Temperature controller for thermal ionization mass spectrometry

We describe the use of a simple voltage stabilizer that controls the filament temperature (T(f)) in the ion source of a thermal ionization mass spectrometer. The filament voltage (V(f)) is measured by means of a separate pair of wires connected inside of the ion source in parallel to the wires supplying power. It has been demonstrated that V(f) is directly proportional to T(f) in a wide range of filament temperature. The T(f) value is solely controlled by the reference voltage (V(r)) that can be manually selected from a voltage divider or by means of a computer. Digital signals from the computer in the form of a series of pulses are transmitted opto-electronically and subsequently converted to analog signals. The temperature controller described here was successfully applied for analysis of potassium concentration by the isotope dilution method.