U LT R A - S E N S I T I V E S O L U T I O N S
F O R R E A L - T I M E T R A C E G A S A N A LY S I S
TECHNOLOGIES OVERVIEW
PROTON TRANSFER REACTION MASS SPECTROMETRY
S E L E C T I V E R E A G E N T I O N I Z AT I O N MASS SPECTROMETRY
I O N I C O N P T R - M S AT A G L A N C E
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Market-leading real-time detection limit (ppqv-/pptv-range)
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No sample preparation (direct air sampling)
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Absolute VOC quantification without calibration
•
Soft and highly efficient chemical ionization
•
High reagent ion purity without the need for a signal-diminishing mass filter
•
Quadrupole or time-of-flight mass spectrometry
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Discrimination of isobaric compounds
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No gas supply or carrier gas necessary, low running costs
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Robust, lightweight, easy to use
I O N I C O N S R I - M S A D D I T I O N A L LY O F F E R S
WHAT IS PTR-MS?
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Selective Reagent Ionization (H3O+, NO+, O2+, Xe+ and Kr+)
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Separation of several isomeric molecules
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Virtually no limitation of analyzable substance classes
•
Very high reagent ion yields that result in ultra-high sensitivity
PTR-MS (Proton Transfer Reaction – Mass Spectrometry) enables simultaneous real-time detection, monitoring and quantification of volatile organic compounds (VOCs) such as acetone,
acetaldehyde, methanol, ethanol, benzene, toluene, xylene and many others present in ambient air. Originally developed by scientists at the Institut für Ionenphysik at the University of
Innsbruck, this technology has been commercialized by IONICON Analytik in 1998. Since
then the IONICON PTR-MS instruments have been known for their outstanding sensitivities and
market-leading detection limits in the single-digit pptv-levels and below.
IONICON TRACE GAS
ANALYSIS TECHNOLOGIES SOLUTIONS FOR ALL YOUR
MONITORING NEEDS!
F R O M T H E W O R L D ’ S L E A D I N G P T R - M S C O M P A N Y.
WHAT IS SRI-MS?
MARKET-LEADING LOW REAL-TIME DETECTION LIMIT
SRI-MS (Selective Reagent Ionization - Mass Spectrometry) represents IONICON’s latest direct
injection mass spectrometry technology: chemical ionization via different selectable reagent
H3O+ ions do not react with any of the major components present in clean air due to their
ions coupled to quadrupole or time-of-flight mass spectrometers. This feature is also optionally
low proton affinity. Unlike other technologies (e.g. SIFT-MS or IMR-MS) PTR-MS does not dilute
available as SRI or SRI+ add-on for all IONICON PTR-MS instruments. With SRI-MS all advan-
samples containing low analyte concentrations with a carrier gas and does not lose reagent
tages of „classical PTR-MS“ are preserved, while the number of analyzable substance classes is
ions on their way through a mass filter between ion source and drift tube. This makes PTR-MS
seriously enhanced, making SRI-MS instruments unique universal trace gas analyzers.
very sensitive to trace gases in the sample air. Very high intensities of reagent ions and thus
real single-digit pptv-range detection limits are the resulting benefits of the IONICON PTR-MS
technology achieved through continuous improvements by IONICON engineers.
The first IONICON trace gas analyzer was sold in 1998 and in the following 15 years we
have marketed more than 250 PTR-MS units to the world‘s leading scientists. In the meantime
PTR-MS has become the standard for ultimate real-time sensitivity in VOC monitoring. True to
our mission we constantly strive to improve our technologies and develop novel solutions for
real-time trace gas analysis setting the benchmark in real-time mass spectrometry.
IONICON PTR-TOF 8000
479
400
276
300
2.0
Concentration (pptv)
A SUCCESS STORY
Sensitivity (cps/ ppbv)
500
200
100
m/z 187.93
Linear Fit
1.5
1.0
ppqv
parts-per-quadrillion
0.5
0.0
25
0.0
0
2009
2012
2013
Figure 1: Sensitivity evolution of the high mass
resolution IONICON PTR-TOF 8000
(determined with certified gas standards)
0.2
0.4
0.6
0.8
1.0
Ion yield (cps)
Figure 2: Detection limits of a high mass resolution IONICON PTR-TOF 8000 in the ppqv-range
(actual measurement results)
02 | 03
CHEMICAL IONIZATION
NO SAMPLE PREPARATION
(DIRECT AIR SAMPLING)
this new technology. Analyzing sub-
quadrupole mass filters and time-of-
stances using different reagent ions
flight analyzers for maximum flexi-
adds a new dimension to the sepa-
bility and adaptation to your needs.
