Tennessee
Valley
Authority
Division of Environmental
Planning
Chattanooga TN 37401
TVA/EP-78/13
United States
Environmental Protection
Agency
Office of Energy, Minerals, arid
Industry
Washington DC 20460
EPA 600 7 78075
May 1978
Research and Development
Determination
of Zinc, Cadmium,
Lead, and Copper
in Water by Anodic
Stripping Voltammetry
Interagency
Energy-Environment
Research
and Development
Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are
1 Environmental Health Effects Research
2 Environmental Protection Technology
3 Ecological Research
4 Environmental Monitoring
5 Socioeconomic Environmental Studies
6 Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8 Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects, assessments of. and development of. control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues
This document is available to the public through the National Technical Informa-
tion Service. Springfield. Virginia 22161
-------
EPA-600/7-78-075
TVA/EP-78/13
May 1978
DETERMINATION CF ZINC, CADMIUM, LEAD, AND CCPFER
IN WATER EY ANODIC STRIPPING VOLTAMMETRY
by
Lyman H. Howe and Isaac E. Jones
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, Tennessee 37401
Interagency Agreement No. D5-E721
Project Ko. E-AP 79EDH
Program Element No. IKE 625C
Project Officer
Gregory D'Alessio
Office of Energy, Minerals, and Industry
U.S. Environmental Protection Agency
Washington, D.C. 20460
Prepared for
OFFICE CF ENERGY, MINERALS, AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
-------
DISCLAIMER
This report was prepared by the Tennessee Valley Authority
and has been reviewed by the Office of Energy, Minerals, and
Industry, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Tennessee
Valley Authority or the U.S. Environmental Protection Agency, nor
does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
-------
ACKNOWLEDGMENTS
This work was conducted as part of the federal Interagency
Energy/Environment Besearch and Development Program with funds
administered through the Environmental Protection Agency (EPA
Contract No. EPA-IAG-D5-0721, TVA Contract No. TV-41967A).
The EPA Project Officer for this research project is
Dr. Gregory D'Alessio, Office of Energy, Minerals, and Industry,
U.S. Environmental Protection Agency, Washington, D.C., and the
TVA Project Director is C. Wayne Bolley, TVA laboratory Branch,
Chattanooga, Tennessee. Their contributions to the direction of
the research and constructive review of the reported results are
gratefully acknowledged. The authors greatly appreciate the
technical information and assistance from Cr. Larry B. Taylcr and
Dr. Jud E. Flato, Princeton Applied Research Corporation, P.O.
Box 2565, Princeton, Hew Jersey 08540.
no.
-------
AESTBACT
The Tennessee Valley Authority developed a method of
differential-pulse anodic stripping voltanunetry for determining
total concentrations of cadmium and lead in water samples from
ash ponds at steam-electric generating plants. After digestion
of the sample and addition of reagents to overcome interferences
by iron (III) and selenium (IV), the peak current for cadmium and
lead is measured and quantified by standard addition. The
effective range for this method is 0.3 to 100 pg/1 of cadmium and
3 to 100 pg/1 of lead. This method gives suitable accuracy for
cadmium and lead in reference water samples and in split samples
of effluent water froir ash ponds that were analyzed by atomic
absorption. limited data show that this method probably also can
be used for 5 to 100 pg/1 copper but that it is unsuitable for
zinc because of a 15-pg/1 sample blank for zinc.
This report was submitted by the Tennessee Valley Authority,
Division cf Environmental Planning, in partial fulfillment of
Energy Accomplishment Plan 79EDH under terms of Interagency
Energy Agreement C5-E721 with the Environmental Protection
Agency. Viork was completed in May 1977.
iv
-------
CONTENTS
Page
Acknowledgments iii
Abstract ............................. iv
Figures vi
Tables ................................. viii
Abbreviations and Symbols ..... .............. x
1. Introduction ...................... 1
2. Conclusions ....... ......... ....... H
3- Recommendations 5
4. Experimental 6
Sample Preparation ............... 6
Equipment .................... 7
Preparation of Equipment and Solutions ..... 7
Determination of Cadmium and lead by ASV .... 9
Determination of Copper and Zinc by ASV ..... 11
5. Results and Discussion ................ 12
References - . ........ 17
-------
FIGURES
Number
Calibration curve for surface area of mercury
drop formed by extrusion with a manually
operated hanging mercury drop electrode ...... 23
Anodic stripping voltammograns for total
recoverable cadmium and lead in 0.2 M ammonium
citrate buffer at pH 3.0 by deposition at -0..800 V
vs. see into a mercury droplet with a surface
area of 0.032 cm2 for 2 min with stirring
plus 30 s without stirring 24
Interference of selenium (IV) on anodic
stripping voltammograms for total recoverable
cadmium and lead in 0.2 M ammonium citrate buffer
at pH 3.0 by deposition at -0.800 V vs. see
into a mercury drop with a surface area of
0.032 cm2 for 2 min with stirring plus
30 s without stirring .................. 25
Ascorbic acid for eliminating interference of
selenium (IV) en anodic stripping voltanur.ograms
for total recoverable cadmium and lead in 0.2 M
ammonium citrate buffer at pH 3.0 by deposition at
-0.800 V vs. see into a mercury droplet with a
surface area of 0.032 cm2 for 2 min with stirring
plus 30 s without stirring ............ 26
Anodic stripping voltammograms for total
recoverable cadmium, lead, and copper in 0.2 M
ammonium citrate buffer at pB 3.0 by deposition at
-0.800 V vs. see into a mercury drop with a surface
area of 0.032 cm2 for 2 min with stirring plus
30 s without stirring 27
Anodic stripping voltammograms for total
recoverable zinc, cadmium, lead, and copper in
0.2 M ammonium citrate buffer at pB 3.0 by
deposition at -1.200 V vs. see into a mercury
drop with surface area of 0.032 cm2 for 2 min
with stirring plus 30 s without stirring ...... 28
-------
Number
Anodic stripping voltammograms for zinc*
cadmium, lead, and copper in raw purified
0.2 M ammonium citrate buffer at pH 3.0 by
deposition at -1.200 V vs. see into a
mercury drop with a surface area of 0.032
cm* for 10 min with stirring plus 30 s
without stirring -. . . . 29
vii
-------
TABLES
Number fag
1 Determinations of Hanging Mercury Drcp Area ...... 33
2 simultaneous Determinations of Cadmium and Lead
Concentrations by Anodic Stripping Voltanrmetry for
Replicate Solutions of Spiked Reagent Kater ...... 34
3 Typical Sensitivities and Peak Height vs.
Concentration Proportionality Tests for
Cadmium, Lead, Copper, and Zinc ............... 35
4 Effect of Ferric Iron and Hydroxylamine en
Analysis of 30-jig/l Cadmium and Lead
Samples by Anodic Stripping Vcltammetry .......... 36
5 Effect of Selenium (IV) and Ascorbic Acid on
Analysis of 30-jjg/l Cadmium and Lead by
Anodic Stripping Voltammetry ............... 37
6 Comparative lest Results of Cadmium and
Lead Determinations for Split Samples from
Ash Ponds ....................... 38
7 lest Results of Cadmium and Lead Determina-
tions by Anodic Stripping Voltammetry for
Standard Reference Samples ...... 39
8 Simultaneous Determinations of Cadmium, Lead,
and Copper by Anodic Stripping Voltammetry
for Replicate Solutions of Spiked Reagent
fiater 39
9 Zinc Determinations by Anodic Stripping
Voltammetry for Replicate Solutions of
Spiked Reagent tiater 40
10 Effect of Reaction lime on Purification
cf Ammonium Citrate Buffer by Electrolysis
with Stirring into a Mercury Cathode at
-1.500 V vs nee 40
viii
-------
Number Pag<
11 Simultaneous Determination of low
Concentrations of Zinc, Cadmium,
Lead, and Copper by Anodic Stripping
Voltaounetry with Purified Ammonium Citrate
Buffer . . . . 41
ix
-------
LIST OF ABBREVIATIONS AND SYMEOIS
ABBREVIATIONS
A —ampere
c- —centi-, X10-2 (as a prefix, e.g., car.)
°C —degrees Celsius (centigrade)
EPA —U.S. Environmental Protection Agency
-------
SECTICK 1
INIBODUCTION
Coal ash from steam-electric generating plants contains
small amounts of cadmium, lead, coffer, and zinc, which are
deposited in ash sluicing water and settling ponds. Although
these metals are largely removed by microflotation (1), seme may
eventually reach surface or ground waters.
