Patent Description:
In operation, a sample is often injected into a chromatographic column filled with a packing material. Typically, the packing material is referred to as a "stationary phase" as it remains fixed within the column. A supply of an inert gas is then provided to the column in order to force the injected sample through the stationary phase. The inert gas is referred to as the "mobile phase" since it transits the column.

As the mobile phase pushes the sample through the column, various forces cause the constituents of the sample to separate. For example, heavier components move more slowly through the column relative to lighter components. The separated components, in turn, exit the column in a process called elution. The resulting components are then fed into a detector that responds to some physical trait of the eluting components.

One type of detector is known as a flame ionization detector. The flame ionization detector is a device that measures an ion current that is produced when an electric field is imposed across a hydrocarbon flame. The flame ionization detector requires a very high gain analog amplifier due to the minute currents involved in most gas chromatographs. By incorporating such a high gain analog amplifier, the amplifier introduces several noise sources that have time-domain variations on the same time scale as the measured current. Additionally, the circuits are very sensitive to a number of factors, e.g. grounding issues, circuit board cleanliness, humidity, vibration, air currents, temperature variations, etc..

To reduce noise, gas chromatographs can also include multiple parallel amplifiers to reduce uncorrelated noise. However, in general, transistor noise is inversely proportional to its area. This means that low noise integrated amplifiers (for time-domain applications) face fundamental size limitations. Furthermore, such electronics are often fairly expensive for consumers. <CIT> discloses an analysis method using a microwave cavity resonator to use an optical galvanic effect in a flame.

The present invention is defined by independent claims as appended. Further embodiments are given in the dependent claims.

In accordance with embodiments of the present invention, a gas chromatograph detector assembly is provided that is relatively small in size, easy to construct, insensitive to environmental factors and is highly sensitive to ions. The detector assembly includes a probe assembly and a meter that allows for a concentration of hydrocarbons, or other ions, to be determined within a sample as will be discussed further with respect to <FIG>. However, in accordance with different examples, the probe assembly of the detector is largely insensitive to the many factors facing current gas chromatograph detectors. This includes measurement noise, high cost, and spatial limitations within the gas chromatograph. Additionally, while the present description will proceed with respect to a detector for a gas chromatograph, it is expressly contemplated that the present detector may also be used in a wide variety of other applications or other types of chromatographs as well.

<FIG> is a diagrammatic view of a gas chromatograph with which embodiments of the present invention may be used. While <FIG> illustrates a model 700XA gas chromatograph <NUM>, available from Rosemount Inc. , methods and embodiments provided herein may be utilized with other exemplary gas analyzers. This can include model 1500XA Process Gas Chromatographs and model <NUM> Natural Gas Chromatographs, both available from Rosemount Inc. , among a variety of other types and models of gas chromatographs. Additionally, it is contemplated that a wide variety of other devices, beyond gas chromatographs, can be utilized with embodiments of the present invention.

<FIG> is a diagrammatic system view of a gas chromatograph in accordance with an embodiment of the present invention. While one example of a gas chromatograph <NUM> will now be provided, it is to be understood that gas chromatograph <NUM> can take a wide variety of other forms and configurations. For example, it is to be understood that gas chromatograph <NUM> may have other configurations for columns, valves, detectors, etc. However, in this example, gas chromatograph <NUM> illustratively includes a carrier gas inlet <NUM>, a sample inlet <NUM>, a sample vent outlet <NUM> and a measure vent outlet <NUM>. In operation, carrier gas is provided to flow panel <NUM> where it passes through a regulator <NUM> and dryer <NUM> before entering analyzer oven <NUM> and passing through carrier gas pre-heater <NUM>.

During measurement, sample gas enters chromatograph <NUM> via sample inlet <NUM> and passes through sample gas pre-heater <NUM> within analyzer oven <NUM>. Both sample gas (during measurement), or calibration gas (during calibration), and carrier gas eventually enter a plurality of pneumatically-controlled multiport selector valves <NUM> in order to selectively flow various volumes of a sample and/or carrier gas through various chromatographic columns <NUM> in accordance with known gas chromatography techniques. Each of pneumatically-controlled multiport selector valves <NUM> is fluidically coupled to a respective solenoid <NUM> that receives its control signal from controller <NUM>.

