Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream
Anal Bioanal Chem
Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream
Harald Moser 0
Walter Pölz 0
Johannes Paul Waclawek 0
Johannes Ofner 0
Bernhard Lendl 0
0 OMV R&M GmbH , 2320 Schwechat , Austria
1 Bernhard Lendl
The implementation of a sensitive and selective as well as industrial fit gas sensor prototype based on wavelength modulation spectroscopy with second harmonic detection (2fWMS) employing an 8-μm continuous-wave distributed feedback quantum cascade laser (CW-DFB-QCL) for monitoring hydrogen sulfide (H2S) at sub-ppm levels is reported. Regarding the applicability for analytical and industrial process purposes aimed at petrochemical environments, a synthetic methane (CH4) matrix of up to 1000 ppmv together with a varying H2S content was chosen as the model environment for the laboratory-based performance evaluation performed at TU Wien. A noise-equivalent absorption sensitivity (NEAS) for H2S targeting the absorption line at 1247.2 cm−1 was found to be 8.419 × 10−10 cm−1 Hz−1/2, and a limit of detection (LOD) of 150 ppbv H2S could be achieved. The sensor prototype was then deployed for on-site measurements at the petrochemical research hydrogenation platform of the industrial partner OMV AG. In order to meet the company's on-site safety regulations, the H2S sensor platform was installed in an industry rack and equipped with the required safety infrastructure for protected operation in hazardous and explosive environments. The work reports the suitability of the sensor prototype for simultaneous monitoring of H2S and CH4 content in the process streams of a research hydrodesulfurization (HDS)
Infrared laser spectroscopy; Quantum cascade lasers; Laser sensor; Hydrogen sulfide; Methane; HDS monitoring
Published in the topical collection Process Analytics in Science and
Industry with guest editor Rudolf W. Kessler.
1 Institute of Chemical Technologies and Analytics, Vienna University
of Technology, 1060 Vienna, Austria
unit. Concentration readings were obtained every 15 s and
revealed process dynamics not observed previously.
Sensitive and selective detection of hydrogen sulfide (H2S) is
essential for production control and environmental monitoring
purposes in the field of petrochemical, paper and pulp, or
biotechnological processes. Despite a variety of online
monitoring options for gaseous hydrogen sulfide, its reliable
quantitative and selective determination still remains challenging in
the field of chemical sensors [
Hydrodesulfurization (HDS) is one of the most important
process operations in the modern petroleum refining industry
and is receiving increased attention due to the stringent
environmental regulations on the sulfur content in transport fuels
(gasoline, diesel, and jet fuel). HDS is a catalytic process by
which sulfur-containing impurities are removed from crude
petroleum feedstocks and fuels during hydrogen exposition
in the presence of cobalt-promoted molybdenum (CoMo) or
nickel-promoted molybdenum (NiMo) catalysts and
formation of H2S [
]. The HDS process is of both industrial and
environmental importance: Firstly, the sulfur-containing
impurities in hydrocarbon fuels are effective catalyst poisons,
preventing untreated crude feedstocks from being used for
subsequent chemical transformations, and secondly, the
severe environmental impact is stemming from the emitted
sulfur oxides during combustion and their contribution to acid
Since its first operational demonstration in 1994 [
quantum cascade laser (QCL) advanced to a powerful and
reliable spectroscopic source of coherent light covering the
mid-infrared (MIR) and terahertz spectral region for sensitive
detection of molecular species on their fundamental
vibrational bands and rendered laser-based absorption spectroscopy a
powerful tool for industrial gas sensing [
highquality implications encompassing stringent single-mode
emission and superior wavelength stability as required for
industrial trace gas sensing are met by distributed feedback
(DFB)-type QCLs . Commercial DFB-type QCLs are
configured as edge-emitting ridge lasers and conventionally
housed in standardized, thermo-electrically (TE) stabilized
semiconductor packages. These lasers can be tuned by either
modulation of the injection current and/or changing the
temperature of the gain medium. The resulting tuning range is
limited to a few wavenumbers only, and thus, typically one
or two analytes can be spectroscopically targeted by a given
Different approaches for QCL-based quantitative gas phase
spectroscopy have been demonstrated, and the technical
details were recently reviewed [
]. The included
cavityenhanced absorption spectroscopy [
photoacoustic spectroscopy [
], and open-path setups
] were all successfully applied to industrial and
environmental monitoring. The Bgolden standard^ for QCL-based
trace gas measurements in the MIR spectral region is
established on absorbance measurements in
multipassreflection cells . While special cell types were successfully
], the basic cell type for laser spectroscopy is the
socalled Herriott cell [
], as the effective optical interaction
pathlength can easily reach up to several tens of meters.
