Apparatus, system, and method for low cost high resolution chemical detection

An apparatus, system, and method are disclosed for low cost high resolution chemical detection. The apparatus includes two outer sealing bodies with flow channels etched into the bodies. Two gas chromatography (GC) columns are between the outer bodies, with a valve that switches flow regimes from series flow through the two GC columns to sample flowing directly to each GC column. The flow regimes are achieved with a single pump or dual pumps, and with one to three flow restrictions. The apparatus includes a preconcentration tube for concentrating chemicals of interest from the sample, and a sample switching valve and sampling pump to switch the sample flow from concentrating sample to delivering concentrated sample. The apparatus includes an engineered leak to equalize flow between a sample channel and a detector circuit. The sample channels may have impermeable inserts allowing the apparatus to measure chemicals in the parts-per-billion range.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to chemical detectors and more particularly relates to gas chromatography sensors.

2. Description of the Related Art

Gas chromatography (GC) is useful in the chemical industry as a separation mechanism and as a sensing mechanism. GC sensors are extremely useful for detecting specific chemicals in a gas with mixed components, but they suffer from the major drawback that they are quite expensive.

The required purities in GC mandate, within most of the current art, the use of valves that cost in the thousands of dollars per valve. One concept has been introduced which allows air pressure to perform some of the gas switching, which allows the expensive valves to be replaced with cheaper solenoid valves, see U.S. Pat. No. 4,970,905. However, the present art for accomplishing this requires complicated machining and assembly causing manufacturing expense and reliability problems.

Another limitation of the present art is that manufacture of GC columns is a tedious and expensive process. For example, the GC column must be heated uniformly while in use, and low cost methods to effectively accomplish this uniform heating are lacking in the present art. One current method to provide effective and affordable heating is to co-axially winding a heating element around the GC column—this method is expensive to implement. There are temperature control methods which are easy to manufacture, but which tend to leave the GC column directly exposed to a heating element and thus allow for non-uniform temperature spikes at places along the GC column.

Another limitation of current GC sensor technology is that the sensors need to be periodically calibrated against an internal standard, and no cheap methods exist to provide for this. The current technology is to provide a chemical, which must be stored, and an injection mechanism which must inject the chemical into the system without interfering with seals and the normal operation of the GC sensor.

GC sensors typically use a preconcentration mechanism, which multiplies the concentration of chemicals of interest in a sample and allows detection of lower initial concentrations than otherwise allowable. Typically, an absorption-desorption material is added into the sample stream to accomplish this. Current methods of adding adsorption-desorption materials tend to cause variable pressure drop in the sensor flow paths.

In the current art, the GC sensor must operate at a design operational temperature. Lower temperatures are desirable for better separation of elution times of different components, while higher temperatures improve the sensor response time. However, the test temperature must be at least as high as the ambient temperature. Typically, an operating temperature is selected that is higher than any predicted ambient temperature when the GC sensor is manufactured. This causes the temperature to be set higher than necessary when the actual ambient temperature is low, making chemical detection more difficult than required, and inducing greater energy loss to heat the GC sensor than would otherwise be required.

In GC sensors that detect a wide range of chemicals, the chemicals can have widely variable elution times from the GC column. Further, the shape of the detection peaks for chemicals with different elution times will vary. As a general principle, later eluting chemicals will have a lower and wider peak than early eluting chemicals. Further, in high resolution GC sensors that are detecting concentrations in the parts-per-million (ppm) and parts-per-billion (ppb) ranges, extraneous peaks and noise will occur in the basic signal. This variability in peak shape makes it difficult for detection algorithms to correlate the concentrations of the various chemicals.

A GC sensor will typically have a long GC column placed into a small area, and will typically be wound up as tight as possible. Further, the GC column may be manufactured in one time and location, and transported and/or stored for a period before assembly of the GC sensor. A cheap method to build uniform GC columns, and to protect the columns from the introduction of impurities between the time of manufacture and the time of assembly is desirable.

A dual hyphenated GC sensor, and any GC sensor that is either utilized to detect many chemicals simultaneously, or utilized to detect chemicals from a complex mixture of gases, suffers in the current art from difficulty in finding chemical elution peaks within a complex signal. Often a significant amount of noise is produced in the signal. The standard Fourier analysis of GC signals suffer from producing ringing in the signal, especially with high frequency components of the signal. Noise suppression wavelets are known in the art, but any particular noise suppression wavelet will still tend to leave some noise peaks in the signal and complex signals continue to be difficult to interpret.

Proper sealing of GC sensors is a known difficulty in the art, and is especially problematic in sensors attempting to detect chemicals at the low parts-per-million (ppm), or even into the parts-per-billion (ppb) range. The internal flowpaths of the sensor must be protected from leakage to the ambient environment, and the analytical flowpaths containing the chemical sample must be further protected from un-designed fluid migration within the sensor.

From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that detects a broad spectrum of chemicals in a GC sensor in an inexpensive and effective manner. Beneficially, such an apparatus, system, and method would allow the use of inexpensive solenoid valves, provide for easy manufacture, provide for uniform and inexpensive heating of sensing elements, allow for a low cost implementation of an internal chemical standard, provide for manufacture of a preconcentration system that is inexpensive and provides uniform pressure drop, allows low energy operation in a wide range of ambient environments, that robustly detects chemicals that have widely varying elution times, and that is protected from leakage from the ambient environment and internally within the analytical flowpaths.

