There are several good reasons to use hydrogen as the carrier gas. Besides the lower cost and guaranteed availability it is one of the most easiest ways to reduce analysis time in GC, see Hydrogen as carrier gas: Always available, Cost effective and Fast.
The optimum velocity for hydrogen is about 2x higher then helium, meaning that analysis time can be reduced by a factor 2. This is valid for isothermal as well as temperature programmed separations. The only limiting factor is the heat rate of the oven as with a two-fold increase in carrier gas velocity, the temperature program also has to increase a factor 2 to get the same elution temperatures (and comparable chromatography).
A question that comes back several times: “can I use mass spectrometric detection when I operate my GC under hydrogen?”
For ion trap instruments, hydrogen cannot be used as these systems require helium. For the wider used quadrupole instruments, the answer may be different.
We asked the MS specialist of 3 leading instrument companies offering a series of MS detection systems. We were surprised by the difference in answers and how little data actually was available about this.
Company 1: There is absolute no problem. The only thing what may be seen are M+1 ions. 95% of NIST spectra are OK using hydrogen. If spectra are different one needs to built their own library. That is what many people also do with ion-trap systems that do not have external ionization.
Company 2: said there were no issues at all. You can use hydrogen without problems. They could not tell me any details;
Company 3: They did not recommend use of hydrogen for normal column dimensions as with a quadrupole MS, the higher H2 flow result in lower sensitivity. H2 will work OK if flow is 0.3-0.4 mL/min. They recommend to use 0.15/0.18mm columns with a linear velocity of 40cm/s; Also they said that H2 will cause hydrocarbons to be extracted from fitting/tubing etc and during a week, high hydrocarbon background is seen.. after that it’s ok
We also asked some specialists in the field about hydrogen and MS. One said its a big risk when power failure and H2 accumulates in the MS happens, ending up in a explosion. Hydrogen could also potentially cause activity development in the ion source;
Another user claimed he had difficulty with “tuning” the system. This may be related to high hydrogen flow as was also referred by company 3.
Other parameters to think about is that you need sufficient pump capacity as the flows will be 2x higher; Also the components will elute 2x faster, so the peaks are 2x narrower and to get sufficient data points, the MS needs sufficient data collection rate.
If you have any suggestions, experiences or comments on using Hydrogen with MS please share.
