Identification of volatile organic compounds by gas chromatography-mass spectrometry in aerosols collected at T1 (Tecamac, Estado de M

1
Identification of volatile organic compounds by
gas chromatography-mass spectrometry in aerosols
collected at T1 (Tecamac, Estado de
México)Sandra I. Ramírez1 and Telma
Castro21Centro de Investigaciones Químicas,
Universidad Autónoma del Estado de Morelos. Av.
Universidad 1001 Col. Chamilpa 62209 Cuernavaca,
Morelos MEXICO. ramirez_sandra_at_ciq.uaem.mx2Centro
de Ciencias de la Atmósfera, Universidad
Nacional Autónoma de México. Circuito Exterior
S/N Ciudad Universitaria, Del. Coyoacán 04510 D.
F. MÉXICO. telma_at_servidor.unam.mx
INTRODUCTION The MILAGRO (Megacity Initiative
Local and Global Research Observation) campaign
was an integrative and collaborative scientific
program with the objective of observing and
quantifying the fate of anthropogenic pollutants
emitted from the worlds second largest city
Mexico City and its metropolitan area. During
March 2006, scientists from Mexico, the United
States and some European countries performed
ground-based and aircraft measurements. The
ground-measurement were mainly performed at three
supersites T0 located at CENICA, T1 located at
the Universidad Tecnológica de Tecamac, and T2
located at Rancho Bisnaga (Figure 1). Among the
specific scientific objectives of MILAGRO
campaign, one was focused on the characterization
of chemical composition and diurnal variation of
volatile organic compounds (VOCs) contained in
particulate matter collected at boundary sites
(Figure 2). In this work we present preliminary
results of the identification of some volatile
organic compounds identified by the gas
chromatography-mass spectrometry coupled
analytical techniques in samples collected on
aluminum filters at 12-hour sampling intervals at
Tecamac.
Figure 5. Coupled gas chromatograph-mass
spectrometer at CIq-UAEM.
Figure 2. Panoramic view of Mexico City, an
evident lost of long-range visibility, mainly due
to suspended particles, is observed.
The VOCs was then immediately introduced, via a
heated stainless steel transfer line and a
pneumatic automatic six-port valve, to the gas
chromatograph (Trace GC ultra, Finnigan) coupled
to an ionic trap mass spectrometer detector
(Polaris Q, Finnigan Figure 5). The
chromatographic separation was based on the TO-15
EPA protocol while the chemical identity of each
compound was done by digital and visual
comparison of individual spectra with the NIST
library (v. 2002). The quantitative analysis of
the detected VOCs were performed using a
certified gas mixture of C-2 and C-3 hydrocarbons
(PRAXAIR, México).
Figure 6. SIM chromatogram (m/z 40, 44, 57, 71)
of VOCs detected at filter form Tecamac
reconstructed by mass spectra (EI at 70
ev) Chromatographic conditions. Column PoraPLOT
Q fused-silica 30 m ? 0.32 mm I.D. ? 20 ?m
thickness polystyrene-divinylbenzene. Carrier
flow He (UHP) 1.2 ml min-1. Program temperature
isothermal 150C for 3 min, 10C min-1 up to
250C for 20 min. Injector temperature 200C.
RESULTS At the moment, 70 of the received
filters have been analyzed. Figure 6 shows a SIM
(Single Ion Monitoring) chromatogram where almost
all the detected compounds are observed. The
areas of each detected compound can be related
with their content as shown in Table 1.
This analytical methodology allowed us to
identified three saturated hydrocarbons, one
aromatic hydrocarbon, four aldehydes, three
ketones, and one halogenated hydrocarbon, as
shown in Table 1.
Table 1. Volatile organic compounds identified by
GC-MS in particulate material collected al
Tecamac, Estado de México during the MILAGRO
campaign.
Figure 1. MILAGRO surface measuring supersites
Figure 4. Pyrex glass device used for the
temperature treatment of the aluminum filters.
METHODOLOGY AND INSTRUMENTATION The analyzed
samples were collected in diurnal and nocturnal
twelve-hour periods on aluminum filters with a
ten-stage MOUDI. The filters were cut in two
parts, one was used for a gravimetric analysis
(results presented in a different work) and the
other half was used for the chemical
identification (Figure 3), that was performed
only on stages 7 and 8. A preliminary test
demonstrated that the quantity of atmospheric
aerosols collected in the rest of the stages was
below the detection limit of the analytical
system. In this work we present an innovation on
the samples pre-treatment. Prior to the
chromatographic separation, each half-filter was
placed into a special glass device designed to
allow the desorption of the VOCs, bounded to the
particles, using a temperature treatment (200C)
in an oxygen-free environment during 60 minutes
(Figure 4).
CONCLUDING REMARKS The improvement on the sample
handling, avoiding manipulation and solvent
extraction, has probe to be a positive change in
the treatment of atmospheric aerosol samples.
The identified compounds correspond to species
derived from the use of carbon-based fuels,
biomass burning, transportation, and other
anthropogenic activities. It is important to
mention the detection of propanone (acetone), a
long-living intermediate marker. It is necessary
to finish the quantitative analysis of all the
identified species, look for correlations of
quantitative data sets, and perhaps use these
information on modelings studies.
Figure 5. Instrumental facilities to handle
gas-phase materials at CIQ-UAEM.