SUMMARY OF THE INVENTION

Based on the foregoing, Applicant asserts that a need exists for a low cost high resolution chemical detector. The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available gas chromatography (GC) sensor technology. Accordingly, the present invention has been developed to provide an apparatus, system, and method for detects chemicals present at low concentrations in a GC sensor package that is inexpensive and simple to manufacture.

A GC sensor is disclosed that includes a first outer sealing body and a second outer sealing body. The sensor includes a plurality of flow channels etched into the outer sealing bodies. The sensor includes a first GC column and a second GC column, both columns between the outer sealing bodies. The sensor further includes a valve that switches between a first flow regime and a second flow regime. The first flow regime includes a sample flowing through the first GC column and then the second GC column. The second flow regime includes a sample flowing to the second GC column without flowing to the first GC column. The sensor includes a preconcentration tube, a sampling pump, and a sample switching valve. The preconcentration tube includes a preconcentration material that adsorbs and desorbs chemicals from the sample. The sample switching valve switches between a concentration mode and a sensing mode. The concentration mode includes an intake air stream flowing through the preconcentration tube in a first direction, and the sampling pump sending a dilute sample through a GC unit that includes the first and second GC columns. The sensing mode includes the intake air stream flowing through the preconcentration tube in a second direction, and the sampling pump sending the sample through the GC unit.

An apparatus is disclosed for low cost high resolution chemical detection. The apparatus includes a plurality of flow channels etched into the outer sealing bodies. The apparatus includes a first GC column and a second GC column, both columns between the outer sealing bodies. The apparatus further includes a valve that switches between a first flow regime and a second flow regime. The first flow regime includes a sample flowing through the first GC column and then the second GC column. The second flow regime includes a sample flowing to the second GC column without flowing to the first GC column. The apparatus includes a preconcentration tube, a sampling pump, and a sample switching valve. The preconcentration tube includes a preconcentration material that adsorbs and desorbs chemicals from the sample. The sample switching valve switches between a concentration mode and a sensing mode. The concentration mode includes an intake air stream flowing through the preconcentration tube in a first direction, and the sampling pump sending a dilute sample through a GC unit that includes the first and second GC columns. The sensing mode includes the intake air stream flowing through the preconcentration tube in a second direction, and the sampling pump sending the sample through the GC unit.

In one embodiment, the apparatus includes a first pump, a first resistance, a second resistance, and a third resistance. Each resistance may be an orifice, a controllable valve, and/or a microboard with porous substrate. The first flow regime further includes a first fluid stream from the first pump that flows through the first GC column and the second GC column, and a second fluid stream directed by the valve that flows through the second resistance and the first resistance. The second flow regime further includes a third fluid stream from the first pump that flows through the first GC column and the first resistance, and a fourth fluid stream directed by the valve that flows through the third resistance and the second GC column, wherein the fourth fluid stream further prevents the third fluid stream from flowing through the second GC column.

In one embodiment, the apparatus includes a first resistance, and a fourth resistance. The first flow regime further includes a first fluid stream from the first pump that flows through the first GC column and the second GC column, and a second fluid stream directed by the valve that flows through the fourth resistance and the first resistance. The second flow regime further includes a third fluid stream from the first pump that flows through the first GC column and the first resistance, and a fourth fluid stream directed by the valve that flows through the fourth resistance and the second GC column, wherein the fourth fluid stream further prevents the third fluid stream from flowing through the second GC column.

In one embodiment, the apparatus includes a first pump, a second pump, and a first resistance. The first flow regime further includes a first fluid stream from the first pump that flows through the first GC column and the second GC column, and a second fluid stream directed by the valve from the second pump that flows through the first resistance, wherein the second stream further prevents the first stream from flowing through the first resistance. The second flow regime further comprises a third fluid stream from the first pump that flows through the first GC column and the first resistance, and a fourth fluid stream directed by the valve from the second pump that flows through the second GC column, wherein the fourth stream further prevents the third stream from flowing through the second GC column.

In one embodiment, the apparatus includes a quartz or ceramic impermeable insert within at least one of the plurality of flow channels. In one embodiment, the apparatus includes a detector circuit that detects a target chemical eluting from the first and second GC columns, wherein the target chemical occurs in an ambient environment at less than about 1,000 parts-per-billion. The apparatus further includes a preconcentration tube, a sampling pump, and a sample switching valve that switches between a concentration mode and a sensing mode. The preconcentration tube includes a preconcentration material that adsorbs and desorbs chemicals from an intake air stream. The concentration mode includes flowing the intake air stream through the preconcentration tube in a first direction, and the sampling pump providing a dilute sample to a GC unit comprising the first and second GC columns. The sensing mode includes flowing the intake air stream through the preconcentration tube in a second direction, and the sampling pump providing a concentrated sample to the GC unit.

The apparatus includes a detector circuit in one embodiment. The detector circuit is between the outer sealing bodies, and includes a detector circuit seal. The apparatus includes, in one embodiment, an independent spring to apply sealing force to enhance the detector circuit seal. The apparatus includes a pressure equalizing channel configured to equalize pressures between the detector circuit and a sample channel.

