A voltage supply system for supplying an RF voltage to an RF resonant load comprising an ion-optical component of a mass spectrometer, said system comprising: a Direct Digital Synthesiser ("DDS") arranged and adapted to output an RF voltage; wherein said voltage supply system is arranged and adapted: (i) to vary the frequency of said RF voltage output by said Direct Digital Synthesiser; (ii) to determine a first resonant frequency of said RF resonant load comprising said ion-optical component; characterized in that the voltage supply system is further adapted (iii) to determine whether or not the generation of an RF voltage at said first resonant frequency by said Direct Digital Synthesiser would also result in the generation of a spur frequency close to said first resonant frequency; wherein if it is determined that a spur frequency would be generated close to said first resonant frequency then said voltage supply system is further arranged and adapted: (iv) to consult a look-up table comprising one or more preferred frequencies and/or one or more undesired frequencies; and (v) to direct said Direct Digital Synthesiser to generate an RF voltage at a second frequency which corresponds with one of said preferred frequencies from said look-up table and/or which does not correspond with one of said undesired frequencies from said look-up table, wherein said second frequency is different to said first resonant frequency; wherein said look-up table is generated through experimentation by checking peak shapes resulting from infusing a known compound into a mass spectrometer and altering drive frequency. a Direct Digital Synthesiser ("DDS") arranged and adapted to output an RF voltage; wherein said voltage supply system is arranged and adapted: (i) to vary the frequency of said RF voltage output by said Direct Digital Synthesiser; (ii) to determine a first resonant frequency of said RF resonant load comprising said ion-optical component; characterized in that the voltage supply system is further adapted (iii) to determine whether or not the generation of an RF voltage at said first resonant frequency by said Direct Digital Synthesiser would also result in the generation of a spur frequency close to said first resonant frequency; (i) to vary the frequency of said RF voltage output by said Direct Digital Synthesiser; (ii) to determine a first resonant frequency of said RF resonant load comprising said ion-optical component; characterized in that the voltage supply system is further adapted (iii) to determine whether or not the generation of an RF voltage at said first resonant frequency by said Direct Digital Synthesiser would also result in the generation of a spur frequency close to said first resonant frequency; wherein if it is determined that a spur frequency would be generated close to said first resonant frequency then said voltage supply system is further arranged and adapted: (iv) to consult a look-up table comprising one or more preferred frequencies and/or one or more undesired frequencies; and (v) to direct said Direct Digital Synthesiser to generate an RF voltage at a second frequency which corresponds with one of said preferred frequencies from said look-up table and/or which does not correspond with one of said undesired frequencies from said look-up table, wherein said second frequency is different to said first resonant frequency; (iv) to consult a look-up table comprising one or more preferred frequencies and/or one or more undesired frequencies; and (v) to direct said Direct Digital Synthesiser to generate an RF voltage at a second frequency which corresponds with one of said preferred frequencies from said look-up table and/or which does not correspond with one of said undesired frequencies from said look-up table, wherein said second frequency is different to said first resonant frequency; wherein said look-up table is generated through experimentation by checking peak shapes resulting from infusing a known compound into a mass spectrometer and altering drive frequency.