A major advantage of PTR-MS and
Proton transfer from H3O is a soft
ration and identification capabilities
Whereas quadrupoles are robust,
SRI-MS is that samples do not need
ionization method, keeping frag-
of compounds. Note: Because of a
cost-efficient and therefore ideal for
to be prepared prior to the measure-
mentation rates low (compared to
highly sophisticated ion source de-
selected compounds monitoring, TOF
ment (e.g. pre-concentration or chro-
e.g. electron impact ionization), thus
sign (hollow cathode discharge) the-
mass spectrometers acquire full mass
matographic separation procedures),
minimizing the complexity of mass
re is no need for a signal-diminishing
spectra in a split-second and permit
thus whole-air samples can be intro-
spectra and improving quantification
mass filter to select the reagent ions,
separation of isobars due to very
duced directly which avoids any sam-
and identification. The outstanding
which helps for achieving the outstan-
high mass resolution, hence provide
pling and storage induced artifacts
efficiency of proton transfer is one of
ding sensitivity IONICON instruments
much more scientific insight.
and is the key to real-time analysis
the reasons why detection limits even
are known for.
(e.g. dynamic headspace sampling
in the ppqv region are possible with
or VOC flux measurements).
IONICON PTR-MS instruments.
+
THE PTR-MS/SRI-MS
TECHNOLOGIES
AN IONICON PTR-MS/SRI-MS SYSTEM
C O N S I S T S O F T H R E E M A I N PA R T S :
PTR-QMS
H3O
+
PTR-TOFMS
Acetone + Propanal
•
1
Ion source: Production of the reagent ions at very high purity
PTR-MS provides absolute quantitative analysis in real-time (response
Ion yield
WITHOUT CALIBRATION
Chemical ionization
processes. This leads to constant and
Acetone
Propanal
Furan
+
25 26 27 28 29 55 56 57 58 59 60
Mass (m/z)
PTR-MS
15
20
25
30
35
Mass (m/z)
40
45
50
MASS SPECTROMETRY (SRI-MS)
SRI-MS technology offers the freedom
to choose the ideal reagent ion for virtually all fields of application. Where
classic PTR-MS reaches its limitations,
Sample introduction
Concentration (ppbv)
40
20
200
400
C6 H6
SRI
C2 H4
30
SO 2
CO 2
40
50
600
800
1000
Figure 3 : Real-time quantification of direct air
samples (schematic illustration)
LOW IN RUNNING COSTS
Our instruments are light-weight,
C6 H6
60
70
80
Mass (m/z)
Figure 6: SRI-MS analysis of a sample containing
traces of C2H4, CO2, SO2 and C6H6 (schematic
illustration)
space-saving and low in energy con-
•
Analyzing system:
Quadrupole based systems: A quadrupole mass filter in conjunc-
mass spectrometer separates the ions according to their mass
to charge (m/z) ratio. The resolution is sufficient to distinguish
between isobaric molecules and makes an unambiguous identification possible.
CON solutions ahead of competing
technologies. Our trace gas analyzers are often used for field campaigns or variable location measureevery environment: e.g. only 15
O2+ (SRI) or Kr+ and Xe+ (SRI+) and
THE LIBERTY TO CHOOSE
minutes after unpacking a PTR-QMS
enjoy utmost flexibility in one IONI-
BETWEEN QUADRUPOLE AND
300 is ready to measure. No gas
CON instrument. Separation of seve-
TIME-OF-FLIGHT (TOF) MASS
supply is necessary to operate an
ral isomeric compounds, detection of
ANALYZERS
IONICON PTR-MS instrument. For
substances with low proton affinities
Time-of-flight based systems: A high resolution time-of-flight (TOF)
sumption which clearly puts IONI-
ments and can be operated in nearly
choose among H3O+ (PTR), NO+ and
Time (ms)
www.IONICON.com
C2 H4
SRI-MS is the solution for your needs:
0
0
ROBUST, RELIABLE AND
SRI+
libration gas feed.
