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Helium to Hydrogen - A Change Would Do You Good
Change is always a scary concept but let us dispel some of the fear associated with changing your helium carrier gas to hydrogen by answering some of the most common questions posed to us. John V. Hinshaw, our GC department editor has written a comprehensive article answering the questions below in great detail. Here, we have highlighted the key points to help get you started. (For a more in depth discussion the full article can be read here »).
Hydrogen carrier gas has many advantages over helium or nitrogen. Higher plate numbers can be achieved at high linear velocities as well as being able to achieve higher linear velocities while utilising lower pressures. Extra hydrogen in the system may; however, affect detectors that use hydrogen fuel gas (in this instance, FID) and MS detectors.
Does hydrogen carrier gas affect retention times?
Yes and no. As linear velocity increases, isothermal retention times decrease in exact proportion, so doubling the velocity will reduce retention times by half. Three particular situations that need to be considered are:
For temperature programming:
How can I manage hydrogen fuel flow in my flame ionisation detector with hydrogen carrier gas?
The simple answer is to reduce the hydrogen fuel gas flow so that the total hydrogen flow through the detector remains close to the manufacturer’s specified optimum flow – usually between 40 – 50 cm3/min. If the column oven temperature drops during the run the flow rate may decrease. With narrow bore columns this may be small enough that the ionization detector will remain within the optimum range, however, with wide bore columns the FID sensitivity may be significantly affected. Electronic pneumatics can be used to overcome this problem, by maintaining a constant total flow of hydrogen through the detector.
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