DOI 10.5162/IMCS2012/P2.3.7
Innovative Colorimetric Sensors for the Detection of
Nitrogen Trichloride at ppb Level
1,2
1
1
3
3
1
T.-H. Nguyen , J. Garcia , T.-D. Nguyen , A.-M. Laurent , C. Beaubestre , T.-H. Tran-Thi
1
CEA-Saclay, DSM/IRAMIS/SPAM/Laboratoire Francis Perrin, URA CEA-CNRS 2453,
91191 Gif-sur-Yvette Cedex, France,
[email protected]
2
ETHERA R&D, CEA-Saclay, Bât. 451, F-91191 Gif-sur-Yvette Cedex, France
3
Laboratoire d’Hygiène de la Ville de Paris, 11 rue Georges Eastman, 75013 Paris, France
Abstract
The control of air quality is a great importance, in particular for the protection of individuals and
workers who can be exposed to harmful gas. We here describe innovative chemical and colorimetric
sensors for the detection of nitrogen trichloride, a pollutant generated in indoor swimming pools.
These sensors are based on the use of nanoporous matrices doped with probe-molecules, which act
as sponges to trap the targeted pollutant and turn from transparent to blue-violet. These chemical
sensors can be used for the detection of low levels of nitrogen trichloride, NCl 3, concentrations in the
ppb range.
Key words: Chloramine, colorimetric sensors, nitrogen trichloride, nanoporous matrices.
Introduction
In swimming pools, chlorine (Cl2) is used as a
disinfectant to minimize the risk to users from
microbial contaminants. In water, Cl2 is
transformed into hypochlorous acid (HOCl)
which reacts with nitrogen compounds like
saliva, sweat, urine and skin, leading to the
formation of several chloramines, such as
monochloramine, dichloramine and nitrogen
trichloride
(NCl3)[1]. Because of its low
solubility in water, the produced NCl3 is
essentially found in the air. This toxic gas
provokes significant eye and respiratory
irritations in swimmers and pool attendants, [2]
and epidemiologic studies have recently shown
that it can induce asthma, especially in children
[3]. The detection and analysis of NCl3 at ppb
level has become a great importance. However,
there is currently no direct and selective method
of measurement of NCl3 in the atmosphere.
The development of innovative chemical
sensors for the direct detection of nitrogen
trichloride, is described. They are based on
nanoporous materials with high adsorptive
properties and whose pores are tailored to
become
efficient
nanoreactors.
These
nanoreactors, are designed to enhance a
specific reaction between a probe molecule and
NCl3, thus providing rapidity and high
sensitivity. These sensors can detect NCl3 at
ppb level (10 ppb – 200 ppb) within 20 minutes
in humid atmospheres (RH: 50-70%) at ambient
pool temperatures. Due to the fast change of
colour, from transparent to violet-blue visible
with the naked eye, these sensors can be used
to monitor the air quality of indoor pools in
public or private areas and in food processing
plants.
Experimental
The preparation of the sensor and its use for
the detection of nitrogen chloride are described
in this part.
Chemical sensors preparation
The chemical sensors doped with probemolecules were prepared via the Sol-Gel
process. The probe-molecules, NaI and
Amylose aqueous solutions are directly
introduced in the Sol containing the
alkoxysilane precursor (Si(OCH3)4), as shown in
Figure 1. After gelation and the drying process,
monolithic blocks with 8x5x2 mm dimensions
were obtained.
IMCS 2012 – The 14th International Meeting on Chemical Sensors
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DOI 10.5162/IMCS2012/P2.3.7
Fig. 1. Preparation of chemical sensors using the
sol-gel process.
Characterization of chemical sensors
The specific surface area and the pore size
distribution of the nanoporous materials were
determined via nitrogen sorption experiments
on an Autosorb 1-LP-MP instrument. The
specific surface area of this material is 700±60
2 -1
m .g and the total pore volume is 0.440.01
3 -1
cm .g . The pore size distribution is centered at
35 A° (see Fig. 2).
Pore volume / cm3.g-1
0.3E-02
0.2E-02
0.2E-02
0.1E-02
5.0E-04
Fig. 3. NCl3 generation set-up.
