We have described a home-made desktop orthogonal-injection time-of-flight (O-ToF) mass spectrometer combining a collisional cooling system. This O-ToF consists of a simple electrospray ion source, an atmosphere-vacuum interface, an area of transmission, including a radio-frequency only quadrupole (RF- only quadrupole, RFQ) as a collisional cooling cell and an orthogonal ToF mass analyzer. In order to detect ions of small m/z value, such as small metal ions, the RFQ has been improved to weaken the mass discrimination effect against low mass ions. Metal salt solutions were used in the experiment. The system has shown a satisfactory resolving power in the spectra (m/Δm = 3500), a good mass stability, a limit of detection of 80 fg and a mass accuracy of 48 ppm. The dynamic range is found to be from 10(-8) mol L(-1) to 10(-5) mol L(-1), allowing the semi-quantitative analysis of metal ions.