Additionally, as shown in <FIG>, each pneumatically-controlled multiport selector valve <NUM> has a pair of states. In the first state, the fluidic connections of each valve <NUM> are shown in solid lines. The fluidic connections of each valve <NUM> in the second state are shown in phantom. Controller <NUM> is also operably coupled to detector <NUM> which allows for an ion concentration within a sample to be determined as will be discussed with respect to <FIG>. Thus, controller <NUM> is able to fully control flow through gas chromatograph <NUM> by virtue of controlling solenoids <NUM>. Additionally, controller <NUM> is able to determine the response of detector <NUM> to determine an ion concentration. In this way, controller <NUM> is able to selectively introduce the sample into a chromatographic column for a selected amount of time, reverse the flow of gas through the chromatographic column; and direct the reverse flow through the detector to observe and/or record the detector response over time. This provides chromatographic analysis relative to the sample.

<FIG> is a diagrammatic view of a gas chromatograph detector assembly in accordance with an embodiment of the present invention. Detector <NUM> illustratively includes a burner assembly <NUM>, a probe assembly <NUM>, a gas delivery subsystem <NUM>, a power supply <NUM>, a vacuum subsystem <NUM>, a meter <NUM>, sensor(s) <NUM>, and a controller <NUM>.

Briefly, to determine a concentration of ions within an eluted sample from any or all chromatographic columns <NUM>, the eluted sample is mixed with hydrogen and, along with an ignition source and zero air, is used to generate flame <NUM> within burner assembly <NUM>. When the eluted sample is mixed with hydrogen and serves as a fuel source for flame <NUM>, an ion-electron pair is produced upon combustion of the mixed sample within burner assembly <NUM>. A dc bias can then be imposed across flame <NUM> using power supply <NUM> to prevent recombination of the disassociated ion-electron pair. As flame <NUM> burns within burner assembly <NUM>, an ion concentration of sample <NUM> is determined using probe assembly <NUM> and meter <NUM>. For example, meter <NUM> can measure scattering parameters, such as a S<NUM> scattering factor, of probe assembly <NUM> as the flame effluent acts on probe assembly <NUM>. Based on the scattering factor, a resonant frequency, ƒr, and quality factor, Qr, of probe assembly <NUM> can be determined which, in turn, allows for an ion concentration to be determined as will be discussed later.

Burner assembly <NUM> illustratively includes an envelope <NUM>, an end cap <NUM> configured to simultaneously couple to meter <NUM> and probe assembly <NUM>, and a burner cell <NUM> configured to receive a gas sample from gas delivery subsystem <NUM> and generate a flame <NUM>. Envelope <NUM> can comprise glass (such as PYREX® from Corning Incorporated) among a variety of other compounds. Additionally, both end cap <NUM> and burner cell <NUM> can each be formed of aluminum or any other metal alloy. In operation, envelope <NUM> can be fixed to both end cap <NUM> and burner cell <NUM> using an epoxy, such a glass bonding epoxy in one example. Additionally, while it is to be understood that envelope <NUM> can take a variety of configurations, in one example, envelope <NUM> includes a glass tube with a length of <NUM>, an outer diameter of <NUM> and an inner diameter of <NUM>. However, this is for example only and it is to be understood that envelope <NUM> can take a variety of other configurations as well.

Sensor(s) <NUM> can include a wide variety of different types of sensors that allow controller <NUM> to monitor a reaction or environment within envelope <NUM>. For example, sensor(s) <NUM> can include a temperature sensor that allows controller <NUM> to determine an operating temperature within or outside of envelope <NUM>. However, a variety of other sensor(s) <NUM> can be used as well.

Gas delivery subsystem <NUM> is configured to receive the eluted products from any or all of chromatographic columns <NUM> and provide the eluted products to burner cell <NUM>. Gas delivery subsystem <NUM> illustratively includes a source of hydrogen <NUM>, a source of zero air <NUM>, eluted sample(s) <NUM> from chromatographic columns <NUM>, a metering system <NUM>, and a variety of other components <NUM>. Metering system <NUM> can meter each of hydrogen <NUM>, zero air <NUM> and/or eluted sample(s) <NUM> into specific amounts prior to providing the mixture to burner cell <NUM>. Additionally, metering system <NUM> can also combine the metered hydrogen <NUM>, zero air <NUM> and/or eluted sample(s) <NUM> into specific mixtures prior to delivering the samples to burner cell <NUM>. For example, metering system <NUM> can meter and combine hydrogen <NUM> with the eluted sample(s) <NUM> prior to providing the mixture to burner cell <NUM>. This is but one example.