Together with phase-sensitive detection techniques, such as
wavelength modulation spectroscopy (WMS) [
generally dominating 1/f electronic noise can be drastically
minimized and generally high detection sensitivities can be
Recently, an FTIR-based sensing approach of H2S, by
using a UV-assisted conversion of H2S into the much more
pronounced responding SO2, is presented in [
H2S monitoring in N2 with a pulsed source of 1253.5 cm−1 is
demonstrated in .
In the present work, a sensitive, selective, and industrial fit
gas sensor setup based on second harmonic wavelength
modulation spectroscopy (2f-WMS) employing an 8-μm
continuous-wave distributed feedback quantum cascade laser
(CWDFB-QCL) was developed and implemented for detecting
H2S at sub-ppm levels in petrochemical process gas streams.
Due to the possibility of molecular discrimination between
H2S and methane (CH4) ro-vibrational transitions, a
simultaneous detection of these two analytes could be implemented.
On-site tests of the sensor were performed at the research
hydrogenation platform of OMV AG.
Materials and methods
Process analytical importance of H2S in the HDS process
In an industrial petrochemical unit, the HDS reaction takes
place in a fixed-bed reactor at temperatures ranging from
300 to 450 °C and pressures ranging from 30 to 130 bar in
the presence of a catalyst typically consisting of an alumina
base impregnated with cobalt or nickel and molybdenum
3 CoMo; NiMo
“½R−S ” þ 2 H2 300−450o→C; “½R−H ” þ H2S
For the production of ultra-low sulfur fuel feedstocks
(<10 ppmw S), more than 99 % of the sulfur compounds
present in the feedstock ought to be removed during this
catalytic hydrotreating process. The shift from normal to
ultradeep desulfurization is a very challenging technical problem,
as many factors such as the catalysts, process parameters,
feedstock source and quality, reactivities of the present sulfur
compounds, and inhibition effects of nitrogen compounds,
aromatics, and predominantly H2S can have significant
influences on the degree of desulfurization of the feedstocks [
As the HDS reaction pathway proceeds mainly via the two
parallel routes—direct desulfurization (DDS) and
hydrogenation (HYD)—the poisoning effects of the main inhibitor H2S
have been found to be different for the two routes. In
particular, H2S is a strong inhibitor for sulfur removal via the DDS
route, but it only has a minor effect on HYD route. Since H2S
is the by-product of HDS reaction, its presence in a
hydrotreating reactor is unavoidable. Susceptibilities to H2S
poisoning are different for the various types of catalysts.
Moreover, at low partial pressures, H2S also plays a beneficial
role in maintaining the sulfide state of the CoMo and NiMo
catalysts and may enhance hydrogenation. H2S partial
pressure also has a strong influence on the susceptibility of the
employed NiMo and CoMo catalysts to H2S poisoning and
thus has a promotional effect on the overall HDS reaction.
Significant improvements in HDS catalysts and reactor
design have been made, and optimum operating strategies have
been developed to minimize the inhibition effects of H2S and
other inhibitory compounds and to enhance the removal of the
last traces of refractory sulfur compounds [
In this context, a selective and sensitive H2S sensor with a fast
response time is of utmost analytical process value in order to
maintain the HDS unit under optimum operational parameters.
Gas chromatography (GC) is considered the standard
petrochemical analytical technique as it is often used for measuring the
entire composition of a sample down to ppmv concentrations
while also measuring the majority component up to 100 %v.
However, to reach sub-ppmv and ppbv measurements along with
high-percent level measurements, a GC usually requires separate
injection and column switching techniques, turning it into a
complex and expensive analyzer. In addition, GC cycle times are
usually in the range of 5–15 min, depending on the application,
and thus, the concentration data is rather periodic than
continuous. A laser-based system for direct and selective measurement
as possible when using QCLs can therefore be the preferred
technique for applications where continuous measurements with
a fast sensor response are required. In terms of sensitivity and
dynamic range, QCL-based sensors can offer better performance
than GC while response times are typically <30 s [
The H2S and CH4 spectral line system in the 8-μm region
In order to assess the applicability for selective and sensitive
H2S measurements for analytical and industrial process
purposes, a synthetic CH4 matrix as a very strong absorbent gas
species was chosen as the model environment. Based on CH4
interference-free H2S lines and commercially available
CWDFB-QCLs, the 8-μm MIR spectral region between 1250 and
1245 cm−1 was chosen for the measurements of H2S and CH4.
