriate electrode material, generally provides low detection limits for many
metal ions with a wide linear dynamic range and good response precision. Additionally, the method possesses multielement detection capability, and requires instrumentation of low cost and low maintenance. The instrumentation
(and analysis method) is field deployable and requires low power without the need for cooling or ventilation.
Chemistry 65.2302*
ANALYTICAL CHEMISTRY
LABORATORY MANUAL
Fall 2006
F. Cassalman
C.L. Chakrabarti
E.P.C. Lai
Department of Chemistry
Carleton University
EXPERIMENTS
1.
Ion Chromatography of Anions in Tap/River Water with
Conductivity Detection.
17
2.
Determination of Fluoride in Drinking Water by Ion-Selective
Electrode Potentiometry.
20
Determination of Lead, Cadmium and Copper
in Tap/River Water by Differential Pulse Anodic
Stripping Voltammetry.
23
4.
Determination of Copper and Zinc in Tap/River Water by Atomic
Absorption Spectroscopy.
27
5.
Gas Chromatography of Polycyclic Aromatic
Hydrocarbons with Flame Ionization Detection.
31
6.
Monitoring of Carbonyls by 2,4-Dinitrophenylhydrazine Derivatization
35
and Reversed-Phase High Performance Liquid Chromatography.
7.
Chemical Oxygen Demand Assay by Standard Method 5200 D.
3.
39
23
Experiment 3
Determination of Lead, Cadmium and Copper in Tap/River
Water by Differential Pulse Anodic Stripping Voltammetry
Cd Uptake in Human Beings
This concerns a very worrying problem. The Cd content of some
Canadian wheat crops largely exceeds the norms fixed by the
World Health Organization.
Therefore bread and Canadian exportations of wheat are potentially
hazardous to human health, by inducing possibly kidney diseases.
Chapter 17
Electroanalytical Techniques
p. 372 Harris (6th)
Voltammetry and Polarography
Voltammetry is a collection of analytical techniques in which the
relationship between current and voltage is observed during
electrochemical processes.
When voltammetry is conducted with a mercury electrode, it is
called polarography.
p. 372 Harris (6th)
17-5
Anodic Stripping Voltammetry
Advantages
The most sensitive of all electroanalytical techniques
detection limits = 10-10 M = 0.01 ppb
Simultaneous multi-component analysis
-- determined by the electrodeposition potential.
Figures of Merit
Electrodeposition potential = -1.0 V
Pulse height = 50 mV
Scan rate = 10 mV/s
Slope
Sensitivity
(A/M)
LOD
%RSD
R2
(M)
Zn
3.038
9.52x10-10
2.76
0.982
Cd
2.253
2.38x10-11
11.2
0.990
Pb
2.262
2.88x10-10
7.19
0.982
Cu
1.981
3.44x10-10
8.49
0.995
Metrohm (Switzerland)
797 VA Computrace
is a PC controlled system for voltammetry
http://www.metrohm.com/products/06/797/797.html
797 VA Computrace
The versatile instrument for voltammetry
797 VA Computrace is a modern voltammetric work station connected to the PC via a USB port. The complementary PC software
controls the determination, records and evaluates the measured data. Thanks to the sophisticated program design, the operation is
unbeatably simple. All the methods that are described in the Metrohm Application Bulletins and Metrohm Application Notes are
already preinstalled. The integrated new designed potentiostat with galvanostat guarantees highest precision with reduced noise. The
well-proven Multi Mode Electrode (MME) as well as rotating disk electrodes (RDE) from different materials are available as working
electrodes, of course.
The most important applications
Stripping Voltammetry
Voltammetric trace analysis of metal ions and other substances
CVS
Cyclic Voltammetric Stripping for the determination of additives in plating solutions
Exploratory
The Metrohm concept for teaching in electrochemistry
8 important advantages

One instrument for voltammetric trace analysis and determinations of additives in metal
finishing

Highest sensitivity due to the combination of the well-proven Multi Mode Electrode with the
new designed potentiostat

Data archiving using the database program Autodatabase with report generator

More than 220 important analysis methods preinstalled

Result in any number of formats

Unique Exploratory mode especially designed for teaching in schools and universities.
Ideal in combination with two Metrohm Monographs «Introduction to Polarography and
Voltammetry» and "Practical Voltammetry"

Integrated quality assurance with the GLP wizard, and the automatic electrode
test

Simple operation due to the Windows oriented, clearly arranged user interface

797 VA Computrace - manual or automated
Without additional accessory the 797 VA Computrace is a fully functional analysis system for
highest demands in accuracy and sensitivity. Higher comfort can be achieved with various
extension possibilities.

Automatic addition of solutions with 800 Dosinos
Calibration in voltammetry is done by standard addition or calibration curve and can be carried out automatically using max. 3 800
auxiliary solutions such as buffers or complexing agents can be added automatically as well.

