Patent Publication Number: US-2022232691-A1

Title: Inductively coupled plasma torches and methods and systems including same

Description:
FIELD 
     The present technology relates to plasma sources and, more particularly, to inductively coupled plasma torches. 
     BACKGROUND 
     An inductively coupled plasma (ICP) torch system is a type of plasma source in which energy is supplied by electric currents that are produced by electromagnetic induction. ICP torch systems are used in some analytical instruments to ionize a sample. 
     SUMMARY 
     In one aspect, an inductively coupled plasma (ICP) torch has a torch axis and a torch distal end. The ICP torch includes an injector tube, an intermediate tube, a plasma tube, and an induction coil. The injector tube defines an injector flow passage to receive a flow of a sample fluid. The intermediate tube is disposed about the injector tube. An auxiliary gas passage is defined between the injector tube and the intermediate tube and configured to receive a flow of an auxiliary gas. The plasma tube is disposed about the intermediate tube. A plasma gas passage is defined between the intermediate tube and the plasma tube and configured to receive a flow of a plasma gas. The induction coil is disposed about the plasma tube. The induction coil is configured to be supplied with radio-frequency electric current to inductively energize the auxiliary gas to produce a plasma proximate the torch distal end. The induction coil extends axially from a coil proximal end to a coil distal end proximate the torch distal end. The plasma tube includes an outlet opening proximate the torch distal end. The outlet opening is at least partially coincident with or axially inset from the coil distal end. 
     In some embodiments, the outlet opening of the plasma tube is coincident with the coil distal end. 
     In some embodiments, the outlet opening of the plasma tube is axially inset from the coil distal end. 
     According to some embodiments, the outlet opening of the plasma tube is axially inset from the coil distal end a distance in the range of from about 1 mm to about 5 mm. 
     According to some embodiments, the outlet opening of the plasma tube is disposed within the induction coil. 
     In some embodiments, a distal end of the plasma tube is coincident with or axially inset from the coil distal end. 
     In some embodiments, the distal end of the plasma tube is coincident with the coil distal end. 
     According to some embodiments, the distal end of the plasma tube is axially inset from the coil distal end. 
     In some embodiments, the distal end of the plasma tube is axially inset from the coil distal end a distance in the range of from about 1 mm to about 5 mm. 
     According to some embodiments, the distal end of the plasma tube is disposed within the induction coil. 
     According to some embodiments, the outlet opening is located at a distal end of the plasma tube and is aligned with the torch axis. 
     In some embodiments, the outlet opening is a radial side opening in the plasma tube. 
     In some embodiments, the plasma tube includes a distal terminal end opening aligned with the torch axis, and the radial side opening intersects the distal terminal end opening. 
     According to some embodiments, the auxiliary gas passage has a narrowed gap proximate a distal end of the auxiliary tube. 
     In some embodiments, the plasma tube is formed of quartz. 
     According to some embodiments, the plasma tube is formed of an opaque material. 
     In some embodiments, the opaque material is selected from the group consisting of silicon nitride or ceramic. 
     The ICP torch may include an ignition electrode disposed radially external of the plasma tube and operable to ignite a plasma in the flow of the auxiliary gas. 
     The ICP torch may include a confining gas tube disposed about the plasma tube, wherein a confining gas passage is defined between the plasma tube and the confining gas tube to receive a flow of a confining gas. 
     According to some embodiments, the confining gas tube protrudes distally beyond a distal end of the plasma tube. 
     In some embodiments, the confining gas tube protrudes distally beyond a distal end of the plasma tube a distance in the range of from about 2 mm to about 9 mm. 
     According to some embodiments, a distal end of the confining gas tube is coincident with or protrudes distally beyond the coil distal end. 
     In some embodiments, the distal end of the confining gas tube is coincident with the coil distal end. 
     In some embodiments, the distal end of the confining gas tube protrudes distally beyond the coil distal end. 
     According to some embodiments, a distal end of the plasma tube is coincident with or axially inset from the coil distal end. 
     The ICP torch may include multiple inlets configured to direct the confining gas into the confining gas passage. 
     The ICP torch may include an inlet to direct the confining gas into the confining gas passage in a direction that substantially radially intersects the torch axis. 
     The ICP torch may include an inlet to direct the confining gas into the confining gas passage in a direction that is transverse to and radially offset from the torch axis. 
     In some embodiments, the confining gas tube is removably attached to the plasma tube. 
     The ICP torch may include an annular ring between the confining gas tube and the plasma tube. 
     According to some embodiments, the confining gas tube comprises at least one of quartz, borosilicate glass, Pyrex glass, or ceramic. 
     In another aspect, a method for generating a plasma includes providing an inductively coupled plasma (ICP) torch having a torch axis and a torch distal end. The ICP torch includes: an injector tube defining an injector flow passage to receive a flow of a sample fluid; an intermediate tube disposed about the injector tube, wherein an auxiliary gas passage is defined between the injector tube and the intermediate tube and configured to receive a flow of an auxiliary gas; a plasma tube disposed about the intermediate tube, wherein a plasma gas passage is defined between the intermediate tube and the plasma tube and configured to receive a flow of a plasma gas; and an induction coil disposed about the plasma tube, the induction coil extending axially from a coil proximal end to a coil distal end proximate the torch distal end. The plasma tube includes an outlet opening proximate the torch distal end. The outlet opening is at least partially coincident with or axially inset from the coil distal end. The method further includes: flowing the auxiliary gas through the auxiliary gas passage; flowing the plasma gas through the plasma gas passage; and supplying a radio-frequency electric current to the induction coil to inductively energize the auxiliary gas to produce a plasma proximate the torch distal end. 
     In another aspect, an inductively coupled plasma (ICP) torch has a torch axis and a torch distal end. The ICP torch includes an injector tube, an intermediate tube, a plasma tube, and a confining gas tube. The injector tube defines an injector flow passage to receive a flow of a sample fluid. The intermediate tube is disposed about the injector tube. An auxiliary gas passage is defined between the injector tube and the intermediate tube and configured to receive a flow of an auxiliary gas. The plasma tube is disposed about the intermediate tube. A plasma gas passage is defined between the intermediate tube and the plasma tube and configured to receive a flow of a plasma gas. The confining gas tube is disposed about the plasma tube. A confining gas passage is defined between the plasma tube and the confining gas tube to receive a flow of a confining gas. The confining gas tube protrudes distally beyond a distal end of the plasma tube. 
     The ICP torch may include multiple inlets configured to direct the confining gas into the confining gas passage. 
     The ICP torch may include an inlet to direct the confining gas into the confining gas passage in a direction that substantially radially intersects the torch axis. 
     The ICP torch may include an inlet to direct the confining gas into the confining gas passage in a direction that is transverse to and radially offset from the torch axis. 
     In some embodiments, the confining gas tube comprises at least one of quartz, borosilicate glass, Pyrex glass, or ceramic. 
     According to some embodiments, the plasma tube and the confining gas tube are formed of different materials from one another. 
