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Gas chromatography (GC) uses a wide range of gases including helium, hydrogen, and nitrogen as the carrier gas. The most common carrier gas is helium. In recent years, however, the availability of helium has decreased and its cost has increased significantly. As a result, many chromatographers are now switching to hydrogen as a GC carrier gas.

The availability of helium

Helium is a minor component of natural gas formed by the natural breakdown of uranium. Fractional distillation of natural gas allows for the purification of helium from the natural gas. Many users worry about the future availability of this non-renewable natural resource.

For information on how to switch from helium to hydrogen as a GC carrier gas, download this easy to use, step by step guide.

Aug 25, 2017 Helium and hydrogen are chemical elements that are mostly found in the atmosphere as gaseous substances due to their very low melting and boiling temperatures. The main difference between Helium and hydrogen is that helium atom exists as a monoatomic gas in the atmosphere whereas hydrogen exists as a diatomic gas in the atmosphere. Hydrogen Molecule Ion Up: Variational Methods Previous: Variational Principle Helium Atom A helium atom consists of a nucleus of charge surrounded by two.

Benefits of hydrogen over helium

Hydrogen offers several advantages over helium as a carrier gas including:

• Increased speed: Increasing the linear flow rate allows for shorter run times, thereby increasing the throughput of a laboratory.
• Achieve lower temperature separations: At the faster elution times, it may not be necessary to increase the column temperature run rate. It is possible to lower the maximum temperature needed for the analysis or remain at those temperatures for shorter periods.
• Longer column life: Lower temperatures lead to less column bleed resulting in longer column life. Hydrogen is a reducing gas and can remove potential acidic sites inside of the column. The removal of these sites leads to less sample absorption and less generation of phase breakdown (column bleed). The result is a longer usable life for the column.
• Environmental concerns: Helium is a by-product of natural gas or petroleum production and there are environmental concerns with the production and purification of the gas. Hydrogen is a green gas in that its production does not contribute to environmental pollution.
• Cost savings: The cost of hydrogen is significantly lower than that of helium.
• Availability: Since hydrogen is generated from the electrolysis of water, there is no need to worry about availability
  

Sources of hydrogen

Hydrogen can be obtained in the form of cylinders or from an on-site hydrogen generator.

Advantages of a hydrogen generator

• Safety: Eliminates the dangers of handling and storing high-pressure hydrogen cylinders. A Parker hydrogen generator contains only 50 ml of stored gas, so there is no large volume of gas that could potentially vent and cause an explosion or asphyxiation. In fact, all Parker hydrogen generators are equipped with automatic shutdown on leak detection and meet NFPA requirements and OSHA 1910.103 regulations governing the storage of hydrogen.
• Convenience: A hydrogen generator will produce a continuous supply of high purity hydrogen, eliminating the need to interrupt important analysis to change cylinders. There is no need to rely on outside vendors. Concerns over uncontrollable price increases, contract negotiations, long-term commitments, and tank rentals are eliminated.
• Space-saving design: A hydrogen generator frees-up valuable laboratory floor space. The compact design only takes up one square foot of bench space.
• Consistent purity: High purity hydrogen is required for carrier gas applications. Contaminant levels can vary from cylinder to cylinder which can affect sensitive analyses. A hydrogen generator will produce a consistent supply of high purity hydrogen on demand. Also, cylinders are often located a distance from the instrument - requiring long gas lines. Gas lines must be checked regularly for leaks. Leaks allow gas to escape and impurities to enter the gas supply which reduces purity and affects the accuracy of analysis. A hydrogen generator, on the other hand, can be placed next to the instrument it is servicing.
• Cost savings: When compared to the total costs associated with cylinders, a Parker hydrogen generator will pay for itself in one or two years.

For information on how to switch from helium to hydrogen as a GC carrier gas, download this easy to use, step by step guide.

This post was contributed by the Gas Generation Technology Blog Team - Parker Industrial Gas Filtration & Generation Division.

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Next:Hydrogen Molecule Ion Up:Variational Methods Previous:Variational Principle
A helium atom consists of a nucleus of charge surroundedby two electrons. Let us attempt to calculate its ground-state energy.