Automatic rinsing with the 772 Pump Units or 823 Membrane Pump Units
Two 772 Pump Units or 823 Membrane Pump Units can rinse and empty the measuring vessel after each analysis automatically. This
option can also be used for manually operated analysis systems as well as for VA Computrace systems with Autosampler. The reproducible and efficient
rinsing minimizes carry-over and increases the accuracy of the analyses.

Fully automated analysis of small sample series with the 813 Compact Autosampler in voltammetric trace analysis
The 813 Compact Autosampler allows the precise and reproducible analysis of several samples. The sample rack holds maximum 18 samples,
that are transferred into the measuring vessel on the 797 VA Computrace using the built-in peristaltic pump.

Fully automated CVS determination of organic additives in plating solutions with the 838 Advanced VA Sample Processor
The flexible and fully unattended determination of organic additives can be realized with the 838 Advanced VA Sample Processor. The
sample rack holds maximum 28 samples for the determination of brighteners and 56 samples or calibration standards for the determination of suppressors.

Autodatabase
All measured data can be stored in a database with the program Autodatabase. The report generator allows to assess all data on the screen and to generate
individually designed hardcopies.
Dosinos. All other
In order to make your work even easier we have made our application know-how available on-line. On our website you can call up a
wide range of application information. Apart from the list of our Application Bulletins you will also find more than 100 VA
Application Notes, which contain many interesting practical examples from our application laboratories. Sample preparation to
remove organic interferences from samples can be performed comfortably with the 705 UV Digester.
Apparatus - Cell and Electrode Assembly for DPASV
I.
Theory
In many environmental applications, trace analysis for Pb, Cd and Cu are
of interest. Anodic stripping voltammetry can be combined with differential
pulse current measurement to provide high sensitivity for these determinations.
In anodic stripping voltammetry the metal ions are first deposited in a hanging
mercury drop for a fixed period of time, with the potential at the mercury drop
set to a value sufficiently negative to ensure reduction of the ions.
The potential is next scanned back towards more positive values. During this
scanning process, each of the deposited metals are re-oxidised at a characteristic
voltage and a current signal can be measured for quantitative analysis.
Procedure
(a)
The analytes from a dilute solution are first concentrated into a single drop
of mercury by electrochemical reduction at a negative potential:
At -1.20 V
(b)
Cu2+ + 2e- + Hg  Cu(Hg)
amalgam
Pb2+ + 2e- + Hg  Pb(Hg)
amalgam
Cd2+ + 2e- + Hg  Cd(Hg)
amalgam
Zn2+ + 2e- + Hg  Zn(Hg)
amalgam
The concentrated analytes (amalgam) are then stripped from the electrode
by oxidizing the metals back into solution at characteristic (less negative)
potentials:
Zn(Hg)  Zn2+ + 2e- + Hg
Ep = -1.0 V
Cd(Hg)  Cd2+ + 2e- + Hg
Ep = -0.6 V
Pb(Hg)  Pb2+ + 2e- + Hg
Ep = -0.4 V
Cu(Hg)  Cu2+ + 2e- + Hg
(c)
Ep = 0.0 V
The peak current measured during the stripping oxidation is related to
the quantity of analyte that was initially deposited:
Ip α [analyte]cell solution
Differential pulse is a current measurement technique that enhances the analytical
(faradaic) current and avoids the background (charging) current, resulting in a
higher signal-to-noise ratio for a better detection limit.
Differential pulse anodic stripping voltammetry (DPASV) is routinely useful for low
concentrations down to 10-9 M, such as in the determination of trace metals in natural
waters.
The Princeton Applied Research model 174 Polarographic Analyzer equipped
with a reference electrode, a counter electrode and a working electrode is a popular
instrument for DPASV.
The function of the Analyzer is to serve not only as a potentiostat to provide a
controlled potential across the reference electrode and the working electrode, but
also as an amplifier to measure the small analytical currents.
Saturated Calomel Electrode
Voltage Conversion between Different Reference Scales
p. 317 Harris (6th)
Eo (vs. SHE)
- 0.241 V
=
E (vs. SCE)
E (vs. Ag/AgCl)
Zn
-0.98 to -0.93 V
Cd
-0.380 V
-0.621 V
-0.61 to -0.58 V
Pb
-0.126 V
-0.367 V
-0.41 to -0.38 V
Cu
+0.339 V
+0.098 V
-0.10 to +0.10V
Versatile Applications of Polarography
Metal ion
E (vs. SCE) in 0.1 M KCl
K+
-2.14 V
Na+
-2.12 V
Mn2+
-1.42 V
Fe2+
-1.30 V
Co2+
-1.20 V
Ni2+
-1.10 V
Zn2+
-1.00 V
Cd2+
-0.60 V
Tl+
-0.48 V
Pb2+
-0.40 V
Bi3+
-0.09 V
Cu2+
+0.04 V
17-5 Voltammetry
p. 388 Harris (6th)
p. 471-509 Harris (5th)
DIFFERENTIAL PULSE VOLTAMMETRY
-- improvements over (direct current) polarography
Same arrangement of electrodes and sample
for dc and differential pulse polarographies.
Pulsed voltage ramp used in differential pulse polarography
Why does differential pulse polarography voltammetry
offer higher sensitivity and better detection limits than
direct-current polarography?
enhancement of the faradaic current (= signal)
a surge of current to lower the analyte
concentration at the Hg drop (in the double
layer) to that demanded by the new pulse
potential.
 analytical sensitivity is increased.
decrease in the condenser charging current
-- measurement of the faradaic current is made
after the condenser current has decayed to
near zero.
 the noise contribution due to fluctuations in
the condenser current is reduced.
Measurements in differential pulse polarography
are made after the condenser current has decayed
to near zero. Therefore, only Faradaic current is
measured, without the noise contribution due to
fluctuations in the condenser current.
Also,
enhancement of the Faradaic current results from a
surge of current that lowers the analyte
concentration in the double layer to that demanded
by the new applied potential of the pulse.
Consequently, baseline noise is reduced and
analytical sensitivity is increased to provide
improved (i.e. lower) detection limits.
Effect of modulation amplitude
As the modulation amplitude is increased, the peak height
increases ( higher sensitivity), but the resolution (separation
of neighbouring peaks) decreases.
Q.
Q.
DPV offers enhanced sensitivity because
(a) a minimal modulation amplitude of 2 mV is used.
(b) it measures and plots the sum of condenser (or
charging) and Faradaic currents versus the applied
potential.
(c) the analyte peak signal can be added to its
neighboring peak signals.
(d) a slow scan rate of 1 mV/s is employed.
(e) a surge of current occurs to lower the analyte
concentration at the Hg drop..
Problem 17-11
p. 497, Harris (6th)
Supposing that a mixture containing 1.00 mM CHCl3 and
1.00 mM DDT (a pesticide) gave differential pulse
polarographic signals in the proportion
Peak height of CHCl3 / Peak height of DDT = 1.40
An unknown solution of DDT was treated with a tiny
amount of pure CHCl3 to give a concentration of 0.500
mM CHCl3, without significantly changing the
concentration of unknown. Now the relative signals are
found to be
Peak height of CHCl3 / Peak height of DDT = 0.86
Find the concentration of DDT in the unknown.
Calculations will be shown in tutorial next Tuesday
Disadvantages of trace analysis by DPASV
o
Long electro-deposition time
(depending on sample concentration)
10-6 M
0.1 ppm
10-8 M
1 ppb
10-10 M
0.01 ppb
< 60 s
> 1 hr
o
Supporting electrolyte must be added to sample solution
Electrostatic attraction of analyte cations by the negative DME
potentials is minimized by the presence of a high concentration of
supporting electrolyte
Precision of trace analysis by DPASV