This region is characterized by the overlapping of the ν2(A1)
bending mode transition of H2S (C2v symmetry) and the
ν4(F2) bending mode of CH4 (Td symmetry) [
]. Further, a
Coriolis coupling of the ν4(F2) and the ν2(E) is present,
causing the presence of ν4-ν2-coupled ro-vibrational transitions
]. For the selection of the most suitable range for the
spectral detection of H2S, reference spectra were calculated
 based on the HITRAN [
In this work, the spectral region (1250–1245 cm−1)
corresponding to the ro-vibrational transitions of the ν2 bending
mode of H2S listed in Table 1 was considered for the laser
tuning and characterization measurements. The rotational
levels of H2S as a three-dimensional asymmetric top rotator
with three different reciprocal moments of inertia are labeled
by the three standard quantum numbers: J, Ka, and Kc [
Table 1 Main ro-vibrational
transitions of the ν2 bending mode
of H2S in the spectral region
Laser characterization and absorption line selection
For spectral H2S assessment, a collimated CW-DFB-QCL in a
high-heat load (HHL) package (sbcw 5704, Alpes Lasers)
emitting at ∼8.0 μm was employed, generating up to 35 mW
of coherent optical radiation. In order to perform selective and
sensitive H2S 2f-WMS measurements, the strongest
absorption lines in the 1250–1245 cm−1 region were targeted. The
single-mode operation and the time-resolved spectral behavior
of the DFB-QCL in the 1250–1245 cm−1 spectral range were
investigated using a step-scan-enabled Fourier transform IR
spectrometer (Bruker Vertex 80v, Bruker Optics, Germany)
with a spectral resolution of 0.075 cm−1 and temporal
resolution of 2 ns [
]. A liquid nitrogen (LN2)-cooled
mercurycadmium-telluride (MCT) detector with a response time <2 ns
(Kolmar Technologies, USA) served as the infrared detector.
The time-resolved spectra of two exemplary 550-Hz
sawtooth laser current ramps at different laser temperatures ranging
from 550 to 700 mA within the achievable QC laser tuning
range recorded in combination with an 8-bit resolution and
500 MS/s sample rate transient recorder board (Spectrum
GmbH, Germany) are shown in Fig. 1. At a laser temperature
of 18 °C and injection current of 550–700 mA, the tuning range
was 1248.1–1246.9 cm−1 (Δν = 1.2 cm−1), whereas at a laser
temperature of 19 °C and injection current of 600–700 mA, the
tuning was measured starting from 1247.7 cm−1 and expanding
to 1246.6 cm−1 (Δν = 1.1 cm−1). Almost linear spectral
evolution is observed during ∼70 % of the current ramp time scale.
The non-linear spectral behavior of the last 30 % of the total
ramp time scale is attributed to the onset of the safety current
soft clamping (asymptotical convergence to the maximum
current of 700 mA) of the laser driver.
H2S sensor prototype architecture
In order to meet the on-site safety regulations, the optical
platform of the H2S sensor was installed in an industry rack
[J′ Ka′ Kc′]
a Quantum numbers of upper and lower local ro-vibrational state (LRVS)
and equipped with the required safety infrastructure as
suggested in the ATEX directive for protected operation in
hazardous and explosive environments. The assembled H2S
sensor prototype combines a purge and pressurization system
with integrated safety electronic devices, achieving a versatile
explosion prevention and malfunction protection.
Figure 2a shows a photograph of the H2S sensor prototype
fully assembled and equipped with the purge, pressurization,
and integrated safety system components in the industry rack.
The top floor is occupied by the driving, data acquisition
(DAQ), and safety electronics. The optical platform, mass
flow controllers (MFCs), pressure indicators, and valve arrays
are installed in the middle floor of the industry rack. Peripheral
components including the main pump, heat exchangers, and
pulsation dampers are accommodated in the lower floor.
The piping, instrumentation, and safety flow diagram is
depicted in Fig. 2b. The high-pressure process gas stream
is sampled (A) and expanded to an intermediate pressure
level (B). In case of over-pressurization, a part of the
process gas stream is discharged via the back-pressure
valve pathway (C). During normal operation, the safety
valve (D) opens the pathway through a fine particulate
filter and ensures the process gas to enter the
MFCcontrolled sample inlet (E) of the multipass cell. The
membrane pump together with the MFCs (F) ensures
constant optimal pressure levels while also maintaining a
constant flow throughout the operation of the sensor
prototype. Finally, the process gas stream is fed back to
the purge system via a back-pressure valve (G).
