Plasma torch for microwave induced plasmas
First Claim
1. A torch for plasma spectrochemical analysis including an outer tube, an intermediate tube and an inner tube, the inner tube being substantially coaxially located within the intermediate tube for injecting a first gas flow for carrying a sample for analysis into a plasma produced in the torch, an intermediate-gas inlet leading into the intermediate tube for admitting a second gas flow into the space between the inner tube and the intermediate tube for controlling the axial position of the plasma produced in the torch, an outer-gas inlet leading into the outer tube for supplying a third gas flow between the outer tube and the intermediate tube for providing a sheathing gas layer for the plasma produced in the torch, wherein the outer-gas inlet is offset from a central axis of the torch to impart a spiral flow to the supplied third gas as it moves along the torch to provide the sheathing gas layer, and means associated with the outer-gas inlet for increasing the gas velocity in the sheathing gas compared to the gas velocity upstream of said means to thereby increase the confining force of the sheathing gas layer on the plasma.
1 Assignment
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Accused Products
Abstract
A Plasma torch (10) for microwave induced plasma spectrochemical analysis of a sample includes a nozzle (30) in an inlet (18) for the main plasma gas flow between outer tube (12) and intermediate tube (14) of the torch (10). The nozzle (30) increases the gas flow velocity in the sheathing gas layer for the plasma which is provided by the gas flow from the annular gap (22) between the tubes (12 and 14). The increased velocity of the gas in the sheathing gas layer “stiffens” that layer and thus better confines the microwave induced plasma (such better confinement not being necessary for an ICP torch). Thus the torch is of improved durability for a microwave induced plasma compared to an ICP torch. The sample injection (inner) tube (16) may have a reduced diameter outlet at its end (34) which is substantially level with the end (35) of intermediate tube (14) to improve injection of a sample into the microwave induced plasma. The inlet end (26) of the sample injection tube (16) may include a heater (36) to assist in preventing blockages in tube (16) near its outlet end.
28 Citations
14 Claims
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1. A torch for plasma spectrochemical analysis including an outer tube, an intermediate tube and an inner tube, the inner tube being substantially coaxially located within the intermediate tube for injecting a first gas flow for carrying a sample for analysis into a plasma produced in the torch,
an intermediate-gas inlet leading into the intermediate tube for admitting a second gas flow into the space between the inner tube and the intermediate tube for controlling the axial position of the plasma produced in the torch, an outer-gas inlet leading into the outer tube for supplying a third gas flow between the outer tube and the intermediate tube for providing a sheathing gas layer for the plasma produced in the torch, wherein the outer-gas inlet is offset from a central axis of the torch to impart a spiral flow to the supplied third gas as it moves along the torch to provide the sheathing gas layer, and means associated with the outer-gas inlet for increasing the gas velocity in the sheathing gas compared to the gas velocity upstream of said means to thereby increase the confining force of the sheathing gas layer on the plasma.
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11. A torch for plasma spectrochemical analysis including
an outer tube, an intermediate tube and an inner tube, the inner tube being substantially coaxially located within the intermediate tube for carrying a first gas flow for conveying an aerosol of a nebulised sample liquid for injection through an outlet thereof into a plasma formed in the torch, an intermediate-gas inlet leading into the intermediate tube for admitting a second gas flow into the space between the inner tube and the intermediate tube for controlling the axial position of a plasma produced in the torch, an outer-gas inlet leading,into the outer tube for supplying a third gas flow between the outer tube and the intermediate tube for providing a sheathing gas layer for a plasma produced in the torch, wherein the outer-gas inlet is offset from a central axis of the torch to impart a spiral flow to the supplied third gas as it moves along the torch to provide the sheathing gas layer, and a heating means associated with a section of the inner tube for heating an aerosol passing through that section to substantially completely evaporate liquid from the aerosol, the section of the inner tube being spaced from the outlet of the. inner tube for the liquid to be substantially completely evaporated before the aerosol reaches the proximity of the outlet.
Specification