As helium costs rise and supply becomes unreliable, labs are reevaluating their carrier gas choices for gas chromatography (GC). Hydrogen offers a cost-effective, readily available alternative, yet switching gases introduces unique safety, performance and system challenges.
To ensure a smooth transition, it’s critical to understand how hydrogen behaves differently in GC systems and what adjustments are needed to maintain analytical quality. This guide addresses key considerations from equipment compatibility to method revalidation.
Download this guide to explore:
- How to prepare your system and ensure hydrogen safety
- Practical adjustments for columns, hardware and methods
- Strategies to handle changes in signal-to-noise and peak tailing
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7 Steps to changing carrier gas
from Helium to Hydrogen
www.peakscientific.com7 Steps to changing
carrier gas from
Helium to Hydrogen
Ed Connor Dr. Sc.
GC-MS Application Specialist
1. Gas Source
Helium is becoming increasingly expensive
with reports of its price having doubled in some
regions between 2013 and 2015. Added to its
increased price, supply cannot be ensured in
certain regions which is increasing the number
of labs looking to change to hydrogen.
Hydrogen generator: A hydrogen generator
providing carrier grade hydrogen (99.9999%)
such as the Peak Scientific Precision Hydrogen
Trace is recommended as a safe source of
hydrogen that will ensure prolonged column
life and the highest quality of analysis.
Supply tubing: Supply of hydrogen should
be provided through new stainless steel or
analytical grade copper tubing. It is important
to change the tubing that was previously used
to supply helium to the GC, since over time,
deposits can build up on the inside of the
tubing which hydrogen will strip out, causing
higher background signal for a longer period
of time.
2. Hydrogen Safety
Safe use of hydrogen: Since Hydrogen is an
explosive gas, it is essential that health and
safety in the lab is not compromised and
many labs will have restrictions on the use of
hydrogen cylinders in the lab.
LEL:The lower explosive level (LEL) of hydrogen
is 4% in air. Therefore a leak of hydrogen from
a cylinder containing around 8000L hydrogen
into a well vented laboratory has the potential
to reach the LEL very quickly without warning
and could create an explosive atmosphere.
Added to concerns about large gas leaks, is
the cumbersome nature of cylinders which
must be moved when replaced, again posing a
potential health and safety hazard.
Gas Generator: A Peak Scientific Precision
hydrogen generator is an ideal source of
hydrogen gas, capable of supplying multiple
GCs with UHP hydrogen for carrier gas and
detector gas, whilst containing a very low
volume of gas (less than 0.3L) at a low pressure.
Precision hydrogen generators have a number
of safety features that will detect any internal or
external leaks between the generator and GC
and will shut down the generator accordingly.
Leak detector: Peak also offer an in-oven
hydrogen detector that will shut down the
generator if a significant hydrogen leak is
detected within the GC oven.
3. Hardware
It is important to check the recommendations
from your GC manufacturer regarding use
of hydrogen carrier gas in your GC. Each
manufacturer will have tested their GCs for
use with hydrogen and may have specific
recommendations depending on the model
that you are using. Hardware changes, if
required, are most likely to need to be made
on GC-MS systems.
Vacuum Pump: If you are using a GC-MS, it is
important to ensure that your vacuum pump
is efficient enough to maintain the vacuum
in the source. Pumping efficiency is reduced
for lighter molecules, so check the guidelines
from your GC manufacturer to ensure that
your pumping system can cope with hydrogen
carrier gas. If you are purchasing a new GCMS system, make your supplier aware that you
plan to use hydrogen carrier gas so that the
correct vacuum pump is supplied.
Ion Source: Depending on the manufacturer
of your GC-MS, it is possible to get hydrogen
upgrade kits, or replacement components for
the ion source which will improve sensitivity
when using hydrogen carrier gas for analysis
of certain compounds. If you are purchasing
a new GC-MS system, consult your supplier
regarding which ion source will be supplied
with the GC-MS to avoid extra cost and
downtime at a later date.