60
gent ions.
Mass (m / z)
tion and detection of the ions.
Ion yield
SELECTIVE REAGENT
without the need for a continuous ca-
SOFT AND HIGHLY EFFICIENT
69.5
C6 H6
PTR
IONIZATION -
80
69.0
tion with a secondary electron multiplier provides mass separaFigure 4: Soft and efficient Proton Transfer Reaction (PTR) ionization (schematic illustration)
of absolute concentrations possible
Substance A
Substance B
Substance C
68.5
Figure 7: Detection of two isobaric compounds
with a PTR-QMS (unit mass resolution) and a PTRTOF 8000 (schematic illustration)
Figure 5: SRI-MS allows for isomer separation
and detection of more species: e.g. Ethylene
(schematic illustration)
like IMS, APCI-MS and similar tech-
100
Drift tube: Trace gases in the sample air undergo either (mostly) non-dissociative proton transfer, charge and hydride ion
Acetone + Propanal
Ethylene
well defined reaction conditions (unnologies) making the determination
•
Isoprene
transfer or association reactions, dependent on the selected rea-
nization of the VOCs are individually
controlled and spatially separated
+
O2
time < 100 ms). The generation of
the reagent ions and the chemical io-
NO
Ion yield
REAL-TIME QUANTIFICATION
Ion yield
levels in a hollow cathode discharge.
Methanol
Ethanol
Acetaldehyde
Electron impact
Ion
Source
Ion
Source
PTR
Drift Tube
PTR
Drift
Tube
Transfer
Lens
System
QuadrupoleMS
Feed Sample
Inlet Inlet
Feed
Inlet
Sample
Inlet
SRI-MS only minute amounts of gas
and detailed investigations of the ion
IONICON offers a broad range of
(e.g. O2 below 10 ml/min) are nee-
chemistry are just a few examples
different PTR-MS and SRI-MS products
ded. Low maintenance and operating
of the wide range of advantages of
and gives you the choice between
costs complete the whole package.
04 | 05
TOF-MS
HOW DOES IONICON SRI-MS WORK?
HOW DOES
IONICON PTR-MS
WORK?
The simplest form of ionization (charge transfer) with
Special case: ionization with NO+
IONICON‘s novel SRI-MS technology is shown in equation
(5): the trace compound B transfers an electron to the rea-
Ionization with NO+ even offers the great ability to identify
gent ion A+. This reaction is feasible when the ionization en-
and separate several isomeric molecules. When aldehydes
ergy of A is close to or higher than the ionization energy of B.
react with NO+ it is very likely that a hydride ion transfer
reaction will take place. Equation (9) describes this pro-
The fundamental ionization process in a PTR-MS instrument
In (2) and (3) [RH+] is the density of protonated trace con-
can be written as
stituents, [H3O+]0 is the density of primary ions, k is the re-
A+ + B —> A + B+
(5)
cess and it can be easily seen that for this mechanism the
product ions will appear at their molecular mass minus one
action rate coefficient and t the reaction time, i.e. the time
However, as charge transfer ionization is a considerably
the H3O+ ions spend in the reaction region. All common
„harder“ ionization method compared to PTR ionization,
constituents of ambient air (N2, O2, Ar, CO2 etc.) have
fragmentation of the product ions is much more likely to
Protonated water (H3O+) interacts with the trace gas mo-
a lower PA than water, and do not get ionized. The air
occur. This is reflected in equation (6) where the reagent
lecule (R). During this interaction a proton transfers from
itself acts as a buffer gas. Therefore assumption (3) is va-
ion is again A+, whereas the trace compound B consists of
For ketones ionization mainly takes place via a simple
the hydronium to the trace gas molecule, which leads to
lid, since only volatile organic compounds (VOCs) with a
C + D. As a result of the reaction the charged fragment D+
charge transfer reaction, which means that the product
a protonated and therefore ionized molecule (RH+) and a
proton affinity (PA) higher than the PA of water undergo a
will be detected at the mass spectrometer.
ions appear exactly at their molecular mass (7).
neutral water molecule (H2O). This proton transfer reaction
PTR reaction. This is the case for a large variety of VOCs,
(1) is energetically possible for all VOCs with a proton
which are usually present in trace amounts. Compared to
affinity higher than that of water (691 kJ/mol).
electron impact ionization, the energy transfer in the PTR
H3O+ + R —> RH+ + H2O
(1)
Ion source
A+ + B —> A + C + D+
(6)
amu (because of hydrogen loss).
