Introduction
Carrier gas for gas chromatography (GC) should be an inert gas that does not react with the sample component. Its main role is to transport the vaporized solute molecules through the column. The selection of the carrier gas and the linear velocity it uses both affect resolution and retention times.
Nitrogen, hydrogen, and helium are the most widely used gases by today’s chromatographer. Each has unique benefits as well as drawbacks. Nitrogen shows the best efficiency, but over a low and narrow linear velocity range. Therefore, it is extremely slow as a carrier gas, and not a great choice for temperature-programmed use. Hydrogen provides the fastest analysis time over a broad linear velocity range. However, safety concerns must be addressed. Helium is a compromise between nitrogen and hydrogen, with regards to efficiency and analysis times. However, it is becoming an expensive choice for a carrier gas.Let’s take a look and compare the advantages of using hydrogen over helium.
Benefits of Hydrogen as a Carrier Gas: Speed 1
The Golay Theory for open tubular columns predicts that optimum gas velocity is proportional to diffusivity. Hydrogen has a higher diffusivity than helium, thus its optimum linear velocity is higher and can be used at a higher flow rate without adversely affecting efficiency. Specifically, under isothermal analysis conditions, the typical linear velocity for hydrogen is 40 cm/sec, which is twice the optimum linear velocity of helium at 20 cm/sec. Therefore, simply switching to hydrogen carrier gas, even while keeping column dimensions and oven conditions constant, can be expected to decrease analysis time.
Figures 1and2illustrate this benefit of hydrogen with the separation of 16 commonly analyzed polynuclear aromatic hydrocarbons. The analysis was performed on a 15 m x 0.10 mm I.D., 0.10 μm Equity®-5 column. A fast temperature-programming rate was used to decrease the run time to less than 12 minutes using helium at its optimal linear velocity. Switching to hydrogen carrier gas (at its optimal linear velocity) under the same conditions resulted in a 25% decrease in run time.
Benefits of Hydrogen as a Carrier Gas: Speed 2
What if carrier gas is run at higher than optimal linear velocity to decrease analysis times? Hydrogen, having a flatter Golay curve, may be operated over a wide range of linear velocities while maintaining a low height equivalent to a theoretical plate (HETP). This allows the use of a linear velocity higher than optimal with little decrease in efficiency, resulting in shorter analysis times.
Benefits of Hydrogen as a Carrier Gas: Cost 1
A shortage of helium began surfacing in 2006. Helium must be extracted from the ground and then refined. However, there are not enough refineries to keep up with the increased demand, such as for applications in the medical, scientific, and industrial fields. As a result, helium is becoming a rare commodity with rising prices. Hydrogen has not seen a drastic rise in price because its production is not dependent on the same factors.
Benefits of Hydrogen as a Carrier Gas: Cost 2/Safety
Because helium generators are not available, it can only be obtained in expensive cylinders. Hydrogen is also available in cylinders, but can also be generated ondemand on-site using a gas generator. In addition to being a much more sensible source of gas from a cost standpoint, generators are safer, more aesthetically pleasing, take up less space, and do not require the labor needed to move bulky cylinders around the lab. The safety benefit of a hydrogen generator over a cylinder is due to the fact that a minimal volume of hydrogen gas is stored at a relatively low pressure.
Conclusion
Hydrogen has several features (higher optimal linear velocity, and flatter Golay curve) that result in desirable benefits (decreased analysis times) when compared to other GC carrier gas choices. If operating exactly at optimal linear velocities, hydrogen results in a faster analysis time. Because hydrogen has the flattest Golay curve, the GC can be operated with an even higher linear velocity without a significant loss in efficiency. As long as the proper safety controls are in place, hydrogen, with its broad working range, may be a more suitable carrier gas choice for capillary GC.
FAQs
Hydrogen has the lowest viscosity of all gases, thereby provides the highest mobile phase velocity and therefore the shortest analysis time. Helium, on the other hand, gives the best overall performance and peak resolutions for many applications, making it an optimum choice of carrier gas in those cases.
Is hydrogen a better carrier gas than helium? ›
Benefits of Hydrogen as a Carrier Gas: Speed 1
Hydrogen has a higher diffusivity than helium, thus its optimum linear velocity is higher and can be used at a higher flow rate without adversely affecting efficiency.