A method is disclosed for low cost high resolution chemical detection. The method includes providing a first outer sealing body and a second outer sealing body, etching a plurality of flow channels into the first sealing body and the second sealing body, and providing a first gas chromatography (GC) column and a second GC column interposed between the first and second outer sealing bodies. The method further includes providing a valve that switches between a first flow regime and a second flow regime. Operating the valve in the first flow regime includes flowing a sample through the first GC column and then the second GC column. Operating the valve in the second flow regime includes flowing the sample through the second GC column without flowing the sample through the first GC column

In one embodiment, the method includes flowing an intake air stream through a preconcentration tube in a first direction to concentrate chemicals on the preconcentration tube, and flowing the intake air stream through the preconcentration tube in a second direction to deliver a concentrated sample through a GC unit comprising the first and second GC columns. In one embodiment, the method further includes heating the preconcentration tube to a specified temperature, thereby releasing a known chemical from the preconcentration tube, and detecting elution of the known chemical from the GC unit. The method may include providing a detector circuit interposed between the first and second outer sealing bodies, and providing a detector circuit seal. In one embodiment, the method includes providing a pressure equalizing channel from a sample channel to the detector circuit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic block diagram illustrating one embodiment of a system100to detect a broad spectrum of chemicals in accordance with the present invention. The system100may comprise a gas chromatography (GC) sensor, and a controller104. The controller may comprise at least one module configured to control one or more aspects of the GC sensor. The modules in one embodiment may comprise a temperature control module106, a GC column switching module108, a sample introduction module110, a similarity sequencing module112, a signal processing module114, and a noise-filtering module116.

The temperature control module106may be configured to control the temperature of one or more GC columns within the GC sensor. The temperature control module may be configured to control the temperature of the GC column(s) based on the current ambient temperature and a set of chemical elution data corresponding to a set of temperatures.

The GC column switching module108may be configured to control gas flows through at least one GC column in the GC sensor102. The GC column switching module108may be configured to control the flows such that a gas flow passes through a first GC column into a second GC column in series. The GC column switching module108may be further configured to control the flows such that a first and second GC column each receive a gas flow in parallel. The GC column switching module108may be further configured to ensure that a first and second GC column receive substantially the same flow rate of gas.

The sample introduction module110maybe configured to introduce a sample gas into at least one GC column. The sample introduction module110may be configured to control a sample flow in a concentration flow regime configured to concentrate a sample gas onto a preconcentration material, which may be configured to adsorb the sampled chemicals of interest. The sample introduction module110may be further configured to control a sample flow in a desorption flow regime to desorb a sample gas from the preconcentration material, and to flow the concentrated sample through the at least one GC column.

The similarity sequencing module112may be configured to take data samples in a constant log-time fashion to ensure that early eluting and late eluting chemicals exhibit qualitatively similar data peaks. The similarity sequencing module112may be configured in one embodiment to take data samples in a constant time fashion, and to process the data to simulate a constant log-time data set.

The signal processing module114may be configured to deconvolute a sampling data set to determine the chemical inputs to the at least one GC column that generate the eluted chemicals observed in the sampling data. The signal processing module114may be configured to deconvolute the sampling data utilizing a Z-transform. The signal processing module114may be configured to convert the sequential sampling data into a high order polynomial, divide the high order polynomial by a polynomial system model, and thereby generate a an input polynomial. The signal processing module114may be further configured to regenerate the predicted input signal by an inverse Z-transform of the input polynomial. The Z-transform may be modified to use the largest polynomial divisor possible without generating negative values. The modified Z-transform may be enabled by the near-constant width in sample space of the chemical elution peaks generated by the similarity sequencing module112.

The noise filtering module116may be configured to operate a noise suppression wavelet and/or other noise suppression method on the sampling data to suppress noise peaks. The noise filtering module116may be further configured to operate a plurality of noise suppression wavelets on the sampling data, and to identify one or more peaks as noise, and one or more peaks as data. The noise filtering module116may be configured to identify relatively stable peaks as data, and relatively unstable peaks as noise.

FIG. 2Ais a schematic block diagram illustrating one embodiment of a controller104for a GC sensor102in accordance with the present invention. The controller104may comprise a plurality of modules to functionally execute the controller104operations.

The controller104may comprise a temperature control module106configured to maintain a GC target temperature206at a lowest feasible temperature to maintain elution time separation of closely related chemicals and to minimize the heating burden on the GC sensor102. The temperature control module106may be configured to determine an ambient temperature202. The temperature control module106may be further configured to read a stored set of temperature-based elution data204. The temperature control module106may then select a GC target temperature206based on the ambient temperature202and the set of temperature-based elution data204.

In one embodiment, the temperature control module106may be configured to select the next available temperature from the set of temperature-based elution data204higher than the ambient temperature202. In one example, the set of temperature-based elution data204comprises elution data204at 50° F., 100° F., and 150° F. In the example, the temperature control module106may select a GC target temperature of 100° F. when the ambient temperature202is 65° F.