Vacuum subsystem <NUM> is coupled to burner assembly <NUM> and allows for burner assembly <NUM> to operate at sub-atmospheric pressures. Vacuum subsystem <NUM> illustratively includes a rotary vane pump <NUM>, a reciprocating pump <NUM>, valve(s) <NUM>, among other components <NUM>. In one example, valve(s) <NUM> can include a needle valve and/or a globe valve to allow the pressure within burner assembly <NUM> to be set between atmospheric pressure and the maximum pressure achievable through rotary vane pump <NUM> and/or reciprocating pump <NUM>. In operation, vacuum subsystem <NUM> can be coupled to an exhaust port of end cap <NUM> as will be discussed with respect to <FIG>.

Meter <NUM> illustratively monitors structural characteristics of probe assembly <NUM> during operation of detector <NUM>. Meter <NUM> can include a reflectometer <NUM>, a network analyzer <NUM>, or a variety of other detectors <NUM>. In one example, meter <NUM> includes reflectometer <NUM> configured to monitor an S<NUM> parameter of probe assembly <NUM> as the flame effluent acts on probe assembly <NUM>. Based on the determined parameters, controller <NUM> can receive the signals from meter <NUM> and determine a resonant frequency, ƒr, and quality factor, Qr, of probe assembly <NUM>. Once the resonant frequency is determined for probe assembly <NUM>, controller <NUM> can determine an electric permittivity surrounding probe assembly <NUM>. The electric permittivity depends on the ion concentration proximate probe assembly <NUM> which, in turn, is directly related to a concentration of ions present within flame <NUM>. Therefore, by determining a resonant frequency for probe assembly <NUM>, controller <NUM> can determine an ion concentration within flame <NUM> and, in effect, an ion concentration within any or all received sample(s) <NUM> from chromatographic columns <NUM>.

Power supply <NUM> generates a voltage to selectively bias probe assembly <NUM> relative to flame <NUM> to maintain a disassociation between an ion-electron pair created through flame <NUM>. In one example, power supply <NUM> can include a voltage supply <NUM>, an ammeter <NUM> and a variety of other components <NUM>. In one example, voltage supply <NUM> can be connected to burner assembly <NUM> to maintain end cap <NUM> and probe assembly <NUM> at ground potential while selectively biasing burner cell <NUM> and flame <NUM> to a predetermined voltage between -<NUM> [kV] to + <NUM> [kV]. However, this is but one example.

Controller <NUM> is operably coupled to meter <NUM>, sensor(s) <NUM>, vacuum subsystem <NUM>, power supply <NUM> and gas delivery subsystem <NUM> and serves to determine an ion concentration within sample <NUM> by controlling and receiving signals from meter <NUM> indicative of scattering parameters of probe assembly <NUM>. Additionally, in one example, controller <NUM> is a microprocessor with suitable memory such that controller <NUM> is able to programmatically execute a series of program steps in order to carry out the functions and calculations mentioned above with respect to meter <NUM>, sensor(s) <NUM>, vacuum subsystem <NUM>, power supply <NUM> and gas delivery subsystem <NUM>. In operation, controller <NUM> receives signals from meter <NUM> indicative of scattering parameters of probe assembly <NUM>, determines a resonant frequency and quality factor of probe assembly <NUM> based on the parameters, and calculates an electric permittivity based on the resonant frequency and quality factor. Based on the electric permittivity, controller <NUM> can determine an ion concentration proximate probe assembly <NUM> and, in turn, within flame <NUM> and sample <NUM>.

Probe assembly <NUM> is coupled to burner assembly <NUM> and undergoes a characteristic modification upon being acted on by the flame effluent. Probe assembly <NUM> includes a resonator, a feed line, fasteners and an adapter as will be discussed in detail with respect to <FIG>. Briefly, however, as the flame effluent acts on the resonator, scattering parameters of the resonator are monitored by meter <NUM> in which a resonant frequency and quality factor are able to be determined for probe assembly <NUM>. Using the resonant frequency, an electric permittivity can be calculated and used to determine a concentration of ions proximate probe assembly <NUM>.