As required by the Federal Water Pollution Control Act, test
procedures have been published for determining concentrations cf
pollutants (cadmium, lead, copper, and zinc) ty atomic absorption
or colorimetry to demonstrate that effluent discharges meet
applicable pollutant discharge limitations (2,3). Although net a
compliance method, the determination of cadmium, lead, copper,
and zinc at the level of micrograirs per liter by anodic stripping
voltammetry (ASV) has been a relatively common practice during
the past few years (4-11).
Despite the recent use of ASV and the environmental,
medical, and legal decisions made en the basis cf results from
ASV, a number of scientists seriously question the methods and
the validity of determinations by ASV at the nicrogram level (4).
The features and problems of trace metal analysis by ASV and
atomic absorption spectroscopy, two of the most widely used
methods fcr trace metal analysis, have been reviewed recently
(4). Although concentrations of 22 metals may be determined by
ASV (4) , most applications are for zinc, cadmium, lead, and
copper. ASV has been used to determine concentrations of zinc,
cadmium, lead, and copper at nanogram and microgram levels in air
samples (5), natural water (6-9), and sea water (8,10,11).
Ihis study evaluates the validity of determinations of low
concentrations of total recoverable cadmium, lead, copper, and
zinc by ASV under carefully controlled conditions. The procedure
is judged on the equivalence of its accuracy and reproducibility
at low concentrations (0 to 100 pg/1) to the accuracy and
reproducibility obtained by the standard reference methods at
higher concentrations (greater than 50 jig/1) (2,3).
The principal objectives of this study are to establish
favorable conditions for analyzing cadmium and lead by ASV and,
afterwards, to modify the conditions for analysis of copper and
zino.
-------
According to Meites (12,13), 0.25 M ammonium citrate tuffer
with a pH of 3 to 4 is an excellent electrolyte for analyzing
zinc, cadmium, lead, and copper; 0.5 M or 0.025 M acetate at pB 6
is also suitable (6,7,12,13), especially when saturated Kith
phenol (12).. For this study 0.2 M ammonium citrate at pH 3.0 was
chosen. A pB of 3.0 is sufficiently acidic to prevent hydrogen
formation at -1.200 V vs. see, thereby eliminating interference
for the zinc stripping peak that appears at -1.200 V vs. see.
Also, because this pB falls within the optimunr range determined
by Sinko and Dolezal (7), small changes in pB will not affect the
stripping peak heights for zinc, cadmium, lead, and copper.
Because digestion to dryness with nitric acid destroys
organic matter that would otherwise cause interference patterns
in the stripping voltammograms (14), wet ashing with nitric acid
is chosen for sample preparation. Also, nitrate is weakly
complexing and does not form the strong mercury complexes (such
as Hg2Cl2) that would be formed if hydrochloric acid were used to
digest samples. Such complexes cause interference ty giving
steeply sloping background currents close to the copper peak at
about 0 V vs.. see (15)-
According to Chau and lum-Shue-Chan (6), iron (III) in 0.025
M acetate tuffer at pB 6 interferes in the determination by ASV
of zinc, cadmium, lead, and copper by depressing their peak
currents. The authors overcome this interference by reducing the
iron (III) to iron (II) with hydroxylamine. Iron (III) is an
important interferer because its concentration in ash pond
effluents from coal-fired power plants typically varies from 20
to 5100 pg/1 (16). Another possible interferer is seleniuor (IV),
which is present at concentrations often greater than 100 jig/1 in
ash pond effluents frcm coal-fired power plants (17); selenium
(IV) is eleetr©chemically active near the lead stripping peak
(18-20). In this study both iron (III) and selenium (IV) were
examined as possible interferers in the determination of zinc,
cadmium, lead, and copper by ASV in 0.2 M ammonium citrate oredia
at pB 3.2.
Surface area (and volume) of the electrode is a recognized
variable that can influence formation of intermetallic amalgams,
especially Zn(Cu). Ibis amalgamation may lead to high stripping
peaks fcr ccpper and low ones for zinc (21-23). Formation cf
amalgams is particularly serious when thin-film mercury
electrodes are used because the sir all volume of mercury leads to
a very high concentration of amalgams (21), especially at higher
metal concentrations. Use of the banging orercury drop ariniirizes
this problev and increases the range of working concentration
because of the larger volume of mercury (21). Eecause cf this, a
hanging mercury drop electrode (BMDE) with the largest possible
surface area commensurate with a stable drop is used.
-------
This report evaluates and describes a method of differential
pulse ASV for determining total recoverable concentrations of
cadmium and lead by (1) deposition in a mercury drop of kncvn
surface area at -0.800 V vs. see and (2) anodic stripping to
measure the peak currents. Section H of this report (1)
describes the sample preparation, including digestion with nitric
acid; (2) gives directions for eliminating interference frcir iron
(III) by warming with hydroxylamine and eliminating interference
from selenium (IV) by adding ascorbic acid; and (3) describes the
optimum conditions for differential pulse ASV and the optimum
surface areas for the HMDE that is used to measure cadmium and
lead in 0.2 M ammonium citrate at pH 3.2.. This technique is also
applied, under similar conditions, to the deternrinaticns of (1)
copper by deposition at -0.800 V vs. see and (2) zinc by
deposition at -1.200 V vs. see. Beproducibility, detection
limits, and sample blanks for analyses cf concentrations ranging
from 0 to 100 pg/1 are critically evaluated.
-------
SECTION 2
CONCLUSIONS
The Tennessee Valley Authority (TVA) used a method based on
differential pulse ASV to determine total cadorium at
concentrations of 0.3 to 100 pg/1 and total lead at
concentrations of 3 to 100 pg/1 in aqueous ash pond effluents
from coal-fired steam electric power plants. This method
involves (1) evaporation to dryness with nirric acid; (2) warming
with hydroxylamine in 0.2 M ammonium citrate (pB 3.0) to
eliminate interference from 20,000 pg/1 of iron (XII); (3)
addition of ascortic acid to eliminate interference from 50 to
1000 pg/1 of selenium (IV); (4) deposition at -0.800 V vs. see
into a mercury drop with a surface area of 0.032 cm2 for 2 or.in
with stirring plus 30 s without stirring; (5) measurement of the
cadmium and lead currents hy differential pulse ASV; and (6)
determination by standard addition. Triplicate analyses at five
concentrations show that cadmium and lead can he determined
precisely. This method gives suitable accuracy for cadmium and
lead in reference water samples and in split samples of effluent
water from ash ponds that were analyzed by atomic absorption*
Limited data show that this method probably is useful for 5 to
100 pg/1 copper but, when modified for deposition at -1.200 V vs.
see, it is not useful for zinc because of a 15-pg/l sample blank
for zinc.
-------
SECTICK 3
RECOMMENDATIONS
Differential pulse ASV is a suitable method for determining
very low concentrations of total cadmium and lead in ast ponds
that receive effluents front steam-electric generating plants.
Further studies should be conducted to determine the
applicability of this method (1) tc copper, (2) with digestion by
ultraviolet irradiation instead of evaporation to dryness with
nitric acid, and (3) to other process waste streams.
-------
SECTICK 4
EXPERIMENTAL
SAMPLE PBEPABATIOK
Field Samples
Field samples were collected in January 1976 frov ash ponds
at all TVA coal-fired steam-electric generating plants and were
analyzed fcr the presence of cadmium and lead. Those samples
containing representative concentrations of these elements Mere
selected for use in this study.
Standard Reference samples
Standard reference samples fcr trace metals were obtained
from the U.S. Environmental Protection Agency (EPA), and
simulated precipitation reference materials fcr trace metals and
minerals were obtained from the National Bureau of Standards
(NBS). Both EPA and KES reference samples, which consisted of
known amounts of concentrated trace metals in very pure water,
were diluted to the desired concentrations according to
accompanying instructions.
Synthetic Samples
Test sclutions containing 0, 5, 10, 30, 60, and 100 pg/1 of
cadmium and lead were prepared ty spiking 10.0 oil of a solution
of one volune of concentrated acid in 160 volumes of water
[(1+160) nitric acid] with 5, 10, 30, 60, and 100 pi cf a 10-ppm
mixed standard of cadmium and lead in (1+160) nitric acid. Test
solutions containing 30 pg/1 cadmium, lead, and copper and 30 or
100 pg/1 zinc, cadnriuir, lead, and ccpper were prepared similarly
by spiking 10.0 ml of (1+160) nitric acid with appropriate
amounts of 10-mg/l multielement standards. The 10,5,5,5- and
5,2.. 5,2.5,2.5-pg/l concentrations of zinc, cadmium, lead, and
copper were prepared ty spiking with 5 pi of the respective
multielement concentrates of 20:10:10:10 and 10:5:5:5 mg/1. Some
test soluticns of 30 pg/1 cadmium and lead were spiked wito
selenium (IV) to achieve concentrations of 30, 50, 100, 500, and
1000 pg/1. Other test solutions were prepared by spiking 5, 10,
20, and 40 vg/1 iron (III) with cadmium and lead to achieve a
concentration of 30 pg/1.
