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