Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
1999-06-02
2003-07-15
Anderson, Bruce (Department: 1881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S282000
Reexamination Certificate
active
06593568
ABSTRACT:
BACKGROUND OF THE INVENTION
Electrospray (ES) and Atmospheric Pressure Chemical Ionization Sources(APCI) produce ions at or near atmospheric pressure and are consequently referred to generically as Atmospheric Pressure Ion (API) Sources. Both ES and APCI sources produce ions for mass spectrometric analysis from liquid samples. Mass spectrometers operate in vacuum which is inherently incompatible with the direct analysis of liquid based samples. API sources serve to produce ions from a liquid sample, remove the unwanted sample liquid or vapor before it enters vacuum and efficiently transport the ions into vacuum for mass analysis with minimum vapor contamination. Electrospray can produce ions from sample liquid flow rates ranging from under 25 nanoliters per minute to over 2 milliliters per minute. APCI can generally be operated over a liquid flow rate range from 1 microliter to over 2 milliliters per minute. In both ES and APCI operating modes, heat must be applied as part of the ion production process to evaporate all or a portion of the solvent in which the sample of interest is dissolved. The Electrospray ion production process consists of both the production of charged liquid droplets and the evaporation of these droplets. During the evaporation of the Electrosprayed charged liquid droplets, ions are produced either substantially at atmospheric pressure or as the droplets are swept into vacuum. Droplet evaporation can be aided by heated capillaries, heated nozzle assemblies, heated “pepper pot” configurations countercurrent drying gas (or curtain gas) and/or heated countercurrent drying gas, concurrent gas flow and heated atmospheric pressure chamber walls, all of which are commercially available. The walls of ES and APCI atmospheric pressure chambers have also been heated to aid in evaporating the liquid droplets produced through gas and vapor conductance with the chamber walls. The use of drying gas and heated drying gas to aid in Electrosprayed droplet evaporation has been described in U.S. Pat. No. 4,531,056. Electrospray ion sources with heated drying gas configured with an external gas heater are commercially available. The disadvantage of an external gas heater as the single source of heat is that the enthalpy delivered to the ES chamber via the drying gas is dependent on the drying gas flow rate and temperature. Heated drying gas entering the ES source with low flow rate from an external heater can cool due to contact with the flow channels. The invention overcomes the disadvantages of an external drying gas heater by locating the drying gas in the ES source endplate. The endplate and capillary entrance temperature is maintained by direct contact with the endplate/gas heater independent of drying gas flow rate.
Heated capillaries and nozzles have been used to dry droplets produced in Electrospray sources in combination with and without drying gas or bath. U.S. Pat. No. 4,531,056 describes the configuration of heated drying gas in an ES source such that the drying gas heats the orifice into vacuum prior to flowing into the ES chamber. Similarly, dielectric capillary orifices into vacuum have been heated With drying gas flowing over a portion of the capillary length. The ability to change ion potential energy by using dielectric capillaries as orifices into vacuum configured in API sources is described in U.S. Pat. No. 4,542,293. Dielectric and metal capillaries configured in API sources are commercially available. U.S. Pat. No. 4,977,320 describes a heated metal capillary configured as an orifice into vacuum in an ES source with no drying gas. A single heater is described running the majority of the capillary length. This heated capillary technique is available in commercial API sources. In some commercially available systems, the walls of an API source have also been heated to generally increase the enthalpy available through gas and vapor heat conductance to aid in the evaporation of liquid sprayed into the API source. Auxiliary gas flows into API chambers have been configured in ES and APCI sources with flow introduction substantially in the direction toward the orifice into vacuum to aid in droplet drying and the transport of vapor. The invention includes the introduction of drying gas which flows in a direction substantially away from the orifice into vacuum. In this manner, unwanted neutral vapor is swept away from the orifice into vacuum minimizing contamination in the vacuum system. Ions, driven by the electric field, move against the drying gas toward the orifice into vacuum where they are entrained in the neutral gas and swept into vacuum. The invention provides control of API endplate, capillary entrance and exit and drying gas temperatures independent of drying gas flow rate. Heat is applied directly where it is required providing a compact cost effective and power efficient means to accomplish the API source requirements of droplet drying, minimizing vacuum system contamination and maximizing the ion transport efficiency into vacuum for mass analysis.
SUMMARY OF THE INVENTION
In accordance with the present invention a multiple purpose heater assembly is configured as an integral part of an Atmospheric Pressure Ion Source (API). The heater is constructed as part of an endplate assembly and is configured to provide heat to the API chamber endplate, the orifice into vacuum and the drying or bath gas which is delivered into the API source chamber. In one embodiment of the invention, the orifice into vacuum comprises a capillary and the integral heater supplies heat to the capillary entrance region. The invention also includes the addition of a second heater mounted near the capillary exit end. The temperature of the capillary entrance and exit ends can be controlled independently. The drying or bath gas passing through the heater achieves a temperature close to the heater temperature prior to entering the API chamber. The gas is not required to heat any elements on its way to the API chamber as is the case with an external gas heater. In the preferred embodiment of the invention, the heater and endplate assembly transfer heat to the bath gas prior to entering the API chamber. In this manner, the drying or bath gas temperature can be set substantially independent of flow rate. The heater assembly is configured such that minimum heat is shed to elements in the API source where heat would serve no purpose. The endplate lens is mounted off the API housing structure and in this embodiment can provide efficient transfer of heat to the gas and liquid in the API chamber with minimum enthalpy losses to the chamber walls. Heat applied to the bath gas, endplate and capillary allows efficient evaporation of droplets produced in an Electrospray source or prevents vapor from recondensing or entering the capillary in an APCI source, with minimum power supplied to the heater. Heat is supplied directly where it is most required minimizing power requirements and cost. The invention allows independent control of capillary entrance and exit temperatures as well as control of bath gas temperature independent of gas flow rate. Higher enthalpy can be transferred into the API source chamber with less wattage and with tighter temperature control, while the majority of API source elements need not be configured to withstand higher temperatures. The invention allows a wider range of optimization of API source variables to maximize performance over a broad range of liquid flow rates, solution chemistries and sample types. The independent heating provided by the integral endplate heater assembly with counter current drying gas and the capillary exit heater allows finer control of temperatures resulting in improved performance in Electrospray and Atmospheric Pressure Chemical Ionization sources operated at atmospheric pressure. The multiple purpose API source heater assembly includes API voltage and gas connections integrated into a single assembly which is configured for simple installation and removal. This integrated assembly facilitates assembly, disassembly and cleaning of the API
Andrien, Jr. Bruce A.
Catalano Clement
Sansone Michael A.
Whitehouse Craig M.
Anderson Bruce
Levishon, Lerner, Berger & Langsam
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