A mass spectrometer is disclosed comprising an atmospheric pressure interface comprising a gas cone 6 having an inlet aperture, wherein the gas cone 6 has a first longitudinal axis arranged along an x-axis and an Electrospray ion source comprising a first capillary tube 2 having an outlet and having a second longitudinal axis and a second capillary tube 3 which surrounds the first capillary tube 2. The mass spectrometer further comprises a desolvation gas supply tube and a first device arranged and adapted to supply an analyte liquid via the first capillary tube 2 so that the liquid exits the outlet of the first capillary tube 2 at a flow rate >200 μL/min. The mass spectrometer further comprises a second device arranged and adapted to supply a nebuliser gas via the second capillary tube 3 at a flow rate in the range 80-150 L/hr, wherein an outlet of the first capillary tube 2 is arranged at a distance x mm along the x-axis as measured from the centre of the gas cone inlet aperture, a distance y mm along a y-axis as measured from the centre of the gas cone inlet aperture and a distance z mm along a z-axis as measured from the centre of the gas cone inlet aperture. The x-axis, the y-axis and the z-axis are mutually orthogonal. The desolvation gas supply tube surrounds the second capillary tube 3 and the mass spectrometer further comprises a third device arranged and adapted to supply a desolvation gas via the desolvation gas supply tube at a flow rate in the range 400-1200 L/hr, a heater 4 arranged and adapted to heat the desolvation gas to a temperature ≥100° C. and a fourth device arranged and adapted to supply a cone gas to the gas cone 6 at a flow rate in the range 40-80 L/hr and wherein x is in the range 2.0-5.0 mm and wherein the ratio z/x is in the range 1-5:1.