Supporting Information Available
See supplemental
Supplemental discussion on detection of N-heterocyclic compounds
Generation of formulas was performed with our samples using Agilent Technologies MassHunter
qualitative software, which uses discrete mathematics and chemical theory (e.g. valence rules) to produce likely
molecular formulas of unknown spectral peaks [Darland et al., 2008; Meija, 2006; Sweeney, 2003]. While
simultaneous evaluation of our field blanks determined several software and/or sampling media artifacts, the
presence of several N-heterocyclic compounds appeared likely (S/N > 10 relative to field blanks). Following manual
extraction of the m/z equivalent to the [M + H]+ ion of several of the N-heterocycles (N-het) and the corresponding
isotopes (due to the natural occurrence of
13
C and
15
N) , injection of an authentic standard was performed to
determine retention times and relative isotope responses. Using [M + H] + as the quantitation ion, a 5-level
calibration was performed using an internal standard (phenylalanine-d8) method, producing a linear response (R2
> 0.99) and good reproducibility (Table 1).
The current study calculated the concentrations of N-het with a multi-level calibration using authentic
standards and an aromatic amino acid internal standard (phenylalanine-d8) that was spiked onto filters prior to
extraction. The concentrations for the three archived samples (stored at – 50 oC until reinjection) discussed in the
article were determined using a same-day 5-level calibration response factor with post-sample calibration checks
to confirm instrument response. This response factor was further applied to estimated N-het concentrations for all
samples (N = 30) from the initial sample analysis and evaluate relative correlations with FAA concentrations. The
estimated concentrations were only used for correlative analysis with FAA and are not reported as mass
concentration values due to quality control considerations.
Only two hydroxy-pyridine isomers (2-HP, 3-HP) were evaluated with authentic standard in this study,
therefore the concentration estimate for 3-HP did not rule out the potential contribution from 4-HP. The method
development presented here suggests that future work can account for N-het compounds with usage of an
alternate (N-het) internal standard (e.g. quinoline-d7), potentially improving method accuracy and precision. For
example, on-going work in our laboratory has indicated similar or improved instrumental sensitivity when using
quinoline-d7 as the internal standard. A more in-depth evaluation of this topic is currently underway and will be
described in a forthcoming publication. Additional MS/MS transitions were confirmed for norharmane (169.0760
m/z) and harmane (183.0917 m/z) in both ambient samples and authentic standards and include the following
daughter fragments: 89.0391 m/z, 116.0500 m/z, 141.0570 m/z, and 142.0650 m/z. A partial list of likely fragment
structures can be found at the METLIN tandem MS database (http://metlin.scripps.edu). 3-HP displayed both the
[M + H – H2O]+ (78.0344 m/z) and [M + H – CO]+ (68.0508 m/z) daughter fragments in ambient samples and
authentic standards, while 2-HP was not detected in ambient samples and displayed the [M + H – H2O]+ (78.0344
m/z) fragment more dominantly at 20V collision energy with an authentic standard. The second most abundant
fragment was observed at 51.0242 m/z for 2-HP, which is in agreement with tandem MS spectra found at the
MassBank spectral repository (www.massbank.jp).
Supplementary information on MARGA QA, raw data adjustments, processing of IN concentrations and average
MARGA compound concentrations during the sampling period
Mass flow controlled MARGA air flow rates were verified weekly by measuring the flow rate at the
atmospheric inlet using a NIST traceable primary standard (DryCal DC-LITE flowmeter, Bios International
Corporation, Butler, NJ). MARGA inlets and air sampling tubing were cleaned with DDI water and dried with zero
grade air weekly. Following the completion of the experiment, a liquid blank was analyzed by sampling the
absorption solution with the air pumps disconnected and denuder inlets sealed. Additionally, an external standard
test was performed by replacing the absorption solution with a known liquid standard containing NH4+, NO3-, and
SO42- with the air pumps disconnected and denuder inlets sealed, to verify analytical accuracy as controlled by the
LiBr internal standard. Prior to calculation of final air concentrations, raw data were adjusted based on differences
between the measured and MARGA recorded air flow rates, liquid blanks and biases in calibration standard checks.
