Journal of Environmental Protection, 2011, 2, 445-453
doi: 10.4236/jep.2011.24051 Published Online June 2011 (http://www.SciRP.org/journal/jep)
445
High-Precision GC-MS Analysis of Atmospheric
Polycyclic Aromatic Hydrocarbons (PAHs) and
Isomer Ratios from Biomass Burning Emissions
Prashant Rajput, Manmohan Sarin*, Ramabadran Rengarajan
Geosciences-Division, Physical Research Laboratory, Ahmedabad, India.
Received February 19th, 2011; revised March 25th, 2011; accepted April 27th, 2011.
ABSTRACT
This manuscript describ es an analytical method for the quantita tive determination of 16-polycyclic aromatic hydrocar-
bons (PAHs) using accelerated solvent extraction (ASE), followed by purification on a silica cartridge, and sub sequent
measurement by gas chromatograph coupled to a mass spectrometer (GC-MS). The solvent extraction parameters (T =
100 ˚C, P = 1500 psi, t = 30 min, V = 30 ml) are optimized with dichloromethan e (DCM) in order to avoid fractiona-
tion effect, thereby achieving quantitative mass recovery of PAHs. The purification of PAHs on silica cartridge elimi-
nates the matrix effect, facilitates their enrichment from extracted solution and quantitative determination in presence
of an internal-standard (Pyrene-D10). The analytical protocol has been successfully used for the quantification of
16-PAHs and their isomer ratios in atmospheric aerosols collected from northern India dominated by agricultural-
waste (post-harvest paddy and wheat residue) burning emissions. Based on the analysis of ambient aerosols, collected
from different sites, the overall recovery efficiency for 2- to 3-ring PAHs is 85% and near 100% recovery for 4- to
6-ring compounds.
Keywords: Agricultural-Waste Burning, PAHs, Accelerated Solvent Extraction, GC-MS
1. Introduction
Atmospheric aerosols are composed of mineral dust, in-
organic constituents (sulphate and nitrate), carbonaceous
matter (organic carbon and elemental carbon) and sea-salts
[1-5]. Among the various components, physical adsorp-
tion characteristics of mineral dust, sea-salt (polar), and
graphitic carbon (non-polar) are well understood [6-8].
These characteristics affect the high precision measure-
ments of organic compounds and compromise their ap-
plication as proxies to trace the aerosol sources and to
understand their chemical reactivity with the atmospheric
oxidants (O3, OH and NOx) [9-12]. It is, thus, essential to
establish an analytical protocol for the measurements of
organic compounds in atmospheric aerosols with varying
mass concentration and matrix.
Analytical schemes for the quantitative determination
of PAHs in environmental samples and standard refer-
ence materials are available in the literature e.g. [12-18].
However, suitability of many of these is limited to low
aerosol loading. More importantly, these analytical meth-
ods have not adequately investigated the matrix effect of
tarry matter (emitted from agricultural-waste burning) on
mass recovery of PAHs. Therefore, development of an
analytical protocol is required for the quantitative mass
recovery of PAHs, by eliminating the matrix from high
atmospheric loading of aerosols. We report here a quan-
titative method for the determination of PAHs by suitable
combination of accelerated solvent extraction (ASE),
followed by purification on a silica cartridge and subse-
quent determination on a gas chromatograph coupled to a
mass spectrometer (GC-MS). The suitability of the ana-
lytical method has been ascertained from the field-based
samples collected from different geographical locations
in India.
