A radio-frequency amplifier for mass spectrometry
A low-cost radio-frequency (RF) amplifier for mass spectrometry has been designed, constructed, and tested for ion excitation in Fourier transformation cyclotron resonance mass spectrometry (FTICR-MS). The amplifier accepts input signals up to 1 Vp-p and has an input impedance set at 50 n, which may easily be adjusted. The total voltage gain is set at 150 (43.5 dB). This gain may also be adjusted, by changing the value of the gain feedback resistors. The gain flatness has been determined to be +/-6% (+/-O.5 dB) from DC to 2 MHz with a 1 W resistive load. The amplifier described here provides an alternative to expensive commercially-available RF amplifiers. Commercially available amplifiers often have higher bandwidth and are capable of driving higher power loads than is necessary for typical FTICR-MS instruments. This amplifier is optimized for FTICR-MS instruments utilizing magnetic fields less than 7 T. It can also be used for driving quadruples and ion funnels by coupling the basic circuit to an LC resonant circuit. Design and implementation of the excitation amplifier is presented in this article; performance is also characterized. Detailed specifications including complete schematics, printed circuit board files, mechanical drawings, and parts lists for those interested in building their own amplifier are available from our website.