-------
All elements used to prepare synthetic samples, except iron
* were drawn froir 1000-mg/l certified atomic ahscrpticn
standards (fisher Scientific Company, Fairlawn. New Jersey). The
1000-mg/l concentration of iron (III) was prepared
gravimetrically from ferric aormonium sulfate dodecahydrate (8.. 634
g in 1000 ml of reagent water) with weights checked against
reference weights certified at the KBS.
EQUIPMENT
All measurements were made with the Princeton Applied
Research (PAR) Model 174 polarographic analyzer with HKCE and
Houston omnigraphic X-Y recorder. Model 2200-3-3. The HMCE
capillary was PAR Fart No. 9303. Cther instruments—the platinum
counter electrode; the salt bridge with slow-leakage Vycor tip
(Corning Glass Works, Corning, New York) to isolate the saturated
calomel electrode from the test solution; the magnetic stirrer
with uniform rotational speed; the cutgassing tube; cell holder;
and cell—were obtained from Princeton Applied Research
Corporation (24). A 15- by 1.5-mm Teflon magnetic stirring bar
(Bel-Art, Pequannock, New Jersey, Part Ko. F-37119) was used fcr
ASV experiments with the PAR K62 pclarographic cell bcttom. An
adjustable digital microliter pipet (Analtech, Newark, Delaware,
Part No. P-20D or P-200D) was used to spike solutions.
PREPARATION OF EQUIPMENT AND SOLUTIONS
The HMCE was cleaned and siliconized by standard procedures
to prevent thread withdrawal and ncisy voltammograms (25.). It
was also necessary to rinse the HMCE by aspiration with nitric
and chromic acid, followed by thorough rinsing with reagent water
(26), and to bake it at 110°C just before siliconizing and use;
this procedure also minimized thread withdrawal.
The surface area of the hanging mercury drop dispensed by
the HMCE was determined graviiretrically. Figure 1 gives a plct
of the surface area of a drop vs. the micrometer reading for
dispensing that drcp for a manually operated EMDE (PAR Part No.
9323)- A irercury drop with a surface area of 0.032 cnr.2,
corresponding to six small micrometer divisions, was used in the
voltammetric determinations given in this report. Raw micrometer
readings (Table 1) plus surface areas calculated by equaticn (1)
in the following discussion are plotted in Figure 1.
Surface area values were obtained by extruding, for each
micrometer setting in small vertical divisions, a series of ten
drops from the HMDE while it was located beneath 4 ml of water in
a 5-ml beaker. After the water was poured off and the residue
was rinsed with three 3-ml portions of acetone, the weight of the
beaker plus mercury was determined; after the mercury was
discarded the beaker was reweighed. The difference divided by
-------
ten gave the weight of a single mercury drop. This weight Has
used to calculate surface area for a mercury drop forced ty
extrusion:
Surface area cf /
mercury drop, cm2 = 4» ( 3M \2/3 , (1)
where tt = weight of a single mercury drop, g,
p = density of mercury for the temperature at which
the determination was made, g/car3 (27).
Calculations were made by entering W and p into a calculator
programmed to yield surface areas directly (28).
Voltammetric cells were cleaned by soaking them cvernight in
concentrated nitric acid. Other glassware that contacted the
sample solution was soaked overnight in a solution cf two volumes
of concentrated nitric acid in three volumes cf water. After
leaching, the glassware was rinsed with reagent water and dried
in an oven at 110°C. Clean glassware and digested sample
solutions were covered with Parafilm (Fisher Scientific Company,
Fairlawn, New Jersey) to prevent contamination from trace
elements in atmospheric particles.
Nitrogen gas, used to deaerate solutions for polarcgraphic
analysis, was purged of oxygen. Zero-grade nitrogen gas was
passed through a furnace containing a special catalytic converter
(a gas purifier, Mcdel 02-2315, purchased from Supelco,
Beliefonte, Pennsylvania) and heated to 600°C. After the gaseous
effluent from the furnace was passed successively through a
Hydro-Purge unit and a Dow Gas Purifier (Applied Science
Laboratories, State College, Pennsylvania), it was passed through
sintered glass frits in three scrubbing towers^ Cne scrubbing
tower contained 100 ml of reagent water, and the other two
contained 100 ml of 0.1 M chromcus chloride in 2.4 K hydrochloric
acid with amalgamated zinc. Ihe amalgamated zinc particles used
in the Jones reductor (Fisher Scientific Company, Fairlawn, New
Jersey) were 0.8 to 3.2 mm in diameter. Details fcr preparing
the chrcmous chloride scrubbers are given by Keites (12).
Beagent-grade chemicals were used to prepare all solutions
except (1) the redistilled nitric acid that was used to digest
the samples, (2) the 1 M potassium chloride used in the reference
electrode of the electrolysis purification cell, and (3) the 0.2
M ammonium citrate buffer, which was purified further in an
electrolysis cell fcr some determinations of low metal
-------
concentrations. Tbe redistilled nitric acid was purchased frcm
G. Frederick Smith Company, 867 McRinley Avenue, Colunrbus, Chio
43223. The 1 M potassium chloride was prepared froir an "Ultrex"
grade salt (Baker Chemical Company, Phillipsburg, New Jersey) by
dissolving 7.45 g of the salt in reagent water and diluting the
solution to 100 ml.. The 0.2 M ammonium citrate buffer was
prepared by dissolving 42 g citric acid in about 800 or.1 reagent
water, adding enough ammonium hydroxide to bring the pH to
3.010.2, and diluting the solution to 1000 ml. the buffer was
sterilized by autoclaving for 15 min at 121°C and 1.03 x 10s
Pascals (15 pounds per square inch). Because this sterilization
eliminated bacterial growth for only a month, tbe buffer was
newly prepared eacb month.
For experiments with low metal concentrations, the 0.2 K amironium
citrate buffer was purified further in a reagent purifier system
(PAR Model 9500) by electrolysis at -1.500 V vs. nee into a
mercury pocl working electrode. The supporting electrolyte was
deaerated and stirred during purification. The calomel reference
electrode was filled with 1 M potassium chloride, which was
prepared from the "Ultrex" grade salt, to minimize metal
contamination from the salt solution in the reference electrode.
The counter electrode was a coiled, 22-guage platinum wire
(Fisher Scientific Company, Fairlawn. New Jersey) in a salt
bridge with unpurified ammonium citrate that contacted tbe
solution through a Vycor disk. A black precipitate slowly formed
on the disk between the platinum counter electrode and the
citrate buffer. This was eliminated by electrolyzing the buffer
at -1.300 V vs. nee, which effectively removed zinc, cadmium,
lead, and ccpper from the buffer.
The 10 percent hydroxylamine solution (100 g/1 as the
hydrochloric acid salt) was free of iron and copper (G. Frederick
Smith Chemical Company, 867 McKinley Avenue, Columbus, Chio
43223)-. The 10 percent (w/v) ascorbic acid reagent was prepared
by dissolving 10 g of I-ascorbic acid powder in reagent water and
diluting to 100 ml. The (1+160) nitric acid was prepared by
diluting 1 volume of nitric acid with 160 volumes of reagent
water, and the (2+3) nitric acid was prepared by diluting 2
volumes of nitric acid with 3 volumes of water.
DETEBKINATION OF CADMIUM AND LEAD EY ASV
The samples were digested by adding 2.0 irl of redistilled
nitric acid to 10.0 ml of sample in a 50-ml beaker and
evaporating the solution on a bet plate without boiling until the
sample just reached dryness. Baking beycnd dryness was avoided
to prevent possible losses by volatilization. After the sairple
was cooled, 5.0 ml of 0.2 M ammonium citrate buffer (pfl 3.0) and
100 pi of 10 percent (w/v) hydroxylamine (except when noted
otherwise) were added. The solution was warmed 15 min to reduce
-------
iron (III) and to dissolve the metals in the buffer. The
solution was transferred quantitatively to the voltamiretric cell
and brought to a volunre of 10 to 12 oil with the ammoniwr citrate
buffer. The cell was precalibrated at about 11 ml by etching it
with a diauond-tipped pencil. The exact voluae need not be known
when standard additions are used tc quantitate. In seme cf the
experiments (as noted) to eliminate interference by seleniunr
(IV), 1 ml cf 10 percent (w/v) asccrbic acid was added to the
solution in the cell.