The analyses of organic compounds by the conven-
tional extraction techniques such as Soxhlet extraction
and ultrasonication [14,19,20], though provide their
quantitative recovery, require large volume of solvents
(>100 mL) and are often labour intensive. In spite of this,
the Soxhlet extraction technique has been successfully
used for the extraction of PAHs from standard reference
materials (SRM-National Institute of Standards and Tech-

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 446
Isomer Ratios from Biomass Burning Emissions
nology) [14,18]. However, the current demand for eco-
friendly environment requires minimum consumption of
solvents and rapid sample preparation, without compro-
mising the accuracy and precision. Among the two con-
ventional techniques (ultrasonication and Soxhlet extrac-
tion), the former provides rapid sample preparation with
comparatively lower consumption of solvent. An alterna-
tive extraction technique involving supercritical fluid
extraction (SFE) requires longer extraction time and also
suffers from the incomplete recovery of PAHs in envi-
ronmental samples due to analyte-matrix interactions
[21]. In contrast, the microwave-assisted solvent extrac-
tion (MASE) and the accelerated solvent extraction (ASE)
approach are beneficial in terms of lower consumption of
solvent and perform extraction in shorter time [12,15,
22-24]. However, the MASE technique requires cen-
trifugation and filtration; thus, amounting to the loss of
analyte. For the quantitative determination of PAHs, gas
chromatography (GC), for its high-resolution and sensi-
tivity, is often preferred rather than liquid chromatogra-
phy (LC). Recently, the wide range of applications of
GC-MS technique has been reviewed [25].
2. Experimental Section
2.1. Materials and Method
The aerosol samples (n = 17) analyzed in this study are
collected from three different sites in India: Patiala (30.2
N; 76.3 E; 250 m asl); Hisar (29.2 N; 75.7 E; 219 m asl)
and Shillong (25.7 N; 91.9 E; 1064 m asl). The first two
sites are located in the Indo-Gangetic Plain (IGP) whereas
the third site lies in the high rainfall region of Northeast-
ern India. The aerosol samples from Patiala and Hisar
represent by and large emissions from large-scale agri-
cultural-waste burning emissions [26-28] in the IGP.
However, aerosol composition at Shillong is influenced
by the long-range transport of chemical constituents from
Southeast Asia. It is relevant to state that the contribution
from sea-salts is insignificant at all the three sites for the
sampling during Oct-May. The ambient samples were
collected onto pre-combusted quartz-fibre filters
(PALLFLEX™, 2500QAT-UP, 20 cm × 25 cm) using
high-volume samplers at a flow rate of ~1.2 m3·min–1.
Soon after their retrieval, filters were covered with
Al-foil, sealed in zip-lock plastic bags and stored at ~
4˚C until analysis. The aerosol mass is determined gra-
vimetrically on a high precision analytical balance (Sar-
torius, Model LA130S-F; 0.1 mg) after equilibrating the
filters at relative humidity of 40% ± 5% at 24 ± 2˚C for ~
10 hrs. The concentrations of elemental carbon (EC) and
organic carbon (OC) are measured on a EC-OC analyzer
(Model 2000, Sunset Laboratory, Forest Grove, USA)
using a thermal-optical transmittance (TOT) protocol [2,9].
The HPLC grade solvents (≥95%), dichloromethane
(DCM), acetone and hexane (Chromasolv® Plus, Sigma-
Aldrich) are used for the extraction and sample prepara-
tion. The 16-PAHs mixture (QTM PAH Mix; 47930-U,
in Methylene Chloride, Supelco) and Pyrene-D10 (in
methanol, 71390 Absolute Standards INC.) are used as
the external and internal standards respectively. The
analytical accuracy of PAHs is determined using a stan-
dard reference material (SRM-1649b), procured from the
National Institute of Standards & Technology (NIST,
Gaithersburg, USA). In SRM, PAHs are extracted using
the accelerated solvent extraction system (ASE 200,
Dionex Corporation, Sunnyvale, USA), followed by
evaporation in an evaporator (Turbo Vap LV® II, Caliper
Life Sciences, Hopkinton, USA). Subsequently, extract
was purified on silica-solid phase extraction cartridge
(SPE; WAT020810, Waters Sep-Pak®, 3cc/500mg) placed
over the vacuum manifold (20 positions, WAT200606).
After removal of matrix, extracts were analyzed for
PAHs on a GC-MS (Agilent: 7890A/5975C). The de-
tailed approach involving optimization of experimental
conditions for the determination of 16-PAHs is described
in the following sections.
