United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-90/091 Jan. 1991
EPA Project Summary
Evaluation of Particle Beam
Liquid Chromatography/Mass
Spectrometry for the Analysis of
Polar Semivolatile Organic
Compounds in Air Samples
Robert S. Whiton
In the last few years, several Inter-
faces have been developed for coupling
high performance liquid chromatogra-
phy (HPLC) and mass spectrometry
(MS). Among the most recent is the
particle beam interface. This report de-
scribes the initial evaluation of a particle
beam HPLC/MS system for the analysis
of polar semivolatile organic com-
pounds. The study focused on examin-
ing and optimizing Instrumental operat-
ing parameters, evaluating the ability of
the Instrument to generate classical
electron impact mass spectra of repre-
sentative compounds, investigating the
performance with chemical ionization,
and evaluating the potential for quanti-
tative analysis with selected com-
pounds. Test compounds included hy-
droxy-polycycltc aromatic hydrocarbons
(PAH), nitro-PAH, amino-PAH, and hy-
droxy-nltro-PAH. The report describes
the results of these experiments and
discusses several problems found in
the current particle beam Interface de-
sign.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to an-
nounce 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
Many current methods for the determi-
nation of nonpolar organic compounds in
air are based on gas chromatography/mass
spectrometry (GC/MS), which utilizes the
high resolution achievable with chromato-
graphic separation and the sensitive, se-
lective detection and compound identifica-
tion of mass spectrometry. For analysis of
polar semivolatile organic compounds
(SVOCs), however, GC methods are limited
by the requirement that the analytes be
volatile and thermally stable. Compounds
that do not meet these requirements can
be analyzed by high performance liquid
chromatography (HPLC), but standard de-
tectors for HPLC lack the sensitivity and
selectivity needed for analysis of air
samples, and they do not provide the com-
pound identification ability of the mass
spectrometer.
Efforts to couple HPLC and MS have
been underway for more than 15 years.
The LC/MS interfaces that have seen sig^
nificant use fall into several categories:
direct liquid introduction, liquid ion evapo-
ration, and solvent removal. Each of these
categories has its characteristic areas of
utility and its particular deficiencies. The
particle beam interface introduced by
Browner and co-workers is one of the most
recent introductions.
The particle beam interface uses a
nebulizer and momentum separator to re-
move the solvent vapor from the effluent
with little sample contact with heated sur-
faces. The analytes enter the MS ion source
as a beam of dry particles and can be
ionized by a variety of conventional pro-
cesses, including electron impact (El) and
chemical ionization (Cl) with any reagent
gas. Since commercial versions of the in-
Printed on Recycled Paper
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terfaca were introduced in 1988, the tech-
nique has been applied to a variety of
compounds of environmental interest, with
mixed results. In analysis of diazo dyes,
the sensitivity was much worse than that
obtained with thermospray. Other classes
of compounds that have been analyzed by
particle beam LC/MS include aromatic
sutfonic acids, phenylurea and carbamate
pesticides, and benzWines. Quantification
has been problematic, with two groups
reporting concave calibration curves and
others reporting a carrier effect resulting in
response enhancement by coeluting com-
pounds.
Procedures
The particle beam LC/MS interface is
optimized by adjusting the nebulizer posi-
tion and helium gas flow while repeating
injections of the compound of interest. The
MS Is tuned with the particle beam interface
inserted and solvent flowing. The tuning
compound (perfluorotributylamine) and/or
reagent gas are introduced through the
interface. Manual tuning generally produces
better results than the instrument auto-
matic tuning procedure.
Results
The particle beam LC/MS interface was
found to be reliable and relatively simple
and straightforward to operate. Routine
optimization involves only adjusting the
position of the nebulizer capillary. It was
beneficial to keep the ion source of the MS
slightly hotter than would be normal for the
corresponding GC/MS experiment. The
instrument produces good classical El
spectra for some classes of PAH deriva-
tives, although the quality of the library
matches is variable. It produces unaccept-
able spectra for nitro-PAH compounds,
which apparently are reduced to amines in
the ion source,J"his.may-result from pro^_
longed contact with the ion source walls
before the analytes are vaporized.
The particle beam interface had diffi-
culties with phenolic compounds due to
adsorption in the interface. The adsorption
problem is manifested as tailing peaks,
carryover and reduced sensitivity for phe-
Robert S. Wh'rton is with NSI Environmental Sciences, Research Triangle Park, NC
27709.
Nancy K. Wilson Is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Particle Beam Liquid Chromatography/
Mass Spectrometry for the Analysis of Polar Semivolatile Organic Compounds in
Air Samples," (Order No. PB91-127746/AS; Cost: $15.00, 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:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
nolic compounds. Hydroxy-nitro-PAHs
could not be detected at levels of approxi-
mately 100 ng. The adsorption problem
was not alleviated by use of an acidic
eiuent or the addition of a deactivated
glass line to the desolvation chamber. The
adsorption may be occurring in the overly
long transfer line and the plastic cones of
the momentum separator.
The interface was compatible with
electron capture negative ionization (ECNI)
for nitro-PAHs, with no apparent interfer-
ence from the solvent. Reduction reac-
tions on the walls of the ion source are a
problem when methane is used as the
ECNI moderating gas. With carbon dioxide
as the moderating gas, the instrument pro-
duces good ECNI spectra for nitro-PAHs,
^._^,,^
but the response is nonlinear. Detection
limits are approximately 1 ng by selected
ion monitoring and 1 0 ng full scan.
Conclusions and
Recom mendations
Overall, the performance of the particle
beam interface has not lived up to expec-
tations, although it is effective for certain
compounds. Future modification and
evaluation pf the system may make it a
more reliable and versatile analytical tool.
Some future activities to be carried out
include: modification of the momentum
separator to replace the plastic cones and
shorten the transfer line, testing of a quartz
plate in the ion source to minimize wall
reactions, testing with pesticides such as
carbamates and triazines, which are diffi-
cult or impossible to analyze by GC, and
testing of capillary column supercritical fluid
chromatography/mass spectrometry as an
alternative to LC/MS for hydroxy-PAH.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
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Penalty for Private Use $300
EPA/600/S3-90/091
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