     In some embodiments, the confining gas tube is transparent or translucent. 
     In some embodiments, the plasma tube is opaque. 
     The ICP torch may include an induction coil disposed about the plasma tube. The induction coil is configured to be supplied with radio-frequency electric current to inductively energize the auxiliary gas to produce a plasma proximate the torch distal end. The induction coil extends axially from a coil proximal end to a coil distal end proximate the torch distal end. 
     In some embodiments, a distal end of the confining gas tube is coincident with or protrudes distally beyond the coil distal end. 
     In some embodiments, the distal end of the confining gas tube is coincident with the coil distal end. 
     In some embodiments, the distal end of the confining gas tube protrudes distally beyond the coil distal end. 
     In a further aspect, an inductively coupled plasma (ICP) torch system includes an ICP torch having a torch axis and a torch distal end. The ICP torch includes an injector tube, an intermediate tube, a plasma tube, an induction coil, and a confining gas tube. The injector tube defines an injector flow passage to receive a flow of a sample fluid. The intermediate tube is disposed about the injector tube. An auxiliary gas passage is defined between the injector tube and the intermediate tube and configured to receive a flow of an auxiliary gas. The plasma tube is disposed about the intermediate tube. A plasma gas passage is defined between the intermediate tube and the plasma tube and configured to receive a flow of a plasma gas. The induction coil is disposed about the plasma tube. The induction coil is configured to be supplied with radio-frequency electric current to inductively energize the auxiliary gas to produce a plasma proximate the torch distal end. The induction coil extends axially from a coil proximal end to a coil distal end proximate the torch distal end. The confining gas tube is disposed about the plasma tube. A confining gas passage is defined between the plasma tube and the confining gas tube to receive a flow of a confining gas. The confining gas tube protrudes distally beyond a distal end of the plasma tube. The ICP torch system further includes a supply of the auxiliary gas fluidly coupled to the auxiliary gas passage, a supply of the plasma gas fluidly coupled to the plasma gas passage, and a supply of the confining gas fluidly coupled to the confining gas passage. 
     In some embodiments, the confining gas has a different chemical composition than the plasma gas. 
     According to some embodiments, the confining gas includes nitrogen gas. 
     In some embodiments, the plasma gas includes argon gas. 
     The ICP torch system may include a positive pressure source configured to supply the confining gas into the confining gas passage with a positive pressure to force the confining gas to flow through the confining gas passage. 
     In some embodiments, the ICP torch system is configured to use a negative pressure to draw a flow of the confining gas through the confining gas passage. 
     In a further aspect, a method for generating a plasma includes providing an inductively coupled plasma (ICP) torch having a torch axis and a torch distal end. The ICP torch includes: an injector tube defining an injector flow passage to receive a flow of a sample fluid; an intermediate tube disposed about the injector tube, wherein an auxiliary gas passage is defined between the injector tube and the intermediate tube and configured to receive a flow of an auxiliary gas; a plasma tube disposed about the intermediate tube, wherein a plasma gas passage is defined between the intermediate tube and the plasma tube and configured to receive a flow of a plasma gas; and an induction coil disposed about the plasma tube, the induction coil extending axially from a coil proximal end to a coil distal end proximate the torch distal end; and a confining gas tube disposed about the plasma tube. A confining gas passage is defined between the plasma tube and the confining gas tube to receive a flow of a confining gas. The confining gas tube protrudes distally beyond a distal end of the plasma tube. The method further includes: flowing the auxiliary gas through the auxiliary gas passage; flowing the plasma gas through the plasma gas passage; flowing the confining gas through the confining gas passage; and supplying a radio-frequency electric current to the induction coil to inductively energize the auxiliary gas to produce a plasma proximate the torch distal end. The confining gas surrounds the plasma in a confinement zone located distally beyond the distal end of the plasma tube. 
     In some embodiments, at least a portion of the confinement zone is disposed within the induction coil. 
     The method may include flowing the plasma gas through the plasma gas passage at a volumetric flow rate of less than 10 liters/minute. 
     The method may include flowing the confining gas through the confining gas passage at a volumetric flow rate of at least 7 liters/minute. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which form a part of the specification, illustrate embodiments of the technology. 
         FIG. 1  is an illustration of an ICP torch system according to some embodiments. 
         FIG. 2  is an illustration of an ICP torch system according to further embodiments. 
         FIG. 3  is an enlarged, fragmentary illustration of the ICP torch system of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the ICP torch system of  FIG. 2  taken along the line  4 - 4  of  FIG. 3 . 
         FIG. 5  is an illustration of an ICP torch system according to further embodiments. 
         FIG. 6  is an illustration of an ICP torch according to further embodiments. 
         FIG. 7  is an illustration of an ICP torch according to further embodiments. 
         FIG. 8  is an illustration of an ICP torch according to further embodiments. 
         FIG. 9  is an illustration of an ICP torch according to further embodiments. 
         FIG. 10  is an illustration of an ICP torch according to further embodiments. 
         FIG. 11  is an illustration of an ICP torch according to further embodiments. 
         FIG. 12  is an illustration of an ICP torch according to further embodiments. 
         FIG. 13  is a cross-sectional view of the ICP torch of  FIG. 12  taken along the line  13 - 13  of  FIG. 12 . 
         FIG. 14  is an illustration of an ICP torch according to further embodiments. 
         FIG. 15  is an illustration of a mass spectroscopy system including an ICP torch system according to some embodiments. 
         FIG. 16  is an illustration of an optical emission spectroscopy system including an ICP torch system according to some embodiments. 
         FIG. 17  is an illustration of an atomic absorption spectroscopy system including an ICP torch system according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional ICP torches include an injector tube, an intermediate tube surrounding the injector tube, a plasma tube surrounding the intermediate tube, and an induction coil surrounding the plasma tube. A sample gas is flowed through the injector tube, an auxiliary gas is flowed between the injector tube and the intermediate tube, and a plasma gas is flowed between the intermediate tube and the plasma tube. A plasma is generated from the auxiliary gas within the induction coil. The plasma tube extends beyond a distal end of the induction coil to protect the induction coil from the hot plasma within the torch. Even though the plasma tube is made from a material that can withstand high temperature (e.g., quartz), the plasma tube may melt if the plasma is too close to the plasma tube. For this reason, the plasma gas is flowed through the plasma tube to cool the plasma tube and provide a buffer between the plasma and the plasma tube. 
     However, the plasma gas typically must be flowed at a high velocity and volumetric flow rate to prevent the plasma gas from assuming a plasma state, and to cool the plasma tube sufficiently to prevent melting of the plasma tube. Argon is commonly used as the plasma gas, and the high consumption of Argon gas can significantly increase the operating cost of the ICP torch. 
     Apparatus and methods according to embodiments of the technology can address shortcomings of conventional ICP torches. In particular, apparatus and methods according to embodiments of the technology can enable the use of lower volumetric flow rates of a plasma gas while still preventing the plasma tube from melting. As a result, apparatus and methods according to embodiments of the technology can reduce the required consumption of the plasma gas (e.g., argon). 