In one embodiment, the temperature control module106may be configured to interpolate elution data between available temperatures in the set of temperature-based elution data204, and may be configured to select a GC target temperature206at any desired temperature. For example, the set of temperature-based elution data204may comprise elution data204at 50° F., 100° F., and 150° F., and the temperature-based elution data204may be configured to select a GC target temperature 10° F. higher than the ambient temperature202, or 75° F. when the ambient temperature202is 65° F. The interpolation may be simple interpolation, or where greater accuracy is required the interpolation could occur through the application of fundamental mass diffusion equations.

The temperature control module106may be further configured to provide a heating element command208, which may be a physical control of a heating element, a datalink command to another portion of the controller104to control the heating element, or the like. The heating element may be controlled through a standard control scheme such as a proportional-integral-derivative (PID) controller to control the GC column(s) to the GC target temperature206.

In one embodiment, the set of temperature-based elution data204contains one set of data for a first GC column, and a second set of data for a second GC column. The GC target temperature206may comprise a target temperature206for each GC column, and the target temperatures206may be different values for each GC column.

The controller104may comprise a GC column switching module108configured to control gas flows through at least one GC column in the GC sensor102. The GC column switching module108may be configured to control the flows in a first flow regime210such that a gas flow passes through a first GC column into a second GC column in series. The GC column switching module108may be further configured to control the flows in a second flow regime210such that a first and second GC column each receive a gas flow in parallel. The GC column switching module108may be further configured to ensure that a first and second GC column receive substantially the same flow rate of gas.

The GC column switching module108may comprise commands to one or more valves and one or more pumps to achieve the flow regime switches. The commands may comprise physical control of the valves and/or pumps, a datalink command to another portion of the controller104, or the like.

The controller104may comprise a sample introduction module110configured to introduce a sample gas into at least one GC column. The sample introduction module110may be configured to control a sample flow in a concentration flow regime212configured to concentrate a sample gas onto a preconcentration material, which may be configured to adsorb the sampled chemicals of interest. The sample introduction module110may be further configured to control a sample flow in a desorption flow regime212to desorb a sample gas from the preconcentration material, and to flow the concentrated sample through the at least one GC column.

The sample introduction module108may comprise commands to one or more valves and one or more pumps to achieve the flow regime switches. The commands may comprise physical control of the valves and/or pumps, a datalink command to another portion of the controller104, or the like.

The controller104may comprise a similarity sequencing module112configured to take data samples in a constant log-time fashion. Early eluting chemicals tend to have a sharper peak shape and to elute in a short period of time. Later eluting chemicals tend to have a flatter peak shape and to elute over a longer period of time. Therefore, the later eluting chemicals tend to have a peak created from a much larger number of samples than earlier eluting peaks, and the different shapes of the peaks tend to make algorithms less likely to detect them. Taking data in a constant log-time fashion tends to clean up the peaks and make early and late eluting chemicals show similar looking peaks. In one example, the similarity sequencing module112may be configured to take data samples214at each 0.2 log seconds, or the normal time value of data point value “n” equals e^n. In the example, data point 12 would be (12*0.2=) log-time 2.4, and the normal time value would be 11.02 seconds. Logarithm values other than base “e”, or the natural logarithm, are possible, as the natural logarithm is used only for illustration.

Many applications have a natural data sampling frequency due to controller104execution times and physical limitations of the sensor102. Therefore, the similarity sequencing module112may be configured in one embodiment to take data samples214in a constant time fashion, and to process the data to simulate a constant log-time data set216. For example, the similarity sequencing module may be configured to physically collect data each 0.2 seconds. To simulate the 15thlog-time data point, the time data from (e^(15*0.2)=) 20.08 seconds to (e^(16*0.2)=) 24.53 seconds would be used. Therefore, the constant time data points (214)101-122, as well as part of data point100, and part of data point123, would be integrated to simulate the 15thlog-time data point216.

A rectangular approximation or other integrating algorithm could be used to integrate the data between the given sample points214. Simpson's rule, trapezoidal, and polynomial approximations can be used as well, although those integrating algorithms provide little benefit of improved accuracy over a rectangular approximation where the constant time data interval is small, and those algorithms, for example Simpson's rule, may amplify high frequency signal noise.

The signal processing module114may be configured to deconvolute a sampling data set216to clarify data peaks and find eluted chemicals in the sampling data. The sampled data set216may be affected in time, or convoluted, due to diffusion and separation in the at least one GC tube. The deconvolution process may recover the original signal, which is typically a chemical concentration in GC sensors102. The signal processing module114may be configured to deconvolute the data set216with the largest polynomial division that does not produce an unstable data response. The signal processing module114may be further configured to utilize a Z-transform in sampling point space to determine the input signal according to the following equation where the Z-transform of the system218may be a transfer function describing the characteristics of the system:

Therefore, the inverse transform of the result of Equation1provides the input data220or the information from the sampling data input. A Fourier transform can also be used in deriving the data, although the Fourier transform is more susceptible to ringing from high frequency noise.

