United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S2-86/120 Apr. 1987
Project Summary
Evaluation of Spark Source Mass
Spectrometry and Plasma
Emission Spectroscopy for
Comprehensive Elemental
Analysis of Environmental
Samples
Alvia Gaskill, Jr.
This report presents the results of an
extensive literature review and evalua-
tion of spark source mass spectrometry,
inductively coupled plasma emission
spectrometry, and direct current plasma
emission spectrometry. The goal of this
study was to determine if these tech-
niques are capable of providing com-
prehensive elemental screening of en-
vironmental samples and, if so, the
limitations to be expected.
Sample preparation, introduction,
identification, and quantitation proce-
dures were evaluated to gain under-
standing of the elemental coverage and
data quality to be expected using each
technique.
This Project Summary was developed
by ERA'S Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Introduction
The complete and cost-effective ele-
mental characterization of environmental
samples may become a requirement
rather than a goal as quality control and
environmental monitoring requirements
become stricter To meet this need, tech-
niques are needed that can provide com-
prehensive elemental analysis in a timely
manner.
The Air and Energy Engineering Re-
search Laboratory (AEERL) of the U.S.
Environmental Protection Agency (EPA),
Research Triangle Park, North Carolina,
for many years has recognized the need
for such techniques and, until recently,
has advocated the use of spark source
mass spectrometry (SSMS) to perform
comprehensive elemental analyses in its
Level 1 environmental assessment
studies.
Until recently, no candidate technique
was available to challenge SSMS m terms
of cost per analysis, comprehensive ele-
mental analysis capability, and data
quality (accuracy, precision, detection
limits) However, the recent development
of commercially available inductively
coupled plasma (ICP) and direct current
plasma (DCP) emission spectrometers,
the interest shown by other Agency lab-
oratories in proposing plasma techniques
as the chief elemental analysis tech-
niques for environmental analyses, and
the reported excellent accuracy and
short-/long-term precision of these tech-
niques have prompted AEERL to reassess
the role SSMS should play in analytical
support work for the laboratory in Level 1
and related analysis activities.
-------
The objectives of this study were to
compare SSMS and the plasma tech-
niques for the following characteristics:
• Elemental coverage or survey
capability
• Ease of sample preparation
• Analysis time
• Interferences
• Accuracy
• Precision
• Detection limit
• Applicability to routine environ-
mental analyses
• Availability of validated protocols
• Commercial availability.
The information generated from this
assessment should prove useful in deter-
mining the future roles of SSMS and
plasma techniques in AEERL sponsored
programs.
Appro ach
A truly effective comparison of the
capabilities of SSMS and plasma tech-
niques necessarily would involve analyses
of the same samples by both techniques.
Because very little comparison data of
this nature exists, a number of other
characteristics that individually and col-
lectively determine overall data quality
must be evaluated.
The ability of a technique to determine
many elements in a simultaneous or
nearly simultaneous fashion in the same
sample is defined here as its potential for
comprehensive coverage. This coverage
capability can provide qualitative, semi-
quantitative, or quantitative data Each of
these levels of specification is evaluated.
The ease with which field samples can
be processed prior to analysis is often a
limiting factor as to (1) how long it will
take to obtain the analytical result, (2)
what fraction of the original matrix can
be analyzed, and (3) what elements can
be determined. Very complex matrices
containing refractory forms of some ele-
ments often require elaborate sample
dissolution/extraction steps that are time
consuming and restrictive as to the final
number of determmable elements. These
factors were evaluated for both plasma
spectroscopy and SSMS. Because no
single sample preparation procedure
exists, several of the most common are
evaluated.
Sample analysis, the part of analyte
determination that begins with sample
introduction into the measurement device
and ends with data acquisition by a
computer or other recording device, were
evaluated with respect to spectral inter-
ferences and sample transport The ad-
vantages and disadvantages of various
detector systems are discussed.