     In a first aspect, an ICP torch according to embodiments of the technology includes an injector tube, an intermediate tube, a plasma tube, and an induction coil. The injector tube defines an injector flow passage through which a sample fluid is flowed toward a distal end of the torch (herein referred to as the forward direction). The intermediate tube is disposed about the injector tube to define an auxiliary gas passage between the injector tube and the intermediate tube. An auxiliary gas is flowed through the auxiliary gas passage in the forward direction. The plasma tube is disposed about the intermediate tube to define a plasma gas passage between the intermediate tube and the plasma tube. A plasma gas is flowed through the plasma gas passage in the forward direction. The induction coil is disposed about the plasma tube. The plasma tube includes an outlet opening proximate the distal end of the torch. The outlet opening is at least partially coincident with or axially inset from a distal end of the coil. In some embodiments, a distal end or tip of the plasma tube is coincident with or axially inset from the distal end of the coil. 
     In use, the plasma becomes progressively hotter in the forward direction. As a result, the plasma tube is subjected to progressively hotter plasma in the forward direction. The placement of the outlet or tip of the plasma tube at or inset from the coil distal end effectively shortens the length of the plasma tube extending along the plasma, and increases the axial distance between the tip of the plasma tube and the hottest portion of the plasma. In this way, heating of the tip of the plasma tube is reduced. Because less heat is transferred to the plasma tube, less plasma gas is required to cool the plasma tube to prevent melting of the plasma tube. 
     In a second aspect, an ICP torch according to embodiments of the technology includes an injector tube, an intermediate tube, a plasma tube, a confining gas tube, and an induction coil. The injector tube defines an injector flow passage through which a sample fluid is flowed toward a distal end of the torch (herein referred to as the forward direction). The intermediate tube is disposed about the injector tube to define an auxiliary gas passage between the injector tube and the intermediate tube. An auxiliary gas is flowed through the auxiliary gas passage in the forward direction. The plasma tube is disposed about the intermediate tube to define a plasma gas passage between the intermediate tube and the plasma tube. A plasma gas is flowed through the plasma gas passage in the forward direction. The confining gas tube is disposed about the plasma tube to define a confining gas passage. A confining gas is flowed through the confining gas passage in the forward direction. The confining gas tube protrudes distally beyond a distal end of the plasma tube. The induction coil is disposed about the confining gas tube. In use, the confining gas flow forms a tubular confining gas curtain, buffer or sheath surrounding the plasma gas stream and the plasma. The confining gas sheath serves to shield the induction coil and the confining gas tube from the heat of the plasma. The confining gas sheath may also serve to cool the confining gas tube. 
     In a third aspect, an ICP torch according to embodiments of the technology is constructed as described for the second aspect in combination with the first aspect (i.e., the plasma tube outlet opening or tip is coincident with or axially inset from a distal end of the coil). In this case, the confining gas tube and the confining gas sheath surround the plasma in the region axially beyond plasma tube outlet opening or tip, thereby shielding the induction coil from the portions of the plasma not surrounded by the plasma tube. 
     With reference to  FIG. 1 , an ICP torch system  10  according to some embodiments is shown therein. The ICP torch system  10  includes a torch  100 , a radiofrequency power generator (electrical power supply)  22 , a sample source  24 , an auxiliary gas source  26 , and a plasma gas source  28 . In use, a sample flow or stream SG (from the sample source  24 ), an auxiliary gas flow or stream AG (from the auxiliary gas source  26 ), and a plasma gas flow or stream PG (from the plasma gas source  28 ) are each forced or flowed through the torch  100  in a forward direction F toward a distal end  106 T of the torch  100 . The ICP torch system  10  generates a plasma P at the distal end  106 T from the auxiliary gas AG. 
     The plasma P may serve as an ionization source. In some embodiments, the plasma P decomposes a sample from the sample stream SG into its constituent elements and transforms those elements into ions. The sample may be an analyte of interest. 
     The sample source  24  may include a supply of a sample to be analyzed. The sample of interest may be provided in a solution or mixture. The sample source  24  may include an injector, nebulizer or other suitable device configured to deliver solid, liquid or gaseous samples to the torch  100 . 
     The auxiliary gas source  26  may include a supply of the auxiliary gas AG. The auxiliary gas AG may be any suitable gas from which the plasma P can be formed or generated as described herein. In some embodiments, the auxiliary gas AG is argon gas. In other embodiments, the auxiliary gas AG is nitrogen gas. The auxiliary gas source  26  is configured to provide a pressurized supply and flow of the auxiliary gas AG to the torch  100 . The auxiliary gas source  26  may include a flow generator (e.g., a pump) and/or may contain a positively pressurized supply of the auxiliary gas AG. 
     The plasma gas source  28  may include a supply of the plasma gas PG. The plasma gas PG may be any suitable gas for serving the functions as described herein. In some embodiments, the plasma gas PG and the auxiliary gas AG have the same gas composition. In some embodiments, the plasma gas PG is argon gas. In other embodiments, the plasma gas PG is nitrogen gas. The plasma gas source  28  is configured to provide a pressurized supply and flow of the plasma gas PG to the torch  100 . The plasma gas source  28  may include a flow generator (e.g., a pump) and/or may contain a positively pressurized supply of the plasma gas PG. 
     The torch  100  has a torch longitudinal axis A-A, a proximal end  106 A and an axially opposing distal, terminal end  106 T. The torch  100  includes a flow control subassembly, unit or system  110  and an induction coil  150 . 
     The flow control system  110  has a flow control axis B-B, a proximal end  112 A, an axially opposing distal, terminal end  112 T. In some embodiments, the axes A-A and B-B are coaxial. 
     The flow control system  110  includes an injector tube  120 , an intermediate tube  130 , and a plasma tube  140 . The intermediate tube  130  circumferentially surrounds the injector tube  120 , and the plasma tube  140  circumferentially surrounds the intermediate tube  130 . The injector tube  120 , the intermediate tube  130 , and the plasma tube  140  terminate at distal, terminal ends  120 T,  130 T, and  140 T, respectively, proximate the torch terminal end  106 T. In some embodiments, the injector tube  120 , the intermediate tube  130 , and the plasma tube  140  are substantially concentric about the torch axis A-A. In some embodiments, the tubes  120 ,  130  and  140  form a unitary member. 
     In some embodiments, the injector tube  120 , the intermediate tube  130 , and the plasma tube  140  are each substantially cylindrical and circular in cross-section. The injector tube  120  has an inlet  122  and an outlet  124 . The intermediate tube  130  has an inlet  132  and an outlet  134 . The plasma tube  140  has an inlet  142  and an outlet  144 . 