2.2. Optimization of GC-MS Parameters
After several initial tests, a 30 min GC programme (Ta-
ble 1) was adopted for the separation of 16-PAHs (listed
in Table 2). Subsequently the MS conditions, especially
the ion-source (filament) temperature were standardized
for optimum intensity of PAHs. The PAHs were ana-
lyzed on a GC-MS in electron impact mode (70 eV). A
1-μL solution of 400 ppb (16-PAHs; QTM mixture)
spiked with 200 ng of Pyrene-D10 (internal standard) is
separated on a GC capillary column (30 m × 0.25 mm ×
0.25 μm; Agilent HP-5MS) at a constant flow rate of 1.3
mL/min of helium gas and analyzed at different filament
temperatures; 280˚C (n = 4), 300˚C (n = 4) and 320˚C (n
= 4). The PAHs are identified by comparing their reten-
tion times (RT) with those for 16-PAHs standard and
their quantification is achieved by comparing the peak
areas with those of the internal standard (Pyrene-D10).
The filament temperature at 300˚C appeared to be the
threshold for optimum relative response factors (RRF)
for 16-PAHs, calculated as



Analyte ISTD
ISTD Analyte
Area *Conc
RRF Area *Conc  (1)
The ISTD stands for Internal Standard. Likewise, re-
tention time of PAHs at varying filament temperatures
(as above), are investigated, and are found to be invariable

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 447
Isomer Ratios from Biomass Burning Emissions
Table 1. Experimental parameters for the measurement of PAHs.
ASE GC-MS
GC
Parameters Optimized conditions
Inlet temp: 300˚C
Solvent DCM (30 mL) Heating Rate Temp Hold Time
˚C/min ˚C Min
System pressure 1500 psi
50 1
25 150 -
Oven temperature 100˚C
25 200 -
3 230 -
Oven heating time 5 min
8 310 3
MS
Static Cycles 3 (of 5 min each)
Interface temp. 280
Nitrogen purge 60 s Ion-source temp. 300
Extraction Time 30 min Quadrupole temp. 180
Table 2. Analysis of 16-PAHs in SRM 1649b, Urban Dust (n=19).
Retention timeDetection limitMeasured Conc.§ Reported Conc.
16-PAHs Molecular
weight (min) (n = 12; pg·m–3)(ng/100mg SRM)
Naphthalene {NAPH}* 128 5.448 ± 0.002 1.9 90 ± 18 112 ± 42
Acenaphthylene {ACY}* 152 7.000 ± 0.004 3.7 15 ± 3 18 ± 3
2-Bromonaphthalene {2-BrNAPH} 206 7.154 ± 0.019 2.5 NR
Acenaphthene {ACE}* 154 7.180 ± 0.003 1.2 10 ± 1 19 ± 4
Fluorene {FLU}* 166 7.760 ± 0.016 1.5 17 ± 2 22 ± 2
Phenanthrene {PHEN} 178 9.173 ± 0.022 2.3 373 ± 18 394 ± 5
Anthracene {ANTH} 178 9.264 ± 0.026 2.6 44 ± 8 51 ± 1
Fluoranthene {FLA} 202 12.775 ± 0.0242.1 587 ± 45 614 ± 12
Pyrene {PYR} 202 12.834 ± 0.0221.6 481 ± 31 478 ± 3
Benzo[a]anthracene {BaA} 228 18.275 ± 0.0412.3 224 ± 22 209 ± 5
Chrysene/Triphenylene {CHRY + TRIP} 228 18.437 ± 0.0401.9 413 ± 28 425 ± 10
Benzo[b + j + k]fluoranthene {B[b,j,k]FLA} 252 22.454 ± 0.0382.4 923 ± 72 947 ± 51
Benzo[a]pyrene {BaP} 252 23.444 ± 0.0472.0 267 ± 19 247 ± 17
Indeno[1,2,3-cd]pyrene {IcdP} 276 26.461 ± 0.0461.6 314 ± 20 296 ± 17
Dibenzo[a,h + a,c]anthracene D[ah,ac]ANTH} 278 26.569 ± 0.0553.6 49 ± 4 50 ± 1
Benzo[g,h,i]perylene {BghiP} 276 26.996 ± 0.0332.5 421 ± 35 394 ± 5
Reference values, otherwise certified values (from NIST). NR (Not reported in NIST certificate).§Standard deviation of the data for n = 19. *

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 448
Isomer Ratios from Biomass Burning Emissions
(RT < 0.001% shift). The optimized GC-MS conditions
for the determination of PAHs are listed in Table 1, and
are used for the measurement of 16-PAHs in ambient
aerosols. Data acquisition and processing for the GC-MS
analysis is performed on a HP-Enhanced Chemstation
Data System.