Data processing is defined here as the
handling of spectral data generated by
the detector systems and recording
devices
Data quality was evaluated by com-
paring plasma techniques and SSMS with
respect to three common measures of
method performance, accuracy, precision,
and detection limit. Analyses of environ-
mental samples of known composition
form the basis for the accuracy assess-
ment. Precision is assessed by comparing
results obtained on repeat analyses of
the same sample or on aliquots of the
same sample taken through a sample
preparation procedure Detection limits
seldom were reported for environmental
matrices. Assessment of method detection
limits was limited to a comparison of the
instrument manufacturer's claims sup-
plemented with available environmental
data.
The applicability of plasma and SSMS
techniques to routine environmental
analyses was assessed by examining the
availability of commercial instrumentation
and analysis protocols as well as the
relative and absolute costs of sample
analysis on a per-element and per-sample
basis.
Results and Discussion
ICP-Atomic Emission Spectroscopy
(AES) and SSMS techniques generally
required a vastly different set of sample
preparation and introduction methods
that depended primarily on the type of
matrix and to a certain extent on the
element(s) of interest
The SSMS technique is superior to the
ICP-AES, with regard to sample prepara-
tion and introduction, for inorganic
powders and other solid materials with
less than 50 percent organic content
amenable to grinding and fabrication of
homogeneous electrodes Thus, most
geological type samples (e g., coal, soil,
silicate rocks, fly ash, air particulates.
and stream sediments) were transported
more easily from the raw sample to the
detector system in SSMS than in ICP-
AES. Samples that were primarily organic
in composition (e g., plant materials, other
biota, animal tissue, oils, other liquid
fuels, and aqueous samples) in general
were better suited to sample preparation
and introduction into the ICP-AES.
The data presented in this study sug-
gest that neither SSMS nor ICP-AES is
entirely suitable for the comprehensive,
precise, and accurate determination of all
elements, in all types of matrices, and at
all levels no single technique offers this
capability When appropriate steps are
included to increase the elements present
at below-instrumental detection limits and
to permit the introduction of elements
present in matrices incompatible with
the instrument sample introduction/ex-
citation systems, the number of elements
that can be determined by each technique
can be extended to a maximum of around
100 elements However, this cannot take
place in a single sample or without putting
forth and unacceptable amount of effort
for the return that is expected
The accuracy and precision of SSMS
were much poorer than for ICP-AES, even
when comparing the analyses for
matrices that are easily compatible with
the SSMS To achieve better accuracy
and precision with SSMS would require
that the number of elements to be deter-
mined be reduced to only a handful
The most significant conclusion to be
drawn from this study is that SSMS and
ICP-AES are complementary techniques
that together provide much greater cover-
age and detection capability than either
technique alone when many different
matrices are considered
The applicability of any measurement
technique to routine environmental
analysis is highly dependent on the
availability to users of documented proto-
cols Ideally, the protocols should be
validated prior to dissemination for general
use and should be compatible with com-
mercially available instrumentation
Several recommended and required test
methods for SSMS and plasma tech-
niques have been prepared by the
American Society for Testing and Materi-
als (ASTM) and EPA in the last seven
years. Some of these protocols are quite
detailed and can almost serve as "stand-
alone" documents for analysis of certain
types of samples Others are, at best,
guidelines for conducting analyses by
these techniques and presume consider-
able prior knowledge on the part of the
analyst
Additional guidance is available in the
operating and applications handbooks
that accompany the instrumentation and
in the open literature However, with the
exception of the EPA ICP-AES method for
water and wastes, there are no satis-
factory comprehensive standard operating
procedures (SOPs) for SSMS or plasma
techniques The EPA method is directly
-------
applicable only to dilute aqueous samples
and thus does not address the analysis of
solids or nonaqueous liquids Until such
comprehensive SOPs are available,
analysts will have to depend on the open
literature and their own specific needs to
develop methods of analysis for these
types of samples
Alvia Gaskill, Jr is with Research Triangle Institute, Research Triangle Park,
NC 27709.
Judith S. Ford is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Spark Source Mass Spectrometry
and Plasma Emission Spectroscopy for Comprehensive Elemental Analysis
of Environmental Samples," (Order No. PB 87-145 686/AS; Cost. $24 95,
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
Air and Energy Engineering Research Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-86/120
0000329 PS
------- |