<FIG> is a diagrammatic view of a burner assembly in accordance with an embodiment of the present invention. Burner assembly <NUM> illustratively includes envelope <NUM>, burner cell <NUM> and end cap <NUM>. As illustratively shown, end cap <NUM> is coupled to an adapter <NUM> and includes an exhaust port <NUM> that, in operation, can couple to vacuum subsystem <NUM>. Adapter <NUM> can be used to couple probe assembly <NUM> to detector <NUM> and, in one example, includes a type N to SMA adapter configured to simultaneously couple to both meter <NUM> and probe assembly <NUM> as illustratively shown in <FIG>. In one example, adapter <NUM> can be coupled to end cap <NUM> using a sealing member <NUM>, which, in one example, can include an O-ring.

Furthermore, as illustratively shown, burner cell <NUM> includes a pressed insert <NUM>, a burner tip <NUM>, a port <NUM>, a threaded plug <NUM> and an ignitor <NUM>. In operation, pressed insert <NUM> can orient burner tip <NUM> such that, when flame <NUM> is produced, it is oriented directly underneath probe assembly <NUM> (shown in <FIG>). Additionally, port <NUM> and threaded plug <NUM> can simultaneously couple to gas delivery subsystem <NUM> to receive any or all of hydrogen <NUM>, zero air <NUM>, sample <NUM>, etc. For example, port <NUM> can couple to gas delivery subsystem <NUM> to receive zero air <NUM>. Threaded plug <NUM>, similarly, can couple to gas delivery subsystem <NUM> to receive a mixture of hydrogen <NUM> and sample <NUM> in one example.

Ignitor <NUM> can include a variety of ignitors that are able to ignite combustion of received samples from gas delivery subsystem <NUM>. In one example, ignitor <NUM> can include a glow-wire ignitor formed from a length of stainless steel tubing with an insulating platform to serve as a mounting point for the glow-wire. In this example, the insulating platform can comprise Ultem and the glow-wire NiCr wire. The glow-wire can be coupled to a power supply which may be the same or different than power supply <NUM>. In operation, ignitor <NUM> can be inserted through the passageway of end cap <NUM> and placed in close proximity of burner tip <NUM>. Power supply <NUM> can then generate current over the glow-wire to ignite the received samples from gas delivery subsystem <NUM>.

<FIG> is a diagrammatic view of a probe assembly in accordance with an embodiment of the present invention. Probe assembly <NUM> illustratively includes a resonator <NUM>, a coupling mechanism <NUM>, a feed line <NUM> and adapter <NUM>. While resonator <NUM> is illustratively in the form of a hairpin resonator, a variety of other resonators can be used as well. However, in one example, resonator <NUM> has a length of <NUM>, a tine radius of <NUM>, an aspect ratio of <NUM> and a drive separation of <NUM>. Additionally, in some examples, resonator <NUM> can be formed of a plated annealed steel wire having a plating material of silver, a plating thickness of <NUM>, a RMS surface roughness of <NUM> and a diameter of <NUM>. The plated wire can be used since the skin depth for silver at the hairpin resonator nominal frequency (ƒr =<NUM> [GHz]) is <NUM> [µm]. In one example, the plating thickness is much larger than the skin depth to ensure the RF current does not interact with the steel core. However, it is contemplated that resonator <NUM> can have a variety of other configurations as well.

Feed line <NUM> is configured to simultaneously couple to resonator <NUM> and adapter <NUM>. In one example, feed line <NUM> comprises a coax cable. For example, feed line <NUM> can include a <NUM> [mm] length of RG402 coax from Fairview Microwave®. However, feed line <NUM> can include other types of coax cable as well. In operation, feed line <NUM> is coupled to adapter <NUM>. Adapter <NUM> can include a variety of types of adapters, but, in one example, includes a type-N to SMA adapter configured to couple meter <NUM> to feed line <NUM>.

In operation, to ensure critical coupling between resonator <NUM> and feed line <NUM>, coupling mechanism <NUM> is utilized to ensure maximum transfer of signal energy between resonator <NUM> and feed line <NUM>. In one example, coupling mechanism <NUM> maximizes a signal-to-noise ratio (SNR) of the measured parameters, ƒr and Qr, through a direct coupling to resonator <NUM>. This is illustratively shown in <FIG>. By having a critical coupling, meter <NUM> can accurately determine scattering parameters for resonator <NUM> as will be discussed further with respect to <FIG>.