2.3. Optimization of Purification Step on Silica
Cartridge
Aerosol samples contain a wide range of matrices in-
volving mineral dust, organic carbon and elemental car-
bon. These matrices cause mass interferences with the
analytes and affect the resolution of measurements, par-
ticularly for the measurements of PAHs on GC-MS. In
this study, we have used the silica-SPE cartridge for the
purification of PAHs [30]. Prior to the application of
silica-SPE cartridges for purification of PAHs in aerosol
samples, the elution recovery from 16-PAHs standard is
investigated . Accordingly, the silica cartridges, installed
over the vacuum manifold are conditioned through 10
mL DCM followed by 10 mL hexane under the vacuum
(<340 millibar). The cartridges are dried under normal
conditions for 5 min. Subsequently, the 16-PAHs liquid
mixture of varying amount 100 ng (n = 3), 400 ng (n = 3)
and, 800 ng (n = 3), in 3 mL hexane are loaded on silica
cartridges. The matrix is allowed to fall under gravity,
and is discarded. The cartridges are dried again for 5 min.
The affect of cartridge drying on the PAHs mass recov-
ery has been discussed elsewhere [30]. Subsequently, the
elution of PAHs from each cartridge is performed under
gravity with 3 mL, 20% DCM in hexane (v/v). The elu-
ate is evaporated to ~ 500 μL under gentle nitrogen gas
stream, to which 200 ng of Pyrene-D10 is added. The
final solution is made to 1 mL in hexane and stored in
amber coloured glass vials at –19˚C until analysis on
GC-MS.
2.4. Optimization of Extraction Parameters on
ASE
The extraction parameters on ASE such as solvent selec-
tion, temperature and extraction time on the recovery
efficiency of PAHs were investigated at a constant pres-
sure of 1500 psi (103 bars). The extraction at 1500 psi
pressure is considered to be optimal for the aerosol sam-
ples [12]. The extraction protocol was developed based
on the analysis of standard reference material (NIST,
SRM-1649b, Urban Dust). The toxic solvents e.g. ben-
zene and its derivatives were not used to assess the ex-
traction efficiency of PAHs. Furthermore, the loss of
analyte during sample processing [16], if any, was
checked with the low boiling point solvents e.g. DCM
(40˚C), which not only extract PAHs quantitatively from
aerosols but also can undergo rapid evaporation. Fur-
thermore, the PAHs were also extracted from SRM in
two different solvents viz. DCM (n = 6) and DCM: Ace-
tone (n = 6; 1:1 v/v) at 100˚C, 1500 psi and 3 static cy-
cles of 5 min each. These extracts were evaporated to 1
mL in evaporator (<30˚C) and further to near dryness by
gentle nitrogen gas purge. The residue was dissolved in 3
mL hexane. Subsequently, the optimized protocol, de-
scribed in the previous sections is used for the purifica-
tion and sample preparation for PAHs analysis. The re-
sults suggest that, within the uncertainty of measure-
ments on GC-MS, the yields for individual PAHs were
equal with DCM or DCM:Acetone (1:1 v/v). However,
DCM was used for the PAHs extraction, due to its rapid
evaporation (b.p. 40˚C) in comparison to its mixture with
acetone (56.3˚C). The analytical accuracy (Table 2) of
the protocol was determined by the SRM analysis (n = 19)
following the protocol listed in Table 1. The molecular
weight (quantification ion), retention times and the de-
tection limits (inferred from analyses of n = 12 blanks)
for 16-PAHs are also given in Table 2.