The signal processing module114may be configured to deconvolute the sampling data set to clarify data peaks and find eluted chemicals in the sampling data by converting the sampling data set216into a high order polynomial, for example by a regression fit. The signal processing module114may be further configured to interpret a model218of the GC column system, which may be a transform function in the form Nz/Dz, or a rational polynomial function. In some embodiments, either Nz or Dz may be 1, reducing the transform function to 1/Dzor Nz, respectively. Those of skill in the art will recognize that if the roots of Dzfall within the unit circle, the signal convolution is stable.

The signal processing module114may be configured to label the input chemical sample function as U, the output function as Y, and the system model as G, and to label the Z-transforms of those functions as Uz, Yz, and Gz. The input function may be convoluted by the GC columns such that Yz=Gz*Uz, where Yzis the measured output at the detector, and Uzis the Z-transformed desired input information. Therefore, it is apparent that equation 2 yields the desired input information.
Z−1(Uz)=Z−1(Yz/Gz)=Z−1((Yz*Dz)/Nz)   Equation 2.

The signal processing module114may be configured to modify the Z-transform division to ensure it is stable. This may be accomplished with a standard division configured to avoid a negative result. In the following example, polynomials are expressed as coefficients only without the related powers (e.g. X2+2X+3=[1 2 3]). In one example, Nzmay be [3 2 1 2 3 2 1] while Dzmay be [1 1 1]. The first factor to check may be 3/1=3, generating a first intermediate result of (3-3*1 2-3*1 1-3*1 2 3 2 1), or (0 −1 −2 2 3 2 1) with the result being (1). Note that the result contains negative values, and is therefore unstable. The second intermediate result is (0 0 −4 0 3 2 1) with the result being (1 −1). The next becomes (0 0 0 −4 −1 2 1) result=(1 −1 −4). The result is beginning to exhibit fluctuations.

Continuing the analysis by testing factors under the restriction of no negative results, it is apparent that the first factor for the example should be 1. With 1 the result will be (2 1 0 2 3 2 1). As there are no negative values this is acceptable. Proceeding to the next factor, 1 is selected. This also produces negative values so it is reduced to 0. The second result would be (2 1 0 2 3 2 1) with the result being (1 0). The third is (2 1 0 2 3 2 1) with the result (1 0 0), The fourth is (2 1 0 0 1 0 1) and (1 0 0 2). Continuing to the end yields (2 1 0 0 1 0 1) and (1 0 0 2 0 0 0).

The signal processing module114may be configured to complete the deconvolution under equation 2. The modified Z-transform takes care of any instability introduced by any problematic zeros. Note that the modified z transform method makes an implicit assumption that all features of interest convolute similarly as the divisor is constant. If the divisor is not constant, for example because the width of peaks of interest increases at later elute times then further modification may be utilized. A first modification is to change the divisor for each time period of interest. This is within the skill of one in the art, but may not be the preferable solution in some circumstances. A second modification is to adjust the time sampling such that the peaks have similar features and the constant divisor remains valid. The similarity sequencing module112may be configured to perform the second modification. In embodiments utilizing a Fourier transform or other deconvolution methods, the divisor issue remains and the modifications listed may still be utilized in some embodiments.

The noise filtering module116may be configured to operate a plurality of noise suppression wavelets222and/or other noise suppression methods on the sampling data, and to identify one or more peaks as noise, and one or more peaks as data. Each noise suppression methodology may make assumptions about the noise shape. These assumptions are known as the noise model. Changing the noise model will affect the result of the noise suppression step, which will introduce or eliminate different noise generated artifacts in the results.

The noise filtering module116maybe further configured to identify relatively stable peaks as data, and relatively unstable peaks as noise. A stable peak in this context is a peak that is present even when several noise suppression methods are used. An unstable peak is one whose presence is dependent on the noise model used and thus is not present in some of the responses. The noise filtering module116may be configured to operate a noise suppression wavelet222or other noise suppression method on the sampling data to suppress noise peaks. The noise filtering module116may be further configured to operate a plurality of noise suppression wavelets222on the sampling data, and to identify one or more peaks as noise224, and one or more peaks as data224. The noise filtering module116may be configured to identify relatively stable peaks as data, and relatively unstable peaks as noise

In one embodiment, the noise filtering module116may be configured to operate a set number of noise filtering wavelets222on the sampling data at each time step, and to identify peaks224which remain substantially constant as data, and peaks224which move or intermittently appear as noise. Substantially constant may comprise a range of amplitudes and a range of time values wherein a peak can appear and still be considered to be the same peak. Moving or intermittently appearing may comprise values outside of the range of amplitudes and the range of time values wherein a peak can appear and still be considered to be the same peak.

In one embodiment, the noise filtering module116may be configured with a larger number of noise suppression wavelets222than the noise filtering module116may run on each execution time step. In one example, the noise filtering module116may comprise ten noise suppression wavelets222, and the noise filtering module116may operate three noise suppression wavelets222at each time step. The three noise suppression wavelets may comprise a random selection from the ten available wavelets222, a rotation within the ten available wavelets222, or a primary noise suppression wavelet222and two wavelets selected from the other nine available wavelets222. This embodiment avoids having a noise suppression wavelet222that may be sensitive in some operating conditions dominate the signal, while improving the operational performance of the controller104compared to running all wavelets222at every execution cycle.

