Patent Publication Number: US-2012037817-A1

Title: System for analyzing a sample or a sample component and method for making and using same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system or apparatus for analyzing a sample or a sample component including a fluorescence detection subsystem and to methods for making and using same. 
     More particularly, the present invention relates to a system or apparatus for analyzing a sample or a sample component and to methods for making and using same, where the system in certain embodiments includes a fluorescent detection subsystem including high voltage, high frequency current and voltage controlled power supply, a software detection correction assembly and light sources including an excimer light source or lamp. 
     2. Description of the Related Art 
     UV fluorescence is a general technique used to detect and quantitatively determine sulfur contents of samples. Most current fluorescent instruments use broad spectrum light sources equipped with filters designed to a narrow wavelength or frequency range of light that is designed to interact with the sample. Generally, the light interacts with fluorescently active compounds in the sample or sample component in a light chamber, where the sample can be supplied directly to the chamber, via a sample loop, or from a chromatography column. 
     Besides broad spectrum light sources, atomic vapor lamps have been used for light sources. These lamps have a narrower wavelength or frequency range and require less filtering, but these lamps are prone to a steady decrease in light production over time. Such reduction in light production over time causes problems in instrument stability and problems in reducing the detection limit of the instrument. For UV fluorescence detection, zinc, cadmium and other metal lamps have been used as light sources. However, many of these lamps generate light that is less than optimal for the detection of certain species such as UV fluorescence detection of SO 2 . SO 2  absorbs UV light between about 190 nm and 230 nm. NO also absorbs UV light in that range, but the NO absorption spectra has a gap (does not absorb light) between about 215 nm and 225 nm. While zinc lamp generates light centered at 220 nm, the generated light is broader than 220 nm even with filtering and includes light capable of exciting NO, which interferes with SO 2  detection. 
     In U.S. Pat. No. 7,268,355, a UV fluorescent instrument was disclosed using a specifically designed excimer lamp as a light source. The lamp used a mixture of krypton and chlorine, which generates light in a narrow wavelength range centered at about 222 nm. 
     Although an excimer light source or lamp has been disclosed for use in analytical instruments, there is a need in the art for improved excimer light sources or lamps for use in UV fluorescent instruments, and especially instruments that include fluorescent light sources such as excimer light sources or lamps having voltage and current control subsystems and/or software detection signal adjustment subsystems to improve instrument stability and reliability and to reduce the detection level for total sulfur and/or total nitrogen. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a system or apparatus for analyzing a sample or sample component including a sample delivery subsystem, optionally an oxidation subsystem, a detection subsystem and an analyzer subsystem. The sample delivery subsystem can comprise a direct injection assembly, a sample loop assembly, in-line sampling assembly, a chromatography unit (e.g., gas chromatography (GC), liquid chromatography (LC), high performance liquid chromatography (HPLC), medium pressure liquid chromatography (MPLC) and low pressure liquid chromatography (LPLC), phased liquid chromatography (PLC), reverse phased liquid chromatography (RPLC)) or any other sample separation unit. The oxidation subsystem includes a combustion tube having an oxidation zone, where the oxidation subsystem is capable of substantially completely converting all oxidizable sample components into their corresponding oxides. The detection subsystem comprises a light source including a high frequency and high voltage power supply having tight current and voltage control, optionally a software detection signal adjustment subsystem, a detection chamber, and a detector. The analyzer subsystem generally includes a digital processing unit (which can be a computer), a memory, a display, a print, a mass storage device, communication hardware and software, other known peripheries and software for receiving and analyzing a detector signal. The light source can be a filtered broad spectrum light source such as a metal vapor lamp, a gas lamp or other broad spectrum light source, a filtered or unfiltered excimer light source, or a filtered or unfiltered laser light source. 
     Embodiments of the present invention also provide a system or apparatus for analyzing a sample or sample component including a sample delivery subsystem, an oxidation subsystem, a detection subsystem and an analyzer subsystem. The sample delivery subsystem can comprise a direct injection assembly, a sample loop assembly, in-line sampling assembly, a chromatography unit (e.g., gas chromatography (GC), liquid chromatography (LC), high performance liquid chromatography (HPLC), medium pressure liquid chromatography (MPLC) and low pressure liquid chromatography (LPLC), phased liquid chromatography (PLC), reverse phased liquid chromatography (RPLC)) or any other sample separation unit. The oxidation subsystem includes a combustion tube having an oxidation zone, where the oxidation subsystem is capable of substantially completely converting all oxidizable sample components into their corresponding oxides. The detection subsystem comprises a light source including a high frequency power supply having tight current and voltage control, optionally a software detection signal adjustment subsystem, a detection chamber, and a detector. The analyzer subsystem generally includes a digital processing unit (which can be a computer), a memory, a display, a print, a mass storage device, communication hardware and software, other known peripheries and software for receiving and analyzing a detector signal. The light source can be a filtered broad spectrum light source such as a metal vapor lamp, a gas lamp or other broad spectrum light source, a filtered or unfiltered excimer light source, or a filtered or unfiltered laser light source. 
     Embodiments of the present invention also provide a method for analyzing a sample or sample component including the step of supplying a sample to a system of this invention. The method may also include the step of separating the sample into components. The method may also include the step of oxidizing the sample or sample components into their corresponding oxides prior to fluorescent detection. Once the sample or sample component is in a proper state for detection, the sample or sample component is then forwarded to a detection subsystem, where the sample or sample component enters a fluorescent reaction chamber, where it absorbs light from a light source. A portion of the sample or sample component is converted to an excited sample or an excited sample component. A portion of the excited sample or the excited sample component then fluoresces and a portion of the fluorescent light exits the light reaction chamber through a detector port entering into a detector. The detector converts a number of photons entering the detector (fluorescent light intensity) into a proportional electric signal. The electrical signal is then analyzed in the analyzer and related back to a concentration of the fluorescently active species in the sample or component, and ultimately to a concentration of an atomic species such as a sulfur, nitrogen, etc. in the sample or sample component. The light source can be a filtered broad spectrum light source such as a metal vapor lamp, a gas lamp or other broad spectrum light source, a filtered or unfiltered excimer light source, or a filtered or unfiltered laser light source. 
     For example, if the fluorescently active species is sulfur dioxide (SO 2 ), then the electrical signal is proportional to the amount of sulfur dioxide in the light reaction chamber and ultimately to the amount of sulfur in the sample or sample component. If more than one sample component includes sulfur, then the sum of the concentration of sulfur in each component containing sulfur yields the total sulfur content in the sample. If the sample included sulfur dioxide as a component, then the signal is directly proportional to the concentration of sulfur in the sample. If the original sample includes chemically bound sulfur or a combination of sulfur dioxide and chemically bound sulfur, then the subsystem includes an oxidization subsystem that converts chemically bound sulfur into sulfur dioxide. If the sample includes chemically bound nitrogen, then NO can be determined by an ozone induced chemiluminescence subsystem. In certain embodiments, the NO chemilumineses upstream of the UV detection subsystem. 
     The present invention also provides a method for performing chromatographic analyses including the step of supplying a sample from a sample delivery system into the a separation unit under conditions to affect a given separation of the sample into components. After separation, the sample components are forwarded to the detector assembly. Optionally, the components may first be oxidized in a combustion assembly. In the detector assembly, the component is brought into contact with light from a light source (in certain embodiments the light source comprises a light source or lamp) in a light reaction chamber, where a portion of a fluorescently active species is excited and a portion of the excited species fluoresce. A portion of the fluorescent light exits the chamber via a detector port into a detector to produce an output electrical signal. The electrical signal is converted into a concentration of the fluorescently active species and, in turn, into a concentration of a corresponding atomic component of interest in the sample, such as sulfur or nitrogen. If the active species is sulfur dioxide, then the analyzer can produce a concentration of sulfur in each component and a total concentration of sulfur in the sample. The light source can be a filtered broad spectrum light source such as a metal vapor lamp, a gas lamp or other broad spectrum light source, a filtered or unfiltered excimer light source, or a filtered or unfiltered laser light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with references to the following detailed description together with the appended illustrative drawings in which like elements are numbered the same: 
         FIG. 1A  depicts an embodiment of a system of this invention including a fluorescent detection subsystem. 
         FIG. 1B  depicts another embodiment of a system of this invention, including an oxidation subsystem and a fluorescent detection subsystem. 
         FIG. 1C  depicts another embodiment of a system of this invention, including an oxidation assembly, a chemiluminescent subsystem and a fluorescent detection subsystem. 
         FIG. 2A  depicts an embodiment of a fluorescent detector subsystem of this invention. 
         FIG. 2B  depicts another embodiment of a fluorescent detector subsystem of this invention. 
         FIG. 2   c  depicts another embodiment of a fluorescent detector subsystem of this invention. 
         FIG. 3  depicts an embodiment of a high voltage power supply of this invention. 
         FIG. 4A  depicts an embodiment of an oxidizing subsystem of this invention. 
         FIG. 4B  depicts another embodiment of an oxidizing subsystem of this invention. 
         FIG. 4C  depicts another embodiment of an oxidizing subsystem of this invention. 
         FIG. 5  depicts an embodiment of a chemiluminescent detector subsystem of this invention. 
         FIGS. 6A&amp;B  depict longitudinal and lateral cross-sectional views of an embodiment of an excimer light source of this invention having a straight outer reflective electrode. 
         FIGS. 6C&amp;D  depict longitudinal and lateral cross-sectional views of another embodiment of an excimer light source of this invention having a tapered outer reflective electrode, where the taper is designed to increase light exiting the light source. 
         FIGS. 6E&amp;F  depict longitudinal and lateral cross-sectional views of another embodiment of an excimer light source of this invention have a tapered outer reflective electrode, where the taper is designed to increase light exiting the light source. 
         FIG. 7A  depicts an output spectrum of an excimer lamp or light source of this invention from 200 nm to 900 nm. 