AH + NO+ —> A+ + HNO
AH + NO+ —> AH+ + NO
(9)
(10)
process is very low. This effectively suppresses fragmenta-
One example, where both reaction pathways can be
These facts lead to a situation that with NO+ ionization
tion and leads to mass spectra that are easy to interpret.
observed is the charge transfer ionization of benzene
isomeric compounds appear on different nominal masses
(C6H6) with Kr+ as the reagent ion. The equations (7) and
and are therefore distinguishable.
For an efficient ionization via reaction (1) an abundant
supply of H3O+ ions is necessary. In IONICON PTR-MS
Determination of concentrations
(8) show the two most abundant reactions, namely simple
instruments these primary ions are generated in a dedica-
The mass analyzing and detection system (quadrupole
charge transfer (7) and charge transfer with hydrogen ab-
ted ion source that has been developed and continuously
mass filter or time-of-flight mass spectrometer) of the PTR-
straction (8).
improved over many years by our renowned experts.
MS instrument delivers count rates (or currents) which are
In the ion source water vapor is broken down in a hollow
proportional to [RH+] and to [H3O+]. The average time t
cathode discharge. In a second step the fragments recom-
can be calculated from system parameters (drift voltage,
bine to protonated water ions (H3O+) with very high purity
pressure, temperature, etc.) and the reaction rate coef-
(up to 99.5%) and can therefore be injected directly into
ficient k can be found in literature for many substances
the PTR drift tube without the need of an interconnected
(alternatively it can be calculated or experimentally deter-
mass filter, which would lead to an inevitable loss of prima-
mined). Knowing all necessary variables in (3) makes it
ry ions and eventually result in a reduced sensitivity.
possible to calculate the concentrations of VOCs in the
Note: NO+ ionization is nearly as soft as proton transfer
from H3O+, which means that fragmentation is considerab-
Kr+ + C6H6 —> Kr + C6H6+
(7)
Kr+ + C6H6 —> Kr + H + C6H5+
(8)
ly suppressed. In addition to charge transfer and hydride
ion transfer sometimes termolecular association reactions
take place and can be used for unambiguous detection.
measured volume of air without the need of gas standards
PTR drift tube
via equation:
In the PTR drift tube the actual ionization process (1) of the
trace gas molecules takes place. It can be easily derived
that the PTR process (1) follows the equation
[RH+] = [H3O+]0 (1 – e–k[R]t )
if
[RH+] << [H3O+] ~
~ [H3O+]0 = const.
www.IONICON.com
(4)
(2)
which can be simplified in good approximation to
[RH+] ~
~ [H3O+]0 [R]kt
[RH+]
[Concentration]ppbv = C *
[H3O+]
(3)
CONCLUSION
The highly sophisticated PTR-MS software automatically ac-
The combination of a highly sophisticated ion source, the efficient PTR ionization process and a state-of-the-art mass analy-
quires and calculates all necessary data for equation (4)
zing system in an IONICON PTR-MS instrument, offers the possibility to monitor and quantify VOCs down to and even below
(constant C which includes k, t and a conversion factor, as
the single-digit pptv range while being compact, low cost in maintenance and reliable for a wide area of applications. The
well as the ratio of the signal intensities) so that the user
additional advantages of SRI-MS complement the unique PTR-MS technology and definitely make IONICON instruments the
can monitor the absolute concentrations of all measured
gold standard for universal real-time trace gas analysis.
VOCs in real-time.
06 | 07
U LT R A - S E N S I T I V E S O L U T I O N S F O R R E A L - T I M E T R A C E G A S A N A LY S I S
IONICON Analytik Gesellschaft m.b.H.
•
Eduard-Bodem-Gasse 3
•
6020 Innsbruck
•
Austria
•
www.IONICON.com