     The injector tube  120  defines an axially extending sample passage  126  fluidly connecting the inlet  122  and the outlet  124 . An annular, radial gap G 1  is defined between the outer surface of the injector tube  120  and the inner surface of the intermediate tube  130 . The gap G 1  defines or forms an axially extending, tubular auxiliary gas passage  136  between the opposing surfaces of the injector tube  120  and the intermediate tube  130 . The auxiliary gas passage  136  fluidly connects the inlet  132  and the outlet  134 . An annular, radial gap G 2  is defined between the outer surface of the intermediate tube  130  and the inner surface of the plasma tube  140 . The gap G 2  defines or forms an axially extending, tubular plasma gas passage  146  between the opposing surfaces of the intermediate tube  130  and the plasma tube  140 . The plasma gas passage  146  fluidly connects the inlet  142  and the outlet  144 . 
     In some embodiments, the nominal width W 1  ( FIG. 1 ) of the gap G 1  is in the range of from about 2 mm to 4 mm. In some embodiments, the nominal width W 2  ( FIG. 1 ) of the gap G 2  is in the range of from about 0.8 mm to 1.5 mm. 
     The sample source  24 , the auxiliary gas source  26 , and the plasma gas source  28  may be fluidly coupled to the inlet  122 , the inlet  132 , and the inlet  142 , respectively, by corresponding conduits  29 . 
     The induction coil  150  (which may also be referred to an as a load coil or work coil) is electrically connected to the radio-frequency (RF) power supply  22 . The RF power supply  22  is configured to provide RF energy or electric current into and through the induction coil  150 . In some embodiments, the induction coil  150  is a helically wound coil. In some embodiments, the induction coil  150  is formed of a suitable material, such as copper or aluminum. 
     In some embodiments, the induction coil  150  includes an electrical conductor  151  that is helically wound into a plurality of windings or turns  153  (i.e., the induction coil  150  is a helically wound coil). The induction coil  150  extends from a proximal end  152 A to an opposing distal, terminal end  152 T. In some embodiments and as illustrated, the proximal end  152 A is defined by the first turn  153  and the distal end  152 T is defined by the last turn  153 . In some embodiments, the induction coil  150  has a coil axis C-C that is substantially coaxial with the torch axis A-A. In some embodiments, the induction coil  150  has a length L 1  ( FIG. 1 ) in the range of from about 16 mm to 20 mm. 
     In some embodiments, the injector tube  120  and the intermediate tube  130  are relatively arranged and configured such that the terminal end  130 T of the intermediate tube  130  extends forwardly of the terminal end  120 T of the injector tube  120  a distance L 2  ( FIG. 1 ). In some embodiments, the distance L 2  is at least 0.5 mm and, in some embodiments, is in the range of from about 1 mm to 4 mm. 
     The intermediate tube  130  and the plasma tube  140  are relatively arranged and configured such that the terminal end  140 T of the plasma tube  140  extends forwardly of the terminal end  130 T of the intermediate tube  130  a distance L 3  ( FIG. 1 ). In some embodiments, the distance L 3  is at least  13  mm and, in some embodiments, is in the range of from about 10 mm to 25 mm. 
     In some embodiments and as illustrated in  FIG. 1 , the plasma tube  140  and the induction coil  150  are relatively arranged and configured such that the terminal end  152 T of the induction coil  150  extends forwardly of the outlet opening  144  of the plasma tube  140  a distance L 4  ( FIG. 1 ). In some embodiments, the distance L 4  is at least 0.5 mm and, in some embodiments, is in the range of from about 1 mm to 5 mm. That is, the outlet opening  144  is rearwardly inset from the distal end  152 T of the induction coil  150  the distance L 4 . In some embodiments and as shown in  FIG. 1 , the outlet opening  144  is located within the induction coil  150  (i.e., axially between the ends  152 A and  152 T). 
     In some embodiments and as illustrated in  FIG. 1 , the plasma tube  140  and the induction coil  150  are relatively arranged and configured such that the terminal end  152 T of the induction coil  150  extends forwardly of the terminal end  140 T of the plasma tube  140  a distance L 5 . In some embodiments, the distance L 5  is at least 0.5 mm and, in some embodiments, is in the range of from about 1 mm to 5 mm. That is, the terminal end  140 T is rearwardly inset from the distal end  152 T of the induction coil  150  the distance L 5 . In some embodiments and as shown in  FIG. 1 , the terminal end  140 T of the plasma tube  140  is located within the induction coil  150  (i.e., axially between the ends  152 A and  152 T). 
     In some embodiments and as illustrated in  FIG. 1 , the outlet opening  144  is axially coincident with the terminal end  140 T, in which case the inset distances L 4  and L 5  are the same. 
     In some embodiments and as illustrated in  FIG. 1 , the outlet opening  144  is aligned with (i.e., centered on) the torch axis A-A. 
     In use, the sample gas SG is flowed through the sample gas passage  126 , the auxiliary gas AG is flowed through the auxiliary gas passage  136 , and the plasma gas PG is flowed through the plasma gas passage  146  in the direction F. It will be appreciated that the auxiliary gas stream AG is segregated from the sample gas stream SG by the injector tube  120  until the injector tube outlet  124 , and is segregated from the plasma gas stream PG by the intermediate tube  130  until the outlet  134 . 
     The induction coil  150  is powered to inductively heat the auxiliary gas stream AG in a coil induction region RI within the induction coil  150 . An electric spark may be applied for a short time to introduce free electrons into the auxiliary gas stream AG. The auxiliary gas AG is thereby energized into a plasma P. The plasma P may generally include a plasma base PB, an analytical zone AZ, and a plasma tail or recombination zone RZ. The sample gas stream SG may enter the plasma P, where the sample gas stream evaporates and the molecules of the sample of interest break apart and the constituent atoms ionize (e.g., in the analytical zone AZ). 
     In some embodiments, the plasma P has a temperature of at least 4000 degrees Celsius and, in some embodiments, a temperature in the range of from about 5000 to 7000 degrees Celsius. 
     The plasma gas stream PG generally flows along the inner wall of the plasma tube  140  to form a tubular curtain or sheath between the plasma P and the plasma tube  140  in a plasma gas separation zone PZ. 
     In other embodiments, the plasma tube  140  and the induction coil  150  are relatively arranged and configured such that the terminal end  152 T of the induction coil  150  and the terminal end  130 T of the plasma tube  140  are axially coincident (i.e., located at the same position along the torch axis A-A). That is, the distance L 1  ( FIG. 1 ) is zero and the terminal end  130 T is not inset from or projecting beyond the terminal end  152 T. 
     As discussed above, the configuration of the torch  100  can prevent or inhibit overheating of the plasma tube  140  sufficient to melt the terminal end of the plasma tube  140 . The plasma tube  140  ends prior to the hottest portions of the plasma P. 
     The injector tube  120  may be formed of suitable material. In some embodiments, the injector tube  120  is formed of quartz, sapphire or platinum. 
     The auxiliary tube  130  may be formed of suitable material. In some embodiments, the auxiliary tube  130  is formed of quartz. 
     The plasma tube  140  may be formed of suitable material. In some embodiments, the injector tube  120  is formed of quartz. 
