COMPARATIVE OF THE ADSORPTION PERFORMANCE OF A MULTI-SORBENT
BED (CARBOTRAP, CARBOPACK X, CARBOXEN 569) AND A TENAX TA
ADSORBENT TUBE FOR THE ANALYSIS OF VOCs
LABORATORI DEL CENTRE DE MEDI AMBIENT
E.Gallego1, F. X. Roca1, F. Perales1, X. Guardino2 and M. G. Rosell2
(E.T.S. D’ENGINYERIA INDUSTRIAL BARCELONA)
Laboratori del Centre de Medi Ambient. Universitat Politècnica de Catalunya (LCMA-UPC). Avda. Diagonal, 647. E 08028 Barcelona
Nacional de Condiciones de Trabajo. INSHT. Dulcet 2-10. E 08034 Barcelona.
Ambient air is a very complex mixture of compounds, and has a very
variable composition and concentration of pollutants. Hence, a good
choice of sorbent or a good combination of different sorbents may allow
the determination of a wide range of target compounds in air samples
(Ribes et al., 2007; Barro et al., 2009), as well as achieve high
breakthrough volumes (Demeestere et al. 2007).
The selective characteristics of the sorbent chosen would determine the
removing of the target compounds from the air matrix (Dąbrowski,
2001). On the other hand, a choice of a proper sorbent for the range of
the studied target compounds would eliminate problems derived from
breakthrough values (Dewulf and Van Langenhove, 1999). The capacity
of a sorbent to retain specific compounds is usually evaluated by
measuring the breakthrough volume of a concrete compound on the
sorbent (Baya & Siskos 1996). To maximize sampling efficiency, the
maximum volume of air that can be sampled without loss of adsorbent
must be known (Harper 1993, Dettmer & Engewald 2003).
Tenax TA has been determined to be a not suitable adsorbent for very
volatile organic compounds (VVOCs, 0<boiling point<50-100ºC (WHO,
1989)). However, Tenax TA continues being one of the most widely used
adsorbents for the preconcentration of VOCs (Sunesson, 2007). In
addition to that, generally, a single adsorbent cannot be appropriate for
the majority of compounds present in ambient air. Hence, a combination
of several adsorbents may result in better performances.
Two types of adsorbent tubes, one containing a mixture of three
adsorbents (Carbotrap, Carbopack X, Carboxen 569) (Ribes et al.,
2007; Gallego et al., 2008) and another containing Tenax TA were
compared to evaluate their usefulness as active adsorbents of ambient
air VOCs, including VVOCs.
MATERIALS AND METHODS
Sampling
Duplicate samples of multi-sorbent bed and Tenax TA tubes of 10, 20,
40, 60 and 90 litres were taken in Barcelona city (Spain) on July 2009.
VOCs were dynamically sampled connecting two custom packed glass
multi-sorbent cartridge tubes in series (Carbotrap 20/40, 70 mg;
Carbopack X 40/60, 100 mg and Carboxen 569 20/45, 90 mg) (Ribes et
al., 2007) and two Tenax TA tubes in series (60/80, 200 mg) to an air
collector pump sampler specially designed in the LCMA-UPC laboratory.
The flow sampling rate was 70 ml min-1. The temperature and relative
humidity during the sampling ranged between 28-31ºC and 35-48%,
respectively.
Desorption and analysis
Analysis of VOCs was performed by Automatic Thermal Desorption
(ATD) coupled with capillary Gas Chromatography (GC)/ Mass
Spectrometry Detector (MSD), using a Perkin Elmer ATD 400 (Perkin
Elmer, Boston, Massachusetts, USA) and a Thermo Quest Trace 2000
GC (ThermoQuest, San Jose, California, USA) fitted with a Thermo
Quest Trace Finnigan MSD. VOCs standards were prepared in methanol
and injected at 30˚C on the tubes under an inert Helium gas flow (100 ml
min-1) using a conventional gas chromatograph packed column injector.