         FIG. 7B  depicts an expanded output spectrum of an excimer lamp or light source of this invention from 200 nm to 250 nm. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The inventors have found that a system or apparatus for analyzing a sample or sample component can be constructed using a specially designed excimer light source, which emits a very narrow wavelength range (even a near monochromatic range) of light centered at a wavelength designed to provide selective excitation of a fluorescently active analyte, without exciting other potentially interfering compounds. For example, an apparatus designed for sulfur or total sulfur analysis using a light source designed to electively excite SO 2  with minimal excitation of NO, a species that interferes with the SO 2  fluorescent detection. The inventors have also found that the system can include a software detection signal adjustment subsystem adapted to improve instrument stability and reliability and to reduce detection limits of the analyte for which the light source is designed. The inventors have found that the software detection signal adjustment subsystem can be used with any light source including an excimer light source. For example, if the analyte is sulfur dioxide, then the light source should be capable of producing light tightly centered around 222 nm. In the case of an excimer light source, the source includes a gas mixturecapable of generating light centered at about 222 nm. If the instrument is intended for analyzing another fluorescently active species, then the excimer light source incudes a gas mixture capable of generating light centered at a wavelength within the absorption spectrum of the species. 
     For additional details of fluorescent detection and chemiluminescence, the reader is referred to the following patents and patent applications: U.S. Pat. Nos. 4,904,606, 4,914,037, 4,916,077, 4,950,456, 5,916,523, 6,075,609, 6,143,245, 6,458,328, 6,636,314, 7,018,845, 7,244,395, 7,291,203, Ser. Nos. 10/970,686, 10/970,353, 11/949,610, 11/834,495, 11/834,509, and 11/834,514, incorporated herein by reference. Several of these patents and applications relate to improvements in oxidizing subsystem design, in fluorescent subsystem design, in chemiluminescent subsystem design, and in general in the area of fluorescent and chemiluminescent measurements of sulfur and/or nitrogen in samples and sample components. 
     In certain embodiments, the present invention broadly relates to a system or apparatus for analyzing a sample or sample component using fluorescence spectroscopy. The apparatus includes a sample delivery subsystem, which can be a direct delivery subsystem or a sample separation subsystem. The system can optionally include an oxidation subsystem for oxidizing an oxidizable component of the sample to its corresponding oxides, where one or more of the oxides can be a fluorescently active species when exposed to light of the proper frequency or frequency range. The system also includes a detection subsystem for detecting fluorescent light emitted by excited fluorescently active species in the sample, components or oxides after exposure to the excitation light. The system also includes an analyzer subsystem, where the analyzer subsystem generally includes a digital processing unit (which can be a computer), a memory, a display, a print, a mass storage device, communication hardware and software, other known peripheries and software for receiving and analyzing a detector signal. The sample delivery subsystem can comprise a direct injection assembly, a sample loop assembly, a gas chromatography unit, a liquid (regular performance, medium performance or high performance) chromatography unit, an electrophoreses unit or any other sample separation unit. The detection subsystem includes a light source apparatus, a detection chamber, a detector, and a software detection signal adjustment subsystem. The light source apparatus comprises a high frequency power supply adapted to tightly control supply voltage, frequency and/or current and to power a light source such as a metal vapor lamp, a gas lamp, an excimer lamp or a laser. 
     In other embodiments, the present invention also broadly relates to a method for performing chromatographic analyses including the step of supplying a sample to a detector assembly. In certain embodiments, the sample is supplied directly to the detector assembly using a direct delivery assembly. In other embodiments, the sample is first separated into components in a separation unit under conditions to affect a given separation of the sample into components prior to supplying the sample components to the detector assembly. In other embodiments, the sample or sample components are oxidized in an oxidation assembly adapted to convert all oxidizable species in the sample or sample components into their corresponding oxides. In the detector assembly, the sample, sample component, oxidized sample, or oxidized sample component is brought into contact with light from a light source in a light reaction chamber, where a portion of a fluorescently active species is excited and a portion of the excited species fluoresce. A portion of the fluorescent light exits the chamber via a detector port into a detector to produce an output electrical signal. The electrical signal is converted in the analyzer into a concentration of the active species in the sample, sample component, oxidized sample, or oxidized sample component. The information can then be used to determine the concentration of an atomic component in the entire sample and/or each sample component. 
     The systems are especially well suited for UV fluorescence chromatography, where the system includes a UV fluorescent detection subsystem. The detection subsystem includes an excimer light source having a high frequency power supply, a detection chamber, a detector, and a software detection signal adjustment subsystem. The excimer light source is designed to generate light of a very narrow frequency or wavelength range within the UV spectrum of the electromagnetic spectrum centered at a wavelength that results in efficient excitation of a desired analyte, while minimizing excitation of interfering species. For example, a krypton-chloride excimer light source emits light centered at 222 nm, which is centered in a gap between absorption bands of a NO absorption spectrum. After filtering, the light generated by a krypton-chloride excimer light source is well suited for selective excitation of SO 2 , while minimizing excitation of NO. However, the system and method can also be practiced with metal vapor lamps, gas lamps, and lasers. 
     In an embodiment of this invention, the light source is an excimer light source. The excimer light sources are generally of an elongated toroidal shaped dielectric barrier discharge gas enclosure including an inner throughbore and a discharge gap. The gas enclosure is adapted to be filled with a gas or gas mixture, where light is produced either by a atomic species or an excimer formed from the gases in the enclosure. An excimer is a multi atom complex or molecular complex, where at least one of the atoms or molecules is in an excited state. This complex then emits light. Depending on the excimer, part of the emitted light will be narrowly centered at a specific wavelength or frequency. 
     The excimer light sources also include a first electrode disposed in the inner throughbore or disposed on an inner surface of the inner throughbore. The excimer light sources also include a light outlet port comprising an end of the enclosure through which light exits the excimer light source. The excimer light sources also include an outer reflective electrode disposed on an exterior surface of the enclosure, where the outer reflective electrode can be tapered or untapered. The outer reflective electrode is designed to concentrate and increase light exiting the light output port. The inner and the outer electrodes are electrically connected to an excimer light source high frequency, high voltage power supply. 
     The power supply assembly applies a potential across the electrodes sufficient to cause the dielectric barrier to breakdown in a controlled manner. The controlled breakdown result in the formation of micro electrical discharges across the gap. These micro discharges excite the gas or gas mixture producing excited species that then emit a very narrow frequency range of light due to the purity of the emitting species. 
     In embodiments designed for sulfur dioxide detection, the gas in the enclosure comprises a mixture of krypton and chlorine, which forms a krypton-chloride excimer or exciplex upon excitation by the micro electrical discharges across the gap. By controlling the composition of the gas mixture and the pressure of the mixture in the enclosure, the krypton-chloride (KrCl) excimer light source can be tuned to produce light tightly centered at 222 nm, ideal for sulfur dioxide fluorescence detection at a given output intensity. Although a KrCl excimer light source generates light mainly centered at 222 nm, under certain conditions light of longer wavelengths are also produced. In certain embodiments, the excimer light is passed through an excitation light filter to reduce or eliminate these longer wavelengths of produced light. 
     In all the systems of this invention, the detection subsystems can optionally include a light or optical filters interposed between the fluorescence reaction chamber and the light source and between the fluorescence reaction chamber and the detector. In all the systems of this invention, the fluorescence reaction chamber includes a sample inlet and a sample outlet. The fluorescence reaction chamber also includes a light inlet port and a fluorescent light outlet port, where the fluorescent light outlet port is disposed at an angle relative to the inlet port, where the angle is adapted to reduce or eliminate excitation light from entering the light outlet port. In certain embodiments, the angle is between about 60° and about 120°. In other embodiments, the angle is between about 70° and about 110°. In other embodiments, the angle is between about 80° and about 100°. In other embodiments, the angle is between about 85° and about 95°. In other embodiments, the angle is about 90°. The fluorescence reaction chamber can also be mirrored as set forth in U.S. Pat. Nos. 6,075,609 and 6,636,314, incorporated herein by reference. 
     For systems that include an oxidation subsystem, the sample or sample components are forwarded to a combustion chamber. The combustion chamber includes a sample inlet and an oxidizing agent inlet and an oxidized sample outlet. The sample and oxidizing agent can be simultaneously introduced into the combustion chamber or separately introduced. In certain embodiments, the oxidizing agent is sequentially supplied to the combustion chamber. In certain embodiments, an inert gas can also be introduced into the combustion chamber along with the sample and oxidizing agent. 
     Once in the combustion chamber, oxidizable components in the sample are converted into their corresponding oxides and water vapor, where the combustion chamber is maintained at an elevated temperature above an ignition temperature for an oxidizing agent-sample mixture or sufficient to oxidize all or substantially all oxidizable sample components into their corresponding oxides. Generally, the elevated temperature is above about 300° C. In other embodiments, the temperature is above about 600° C. In other embodiments, the temperature is above about 900° C. In other embodiments, the temperature is between about 300° C. and about 2000° C. In other embodiments, the temperature is between about 600° C. and about 1500° C. In other embodiments, the temperature is between about 800° C. and about 1300° C. The combustion apparatuses of this invention can be operated at ambient pressure, at reduced pressure down to ten of millimeters of mercury, or at higher than ambient pressures up to a 1000 or more psia. 
     The inlet to the combustion zone can include a nebulizer adapted to atomize the sample within the oxidizing agent and an optional inert gas to improve oxidation efficiency. 
     The term “substantially all” in the context of oxidation means that at least 90% of the oxidizable components in the combustible material have been converted to their corresponding oxides. In other embodiments, the term “substantially all” means that at least 95% of the oxidizable components in the combustible material have been converted to their corresponding oxides. In other embodiments, the term “substantially all” means that at least 98% of the oxidizable components in the combustible material have been converted to their corresponding oxides. In other embodiments, the term “substantially all” means that at least 99% of the oxidizable components in the combustible material have been converted to their corresponding oxides. 
     Suitable Devices for Use in the Systems of this Invention 
     Suitable detection systems include, without limitation, any device that converts light intensity into a proportional electrical signal. Exemplary devices include a photo-multiplier tube (PMT), Charge-coupled Device (CCD), an Intensified Charge Coupled Devise (ICCD) or the like. 
     Suitable sample supply systems include, without limitation, any sample supply system including an auto-sampler, a septum for direct injection, a sampling loop for continuous sampling, an analytical separation system such as a GC, LC, MPLC, HPLC, LPLC, or any other sample supply system used now or in the future to supply samples to analytical instrument combustion chambers or mixture or combinations thereof. 
     Suitable light sources include, without limitation, metal vapor light sources, gas light sources, excimer light sources, laser light sources or any other light source capable of generating UV light. Exemplary metal vapor light sources or lamps include, without limitation, zinc lamps, cadmium lamps, mercury lamps, mercury halide lamps, and other metal lamps that have been used as light sources. Exemplary gas lamps include, without limitation, xenon lamps, deuterium lamps, or other gases that emit UV light. 
     Suitable excimer light sources for use in this invention are set forth in Table I. 
     
