The present invention relates to an atmospheric pressure interface and an ion source for a mass spectrometer. According to the preferred embodiment the atmospheric pressure interface and ion source form part of a miniature mass spectrometer.
A known miniature mass spectrometer is disclosed in FIG. 9 of US 2012/0138790 (Microsaic) and Rapid Commun. Mass Spectrom. 2011, 25, 3281-3288. The miniature mass spectrometer as shown in FIG. 9 of US 2012/0138790 comprises a three stage vacuum system. The first vacuum chamber comprises a vacuum interface. No RF ion guide is located within the vacuum interface and the vacuum interface is maintained at a relatively high pressure of >67 mbar (>50 Torr). A small first diaphragm vacuum pump is used to pump the vacuum interface.
The second vacuum chamber contains a short RF ion guide which is operated at a pressure-path length in the range 0.01-0.02 Torr·cm and is vacuum pumped by a first turbomolecular vacuum pump which is backed by a second diaphragm vacuum pump. The second separate diaphragm vacuum pump is required due to the relative high pressure (>67 mbar) of the first vacuum chamber. The high pressure in the first vacuum chamber effectively prevents the same diaphragm vacuum pump from being used to back both the first turbomolecular vacuum pump and also to pump the first vacuum chamber due to the fact that turbomolecular vacuum pumps are generally only able to operate with backing pressures of <20 mbar.
The known miniature mass spectrometer is used in conjunction with a microspray ion source wherein a nebulising gas is supplied at a rate of 2.5 L/min and the liquid flow rate to the emitter tip is 0.3-0.8 μL/min.
Known Electrospray ion sources as used with conventional full size mass spectrometers have many degrees of freedom which allows the ion source to be tuned or optimised for a variety of different compounds and circumstances.
Conventional full size Electrospray ion sources also typically have substantially higher liquid flow rates of several mL/min and the nebuliser may be surrounded by a heater which supplies a flow of heated desolvation gas in addition to the nebulisation gas emitted from the nebuliser.
Conventional full size Electrospray ion sources are complex and have many degrees of freedom which can make it difficult for an unskilled or inexperienced user of a mass spectrometer to interact with and operate both the ion source and the mass spectrometer.
US 2003/0189170 (Covey) discloses an arrangement comprising a nebuliser source probe 72 as shown in FIG. 3 of US 2003/0189170 (Covey). The probe comprises a central capillary tube and an annular chamber around the capillary tube for providing an annular flow of gas around the capillary tube as discussed at paragraph [0079]. The central capillary tube is not shown in FIG. 3. Although a heater 71 is shown surrounding the nebuliser probe 72, as detailed at paragraph [0080] the heater 71 is not used when the ion source comprises a nebuliser. Instead, the heater 71 just functions as a holder or receptacle. FIG. 7 of US 2003/0189170 (Covey) shows two gas sources 110 which are arranged either side of the ion source 70 and which produce gas jets 104 that impinge upon the expanding spray cone 106 from the ion source 70 as discussed at paragraph [0093].
GB-2446960 (Micromass) discloses using sulphur hexafluoride as a cone or curtain gas.
GB-2437819 (Micromass) discloses an ionisation source wherein one or more wires are provided within a capillary tube forming the ionisation source.
It is desired to provide an improved mass spectrometer and method of mass spectrometry.