> 2% depending on the artistry of the person doing the analysis
and sample preparation.
Peak height is directly proportion to
[Mn+]
negative potential for electrodeposition
time of electrodeposition

All experimental conditions and parameters must be kept as
constant and reproducible as possible.
Accuracy of trace analysis by DPASV
 In trace analysis, extreme precautions are necessary to avoid extrinsic
contamination by impurities present in supporting electrolyte or buffer
solution
A reagent blank analysis should be performed to correct for possible
contamination.
Experiment 3
Determination of Lead, Cadmium and Copper in Natural Waters by DPASV
Standard Addition Method (graphic procedure)
50 mL of electrolyte solution (1 M HCl) in cell.
Add 1 mL of unknown sample solution.
Add 1 mL of standard solution (1x10-5 M)
Keep adding the standard for another 3 times.
p. 88, Harris (6th)
5-3 Standard Addition
The matrix affects the magnitude of the analytical signal.
In standard additions, all samples are in the same matrix.
p. 336, Harris (6th)15-7
Standard Addition with Ion-Selective Electrodes
It is important that the composition of the standard
solution closely approximates the composition of the
unknown.
For complex or unknown matrices, the standard addition
method can be used.
p. 391, Harris (6th)
17-5 Square Wave Voltammetry
is the most efficient voltage profile for polarography or voltammetry
uses the waveform in Fig. 17-18 (on p. 393) which consists of a
square wave superimposed on a staircase wave
Graphic procedure
Plot the DPASV peak current vs. the concentration of standard added:
Conc. of standard in sample solution after 1st addition
= (1x10-5 M)[1 mL/(1 mL+1 mL+50 mL)] = 1.9x10-7 M
Conc. of standard in sample solution after 2nd addition
= (1x10-5 M)[2 mL/(2 mL+1 mL+50 mL)] = 3.8x10-7 M
Conc. of standard in sample solution after 3rd addition
= (1x10-5 M)[3 mL/(3 mL+1 mL+50 mL)] = 5.6x10-7 M
Conc. of standard in sample solution after 4th addition
= (1x10-5 M)[4 mL/(4 mL+1 mL+50 mL)] = 7.3x10-7 M
Standard Addition Graph