Changing the Carrier Gas

Helium is normally used as the carrier gas for GCMS analysis. However, helium cannot be used in some situations; for those analyses, hydrogen can be used. Shimadzu's gas chromatograph mass spectrometers (GCMS) are compatible with hydrogen carrier gas, allowing hydrogen to be used as a carrier gas for the GC unit. Hydrogen gas (H2) is easier to obtain and less expensive than helium gas, and can maintain high separation performance for a given linear velocity. If used safely, it can also significantly reduce running costs. On the other hand, hydrogen is a dangerous gas that can easily explode. The following explains the risks, precautions, and other information about using hydrogen gas safely.

- Precautions for Using (Handling) Hydrogen Gas Safely

- Convenient Safety Features of Shimadzu Gas Chromatographs

Be sure to do the following when using hydrogen gas.

 

If a leak error occurs using an electronic flow controller and APC/AFC unit, even though the gas supply pressure is normal, stop using the system and request service from a Shimadzu representative. If no leaks are found, leakage does not stop, or normal performance is not restored after stopping the leak, stop using the system and request service from a Shimadzu representative.

 

Fully loosen the front door knob on the MS unit after a vacuum has been pulled. * When the system is under vacuum, the door will not open due to the pressure differential even if the knob is loosened.) Also, when the vacuum pump is not running, fully loosen the knob on the MS front door. Both actions help ensure hydrogen within the MS is vented more easily when the vacuum is released. Note: The GCMS-QP2050 Series does not have a knob on the MS front door.

Precautions for Using (Handling) Hydrogen Carrier Gas Safely

Hydrogen is a dangerous gas that can easily explode. A Safety Manual was prepared that lists the possible risks associated with using hydrogen gas in a gas chromatograph mass spectrometer and indicates considerations for ensuring the systems are used safely.

>> Using hydrogen carrier gas safely in GCMS-QP2010 series, GCMS-QP2020, and GCMS-TQ8030/8040 systems　 (228 KB)

* The same applies to the GCMS‑NX Series and the GCMS‑QP2050 Series. However, the GCMS‑QP2050 Series does not have a knob on the MS front door.
 

Considerations That Could Affect Analysis

It will increase noise in terms of sensitivity (S/N). For S/N values using hydrogen gas in respective systems, refer to product specifications. Equivalent separation results can be obtained by using an optimal column and creating a method. Most compounds can be analyzed, but hydrogen is not an inert gas, so it can dissociate at the injection port in some cases.

Carefully review the condition settings before switching the carrier gas to nitrogen.
Nitrogen gas (N2) is an inexpensive and safe gas. However, if nitrogen gas is used in a capillary GC system with the same analytical condition settings as for helium, then separation capabilities will decrease in most cases. If there are no adjacent peaks involved, then the carrier gas can be changed to nitrogen without changing the condition settings. If there are many adjacent component peaks and a certain level of separation is required, then the condition settings need to be reconsidered before using nitrogen gas.
Improving separation capabilities for nitrogen gas will require reconsidering the carrier gas linear velocity and temperature settings and will probably result in a longer analysis time. The vaporization state and detector sensitivity will probability change and the peak area percent might differ from when helium gas was used.

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.