The instrumental settings and operating conditions are shown in Table 1.
Table 1. - Instrumental settings and operating conditions.
TD
Desorption temp.:
Desorption time:
Transfer line:
Cold trap sorbent
Cold trap low:
Cold trap high:
Desorption flow rate:
Inlet split:
Outlet split:
Split ratio:
300 ºC
10 min
200 ºC
Tenax TA +
Carbotrap
-30 ºC
300 ºC
He (50 ml/min)
4 ml/min
7 ml/min
12 %
Breakthrough comparative
Breakthrough values for the different
volumes sampled are shown in Table 3.
Typical VOCs recommended breakthrough
value is <5% (U.S. EPA, 1999). For the
concentrations obtained, Tenax TA present
high breakthrough values for mainly all
compounds and sampling volumes studied.
On the other hand, multi-sorbent bed tubes
do not exhibit important breakthrough values
for these compounds, except the VVOCs
ethanol (for all sampled volumes), and
acetone, dichloromethane and isopropanol
(for sampling volumes over 40 litres).
Tenax TA has a surface area of 20-35 m2 g-1,
whereas Carbotrap, Carbopack X and
Carboxen 569 have surface areas of 95-100
m2 g-1, 240-250 m2 g-1 and 387-485 m2 g-1,
respectively. Total surface areas are
approximately of 6 and 70 m2 for Tenax TA
and multi-sorbent bed tubes, respectively.
Therefore, multi-sorbent bed tubes have
approximately 12 times more surface area
than Tenax TA tubes.
Compounds
Ethanol
Acetone †
Isopropanol ‡
Carbon disulphide ‡
Dichloromethane †
n-hexane ‡
Chloroform ‡
Carbon tetrachloride ‡
Acetic acid
Benzene ‡
n-heptane1 †
1-butanol ‡
Trichloroethylene ‡
Methylisobuthylketone
Toluene ‡
Tetrachloroethylene ‡
Butyl acetate
NN-dimethylformamide
Ethylbenzene
m+p-xylene
o-xylene
2-buthoxyethanol
a-pinene ‡
Benzaldehyde
Limonene
p-dichlorobenzene
Phenol ‡
Average ± SD
Multi-sorbent
Tenax TA
29.7 ± 23.9
27.3 ± 19.1
205.3 ± 213.4
13.6 ± 14.7
23.2 ± 16.6
1.0 ± 0.8
0.9 ± 0.4
0.2 ± 0.1
14.3 ± 15.1
0.5 ± 0.5
4.7 ± 0.9
0.4 ± 0.2
33.7 ± 15.3
1.2 ± 1.0
6.4 ± 2.6
0.7 ± 0.4
97.6 ± 21.8
106.6 ± 77.2
6.8 ± 3.1
0.9 ± 0.4
15.0 ± 10.4
4.7 ± 1.2
11.4 ± 3.8
2.9 ± 2.4
1.2 ± 0.5
0.2 ± 0.2
1.1 ± 0.2
0.7 ± 0.4
83.4 ± 22.6
51.6 ± 13.0
1.2 ± 0.4
0.6 ± 0.3
4.2 ± 1.4
4.5 ± 1.3
7.0 ± 4.1
5.4 ± 3.3
31.0 ± 17.4
27.0 ± 13.4
74.2 ± 28.8
67.6 ± 24.9
33.9 ± 16.1
28.3 ± 11.4
9.4 ± 4.6
7.7 ± 1.8
4.8 ± 0.9
0.8 ± 0.5
4.7 ± 1.4
5.7 ± 1.7
16.5 ± 10.3
13.3 ± 6.8
0.09 ± 0.02
0.09 ± 0.01
1.7 ± 0.4
2.7 ± 0.3
Median
Multi-sorbent
Tenax TA
20.7
21.1
73.0
5.9
14.5
0.8
1.0
0.1
6.0
0.4
4.6
0.4
27.3
0.7
6.6
0.7
96.1
75.0
6.9
0.9
13.4
4.8
10.9
2.4
1.3
0.2
1.1
0.7
77.7
49.2
1.0
0.6
4.2
4.5
5.2
4.8
32.9
27.4
70.8
63.0
33.3
26.1
8.3
7.1
4.7
0.6
4.6
5.4
12.7
11.5
0.09
0.09
1.5
2.7
1The
line indicates the limit of 100ºC of boiling point of the compounds. Above the line all
compounds have a boiling point <100ºC. Below the line, all compounds have a boiling point
>100ºC, except trichloroethylene.