       
         
           
               
             
               
                 TABLE I 
               
               
                   
               
               
                 Near and Far Ultraviolet Excimer Gas Emission Species and 
               
               
                 Emission Frequency 
               
               
                   
               
             
            
               
                 NEAR ULTRAVIOLET 
               
            
           
           
               
               
               
               
            
               
                   
                 Argon 
                 Gas-Ion 
                 364 nm (UV-A) 
               
               
                   
                 XeF 
                 Gas (excimer) 
                 351 nm (UV-A) 
               
               
                   
                 N 2   
                 Gas 
                 337 nm (UV-A) 
               
               
                   
                 XeCL 
                 Gas (excimer) 
                 308 nm (UV-B) 
               
            
           
           
               
            
               
                 FAR ULTRAVIOLET 
               
            
           
           
               
               
               
               
            
               
                   
                 Krypton SHG* 
                 Gas-Ion/BBO crystal 
                 284 nm (UV-B) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 264 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 257 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 250 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 248 nm (UV-C) 
               
               
                   
                 KrF 
                 Gas (excimer) 
                 248 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 244 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 238 nm (UV-C) 
               
               
                   
                 Argon SHG 
                 Gas-Ion/BBO crystal 
                 229 nm (UV-C) 
               
               
                   
                 KrCl 
                 Gas (excimer) 
                 222 nm (UV-C) 
               
               
                   
                 ArF 
                 Gas (excimer) 
                 193 nm (UV-C) 
               
               
                   
                   
               
               
                   
                 *SHG means UV Gas-Ion Second Harmonic Generation Light 
               
            
           
         
       