     In some embodiments, the plasma tube  140  includes an opaque material at least in the portion  143  of the plasma tube  140  adjacent its terminal end  140 T. In some embodiments, the portion  143  includes an opaque material having a higher melting point than quartz. In some embodiments, the portion  143  includes silicon nitride or ceramic. Because the plasma tube  140  terminates at or inset from the end  152 T of the induction coil  150 , the opaque end portion  143  does not block an operator&#39;s view of the plasma P extending axially forward of the induction coil  150 . 
     With reference to  FIGS. 2-4 , an ICP torch system  12  according to further embodiments is shown therein. The ICP torch system  12  includes a radiofrequency power generator  22 , a sample source  24 , an auxiliary gas source  26 , and a plasma gas source  28  corresponding to the like numbered components of the ICP torch system  10 . The ICP torch system  12  further includes a torch  200  and a confining gas source  30 . The torch  200  includes a flow control subassembly, unit or system  210  and an induction coil  250 . The flow control system  210  includes an injector tube  220 , an intermediate tube  230 , and a plasma tube  240  corresponding to the injector tube  120 , the intermediate tube  130 , and the plasma tube  140 , respectively. The components  22 ,  24 ,  26 ,  28 ,  220 ,  230 ,  240 , and  250  are constructed and connected and operate in the same manner as described herein with regard to the ICP torch system  10 . 
     The ICP torch system  12  further includes confining gas tube  260  forming a part of the flow control system  210 . The torch  200  has a torch axis A-A, a proximal end  206 A and an axially opposing distal, terminal end  206 T. In use, a flow or stream of a confining gas CG (from the confining gas source  30 ) is additionally forced or flowed through the torch  200  in the forward direction F toward the distal end  206 T of the torch  200 . 
     The confining gas source  30  may include a supply of a confining gas CG. The confining gas CG may be any suitable gas for serving the functions as described herein. In some embodiments, the confining gas CG includes air. In other embodiments, the confining gas CG is nitrogen, oxygen, or a mixture of both. The confining gas source  30  is configured to provide a pressurized supply and flow of the confining gas CG to the torch  200 . The confining gas source  30  may include a flow generator (e.g., a pump) and/or may contain a positively pressurized supply of the confining gas CG. 
     The confining gas tube  260  terminates at a distal, terminal end  260 T proximate the torch terminal end  206 T. In some embodiments, the confining gas tube  260  is also substantially concentric about the torch axis A-A. In some embodiments, the confining gas tube  260  substantially cylindrical and circular in cross-section. 
     The confining gas tube  260  circumferentially surrounds the plasma tube  240 . An annular, radial gap G 3  is defined between outer surface of the plasma tube  140  and the inner surface of the confining gas tube  260 . The gap G 3  defines or forms an axially extending, tubular confining gas passage  266  between the opposing surfaces of the plasma tube  240  and the confining gas tube  260 . The confining gas passage  266  fluidly connects the inlet  262  and the outlet  264 . 
     In some embodiments, the nominal width W 3  ( FIG. 3 ) of the gap G 3  is at least 0.5 mm and in some embodiments, is in the range of from about 1 mm to 2.5 mm. 
     The confining gas source  30  may be fluidly coupled to the inlet  262  by a conduit  29  ( FIG. 2 ). 
     In some embodiments, the tubes  220 ,  230 ,  240 , and  260  form a unitary member. 
     The plasma tube  240  and the confining gas tube  260  are relatively arranged and configured such that the terminal end  260 T of the confining tube  260  extends or protrudes forwardly of the terminal end  240 T of the plasma tube  240  a distance L 9  ( FIG. 3 ). That is, a section  267  of the confining gas tube  260  projects or protrudes forwardly beyond the plasma tube  240 . In some embodiments, the distance L 9  is at least 3 mm and, in some embodiments, is in the range of from about 2 mm to 9 mm. 
     In some embodiments and as illustrated in  FIG. 3 , the confining gas tube  260  and the induction coil  250  are relatively arranged and configured such that the terminal end  260 T of the confining gas tube  260  extends forwardly of the distal terminal end  252 T of the induction coil  250  a distance L 10  ( FIG. 3 ). In some embodiments, the distance L 10  is at least 3 mm and, in some embodiments, is in the range of from about 2 mm to 10 mm. That is, the terminal end  260 T protrudes forwardly beyond the distal end  252 T of the induction coil  250  the distance L 10 . 
     In other embodiments, the confining gas tube  260  and the induction coil  150  are relatively arranged and configured such that the terminal end  252 T of the induction coil  250  and the terminal end  260 T of the confining gas tube  260  are axially coincident (i.e., located at the same position along the torch axis A-A). That is, the distance L 10  ( FIG. 3 ) is zero and the confining gas tube  260  does not protrude forwardly beyond the terminal end  252 T. 
     In use, the torch system  12  is operated in substantially the same manner as described above for the torch system  10 , except for the additional provision of a confining gas stream CG. The sample gas SG is flowed through the sample gas passage  226 , the auxiliary gas AG is flowed through the auxiliary gas passage  236 , and the plasma gas PG is flowed through the plasma gas passage  246  in the forward direction F. Additionally, the confining gas CG is flowed through the confining gas passage  266  in the forward direction F. The auxiliary gas stream AG is segregated from the sample gas stream SG by the injector tube  220  until the injector tube outlet  224 , and is segregated from the plasma gas stream PG by the intermediate tube  230  until the outlet  234 . The plasma gas stream PG is segregated from the confining gas stream CG by the plasma tube  240  until the plasma tube outlet  244 . 
     The induction coil  250  is powered to inductively heat the auxiliary gas stream AG in a coil induction region RI ( FIG. 2 ) within the induction coil  250 . An electric spark may be applied for a short time to introduce free electrons into the auxiliary gas stream AG. The auxiliary gas AG is thereby energized into a plasma P. The plasma P may generally include a plasma base PB, an analytical zone AZ, and a plasma tail or recombination zone RZ. The sample gas stream SG may enter the plasma P, where the sample gas stream evaporates and the molecules of the sample of interest break apart and the constituent atoms ionize (e.g., in the analytical zone AZ). 
     The plasma gas stream PG flows along the inner wall of the plasma tube  240  to form a tubular plasma gas curtain or sheath PS between the plasma P and the plasma tube  240  in a plasma gas separation zone PZ ( FIG. 3 ). 
     The confining gas stream CG flows along the inner wall of the confining gas tube  260  to form a tubular confining gas curtain or sheath CS ( FIGS. 3 and 4 ) between the plasma P and the confining gas tube  260  in a confinement zone CZ downstream of the plasma tube terminal end  240 T. Because the confining gas tube  260  is radially interposed between the plasma P and the induction coil  250 , the confining gas sheath CS also separates the plasma P from the induction coil  250 . The induction coil  250  is thus shielded from contact with the plasma by the confining gas sheath CS and the confining gas tube  260 . The confining gas sheath CS provides a thermal buffer between the plasma P and the confining gas tube  260 . The bulk flow of the confining gas sheath CS also convectively transfers heat from the plasma P out of the torch  200 , away from the confining gas tube  260 . 
