Chromatography Techniques » June 2013 CT12
Hydrogen Facilitates Faster, Safer GC Runs
As helium becomes a rarer resource for gas chromatography practitioners, hydrogen is filling the void
as a viable alternative that can offer superior results.
The most common carrier gas used for gas chro- matography (GC) in the U.S. is helium. But because of dwindling supplies, costs are rising and delivery delays are
increasing. Chromatographers are increasingly choosing to switch to hydrogen, a gas
easily and inexpensively produced safely
through an on-site generator.
Helium has always been a prized
resource, sealed in caverns to create the
Helium National Reserves in the 1920s.
Helium is a byproduct of the petrochemical industry, which discovers pockets of the
gas during oil drilling (the gas is produced
on Earth when radioactive elements decay deep
underground). It can also be refined when methane
is super-cooled. The U.S. government began privatiz-ing helium reserves in 1996. The Bureau of Land Management
estimates that 16.2 billion scf, or around 60 percent of national reserves, have
now been sold. This year, legislation is being drafted that would reduce the
availability of reserve helium after 2014.
At the same time, helium mining is suffering. Natural gas found in shale
rock is fast becoming the number one source of fossil fuel in the U.S. over
oil, but helium cannot be collected from mining porous
shale rock. As more shale gas is collected, less helium
is being found and mined by the petrochemical
industry. Between 2008 and 2012, U.S. helium
production fell by more than 6 percent,
according to the U.S. Geological Survey.
In 1996, helium was priced at around
$40/1000 scf. But, because of increasing
demand and dwindling supply, helium prices
rose to $170/1000 scf in January 2013, its
highest rate since reserves were released.
Helium continues to be in demand by
various industries. Worldwide consumption
rose 3.6 percent per year between 1990 and 2008,
from 3.28 billion scf to 6.3 billion scf, according to
the National Research Council. Some of this increase
is because of an increase in semiconductor production
and the use of more than 22,000 MRI machines globally, where
helium is used exclusively with no alternative. These, and the analytical appli-
cations that require the gas, such as gas chromatography mass spectrometry
(GCMS), are growing each year. Gas importers predict helium gas prices
could now rise by 20 percent per year, every year.
For life-saving applications, helium will still be delivered on time. But for
many laboratories further down the waiting list, it will become harder to
maintain regular, inexpensive helium deliveries. Labs will have to consider
alternative plans to maintain their operations.
Luckily for GCMS practitioners, hydrogen gas is an abundant, less
expensive alternative carrier gas that produces superior results.
» by John Speranza, Vice President of Global Hydrogen Sales, Proton OnSite, Wallingford, Conn.
Figure 1: The van Deemter Curve shows variance per unit length of a separation column to the linear mobile phase velocity by considering physical,
kinetic and thermodynamic properties of a separation.
Hydrogen is the most efficient carrier gas for GC applications thanks to
its unique properties. Using the van Deemter equation, which predicts an
optimum velocity at which there will be the minimum variance per unit
column length and, therefore a maximum efficiency, it can deduced that
the linear flow rate of hydrogen can be greater than that of helium but also
offer equal efficiency in the gas’s ability to separate peaks.
The traditional GC run using helium is between 140 and 160 minutes.
By using high-efficiency, smaller helium columns, GC practitioners can
reduce a run to 75 minutes. But by switching to hydrogen, the optimum
linear velocity of which is approximately 40 cm/sec, GC practitioners have
experienced run times as little as 40 minutes without adversely affecting
peak separation performance.
Hydrogen also produces more efficient results than helium with less
maintenance. Viscosity is determined by the molecular weight of the gas
and its temperature. Hydrogen’s viscosity is influenced less by temperature