4. Consumables
Column: For standard GC, there is very little
that needs to be changed when switching
from helium to hydrogen. By using a method
translation software, you can simulate the
effect of changing carrier gas on carrier gas
pressure and oven ramp rates so that you can
produce a revalidated method. Depending
on your GC method parameters, it may not
be necessary to change to a narrower bore
column, unless the inlet pressure becomesvery low in the translated method, however
there are benefits to using a narrow bore
column, which the properties of hydrogen
carrier gas facilitates. By moving to a narrower
bore column, the number of theoretical plates
is increased, giving potential for improved
efficiency and better sample separation.
Inlet: Inlet liners should be changed regularly
to ensure that the system stays free of
contaminants. When running samples with
hydrogen carrier gas, tapered liners are
recommended since these minimise contact
with the gold seal in GC systems that have a
gold seal.
Septa: Changing inlet septa is a routine part
of GC maintenance and should be conducted
regularly to avoid leaks in the system and
prevent contamination.
5. Method
It is essential to confirm that your method can
be used with hydrogen carrier gas. If you are
using any regulated methods (eg. EPA, ASTM),
first check what carrier gases are permitted.
If hydrogen is permitted, then research your
method(s) of interest to see whether there are
any application notes on this method?
Method translation software: Method
translation software is available from a variety
of sources and can be used to calculate GC
settings when using hydrogen carrier gas.
This will enable you to optimise your method
and explore column options prior to actually
setting the system up with hydrogen carrier
gas.
Use of chlorinated solvents: Formation of
hydrochloric acid (HCl) through reaction of Cl
and H2 is often cited as a potential problem
for GC and GC-MS when using hydrogen
carrier gas since HCl will damage the GC
system. Reactions between H2 carrier gas
and analytes or solvent will normally occur
in the inlet, so reducing the residence time of
your sample in the inlet is key. Use of pulsed
splitless or pulsed split injection can help with
reducing residence time of sample in the inlet,
reducing the opportunity for formation of HCl
or reactions between hydrogen and analytes
occurring.
Inlet temperature: Using the lowest inlet
temperature possible for the method will
reduce the potential for reactions between
solvents, analytes and hydrogen.
6. System setup
Column conditioning: When setting up a new
GC system with hydrogen carrier gas, you will
need to condition the column. Ensure that
the end of the column is outside the GC oven
when you condition the column to prevent a
build-up of hydrogen within the GC oven as
this could present a risk of explosion.
Ion source bakeout: If you are setting up a GCMS, it is common to see performance problems
when tuning the system, or running samples
shortly after setting up with hydrogen carrier
gas. This can be seen as high hydrocarbon-like
background and a high m/z 29 peak. Baking
out the ion source can quickly resolve these
issues, with background settling down after an
overnight back-out. Details of how to bake out
your MSD can be found manufacturers’ guides
and webinars covering use of GC-MS systems
with hydrogen carrier gas.
7. Performance checkout
Signal to noise: Signal to noise is often reduced
when comparing results of samples run with
helium compared with hydrogen (2-5 times
depending on the system). The reduction in
signal to noise can be improved by using SIM
detection on a single quadrupole system.
Fragmentation patterns: If ion ratios change,
it is likely that too much Hydrogen is present in
the ion source. This problem can be mitigated
by reducing the column ID and therefore
reducing the carrier gas flow rate, thus
reducing the volume of Hydrogen entering the
ion source.
Peak tailing: Polar components may suffer
more significantly from Peak tailing when
using hydrogen carrier gas. After baking out
the ion source, peak tailing should reduce and
will normally reduce for most compounds after
a few days.
Background: A few days following changing
carrier gas, the background signal should drop
to a consistent level.
Ed Connor Dr.Sc. is a GC-MS Application Specialist,
Peak Scientific, Inchinnan Business Park, Scotland,
UK . Prior to joining Peak, Ed completed his Dr.Sc. at
ETH Zurich in Switzerland using GC-MS to look at
herbivore induced plant volatiles and their interaction
with beneficial insects. He then joined the University
of Zurich where his work focused primarily on volatile
collection methods and analyses using GC-MS and GC-FID.www.peakscientific.com
Tel +44 141 812 8100 Email marketing@peakscientific.com
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