The optical layout of the H2S sensor is outlined in Fig. 2c.
The MIR laser radiation of the CW-DFB-QCL was overlaid
with a visible 532-nm diode-pumped solid-state (DPSS) trace
laser beam, collimated with a plano-convex lens (f = 500 mm)
and coupled into an astigmatic Herriott multipass gas cell with
a total pathlength of 100 m (AMAC100, Aerodyne Inc.). The
laser wavelength was scanned at 1 Hz over the tuning range of
the QCL and additionally sinusoidally modulated in the range
of 1–50 kHz. This wavelength-modulated laser beam is
transmitted through the absorbing, gaseous path in the multipass
sample cell, giving rise to harmonic components in the optical
signal. The laser radiation exiting the multipass sample cell
containing the spectral information of the target analytes
encoded in the modulated optical signal was focused onto an
optically immersed TE cooled MCT detector (PCI-2TE-12,
Vigo Systems). The recorded signals were digitized with a
1 6 - b i t 5 M S / s D A Q u n i t ( N I U S B 6 3 6 6 , N a t i o n a l
Instruments) and further demodulated and processed using a
software-implemented lock-in amplifier. Averaging of over 10
sweeps resulted in a total response time of ∼15 s.
Results and discussion
Laboratory-based H2S assessment in a CH4 matrix
Different H2S and CH4 concentration levels were prepared by
5.0 N2 (99.999 %) dilution from 2000 ppmv H2S- and
50,000 ppmv CH4-standardized gas bottles (matrix N2) with
a mass flow and pressure-controlled in-house developed gas
handling system. Pressure monitoring was performed with a
digital manometer (Leo3, Keller). The multipass cell was
operated at room temperature (295 ± 2.5 K) and at total pressures
ranging from 50 to 100 mbar in order to spectrally resolve the
ro-vibrational bands of the analyte and matrix molecules.
Driving the QCL with a current ramp ranging from 500 to
700 mA enabled a maximum spectral bandwidth of ∼1.2 cm−1
(Fig. 1) which allowed for the examination of multiple
selected target analyte peaks in a CH4 matrix (compare with
Table 1). The first step towards a successful multi-analyte
detection was the evaluation of a selective and sensitive H2S
assessment with the help of two reference cells. These cells,
designed with an optical pathlength of 5 cm, are filled with the
single-target analytes with 98 %v H2S and 5 %v CH4
backfilled with N2 to a total pressure of 50 mbar. They are
sealed with wedged and Brewster angle-tilted CaF2 windows.
Taking advantage of spectral line resolution at the
lowpressure conditions of ∼50 mbar, a sufficient separation of
Δν = 0.509 cm−1 from the interfering CH4 transitions (marked
with BA^) and Δν = 0.377 cm−1 (marked with BB^) could be
demonstrated with the two reference cells (Fig. 3). Thus,
selective and interference-free H2S assessments in a CH4 matrix
can be expected in an industrial matrix.
In order to assess the applicability of analytical and
industrial process purposes, a synthetic CH4 matrix of up to
1000 ppmv together with a varying H2S content was prepared
with the custom-built gas handling system and chosen as the
model environment for subsequent measurements in the
optical multipass gas cell.
In this context, it was possible to conduct and demonstrate
selective and interference-free H2S assessments in a synthetic
CH4 matrix. In Fig. 4, the according 2f-WMS spectra of 5–
Fig. 3 (a) 2f-WMS reference gas
cell spectra with H2S and CH4
contribution. The interfering CH4
transitions are marked with (A).
(b) 2f-WMS spectra of the
isolated H2S signal contributions.
Baseline ripples are due to
etaloning effects of the 5-cm
reference cell. (c) 2f-WMS
spectra of the isolated CH4 signal
contributions with a 26 times
magnified inset of the interfering
CH4 transitions (marked with
(B)). (d) Tuning curves for a laser
injection current ramp of 550–
700 mA and a laser temperature
of 18 °C (blue) and for an
injection current ramp of 600–
700 mA and a laser temperature
of 19 °C (red)
50 ppmv H2S in a 1000 ppmv CH4 matrix (Fig. 4(a)) and the
isolated H2S contribution of 0–100 ppmv in the same tuning
range (Fig. 4(b)) are shown.
which can be described as the minimum detectable
absorption scaled to pathlength and noise-equivalent
detection bandwidth [
Determination of noise-equivalent absorption sensitivity and limit of detection
Quantitative measurements of H2S were performed using
dry H2S gas mixtures in order to investigate the sensitivity
and linear response of the 2f-WMS-based sensor system.