FIG. 2Bis a schematic block diagram illustrating one embodiment of a controller104for a GC sensor102in accordance with the present invention. In the embodiment ofFIG. 2B, the apparatus includes a preconcentration tube (refer to the sections referencingFIGS. 4 through 8B) having a preconcentration material that adsorbs and desorbs chemicals from an intake air stream. The preconcentration material, in one embodiment, releases a known chemical at a specified temperature226. The GC sensor102includes an internal standard delivery module228that heats the preconcentration material to the specified temperature226.

The internal standard delivery module228may heat the preconcentration material by issuing a heat preconcentration command230to an actuator such as a resistive heater, and/or similar method known in the art. The internal standard delivery module228may be configured to heat the preconcentration material on a maintenance schedule, upon a request, upon the detection of a GC sensor fault102, and the like. Upon heating to the specified temperature226, the preconcentration material creates a known chemical release232, which a calibration module234is configured to detect. The calibration module234detects elution of the known chemical from a GC unit comprising a first and second GC column (refer to the description referencingFIGS. 8A and 8B, for example), and provides known chemical elution data236. The system100may be configured to utilize the known chemical elution data236to provide dynamic information about the system (e.g. a system transfer function), to determine a sensor102fault condition, and the like.

FIG. 3is a schematic block diagram illustrating one embodiment of an apparatus300to seal a GC sensor102and detector circuit316in accordance with the present invention. The apparatus300may comprise a first sealing surface304configured to seal the sensor102from an ambient environment. The first sealing surface304may be an epoxy or similar sealant configured to seal the material of the sensor102body which may comprise a machineable ceramic. In one embodiment, an acrylic GP sealant is used at the sealing surface304. The apparatus300may further comprise a second sealing surface306configured to seal a detector circuit316from internal leaks within the sensor102.

The first sealing surface304may seal the faces of a first outer sealing body and a second outer sealing body, wherein the outer sealing bodies together comprise the body of the sensor102. Refer to the description referencingFIG. 10.

The apparatus may further comprise a GC unit308which may comprise at least one GC column, and a sample unit310configured to provide the sample gas to the sensor102and GC unit308. The sample may pass from the GC unit308to the detector316. The detector316may comprise any detection device used in the GC art—including a thermal conductivity detector (TCD), a mass spectrometer, flame ionization detector, photo-ionization detector, electron capture detector, Hall electrolytic conductivity detector, and the like. In one embodiment, the detector316comprises a TCD, and the detector316is configured to generate an electrical signal based on the detected thermal conductivity of the sample gas on one side of a Wheatstone bridge, with an electrical signal based on the detected thermal conductivity of a reference gas on the other side of the Wheatstone bridge. This known compensation technique removes common mode noise, or background noise, from the signal and focuses the detection on the sample310gas.

The apparatus300may comprise a controller104, which may communicate with the detector316, an ambient temperature sensor312, and a GC unit temperature sensor314. The temperature control module106may be configured to utilize the temperature sensors312,314to control the temperature of the GC column(s) within the GC unit308.

RegardingFIGS. 4 through 8B, embodiments with two different switching schemes are described. The first switching scheme is designed to implement the switching between two GC columns GC1, GC2, and embodiments of this scheme are described inFIGS. 4 through 7. The second switching scheme is used to load and unload sampled chemicals on a preconcentration tube402, and to alternate sample air and clean air to the inlet of GC1. One embodiment of the second switching scheme is detailed inFIGS. 8A and 8B. A given embodiment of the invention may comprise either or both switching schemes. They are illustrated separately to clarify the features of the invention, and it is a mechanical step for one of skill in the art to combine embodiments of the first and second switching schemes in a given embodiment of the invention.

FIG. 4is a schematic block diagram illustrating one embodiment of an apparatus400to control flows to GC columns within a GC sensor102in accordance with the present invention.FIGS. 4 through 8Buse the standard convention that where a flow depends upon the position of a valve, a dashed line indicates that the given flow is not occurring with the valve in the position as shown within that Figure. The apparatus400may comprise a first GC column GC1, a second GC column GC2, and a plurality of flow resistances (restrictions) R1, R2, R3. The first and second GC columns GC1, GC2are interposed between the first and second outer sealing bodies. The GC columns may be disposed within a cavity machined or cast into the sealing bodies.

The flow resistances R1, R2, R3may comprise orifices, controllable valves, inserted microboard with porous substrate, or any other type of configurable pressure drop available in the art. In one embodiment, the flow resistances comprise flow channels sized to achieve a specified pressure drop at a specified flow rate. The flow channels of the apparatus400may be etched on the surfaces of opposing faces of the sensor102body, or they may be machined flow paths within a sensor102body.

The apparatus400may comprise a preconcentration tube402, a pump404, and a molecular sieve406. The molecular sieve406may be configured to remove water and/or other impurities from the gas flow in the apparatus400, and may be affixed between the pump404inlet and outlet. The apparatus400shows only the relative flows of GC1and GC2, while other flows into and out of the apparatus400are not shown to avoid cluttering the essential aspects of the embodiment of the invention. Significantly, the introduction of sample310gas into the system is not shown. Sample310gas may be introduced at the pump404through the molecular sieve, for example.