     
     Software Detector Signal Adjustment 
     Background 
     While not mandatory, typically before use, an instrument of this invention is calibrated to generate a calibration curve. A calibration curve is produced by analyzing or running several samples having known, but different, concentrations of target fluorescently active species of an element, such as SO 2  for sulfur or NO for nitrogen. The measured responses are then plotted producing the calibration curve. A response of an unknown sample is then measured and compared to the calibration curve. The comparison yields a concentration of target species in the unknown sample. This approach, however, assumes that instrument conditions such as an intensity of light generated by the light source, light source drift, etc., remain constant. 
     Aging effects of a light source often cause the light source output to change, typically to decrease, over time and cause a change, typically an increase, in an output noise level. Both changes in light output and output noise level directly impact instrument results, reproducability and repeatability. In certain embodiments of the present invention, the system includes control features to compensate for changes in light output and noise level without changing the operating conditions of the light source. These types of controls operate well with light sources that include power supplies optimized for the best performance and longevity of the light source and are adapted to enable ideal conditions for lamp operation, while enabling for lamp output or intensity corrections over time, such as a decrease in lamp intensity over time. 
     One aspect of the control features is to adjust a detector signal by software based on information concerning changes in light source performances over time. This type of software signal adjustment is adapted to significantly increase an interval between calibrations and is ideally suited for all types of light sources including lower quality light sources such as Zn lamps and high quality light sources such as excimer lamps. Additionally, digital conditioning of the output of a light source provides additional details on light source performance and additional procedures for software correction of the detector signal based on such conditioning. These type of control systems can also provide information critical for predicting or indicating when lamp servicing or replacement is required, reducing instrument down time—improving maintenance scheduling. 
     Signal filtering of the light source output is adapted to reduce or minimize the output noise level of the light source resulting in improvement or repeatability of instrument measurements. Such filtering and signal adjustment also serve to lower instrument down time as well as to improve performance of the instrument. 
     Application 
     The software detection signal adjustment or conditioning subsystem of the invention includes a light detector/sensor, such as a photodiode, adapted to monitor the light output of the light source. In certain embodiments, the light detector/sensor is located at the back of the fluorescence chamber. However, the light detector/sensor can also be located anywhere else, provided it is measuring the light output of the light. The light detector/sensor is adapted to detect and monitor the light output of the light source to produce present light source output characteristics including an intensity value, a noise valve, etc. and to provide continuous information on light source output characteristics. The present light source intensity value and other characteristics detected by the light detector/sensor is converted to a digital signal. The light output intensity value is compared with a stored light source output intensity value. Values for other characteristics captured during the last calibration can also be compared. A difference between the present light source intensity value and the stored light source intensity value is either subtracted from or added to the fluorescent detector signal for an unknown sample to adjust the signal for a shift or change in lamp intensity. This correction is adapted to compensate for a difference between the light source output at the last calibration and actual light source output during each sample analysis. 
     Furthermore, the signal from the light detector/sensor can be digitally processed and digital filtering can be applied to the fluorescent detector signal to reduce or minimize light source noise further improving repeatability of measurements of unknown samples between calibration runs. 
     Parts of the System 
     Light Detector/Sensor 
     The software feedback assembly includes a stable light detector/sensor such as a stable photodiode used to detect the light source output level and is adapted to convert light intensity into a proportional electrical signal. The light detector/sensor provides a continuous signal for software feedback and detector signal processing. 
     A/D Converter 
     The software feedback assembly also includes a high resolution analog to digital converter (e.g., a sigma delta A/D converter). The converter is adapted to convert the light sensor signal into a digital signal for software feedback control through signal digital processing. 
     Digital Signal Conditioning 
     The software feedback assembly also includes a microprocessor based unit. The unit is adapted to store a light source output value captured during calibration. The stored light source output value is compared to a present light source output value and based on the comparison, the unit adjusts a signal from the detector such as a photomultiplier to reduce or minimize the aging effects of the light source on measured value of unknown samples. The unit also provides filtering of the signal. The unit can also be adapted to perform other needed functions as required. 
     High Voltage Power Supply with Tight Current and Voltage Control 
     In the present invention, a DC power supply is used to power an excimer light source. The DC power supply is used to ensure that powering of a bridge controller and MOSFET switch unit is well controlled. An input voltage to the controller and the MOSFET switch unit is tightly regulated between about 8V and about 30V. The bridge controller is used for driving gates of the MOSFET switch unit, measuring an excimer light source current and voltage to ensure an over current protection and an over voltage protection and to tightly control excimer light source brightness control. The power supply of this invention is specially designed or adapted to provide best conditions for lamp operation—optimized and controlled operating current, optimized and controlled operating voltage, optimized and controlled operating frequency, etc. 
     Gate drive outputs are connected directly to the gates of the MOSFET switch unit. The gates are designed to allow current to flow only into a transformer, if one of the high-side switches of the MOSFET switch unit is turned on and at the same time a low-side switch on the other half-bridge is turn on. Maximum output power can be achieved if the turn on time of the high-side switch on one half-bridge exactly overlaps with the turn on time of the low-side switch on the other half-bridge of the MOSFET switch unit. 
     To set the lamp brightness, two basic dimming methods are used: analog dimming and burst dimming. The analog dimming method comprises regulating lamp current via a DC voltage program, where the lamp current is regulated by a current regulator, i.e., the lamp current is controlled directly. The burst dimming method comprising turning the lamp on and off at a low frequency with a certain duty cycle. Burst dimming can be internal (DC voltage programs duty cycle of the generated burst pulses) or external (external PWM signal is directly used for burst dimming). 
     Dimming circuits are integrated into the bridge controller. Each dimming method can be applied independent of each other. Although a bridge controller capable of providing high frequency power to a lamp with analog and burst dimming can be used, the inventors of this invention used a TPS68000 highly efficient phase shift full bridge CCFL controller available from Texas Instruments Incorporated. For additional information the reader is directed to the TI specification publication SLVS524A—October 2005—Revised February 2006. 
     The bridge controller includes an oscillator component that produces a high frequency output. The internal operating frequency is set by a resistor connected to frequency programming input. Over current protection input is used to monitor a voltage derived from a current sensor. The lamp current is derived from voltage on a shunt resistor. Measured voltage is used to regulate lamp current. The lamp voltage is divided in a capacitance divider. Measured voltage is used to regulate lamp voltage and to provide over voltage protection. The high frequency of energy input to the lamp increases lamp output. Alternatively, lamp output can be increased by increasing applied voltage, but increasing voltage is limited by the dielectric breakdown limit of the lamp&#39;s envelope. 
     Systems 
     Referring now to  FIG. 1A , an embodiment of a system of this invention, generally  100 , is shown to include a sample supply or introduction subsystem  102 . The system  100  also includes a fluorescent detection subsystem  104  connected to the sample supply or introduction subsystem  102  via a first conduit  106 . The system  100  also includes an analyzer subsystem  108  connected to the fluorescent subsystem  104  via a first signal conduit  110 . 
     Another embodiment of a system  100  is shown in  FIG. 1B , where the system  100  further includes an oxidation subsystem  112  interposed between the sample supply or introduction subsystem  102 . The oxidation subsystem  112  is connected to the sample supply or introduction subsystem  102  via a second conduit  114  and to the fluorescent detection subsystem  104  via a third conduit  116 . 
