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T e c h n i c a l
The Use of Hydrogen
Carrier Gas for GC/MS
N o t e
Gas Chromatography/
Mass Spectrometry
Highlights
• Guidelines that can mitigate dangers and
leverage benefits of using hydrogen
• Key safety factors for chemical laboratories
• Practical considerations for GC/MS method
development
Introduction
Helium, as a limited natural resource, is increasingly expensive and, in some regions, in
limited supply due to rationing. As such, the use of hydrogen as a carrier gas for gas
chromatography mass spectrometry (GC/MS) is becoming more and more prevalent.
Physical differences between hydrogen and helium give rise to chromatographic
differences and the flammable nature of hydrogen increases safety concerns as well. In
this document we will demonstrate the effective use of hydrogen with the PerkinElmer®
Clarus® SQ 8 GC/MS and provide recommendations for ensuring laboratory safety.
While the dangers of using hydrogen in a laboratory can be mitigated, every laboratory
faces unique challenges and it is the responsibility of the laboratory manager and safety
officer to address these issues to ensure the safety of their laboratory personnel. Extra
caution must be taken in the design of both the laboratory and the experimental set-up.
The development of safety conscious Standard Operating Procedures (SOP), including a
thorough chemical hygiene plan, is a must.
Polycyclic Aromatic Hydrocarbons by GC/MS Using Hydrogen Carrier Gas
The determination of polycyclic aromatic hydrocarbon (PAH) compounds demonstrates
the functionality of the PerkinElmer Clarus SQ 8 GC/MS using hydrogen carrier gas. The
chromatograms presented in Figure 1 demonstrate the effectiveness of this system using
both helium (Figure 1A) and hydrogen (Figure 1B) as carrier gas. A comparison of the two
chromatograms clearly illustrates the faster elution times and improved peak sharpness
one can expect when switching from helium to hydrogen.
!
Hydrogen is a flammable gas and
when used incorrectly can pose a
threat to both life and property.
Prior to using hydrogen in a laboratory setting, safety precautions
must be developed and subsequently
observed to ensure safety.
A.
Acenaphthene-d10
9.24 Phenanthrene-d10
11.19
Naphthalene-d8
7.00
100
%
Chrysene-d12
14.90
1,4-Dichlorobenzene
5.53
Perylene-d12
17.60
Scan EI+
TIC
1.94e8
0
B.
100
Acenaphthene-d10
Naphthalene-d8
6.92 Phenanthrene-d10
4.77
8.80
1,4-Dichlorobenzene
% 3.42
0
3.30
5.30
7.30
9.30
Scan EI+
TIC
2.86e8
Chrysene-d12
12.21
Perylene-d12
14.02
11.30
13.30
15.30
17.30
Time
19.30
Figure 1. Chromatogram of standard PAH mix using (A) helium and (B)
hydrogen as the carrier gas with standards labeled with retention time in
minutes and compound name.
Guidelines for Using Hydrogen
The following sections highlight the safety and performance
considerations a laboratory will face when electing to use
hydrogen as the carrier gas for their GC/MS experiments.
The information presented here is provided as a guide
only, and especially in the case of hydrogen safety, a full
assessment of the dangers and benefits of using hydrogen
should be explored prior to initiating any laboratory work.
General Safety Considerations
The main safety concern when using hydrogen in a
laboratory is the ever-present danger of explosion stemming
from its flammability. Hydrogen is flammable over a wide
concentration range, and during the rapid expansion
from a high pressure source, can self-ignite. While this is
certainly possible when using a compressed gas cylinder as
the hydrogen source, the development of a high pressure
hydrogen pocket within the instrument is unlikely. The
larger threat is the ignition of any accumulated hydrogen
from an electrical spark. Carrier gas passes through a
number of fittings and the thin-walled and somewhat
brittle GC column before passing into the vacuum of the
MS. A small leak could develop at any stage resulting in
the hydrogen build-up in the GC oven. Accumulation of
hydrogen within the MS is predominantly associated with
the loss of functionality of the pumping system. While
the pumping system is functioning properly all carrier gas
that is introduced into the MS will be captured by the
turbomolecular pump then vented to the exhaust by the
rotary pump. Loss of function, through loss of electrical
power or hardware failure, will cause the carrier gas to pool
within the vacuum chamber at increasing concentrations
resulting in a situation where ignition of hydrogen can occur.
2
For hydrogen use, as with all procedures performed in the
laboratory, a thorough review of local Environmental Health
and Safety requirements is essential. Successful safety
procedures in lab operations begin with a combination of
design and planning, which is supported by a company
culture that considers it to be mandatory and of the highest
priority. The most effective chemical hygiene plans are ones
that are built around a company culture of safety where all
personnel strictly adhere to the guidelines and regulations.