Can hydrogen be used as a carrier gas? ›
Hydrogen is the fastest carrier gas (uopt), with an optimum linear velocity of 40cm/sec, and exhibits the flattest Van Deemter profile. Hydrogen's high uopt (optimal linear velocity) results in the shortest analysis times.
What is the alternative to helium gas? ›
Argon can be used instead of Helium and is favoured for some metals. Helium is used for many lighter-than-air applications, and Hydrogen is a possible substitute for many where the flammability of Hydrogen is not a concern.
Can hydrogen used as carrier gas in FID? ›
Commonly used and popular carrier gases include helium, hydrogen, and nitrogen, although argon, ammonia, and carbon dioxide also have been used to a minor extent. Also, hydrogen has long been used as a fuel gas for flame ionization detection (FID) as well as other detection methods in GC.
Why don't we use hydrogen instead of helium? ›
Hydrogen is lighter than air but it is flammable and as oxygen is present in the air, so the risk of explosion and fire is there. Helium is lighter than air and it is a non-combustible gas so it used to fill balloons.
Why is hydrogen not preferred as a carrier gas? ›
Hydrogen is considered the optimal choice, combining high efficiency separations with short analysis times. However, hydrogen has a safety risk with a 4% concentration in air will lead to explosions. To date, the worldwide carrier gas of choice has been the second most efficient gas; helium.
What are the disadvantages of hydrogen as a carrier gas? ›
However, migrating to carrier hydrogen for GC and GC-MS applications also has some drawbacks, or at least it requires precautions and method optimization. The main concern is safety, as hydrogen is flammable and explosive.
Why helium is not used as carrier gas? ›
Helium is a preferred carrier gas due to its high inertness and good separation abilities. However, it is a limited natural resource, and demand has been rapidly increasing for use in ever more applications in the medical, scientific, and industrial fields.
What is the best carrier gas for GC? ›
Helium and nitrogen are most commonly used and the use of helium is desirable when using a capillary column. Although expensive, it is safe and has a relatively wide optimum linear velocity range.
Although both gases have lightweight natures, hydrogen offers many benefits over helium. Hydrogen is better if you require a more substantial lift for your balloons as it is lighter than helium. It is also much easier to make than helium, making it the cheaper solution to your balloon needs.
Why is helium being banned? ›
Another reason for a ban calling to end all helium balloons is that the gas, helium, is becoming scare. Once it is used up, there is no way to create more helium. It is a non-renewable resource. Many feel that the remaining Earth's helium should be used for more important uses, industrial, medical and scientific.
Which is cheaper hydrogen or helium? ›
Simply because Hydrogen gas is lighter than air, cheaper than Helium and suppliers use this to make some money.
What is the best carrier for hydrogen? ›
Hydrogen pipelines and trucks are the best solutions for transport over smaller distances. However, when quantities or distances become greater, other techniques are needed. Three energy carriers that can make this transport possible are ammonia, LOHCs, and liquid hydrogen.
Why is hydrogen used as a carrier of energy? ›
Hydrogen as an Energy Carrier
Because hydrogen typically does not exist freely in nature and is produced from other sources of energy, it is known as an energy carrier. It is a clean-burning fuel, and when combined with oxygen in a fuel cell, hydrogen produces heat and electricity with only water vapor as a by-product.
Is hydrogen a carrier gas in GC MS? ›
Hydrogen as a carrier gas in GC/MS is a low-cost, renewable gas suitable for several GC/MS applications. Hydrogen carried gas is commonly used as an alternative option to helium.
Why is hydrogen better than helium? ›
Hydrogen spreads quicker in a given volume because of its high molecular velocity • It finds and passes through leaks faster • It is easier to flush out and vent away and therefore gives less background interference. Hydrogen molecules do not stick to surfaces as easily as Helium atoms.
What is the best carrier gas? ›
Helium (He), nitrogen (N2), hydrogen (H2), and argon (Ar) are often used. Helium and nitrogen are most commonly used and the use of helium is desirable when using a capillary column. Although expensive, it is safe and has a relatively wide optimum linear velocity range.