     In some embodiments, the confining gas stream CG cools the confining gas tube  260 . 
     The confining gas sheath CS and the confining gas tube  260  also serve to prevent the plasma gas from diffusing into the induction coil  250 . 
     The confining gas sheath CS and the confining gas tube  260  may also serve to focus the plasma P or maintain the density and shape of the plasma P in the confinement zone CZ. This may improve the robustness of the plasma P. 
     Although the plasma tube  240  and the plasma gas sheath PS may not be necessary to protect the induction coil  250  from the plasma P, the plasma tube  240  and the plasma gas sheath PS may serve to ensure that the composition of the gas(es) delivered to the plasma region are suitable for ignition and analysis. The plasma tube  240  delivers the auxiliary gas AG to the interior of the induction coil  250 . 
     For example, in some embodiments the auxiliary gas AG and the plasma gas PG are both argon gas. In this case mixing between the gas streams AG and PG does not dilute the argon concentration, ensuring that the argon concentration of the gas at the point of plasma ignition (within the induction coil  250 , near the proximal end  252 A) is sufficient to be ignited and sustain the plasma base PB. Once the argon gas is ignited, the ionized argon (i.e., plasma) will be electrically conductive to absorb more RF power from the remainder of the induction coil  250  to sustain a stable plasma. If too much of another gas (e.g., nitrogen) became mixed in with the argon gas, ignition of the plasma may be prevented by the greater energy requirement to ignite the mixed gas. 
     Similarly, the plasma tube  240  and the plasma gas sheath PS can prevent air or other undesired material from becoming entrained in or diffusing into the region of the torch  200  where the plasma P is analytically helpful. 
     Because the confining gas stream CG is segregated and from the gas supply to the plasma P by the plasma tube  240 , and is segregated from the plasma P by the plasma gas sheath PS, the confining gas CG can be selected from a wider range of potential gases without undermining the performance of the torch  200 . In particular, the selected confining gas CG material may be a gas that has higher thermal conductivity and/or lower cost than the plasma gas 
     PG. 
     The confining gas CG may be any suitable gas or mixture of gases. In some embodiments, the confining gas CG includes nitrogen gas. In some embodiments, the confining gas CG includes carbon dioxide gas. In some embodiments, the confining gas CG includes argon gas. In some embodiments, the confining gas CG includes air. In some embodiments, the confining gas CG includes a mixture of two or more of nitrogen gas, carbon dioxide gas, oxygen gas, and argon gas. 
     The use of a confining gas CG material (e.g., nitrogen) that requires higher energy input to ionize than the auxiliary gas AG material (e.g., argon) can also enhance the ability of the confining gas sheath CS to confine, shape or focus the plasma P and physically separate the plasma P from the confining tube  260 . The confining gas sheath CS operates effectively as a chemical insulator about the formed plasma P that is less susceptible to ionization, thereby limiting or inhibiting radial expansion of the plasma P. 
     In some embodiments, the volumetric flow rate of the confining gas CG through the torch  200  is at least 7 liters/minute and, in some embodiments, is in the range of from about 4 to 10 liters/minute. 
     In some embodiments, the volumetric flow rate of the confining gas CG through the torch  200  is at least 1 times the volumetric flow rate of the plasma gas PG through the torch  200 . In some embodiments, the volumetric flow rate of the confining gas CG through the torch  200  is in the range of from about 0.25 to 1.25 times the volumetric flow rate of the plasma gas PG through the torch  200 . 
     In some embodiments, the volumetric flow rate of the plasma gas stream PG is less than 10 liters/minute and, in some embodiments, is in the range of from about 6 to 16 liters/minute. 
     In some embodiments, the volumetric flow rate of the sample stream SG is in the range of from about 0.8 to 1.2 liters/minute, the volumetric flow rate of the auxiliary gas stream AG is in the range of from about 0.5 to 1.2 liters/minute, the volumetric flow rate of the plasma gas stream PG is in the range of from about 6 to 16 liters/minute, and the volumetric flow rate of the confining gas stream CG is in the range of from about 4 to 10 liters/minute. 
     Advantageously, the provision of the confining gas sheath CS, the confining gas tube  260 , and a truncated plasma tube  240  can significantly lower the consumption of argon or other plasma gas PG necessary to cool the torch  200  sufficiently to prevent melting of the torch. Because the plasma tube  240  is shortened relative to the induction coil  250 , the plasma tube  250  is not exposed to the greater temperatures to which plasma tubes in conventional torches are subjected. The confining gas sheath CS and the confining gas tube  260  serve to protect the induction coil  250  from the portion of the plasma not separated by the shortened plasma tube  240 , and to confine, focus or shape the plasma P in the region where the plasma is not controlled by the plasma tube  240 . 
     The confining gas tube  260  may be formed of suitable material. In some embodiments, the confining gas tube  260  includes quartz, borosilicate glass, Pyrex glass, and/or ceramic (e.g., alumina). 
     In some embodiments, the confining gas tube  260  is substantially transparent or translucent. In some embodiments, the confining gas tube  260  is substantially transparent or translucent and the plasma tube  240  includes an opaque material at least in the portion  243  ( FIG. 3 ) of the plasma tube  240  adjacent its terminal end  240 T, as described above. In some embodiments, the portion  243  includes an opaque material having a higher melting point than quartz. In some embodiments, the portion  243  includes silicon nitride. Because the plasma tube  240  is shortened to an axial termination at or inset from the end  252 T of the induction coil  250 , the opaque end portion  243  does not block an operator&#39;s view of the plasma P extending axially forward of the induction coil  250 . Because the confining gas tube  260  is substantially transparent or translucent, the portion of the plasma P extending axially forward of the induction coil  250  is visible through the confining gas tube  260 . 
     In some embodiments, the confining gas CG is supplied to the torch  200  with a positive pressure to force the confining gas CG into and through the confining gas passage  266 . For example, the confining gas CG may be supplied as compressed air or other gas from a liquid gas source. A gas regulator and mass flow meter may be provided to control the flow rate of the confining gas CG. In further embodiments, the confining gas CG may be supplied using a fan or pump. 
     In some embodiments, the confining gas CG is supplied to the torch  200  using a negative pressure to draw the confining gas CG into and through the confining gas passage  266 . In an example torch system  14  as shown in  FIG. 5 , the torch  200  is mounted in a torch enclosure  370 . The torch enclosure  370  has an inlet  370 A providing fluid communication between the confining gas tube inlet  262  and a confining gas supply (e.g., ambient air). The torch enclosure  370  defines a chamber  370 D containing the torch  200 , and an outlet  370 B fluidly communicating with the chamber  370 D. A ventilation fan or blower  370 C is operable to pull the exhaust gases from the torch  200  out of the enclosure  370  through the outlet  370 B. The suction from the ventilation fan  370 C introduces a negative pressure that draws the confining gas CG into the confining gas tube inlet  262  and through the confining gas passage  266 . 