     Another embodiment of a system  100  is shown in  FIG. 1C , the system  100  further includes a chemiluminescent detection subsystem  118  interposed between the oxidation subsystem  112  and the fluorescent detection subsystem  104 . The chemiluminescent detection subsystem  118  is connected to the oxidation subsystem  112  via a fourth conduit  120  and to the fluorescent subsystem  104  via a fifth conduit  122 . The chemiluminescent detection subsystem  118  is also connected to the analyzer subsystem  108  via a second signal conduit  124 . Optionally, the subsystem  118  may simply include an ozone generator that introduces ozone into the oxidized sample or sample component to reduce or eliminate NO converting it into NO 2 , a non-interfering nitrogen oxide. In this type of an alternative arrangement, the subsystem  118  can also include a chamber in which ozone is allowed to mix with the oxidized sample or sample component. 
     Each subsystem will be described in detail below. 
     The sample supply or introduction system  102  of use in this invention can be any sample supply system including an auto-sampler, a septum for direct injection, a sampling loop for continuous sampling, an inline injection system, an analytical separation system such as a GC, LC, MPLC, HPLC, LPLC, electrophoresis, or any other sample supply or introduction system used now or in the future to supply or introduce a sample into an analytical instrument of this invention. In the system of  FIG. 1A , the sample is introduced directly into the fluorescent detector without any preconditioning such as oxidation. Such systems are generally suitable for testing samples known or expected to contain SO 2 . While the systems of  FIGS. 1B and 1C  rely on sample oxidation to produce SO 2 , for subsequent analysis. Of course, the system of  FIGS. 1B and 1C  can be used for samples that are known or expected to contain SO 2  as well as samples containing non-oxidized sulfur or chemically bound sulfur. 
     In all the above system embodiments, the analyzer subsystem is generally a digital processing system including a digital processing unit, memory (cache, RAM, ROM, etc.), a mass storage device, peripheral or the like. The analyzer takes as input the output from the detector associated with the detection subsystem such as a PMT and converts the signal into a concentration of an element of interest in the original sample. The data can then be displayed, printed, or the like. 
     Fluorescent Detection Subsystems 
     Referring now to  FIG. 2A , an embodiment of a UV fluorescent detection subsystem of this invention, generally  200 , is shown to include a light source assembly  202 , a fluorescent reaction assembly  240 , and a detector  280 . 
     The light source assembly  202  includes an excimer light source  204 , a power supply  206  and optionally an excitation light filter  208 . The power supply  206  is connected to the excimer light source  204  via electrical conduits  210   a  and  210   b . If present, the filter  208  is adapted to receive an excitation light beam  212  and filter the excitation light beam  212  to produce a filtered excitation light beam  214  having a narrow wavelength (or frequency) range of light, i.e., a range narrowly distributed around a desired wavelength. In certain embodiments, the desired wavelength is about 220 nm, which is a wavelength optimal for SO 2  absorption. 
     The fluorescent reaction assembly  240  includes a fluorescent reaction chamber  242 . The chamber  242  also includes a sample inlet  244  connected to a sample inlet conduit  246  and a sample outlet  248  connected to an outlet conduit  250 . The chamber  242  also includes an excitation light port  252  in optical communication with the excitation light beam  212  or the filtered excitation light beam  214  and a detector port  254  in optical communication with the detector  280 . The detector port  254  is situated at a right angle to the excitation port  252 ; however, the angle can be any angle provided the angle is sufficient to reduce an amount of excitation light from entering the detector port  254 . The inner chamber walls  256  can be mirrored to increase an amount of fluorescent light entering the detector port  254  and the detector  280  as set forth in U.S. Pat. Nos. 6,075,609 and 6,636,314, incorporated herein by reference. 
     The detector  280  is connected to an analyzer subsystem  108  described previously, via a signal conduit  282 . 
     Referring now to  FIG. 2B , an embodiment of a UV fluorescent detection subsystem of this invention, generally  200 , is shown to include a light source assembly  202 , a fluorescent reaction assembly  240 , and a detector  280 . 
     The light source  202  includes an excimer light source  204 , a power supply  206  and optionally an excitation light filter  208 . The power supply  206  is connected to the excimer light source  204  via electrical conduits  210   a  and  210   b . If present, the filter  208  is adapted to receive an excitation light beam  212  and filter the excitation light beam  212  to produce a filtered excitation light beam  214  having a narrow wavelength (or frequency) range of light, i.e., a range narrowly distributed around a desired wavelength. In certain embodiments, the desired wavelength is about 220 nm, which is a wavelength optimal for SO 2  absorption. 
     The fluorescent reaction assembly  240  includes a fluorescent reaction chamber  242 . The chamber  242  includes a sample inlet  244  connected to a sample inlet conduit  246  and a sample outlet  248  connected to an outlet conduit  250 . The chamber  242  also includes an excitation light port  252  in optical communication with the excitation light beam  212  or the filtered excitation light beam  214  and a detector port  254  in optical communication with the detector  280 . The detector port  254  is situated at a right angle to the excitation port  252 ; however, the angle can be any angle provided the angle is sufficient to reduce an amount of excitation light from entering the detector port  254 . The inner chamber walls  256  can be mirrored to increase an amount of fluorescent light entering the detector port  254  and the detector  280  as set forth in U.S. Pat. Nos. 6,075,609 and 6,636,314, incorporated herein by reference. The chamber  242  can also include an optional light intensity detector/sensor  258 , which is connected to the analyzer  108  via a signal conduit  260  for use in the software feedback control described above. 
     The detector  280  is connected to an analyzer subsystem  108  described previously, via a signal conduit  282 . 
     Referring now to  FIG. 2C , another embodiment of a UV detection subsystem of this invention, generally  200 , is shown to include a light source assembly  202 , a fluorescent reaction assembly  240 , and a detector  280 . 
     The light source  202  includes an excimer light source  204  and a power supply  206  and an excitation light filter  208 . The power supply  206  is connected to the excimer light source  204  via electrical conduits  210   a  and  210   b . The filter  208  is adapted to receive an excitation light beam  212  and filter the excitation light beam  212  to produce a filtered excitation light beam  214  having a narrow wavelength (or frequency) range of light, i.e., a range narrowly distributed around a desired wavelength. In certain embodiments, the desired wavelength is about 220 mm, which is a wavelength optimal for SO 2  absorption. The filtered excitation light beam  214  then passes through a spreader or collimator  216  to form a spread beam  218 . 
     The fluorescent reaction assembly  240  includes a fluorescent reaction chamber  242 . The chamber  242  includes a sample inlet  244  connected to a sample inlet conduit  246  and a sample outlet  248  connected to an outlet conduit  250 . The chamber  242  also includes an excitation light port  252  in optical communication with the spread beam  218  and a detector port  254  in optical communication with the detector  280 . The detector port  254  is situated at a right angle to the excitation port  252 ; however, the angle can be any angle provided the angle is sufficient to reduce an amount of excitation light from entering the detector port  254 . The inner chamber walls  256  can be mirrored to increase an amount of fluorescent light entering the detector port  254  and the detector  280  as set forth in U.S. Pat. Nos. 6,075,609 and 6,636,314, incorporated herein by reference. The fluorescent reaction chamber  242  can also include a fluorescent light filter  262 . 
     The detector  280  is connected to an analyzer subsystem  108  described previously, via a signal conduit  282 . 
     In those systems designed to detect both nitrogen and sulfur, the oxidized sample can be split into two parts, one part going to a sulfur detection system and the other part going to a nitrogen detection system. In those systems having a fluorescent subsystem and a chemiluminescent subsystem, the chemiluminescent subsystem measured measures nitrogen in the form NO, while the chemiluminescent subsystem measures sulfur in the form of SO 2 . 
     High Voltage Power Supply 
     Referring now to  FIG. 3 , in an embodiment of a feedback/closed loop control subsystem of this invention, generally  300 , a DC power supply  302  is used as the main power for the light source such as the excimer light source  204 . The DC power supply  302  is used to supply power to a bridge controller  304  and MOSFET switch unit  306 . The bridge controller  304  includes thirteen input and output channels a-m. The switch unit  306  includes switches  308   a &amp; b  and  310   a &amp; b . The switch unit  306  also includes seven input and output channels t-z. The DC power supply  302  is adapted to supply a well controlled initial voltage to the bridge controller  304  at the input channel via supply line  312   +  and to the MOSFET switch unit  306  at the input channel  4  via supply line  312 ″. An input voltage to the controller  304  and the MOSFET switch unit  306  is tightly regulated to a value between about 8V and about 30V. The bridge controller  304  includes gate drive outputs  314   a - d  used for driving gates  316   a - d  of the MOSFET switch unit  306 . The gates  314   a - d  and  316   a - d  are adapted to measure a light source current and voltage to ensure over current protection and over voltage protection and to tightly control light source brightness. 
     The bridge controller channels a-m are defined as follows: 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Bridge Controller Channel Descriptions 
               