To obtain gas mixtures with various humidity
(RH=50-70%), the NCl3 mixture is again diluted
with humid N2 gas.
The concentrations of NCl3 in the calibrated
mixtures were checked, on-line, by bubbling the
gas in a solution of KI, followed with the
quantitative determination of triiodide ions. The
absorbance of I3 at 353 nm is proportional to
the NCl3 concentration.
Principle of NCl3 detection
For the colorimetric detection of NCl3, amylose
and sodium iodide were used as probemolecule. NCl3 reacts with iodide ions
entrapped in amylose to give the triiodide ions.
A blue-violet complex I3 /Amylose is formed,
whose visible absorption band peaks around
540 nm (see Fig. 4).
0.0E+00
Pore size / A°
Fig. 2.
Pore size distribution in volume.
Generation of calibrated gas mixtures
As NCl3 is not commercially available, we
generate the pollutant using the system
described by Gérardin’s group [4]. The reaction
that takes place in swimming pool is
reproduced. In a reactor, a nitrogen precursor
((NH4)2SO4) reacts with a chlorine precursor
(NaOCl) to give chloramines (mono-, di- and
trichloramine). The solution containing the
chloramines is flowed through a stripping
column. The gaseous chloramines are
extracted from the aqueous phase by passing a
flow of nitrogen through the stripping column.
(see Fig. 3). Mono- and dichloramine are
eliminated by bubling the gas mixture in a
sulfamic acid solution. The gas mixture (N2 and
NCl3) is then dried by passing through a sulfuric
acid solution before being diluted to ppb
concentrations in the dilution line equipped with
various mass flow meters.
Fig. 4. Evolution of the absorbance spectrum of
monolith doped with Amylose/I and exposed to
49.75 ppb NCl3. Flow = 200ml.min-1.
By exposing the sensor at different
concentrations of NCl3 and by plotting the rate
of the complex formation (Δabs/Δt) as a
function of the pollutant concentration, we
produce the NCl3 calibration curve (see Fig. 5).
The NCl3 sensor is sensitive and NCl3 can be
measured over a wide domain of concentration
(10 ppb – 200 ppb).
IMCS 2012 – The 14th International Meeting on Chemical Sensors
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DOI 10.5162/IMCS2012/P2.3.7
ΔAbs/Δt (540 nm) / 10-4.min-1
35
30
25
20
y = 0,1727x
R² = 0,9944
15
10
5
0
0
50
100
[NCl3] / ppb
150
200
Fig. 5. Calibration curve for NCl3 detection, Flux =
-1
200 ml.min , %RH=60%.
Conclusion
The colorimetric sensor is able to detect the
NCl3 in the ppb range over a wide domain of
concentration (10-200 ppb). The reaction is
extremely fast and gives rise to a complex,
easily detectable in the visible domain. Lowcost sensors can be produced by combining the
colorimetric solid sensor with a low-cost
photometric reader equipped with a light
electroluminescent diode.
References
[1] C. Colin, M. Brunetto, R. Rosset, Analusis 15,
265-274 (1987); doi:10.1051/water/19881902179
[2] M. Héry, G. Hecht, J. M. Gerber, J. C. Gendre, G.
Hubert, J. Rebuffaud, Annals of Occupational
Hygiene,
39,
427-439
(1995);
doi:
10.1093/annhyg/39.4.427
[3] A. Bernard, S. Carbonnelle, X. Dumont, M.
Nickmilder, Pediatrics 119, 1095-1103 (2007);
doi: 10.1542/peds.2006-3333
[4] F. Gérardin and I. Subra, INRS, Cahiers de Notes
Documentaires, 194, 39-49 (2004)
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