A stirring bar was inserted into the solution, and the
solution was deaerated for 10 min at 100 ml/min with nitrogen gas
that had been treated to remove oxygen. A mercury drop, with a
surface area of 0.032 cm?, was extruded by rotating the BKLE
micrometer six small vertical divisions (see figure 1). lie
magnetic stirrer was turned on, and the stirring rate was
adjusted so that the solution beneath the mercury drop was well
stirred without visible movement cf the mercury drop. The
stirrer was turned on 15 s before deposition to assure uniform
rctaticnal speed.
After connecting the voltammetric cell, cadmium and lead
were determined by deposition in the mercury drcp at -0.800 V vs.
see for exactly 2 min with stirring and then allowing ccnvection
currents to cease for 30 s without stirring. Immediately
thereafter, a differential pulse anodic vcltairmetric scan was
made between -0.800 and -0.200 V vs. see under suitable
conditions. The peak for cadmium appeared at about -0.600 V vs.
see, and the one for lead appeared at about -0.420 V vs. see.
Typical conditions used for the PAF 174 pclarcgraphic analyzer
were initial potential, -0.800 V vs. see; scan rate, 5 mV/sec;
range, 0.750 V; scan direction, positive; modulation amplitude,
25 mV; sensitivity, 2 pA for 0 to 10 pg/1 of cadmium and lead, 5
pA for 20 to 50 pg/1 of cadmium and lead, and 10 pA for 60 to 100
pg/1 of cador.ium and lead; drop time, 0.5 s; display directicn,
negative; operation nrode, differential pulse; output offset,
negative settings as required. Kith the Houston omnigraphic
2200-3-3 recorder, recorder Y-axis was adjusted to 1 V/in. (0.039
V/mm) and X-axis was adjusted to 100 mV/in. (3.94 mV/rrm).
To calculate unknown concentrations cf cadmium and lead in
samples, the method of standard addition was used (12). After
the differential pulse anodic stripping curve for the sairple was
determined, an appropriate aliquot of cadmium and lead stock
solution (usually 10 mg/1) was added to the sample (normally
between 5 and 100 pi) in the cell by use of an adjustable digital
microliter pipet, and the solution was deaerated for an
additional 5 min tc mix the solution and remove oxygen added with
the spike. Thereafter, ancther differential pulse ancdic
stripping curve was determined under conditions identical tc
10
-------
those for determining the sample. The concentration cf each
metal was calculated by the equation given ty Meites (12):
C2 = _ itvCt (1000) . (2)
i2v + (ia-it) (V) (1000)
where it = stripping peak height for the sample, jiA,
iz = stripping peak height fcr the sample plus standard, pA,
v = volume cf standard taken for spiking, pi,
V = volume cf sample dispensed for digestion, nrl,
Ct = concentration of standard used to spike, mg/1,
C2 = concentration of the unknown in the sample, pg/1.
Calculations were trade by entering i*, v, C4, i2, and V intc a
calculator programmed to yield C2 directly in micrograms per
liter (28) .
DETERMINATION CF COPPER AND ZINC £Y ASV
Concentrations of copper alone or cadmium, lead, and copper
were determined under the same conditions as were concentrations
of cadmiunr. and lead except that the differential-pulse anodic
voltammetric scan was made between -0.80 and +0.10 V vs. see, and
the range was 1.500 V. The peak fcr copper appeared at about
-0.030 V vs. see.
Concentrations of zinc alone cr zinc, cadmium, lead; and
copper were determined under nearly the same conditions as were
concentrations of cadnrium and lead except that the depositicn was
conducted at -1.200 V vs. see, the voltammetric scan tas trade
between -1.200 and +0.100 V vs. see, and the range was 1.500 V.
The peak for zinc appeared at about -1.000 V vs. see.
low concentrations of zinc, cadmium, lead, and ccpper uere
determined simultaneously under tie same conditions as sere
concentrations of zinc except that a 10-min deposition %»as used.
11
-------
SICTICK 5
RESULTS ANC EISCUSSICN
A sensitive method of differential pulse ASV was developed
for determining cadmium and lead in aqueous ash pond effluents
from coal-fired steam-electric pover plants. Ibis methcd
involves evaporating a 10.0-ml sample to dryness with 2.0 ml of
concentrated, redistilled nitric acid; warming Kith 100 pi cf 10
percent (w/v) hydrcxylamine in 0.2 K ammonium citrate (pH 3.0) to
eliminate interference from 20,000 pg/1 cf iron (III); adding 1
ml of 10 percent (w/v) ascorbic acid to eliminate interference
from 50 to 1000 pg/1 of selenium (IV); depositing at -0.800 V vs.
see into a mercury drop with a surface area of 0.032 cm* for 2
min with stirring plus 30 s without stirring; measuring the
cadmium and lead current by differential pulse ASV; and
determining cadmium and lead concentrations by standard addition.
As a result of this and other work, a version of this method of
ASV has been published as a proposed standard in Fart 31 cf the
1977 Annual Book cf Standards, American Scciety of Testing and
Materials (29). The method described in Section 4 is being
inter laboratory tested (29). In addition, liorited data indicate
that this nrethod is probably useful for determining
concentrations of copper but, when modified for deposition at
-1.200 V vs. see, it is probably not useful fcr determining zinc
because of the high sample blanks.
Inspection of data in Table 2 for simultaneous determination
of cadmium and lead by ASV for replicate solutions of spiked
reagent water reveals that (1) the range cf the method is 0.3 to
100 pg/1 fcr cadmium and 3 to 100 pg/1 for lead and (2) the
lowest quantifiable concentration cf the method is limited by the
sample blank, which is about 0.3 pg/1 tctal recoverable cadmium
and 3 pg/1 lead. The precision and accuracy with which cadmium
and lead are recovered by this method frcm triplicate standard
solutions containing 5, 10, 30, 60, and 100 pg/1 of both metals
were determined by standard additions (12). Table 2 gives the
analytical results. Respectively, the standard deviations are
0.6, 2.4, 4.6, 2.0, and 9..1 pg/1 fcr cadmium and 1.2, 2.1, 3.0,
0..0, and 8.0 pg/1 for lead; the relative standard deviations are
11.1, 22.8, 15.9, 3.8, and 9.9 percent for cadmium and 19.0,
18.4, 10.0, 0.0, and 8.4 percent fcr lead; and the percentage
accuracies (biases) are +8.0, +5.0, -3.3, -11.7, and -8.0 for
cadmium and +26, +14, 0.0, -6.7, and -5.0 for lead (30).
According to a one-sample t test, the percentage accuracies,
except those at 60 pg/1, are not statistically significant at the
12
-------
95 percent confidence level (31). Ibis information aids in
establishing tbe validity cf trace analyses by tbis method at 0
to 100 pg/1 (H).
Figure 2 gives typical differential pulse anodic stripping
voltammograirs for total recoverable concentraticns of cadmium and
lead in 0.2 M ammoniunr citrate buffer (pH 3.0) by deposition at
-0.800 V vs. see in a mercury drop with a surface area cf 0.032
cm2 for 2 min with stirring plus 30 s without stirring. As shown
in Figure 2, the stripping voltammcgrams are well defined fcr
both cadmiutr and lead at 10 and 100 pg/1. Ibis verifies tfcat the
conditions proven for analysis at high concentrations by
polarcgrapby (voltairmetry at the dropping mercury electrode)
(12,13) are equally applicable to analysis at low concentrations
by differential pulse ASV at the HKDE. Table 3 gives typical
sensitivities (in microamperes per micrcgram per liter) cf
cadmium and lead in digested samples and in samples spiked for
quantitaticn by standard additions. These data illustrate (1)
linearity of the method up to at least 100 pg/1 of cadmium and
lead and (2) the extreme sensitivity of both elements—abcut 0.03
pA |jg~* I"1 for cadmium and 0.02 pA p-» 1~» for lead.
Cne disadvantage is that, even when sterilized, the airaonium
citrate (pH 3.0) electrolyte in which cadmium and lead are
determined will not resist bactericlogical grcwtb indefinitely;
it gives erratic vcltammograms about a month after sterilization
and therefore must be prepared eacb month. Fcr this reascn
alone, the 0.025 N sodium acetate (pH 6) used by Chau and Sinkc
(6,7) may be equally suitable, although Meites (12) claims that
the results for cadmium are improved when the acetate is
saturated with phenol.
It is well known that 0.0007 percent (w/v) hydroxylairine
hydrochloride eliminates the suppression cf anodic stripping
peaks of cadmium and lead that is caused by 280 pg/1 ircn (III)
in 0.04 K sodium acetate (pH 6) (6). The interference frov
20,000 pg/1 of iron (III) on the anodic stripping peaks for 30
Mg/1 of cadmium and lead in 0..2 M ammonium citrate (pfi 3.0) is
eliminated by warming the solution for 15 min with hydroxylamine
hydrochloride in 5.0 ml of 0.2 M ammonium citrate buffer (pfi 3.0)
in a concentration of 0.1 percent (w/v) (100 pi of 10 percent
hydroxylairine for 10 ml of sample analyzed). Many asb pond
effluents from coal-fired steam-electric pcwer plants ccntain
iron (III) , but most of their contain iron (III) in iraxiirum
concentrations of 5,100 pg/1 (16). Dilution nray be required for
sanjples tbat contain more than 20,000 pg/1 ircn (III), such as
drainage from strip mines.
