Current measuring system

A mass spectrometer comprising:

• means for ionizing a sample to produce charged fragments including negative ions;
• means for separating the charged fragments based on charge to mass ratio;
• an analog electron multiplier including a tube, including a first voltage application electrode connected to a first positive voltage, including an ion input horn directly receiving negative ions and directing them into the tube, including a second voltage application electrode connected to a second positive voltage greater than the first positive voltage, and including an output detection electrode;
• an electrometer having a first electrode at ground potential, and a second electrode;
• and
• a capacitor having a first electrode electrically connected to the output detection electrode of the electron multiplier and having a second electrode electrically connected to the second electrode of the electrometer, whereby there is no need to employ a dynode external to the electron multiplier to convert negative ions to positive ions.

A method of detecting negative ions, the method comprising:

• providing an electron multiplier having a first voltage application electrode, having a second voltage application electrode, having an ion input, and having an output detection electrode;
• operating the electron multiplier in analog mode;
• applying appropriate voltages to the first voltage application electrode, and the second voltage application electrode, such that the electron multiplier is capable of directly receiving negative ions at the ion input and generating an output signal at the output detection electrode;
• providing a capacitor having a first plate connected to the output detection electrode and having a second plate;
• coupling an electrometer between the second plate of the capacitor and a ground potential;
• and
• coupling the ion input directly to a source of negative ions.

A method of mass spectrometry comprising:

• ionizing a sample to produce charged fragments
• including negative ions;
• separating the charged fragments based on charge to mass ratio;
• providing an analog electron multiplier including a tube, including a first voltage application electrode connected to a first positive voltage, including an ion input horn, including a second voltage application electrode connected to a second positive voltage greater than the first positive voltage, and including an output detection electrode;
• directing separated negative ions into the tube;
• providing an electrometer having a first electrode at ground potential, and a second electrode, and outputting a signal used for generating mass spectrum data;
• and
• providing a capacitor having a first electrode electrically connected to the output detection electrode of the electron multiplier and having a second electrode electrically connected to the second electrode of the electrometer.