A commonly accepted metric for instrument comparison
is the noise-equivalent absorption sensitivity (NEAS),
Fig. 5 Determination of the
sensitivity (NEAS) of H2S
where ΔI/I is the 1σ value of the limiting noise level in the
spectrum, normalized by the total intensity (I); L is the optical
pathlength; BW is the detection bandwidth; and N is the
number of averages.
For the NEAS determination, 2f-WMS spectra of
12.5 ppmv H2S at 65 mbar were acquired with a lock-in
Fig. 6 Calibration curve of 0–
50 ppmv H2S. The calculated
LOD (3σ) is 150 ppbv H2S
time constant of 2 ms, a filter slope (roll-off) of 24 dB/
octave, and averaged 10 times which resulted in a
noiseequivalent bandwidth of the low-pass filter of 39 Hz (refer
to Fig. 5). The estimated value of the NEAS for H2S at
∼1247.2 cm−1 was found to be 8.419 × 10−10 cm−1 Hz−1/2.
The 2f-WMS technique measures a signal roughly
proportional to the second derivative of the scanned
absorption line shape, hence decreasing the vulnerability to slow
baseline drifts and effectively rejecting 1/f noise. In
comparison to direct absorption spectroscopy approaches,
instrument sensitivity is typically improved by one order of
magnitude. Due to the more complex nature of the
measured signals, the implementation of 2f-WMS reference
spectra for derived concentration measurements requires
elaborate analytical or numerical simulation of taking
crucial parameters of laser wavelength, optical power,
modulation depth, absorption line shape, residual amplitude
modulation (RAM) of the laser power, and detector
response into account. In practice, the majority of
2fWMS-based trace gas sensors are preferred to be
calibrated using reference calibration gas mixtures [
despite the availability of precise modeling of 2f-WMS
22, 43, 44
For the evaluation of the limit of detection (LOD) of
the 2f-WMS sensor prototype, different H2S concentration
levels within a range from 0 to 50 ppmv were prepared by
diluting a certified 100 ppmv H2S:N2 calibration mixture
with 5.0 N2 (99.999 %). Each concentration step was
Fig. 7 Exemplary process
spectrum of a HDS run. The
positions of the H2S and CH4
features are marked
measured 10 times, and the resulting data were averaged
and plotted as a function of concentration (refer to Fig. 6).
The good linearity between signal amplitudes and H2S
concentrations was observed for the 2f-WMS-based
sensor. The corresponding LOD was ascertained with the
Validata software package [
] at three times the standard
deviation (3σ) of the intercept divided by the slope of the
calibration curve, which resulted in 150 ppbv.
Results from online measurements at the project partner
OMV AG are depicted in the following figures. The
exemplary data is typically plotted over several hours to
several days. Absolute values of concentration scales
and additional plant parameters (catalyst compositions,
temperature, and pressure levels) are omitted due to
company regulations. However, a general description of the
fundamental process is given.
The H2S concentration is derived from the correlation
of the measured 2f-WMS spectra with the reference
spectra of a precisely validated gas standard, acquired during
the calibration procedure. With this calibration technique,
high-precision gas concentration measurements can be
performed, as the absolute accuracy of the instrument
calibration is predominantly related to the precision of the
applied certified gas standard. Moreover, this approach
does not rely on the determination of any of the
Fig. 9 Continuous monitoring of
the H2S and CH4 content during a
65-h HDS run. At points (A) and
(B), the feedstock was changed.
Interesting to note is the periodic
fluctuation of the CH4 content
during the first 15 h of operation.
Transient reactor dynamics
resulting in concentration dips
due to likely upsets and
instabilities in the flow rates at
t = 20 h, t = 30 h, and t = 45 h are
marked by arrows
previously stated parameters, which are required for
2fWMS spectral simulation [
Although no explicit calibration curve was recorded for
CH4, the concentration was calculated by applying the
deduced H2S sensitivity to the measured 2f-WMS signal of the
CH4 transitions centered around 1246.8 cm−1, as these CH4
transitions exhibit similar linestrengths compared to the H2S
feature at 1247.2 cm−1.
An exemplary online purge gas process spectrum of the
hydration reaction plant containing ∼300 ppmv H2S and
∼500 ppmv CH4 together with the referenced analyte
positions is shown in Fig. 7.