<FIG> are diagrammatic views of a resonator coupling in accordance with an embodiment of the present invention. While one example of a coupling mechanism <NUM> will be discussed for resonator <NUM> and feed line <NUM>, it is contemplated that other coupling mechanisms <NUM> can be utilized as well that maximize a signal-to-noise ratio (SNR) of the measured parameters. However, in this example, coupling mechanism <NUM> includes a solder <NUM> that directly couples resonator <NUM> and feed line <NUM>. In one example, solder <NUM> couples to junctions <NUM> and <NUM> of resonator <NUM>, however, solder <NUM> can directly couple to other junctions as well.

As illustratively shown in <FIG>, coupling mechanism <NUM> includes solder <NUM> that directly couples to junctions <NUM> and <NUM> to optimize measurement of scattering parameters of resonator <NUM>. In one example, this allows for the accurate measurement of a resonant frequency and quality factor of resonator <NUM> during which a flame effluent acts on resonator <NUM> within a burner assembly.

<FIG> is a graph illustratively showing scattering parameters of a resonator in accordance with an embodiment of the present invention. As illustratively shown, S<NUM> parameters <NUM> for resonator <NUM> of probe assembly <NUM> were monitored and plotted as flame effluent acted on probe assembly <NUM> within burner assembly <NUM>. Additionally, from the graph, it can be observed that a critical coupling was maintained for resonator <NUM> and feed line <NUM> as the observed resonant notch is tall and narrow. From this, a resonant frequency of <NUM> [Hz] can be observed for resonator <NUM>.

<FIG> is a graph illustratively showing resonant frequencies of a resonator as a concentration of gas is increased in accordance with an embodiment of the present invention. As illustratively shown, as the hydrocarbon/hydrogen concentration ratios were increased within a sample, an observed shift in resonant frequency, ƒr, was exceptionally linear as shown by line <NUM>. The plotted points <NUM> correspond to a mean value of <NUM><NUM> readings while the error bars represent a population standard deviation of the points.

<FIG> is a graph illustratively showing quality factors of a resonator as a concentration of gas is increased in accordance with an embodiment of the present invention. From the graph, it can be illustratively seen that the resonator Q factor was observed to decrease at a relatively constant rate prior to leveling off as a hydrocarbon/hydrogen concentration was increased within a sample. In one example, this can be attributed to oxidation (tarnishing) of the silver plating used on the resonator wire. Through an oxidation of the silver plating, a resistance of the resonator tines is increased while also reducing the resonator Q factor. As shown, Q-factors were plotted <NUM> and a best-fit-line <NUM> fit to the data points.

<FIG> is a method of determining an ion concentration within a sample in accordance with embodiments of the present invention. It is to be understood that method <NUM> can be utilized in a variety of different chromatographs to determine an ion concentration within a sample.

Processing begins at block <NUM> where burner assembly <NUM> is sterilized. In one example, probe assembly <NUM> can be sterilized along with burner assembly <NUM> as indicated by block <NUM>. However, a variety of other components and systems can be sterilized as well as indicated by block <NUM>. In order to sterilize burner assembly <NUM>, a variety of different techniques may be used, but, in one example, burner assembly <NUM> may be sterilized by generating an initial flame to burn off contaminants present within burner assembly <NUM> as indicated by block <NUM>. However, burner assembly <NUM> can be sterilized using a variety of other techniques as well as indicated by block <NUM>.

Once burner assembly <NUM> is sterilized, processing proceeds to block <NUM> where controller <NUM> generates control signals for power supply <NUM> to generate power to selectively bias burner assembly <NUM>. In one example, this includes biasing end cap <NUM> and burner cell <NUM>, as indicated by block <NUM>, to allow a disassociated ion-electron pair created within flame <NUM> to maintain a disassociated state. However, other components may be biased as well as indicated by block <NUM>.

Processing then turns to block <NUM> where controller <NUM> generates control signals for gas delivery subsystem <NUM> to provide zero-air sample <NUM> to burner cell <NUM>. Upon receiving the zero-air sample <NUM>, controller <NUM> generates control signals for ignitor <NUM> to generate flame <NUM> within burner assembly <NUM> as indicated by block <NUM>.

