Environmental Engineering Reference
In-Depth Information
7.4.10 H
igH
-P
erForMance
l
iquid
c
HroMatograPHy
-uv/v
is
For
t
Hree
M
ajor
wsoc c
lasses
Since WSOC consists mostly of polar compounds, organic solvent extraction, derivatization, and
identiication using GC-MS is needed for a large range of compounds (Rogge et al., 1993; Samy
et al., 2010; Yang et al., 2005). A simpler, but useful, analysis divides WSOC from a portion of the
water extract into three classes (i.e., neutral/basic compounds [NC], mono- and di-carboxylic acids
[MDA], and poly-carboxylic acid [PA]) using high-performance liquid chromatography (HPLC) or
IC with UV-Vis detection (Chang et al., 2005; e.g., Decesari et al., 2000).
A 1 mL portion of the water extract is injected into an HPLC with vacuum degasser, quaternary
pump, anion exchange column (5 × 5 mL, GE HiTrap DEAE FF), UV/Vis diode array detector (at
254 nm) (Engling et al., 2006; Falkovich et al., 2005), and fraction collector (Agilent 1200 series,
Santa Clara, CA). The initial mobile phase is pure water, isocratically operated to elute the NC frac-
tion. After 16 min, the mobile phase is switched to a 0.04 M sodium hydroxide (NaOH) solution to
elute the trapped MDA fraction. The mobile phase is then switched to a 1 M NaCl; the strong ionic
interactions elute PA fractions within ∼16 min. Measuring the ratio of absorbance in UV/Vis chro-
matograms at 250 nm (E
2
) over 340 nm (E
3
) for the PA fraction provides structural information of
HULIS (Duarte et al., 2005; Krivacsy et al., 2008). Sampling sites with aromatic precursors result-
ing from biomass burning have lower ratios (e.g., E
2
/E
3
= 2.88; Chamonix, France, in December
2007), consistent with an inverse correlation between E
2
/E
3
and HULIS aromaticity. In contrast,
summer urban aerosol has high ratios (e.g., E
2
/E
3
= 5.90; Marseilles, France, in July 2008), suggest-
ing abundant aliphatic HULIS. SOA of biogenic and anthropogenic origin is known to contribute in
the aliphatic HULIS (Decesari et al., 2007).
7.4.11 ic
witH
P
ulsed
a
MPeroMetric
d
etector
a
nalysis
For
c
arboHydrates
and
ic
witH
c
onductivity
d
etector
a
nalysis
For
o
rganic
a
cids
Seventeen carbohydrates from C
3
to C
12
can be detected and quantiied by IC with a pulsed ampero-
metric detector (PAD): glycerol, erythritol, arabinose, xylose, arabitol, xylitol, levoglucosan, man-
nosan, galactose, fructose, glucose, inositol, sorbitol, mannitol, trehalose, sucrose, and maltitol.
Levoglucosan, mannosan, and galactose derive from biomass burning (Mazzoleni et al., 2007;
Rinehart et al., 2006; Ward et al., 2006). Quantiication of these compounds (e.g., Dionex ICS 3000
series, IC, Sunnyvale, CA) uses a CarboPac MA1 analytical column (4 × 250 mm, Cat. No.044066),
a CarboPac MA1 guard column (4 × 50 mm, Cat. No.044067), and a GM-4 (2 mm, Cat. No.049135)
gradient mixer, with a 600 mM NaOH eluent at a low rate of 0.400 mL/min. Detection is carried
out with an electrochemical detector (ECD; e.g., Dionex ED50) in PAD mode equipped with an
electrochemical cell (e.g., Dionex ED50/ED50A), utilizing a gold working electrode and PAD. The
analytes are identiied by their retention times and quantiied by amperometric peak areas.
In the MDA class, four monocarboxylic acids from C
1
to C
4
(i.e., formic, acetic, methane-
sulfonic, and lactic) and ive dicarboxylic acids from C
2
to C
5
(i.e., oxalic, malonic, maleic,
succinic, and glutaric) are analyzed by IC with a conductivity detector. Oxalic acid is the most
abundant organic acid in aerosol samples and has been found to correlate positively with the
concentration of HULIS (Samburova et al., 2005). For the aforementioned nine organic acids,
the IC is equipped with an IonPac AS11-HC (4 × 250 mm, Cat. No. 052960) analytical column, an
IonPac AG11-HC (4 × 50 mm, Cat. No. 052962) guard column, and an ATC-3 anion trap column
(4 mm, Cat. No. 059660) with a 100 mM NaOH eluent at a low rate of 1.5 mL/min. An ECD
(e.g., Dionex ED50) in conductivity mode is used along with a detection stabilizer conductivity
cell (e.g., Dionex DS3, Cat. No. 044130). A 4 mm suppressor (e.g., Dionex ASRS-300), operated
in the anion self-regenerating suppression mode, is also included in this coniguration to sup-
press the eluent signal. The analytes are identiied by their retention times and quantiied by
conductivity peak areas.
Search WWH ::
Custom Search