The continuous monitoring of the H2S and CH4 content
during a 65-h-lasting HDS run of straight-run oil is visualized
in Fig. 8. The defined feed change event at t = 6 h (marked
with A) as well as the transient HDS reactor response due to a
GC sampling event at t = 10.7 h (marked with B) could be
revealed by the fast sensor response.
The continuous monitoring of the H2S and CH4
content during a 65-h-lasting HDS run of low-sulfur
feedstocks is visualized in Fig. 9. The defined feed change
events at t = 26 h (marked with A) and t = 58 h (marked
with B) are indicated. During the first 15 h of operation,
an interesting and still unexplained effect of the periodic
fluctuation of the CH4 content was observed. Moreover,
transient reactor dynamics resulting in concentration dips
due to likely upsets and instabilities in the flow rates at
t = 20 h, t = 30 h, and t = 45 h could be discovered during
Summary and conclusions
A MIR optical gas sensor prototype based on wavelength
modulation spectroscopy with second harmonic detection
(2f-WMS), employing a continuous-wave distributed
feedback quantum cascade laser (CW-DFB-QCL) emitting at
8 μm, for fast, sensitive, and selective sub-ppmv H2S
detection was developed.
In order to assess the applicability for analytical and
industrial process purposes aimed at petrochemical
environments, a synthetic methane (CH4) matrix of up to
1000 ppmv together with a varying H2S content in an
optical 100-m multipass gas cell was chosen as the model
environment. A noise-equivalent absorption sensitivity
(NEAS) for H2S at ∼1247.2 cm−1 was found to be
8.419 × 10−10 cm−1 Hz−1/2. In the same spectral region, a
limit of detection (LOD) of 150 ppbv H2S could be
Subsequently, a sensor prototype was developed,
installed in an industry rack, and equipped with the
required safety infrastructure for protected operation in
hazardous and explosive environments, in order to meet the
company on-site safety regulations. The sensor prototype
was deployed and successfully tested for on-site
measurements under the imperative on-site safety regulations for
hazardous and explosive environments at the
petrochemical research hydrogenation platform of the industrial
partner OMV AG.
In comparison with the industrially established
reference GC method, the sensor prototype clearly acted as a
new tool for monitoring the H2S content with faster
response times and allowed to access additional CH4
Important analytical process advantages of the developed
H2S sensor prototype are identified in its high selectivity
paired with sub-ppmv sensitivity and fast response time,
which allow a continuous, direct pre-treatment-free
measurement of the process gas streams.
Clearly, a major challenge for the industrial
implementation of QCL technology is finding a precisely tailored
application with recognizable advantages while exhibiting
a pronounced cost benefit for using QCLs. For
spectroscopic applications, the MIR spectral region is favored
over the near-infrared region due to the considerably
stronger cross sections of the chemicals under
investigation. But, it is much less desirable when considering the
availability and system costs of the expensive optical
components and materials. As a consequence, it is
believed that the QCL technology will start to penetrate
industrial markets, where process gas detection is deemed
necessary and no other solutions with current techniques
Planned research will benefit from the generic nature
and flexibility of the QCL-based sensor classes.
Implementation of new QCL designs, such as multiple
DFB chips [
], RCSE arrays [
], or Vernier-effect
], will allow for a further extended
spectral coverage. Thus, other ro-vibrationally accessible
analytes of particular interest can be measured as well.
In addition, integration of laser source and detectors in
one device is possibly opening the path for highly
miniaturized, sensitive gas sensors for detecting multiple
gas species [
Further development and extension of the integrated
safety and malfunction protection infrastructure in order
to achieve a certified ATEX status will assure proper
operation under the mandatory petrochemical safety
regulations and prepare the ground for true on-site applicability
of the QCL-based sensor prototype.
Acknowledgments Open access funding provided by TU Wien
(TUW). The authors acknowledge the work of Thomas Placzek for
designing and equipping the industry rig. The financial support was
provided by the Austrian Research Funding Association (FFG) under the scope
of the COMET program within the research project BIndustrial Methods
for Process Analytical Chemistry—From Measurement Technologies to
Information Systems (imPACts)^ (contract no. 843546). This program is
promoted by the BMVIT, BMWFW, the federal state of Upper Austria,
and the federal state of Lower Austria.
Compliance with ethical standards This paper does not contain any
studies with human participants or animals performed by any of the
Conflict of interest The authors declare that they have no conflict of
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