Experimental characterization of the effect of skimmer cone design on shock formation and ion transmission efficiency in the vacuum interface of an inductively coupled plasma mass spectrometer

Laser-induced fluorescence has been used to evaluate five commercially available skimmer cone designs from inductively coupled plasma mass spectrometers in terms of shock formation at the skimmer tip and transmission efficiency. Efficiency was measured as the ratio of analyte density downstream from the skimmer tip to analyte density upstream from the skimmer tip. The strongest shock was recorded for a skimmer with a cylindrical throat, and the weakest shock was produced by the skimmer with the largest diameter and a conical throat. Transmission efficiency increased with increasing orifice diameter. Coulombic effects, revealed in a comparison between the behaviors of neutral barium atoms and barium ions, were small. Transmission efficiencies recorded for calcium ions were lower than those recorded for barium ions by more than a factor of two.

► We examined the relationship between skimmer cone design and performance in ICP-MS.
► All five skimmer designs produced shocks at the skimmer tips.
► Shock formation was most pronounced for skimmers with cylindrical throats.
► Transmission efficiency was best for the skimmer with the largest orifice.
► Transmission efficiency for Ca ions was less than half that measured for Ba ions.