Atmospheric-pressure ionization and fragmentation of molecules for structural elucidation
A solution-cathode glow discharge (SCGD) spectrometry apparatus may comprise an SCGD source and a mass or ion mobility spectrometer. A method for ionizing a molecular analyte may comprise contacting the molecular analyte with a plasma discharge to form ions and separating the ions in a mass spectrometer or ion mobility spectrometer. The contacting step may occur under atmospheric pressure and/or ambient conditions. The molecular analyte may be fragmented by the plasma discharge.
1. A method for ionizing a molecular analyte, the method comprising:
contacting the molecular analyte with a plasma discharge under ambient conditions to form ions by flowing an electrically conductive liquid through a capillary onto a first conductive rod that surrounds the capillary and applying an electric potential to a second conductive rod such that the plasma discharge forms between the second conductive rod and the electrically conductive liquid to produce the ions, and
separating the ions in a mass spectrometer.
2. The method of claim 1 , wherein the molecular analyte is not multiply charged.
3. The method of claim 1 , wherein the molecular analyte is electrically neutral.
4. The method of claim 1 , wherein the molecular analyte is not subjected to a subsequent fragmenting step after the contacting step.
5. The method of claim 1 , wherein the molecular analyte is dissolved in the electrically conductive liquid.
6. The method of claim 1 , wherein the molecular analyte is a solid.
7. The method of claim 1 , wherein the molecular analyte is a polypeptide.
8. The method of claim 1 , wherein the ions are polypeptide sequence ions each having a type selected from the group consisting of a-ions, b-ions, c-ions, x-ions, y-ions, d-ions, v-ions, and w-ions.
9. The method of claim 7 , wherein the polypeptide has been digested with an enzyme.
10. The method of claim 1 , wherein the molecular analyte is a chemical complex.
11. The method of claim 1 , wherein the molecular analyte is a charged molecular analyte.
12. The method of claim 1 , wherein the plasma discharge is generated by an electric current of about 35 mA to about 95 mA.
13. The method of claim 12 , further comprising varying the electric current between a high current and a low current, wherein the high current is from about 50 mA to about 200 mA, and the low current is from about 1 mA to about 50 mA.
14. The method of claim 1 , wherein the method does not comprise reducing pressure where the plasma discharge forms.
15. The method of claim 1 , wherein the molecular analyte is dissolved in an electrically conductive liquid that flows toward the plasma discharge at a rate of about 1 mL/min to about 5 mL/min.
16. The method of claim 1 , wherein the molecular analyte is dissolved in an electrically conductive liquid that comprises an electrolyte solute.
17. The method of claim 16 , wherein the concentration of the electrolyte solute is about 0.05M to about 2M.
18. The method of claim 1 , wherein the plasma discharge is about 0.2 cm to about 1 cm from an inlet of the mass spectrometer.