Table 3 displays raw data for 30 pg/1 of cadnrium and lead
recovered from 10.0 ml of aqueous standards containing 5000,
10,000, 20,000, or 10,000 pg/1 of iron (III) that were (1)
13
-------
digested with nitric acid, (2) treated with 0, 100, or 500 pi of
10 percent (w/v) hydroxylamine, and (3) analyzed by differential
pulse ASV in 0.2 M ammonium citrate (pH 3.0). As shown in Table
4, the addition of 100 pi of 10 percent (w/v) hydroxylamine gives
nearly quantitative recoveries of 30 pg/1 of cadmium and lead in
the presence of 5000, 10,000 and 20,000 pg/1 cf iron (III). The
absence of hydroxylamine causes high results at 20,000 pg/1 iron
(III). At aO,000 pg/1 iron (III), an erratic baseline is
observed at voltages more positive than -0.350 V vs. see. This
behavior warns that the level of iron (III) is higher than the
analytical method can tolerate.
Selenium (IV), which was determined in seme ash pond
effluents in concentrations of 100 pg/1 (17), may interfere
because it has a stripping peak at voltages near these voltages
at which lead has a stripping peak (18-20). figure 3 shows that,
at -0.340 V vs. see, 30 pg/1 of selenium (IV) appears as a slight
shoulder on the stripping peak caused by 30 pg/1 of lead. The
selenium (IV) shoulder is more evident at 50 pg/1.. At 100 pg/1
the selenium (IV) peak is well defined and causes a depression in
the lead peak from about 0.6 to 0.2 pA (see Figure 3) that leads
to the low results for lead in Table 5. figure 4 illustrates
that 1000 pg/1 of selenium (IV) causes a depression in not cnly
the lead but also the cadmium peaks at 30 pg/1 that makes tbeir
determination impossible. However, as seen in figure 4, the
additicn cf 1 ml cf 10 percent (w/v) ascorbic acid befcre the
sample is deaerated destroys the selenium (IV) peak and restores
the cadmium and lead peaks to their normal values. The data in
Table 5 prove that ascorbic acid can be added tc give a
satisfactory analysis of cadmium and lead at 30 pg/1 in tbe
presence of 100, 500, and 1000 pg/1 of selenium (IV). Ascorbic
acid is net necessary at selenium (IV) concentrations below 50
pg/1; the appearance of the selenium (IV) shoulder adjacent to
the stripping peak for lead indicates that ascorbic acid is
needed.
The method of differential pulse ASV described in Section 4
was compared with the reference atomic absorption method (3) for
recovering cadmium and lead from samples of effluent water taken
from ash ponds in the Tennessee Valley.. The reference atomic
absorption method was used to recover cadmium and lead that are
soluble in hot, dilute HC1-HN03 with chelation by ammonium
pyrrolidine dithiocarbonate and concentration by solvent
extraction with methylisobutylketone to improve sensitivity (3).
Analytical results are given in Table 6 for ccncentraticns cf
cadmium and lead recovered from the split samples of asb pond
water by the ASV and atomic absorption methods. Althcugh
severely limited, the data on split samples in Table 6 indicate
that the two methods compare favorably. Most of these samples
contained too little cadmium and lead to give a measurable amount
by atcmic absorption, which, even with concentration by solvent
14
-------
extraction, cannot determine the concentrations that can te
quantitated by the ASV method described in this report.
Concentrations of cadmium and lead have been determined in
standard reference water samples (32,33). Cur test results,
which are given in Table 7, agree reasonably veil with the
certified values.
The ASV method fcr recovering cadmium and lead by digestion
with nitric acid and deposition at -0.800 V vs. see in airnrcnium
citrate buffer was also tested for determining copper
concentrations by scanning to a voltage of +0.100 V vs. see
rather than ending the scan at -0.200 V vs. see. Table 8 stows
that copper, as well as cadmium and lead, is recovered in
quantifiable concentrations by standard additicn frcm triplicate
standard solutions of 30 pg/1 cadmium, lead, and copper and 30
fjg/1 zinc, cadmium, lead, and copper. The lowest quantifiable
concentration of copper is limited to the sample blank, which is
about 5 jjg/1. The stripping voltaomograms in Figure 5 fcr 30
jjg/1 of cadmium, lead, and copper give well-defined peaks fcr
total recoverable copper quantified by standard addition with a
sensitivity of about O.OU pA pg~» 1~*. Exact sensitivities for
copper are listed in Table 3.
Ey changing the deposition voltage to -1.200 V vs. see, this
method was tested for zinc recovered by standard addition from
triplicate standard solutions of 100 pg/1 zinc and 100 pg/1 zinc,
cadmium, lead, and copper. Table 9 shows that fairly
quantitative recoveries of zinc are possible, but that erratic
recoveries are probably caused by a high sample blank cf 15 pg/1-
Figure 6 gives the vcltammograms fcr the fcur metals analyzed
simultaneously by digestion, ASV analysis in citrate media, and
quantitation by standard additions. The sensitivity cf the
method for zinc is about 0.02 j*A pg-1 1~f, which is about tbe
same as that for cadmium (see Table 3).
A high concentration of copper causes amalgamation cf capper
and zinc when a sufficiently high concentration of zinc is
present during the deposition in a mercury drcp cr iilm cf
sufficiently small volume (21). Tbe copper-zinc amalgam is
stripped with the ccpper peak; this causes high stripping
currents fcr ccpper and low stripping currents for zinc (21-23).
As shown in Table 9, the presence of 100 pg/1 cf copper does not
affect the recovery of 100 pg/1 of zinc, probably because cf the
low concentrations tested, the large volume of the HMCE, and the
short deposition period. The absence of interference by ccpper
on'zinc in our study agrees with the work of Shuman and Kocdward
in which an HMDE with a volume of 6..23 x 10~* cm-* was used (21).
In our study the volume of the HMCE is 5.38 x 10~* cm.a, which
corresponds to a surface area of 0.032 cm*. The interference by
copper on zinc is more severe with electrodes plated witb a thin
15
-------
film of mercury because their volume is 1.44 x 10~7 cnr3 (21),
which is about 3700 times smaller than the HMCE used in our
study.
In an attempt to lower sample blanks for zinc, cadmium,
lead, and copper, the electrolytically purified 0.2 K ammonium
citrate (pH 3.0) was tested for determination of low
concentrations of the four metals simultaneously. After 192 hr
of purification, assay of the raw 0.2 K ammonium citrate buffer
(pH 3.0) by differential pulse ASV after deposition at -1.200 V
vs. see for 10 min leads to values of 1.0, <0.2, 0.5, and 0.2 for
zinc, cadmium, lead, and copper, respectively (Table 10).
Voltammograirs are shown in Figure 7.. But after the reagent water
is digested and the metal concentrations are quantified in the
purified annronium citrate, the zinc, cadmium, lead, and ccpper
values increase to 7 to 9, 0.2 to 0.3, 1.4 to 2.1, and 0.3 to 2.7
pg/1, respectively (Table 11). As shown in Tables 2, 8, and 9,
the respective sample blanks are 14 to 15, 0.1 to 0.3, 0.8 to
3.4, and 2.4 to 5.3 pg/1 for digesting reagent water and
quantifying concentrations in unpurified citrate. Purification
does not improve the sample blanks for cadmium and lead, but it
does improve the blanks for copper and zinc by a factcr cf two.
Thus, comparison of the values befcre and after digestion, with
and without purification, shows that digestion is the principal
source of contamination in the lead blank, but that it acccunts
for only half of the contamination in the zinc and copper blanks.
The cadmium blank is not a problem, probably because it is not
found ubiquitously.
Table 11 gives results for zinc, cadirium, lead, and copper
at concentrations of 10,5,5,5 and 5,2.5,2.5,2-5 jjg/1 analyzed by
ASV. To minimize blanks. Elutstein and Bond (34) suggest that
analysis of very low concentrations be performed withcut
digestion directly on samples acidified with nitric acid;
however, soire industrial effluents give interference patterns in
the anodic stripping voltammograms that must be eliminated by
digestion with nitric acid (14). The sample blanks fcr lead,
copper, and zinc probably can be improved by digestion by
ultraviolet irradiation in quartz tubes with hydrcgen peroxide
and hydrochloric acid added (8,35).