The apparatus may further comprise a valve408configured to direct flow through resistance R2or resistance R3. The valve408may comprise a solenoid valve. InFIG. 4, the valve408is directing flow through resistance R2. The flow through R2carries the flow out of GC1into GC2, thereby connecting the GC columns in series, and sending the output of GC1and GC2into the detector316. The detector316effluent may vent to the atmosphere410. In one embodiment, a majority of the flow through R2may flow through R1and recycle through the pump404.

FIG. 4illustrates the valve408set to the first flow regime. In the embodiment ofFIG. 4, a first fluid stream412from the pump408flows through the first GC column GC1and the second GC column GC2. A second fluid stream414directed by the valve408flows through the second resistance R2and the first resistance R1.

The depiction inFIG. 4thereby describes a valve408that switches between a first flow regime (as depicted inFIG. 4) and a second flow regime (as depicted in FIG.5). The flow channels depicted inFIGS. 4 through 8Bare etched into the first sealing body and the second sealing body such that when the sealing bodies are placed together, sealed flow channels are thereby created. The first flow regime comprises a sample (starting at the pump404) flowing through the first GC column GC1and then the second GC column GC2. The second flow regime (refer toFIG. 5) comprises a sample (starting at the pump404) flowing through the second GC column GC2without flowing through the first GC column GC1.

Referring toFIG. 5, the valve408is directing flow through restriction R3. The flow through R3forces the flow from GC1away from GC2, and through R1for venting or recycling. The flow through GC2is provided by the pump404. It is apparent fromFIGS. 4 and 5that the apparatus400is configured to direct gas flows through the GC columns GC1, GC2in series or parallel with the use of a solenoid valve408.

FIG. 5illustrates the valve408set to the second flow regime. In the embodiment ofFIG. 5, a third fluid stream502from the pump408flows through the first GC column GC1and the first resistance R1. A fourth fluid stream504directed by the valve flows through the third resistance R3and the second GC column GC2. The fourth fluid stream504further prevents the third fluid stream502from flowing through the second GC column GC2.

FIG. 6is a schematic block diagram illustrating an alternative embodiment of an apparatus600to control flows to GC columns GC1, GC2within a GC sensor102in accordance with the present invention. Referring toFIGS. 4 and 5, it is apparent that for the flow rates through GC1and GC2to be identical in either position of the valve408, a condition which may be desirable for the detector316, the flow restrictions R2, R3must be identical. Referring back toFIG. 6, those flow restrictions may be replaced with a single restriction R4before the valve408which enforces this condition more effectively. The embodiment ofFIG. 6is otherwise identical to the embodiment ofFIG. 5.

The embodiment ofFIG. 6thus depicts a first flow regime comprising a first fluid stream from the pump408that flows through the first GC column GC1and the second GC column GC2, and a second fluid stream directed by the valve408that flows through the fourth resistance R4and the first resistance R1. The valve408inFIG. 6is depicted in the position to induce the first flow regime.FIG. 6further depicts a second flow regime comprising a third fluid stream from the pump408that flows through the first GC column GC1and the first resistance R1, and a fourth fluid stream directed by the valve408that flows through the fourth resistance R4and the second GC column GC2. The fourth fluid stream further prevents the third fluid stream from flowing through the second GC column GC2. The valve408would be turned—similar to the embodiment depicted in FIG.5—to induce the second flow regime.

FIG. 7is a schematic block diagram illustrating an alternative embodiment of an apparatus700to control flows to GC columns GC1, GC2within a GC sensor102in accordance with the present invention. Referring toFIG. 6, it is apparent that for the flow rates through GC1and GC2to be identical in either position of the valve408, the flow restriction R4must dominate the observed pressure drops for flow throughout the apparatus600. Referring back toFIG. 7, the single pump404is replaced with two pumps702,706which may comprise corresponding molecular sieves704,708.

The two pumps702,706may enforce the flow rates through GC1and GC2to be identical because the pump607controls the flow rate through GC1, and the pump702can control the flow rate through GC2. The controller104may be configured to control the pumps702,704. The restriction R4may be removed in the apparatus700, although it may be included (not shown), or lumped with R1to place the restriction on the low pressure side of the pump702instead of the high pressure side if desired. The removal of the restriction R4may cause a lower nominal pressure in the analysis flowpaths of the sensor102, and thereby increase the sensitivity of the GC sensor102to leaks. It is within the skill of one in the art to weigh the increased manufacturing costs to manage leaks, a higher pressure load on the pump702, and a loss in sensor102measurement capability due to unmanaged leaks when determining the inclusion of the restriction R4.

Thus,FIG. 7depicts an embodiment comprising a first pump706and a second pump702. In the embodiment ofFIG. 7, a first flow regime comprises a first fluid stream from the first pump702that flows through the first GC column GC1and the second GC column GC2. The first flow regime further includes a second fluid stream directed by the valve408from the second pump702that flows through the first resistance R1. The second stream further prevents the first stream from flowing through the first resistance R1. The valve408inFIG. 7is positioned to induce the first flow regime.