‡ Significant differences observed between average concentrations obtained from multi-sorbent
bed and Tenax TA tubes (t-test, p<0.05). Normal data.
† Significant differences observed between average concentrations obtained from multi-sorbent
bed and Tenax TA tubes (U of Mann-Whitney, p<0.05). Not normal data.
Table 3. Average ± standard deviation breakthrough values for each sampling volume (% VOC found in the back tube) for multisorbent bed and Tenax TA tubes. Compounds are listed by elution order.
10 litres
Multi-sorbent
Tenax TA
33.7 ± 2.0
54.1 ± 1.0
0.6 ± 0.3
54.1 ± 2.2
2.1 ± 1.1
53.5 ± 3.0
3.7 ± 0.2
44.0 ± 4.0
6.0 ± 1.6
53.2 ± 1.6
0.4 ± 0.2
56.0 ± 2.5
0.3 ± 0.1
55.6 ± 2.2
0
50.6 ± 3.0
0.8 ± 0.7
22.3 ± 3.6
0.6 ± 0.9
49.0 ± 4.1
0.3 ± 0.4
25.9 ± 3.7
0.7 ± 0.9
45.9 ± 15.2
0
54.9 ± 4.3
0
15.0 ± 3.5
0.5 ± 0.3
19.1 ± 2.4
0
16.3 ± 2.4
0.3 ± 0.4
2.1 ± 0.3
0
7.5 ± 0.6
0.1 ± 0.2
1.9 ± 0.1
0.2 ± 0.2
1.7 ± 0.2
0.1 ± 0.2
2.1 ± 0.1
0
1.7 ± 0.3
0
48.3 ± 3.6
0.6 ± 0.8
3.0 ± 0.4
0
0.6 ± 0.1
0
0
0.6 ± 0.8
8.8 ± 0.3
Compounds
Ethanol
Acetone
Isopropanol
Carbon disulphide
Dichloromethane
n-hexane
Chloroform
Carbon tetrachloride
Acetic acid
Benzene
n-heptane1
1-butanol
Trichloroethylene
Methylisobuthylketone
Toluene
Tetrachloroethylene
Butyl acetate
NN-dimethylformamide
Ethylbenzene
m+p-xylene
o-xylene
2-buthoxyethanol
a-pinene
Benzaldehyde
Limonene
p-dichlorobenzene
Phenol
20 litres
Multi-sorbent
Tenax TA
18.8 ± 0.5
54.1 ± 4.1
1.3 ± 1.0
55.0 ± 3.8
4.3 ± 2.2
55.8 ± 2.8
3.6 ± 1.3
40.2 ± 15.4
7.3 ± 3.0
54.3 ± 3.3
0.5 ± 0.01
59.3 ± 1.9
0.3 ± 0.1
56.6 ± 4.6
0
55.1 ± 5.1
1.0 ± 0.7
29.6 ± 15.7
0.9 ± 0.1
60.1 ± 2.3
0.1 ± 0.1
45.2± 7.8
0.8 ± 0.1
51.7 ± 14.1
0
58.2 ± 4.5
0
21.5 ± 4.4
0.2 ± 0.2
41.6 ± 11.4
0
34.3 ± 12.3
0.4 ± 0.04
3.5 ± 2.3
0
21.9 ± 4.6
0.2 ± 0.2
4.5 ± 2.1
0.2 ± 0.1
4.8 ± 3.0
0.1 ± 0.1
4.3 ± 1.9
0
3.5 ± 0.2
0
56.7 ± 5.3
0.6 ± 0.2
3.4 ± 0.1
0.1 ± 0.1
1.3 ± 0.8
0