Control signals are subsequently generated for gas delivery subsystem <NUM> to provide a sample/hydrogen mixture to burner assembly <NUM> as indicated by block <NUM>. An ion-electron pair is subsequently generated within flame <NUM> resulting from sample <NUM>. As flame <NUM> burns within burner assembly <NUM>, a flame affluent, comprising the disassociated ion-electron pair, acts on probe assembly <NUM> within burner assembly <NUM>. Processing subsequently turns to block <NUM> where controller <NUM> generates control signals for vacuum subsystem <NUM> to reduce a pressure within burner assembly <NUM>. While a variety of pressures may be obtained within burner assembly <NUM>, in one example, a pressure can correspond to <NUM> [kPa] as indicated by block <NUM>. However, other pressures may be obtained as well as indicated by block <NUM>.

Upon establishing a desired pressure within burner assembly <NUM>, processing proceeds to block <NUM> where controller <NUM> receives sensor signals from sensor(s) <NUM> indicative of operating characteristics of burner assembly <NUM>. In one example, sensor(s) <NUM> can include a temperature sensor, coupled to burner assembly <NUM>, configured to generate sensor signals indicative of an operating temperature of burner assembly <NUM> as indicated by block <NUM>. In this example, prior to collecting scattering data for probe assembly <NUM>, controller <NUM> can receive sensor signals and wait a predetermined duration to allow a burner assembly temperature to stabilize. However, other characteristics of burner assembly <NUM> can be determined as well as indicated by block <NUM>.

Once various characteristics of burner assembly <NUM> are determined and, in some examples, allowed to stabilize, processing turns to block <NUM> where controller <NUM> receives signals from meter <NUM> indicative of scattering parameters of probe assembly <NUM>. In one example, scattering parameters can include S<NUM> parameters, as indicated by block <NUM>. Upon receiving the signals from meter <NUM>, controller <NUM> can determine a resonant frequency and quality factor of probe assembly <NUM> based on the determined scattering parameters as indicated by block <NUM>. Once a resonant frequency and quality factor are determined for probe assembly <NUM>, controller <NUM> can determine an ion concentration present within sample <NUM> as indicated by block <NUM>. In one example, to determine an ion concentration, controller <NUM> determines an electric permittivity surrounding probe assembly <NUM> based on the resonant frequency of probe assembly <NUM>.

For example, an electric permittivity surrounding probe assembly <NUM> depends on an ion concentration proximate probe assembly <NUM>. An ion concentration proximate probe assembly <NUM> is related to a concentration of ions present within flame <NUM>. Therefore, based on a calculated electric permittivity adjacent to probe assembly <NUM>, controller <NUM> can determine an ion concentration within sample <NUM> as it forms disassociated ion-electron pairs within flame <NUM>. However, other characteristics and parameters of burner assembly <NUM> can be determined as well as indicated by block <NUM>.

Once an ion concentration is determined for sample <NUM>, processing turns to block <NUM> where it is determined whether there are additional samples. If there are additional samples from chromatographic columns, processing reverts back to block <NUM> where controller <NUM> generates control signals for gas delivery subsystem <NUM> to provide a hydrogen/sample mixture to burner cell <NUM>. If there are no additional samples, processing subsequently ends.

Claim 1:
A microwave resonator flame ionization detector assembly (<NUM>), comprising:
a probe assembly (<NUM>) having a microwave resonator (<NUM>) that is disposed proximate a flame to evaluate an ion concentration in a flame effluent,
characterised by further comprising:
a meter (<NUM>) coupled to the resonator (<NUM>) configured to detect a reflection coefficient of the resonator (<NUM>) as the flame effluent acts on the resonator (<NUM>) and generate signals indicative of the reflection coefficient; and
a controller (<NUM>) coupled the meter (<NUM>) configured to receive the signals from the meter (<NUM>) to determine a resonant frequency of the resonator (<NUM>) based on the reflection coefficient of the resonator (<NUM>), and to determine an electric permittivity of a material in which the resonator (<NUM>) is immersed, given that the electric permittivity depends on an ion concentration proximal to the resonator (<NUM>), and that the ion concentration is related to the concentration of hydrocarbons present in the flame.