            
           
           
               
               
               
            
               
                   
                 ID 
                 Description 
               
               
                   
                   
               
               
                   
                 a 
                 DC Input Voltage 
               
               
                   
                 b 
                 Chip Enable ON/OFF 
               
               
                   
                 c 
                 Analog dimming input (0 to 3.3 V DC) 
               
               
                   
                 d 
                 Internal burst dimming input (0 to 5 V DC) 
               
               
                   
                 e 
                 External burst dimming input (PWM signal) 
               
               
                   
                 f 
                 Operating frequency programming 
               
               
                   
                 g 
                 Light source current regulation 
               
               
                   
                 h 
                 Over current protection 
               
               
                   
                 i 
                 over voltage protection/Light source voltage regulation 
               
               
                   
                 j 
                 Gate drive output 314d 
               
               
                   
                 k 
                 Gate drive output 314c 
               
               
                   
                 l 
                 Gate drive output 314b 
               
               
                   
                 m 
                 Gate drive output 314a 
               
               
                   
                   
               
            
           
         
       
     
     The switch unit channels t-z are defined as follows: 
     
       
         
           
               
             
               
                 TABLE II 
               
             
            
               
                   
               
               
                 Switch Unit Channel Descriptions 
               
            
           
           
               
               
               
            
               
                   
                 ID 
                 Description 
               
               
                   
                   
               
               
                   
                 t 
                 DC Input Voltage 
               
               
                   
                 u 
                 Driving gate 316a 
               
               
                   
                 v 
                 Driving gate 316b 
               
               
                   
                 w 
                 Driving gate 316c 
               
               
                   
                 x 
                 Driving gate 316d 
               
               
                   
                 y 
                 Transformer positive voltage output 
               
               
                   
                 z 
                 Transformer negative voltage output 
               
               
                   
                   
               
            
           
         
       
