Measures and Proposals to Reduce Helium Gas Consumption
There is an increased focus on lowering running costs and reducing the burden on the environment. Helium gas (He) is a precious resource and must be used carefully by consuming as little of it as possible. Here, we introduce functions to reduce the rate of helium gas consumption and describe important precautions when switching to another carrier gas.
Saving Helium Gas during Analysis (Carrier Gas Saver Mode)
High-concentration target samples are analyzed using a large split ratio in order to reduce the amount of sample introduced into the column. However, during normal GC analysis it is not necessary to maintain the large split ratio throughout the entire analysis time, as the sample is vaporized immediately after injection and then transported by the carrier gas.
The carrier gas saver mode changes the split ratio at a specified time after sample injection to reduce helium gas consumption. This function is introduced here.
The carrier gas saver mode is offered as standard with Nexis GC-2030，GC-2010 Plus，GC-2025，GC-2014.
In this example, the carrier gas saver mode reduces the split flow rate from 175 mL/minute to 25 mL/minute one minute after the sample is injected. When an autoinjector is used, the reduced split flow rate is maintained throughout the analytical run and until analysis starts the next day. This function reduces helium gas consumption by approximately 83 % per analysis under the conditions below. Analysis time: 30 minutes, Split ratio: 100 Carrier gas saver function: Split ratio 15 after 1 minute Column temperature: 100 °C Column: Inner diameter 0.25 mm, length 30 m, thickness 0.25 μm
Changing to Hydrogen Carrier Gas
Compared to helium gas, hydrogen (H2) gas is easier to obtain, cheaper, and maintains separation performance with respect to linear velocity. As long as attention is paid to the safety, using hydrogen can also significantly reduce running costs. The Shimadzu Nexis GC-2030，GC-2010 Plus，GC-2025，GC-2014 offer a function that automatically stops the carrier gas. The AFC electronic flow controller controls the carrier gas flow rate. If the column inlet pressure or total flow rate does not reach the set value under the prescribed conditions, the AFC deems that a problem, such as a major gas leak, has occurred and automatically stops the carrier gas flow and GC operation. Nexis GC-2030，GC-2010 Plus，GC-2025 also feature an APC electronic flow controller for the gas flow rate detector. The APC automatically shuts off the hydrogen gas if there is a power failure.
Using a Safe Hydrogen Gas Supply and/ or Hydrogen Gas Generator Are Recommended
A hydrogen gas generator is far safer than gas cylinders. As the hydrogen gas is generated by the electrolysis of water, the gas flow rate cannot exceed a certain level even if a gas leak occurs. Using a hydrogen gas generator eliminates the need for dangerous and expensive hydrogen cylinders.
Using Hydrogen Gas Safely(Precautions)
Hydrogen is a dangerous gas that readily explodes. The potential dangers and precautions that must be followed are summarized on a separate page. (Click the link below.)
Using Hydrogen Gas Safely(Precautions)
Changing to Nitrogen Carrier Gas
Nitrogen (N2) gas is a safe and cheap gas; however,separation performance usually deteriorates when nitrogen gas is used for analysis in a capillary GC under the same conditions as helium gas. Nitrogen carrier gas can be used under the same conditions as helium gas when no nearby peaks exist. If many nearby components do exist and fine separation is required, the appropriate conditions must be determined for nitrogen gas.
To improve the separation performance with nitrogen gas, the carrier gas linear velocity and the temperature conditions must be investigated. Longer analysis times are likely to result. The vaporization state and detection sensitivity will probably change slightly and the area percentage may differ from when helium gas is used. Carefully investigate the analysis conditions when changing the carrier gas to nitrogen.
Separation with Helium Gas and Nitrogen Gas
Separation examples for helium and nitrogen gases at different linear velocities are shown below.
Using helium gas, the separation is virtually unchanged across the range from 20 to 47 cm/s linear velocity. With nitrogen gas, however, the separation deteriorates at 47 cm/s linear velocity. This occurs because the optimal linear velocity for separation is lower with nitrogen than with helium and the optimal linear velocity range for nitrogen is narrower than for helium.
Changing the Split Ratio during Analysis Using the Carrier Gas Saver Mode This section introduces the carrier gas saver mode that changes the split ratio a specified time after sample injection to reduce the consumption of helium gas.
1. Read the method file
In the [GC Real Time Analysis] window, select [Open Method File] in the [File] menu. If no method file exists, create a new one.
2. Set the carrier gas saver mode
Double-click the [SPL] tab (1) in the [GC Real Time Analysis] window to show the settings for [ Injection Unit ] Tab
Click the [Advanced] button (2) in this tab page to open the [SPL Advanced] dialog box.
Select the [Carrier Gas Saver] checkbox (3) in the [SPL Advanced] dialog box to enable the carrier gas saver mode.
In the [Split Ratio] field (4), enter the split ratio to use in the carrier gas saver mode. (Set a lower split ratio than the one used during analysis.)
In the [Time] field (4), enter the time at which the split ratio changes.
The split ratio set for the carrier gas saver mode takes priority over the split ratio set in the program. After the set time elapses, the split ratio for the carrier gas saver mode remains set.
Click the [Set] button (5) to complete the settings.
3. Save the method file
In the menu bar, select [File] → [Save Method File As]. Enter the name of the method file and save it.