United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA-600/S4-83-006 May 1983
oEPA Project Summary
Preconcentration Methods for
Trace Element Determination
D. E. Leyden
Monitoring the safety of drinking
water and water supplies requires an
analytical capability to determine many
toxic elements at low part-per-billion
concentrations. Ideally, all elements of
concern should be measured
inexpensively. Inductively coupled
plasma (ICP) atomic emission
spectrometry is a cost-effective
technique for the direct analysis of
water samples for the elements of most
concern. At the start of this project,
however, ICP did not have adequate
sensitivity to guarantee compliance
with drinking water standards and was
subject to interference from the more
prevalent elements, such as Na and Ca.
Thus, some form of separation and
preconcentration was required to make
ICP applicable to drinking water.
In this study, seven concentration
techniques were examined, including
several that involved precipitation with
selected reagents. Although the
precipitates could be redissolved for
analysis with ICP, their concentrated
and solid form made them especially
amenable to direct analysis by energy-
dispersive X-ray fluorescence (EDXRF).
Consequently, EDXRF was given
considerable attention in evaluating the
concentration methods. The study was
extended to include the EPA Priority
Pollutant elements exclusive of Be,
which is not sufficiently amenable to X-
ray excitation.
From the systematic study of seven
preconcentration techniques, it was
concluded that precipitation with salts
of dibenzyldithiocarbamate was best
overall. An added benefit of the
technique was the possibility of
distinguishing the valence states of
several elements by selective
precipitation. The recommended
method was verified by analysis of
certified reference materials and by
comparison with atomic absorption
spectrometry (AAS) in the analysis of
14 potable and surface water
specimens.
This Project Summary was developed
by EPA's Environmental Research
Laboratory, Athens. GA. to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
As the amount and diversity of the
anthropogenic input to the environment
changes, so too does the demand on
analytical techniques to monitor environ-
mental changes. This is particularly so in
the case of trace elements in natural and
processed water systems where the
balance between biological toxicity and
dietary necessity is narrow and ill-defined.
The need to measure a relatively large
number of elements at ever lower con-
centrations in a wide variety of samples
continues to be a high priority of the U.S.
Environmental Protection Agency (EPA).
This study of published preconcentration
methods for measuring trace elements
was instituted to aid in determining the
"best" method for preconcentrating the
elements in the Priority Pollutants list for
subsequent X-ray fluorescence analysis.
Procedures
The preconcentration procedures
were:
Complexation by 8-hydroxyquino-
line (oxine) and adsorption of the
complexes on activated carbon.
Precipitation by ammonium pyrro-
lidinedithiocarbamate,
Complexation by a dithiocarbamate
previously immobilized on
controlled pore glass,
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• Precipitation by sodium diethyldi-
thiocarbamate,
• Precipitation by sodium dibenzyldi-
thiocarbamate,
• Precipitation by thionalide using
poly(vinylpyrrolidone) as a carrier,
and,
• Filtration through a cation
exchange resin impregnated filter
paper.
Each of the seven procedures had to
produce a product conducive to multi-
element analysis using energy or
wavelength dispersive X-ray fluores-
cence analysis. Each procedure was
evaluated using eight criteria:
• Ability to form a homogeneous thin
film sample,
• Ability to recover and detect 15
elements (excluding beryllium) on
the EPA list of Priority Pollutants,
• Extent of calibration range,
• Linearity of calibration,
• Overall method precision,
• Applicability to natural waters,
• Resistance to concomitant
element, organic compound, and
matrix interferences, and
• General analytical utility,
ruggedness, and availability of
reagents and materials.
Conclusions and
Recommendations
The results of the studies proved that
precipitation of trace ions with the
sodium salt of dibenzyldithiocarbamate
with subsequent filtration on a
membrane filter and analysis of that filter
with energy dispersive X-ray spectro-
metry (EDXRF) can provide reliable,
simultaneous determinations of as many
as 15 elements from the EPA Priority
Pollutants list (Cr, Mn, Fe, Co, Ni, Cu, Zn,
As, Se, Ag, Cd, Sb, Hg, Tl, Pb).
Concentrations as low as 2-5 pgL-1 may
be determined in a 100 mL sample with
an accuracy and a precision of approxi-
mately 5-10%. Analysis time and cost are
reasonable and certainly competitive
with AAS and ICP. The conclusions fall
short of supporting the recommendation
of preconcentration/EDXRF as a
replacement method for AAS or ICP.
However, they do strongly suggest the
method as an alternative. The successful
use of UV-irradiation to reduce the
concentration of organic interferents
provides a simple method for the
elimination of the problem. In most
natural water analyses, the preconcentra-
tion/EDXRF method was less subject to
interferences and matrix problems than
AAS. This is the most obvious in cases of
large variations in the concentration of
minor elements in the sample.
The results clearly suggest that pre-
concentration/EDXRF should serve as a
reliable and economical method for trace
element determinations in natural,
drinking, and effluent waters. The
technique should definitely be
considered for multielement screening
analyses such as those conducted on
industrial effluent waters. It is probable
that the development of a detailed
procedure would be required for each
case. However, this is true with other
spectroscopic techniques as well. One
cannot expect good results from atomic
emission techniques without the use of
matrix matching or other precautions
specific to the problem. The simplicity of
sample preparation, the durability and
longevity of the prepared specimens,and
the economy of the use of energy
dispersive X-ray spectrometry for simul-
taneous multielement determinations
are significant advantages. It is
recommended that the EPA support such
analytical methods for the rapid and
reasonably accurate screening of
industrial effluent and environmental
waters. Such a capability could protect
against serious spike pollution resulting
from failure of industrial water treatment
processes.
The cases in which the preconcentra-
tion/EDXRF method fails to provide total
elemental concentration in the sample
are often related to some type of
speciation such as oxidation state of the
ion. These limitations can be turned into
an advantage. This report illustrates
several examples such as the determina-
tion of the concentration of oxidation
states of Cr, As, and Se in water samples.
D. £ Leyden is with the University of Denver. Denver, CO 802O8.
R. V. Moore is the EPA Project Officer (see below).
The complete report entitled "Preconcentration Methods for Trace Element
Determination," (Order No. PB 83-172 536; Cost: $11.50, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
College Station Road
Athens. GA 30613
United States
Environmental Protection
Agency
ftU.S. Government Printing Office 1983-659-017/7050
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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