Let the nucleus lie at the origin of our coordinatesystem, and let the position vectors of the two electrons be and , respectively. The Hamiltonian of the system thustakes the form

where we have neglected any reduced mass effects.The terms in the above expression represent the kinetic energy of the firstelectron, the kinetic energy of the second electron, the electrostaticattraction between the nucleus and the first electron, the electrostaticattraction between the nucleus and the second electron, and theelectrostatic repulsion between the two electrons, respectively.It is the final term which causes all of the difficulties. Indeed, if thisterm is neglected then we can write

(1181)

Helium Hydrogen And Oxygen Are Examples Of

where
In other words, the Hamiltonian just becomes the sum of separate Hamiltonians for each electron. In this case, we would expect thewavefunction to be separable: i.e.,

(1183)

Hence, Schrödinger's equation
reduces to

(1185)

where
Of course, Eq. (1185) is the Schrödinger equation of a hydrogen atom whosenuclear charge is , instead of . It follows, from Sect. 9.4 (making the substitution ), that if both electrons are in their lowest energystates then

(1187)

(1188)

where
Here, is the Bohr radius [see Eq. (679)]. Note that is properly normalized. Furthermore,

(1190)

where is the hydrogen ground-stateenergy [see Eq. (678)]. Thus, our crude estimatefor the ground-state energy of helium becomes
Unfortunately, this estimate is significantly different from the experimentallydetermined value, which is . This factdemonstrates that the neglected electron-electron repulsion term makes alarge contribution to the helium ground-state energy.Fortunately, however, we can use the variational principle to estimate this contribution.

Let us employ the separable wavefunction discussed above as our trialsolution. Thus,

(1192)

The expectation value of the Hamiltonian (1180) thus becomes
where

(1194)

The variation principle only guarantees that (1193) yields anupper bound on the ground-state energy. In reality, we hopethat it will give a reasonably accurate estimate of this energy.

It follows from Eqs. (678), (1192) and (1194) that

where . Neglecting the hats, for the sake of clarity, the aboveexpression can also be written

(1196)

where is the angle subtended between vectors and .If we perform the integral in space before that in space then
where

(1198)

Our first task is to evaluate the function . Let be a set of spherical polar coordinates in space whose axis of symmetry runs in the direction of . It followsthat . Hence,

which trivially reduces to

(1200)

Making the substitution , we can see that
Now,

(1202)

giving
But,

(1204)

(1205)

yielding

Since the function only depends on the magnitude of ,the integral (1197) reduces to

(1207)

which yields
Hence, from (1193), our estimate for the ground-stateenergy of helium is

(1209)

This is remarkably close to the correct result.

We can actually refine our estimate further. The trial wavefunction (1192) essentially treats the two electrons as non-interacting particles. Inreality, we would expect one electron to partially shield the nuclearcharge from the other, and vice versa. Hence, a bettertrial wavefunction might be

where is effective nuclear charge number seen by eachelectron. Let us recalculate the ground-state energy of heliumas a function of , using the above trial wavefunction, and thenminimize the result with respect to . According tothe variational principle, this should give us an even better estimatefor the ground-state energy.

We can rewrite the expression (1180) for the Hamiltonianof the helium atom in the form

(1211)

where
is the Hamiltonian of a hydrogen atom with nuclear charge ,

(1213)

is the electron-electron repulsion term, and
It follows that

(1215)

where is the ground-state energy of a hydrogenatom with nuclear charge , is the value of the electron-electron repulsion term whenrecalculated with the wavefunction (1210) [actually, all weneed to do is to make the substitution ], and

Helium Hydrogen Balloon

Here, is the expectation value of calculatedfor a hydrogen atom with nuclear charge . It follows fromEq. (695) [with , and making the substitution ] that

(1217)

Hence,
since . Collecting the various terms, our new expression for the expectationvalue of the Hamiltonian becomes

Compare Hydrogen And Helium

Sun Helium Hydrogen

(1219)

The value of which minimizes this expression is the root of

Helium Hydrogen Compound

It follows that

(1221)

The fact that confirms our earlier conjecture that the electrons partiallyshield the nuclear charge from one another. Our new estimatefor the ground-state energy of helium is
This is clearly an improvement on our previous estimate (1209) [recall that thecorrect result is eV].

Obviously, we could get even closer to the correct value of thehelium ground-state energy by using amore complicated trial wavefunction with more adjustable parameters.

Note, finally, that since the two electrons in a helium atom are indistinguishable fermions, the overall wavefunction must be anti-symmetric with respect to exchange of particles (see Sect. 6).Now, the overall wavefunction is the product of the spatial wavefunctionand the spinor representing the spin-state. Our spatial wavefunction (1210) is obviously symmetric with respect to exchange ofparticles. This means that the spinor must be anti-symmetric. It is clear, from Sect. 11.4, that if the spin-state ofan system consisting of two spin one-half particles (i.e., two electrons)is anti-symmetric with respect to interchange of particles then the system isin the so-called singlet state with overall spin zero. Hence,the ground-state of helium has overall electron spin zero.

Next:Hydrogen Molecule Ion Up:Variational Methods Previous:Variational PrincipleRichard Fitzpatrick2010-07-20