Nitrogen and hydrogen as carrier and make‐up gases for GC‐MS with Cold EI

Abstract

Gas chromatography–mass spectrometry (GC‐MS) with Cold EI is based on interfacing GC and MS with a supersonic molecular beam (SMB) and sample compounds ionization with a fly‐through ion source as vibrationally cold compounds in the SMB (hence the name Cold EI). We explored the use of nitrogen and hydrogen as carrier and make‐up gases with Cold EI and found: Nitrogen is very effective in cooling compounds in SMB and while helium requires 60 ml/min nitrogen provides effective cooling with only 7–8 ml/min combined column and make‐up flow rate. Hydrogen is less effective than helium and requires higher flow rates. The transition from helium to nitrogen (or hydrogen) is simple and fast and requires just closing the helium valve and opening the nitrogen valve. The same column used with helium can be used with nitrogen or hydrogen. The same elution times could be obtained with nitrogen or hydrogen as with helium. The GC separation with nitrogen was reduced compared with helium and peak widths were increased by an average factor of 1.5 for similar elution times. Hydrogen provided ~0.7 narrower peak widths than helium. The signal with nitrogen was reduced compared with helium by an average factor of 3.3 and the signal loss was reduced with higher compounds mass. With hydrogen the signal loss was about a factor of 1.5 but the baseline noise was higher thus with similar S/N as with nitrogen. USEPA 8270 semivolatile mixture was easily analyzed with both nitrogen and hydrogen carrier gases.

Beyond helium: hydrogen as a carrier gas in multiresidue pesticide analysis in fruits and vegetables by GC-MS/MS

“…In addition, there is a noticeable sensitivity reduction since the ionization yield is approximately nine times higher than of helium. 5 However, it has demonstrated to be an alternative to helium for the analysis of petroleum biomarkers 6 and pesticides using atmospheric pressure chemical ionization (APCI). 7 Hydrogen has the higher diffusion coefficient of the carrier gases used in GC-MS and about half the viscosity of helium and nitrogen.…”

Comprehensive Controller for Super Sonic Molecular Beam Gas Chromatograph Mass Spectrometer

“…GC-MS with Cold EI improves all the central performance aspects of GC-MS and uniquely provides enhanced molecular ions, improved sample identification, significantly extended range of compounds amenable for analysis, uniform response to all analytes (internal quantitation), faster analysis, greater selectivity, and lower limits of detection [25][26][27][28][29][30][31][32][33].…”

“…The molecular ion is the most (and many times the only) characteristic ion as the fragmentation pattern can be similar for many compounds, and therefore it is often vital for sample compound identification. GC-MS with Cold EI improves all the central performance aspects of GC-MS and uniquely provides enhanced molecular ions, improved sample identification, significantly extended range of compounds amenable for analysis, uniform response to all analytes (internal quantitation), faster analysis, greater selectivity, and lower limits of detection [25][26][27][28][29][30][31][32][33].…”