Abstract: There is provided a mass spectrometry apparatus comprising: an ion source arranged in a substantially horizontal orientation and from which a quantity of ions may be sourced, an ion filter device arranged for receiving a stream of ions for filtering thereof; and, an ion guide arranged so as to guide ions sourced from the ion source toward the ion filter device. The ion source and the ion filter device are arranged relative to one another so that the profile of the apparatus is reduced so as to minimise the effective footprint of the apparatus.