0
1.6 ± 0.5
5.3 ± 0.5
40 litres
Multi-sorbent
Tenax TA
27.2 ± 8.6
54.6 ± 2.3
6.4 ± 3.0
53.7 ± 3.2
9.7 ± 1.0
56.3 ± 3.6
5.5 ± 3.8
41.8 ± 0.3
22.1 ± 15.1
53.1 ± 0.8
0.8 ± 0.2
59.1± 4.5
1.2 ± 1.3
52.8 ± 2.2
0.1 ± 0.1
62.3 ± 3.1
0.7 ± 0.3
44.2 ± 1.5
0.8 ± 0.1
55.7 ± 4.7
0.1 ± 0.1
52.1 ± 1.8
0.6 ± 0.3
43.8 ± 29.8
0
56.8 ± 3.1
0.4 ± 0.2
34.8 ± 0.6
0.2 ± 0.1
50.1 ± 0.3
0.3 ± 0.1
43.9 ± 0.7
0
6.0 ± 0.9
0
30.7 ± 3.6
0.1 ± 0.01
8.6 ± 3.6
0.1 ± 0.01
7.4 ± 3.4
0.1 ± 0.03
6.6 ± 2.2
0.5 ± 0.1
8.6 ± 0.2
0.1 ± 0.1
54.7 ± 2.1
1.1 ± 0.3
3.5 ± 0.3
0.1 ± 0.1
2.2 ± 1.2
0
0.7 ± 1.0
1.4 ± 0.2
4.8 ± 0.5
60 litres
Multi-sorbent
Tenax TA
52.8 ± 2.0
51.0 ± 1.9
15.9 ± 8.6
41.9 ± 3.0
30.9 ± 2.2
48.5 ± 1.1
3.5 ± 2.9
50.5 ± 15.9
30.5 ± 3.4
50.4 ± 7.1
0.2 ± 0.1
55.8 ± 9.9
0.3 ± 0.01
50.6 ± 1.0
0
51.9 ± 10.2
0.5 ± 0.3
42.4 ± 6.3
1.4 ± 1.7
57.4 ± 0.6
0.04 ± 0.05
47.3 ± 1.7
0.2 ± 0.003
41.6 ± 22.3
0
41.5 ± 0.9
0
45.7 ± 2.5
0.1 ± 0.1
42.3 ± 5.2
0
53.1 ± 1.3
0
18.5 ± 1.2
0
49.3 ± 3.3
0.02 ± 0.01
16.5 ± 1.1
0.03 ± 0.02
21.8 ± 2.6
0.02 ± 0.01
14.6 ± 0.2
0.2 ± 0.1
30.8 ± 1.4
0
47.5 ± 4.0
0.9 ± 0.3
7.3 ± 1.4
0
6.2 ± 0.2
0
1.4 ± 0.9
2.6 ± 0.4
8.3 ± 1.5
90 litres
Multi-sorbent
Tenax TA
55.5 ± 1.2
46.2 ± 0.6
25.5 ± 3.1
42.1 ± 2.1
62.6 ± 17.3
56.3 ± 2.4
10.3 ± 7.8
55.8 ± 23.0
61.4 ± 0.7
58.2 ± 2.8
0.1 ± 0.004
60.4 ± 3.1
13.3± 10.7
57.7 ± 3.6
0.1 ± 0.2
57.1 ± 3.3
1.6 ± 0.1
47.2 ± 14.3
0.1 ± 0.1
62.9 ± 2.7
0.1 ± 0.003
77.4 ± 5.9
0.5 ± 0.2
43.6 ± 24.0
0
58.4 ± 3.1
0
64.2 ± 0.9
0.1 ± 0.1
61.4 ± 4.7
0
61.5 ± 3.9
0.1 ± 0.03
39.8 ± 1.9
0.6 ± 0.8
63.5 ± 2.2
0.04 ± 0.03
36.6 ± 2.4
0.1 ± 0.1
41.6 ± 1.5
0.1 ± 0.1
37.7 ± 2.3
0.2 ± 0.1
24.0 ± 1.5
0.01 ± 0.02
60.3 ± 1.5
0.8 ± 0.1
8.6 ± 3.2
0.02 ± 0.01
12.3 ± 4.3
0.9 ± 0.05
2.2 ± 1.8
1.8 ±0.5
13.6 ± 4.9
Figure 1. Comparison of different compounds concentrations (µg m-3) using multi-sorbent bed tubes (Carbotrap, Carbopack X
and Carboxen 569) and Tenax TA tubes.