The average measured flow rates were 16.48 l min-1 and 15.98 l min-1 for MARGA unit (MU) 1 and MU 2,
respectively. The MARGA calculates concentrations based on a flow rate of 16.7 l min-1, therefore the raw data
concentrations were adjusted by 1.4% (MU1) and 4.5% (MU2), respectively. Liquid blanks for all the compounds
(SO42-, NO3-, and NH4+) ranged from 0-0.15 µg m-3 for both MU1 and MU2. External standard accuracy % for SO 42and NO3- was very good ranging from 104.5%-111.2% for MU1 and 103.5%-110.7% for MU2. However, the external
standard accuracy % was not as good for NH4+, with values ranging from 77.3% -85.5 % for MU1 and 75.6%-78.9%
for MU2. The poorer performance of the MUs in measuring NH 4+ is likely due to consumption of NH4+ by bacteria
in the MUs. Consequently, NH3 and NH4+ were adjusted for the external standard results as an offset. To determine
the extent to which NH3 and NH4+ concentrations were affected by bacterial consumption, concentration trends
between the denuder/filter pack and the MARGA were examined. In addition for NH 4+, NH4+/ SO42- ratios were also
examined.
One-hour concentrations for each MU were averaged to correspond with ON sampling periods. Hourly
detection limit values were 0.04 µg m-3 for SO2, 0.1 µg m-3 for HNO3, 0.05 µg m-3 for NH3, 0.06 µg m-3 for SO42-, 0.1
µg m-3 for NO3-, and 0.05 µg m-3 for NH4+. Precision between the two duplicate MARGA units was assessed by
calculating the absolute relative percent difference between each corresponding sampling period, and then taking
the median value. The precision was < 10% for SO2, SO42- and NH4+, and <25% for NH3, HNO3, and NO3-.
The average concentrations of compounds measured during the ON sampling period by the MARGA were
539 ng-N m-3 for NH3, 185 ng-N m-3 for HNO3, 706 ng-N m-3 for NH4 and 108 ng-N m-3 for NO3-. SO42- average
concentrations during the ON sampling period was 2568 ng m-3.
Figure S1. FAA percent distribution for subset of samples (N=17) processed for CAA.
Figure S2. HNO3 + NO3 least squares correlation with percent serine (ser) + glutamine (glut) + threonine
(threo).
Figure S3. Winter sample results.
Figure S4. N-het extracted ion chromatograms (EIC) of PM2.5 collected at RTP.
Supplemental Table S1. List of target AA with compound formula, molecular weight (MW),
quantitation ion, and internal standards. Method details available in Samy et al (2011).
