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Handle the Hassles of the Helium Shortage

Helium shortage FAQ

Two lab technicians working next to two helium tanks

Frequently asked questions

Why should hydrogen not be used as a carrier gas with a time-of-flight mass spectrometer?

The flight tube has a large volume and filling it with hydrogen is not safe.

Can I continue using copper tubing if I switch to hydrogen or nitrogen carrier gas?

Copper tubing can be used if you are using nitrogen or evaluating hydrogen as a carrier gas. However, before switching to hydrogen, it’s a good idea to use new tubing because hydrogen is a very efficient scrubber and will pick up any contaminants along the flow path, including tubing. This can lead to interferences or a noisy background. Inert GC components also should be used, and the system should be conditioned overnight.

Copper tubing can become brittle over time when using hydrogen as a carrier gas. So to avoid potential breaks, chromatographic-quality stainless steel tubing and fittings are recommended for long-term use.

Are there other considerations for using hydrogen carrier gas with GC/MS?

For Agilent GC/MS systems, the extractor, inert, and stainless steel EI sources all come standard with a 3-mm drawout lens (inert and stainless steel sources) or 3-mm extractor lens (extractor source). The 3-mm diameter works well with helium carrier gas but can cause problems when used with hydrogen. The most active area causing the in-source reactions (but not the only one) is metal around the aperture in the lens. Thus, expanding the aperture diameter to 9 mm significantly reduces the problems. Agilent offers both 6- and 9-mm lenses for this purpose. The 9-mm lens is recommended for most applications with hydrogen carrier gas, as it provides the best overall performance, balancing linearity, sensitivity, peak shape, and source reactivity. The 6-mm lens can be used if greater sensitivity is required, but it is best to start with the 9-mm lens first, as the 6-mm lens will have somewhat increased activity.

It is recommended to use the Agilent HydroInert source with a 9-mm lens for the 5977A/B/C GC/MSD or Agilent 7000C/D/E triple quadrupole GC/MS. Both 6-mm and 3-mm extractor lenses are available for the HydroInert source. These can be used to increase the signal-to-noise ratio of analytes, but at the cost of increased reactivity for some compounds.

If possible, use constant flow methods with GC/MS systems. Constant pressure methods with an oven temperature program have a negative impact on MS performance due to the changing flow into the source. Also, determine the hydrogen pumping capacity of the MS hardware. With diffusion pump systems, try to use flows in the range of 0.5 to 0.7 mL/min and for turbo pump systems, 0.5 to 2 mL/min.

When first converting a GC/MS method to hydrogen carrier gas, significant peak tailing is possible. To avoid this, the source should be conditioned overnight. For a detailed procedure, see page 30 in the Agilent EI GC/MS Instrument Helium to Hydrogen Carrier Gas Conversion user guide.

If I switch to hydrogen carrier gas, should I use gas cylinders or a gas generator?

Either can be used as long as they deliver ultra-high purity hydrogen.

Cylinders are often less expensive initially. If you are evaluating hydrogen as a carrier gas for the first time and are not certain you will be adopting it for routine use, cylinders may be the simpler option. Make sure to obtain hydrogen with a purity specification of 99.9999% or greater and with low oxygen and water levels. Also, use a cylinder regulator designed for use with high purity hydrogen applications. Consult your gas supplier for selecting an appropriate regulator.

Hydrogen generators are another option for providing hydrogen carrier gas. They typically have a higher initial cost than cylinders but can be more economical over time. Only those with a purity specification of 99.9999% or greater and with low oxygen and water levels should be considered. When selecting a hydrogen generator, make sure the maximum delivery pressure and flow rate are high enough to meet the needs of your chromatographic methods and all the simultaneously operating instruments that will be supplied by the hydrogen generator. Hydrogen generators offer some useful safety features:

  • Hydrogen is only generated at the needed pressure (for example, 40 psi)
  • Maximum flow is limited (for example, 250 mL/min)
  • Automatic shutdown if the setpoint pressure cannot be maintained
  • Minimal stored gas (for example, 50 mL at 40 psi) of hydrogen at any given time

How do I find leaks in the GC or GC/MS flow path?

A pressure-drop test can determine if there are any leaks in the gas supply between the tank and the back of the GC. First, start with a pressurized line. Then, turn off the GC; this will close all the proportional valves on the back of the instrument (older GCs will benefit from an isolation valve on the gas line). Set the regulator pressure to 60 psi, fully close the regulator pressure adjustment valve, and wait 10 minutes. If the pressure on the regulator drops even 1 psi, there is a leak—if it drops more than that, there is a significant leak. With the latest Agilent intelligent GCs, there is an automated diagnostic function that is user-initiated or performed every injection to check for leaks within the GC.

If a leak is found, the next step is to determine where the leak is originating.

  • The Agilent GC leak detector can detect helium and hydrogen. It does not work well for detecting small nitrogen leaks because it cannot differentiate between a leak and the nitrogen naturally present in the air.
  • A liquid leak detector, which works for all gases, can be used to check tube fittings. When a leak is present, bubbles form in the liquid. Though Snoop has been used often in the past, it is not recommended for newer GCs with modern electronic pressure control. Instead, use a 50/50 mixture of isopropanol and water.
  • The Agilent 7000E or 7010C triple quadrupole GC/MS has convenient capabilities in MassHunter Acquisition 10.2 software to assist in leak checking. The Leak Test tool helps users to easily find the source of leaks in real time. Users can manually input up to 10 ions to monitor while testing the spots prone to leaks in the GC flow path and in the TQ. This functionality makes using an air duster for leak tests simple and quick.

Will I have to use a GC column with different dimensions when switching carrier gas?

Possibly, although it is less likely with GC than GC/MS. Because hydrogen is not as viscous as helium, the inlet pressure to obtain the same flow rate is significantly lower. Column dimensions and flow setpoints must be chosen that maintain adequate inlet pressures, preferably 5 psi or greater, to permit precise control of column flow and retention times. Sub-ambient inlet pressures must be strictly avoided as these can cause inlet flow shutdowns and may damage inlet liners and columns due to air being drawn into the system.

Options to address low inlet pressure include longer columns with the same internal diameter (which offer better separation and capacity but result in longer run times) or shorter columns with smaller internal diameters (which may require smaller injection volumes due to reduced column capacity but may provide better separation and/or reduced analysis times).

The method translator software and pressure flow calculator are useful tools to help choose acceptable column dimensions and operating conditions when switching from helium to an alternative carrier gas under atmospheric conditions (GC detectors) and vacuum (mass spectrometers).

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