3. Results & Discussion
3.1. Temporal Variations in PM2.5 and
Carbonaceous Species (OC, EC)
The PM2.5 samples, selected for the evaluation of ana-
lytical protocol for PAHs analysis, show temporal vari-
ability in aerosol mass from 48 to 391 μg·m–3. The or-
ganic and elemental carbon (OC, EC) varied from 15 to
188 μg·m–3 and 2.2 to 18.5 μg·m–3 respectively, whereas
Σ PAHs varied from 2 to 46 ng·m–3. The high OC/EC
ratios (range: 4 to 19) indicate the dominant contributions
of carbonaceous species from biomass burning emissions
(agricultural-waste burning and the wood fuel combus-
tion) [2,3,31].
3.2. Sample Preparation for PAHs Analysis
The elution recovery of 16-PAHs on silica-SPE cartridge
is optimized using 16-PAHs standard, prior to the analy-
sis of aerosol samples (Figure 1). The 16-PAHs standard
of varying concentrations; 100 ng (n = 3), 400 ng (n = 3)
and, 800 ng (n = 3) in 3 mL hexane was eluted from the
silica-SPE cartridges. A near quantitative recovery for all
16-PAHs (Figure 1) was achieved with the adopted pro-
tocol (as discussed in section 2.3). The assessment of
extraction parameters (Figure 2) on ASE suggests that
extraction at 100˚C for 30 min (@ 1500 psi) is optimum
for the quantification of PAHs in SRM. Moreover,
analysis of SRM extracts (n = 12) for different conditions
on ASE (tested range: 90˚C - 120˚C; 5 - 15 min static
cycle), suggest that though the mass recovery of PAHs

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and
Isomer Ratios from Biomass Burning Emissions
449
depends on the extraction conditions, their isomers do
not fractionate under these conditions on ASE (Figure 2).
A one-eighth or one-fourth portion of the quartz filter
(based on Total Carbon/ Aerosol Mass) was cut into strips
and loaded on the ASE. The PAHs were extracted fol-
lowing a developed protocol (Table 1) in 30 mL DCM.
Figure 1. Recovery of 16-PAHs after purification on silica cartridge, as ascertained from a standard (QTM PAH Mix;
47930-U, in Methylene Chloride). The consistent recovery of PAHs (~100%) at varying concentrations of standard solution is
noteworthy.
Figure 2. Replicate analysis (n = 12) of three different isomer pairs in SRM ascertain that accelerated solvent extraction (ASE)
does not lead to fractionation of PAHs isomers. The extraction of PAHs at 100 ˚C for 15 min has been used as an optimized
tep for quantitative recovery in aerosol samples. s

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 450
Isomer Ratios from Biomass Burning Emissions
The extracts were concentrated to 1 mL in the evaporator
(<30˚C) and further to near dryness under a gentle stream
of nitrogen gas. The residue was dissolved in 3 mL hex-
ane for purification on a silica-SPE cartridge (for details
refer to experimental section 2.3). The analytical accu-
racy for an individual PAH (except 2-BrNAPH, not re-
ported in SRM certificate) was monitored, based on the
analysis of SRM with every batch of samples. Qual-
ity-control of the data was checked by analyzing the
blank filters routinely.
