Sub-atmospheric pressure laser ionization source using an ion funnel

A method for sample analysis utilizing a laser ionization source operated at a sub-atmospheric pressure range and a spectrometer, comprising:

• placing a sample containing analyte molecules on a holder;
• generating ionized species from said sample using a laser ionization technique;
• extracting analyte ions from said ionized species by an extraction electric field Es near the sample;
• directing the extracted analyte ions into an ion funnel structure having an entrance and an exit, the structure being comprising orifice electrodes each having an aperture through which an ion funnel pathway extends in an ion funnel pathway direction, said structure having an entrance electrode having an aperture with size D and an exit electrode, sizes of apertures generally decreasing from the size D to a smallest aperture of said exit electrode;
• applying DC voltages to the orifice electrodes generating an axial electric field Ez transferring ions toward the exit electrode;
• and
• transferring said extracted analyte ions from the entrance to the exit of said ion funnel structure by the axial electric field Ez along the funnel pathway direction for analysis,
• wherein said extraction electric field Es is at least twice that of the axial electric field Ez.

An apparatus for sample analysis having a laser ionization source operated at sub-atmospheric pressure conditions, comprising:

• a holder configured to hold a sample containing analyte molecules;
• a laser ionizer utilizing a pulsed laser configured to generate ionized species from the sample;
• an ion extractor adjacent to said holder and configured to create a DC extraction electric field Es and to extract analyte ions from said ionized species;
• and
• an ion funnel structure comprising orifice electrodes located along an ion funnel pathway direction z;
• said structure having an entrance electrode having an aperture with a size D and an exit electrode, the exit electrode having a smallest aperture in the structure;
• said structure configured to accept said analyte ions at the entrance and transfer at least a portion of the analyte ions toward the exit using an axial electric field Ez along the direction z produced by applying DC voltages to the electrodes generating the axial electric field Ez transferring portion of the analyte ions toward the exit electrode;
• a controller programmed to control an average axial electric field from the entrance to the exit inside the structure <Ez>;
• and
• a vacuum chamber enclosing said holder, said ion extractor, and said ion funnel structure, wherein an operational pressure p in the vacuum chamber is maintained in the pressure range from 0.01 to 100 Torr,
• wherein the average axial electric field <Ez> is at least twice smaller than the extraction electric field Es.