600
50
2,0
1,8
500
40
2
R = 0,9874
400
300
200
1,6
R2 = 0,9389
R2 = 0,5459
1,4
30
20
1,2
1,0
0,8
0,6
10
100
DB-624
(60 m x 0.25 mm x 1.4 µm)
Temperature program: 40 ºC (1 min),
6 ºC/min until 230 ºC (5min)
Carrier gas:
He (19.1 psi)
Trichloroethylene
Isopropanol
Acetone
GC
Capillary column:
MS
Interface:
Ionization source:
Ionization mode:
Electron energy:
Mass range
Table 2. Average ± standard deviation and median values for indoor
air concentrations (µg m-3) for multi-sorbent bed and Tenax TA tubes.
Compounds are listed by elution order.
Tenax TA
INTRODUCTION
Tenax TA
2 Centro
Tenax TA
1
0,4
0,2
0
0
0
100
200
300
400
500
0,0
0
600
10
30
40
50
0,0
0,5
Multi-sorbent
Multi-sorbent
250 ºC
200 ºC
Electron impact
70 eV
20 - 300 amu
20
7
1,5
2,0
Multi-sorbent
Ethylbenzene
Butyl acetate
1,0
m+p-Xylene
60
120
6
Differences between multi-sorbent bed and Tenax TA tubes
concentrations are shown in Table 2. Average ± SD and median values
are exposed for all samples. Significant differences between
concentrations are observed for the very volatile compounds and for
alcohols and chlorinated compounds (e.g. acetone, isopropanol, carbon
disulphide, dichloromethane, chloroform, carbon tetrachloride).
On the other hand, mainly all compounds with boiling points higher than
100ºC (except α-pinene, chlorinated and polar compounds) do not show
significant differences between the obtained multi-sorbent bed and Tenax
TA tubes concentrations (Table 2, Figure 1). The boiling point of 100ºC is
often advised as a guidance value below which the adsorption of the
compound is not satisfying for Tenax TA (Sunesson, 2007).
2
4
3
2
40
30
80
60
40
20
20
10
1
2
R = 0,9539
100
R = 0,984
Tenax TA
Tenax TA
Multi-sorbent bed (Carbotrap, Carbopack X, Carboxen 569)Tenax TA concentrations comparative
50
5
Tenax TA
RESULTS AND DISCUSSION
R2 = 0,8936
0
0
0
0
1
2
3
4
Multi-sorbent
5
6
7
0
0
10
20
30
40
Multi-sorbent
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Chromatography A 1153, 130-144.
• Dettmer, K.; Engewald, W. Chromatographia Suppl. 2003, 57, S339-S347.
• Dewulf, J., Van Langenhove, H., 1999. Journal of Chromatography A 843, 163177.
50
20
40
60
80
100
120
60
Multi-sorbent
•Gallego, E., Roca, F.J., Perales, J.F., Guardino, X., 2008. In: Romano, G.C., Conti
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Chemistry 48, Elsevier, 57-83.
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U.S. EPA.
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