3.3. PAHs Analyses on GC-MS: Evaluation of
Protocol for High Aerosol Mass Loading
The operating conditions for PAHs analysis on GC-MS
are given in Table 1. The DCM based commercial stan-
dard of 16-PAHs mixture is diluted in hexane to prepare
a 2 ppm stock solution. From this stock solution, seven
working standards between the concentration ranges
from 0 to 1500 ppb are prepared in hexane and analyzed
routinely on GC-MS. The one year record in temporal
variations (insignificant for n = 35 injections of 16-PAHs
standard) of the RRF of 16-PAHs (equation 1) show the
stability of GC-MS (Figure 3). Furthermore, several
analyses of SRM aliquots (~100 mg; n = 19) over a period
of one year, determine the analytical accuracy (Table 2).
A total of (n = 17) ambient aerosol samples, collected
from different geographical locations in India; from Pa-
tiala (n = 8), Hisar (n = 2) and Shillong (n = 7), were
Figure 3. Time dependent analyses (n = 35; over 250 days) of 16-PAHs (QTM PAH Mix; 47930-U, in Methylene Chloride)
studied to ascertain the variability in response factors on GC-MS.

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 451
Isomer Ratios from Biomass Burning Emissions
analyzed for the mass recovery of PAHs. Repeat extrac-
tions and analyses of these samples (n = 17; Figure 4)
reveal that the extraction efficiency for 2- to 3-ring PAHs
is 85 % whereas the recovery is ~100% for 4- to 6-ring
compounds. The overall extraction efficiency of PAHs is
97% ± 2%. The extraction efficiency of PAHs in aerosol
samples (Figure 4) is calculated as
 
PAHs recovery in first extraction
100* PAHs recovery infirst+secondextraction (2)
Analysis of several sample repeats (n = 17) showed that
on an average the external precision of the measurements
is ± 4 %. We reemphasis that these samples are repre-
sentative of tarry matter and soot (along with the mineral
dust), and therefore, the analytical protocol investigate
the extraction efficiency of PAHs in the presence of
varying matrices.
3.4. Investigation of Loss of 2- to 3- ring PAHs
During Sample Processing
The 100 ng of 16-PAHs mixture (QTM PAH Mix;
47930-U, in Methylene Chloride, Supelco) was spiked
on pre-cleaned quartz fibre filters (1.5 sq cm; n = 6). The
extraction of PAHs, followed by matrix purification and
sample preparation is done in the similar way to aerosol
samples. The analyses on GC-MS ensure recovery close
to 100% for the individual PAHs. In contrast to the low
recovery for 2- to3-ring PAHs in aerosol samples, the
high recovery for all 16-PAHs from spiked filters (~100%),
indicate the low concentrations of these PAHs (lighter
mass) in aerosol samples lead to their low recovery.
4. Conclusions
An analytical method developed for the quantitative de-
termination of PAHs from standard reference material
(NIST-1649b), show analytical accuracy of (100% ±
15%). The adopted protocol for the quantification of
PAHs include ASE extraction with DCM at 100˚C for 3
static cycles (of 5 min each) at a constant pressure of
1500 psi, followed by the matrix purification on a
pre-cleaned silica cartridge and subsequent analysis on
GC-MS, operated at 300˚C as the optimum ion-source
temperature. Analysis of field-based aerosol samples
show the average extraction efficiency (equation 2) for
4- to 6- ring PAHs is ~100%. The somewhat lower re-
covery (mean ~85%) for 2- to 3- ring PAHs in the
field-based samples is attributable to their lower concen-
trations in the aerosols. The analytical protocol, for
PAHs analysis is ideal to eliminate the matrix effect from
tarry matter, soot and mineral dust associated with high
atmospheric loading of aerosols.
Figure 4. The extraction efficiency of PAHs, as determined in aerosol samples collected from different geographical regions.
The 4- to 6- ring PAHs are recovered with ~100 % efficiency, whereas 2- to 3- ring PAHs show somewhat lower recovery (~85%)
in the first extraction.

High-Precision GC-MS Analysis of Atmospheric Polycyclic Aromatic Hydrocarbons (Pahs) and 452
Isomer Ratios from Biomass Burning Emissions
5. Acknowledgements
We acknowledge the partial financial support from the
ISRO-Geosphere Biosphere Programme (Bangaluru, In-
dia).
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