     
     The gate drive outputs  314   a - d  are connected directly to the gates  316   a - d  of the MOSFET switch unit  306 . The gates  314   a - d  and the gates  316   a - d  are designated to allow current to flow only into a transformer  318 , if a switch  308   a  is turned ON in one half bridge  320   a  and at the same time a switch  310   a  on the other half-bridge  320   b  is turned ON. Maximum output power can be achieved if a turn ON time of the switch  308   a ,  308   b  on one half-bridge  320   a ,  320   b  exactly overlaps with a turn ON time of the switch  310   a ,  310   b  on the other half-bridge  320   b ,  320   a.    
     To set the light source  204  brightness, the apparatus and methods of this invention utilize two basic dimming methods. The first dimming method comprises analog dimming, where a DC voltage programs the light source  204  current regulated by a current regulator so that the light source  204  current is controlled directly. The second dimming method comprises burst dimming, where the light source  204  is turned ON and OFF at a low frequency with a certain duty cycle. The burst dimming method can be internal (i.e., the DC voltage programs the duty cycle of the generated burst pulses) or external (i.e., an external PWM signal is directly used for burst dimming). The dimming circuits are integrated into bridge controller  304 . The dimming methods can be applied independent of each other. 
     The high voltage power supply  300  also includes a frequency setting resistor  322  adapted to control an internal operating frequency, which serves as the frequency programming input channel f of the bridge controller  304 . The over current protection input is used to monitor a voltage derived from a current sensor  324 . The light source current is derived from a voltage on a shunt resistor  326 . A current measuring apparatus  328  measures a current used for light source current regulation. The light source voltage is derived from a capacitance divider  330  including a first capacitor  332  and a second capacitor  334 . A voltage measuring apparatus  336  measures a voltage used for lamp voltage regulation and light source over voltage protection. The high voltage power supply  300  produces high voltage outputs  338  and  340 . 
     Oxidation Subsystems 
     Referring now to  FIG. 4A , an embodiment of an oxidizing or combustion subsystem of this invention, generally  400 , is shown to include a furnace  402  and an oxidizing agent supply  404 . 
     The furnace  402  includes a sample inlet  406  connected to a sample input conduit  408  and an oxidized sample outlet  410  connected to an oxidized sample conduit  412 . The furnace  402  also includes an oxidizing zone  414  and a heater  416 . The furnace  402  also includes an oxidizing agent inlet  418  connected to an oxidizing agent conduit  420 . 
     Referring now to  FIG. 4B , an embodiment of an oxidizing subsystem of this invention, generally  440 , is shown to include a furnace  442  and an oxidizing agent supply  444 . 
     The furnace  442  includes a nebulizer  446  including a sample inlet  448  connected to a sample input conduit  450  and an oxidizing agent inlet  452  connected to an oxidizing agent conduit  454 . The furnace  442  also includes an oxidizing zone  456  and a heater  458 . The furnace  442  also includes an oxidized sample outlet  460  connected to an oxidized sample conduit  462 . 
     Referring now to  FIG. 4C , an embodiment of an oxidizing subsystem of this invention, generally  470 , is shown to include a furnace  472  and an oxidizing agent supply  474 . 
     The furnace  472  includes a nebulizer  476  including a sample inlet  478  connected to a sample input conduit  480  and an oxidizing agent inlet  482  connected to an oxidizing agent conduit  484 . The furnace  472  also includes an oxidizing zone  486  and a heater  488 . The furnace  472  also includes a second oxidizing agent inlet  490  connected to a second oxidizing agent conduit  492 . The furnace  472  also includes an oxidized sample outlet  494  connected to an oxidized sample conduit  496 . The oxidizing zone  486  includes two static mixers  498 . The two static mixers  498  and the second oxidizing agent inlet  490  are adapted to improve combustion efficiency. 
     Chemiluminescent Detection Subsystems 
     Referring now to  FIG. 5 , an embodiment of a chemiluminescent subsystem of this invention, generally  500 , is shown to include an ozone reaction chamber  502 , an ozone source  503  and a detector  504 . 
     The ozone reaction chamber  502  includes an ozone inlet  508  connected to an ozone conduit  510 . The ozone reaction chamber  502  also includes a sample inlet  512  connected to a sample conduit  514 . The ozone reaction chamber  502  also includes a sample outlet  516  connected to a sample outlet conduit  518 . The ozone reaction chamber  502  also includes a detector port  520 . The inner chamber walls can be mirrored to increase an amount of chemiluminescent light entering the detector port  520  and the detector  504  as more fully described in U.S. Pat. Nos. 6,075,609 and 6,636,314, incorporated herein by reference. 
     The ozone source  503  includes an ozone generator  522  and an ozone generator power supply  524 , where the power supply  524  is connected to the ozone generator  522  via an electric conduit  526 . The ozone generator  522  includes an ozone outlet  528  connected to the ozone conduit  510 . The ozone generator  522  also includes an oxygen or air inlet  530  connected to an oxygen or air supply  532  via an oxygen or air electrical conduit  534 . The ozone source  503  is adapted to supply sufficient ozone to the ozone reaction chamber to cause NO to be oxidized to a chemiluminescently inactive species and reduce nitrogen interference with SO 2  detection in the fluorescent subsystem. 
     The detector  504  is connected to an analyzer subsystem described previously, via a data conduit  536 . 
     Alternatively, ozone can simply be added to the oxidized sample or sample components to remove any NO so that NO cannot interfere with SO 2  detection as more fully described in U.S. Pat. No. 7,244,395, incorporated herein by reference. 
     Excimer Light Sources 
     Referring now to  FIGS. 6A&amp;B , an embodiment of an excimer light source subsystem of this invention, generally  600 , is shown to include housing  602 , an excimer light source assembly  620 , and a light source power supply assembly  670 , where the housing surrounds the excimer light source assembly  620 . 
     The excimer light source assembly  620  includes a dielectric barrier gas enclosure  622 . The enclosure  622  includes an outer dielectric barrier  624 , an inner dielectric barrier  626 , and end dielectric barriers  628 , defining an enclosure interior  630 . The assembly  620  also includes an output light window  632  situated at a distal end  634  of the enclosure  622  and disposed at a distal end  604  of the housing  602 , while a proximal end  636  is situated near a proximal end of the housing  606 . The assembly  620  also includes a hollow interior region  638 , in which an inner electrode can be disposed as described below. The interior  630  is adapted to be filled with an excimer gas  640  that produces light of a narrow frequency range centered around a desired frequency. Of course, all excimer so produce some light centered around other frequencies. Often this other light can contribute to unwanted background in the fluorescent chamber or may excite other species that may be present in the fluorescent chamber other than SO 2 . If this is the case, then the assembly  620  can also include a filter as described in a subsequent embodiment. 
     The power supply assembly  670  includes power supply  672 , an inner electrode  674  comprising a mesh of a conductive material and an outer electrode  676  comprising a solid conductive material (i.e., in the form of a shell or hollow tube) and including an inner mirrored surface  678 . The inner electrode  674  is connected to the power supply  672  via a first conductive conduit  680 . The outer electrode  676  is connected to the power supply  672  via a second conductive conduit  682 . The first conductive conduit  680  and the second conductive conduit  682  are connected to outputs of the power supply  672 . The power supply  672  is adapted to produce an output capable of producing excimer gas species  640  in the interior  630  of the gas enclosure  622 . The output is generally in the form of a high frequency waveform output optimized to produce a stable light output. The waveform is an oscillator and can comprise a pure sinusoidal waveform, a combination of sinusoidal waveforms (squares waves, etc.) or any other continuously oscillatory waveforms capable of producing a stable excimer light source output. 