16
-------
REFERENCES
1. Melville, J. £., and E. Matijevic. Removal cf Copper, lead,
and Cadmium lens by Micrcflotation. J^ Colloid Interface
Sci. 57(1); 94-103, 1976.
2. Guidelines Establishing lest Procedures for the Analysis of
Pollutants, fed. Regist. 41(2321; 52780-52786, 1976.
3. U.S.. Environmental Protection Agency. Methods fcr Cheirical
Analysis of Mater and Hastes. EPA-625/6-74-003a,
Cincinnati, Ohio, 1976. pp. 79, 83, 89, 101-102, 112-113.
4. Cahill, E~ P. J., and G. H. VanLoon. Trace Analysis by Atomic
Absorption Spectroscopy and Anodic Stripping Vcltaitir.etry.
Amer. lab. 8: 11-15, 1976.
5. Colovos, G., G. £. Wilson, and J. Meyers. The Determination
cf Zinc, Cadmium, Lead and Copper in Airborne Particulate
Matter by Anodic Stripping Vcltammetry. Anal. Cbim. Acta
64: 457-464, 1973.
6. Chau, Y. K., and K. Lum-Shue-Chan. Determination cf labile
and Strongly Ecund Metals in lake Hater. Hater Fes. J3:
1-6, 1974.
7. Sinko, I., and J. Oolezal. Simultaneous Cetermination of
Copper, Cadmium, lead and Zinc in Hater by Anodic Stripping
Polarcgraphy. J. Electroanal. Che in. 25: 299-306, 1970.
8. Gardiner, J., and M. J. Stiff. The Determination of Cadmium,
lead. Copper and Zinc in Ground Hater, Estuarine Hater,
Sewage and Sewage Effluent by Anodic Stripping Vcltammetry..
fcater Res.. J: 517-523, 1975.
9. Pichet, P~, and M. Grandmaiscn. Analysis cf Zn**, Cd**, and
Pb*+ in Natural Haters by Anodic Stripping Vcltammetry Using
a Rotating Pt:Hg Electrode. In: Hater Quality Parameters.
ASTM SIP 573, American Society for Testing and Materials,
1975.. pp. 30-34.
10*. Rojahn, T. Determination cf Copper, Lead, Cadmium and Zinc
in Estuarine Hater by Anodic-Stripping Alternating-Current
Voltanrnretry on the Hanging Mercury Drop Electrode. Anal.
Chim, Acta. 62: 438-441, 1972.
17
-------
11. Lund, fc., and D. Cnshus. The Determination of Copper, lead
and Cadmium in Sea Water by Differential Pulse Ancdic
Stripping Vcltammetry. Anal. Chim. Acta 86: 109-122, 1976.
12. Neites, L. Pclarograpbic Techniques. Seccnd Edition.
Interscience Publishers, New York, 1967. pp. 89-90,
398, 623-625, 634-635.
13. Neites, L. (Ed.)- Handbook of Analytical Chemistry, first
Edition. McGraw-Hill Publishers, New York, 1963. pp. 5-63,
5-66, 5-98.
14. Millscn, M., and J. Kopp. Personal communication en
applicability of anodic stripping tc water and waste analysis.
U.S.. Environmental Protection Agency, National Environmental
Fesearch Center, Cincinnati, Chio, Jan. 24, 1975.
15. Csejka, 0. A., and B. M. Visinski. Personal comirunicaticn on
method for zinc, cadmium, lead and copper under jurisdiction
of ASTM Task Group on Voltammetry. Clin Eesearch Center,
Kew Haven, Connecticut, Sept. 9, 1975.
16. Howe, I. H. Trace Analysis cf Arsenic by Ccloriaetry,
Atomic Absorption, and Polarcgraphy. EPA-600/7-77-036,
Tennessee Valley Authority, Chattanooga, TK, 1977. 42 pp.
17. Howe, I. H. Personal communication en method cf test for
selenium in water. TVA laboratory Eranch, Chattanooga,
Tennessee. June 12, 1974.
18. Christain, G. D., and E. C. Knoblock. Pclarcgraphy of
Selenium (IV). Anal. Chem. 35(9); 1128-1132, August 1963.
19. Vajda, F. stripping Voltammetry of Se (IV) Compounds with
the Hanging Mercury Drop Electrode.. Acta Chim. Acad. Sci.
Hung. 63(3); 257-265, 1970.
20. Alam, A. M. £., C. Vittori, and M. forthault. Ceterminaticn of
Selenium (IV) in Acidic Solutions with A. C. Polarography
and Differential Pulse Pclarcgraphy. Anal. Chim. Acta
87: 437-444, 1976.
21. Shuman, M. S., and G. P. Noodward, Jr. Intermetallic Compound
formation Between Copper and Zinc in Mercury and Its Effects
on Anodic Stripping Vcltammetry.. Anal. Cbem. 48(131; 1979-
1983, November 1976.
22. Copeland, T. fi., R. A. Csterycung, and B. R. Skogertoe.
Elimination cf Ccpper-Zinc Intermetallic Interferences in
Anodic Stripping Voltammetry. Anal. Cheor. 46(14); 2093-
2097, December 1974-
18
-------
23. Jagner, 0., and I. Kryger. Computerized Electroanalysis.
Fart III. Multifle Scanning Anodic Striffing and Its
Application to Sea Mater. Anal. Chim. Acta 80: 255-266,
1975. ~~~
24. Princeton Applied Research Corporation. Electrochemical
Accessories. T359-10M-3/76-CF, P.C. Box 2565, Princeton,
Kew Jersey, 1976. pp. 7-12.
25. Princeton Applied Research Corporation. Stripping Voltam-
metry - Some Helpful Techniques. Technical Kote 109A,
P.O. Box 2565, Princeton, New Jersey. 1974.
26. Princeton Applied Research Ccrporaticn. Instruction Manual.
Hanging Mercury Drop Electrode Model 9323. futlicaticn tio.
M200; 2/73, Princeton, New Jersey. 1973.
27. Keast, R. C. (Ed.). Handbook of Cheiristry and Physics.
Chemical Rubter Co., Publishers, Cleveland, 1973.. p. f-6.
28. Texas Instruments. Owner's Manual for Programmable Slide-
Rule Calculator SR-52. Texas Instruments, Inc.,
Publishers, Dallas, 1975. pp. 12-17.
29. American Society for Testing and Materials. Annual EocJc
cf Standards. Part 31 on Mater. 1916 Face St.,
Philadelphia, PA., 1977. pp. 1052-1058.
30. Editors, Anal. Chem. .47: 2527, 1975.
31. Miller, I~, and J. E. Ereund. Probability and Statistics for
Engineers. Prentice-Hall, Inc., Publishers, 1965. pp. 164,
399.
32. Taylor, J. K., £. R. Deardorff, R. A. Durst, E. J. Maienthal,
T. C. Fains, and E. P. Scheide. Simulated Precipitaticn
Reference Materials. NBSIR 75-958, National Bureau of
Standards, Department of Commerce, Washington, D.C, October
1975. pp. 18-21.
33. U.S. Environmental Protection Agency. EPA Quality Control
Samples. Publication No. 575, Environmental Monitoring
and Support laboratory, Quality Assurance Branch,
Cincinnati, Chio.
34. Blutstein, H., and A. M. Bond. Trace Zinc Determination in
Acid Media by Differential Pulse Anodic Stripping Vcltammetry
at a Banging Drop Mercury Electrode. Anal. Chem. .48: 759-
761, 1976.
35. Afghan, B. K., P. D. Goulden, and J. F. Fyan. Ose of Dltra-
19
-------
violet Irradiation in the Determination of Nutrients in Kater
with Special Feference to Nitrogen. Technical Bulletin
Ko. 40, Inland Viaters Branch, Department of Energy, Mines
and Fesources, Ottawa, Canada, 1971. p. 22.
20
-------
FIGURES
-------
0.04H
0.03
to
LO
-------
to
IO//Q/I CADMIUM SPIKE
I00//g/l Cd SPIKE
I0//g/l LEAD SPIKE
!2.5//g/l LEAD
I00//g/l LEAD SPIKE
I06//g/l LEAD
1
1
-0.8
-07
-0.6
-0.5
VOLTS vs
-0.4
S. C. E.
-0.3
-0.2
Figure 2. Anodic stripping vcltav.irograms for total recoverable
cadmium and lead in 0.2 M ammonium citrate buffer at pH 3.0 Joy
deposition at -0.800 \ vs. see into a mercury droplet witta a
surface area of 0.032 cm2 for 2 min with stirring plus 30 s
without stirring.
