Chemical Analyses of Particle Filter Deposits* - Aerosols: Measurement, Dosimetry, and Health Effects - page 192

The HPLC-UV/Vis, IC-PAD, and IC-conductivity detection methods each require 1ml of DDW
which may require a larger sample deposit or more parallel ilters than illustrated in Figure 7.1.
7.4.12 t HerMal d esorPtion -g as c HroMatograPHy -M ass s PectroMetry
a nalysis For n onPolar o rganic c oMPounds
Organic compounds are important source markers (Chow et al., 2007b; Daisey et al., 1986; Labban
et al., 2006; Zielinska et al., 2008) and have potentially adverse health effects (Mauderly and Chow,
2008; McDonald et al., 2004). OC consists of thousands of organic compounds, more than is practi-
cal or desirable to measure. Table 7.2 lists functional groups and some of the speciic compounds
that can be practically measured with current technology.
Thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) (Chow et al., 2007c;
Falkovich and Rudich, 2001; Greaves et al., 1985; Hays et al., 2003; Ho and Yu, 2004; Schnelle-
Kreis et al., 2005) has returned results that are comparable to those from solvent extraction methods
(Ho et al., 2008). TD-GC-MS is a cost-effective alternative approach for qualitative and quantitative
analysis of nonpolar organic compounds on aerosol-loaded ilters (Ho and Yu, 2004).
Filter punches are removed following the TOR procedure and spiked with 1 μL of two internal
standard solutions (e.g., n C 16 D 34 and n C 24 D 50 for alkanes and phenanthrene-d 10 , and chrysene-d 12
for polycyclic aromatic hydrocarbons [PAHs]) to normalize the MS response. The punches are
divided with a clean, sharp blade to facilitate loading of the ilter pieces into a Pyrex glass tube
that is matched to the size of the GC-MS (e.g., Agilent 6890 GC with Model 5973 or 5975 model
MS, Santa Clara, CA) injection port. A small amount of prebaked glass wool holds the ilter parts
in position after placing the glass tube loaded with the ilter. For in-injection port TD-GC-MS, the
injector port temperature is hold at 50°C prior to analysis. After placing the glass tube loaded with
the ilter, the septum cap is closed, and the injector port temperature is increased to 275°C for 11 min
to desorb the organic materials in splitless mode. The GC oven is maintained at 30°C during sample
heating to focus the released organic analytes on the head of the GC column. After the sample
temperature achieves 275°C, the GC oven temperature is retained at 30°C for 2 min, increased at
a rate of 10°C/min to 120°C, followed by an increase of 8°C/min to 310°C, and then held at 310°C
for 20 min. An HP-5 ms capillary column (5% diphenyl/95% dimethylsiloxane; 30 m long × 0.25 mm
I.D. × 0.25 μm ilm thickness; Agilent Technologies, Santa Clara, CA) separates the peaks in an
ultrahigh purity (99.9999%) He carrier gas. The MS detector scans from 50 to 650 amu at 230°C
and 70 eV electron ionization. Species are identiied by comparing mass spectra and retention times
with standards that also relate the peak areas to concentration levels, after normalization to internal
standards. Periodic cleaning is needed for the injection port and gold seal, the column head where
the eluted sample is focused, and the ion source after every 50-100 samples, depending on sample
loading (Ho et al., 2011). Although normalization to the internal standard accounts for changes
in the instrument response, the detection limits degrade after 50-100 sample runs especially for
samples containing high amounts of polar organic compounds.
7.4.13 c oMPuter -c ontrolled s canning e lectron M icroscoPy For
s ingle -P article M orPHology and c oMPosition
Shapes and compositions of individual particles are often useful for evaluating source contributions
(Casuccio et al., 1989) and the effects of nonspherical particles on radiative transfer (Chakrabarty
et al., 2009). Scanning electron microscopy (SEM) (Burleson et al., 2004; Jambers et al., 1995;
Maynard, 2000) uses electrons (rather than light as in an optical microscope) to form magniied
images. Electrons provide for better feature resolution, wider range of magniication, and a greater
depth-of-ield than is available in the conventional optical microscope for particles with diame-
ters of 0.2-1 μm. Computer-controlled scanning electron microscopy (CCSEM) couples the SEM
with software that locates a particle, obtains an image, conducts an elemental analysis, records the