Some practical considerations to lessen the danger of
hydrogen accumulation include:
• Always vent the roughing pump exhaust and injector vent
lines to a fume hood.
• Always leak check the system after changing gas
cylinders or installing/repairing the gas lines using a fully
functioning hand-held leak sensor suitable for hydrogen
applications.
• If you are using compressed gas cylinders always install
the Hydrogen Snubber, as shown in Figure 2, and
warning label (not shown) that comes with every Clarus
GC. The Hydrogen Snubber attaches directly to the exit
of the regulator and will prevent a sudden discharge of
hydrogen into the lab should a gas line break.
• Consider using a hydrogen generator. Hydrogen
generators produce high purity hydrogen at low pressure
(relative to compressed gas cylinders), which eliminates
the risk of high pressure discharge and subsequent selfignition.
• Consider using a hydrogen sensor in the GC oven or in
the general area the instrument is located.
• It is highly recommended to utilize the optional Nitrogen
Purge Vent kit if you are using hydrogen as a carrier
gas. The Nitrogen Purge Vent kit will allow nitrogen to
be introduced into the mass spectrometer upon venting.
This will lower the risk of hydrogen build-up within the
vacuum chamber should the carrier gas not be shut off
along with the pumping system.
• Always turn off the hydrogen at the cylinder or hydrogen
generator every time you shut down the GC or MS.
• Never depressurize a gas cylinder, especially a hydrogen
gas cylinder, in the lab. The high pressure venting could
result in self-ignition and subsequent explosions.
• After a power failure, the mass spectrometer may have
collected hydrogen regardless of whether or not the
pumping system was automatically reactivated. It is
recommended to utilize the Nitrogen Purge Vent kit
function for 30 minutes prior to returning the system to
full operation. If the purge kit is not installed the source
may be removed to allow the vacuum chamber to vent to
atmosphere.
Table 1. Required inlet carrier gas pressures, in psig, for
30 cm/s helium at 50 °C.
Column Length (m)
Column
i.d. (mm)
10
15
30
60
100
0.10
31.6 49.1 >100.0 >100.0>100.0
0.18
9.1 13.9 29.0 61.9>100.0
0.25
5.7 7.014.4 30.2 52.7
0.32
<5.0<5.0 8.6
17.8 30.7
0.53
<5.0 <5.0<5.0
6.3 5.0
Table 2. Required inlet carrier gas pressures, in psig, for
40 cm/s hydrogen at 50 °C
Column Length (m)
Column
i.d. (mm)
10
15
30
60
Figure 2. Hydrogen Snubber attached to the exit of the dual-stage stainless
steel gas regulator. The installation of a Hydrogen Snubber will prevent the
rapid discharge of hydrogen into the laboratory should a gas line break.
100
0.10
18.5 28.6 60.8 >100.0>100.0
0.18
5.5 8.317.0 35.9 62.8
0.25
<5.0<5.0 8.6
0.32
<5.0 <5.0<5.0 10.6 18.0
0.53
<5.0 <5.0<5.0 <5.0 6.3
17.7 30.6
Experimental Set-up (Configuration, Pressures, and Flows)
Column Compatibility
Because hydrogen has a different viscosity from helium and
the maximum column efficiency occurs at a different gas
velocity, the applied carrier gas pressure will be different
for the two gases when run under optimum conditions. In
some instances it may enable or constrain column types
when used with an MS detector. Tables 1 and 2 indicate
the carrier gas inlet pressure necessary to run under near
optimum conditions on columns connected to an MS with a
variety of geometries for the two gases respectively. These
tables show that most of the commonly used columns are
suitable for use with either helium or hydrogen. At the
extremes, helium is better with shorter and/or wider-bore
columns whereas hydrogen is better with longer and/or
narrower-bore columns. When swapping carrier gases, refer
to these tables to ensure that the column being used will
still work with practical pressures with the new gas.
Setting up the instrumentation to use hydrogen was quite
straightforward. The installation included:
• Ultra high purity hydrogen gas cylinder (99.999%)
• Hydrogen Snubber on the hydrogen gas cylinder (and
label)
• Nitrogen Purge Vent kit
• Roughing pump exhaust and injector vent lines vented to
the laboratory fume hood
No further modifications of the hardware were necessary
to perform this work. Setting up the GC to operate using
hydrogen as the carrier gas required the selection of
hydrogen on the touch screen of the GC. This was achieved
by navigating into the Programmed Pneumatic Control (PPC)
configuration window on the touch screen and selecting
hydrogen as the “Gas” under the correct Channel tab
as illustrated in Figure 3. Selecting a different gas in this
window changes the mass-flow calibration parameters used
by the firmware. The calibration parameters are traceable to
the National Institute of Standards and Technology (NIST®)
standards; however, it is prudent to check and recalibrate
locally if necessary using a certified flow meter periodically.