     Referring now to  FIGS. 6C&amp;D , another embodiment of an excimer light source subsystem of this invention, generally  600 , is shown to include housing  602 , an excimer light source assembly  620 , and a light source power supply assembly  670 , where the housing surrounds the excimer light source assembly  620 . 
     The excimer light source assembly  620  includes a dielectric barrier gas enclosure  622 . The enclosure  622  includes an outer dielectric barrier  624 , an inner dielectric barrier  626 , and end dielectric barriers  628 , defining an enclosure interior  630 . The assembly  620  also includes an output light window  632  situated at a distal end  634  of the enclosure  622  and disposed at a distal end  604  of the housing  602 , while a proximal end  636  is situated near a proximal end of the housing  606 . The assembly  620  also includes a hollow interior region  638 , in which an inner electrode can be disposed as described below. The assembly  620  also includes a light filter  642  adapted to reduce light not centered about a desired frequency. The interior  630  is adapted to be filled with an excimer gas  640  that produces light of a narrow frequency range centered around a desired frequency. Of course, all excimer so produce some light centered around other frequencies. Often this other light can contribute to unwanted background in the fluorescent chamber or may excite other species that may be present in the fluorescent chamber other than SO 2 . If this is the case, then the assembly  620  can also include a filter as described in a subsequent embodiment. 
     The power supply assembly  670  includes power supply  672 , an inner electrode  674  comprising a solid conductive material (i.e., in the form of a shell or hollow tube) and an outer electrode  676  comprising a solid conductive material (i.e., the form of a shell or hollow tube) and including an inner mirrored surface  678 . The inner electrode  674  is connected to the power supply  672  via a first conductive conduit  680 . The outer electrode  676  is connected to the power supply  672  via a second conductive conduit  682 . The first conductive conduit  680  and the second conductive conduit  682  are connected to opposed poles of the power supply  672 . The power supply  672  is adapted to produce an output capable of producing excimer gas species  640  in the interior  630  of the gas enclosure  622 . The output is generally in the form of a high frequency waveform output optimized to produce a stable light output. The waveform is an oscillator and can comprise a pure sinusoidal waveform, a combination of sinusoidal waveforms (square waves, etc.) or any other continuously oscillatory waveforms capable of producing a stable excimer light source output. 
     Referring now to  FIGS. 6E&amp;F , another embodiment of an excimer light source subsystem of this invention, generally  600 , is shown to include housing  602 , an excimer light source assembly  620 , and a light source power supply assembly  670 , where the housing surrounds the excimer light source assembly  620 . 
     The excimer light source assembly  620  includes a dielectric barrier gas enclosure  622 . The enclosure  622  includes an outer dielectric barrier  624 , an inner dielectric barrier  626 , and end dielectric barriers  628 , defining an enclosure interior  630 . The assembly  620  also includes an output light window  632  situated at a distal end  634  of the enclosure  622  and disposed at a distal end  604  of the housing  602 , while a proximal end  636  is situated near a proximal end of the housing  606 . The assembly  620  also includes a hollow interior region  638 , in which an inner electrode can be disposed as a described below. The assembly  620  also includes a light filter  642  adapted to reduce light not centered about a desired frequency. The interior  630  is adapted to be filled with an excimer gas  640  that produces light of a narrow frequency range centered around a desired frequency. Of course, all excimer so produce some light centered around other frequencies. Often this other light can contribute to unwanted background in the fluorescent chamber or may excite other species that may be present in the fluorescent chamber other than SO 2 . If this is the case, then the assembly  620  can also include a filter as described in a subsequent embodiment. 
     The power supply assembly  670  includes power supply  672 , an inner electrode  674  comprising a solid rod conductive material and an outer electrode  676  comprising a solid conductive material (i.e., in the form of a shell or hollow tube) and including an inner mirrored surface  678 . The inner electrode  674  can also be mirrored and tapers as shown in  FIG. 6E  or untapered as shown in  FIG. 6F . The tapered electrode  674  tapers towards the end  604 . The taper is adapted to further increase light exciting the window  632  acting in concert with the taper of the outer electrode  676 . The inner electrode  674  is connected to the power supply  672  via first conductive conduit  680 . The outer electrode  676  is connected to the power supply  672  via a second conductive conduit  682 . The first conductive conduit  680  and the second conductive conduit  682  are connected to opposed poles of the power supply  672 . The power supply  672  is adapted to produce an output capable of producing excimer gas species  640  in the interior  630  of the gas enclosure  622 . The output is generally in the form of a high frequency waveform output optimized to produce a stable light output. The waveform is an oscillator and can comprise a pure sinusoidal waveform, a combination of sinusoidal waveforms (square waves, etc.) or any other continuously oscillatory waveforms capable of producing a stable excimer light source output. 
     Although three different inner electrodes  674  have been shown, the exact nature of the inner electrode can be any combination of these three general types of electrodes or any other type electrode that can be disposed in the interior region  638  adjacent the inner dielectric barrier  626 . The outer electrode  676  can also be constructed to have straight portions and tapered portions provided that the interior surface is mirrored to reflect UV light between the interior surfaces of the outer electrode. 
     Excimer Light Source Output 
     Referring now to  FIGS. 7A&amp;B , light output spectra of an embodiment of an excimer light source subsystem of this invention are shown. Looking at  FIG. 7A , the output spectrum is shown for the light source from 200 nm to 900 nm. Looking at  FIG. 7B , the output spectrum is shown in an expanded format focusing on the light of wavelength between 200 nm to 250 nm. It is clear from both spectra that the lamp or light source produces a large signal centered at 222 nm. The excitation light filters are designed to reduce or to cut off all wavelength greater than about 225 nm. The excitation light filters are designed to reduce or to cut off all wavelength greater than about 225 nm. In other embodiments, the filters cut off light having wavelengths greater than 224 nm. The reason for producing light of a narrow wavelength centered at 222 nm and having a range between about 205 nm and about 225 nm or in other embodiments between 205 nm and 224 nm is to reduce or eliminate the concurrent excitation of NO that may be present in the sample. The absorption spectra and emission spectra of SO 2  and NO occur in the same UV region of the electromagnetic spectrum between about 190 mm and about 230 nm. However, the NO absorption spectrum consists of a number of relatively broadly spaced sharp absorption peaks, while the SO 2  absorption spectrum consists of many more narrowly spaced sharp absorption peaks. Light narrowly centered about 222 nm is situated between two absorption peaks of NO, while overlapping with a SO 2  absorption peak. Thus, light having a narrow wavelength range centered at 222 nm such as light from a filtered excimer light source or even more ideally from a laser that may be available in the future, is well suited for exciting SO 2  absorption, while reducing or minimizing NO excitation and thus reduce NO interference with SO 2  detection. As set forth in U.S. Pat. No. 7,244,395, the addition of ozone to the sample prior to irradiation with the UV light in the fluorescent reaction chamber can reduce or eliminate NO interference by destroying NO, the disclosure of which is incorporated herein by reference. Thus, in one embodiment of this invention, the NO chemiluminescence apparatus is simply an ozone introduction unit designed to convert any NO to NO 2 , a nitrogen oxide that is inert to UV light centered at 222 nm. 
     All references cited herein are incorporated by reference for all purposed permitted by law, even if certain cited references are incorporated by reference at the instance of referral. Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modifications that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter.