1
Supplementary information
2
1. Section 1 – Sampling procedure
3
1.1 Preparation of the needle traps
4
First, a stainless wire was pressed by two steel guides and fixed into the desired position as a
5
spring plug. Then, sorbent particles were aspirated into the needle by a tap-water aspirator and
6
held by the spring plug. After packing the desired length of sorbent bed, a small amount of epoxy
7
glue was used to immobilize the sorbent in the opening end. During the packing process, the
8
aspirator was kept running until the epoxy glue was cured so as to avoid the blockage of the NT
9
by the epoxy glue. The sorbent beds packed inside the needles for this work were 1 cm 100/120
10
mesh DVB plus 1 cm 60/80 mesh Car. After packing, the NTs were conditioned in a GC injector
11
for 3 hours with helium gas continuously flowing through the needle. The conditioning
12
temperature was 260 °C. This process was similar to previous works 1–6.
13
14
1.2 Sampling chambers
15
The sampling chamber employed for the MFX evaluation consisted of a custom made 1.5 L glass
16
bulb with several sampling ports that were plugged with Thermogreen® LB-2 predrilled septa.
17
Omega 120 W heating tape was wrapped around the glass bulb to control the temperature inside
18
the bulb. An Omega K-type thermocouple was attached to the outside surface of the glass bulb
19
in order to control its internal temperature. Heating tape and thermocouple were connected to an
20
electronic heat control device constructed by the Electronic Science Shop at the University of
21
Waterloo (UW). Air temperatures in the vicinity of the SPME fibres were maintained within
22
±1.2% of the adjusted temperature. The standard gas generator consisted of a permeation chamber
23
where Teflon tubes filled with the model compounds were placed and maintained at constant
24
temperature and nitrogen flow. Standard gas flow rates ranged from 50 to 3000 mL/min, resulting
25
in mean air velocities similar to those encountered in indoor air environments. Standard gas
26
generators and sampling chambers were validated using a multi-bed needle trap.
27
28
1.3 Indoors time-weighted average sampling
29
A diffusive fibre holder (DFH), as well as bare 85 μm FFA CAR/PDMS fibres were used for
30
passive sampling. A magnetic plunger was built at the machine shop of the University of
31
Waterloo to control the diffusion path of the bare FFA fibre. Rare-earth magnets employed to
32
manufacture this plunger were acquired at Lee Valley (Waterloo, Ontario, Canada). Samplings
33
were performed over a period of 8 hours, between 9 am and 5 pm, during three different days in
34
the same week. For DFH evaluation, as described below, one of the fibres was installed on the
35
diffusive fibre holder while another two were used as controls.
36
37
1.4 Indoors air sampling in active mode
38
A portable dynamic air sampling device (PDAS) for SPME, described in Section 1 of the
39
Supplementary Information (Figure S10), was employed in the quantification of indoor
40
contaminants present in the air of a polymer synthesis laboratory at the University of Waterloo 7.
41
A magnetic plunger was used to expose the fibre coating; measurements exposing a SPME-FFA
42
Car/PDMS fibre for 30 s were performed four times within a day, using independent fibres. The
43
concentration of the target analytes was calculated using the diffusion-based SPME quantitative
44
model defined by Equation S1 in Section 2 of the Supplementary Information. A complete
45
description of the parameters used in these calculations is listed in Table S1.
46
47
1.5 Sampling and desorption of needle traps
48
For indoor air sampling and verification of concentrations in the exposure chamber, the NTD was
49
connected to the sampling pump while a volume of the gaseous sample was pumped at a flow rate
50
of 5 mL min-1. After sampling, the NTD was connected to a 1 mL gas-tight syringe filled with
51
helium, and introduced into a GC injector for desorption. Helium was consistently pushed out to
52
assist desorption throughout the whole desorption period. For NTDs packed with DVB/Car, the
53
needle was injected into the hot GC injector at a temperature of 260 °C for 1 min, assisted by 0.3
54
mL of helium 5,6.
55
56
2. Section 2- SPME diffusion based calibration approach
57
Significant research with SPME has focused on applications for air sampling and analysis. The
58
theory behind equilibrium and non-equilibrium extractions for liquid coatings is well understood
59
and described in the literature. Despite the sensitivity of solid coatings for the extraction of VOCs
60
being higher when compared to PDMS, competitive adsorption and displacement effects make
61
mass calibration and quantification particularly challenging. In order to solve this issue, Koziel et
62
al.
63
critical restrictions: short sampling times and non-equilibrium conditions. Following these rules,
64
the effects of competitive adsorption are diminished, and the coating can be calibrated on the initial
65
linear extraction region. If the concentration of the analyte is assumed to be constant for a very
66
short sampling time, the concentration can be estimated from the following equation:
7,8
proposed an approach that relies on diffusion-controlled extraction. This method has two
67
68
69
70
71
72
73
74
where n is the mass of extracted analyte in nanograms over sampling time t; Dg is the gas-phase
75
molecular diffusion coefficient (cm2/s); b is the outside radius of the fibre coating (cm); L is the
76
length of the coated rod (cm); δ is the thickness of the boundary layer surrounding the fibre coating
77
(cm); t is the sampling time (s), and Cg is the analyte concentration in bulk air (ng/mL). L and b
78
are constant for each type of fibre coating, and n can be estimated from the detector response. The
79
diffusion coefficients of the analytes can be estimated from physicochemical properties using the
80
method proposed by Fuller, Schettler, and Giddings (FSG)9:
𝐶𝑔 =
𝑛 ln((𝑏 + 𝛿)/𝑏)
2𝜋𝐷𝑔 𝐿𝑡
Equation S1
81
0.001 × 𝑇 1.75 1/𝑀𝑎𝑖𝑟 + 1/𝑀𝑉𝑂𝐶
𝐷𝑔 =
𝑝
𝑉𝑎𝑖𝑟 1/3 +
𝑉𝑉𝑂𝐶 1/3 2
82
Equation S2
83
84
Where Dg is expressed in cm2/s, T is the absolute temperature (K), Mair and MVOC are molecular
85
weights for air and the VOC of interest, p is the absolute pressure (atm), and Vair and VVOC are the
86
molar volumes of air and the VOC of interest (cm3/mol). Additionally, based on Koziel and
87
collaborators, the effective thickness of the boundary layer can be estimated using the following
88
equation:
89
90
𝛿 = 9.52 (𝑏/𝑅𝑒 0.62 𝑆𝑐 0.38 )
Equation S3
33
91
Where Re is the Reynolds number, Re = 2ub/v, u is the linear air velocity (cm/s), v is the kinematic
92
viscosity for air (cm2/s), Sc is the Schmidt number, and Sc = v/Dg. Particular attention should be
93
paid to control convection conditions during extraction in order to maintain a constant boundary
94
layer, and hence avoid variations in the extracted amounts of analyte. In addition, by using forced
95
air, the sensitivity of the solid coatings is enhanced. In order to facilitate control of convection
96
conditions, Augusto et al. designed a Portable Dynamic Air Sampler (PDAS) for SPME. Figure
97
S7 presents the schematic of the device built using a hair-dryer. This instrument was modified to
98
revert the air flow direction and to disable the internal heating coil. When compared to standard
99
methodologies, the authors demonstrated that a 30 s sampling time using PDAS-SPME allowed
100
measurement of VOC concentrations that were not detected by the NIOSH standard method, even
101
after several hours of extraction using expensive and non-reusable materials. It should be also
102
emphasized that short sampling times are important so that the effect of relative humidity on the
103
adsorption of VOCs on the solid coatings is minimized. Indeed, to obtain accurate and precise
104
concentrations, the sampling time should be properly measured. One interesting advantage of this
105
method is that external calibration is not needed since sampling conditions and constants are
106
known. Also, since the method depends on the dimensional parameters of the fibres, its dimensions
107
and integrity should be checked prior to sampling.
108
109
110
111
112
113
114
115
116
117
118
119
120
121
Supplementary Figures
122
Lexan™ case
124
123
Glass bulb
Septa
e
125
FFA device
126
d
Heating tape
a
Insulation
c
127
b
Standard gas
Heat control
Upper view
128
Front view
129
130
131
Figure S1 Glass container for live plants BVOC extraction: 1, silanized glass cylindrical body
132
(120 mm x 60 mm); 2, silanized glass lid; 3, sampling holes topped with Thermogreen LB-2 septa;
133
4, thermocouple; 5, SPME-FFA 65μm DVB/PDMS; 6, microfan (40 mm x 40 mm x 6 mm); and
134
7, Teflon tape seal 10.
135
136
137
138
139
140
141
142
35.0
143
144
Amount extracted (ng)
30.0
145
25.0
146
20.0
147
15.0
148
10.0
5.0
149
0.0
150
Benzene
Toluene
FB
FF
FL
o-Xylene
FM
FV
151
152
Figure S2 Amount extracted of BTX in nanograms using passive sampling with 5 different
153
Car/PDMS fibres (n=5). Samples were taken from a standard gas generator using SPME in passive
154
sampling mode (Z=0.2 cm, t = 15 minutes).
155
156
157
158
159
160
161
162
163
164
165
1.0
FL
166
FM
167
0.5
FB
169
170
171
Factor 2: 23.62%
168
0.0
-0.5
172
173
174
FF
FV
-1.0
-2
-1
0
1
2
Factor 1: 76.32%
175
176
Figure S3 Principal component analyses of 5 Car/PDMS SPME-FFA fibres. Samples were taken
177
from a standard gas generator using SPME in passive sampling mode (Z=0.2 cm, t = 15 minutes).
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
Figure S4 Schematic drawing of the Diffusive Sampling Fibre Holder (DFH).
204
Concentration of Toluene (ng/mL)
1.8
205
206
207
208
209
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
210
0.0
Day 3
211
Day 2
AVG-TWA
Day 1
DFH
212
Figure S5 Evaluation of the diffusive fibre holder (DFH) versus conventional FFA-SPME devices
213
using 85μm Car/PDMS (Z=0.147 cm, t = 8 hours). AVG-TWA is the mean toluene concentration
214
value obtained with two fibres without holder. DFH is the value obtained using a single FFA device
215
placed on the DFH.
216
218
219
220
221
222
Percentage of BTX left on the fibre (%)
217
110
100
90
80
70
60
50
Benzene
223
Toluene
0h
Ethylbenzene
12h
224
Figure S6 Evaluation of the storage stability up to 12 hours of the diffusive fibre holder (DFH)
225
using 85 μm Car/PDMS (Z=0.147 cm, t = 8 hours, n=5).
226
227
228
229
230
231
232
233
234
Figure S7 Schematic of the portable dynamic air sampling device for SPME developed by
235
Augusto et al. Image was taken with permission from reference 7.
236
237
238
239
Supplementary tables
240
Table S1 Latin-square design used for the evaluation of 5 different 85 μm CAR/PDMS fibres.
241
Positions on the MFX tray and the sampling chamber were both randomized. F#Xx, where # is the
242
number of the fibre, X is the position on the chamber, and x is the position on the MFX tray. a,
243
position 1; b, position 5; c, position 21; d, position, 25, and e, position 13.
244
245
246
247
248
Replicate
1
2
3
3
5
F1Aa
F2Ab
F3Ac
F4Ad
F5Ae
Fibre Position (F#Xx)
F5Bd
F4Cd
F3De
F1Be
F5Cc
F4Da
F2Ba
F1Cd
F5Db
F3Bd
F2Ce
F1Dc
F4Bc
F3Ca
F2Dd
F2Ec
F3Ed
F4Ee
F5Ea
F1Eb
249
Table S2 Experimental parameters used to determine the concentration of toluene in indoor air in
250
a polymer synthesis laboratory using SPME diffusion-based calibration.
Parameters/Day time (h)
10:30
11:45
15:30
16:35
Units
Concentration
1.62
0.21
0.14
0.10
ng/mL
37
5
3
2
ng
Temperature
295.6
295.6
295.3
295.2
K
Diffusion coefficient (Dg)
0.0793
0.0793
0.0791
0.0791
cm2/s
Boundary layer thickness
0.0135
0.0135
0.0135
0.0135
cm
Reynolds number
28.339
28.339
28.391
28.407
-
Air kinematic viscosity (v)
0.1535
0.1535
0.1532
0.1531
cm2/s
Schmidt number
1.937
1.937
1.937
1.937
-
Amount extracted
Fibre radio (b)
0.0145
cm
Fibre length (L)
1
cm
Sampling time (t)
30
s
Pressure (P)
1
atm
Mass air
28.97
g/mol
Volume air
20.1
cm3/mol
Mr
0.045
mol/g
Mass toluene
92.14
g/mol
Volume toluene
111.14
cm3/mol
150
cm/s
Linear velocity of the air (u)
251
252
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253
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