Name
Formula
MW
(g mol-1)
Quantitation
Ion [M + H]+
Internal
Standard
Glycine
C2H5NO2
75.03
76.0401
Alanine
C3H7NO2
89.05
90.0554
Serine
C3H7NO3
105.04
106.0502
Glycine-2,2-D2
Alanine2,3,3,3-D4
Serine-D3
Proline
C5H9NO2
115.06
116.0708
Valine
C5H11NO2
117.08
118.0864
C4H9NO3
119.06
C3H7NO2S
Threonine
Cysteine
1
Hydroxyproline
Isoleucine
Leucine
Asparagine
Ornithine
1
1
1
MW
(g mol-1)
77.08
Quantitation
Ion [M + H]+
78.0526
93.12
94.0803
108.11
109.0689
Histidine-U-13C6
161.15
162.0958
125.2
126.1362
120.0655
Valine-D8
Serine-D3
108.11
109.0689
121.02
122.0271
Cysteine-D2
123.17
124.0394
C5H9NO3
131.05
132.0654
Glycine-2,2-D2
77.08
78.0526
C6H13NO2
131.09
132.1020
Leucine-D3
134.19
135.1204
C6H13NO2
131.09
132.1021
134.19
135.1204
C4H8N2O3
132.05
133.0605
Leucine-D3
Serine-D3
108.11
109.0689
138.2
139.1342
136.12
137.0630
108.11
109.0689
C5H12N2O2
132.09
133.0970
Aspartic Acid
C4H7NO4
133.04
134.0446
Glutamine1
C5H10N2O3
146.07
147.0758
Ornithine-D6
Aspartic Acid2,3,3-D3
Serine-D3
Lysine
C6H14N2O2
146.10
147.1128
Arginine-D7
Glutamic Acid
C5H9NO4
147.05
148.0598
Glutamic Acid2,3,3,4,4-D5
152.16
153.0909
Methionine
C5H11NO2S
149.05
150.0578
Methionine-D3
152.23
153.0763
Histidine
C6H9N3O2
155.07
156.0761
161.15
162.0958
Phenylalanine
C9H11NO2
165.08
166.0853
Histidine-U-13C6
PhenylalanineD8
173.24
174.1352
Arginine
C6H14N4O2
174.11
175.1184
181.25
182.1621
Tyrosine
C9H11NO3
181.07
182.0799
173.24
174.1352
Tryptophan1
C11H12N2O2
204.09
205.0957
Arginine-D7
PhenylalanineD8
PhenylalanineD8
173.24
174.1352
Cystine
C6H12N2O4S2
240.02
241.0291
Cysteine-D2
123.17
124.0394
1
added to NIST mixture.
182.1621
Supplemental Table S2
Speciated compound results for RTP, North Carolina.
Amino Acid
Glycine
Alanine
Aspartic Acid
Arginine
Glutamic Acid
Serine
Glutamine
Threonine
Valine
Proline
Tyrosine
Asparagine
Hydroxyproline
Methionine
Histidine
Phenylalanine
Leucine
Isoleucine
Lysine
Ornithine
Total
PM2.5 FAA
(ng m-3)
3.9±2.6
1.4±0.9
1.4±0.8
1.3±0.9
0.7±0.7
0.7±0.5
0.4±0.7
0.4±0.2
0.2±0.1
0.2±0.1
0.1±0.1
0.1±0.1
0.1±0.1
Trace
Trace
Trace
ND
ND
ND
ND
11±6
Minimum
(ng m-3)
Maximum
(ng m-3)
0
0.3
0.2
0.4
0.2
0.1
0
0.1
0
0
0
0
0
0
0
0
0
ND
ND
ND
2
12.1
4.3
3.8
3.1
3.9
1.8
3.6
1.1
0.4
0.5
0.3
0.5
0.2
0.4
0.3
0.2
0.1
ND
ND
ND
31
%FAA
35.66
12.46
12.37
11.71
6.73
6.50
4.08
3.40
1.43
1.41
1.02
1.01
0.52
0.32
0.52
0.35
0.15
0.00
0.13
0.00
100
PM2.5 CAA
(ng m-3)
8.2±5.3
18.2±9.1
2.1±1.4
Trace
7.7±5.5
0.9±0.8
-3.1±2.3
0.6±0.3
0.9±0.6
1.9±1.9
-Trace
0.7±0.8
0.1±0.1
0.4±0.2
0.6±0.3
0.3±0.2
Trace
Trace
46±21
Minimum
(ng m-3)
0
5.1
0
0
2.9
0
-0.3
0.2
0
0
-0
0
0
0.1
0.3
0.1
0
0
14
Maximum
(ng m-3)
18.0
37.2
5.6
0.3
26.7
3.3
-8.3
1.5
1.9
5.7
-0.7
3.2
0.4
0.8
1.7
0.8
0.5
0.4
92
%CAA
17.74
39.65
4.54
0.04
16.70
2.04
-6.74
1.21
1.92
4.21
-0.09
1.48
0.28
0.93
1.37
0.70
0.31
0.04
100