3
H2
A.
B.
C.
D.
Figure 3. Procedure to change the carrier gas to hydrogen on the GC touchscreen. A) Access the Configuration screen from the Tools menu, B) Select the pneumatics
control using the Pneumatics button, C) Choose PPC Configure, D) In the Carrier tab select the proper Channel and select “H2” as the “Gas” and click OK.
Vacuum System Performance
140
120
Carrier Velocity (cm/s)
100
80
Helium
60
Hydrogen
40
20
0
1
1.5
2
2.5
3
3.5
4
4.5
5
Column Flow (mL/min)
Figure 4. Carrier Velocity vs. Column Flow for hydrogen and helium.
Using a 30 m x 0.25 mm x 0.25 μm column the following
carrier velocity versus flow setting was generated (see
Figure 4). The velocity numbers were obtained from the GC
screen. Hydrogen achieves a much higher carrier velocity
and demonstrates more linear behavior over the flow
range. This can result in shorter elution times and better
chromatography (sharper peaks) however the performance
of the mass spectrometer pumping system must also be
taken into consideration.
4
Two pumping systems are available with Clarus mass
spectrometers; the standard “S” model equipped with a
55 L/sec turbomolecular pump and the larger capacity “T”
and “C” models equipped with a 255 L/sec turbomolecular
pump. The compression of the pumped gas, and thus
pumping efficiency, varies according to the square of its
molecular mass such that heavier compounds are pumped
more efficiently. The resulting compression ratios decrease
with molecular weight, see Table 3, and it is recommended
to only use the “T” and “C” models if hydrogen is to be
used as the carrier gas.
All Clarus mass spectrometers use a single wide range
gauge (WRG) that operates using a combined Pirani/inverted
magnetron ionization sensor. The pressure reading of the
WRG is dependent on the type of gas pumped and is factory
set to operate with helium. Converting to hydrogen does not
require further actions, however, due to the relative molecular
mass (RMM) of hydrogen relative to helium the absolute
vacuum reading can be up to a factor of 2 off. In Figure 5 we
report vacuum readings relative to flow rate using the same
30 m x 0.25 mm x 0.25 μm column mentioned above. As
expected, as more gas is pushed into the mass spectrometer
the pressure increases. This effect is more drastic with
hydrogen due to the effects previously described. Even when
taking up to a factor of 2 difference in the reading, the level
of hydrogen raises rapidly relative to helium. Because of this,
higher flow rates combined with larger diameter columns are
not recommended for use with hydrogen.
30
Vacuum Reading (*e5)
25
20
15
Helium
Hydrogen
10
5
0
appropriate for their environment. Hydrogen cylinders
offer maintenance free operation but can be expensive
and in the event of release, can present a safety concern.
Hydrogen generators require regular upkeep but operate
at low pressures thus improving safety. Additionally, the
operation of the unit can be tied to the operation of the
GC/MS system so in the event of a loss of electrical power
or hardware failure, the generator can be automatically
shut off. The initial cost of a hydrogen generator must be
weighed against the both improved safety and long term
savings versus compressed gas cylinders.
Conclusion
1
1.5
2
2.5
3
3.5
4
4.5
5
Column Flow (mL/min)
Figure 5. Wide range gauge reading.
Table 3. Compression ratios of nitrogen, helium, and
hydrogen gas for the large capacity “T” and “C” model
turbomolecular pump.
Compound
Compression ratio
N 2
>1 x 1011
He
3 x 105
H 2
1 x 104
Sources of Hydrogen
In general, two sources of hydrogen are available – high
pressure gas cylinders and hydrogen generators. Both
sources have advantages and disadvantages and it falls
upon the laboratory manager to select the source most
The use of hydrogen as a carrier gas for GC/MS-based
experimentation offers many advantages in both cost
and performance yet does not come without risks. The
flammable nature of hydrogen presents researchers with
specific challenges, which when addressed using clear
planning and stringent standard operating procedures,
can be mitigated such that the safety of both laboratory
personnel and property can be reasonably assured. In all
cases a regular review of standard operating procedures
and a thorough chemical hygiene plan is required. While
the dangers of working with hydrogen can never be fully
eliminated, many inherently dangerous processes are already
commonly performed in lab operations, whose risks are
mitigated with the development and observance of well
thought out and implemented SOPs and chemical hygiene
plans.
Additional information available on the OSHA web site:
http://www.osha.gov. Keyword: Hydrogen.
PerkinElmer, Inc.
940 Winter Street
Waltham, MA 02451 USA
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com
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