These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Measurement of helium metastable atom densities in a plasma-based ambient ionization source.
    Author: Heywood MS, Taylor N, Farnsworth PB.
    Journal: Anal Chem; 2011 Sep 01; 83(17):6493-9. PubMed ID: 21744805.
    Abstract:
    We describe direct imaging of the densities of helium metastable atoms in the afterglow of a helium dielectric-barrier discharge (He-DBD) using collisionally assisted laser-induced fluorescence (LIF). For the conditions tested, comparison of fluorescence images of a He-DBD with analogous maps of emission from highly excited helium atoms revealed that helium metastable atom densities did not correlate well with emission from the plasma. Fluorescence images also showed that helium metastable atom densities increased substantially when a glass slide was placed 10.0 mm from the discharge capillary in a geometry typical for desorption-ionization experiments. We also studied the effect hydrogen has on the helium metastable atom densities. The hydrogen severely quenched the metastable state leaving it virtually undetectable. Emission was quenched as well, but to a lesser extent. The addition of 1% H(2) to the helium in the source provided nearly a factor of 2 improvement in the sensitivity of the signal for coumarin 47 when the plasma was used to ionize the dye under ambient conditions, despite the quenching of the helium metastable atom population.
    [Abstract] [Full Text] [Related] [New Search]