     With reference to  FIG. 6 , a torch  400  according to further embodiments is shown therein. The torch  400  is constructed in the same manner as the torch  200 , and may be used in the same manner as the torch  200 , except as follows. 
     The plasma tube  440  of the torch  400  includes a radial side opening in the form of a side cut out opening  449  intersecting the terminal outlet opening  444  of the plasma tube  440 . The plasma tube  440  and the induction coil  450  are relatively arranged and configured such that the terminal end  452 T of the induction coil  450  is located forward of a portion of the cut out opening  449 . At least a portion of the cut out opening  449  is located inside of the induction coil  450 . 
     In the illustrated embodiment, the distal, terminal end  440 T of the plasma tube  440  projects forwardly of the coil distal end  452 T. However, in other embodiments, the terminal end  440 T may also be coincident with or inset from the coil distal end  452 T. 
     With reference to  FIG. 7 , a torch  500  according to further embodiments is shown therein. The torch  500  is constructed in the same manner as the torch  400 , and may be used in the same manner as the torch  400 , except that the torch  500  includes two side cut out openings  549  that intersect the terminal outlet opening  544  of the plasma tube  540  and have a portion located inside the induction coil  550 . 
     With reference to  FIG. 8 , a torch  600  according to further embodiments is shown therein. The torch  600  is constructed in the same manner as the torch  400 , and may be used in the same manner as the torch  400 , except that the torch  600  includes a side cut out opening  649  having an alternative shape. The side cut out  649  is located within the induction coil  650 . 
     With reference to  FIG. 9 , a torch  700  according to further embodiments is shown therein. The torch  700  is constructed in the same manner as the torch  400 , and may be used in the same manner as the torch  400 , except that the torch  700  includes a radial side opening in the form of a side opening  749  that does not intersect the terminal end  740 T of the plasma tube  740 . The side opening  749  is located within the induction coil  750 . 
     It will be appreciated that different numbers, shapes, and distributions of side cut outs and other openings may be employed. 
     With reference to  FIG. 10 , a torch  800  according to further embodiments is shown therein. The torch  800  is constructed in the same manner as the torch  200 , and may be used in the same manner as the torch  200 , except as follows. 
     The auxiliary tube  830  of the torch  800  is provided with a radially enlarged distal end section  838 . The increased outer diameter of the distal end section  838  creates a narrowed gap G 4  in the plasma gas passage  846  proximate the distal end  830 T of the auxiliary tube  830 . In some embodiments, the width W 11  of the narrowed gap G 4  is in the range of from about 0.7 mm to 1.7 mm. 
     With reference to  FIG. 11 , a torch  900  according to further embodiments is shown therein. The torch  900  is constructed in the same manner as the torch  200 , and may be used in the same manner as the torch  200 , except as follows. In the torch  900 , the confining gas tube  960  is provided with multiple confining gas tube inlets  962  through which the confining gas CG is flowed in. In the torch  900 , the confining gas tube inlets  962  direct each of the incoming gas streams in a radial direction that substantially intersects the torch axis A-A. 
     With reference to  FIGS. 12 and 13 , a torch  1000  according to further embodiments is shown therein. The torch  1000  is constructed in the same manner as the torch  900 , and may be used in the same manner as the torch  900 , except as follows. In the torch  1000 , the confining gas tube  1060  is provided with multiple confining gas tube inlets  1062  through which the confining gas CG is flowed in. In the torch  1000 , the confining gas tube inlets  1062  direct each of the incoming gas streams in a radial direction that is transverse to and radially offset from the torch axis A-A. This configuration may cause the confining gas stream to swirl helically about the plasma tube  1040 . 
     With reference to  FIG. 14 , a torch  1100  according to further embodiments is shown therein. The torch  1100  is constructed in the same manner as the torch  200 , and may be used in the same manner as the torch  200 , except as follows. 
     In the torch  1100 , the confining gas tube  1160  is provided as a separate component that is removably secured to the remainder of the torch  1100 . The confining gas tube  1160  is mechanically detachable from the plasma tube  1140 . This may be useful to enable an operator to replace a damaged confining gas tube  1160 , to re-install the confining gas tube  1160  on a new plasma tube  1140 , or to replace the confining gas tube  1160  with a confining gas tube having a different size and/or shape, for example. 
     In some embodiments, an annular ring  1163  is mounted between the confining gas tube  1160  and the plasma tube  1140 . The ring  1163  may serve as a mechanical coupling between the confining gas tube  1160  and the plasma tube  1140  that retains the tubes  1140 ,  1160  in proper alignment. In some embodiments, the ring  1163  serves as a fluid seal between the confining gas tube  1160  and the plasma tube  1140 . 
     The ring  1163  may be formed of any suitable material(s). In some embodiments, the ring  1163  is formed of polyether ether ketone (PEEK). 
     The torch  1100  may further include metal plasma ignition electrodes  1170 . The electrodes  1170  extend between the confining gas tube  1160  and the plasma tube  1140 , and radially external of the plasma tube  1140 . Each electrode  1170  includes a portion  1170 A adjacent or contacting the outer surface of the plasma tube  1140 . The ignition electrodes  1170  are electrically connected to a high voltage electrical power supply  34 . In some embodiments, the power supply  34  is operable to generate a voltage between the electrodes  1170  and ground in the range of 1 kV or greater. In use, the power supply  34  and the electrodes are used to generate a spark or sparks in the auxiliary gas stream AG to initiate the creation of the plasma P. 
     In certain configurations, a torch as described herein can be used in a system configured to perform mass spectrometry (MS). For example and referring to  FIG. 15 , an ICP-MS device or system  1400  includes a sample introduction device  1420 , an ICP torch  1410  as described herein that can be used to sustain an atomization/ionization source, a mass analyzer  1424 , a detector or detection device  1426 , a processing device  1428  and a display  1430 . The torch  1410  may take any of the configurations described herein (e.g., any one of the torches  100 - 1200 ), for example. The system  1400  also includes (but not depicted in  FIG. 15 ) an RF power supply  22 , a sample supply, an auxiliary gas source  26 , a plasma gas source  28 , and a confining gas source  32  (in the case of a torch  1410  employing a confining gas stream CG as disclosed herein) operably connected to the torch  1410 . 
     The sample introduction device  1420 , the torch  1410 , the mass analyzer  1424  and/or the detection device  1426  may be operated at reduced pressures using one or more vacuum pumps. 
     The sample introduction device  1420  may include an inlet system configured to provide sample to the torch  1410 . The inlet system may include one or more batch inlets, direct probe inlets and/or chromatographic inlets. The sample introduction device  1420  may be an injector, a nebulizer or other suitable devices that may deliver solid, liquid or gaseous samples to the torch  1410 . 
     The mass analyzer  1424  may take numerous forms depending generally on the sample nature, desired resolution, etc. and exemplary mass analyzers may comprise one or more rod assemblies such as, for example, a quadrupole or other rod assembly. 
