Plasma torch

• US 20040183008A1
• Filed: 12/19/2003
• Published: 09/23/2004
• Est. Priority Date: 07/03/2001
• Status: Active Grant

• Current Assignee: Agilent Technologies Australia (M) Pty., Ltd. (Agilent Technologies, Inc.)
• Original Assignee: Varian Australia Pty., Ltd. (Agilent Technologies, Inc.)
• Inventors: Wiseman, Alan G
• Granted Patent: US 6,989,529 B2
• Time in Patent Office: Days
• US Class Current: 250/288
• CPC Class Codes: G01N 21/73 using plasma burners or torches
• CPC Class Codes: H01J 49/105 using high-frequency excitation, e.g. microwave excitation, Inductively Coupled Plasma [ICP]
• CPC Class Codes: H05H 1/30 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/28 takes precedence

Abstract

A torch for producing an inductively coupled or microwave induced plasma for use in spectrochemical analysis. The torch includes a central tube (25) for conveying a flow of a gas carrying sample aerosol to a plasma (17) produced in the torch. The tube (25) has an inlet (31) and an outlet (39) of smaller size than the inlet and is shaped to deliver a substantially laminar flow of the gas at the outlet (39). The tube (25) is tapered along at least a substantial portion of its length such that its cross-sectional area gradually and smoothly reduces towards its outlet (39) along at least a substantial portion of its length. It has been found that such a tapered tube is resistant to obstruction by salts deposited from samples containg high levels of dissolved solids.

Claims

1. A torch for producing a plasma for use in spectrochemical analysis including

a tube for conveying a flow of a gas carrying sample aerosol to a plasma produced in the torch by an electomagnetic field, the tube having an inlet and an outlet of smaller size than the inlet, and being shaped to deliver a substantially laminar flow of the gas at the outlet, wherein the tube is tapered along at least a substantial portion of its length such that its cross-sectional area gradually and smoothly reduces towards its outlet along said at least a substantial portion of its length.

2. A torch as claimed in claim 1 wherein the tube is tapered along its length for a distance that is at least five times the internal diameter of the inlet of the tube.

3. A torch as claimed in claim 2 wherein the tube is tapered along its length for a distance that is from five to ten times the internal diameter of the inlet of the tube.

4. A torch as claimed in any one of claims 1 to 3 wherein the tube includes a parallel walled portion extending to the outlet, wherein the tapered portion of the tube smoothly blends into the parallel walled portion.

5. A torch as claimed in any one of claims 1 to 4 wherein the tapered portion of the tube commences at the inlet.

6. A torch as claimed in claim 1 wherein the tube is tapered along substantially its whole length.

7. A torch as claimed in any one of claims 1 to 4 wherein the tube includes an inlet portion that is smoothly curved through an angle of about 90°

and smoothly bends into the tapered portion.

8. A torch as claimed in any one of claims 1 to 7 wherein the taper of the tapered portion of the tube is constant.

9. A torch as claimed in any one of claims 1 to 8 wherein the tube is concentrically located within a second tube and the second tube is concentrically located within a third tube, the third tube including an inlet for supplying a flow of a plasma forming gas to the annular outlet formed between the second and third tubes, the second tube also including an inlet for supplying a flow of gas to the annular outlet formed between the first defined tube and the second tube for keeping a plasma away from the outlet ends of the first defined tube and the second tube.