Online Supplement
METHOD VALIDATION FOR THE ANALYSIS OF PARTICULATE ORGANIC
COMPOUNDS
After initial optimization of the ATD parameters, desorption recovery efficiencies were determined by
performing two consecutive thermal desorptions of each sample and calibration standard. Recovery
efficiencies in excess of 99.5% were achieved for all analytes when working with the calibration
standards, >99 % for SRM 1649b, >97.5 % for the ammunition particle samples, and >93 % for SRM
1650b. The linearity and limit of quantification (LOQ) of the ATD-GC-MS method were validated by
desorbing and analyzing calibration standards. For the PAHs (15 analytes) and most of the oxy-PAHs
(11 of 15 analytes) the LOQ values (i.e. the analyte quantities that could be detected with a signal to
noise ratio above 10:1) were 5-25 pg per sample and the relative calibration curves showed good
linearity (0.994<r2<1.000, calibration range LOQ-9000 pg). The oxy-PAHs Naphthalene-1,4-dione
and 10H-anthracene-9-one had higher LOQ values (80 pg and 50 pg per sample, respectively).
Chrysene-1,4-dione and 9,10-dihydrobenzo[a]pyrene-7(8H)-one also had higher LOQ values (380 pg
and 93 pg per sample, respectively) and these two species were not positively identified in the gunshot
particles, SRM 1649b or SRM 1650b. The LOQs calculated per GC-injection were about 4 times
higher for ATD-GC-MS than for solvent extraction GC-MS (28). However, when calculated on a per
sample basis, the LOQs for ATD-GC-MS were about 50 times lower than those achieved using
solvent extraction because the whole sample load was used for desorption. The accuracy and precision
of the method were validated by performing replicate analyses of two standard reference materials
(SRM 1649b and SRM 1650b). Figures 4 and 5 show the PAH concentrations determined using ATDGC-MS alongside the certified/reference concentrations. The PAH concentrations measured using
ATD-GC-MS were in good agreement with the reference data for both SRM 1649b and SRM 1650b:
the average deviation of the experimental values from the references was 22% for SRM 1649b and 4%
for SRM 1650b. The NIST certified/reference summed.
8
NIST Cert./Ref. Conc.
ATD-GC-MS
7
6
ng/mg
5
4
3
2
1
0
FIGURE I. PAH concentrations in NIST Standard Reference Material 1649b as determined by ATDGC-MS (~600 µg SRM 1649b, n = 5) compared to the NIST certified/reference concentration values.
Values are shown as average ± expanded uncertainties at the 95 % level of confidence.
80
70
NIST Cert./Ref. Conc.
ATD-GC-MS
60
ng/mg
50
40
30
20
10
0
FIGURE 5. PAH concentrations in NIST Standard Reference Material 1650b as determined by ATDGC-MS (~400 µg SRM 1650b, n=5) compared to the NIST certified/reference concentration values.
Values are shown as averages ± expanded uncertainties at the 95 % level of confidence.
PAH concentrations (mean±SD) for SRM 1649b and SRM 1650b are 42.9±0.21 ng/mg and 248±1.8
ng/mg, respectively, while the corresponding measured values were 44±1.5 ng/mg and 245±7.1
ng/mg. The reference materials were analyzed in quintuplicate in order to evaluate the method’s
reproducibility. The relative standard deviations (RSD) for each analyte over the five runs ranged from
6-33% (average RSD= 14%) for SRM 1649b and 4-26% (average RSD=10%) for SRM 1650b.
Because there were no certified reference values for the oxy-PAH contents of the reference materials
when the experiments were conducted, literature data (15, 29-32) were used for comparative purposes.
On average, the oxy-PAH concentrations determined using our ATD-GC-MS method deviated by
41% from those obtained using a method based on solvent extraction (28) (see Figure 6). In general,
the concentrations of the heavier oxy-PAHs determined using ATD-GC-MS were somewhat lower
than the values obtained by solvent extraction. However, no such trend was apparent relative to the
concentrations obtained using other methods. In fact, the ATD-GC-MS values were in better
agreement with the literature data on the oxy-PAH concentrations in the tested reference materials
than were those obtained by solvent extraction for all species other than B[cd]Pyr-O. For those oxyPAHs for which two or more literature values were available (9Flu-O, Ant-9,10-DO, C[def]Phen-O,
B[a]Flu-O, B[de]Ant-O and B[a]Ant-DO), the ATD-GC-MS data were reasonably consistent with
those reported previously, differing by 25% on average. However, the divergence between the ATDGC-MS concentrations and the literature data were more pronounced in cases where only one
literature value was available, especially for B[cd]Pyr-O. The reproducibility of the oxy-PAH
concentrations measured in the five replicate analysis of SRM 1649b was comparable to that achieved
for PAHs, with relative standard deviations (RSD) ranging from 4-30% (average RSD= 15%).
16,00
ATD-GC-MS
14,00
Solvent extraction-GC-MS
Published concentrations
12,00
ng/mg
10,00
8,00
6,00
4,00
2,00
0,00
FIGURE II. Oxy-PAH concentrations in NIST Standard Reference Material 1649b as determined by
ATD-GC-MS (≈600 µg SRM 1649b, n=5) and solvent extraction/GC-MS as reported by Wingfors et
al. (28) compared to previously published data for (SRM 1649a or SRM 1649b obtained using various
techniques (15, 29- 32). Values for ATD-GC-MS and solvent extraction/GC-MS are shown as
averages ± expanded uncertainties at the 95% level of confidence. Literature data are shown as
averages with error bars indicating the highest and lowest reported values; in cases where only data
from a single study were available, no error bars are shown.
REFERENCES
28. Wingfors H., L. Hägglund and R. Magnusson: Characterization of the size-distribution of
aerosols and particle-bound content of oxygenated PAHs, PAHs, and n-alkanes in urban
environments in Afghanistan. Atm. Env. , 45: 4360-4369 (2011).
29. Layshock, J.: 2010. “Beyond the 16 EPA Priority Pollutants PAHs: Environmental
Characterizations of Oxygenated PAHs and Dibenzopyrene Isomers” PhD diss., Toxicology,
Oregon State University, Oregon, 2010.
30. Albinet A., E. Leoz-Garziandia, H. Budzinski, and E. Villenave: Simultaneous analysis of
oxygenated and nitrated polycyclic aromatic hydrocarbons on standard reference material
1649a (urban dust) and on natural ambient air samples by gas chromatography-mass
spectrometry with negative ion chemical ionisation. J. of Chrom. A 1121:106-113. (2006).
31. Durant J.L., W.F. Busby, A.L. Lafleur, B.W. Penman, and C.L. Crespi: Human cell mutagenicity
of oxygenated, nitrated and unsubstituted polycyclic aromatic hydrocarbons associated with
urban aerosols. Mut. Res.-Gen. Tox. 371 : 123–157 (1996).
32. Fernández P. and J. M. Bayona: Use of off line GPC/Normal Phase LC for the determination
of polycyclic aromatic compounds in substance reference material (air particulate matter and
marine sediment) J. of Chrom. 625: 141-149 (1992).