     The detection device  1426  may be any suitable detection device that may be used with existing mass spectrometers, e.g., electron multipliers, Faraday cups, coated photographic plates, scintillation detectors, multi-channel plates, etc., and other suitable devices that will be selected by the person of ordinary skill in the art, given the benefit of this disclosure. 
     The processing device  1428  typically includes a microprocessor and/or computer and suitable software for analysis of samples introduced into the MS device  1400 . One or more databases may be accessed by the processing device  1428  for determination of the chemical identity of species introduced into the MS device  1400 . 
     In certain configurations, an ICP torch described herein can be used in optical emission spectroscopy (OES). Referring to  FIG. 16 , an ICP-OES device or system  1500  includes a sample introduction device  1520 , an ICP torch  1510  as described herein and optionally comprising one or more induction devices, and a detection device  1526 . The torch  1510  may take any of the configurations described herein (e.g., any one of the torches  100 - 1200 ), for example. The system  1500  also includes (but not depicted in  FIG. 16 ) an RF power supply  22 , a sample supply, an auxiliary gas source  26 , a plasma gas source  28 , and a confining gas source  32  (in the case of a torch  1510  employing a confining gas stream CG as disclosed herein) operably connected to the torch  1510 . 
     The sample introduction device  1520  may vary depending on the nature of the sample. In certain examples, the sample introduction device  1520  may be a nebulizer that is configured to aerosolize liquid sample for introduction into the torch  1510 . In other examples, the sample introduction device  1520  may be an injector configured to receive sample that may be directly injected or introduced into the torch  1510 . Other suitable devices and methods for introducing samples will be readily selected by the person of ordinary skill in the art, given the benefit of this disclosure. 
     The detector or detection device  1526  may take numerous forms and may be any suitable device that may detect optical emissions, such as optical emission  1524 . For example, the detection device  1526  may include suitable optics, such as lenses, mirrors, prisms, windows, band-pass filters, etc. The detection device  1526  may also include gratings, such as echelle gratings, to provide a multi-channel OES device. Gratings such as echelle gratings may allow for simultaneous detection of multiple emission wavelengths. The gratings may be positioned within a monochromator or other suitable device for selection of one or more particular wavelengths to monitor. In certain examples, the detection device  1526  may include a charge coupled device (CCD). In other examples, the OES device  1500  may be configured to implement Fourier transforms to provide simultaneous detection of multiple emission wavelengths. 
     The detection device  1526  may be configured to monitor emission wavelengths over a large wavelength range including, but not limited to, ultraviolet, visible, near and far infrared, etc. The OES device  1500  may further include suitable electronics such as a microprocessor and/or computer and suitable circuitry to provide a desired signal and/or for data acquisition. Suitable additional devices and circuitry are known in the art and may be found, for example, on commercially available OES devices such as AVIO 200 series and AVIO 500 series OES devices commercially available from PerkinElmer Health Sciences, Inc. The optional amplifier  1530  e.g., a photomultiplier tube, may be operative to increase a signal  1528 , e.g., amplify the signal from detected photons, and provides the signal to display  1532 , which may be a readout, computer, etc. In examples where the signal  1528  is sufficiently large for display or detection, the amplifier  1530  may be omitted. In certain examples, the amplifier  1530  is a photomultiplier tube (PMT) configured to receive signals from the detection device  1526 . Other suitable devices for amplifying signals, however, will be selected by the person of ordinary skill in the art, given the benefit of this disclosure. If desired the PMT can be integrated into the detector  1526 . 
     In certain examples, an ICP torch as described herein can be used in an atomic absorption spectrometer (AAS). Referring to  FIG. 17 , a single beam ICP-AAS  1600  comprises a power source  1620 , a lamp  1622 , a sample introduction device  1626 , a torch  1610  as described herein, a detector or detection device  1632 , an optional amplifier  1636  and a display  1638 . The torch  1610  may take any of the configurations described herein (e.g., any one of the torches  100 - 1200 ), for example. The system  1600  also includes (but not depicted in  FIG. 17 ) an RF power supply  22 , a sample supply, an auxiliary gas source  26 , a plasma gas source  28 , and a confining gas source  32  (in the case of a torch  1610  employing a confining gas stream CG as disclosed herein) operably connected to the torch  1610 . 
     The power source  1620  may be configured to supply power to the lamp  1622 , which provides one or more wavelengths of light  1624  for absorption by atoms and ions. Suitable lamps include, but are not limited to mercury lamps, cathode ray lamps, lasers, etc. The lamp may be pulsed using suitable choppers or pulsed power supplies, or in examples where a laser is implemented, the laser may be pulsed with a selected frequency, e.g. 5, 10, or 20 times/second. The exact configuration of the lamp  1622  may vary. For example, the lamp  1622  may provide light axially along the torch  1610  or may provide light radially along the torch  1610 . The example shown in  FIG. 17  is configured for axial supply of light from the lamp  1622 . 
     As sample is atomized and/or ionized in the torch  1610 , the incident light  1624  from the lamp  1622  may excite atoms. That is, some percentage of the light  1624  that is supplied by the lamp  1622  may be absorbed by the atoms and ions in the torch  1610 . The remaining percentage of the light  1630  may be transmitted to the detection device  1632 . The detection device  1632  may provide one or more suitable wavelengths using, for example, prisms, lenses, gratings and other suitable devices such as those discussed above in reference to the OES devices, for example. The signal  1634  may be provided to the optional amplifier  1636  for increasing the signal provided to the display  1638 . To account for the amount of absorption by sample in the torch  1610 , a blank, such as water, may be introduced prior to sample introduction to provide a 100% transmittance reference value. The amount of light transmitted once sample is introduced into the torch  1610  may be measured, and the amount of light transmitted with sample may be divided by the reference value to obtain the transmittance. 
     AAS device  1600  may further include suitable electronics such as a microprocessor and/or computer and suitable circuitry to provide a desired signal and/or for data acquisition. Suitable additional devices and circuitry may be found, for example, on commercially available AAS devices such as AAS spectrometers commercially available from PerkinElmer Health Sciences, Inc. 
     Where the torch  1610  is configured to sustain an inductively coupled plasma, a radio frequency generator electrically coupled to an induction device may be present. In certain embodiments, a double beam AAS device, instead of a single beam AAS device could instead be used. 
     While certain shapes have been depicted in the drawings for the tubes of the torches (e.g., tubes  120 ,  130 ,  140 ,  260 ), these shapes are provided for illustrative purposes. It will be appreciated that other shapes may be employed in some embodiments of the technology. 
     The present technology has been described herein with reference to the accompanying drawings, in which illustrative embodiments of the technology are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This technology may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the technology to those skilled in the art. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present technology. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90° or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of present disclosure, without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the invention as defined by the following claims. The following claims, therefore, are to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described herein, what is conceptually equivalent, and also what incorporates the essential idea of the invention.