Analytic spectrometers with non-radioactive electron sources
In an analytical spectrometer in which accelerated electrons are used to ionize analytes, a non-radioactive electron source uses a gas discharge to generate the electrons. The gas discharge is located in a substantially hermetic source chamber and the free electrons in the plasma of the gas discharge are accelerated in an electric acceleration region towards a partition wall which separates the source chamber from a reaction chamber. The partition wall is permeable to the accelerated electrons but impermeable to gas in the source chamber so that the electrons penetrate the partition wall into the reaction chamber and generate primary ions that chemically ionize the analytes.
1. An analytical spectrometer comprising:
a substantially hermetic source chamber;
a non-radioactive electron source that is located in the source chamber filled with a gas having a pressure between 10 and 1000 pascal and uses a gas discharge to generate electrons;
a reaction chamber which is separated from the source chamber by a partition wall that is permeable to electrons and impermeable to gas; and
a voltage source that is located in the source chamber and applies an electric acceleration voltage with a value between 2 and 100 kilovolts to the electrons in an electric acceleration region.
2. The spectrometer of claim 1 , wherein the electric acceleration region is formed by electrodes used to generate the gas discharge.
3. The spectrometer of claim 1 , wherein the gas discharge comprises one of the group consisting of a glow discharge, a corona discharge, a hollow cathode discharge, an arc discharge and a dielectric barrier discharge.
4. The spectrometer of claim 1 , wherein the gas in the source chamber is one of a noble gas and hydrogen.
5. The spectrometer of claim 1 , wherein the reaction chamber is filled with a gas having a pressure between 6×10 4 and 1.2×10 5 pascal.
6. The spectrometer of claim 1 wherein the spectrometer is an ion mobility spectrometer.
7. The spectrometer of claim 1 wherein the spectrometer is an electron capture detector.
8. The spectrometer of claim 1 wherein the spectrometer is a mass spectrometer.
9. A method for the chemical ionization of analytes in a spectrometer having a source chamber, a reaction chamber and a partition wall that separates the source chamber and the reaction chamber and is permeable to electrons but impermeable to gas, the method comprising:
(a) generating free electrons with a gas discharge in a source chamber filled with a gas having a pressure between 10 and 1000 pascals;
(b) accelerating the free electrons in an electric field to energies between 2 and 200 kiloelectronvolts and towards the partition wall;
(c) passing the accelerated electrons through the partition wall into the reaction region; and
(d) using the accelerated electrons in the reaction region to form primary ions that chemically ionize the analytes.
10. The method of claim 9 , wherein step (d) comprises introducing the analytes into the reaction chamber.
11. The method of claim 9 , further comprising:
(e) detecting and measuring signals produced by ionized analytes in the reaction chamber;
(f) measuring a value of electron current at the partition wall; and
(g) correcting the signals detected and measured in step (e) using the value of the electron current measured in step (f).
12. The method of claim 9 , further comprising:
(e) measuring a value of electron current at the partition wall; and
(f) adjusting the value of the electron current measured in step (e) to a predetermined constant.
13. The method of claim 9 , further comprising:
(e) measuring a value of ion current of primary ions in the reaction chamber;
(f) measuring a value of electron current at the partition wall; and
(g) adjusting the value of the electron current measured in step (f) based on the value of the ion current measured in step (e).
14. The method of claim 9 , further comprising:
(e) measuring a pressure of gas in the source chamber;
(f) measuring a value of electron current at the partition wall; and
(g) adjusting the value of the electron current measured in step (f) based on the gas pressure measured in step (e).
15. The method of claim 9 , further comprising:
(e) measuring an electromagnetic emission of the gas discharge;
(f) measuring a value of electron current at the partition wall; and
(g) adjusting the value of the electron current measured in step (f) based on the electromagnetic emission measured in step (e).