-------
1 1 1 I
23//g/l CADMIUM
0.5//A
20//g/l LEAD
I00//g/l SELENIUM (IV)
29//g/l CADMIUM
30//g/l LEAD
Ul
50//g/l SELENIUM (IV)
28//g/l CADMIUM
34^/g/l LEAD
30//g/l SELENIUM (IV)
-0.8
-0.7
-0.6
-0.5 -0.4
VOLTS vs S.C.E.
-0.3
-0.2
Figure 3. Interference of seleniuir (IV) on anodic
voltairirograir.s for total recoverable cadmium and lead in 0.^ K
ammonium citrate tuffer at pH 3.0 ty deposition at -0.800 v vs.
see into a mercury drop with a surface area of 0.032 cm* tor
2 min with stirring plus 30 s without stirring.
-------
0.5//A
25 //g/l CADMIUM
30//g/l LEAD
Ni
ON
I ml 10% ASCORBIC ACID ADDED
I000//g/l
SELENIUM
WITHOUT ASCORBIC ACID
l
-0.8
-07
-0.6
-0.5
VOLTS vs
-0.4
S. C. E.
-0.3
-0.2
Figure 4. Ascorbic acid for eliminating interference of selenium
(IV) en anodic stripping vcltammograms for total recoverable
cadmium and lead in 0.2 M ammonium citrate buffer at pfi 3.0 by
deposition at -0.800 V vs. see into a mercury droplet with a
surface area of 0.032 cm* for 2 nin with stirring plus 30 s
without stirring.
-------
10
I I I
30//g/l COPPER SPIKE
30//g/l CADMIUM SPIKE
30//g/l LEAD
SPIKE
32//g/l COPPER
30//g/l CADMIUM
32/>9/l LEAD
-0.3 -0.2 -O.I 0.0
VOLTS vs S. C.E.
Figure 5. Anodic stripping voltawrograms for total recoverable
cadmium, lead, and ccpper in 0.2 M ammonium citrate tuffer at
pH 3.0 fcy deposition at -0.800 V vs. see into a mercury drop with
a surface area of 0.032 cm« for 2 min with stirring plus 30 s
without stirring.
-------
to
00
I I I I
100//g/l COPPER SPIKE
100/yg/l CADMIUM SPIKE
IOO//g/IZINC SPIKE
I00//g/l LEAD
SPIKE
H4//g/l ZINC
89//g/l
COPPER
82//g/l
CADMIUM
86//g/l LEAD
-1.2 -I.I
-1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -O.I
VOLTS vs S.C.E.
Figure 6. Anodic stripping vcltair.irogran:s for total recoverable
zinc, cadffium, lead, and copper in 0.2 K aounoniuoi citrate tuffer
at pH 3.0 ty deposition at -1.200 V vs.. see into a mercury drop
with surface area of 0..032 cm2 for 2 min with stirring plus 30 s
without stirring.
0.0 +0.
-------
10
vo
5//g/l ZINC SPIKE
5^/g/l CADMIUM SPIKE
COPPER
SPIKE
5//g/l LEAD SPIKE
-1.2
-1.0 -0.9 -0.8 -0.7
-0.6 -0.5
VOLTS vs
-0.4
S. C. E.
-0.3 -0.2 -0.! 0 O.I 0.2
Figure 7. Anodic stripping vcltainrograirs for zinc, cadir-ium,
lead, and ccpper in raw purified 0.2 K ammonium citrate tu±±er
at pH 3.0 ty deposition at -1.200 V vs. see into a irercury drop
with a surface area of 0.032 cm* fcr 10 min with stirring plus
30 s without stirring.
-------
TABLES
-------
TABLE 1. DETERMINATIONS CF HANGING MEBCUBY DBCF ABEA
Beading
(small vertical
divisions)
2
2
2
4
4
4
6
6
6
6
8
8
Tempera-
ture <°C)
22.8
22.8
22.8
22.8
22.8
22.8
23.1
23.1
22.8
22.8
22.8
22.8
height of 10
drops (mq)
24.97
25.43
25.53
50.. 05
53.20
52-87
64.. 5 9
64.89
72-80
76.17
81.52
90.54
Surface area
cer droE icm2)
0.01567
0.01586
0.015SO
0.. 02491
0.02594
0.02584
0.02953
0.02962
0.03198
0.03296
.0.03448
0.03698
33
-------
TABLE 2. SIMULTANEOUS DETERMINATIONS CF CADKICM AND LEAD CONCEKTBAUCK£ £X
ANODIC STRIPPING VCLTAMMETRY FOB BEPLICATE SCIUTICNS OF SPIKED FEAGEN1 KATE**
••^^•^ ~^^^^ — . 1__1 _^ — 11_ j JM^ " ' " " ^"~**^tT
Cadmium and lead Cadmium lead
concentration determination determination
(pg/1) (P9'l) (fg^l)
0 0.2, 0.1, 0.1, 0.1, 0.2, 0.1, 0«2, 1.9, 2.5, 2.8, 0..8, 1.8, 3.0, 3..4,
0.2, 0.3, 0.2, 0.2, 0.1, 0.2 2.6, 3.4, 2.4, 3«2, 2.9, 3.0
5.0 6.0, 4.8, 5.5 6.5, 7.4, 5.1
10..0 a.7, 9.6, 13.3 10.2, 10.3, 13.8
30 25, 34, 28 27, 33, 30
* 60 53, 55, 51 56, 56, 56
100 102, 91, 84 103, 94, 87
Determination was made by deposition at -0.800 V vs. see in a mercury drcf with a surface
area of 0.032 cm* for 2 min with stirring plus 30 s without stirring.
-------
in
Copper
H9/1
Zinc
MA
tig/1
TABLE 3. TYPICAL SENSITIVITIES AND PEAK BEIGH1 VS. CCKCIEUA1ICK
PBOfCJUOHAUTY TESTS JOB CADMIUM, LEAD, CCPPEI), ABC UKC"
Metal
CadaiuB
MA
M9/1
pApg-
lead
MA
M9/1
MA M9~<
, le«t 1
Raw 1* 10-
0.388
9.78
i t-« 0.0397
0.254
12.54
i 1-» 0.0203
M9/1 Spike c
0.784
19.78
0.0396
0.456
22.54
0.0202
Ban 2>
0.995
33.9
0.0293
0.510
34.5
0.0148
Teat 2
30-|ig/l Spiket
4.87
63.9
0. 0293
0.950
64.5
0.0147
Ban 3b
1.90
53.2
0.0357
1.08
59.3
0.0182
lea* 3
60-tig/l 8piJcec
4.02
113.2
0.0355
2.46
119.3
0.0481
Ca« 4 "
3.09
402.6
0.0304
1.64
406.3
0.0154
lest 4 . Teat 5 Test 6
100-ig/l Epikec Raw 5" 30-ug/l Spikec Ban 6° 100-ug/l Spike ^
6.04
202.6
0.0298
3.15
206.3
0.0452
1.20
31.6
0.0380
2.33
61.6
0.0378
2.41
113.7
0.0212
4.48
213.7
0.0210
• DeterBinationa of cadBiiw, lead, and capper Mere Bade ty decoaition at -0.800 V vs.. ace in * icrcury
drop with a aurface area of 0.032 cm* tor 2 vin with stirring piua 30 a nitccut atirrinq. Cctcrainaticnt
of zinc tiere Mde ty deposition at -1.200 V va. ace under the aaoe conditiona.
Raw 1. 2, 3. and 4 are digested standard Mixtures 10, 30, 60, and 100 ug/1 of cadniua
Raw 5 and 6 are digested standards with 30 pg/1 copper and 100 pg/1 .inc.
C8pike ia the standard addition used to quantitate the raw sample adjacent to it.
and lead.
-------
TAEIE 4.. EFFECT OF FERRIC IFCN AKD HYDBCXYLAMIKE
CN ANALYSIS CF 30-pg/l CADMIUM AMD LEAD SAKfIE£
EY ANODIC STFIPPIKG VOIlAMME7£Ya
Ferric iron
concentration
lug/1)
Cadmium
determination
(uq/11
lead
determination
20,000
40,ooob
5,000
10,000
20*000
40,000b
20,000
40,000b
No h vdr cxy lamine
36
24
100 jjl of 10% hvdroxylair.ine
32
30
33, 24, 24, 20
24
500 pi of 10% hydroxylamine
24
27
50
33
34
30
66, 32, 34, 24
34
24
26
aDetermination was made by deposition at -0.800 V vs.. see in
a mercury drop with a surface area of 0..032 cm2 for 2 Kin
with stirring plus 30 s without stirring.
bAt 40,000 |ig/l Fe(III), an erratic baseline is observed at
voltages mere positive than -0.350 V vs. see, the region
where the tail end of the stripping peak for lead appears.
36
-------
TAELE 5. EFFECT OF SELENIUM (IV) AND ASCCFEIC ACIC CN
ANALYSIS CF 30-pg/l CADMIUM ANC LEAD SAMPLES
EX ANODIC STFIPPIKG VCLIAMMEIBY3
Selenium Cadmium Lead
concentration determination determination
fuq/11 (iiq/ll (uq/11
30 27 32
50 28 27
100 23 17
No ascorbic acid
1 ml of 10% ascorbic acid
100 31 29
500 29 36
1000 25 27
a Determination was nrade by deposition at -0.800 V vs. see in
a mercury drop with a surface area of 0.032 cm2 for 2 min
with stirring plus 30 s without stirring.
37
-------
TABLE 6. COMPARATIVE TEST RESULTS Cf CACMIUK AND LEAD
DETERMINATIONS FOR SPLIT SAMPLES FROM ASH fCKDS
Location
Allen
Bull Run
Colbert
Cumberland
Gallatin
John Sevier b
John Sevier c
Johnsonville
Kingston
Paradise b
Paradise c
Shawnee
Watts Bar
Widows Creek
HaHnH iim (jia/T}
Atomic
Voltammetric* absorption
9-7 10, 12
0.6 <1, <1
<0.2 <1, <1
<0.2 <1, <1
0-4 <1, <1
5.8 5.2, 7.0
<0.2 <1, <1
0.2 <1, 2
2.8 1.1
128, 106 120, <1
1.5 <1, <1
0.3 <1, 3
2-4 <1, 3
0-2 <1, <1
Lead (fif
Voltamnretric a
16
10, 12
7.2
4.0
7-3
7.2
15
8.0
15
34, 36
6.0
4.0
8.0
4.6
/•n
Atomic
abscrption
<10, <10
<10, <10
<10, <10
<10. <10
<10, 11
<10, <10
<10, <10
<10, <10
<10, <10
34
<10, <10
<10, <10
<10, <10
<10. <10
aDetermination was made by deposition at -0.800 V vs. see in
a mercury drop with a surface area of 0.032 cm2 for 2 IT in
with stirring plus 30 s without stirring.
bSamples of water fro0 the fly ash pond were collected and
analyzed.
csamples of water frov the bottom ash pond were collected and
analyzed.
38
-------
TABLE 7. TEST RESULTS OF CADMIUM AND LEAD DETERMINATIONS BY
ANODIC STRIPPING VCLTAMMETFY FOB STANDARD BEFEREKCI SAMPLES
Description
Cadmium (ug/1)
Lead (ng/1)
Certified Voltammetric Certified Vcltanunetric
EPA trace metals
reference sample
575 (No. 1)
5-2
5.. 5
22
27
NBS simulated pre-
cipitation reference
sample A
NBS simulated pre- 578
cipitation reference
sample C
Recommended Voltammetric Recommended VoltaniBietric
30 34 18 16
510
152
170
aDeposition was made at -0.800 V vs. see in a mercury drop vith
surface area of 0.032 cm2 for 2 min with stirring plus 30 s
without stirring.
TABLE 8. SIMULTANEOUS DETERMINATIONS OF CADMIUM,
LEAC, AND COPPER BY ANODIC STRIPPING VCLTAMMETRY
FOR REPLICATE SOLUTIONS OF SPIKED REAGENT WATER3
Concentration of
cadmium, lead,
and copper
Cadmium
determination
Lead Ccpper
determination determination
(pg/1) (P9/1)
0
30
Ko zinc
0.2 1.9
27, 29, 30 30, 34
5.. 3
25, 29, 26
0
30
Mith 30 uQ/1 zinc
0.2 1-6
25, 23, 29 25. 24, 28
2.4
27, 26, 30
aDetermination was made by deposition at -0.800 V vs. see in a
mercury drcp with a surface area cf 0.032 cm* for 2 Bin with
stirring plus 30 s without stirring.
39
-------
TABLE 9. ZINC DETERMINATIONS BY ANODIC
STRIPPING VCLTAMMETFY FOR REFLICATE
SOLUTIONS Of SflKEC REAGENT
Zinc concentration Zinc determination
0 14
100 69, 99, 79
Kith 100 fig/1 cadmium, lead, and copper
0 15
100 93, 99
aDetermination was made by deposition at -1.200 V vs. see in a
mercury drcp with a surface area cf 0.032 cm2 for 2 IT in with
stirring plus 30 s without stirring.
TABLE 10. EFFECT OF REACTION TIME ON EURIFICATICK
CF AMMONIUK CITRATE EUFFER BY ELECTROLYSIS KITE
STIBPING INIC A MERCURY CATBCDE AT -1.500 V VS. neea
Metal determination (uq/1)
Reaction tinr.e (hr)
Raw
sclution
19
48
168
192
Zinc
11
4.1
2.7
1.0
1.0
Cadmium
0.2
<0..2
<0.2
0.2
<0.2
Lead
2.5
1.6
0.5
0.7
0.5
Cccper
3.3
0.6
0.3
0.3
0.2
aDetermination was made by deposition at -1..200 V vs. see in a
mercury drop with a surface area of 0.032 cm* for 2 min with
stirring plus 30 s without stirring.
40
-------
TABLE 11. SIMULTANEOUS DETERMIKATIOK CF LCfc CCNCEKIRATICNE
OF ZINC, CADMIUM, LEAD, AND COPPER BY ANCDIC STRIFEIKG
VCLTAMMETRY WITH PURIFIED AMMONIUM CITRATE BUFFER a
Solution 1 Oug/1)
Metal
Zinc
Cadmium
Lead
Copper
Concen-
tration
10
5
5
5
Determi-
nation b
9±7
5.0±1.8
4.2±1.6
3.8±2.1
Blank
9
0.3
2.1
2.7
Solution 2 (jig/1)
Concen-
tration
5
2.5
2.5
2.5
Determi-
nation13
2±3
2.7±0.8
2.5±1.1
4.4±i.7 c
Blank
7
0.2
1,4
0.3
aDetermination was made by deposition at -1.200 V vs. see in a
mercury drop with a surface area of 0.032 cm2 for 10 min with
stirring plus 30 s without stirring. The ammonium citrate tuffer
that was used in the determination was purified to values cf
1,0, <0.2, 0.5, and 0.2 pg/1 for zinc, cadmium, lead, and copper,
respectively, by electrolysis into a mercury cathode at -1.500 V
vs. nee-
bAverage value and standard deviation for triplicate determina-
tions minus blank determination.
°From a duplicate determination.
41
-------
TECHNICAL REPORT DATA
(Please read /Nstmctions on the reverse before completing)
REPORT NO.
EPA-600/7-78-075
3. RECIPIENT'S ACCESSION" NO.
4. TITLE ANOSUBTITLE
DETERMINATION OF ZINC, CADMIUM, LEAD, AND COPPER
IN WATER BY ANODIC STRIPPING VOLTAMMETRY
5. REPORT DATE
May 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Lyman H. Howe and Isaac E. Jones
8. PERFORMING ORGANIZATION REPORT NO.
TVA/EP-78/13
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, TN. 37401
10. PROGRAM ELEMENT NO.
INE 625C
11. CONTRACT/GRANT NO.
79 BDH
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Research & Development
Office of Energy, Minerals & Industry
Washinaton, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Milestone
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
This project is part of the EPA-planned and coordinated Federal Interagency
Energy/Environment R&D Program.
16. ABSTRACT
The Tennessee Valley Authority developed a method of differential pulse anodic
stripping voltammetry for determining total concentrations of cadmium and lead
in water samples from ash ponds at steam-electric generating plants. After
digestion of the sample and addition of reagents to overcome interferences by
iron (III) and selenium (IV), the peak current for cadmium and lead is measured
and quantified by standard addition. The effective range for this method is
0.3 to 100 yg/1 of cadmium and 3 to 100 yg/1 of lead. This method gives
suitable accuracy for cadmium and lead in reference water samples and in split
samples of effluent water from ash ponds that were analyzed by atomic absorption.
Limited data show that this method probably also can be used for 5 to 100 yg/1
copper but that it is unsuitable for zinc because of a 15-yg/l sample blank.
7.
(Circle One or More)
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
_Envir-inments J
Earth Atmosphere
Environmental Engineering
Geography
Hydrology. Limnology
Biochemistry
Earth Hydrosphere
Combustion
Refining
Energy Conversion
Physical Chemistry
Materials Handling
Clnorganic Chemistry
Organic Chemistry
CherriK-a! Engineering
6F 8A 8F
8H 10A 10B
7C 13',
13. DISTRIBUTION STATEMEN1
Release to Public
19. SECURITY CLASS (This Report/
Unclassified
21. NO. OF PAGES
41
20. SECURITY CLASS (Tillspage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
------- |