FIG. 7further depicts a second flow regime comprising a third fluid stream from the first pump706that flows through the first GC column GC1and the first resistance R1, and a fourth fluid stream directed by the valve408from the second pump702that flows through the second GC column GC2. The fourth stream further prevents the third stream from flowing through the second GC column GC2. The valve408would be turned—similar to the embodiment of FIG.5—to induce the second flow regime. In the embodiment ofFIG. 7, sample may be introduced at the first pump706.

FIG. 8Ais a schematic block diagram illustrating one embodiment of an apparatus800to control sampling flows within a GC sensor102in accordance with the present invention. The flow channels of the apparatus800may be etched on the surfaces of opposing faces of the sensor102body, or they may be machined flow paths within a sensor102body. In one embodiment, the flow channels may comprise ceramic or quartz inserts in the analytical (i.e. sample-containing) portions of the sensor102to further enhance sealing of the sensor102and allow lower concentrations of chemicals in the sample310to be detected. Such inserts are estimated to allow detections down into the parts-per-billion (ppb) range—for example below about 1,000 ppb. The apparatus800may comprise a valve804configured to operate the apparatus800in the concentration or desorption modes. The apparatus800ofFIG. 8is shown in the concentration mode. Some of the valves and flow paths similar to those depicted inFIGS. 4 through 7are removed fromFIG. 8to avoid obscuring aspects of the present invention. However, in one embodiment,FIG. 8retains the pump(s)404,702,706, and valve404to allow flow through the GC columns GC1, GC2in series and/or parallel as shown inFIGS. 4 through 7.

In the embodiment ofFIG. 8A, the sample310is introduced to the preconcentration tube402which may adsorb the chemicals of interest. A pump806may send gas through a carrier gas flow restriction R6and to the GC unit308. Some of the pump806effluent may recycle through a desorption flow restriction R7and return to the pump806through the valve804. The flow may pass from the GC unit308to the detector316, where it may flow through a system flow restriction R5and to an atmospheric vent808or back to the pump806. Therefore, in one embodiment of the concentration mode, the preconcentration tube402is concentrating the sample gas, and the GC unit308is receiving clean ambient or carrier gas.

In one embodiment,FIG. 8Adepicts a preconcentration tube402, a sampling pump806, and a sample switching valve804. The sample switching valve804switches between a concentration mode and a sensing mode. The embodiment ofFIG. 8Adepicts the valve804in the concentration mode. The concentration mode comprises an intake air stream810flowing through the preconcentration tube402in a first direction (e.g. left to right inFIG. 8A), and the sampling pump806sending a dilute sample812through a GC unit308comprising the first and second GC columns GC1, GC2.

Referring toFIG. 8B, an embodiment is illustrated with the apparatus800in the desorption flow regime. The valve804is directing flow from the pump806reversed through the preconcentration tube402. Note that the valve804has shut down the flow from the pump806through the carrier flow restriction to the GC unit308, although the physical connection of the valve304to that flow channel is not shown inFIG. 8Bto prevent cluttering the Figure. The sample310gas flows through a tube shunt flow restriction R9to the valve804and through the preconcentration tube402, while the pump806flow that went to the GC unit308is redirected to the valve804through a sample flow restriction R8. Therefore, in one embodiment of the desorption mode, the preconcentration tube402is desorbing sample gas to the GC unit308.

In one embodiment,FIG. 8Bdepicts the valve804in the sensing mode. The sensing mode comprises an intake air stream814flowing through the preconcentration tube402in a second direction (right to left inFIG. 8B), and the sampling pump806sending a concentrated sample816through the GC unit308.

FIG. 9is a schematic block diagram illustrating one embodiment of an engineered pressure equalizing channel902in accordance with the present invention. The detector circuit seal306protects the detector316from intruding gases which may ruin the sample from the GC unit308. In one embodiment, the detector seal306is considerably more effective if the detector316circuit is at an equal pressure with sample310channel. If a pressure equalizing channel902is engineered between the sample310flow path and the detector316, equalizing a first pressure in the sample channel with a second pressure in the detector316circuit. In one embodiment, the pressure equalizing channel902is engineered in parallel along the sample channel, from the sample310introduction through the GC unit308.

FIG. 10is a schematic block diagram illustrating one embodiment of an apparatus1000to seal a GC sensor102and detector circuit316in accordance with the present invention. The sensor seal304may comprise an adhesive between faces of a first outer sealing body1008and a second outer sealing body1010of the sensor102body. The faces of the first outer sealing body1008and the second outer sealing body1010may be pressed together by a plurality of fasteners1004with a pressure maintenance mechanism such as a plurality of lock washers1006.

The detector circuit316may be within a cavity in the sensor102, and may have a sealing surface306which may comprise an adhesive between the surfaces306. The detector seal may further comprise a pressure mechanism1002independent from the pressure mechanism1006of the sensor seal304. The pressure mechanism1002may comprise one or more springs configured to apply pressure to the detector circuit316faces306to keep them sealed.

The sealing surface306may include a pressure equalizing channel902. In one embodiment, the apparatus1000includes at least one spring1002interposed between the first and second outer sealing bodies1008,1010, wherein the spring(s)1002apply force to enhance the detector circuit316seal.

FIG. 11is a schematic block diagram illustrating one embodiment of an apparatus1100to uniformly heat a GC column GC1in accordance with the present invention. The apparatus1100may comprise a heating element1102. The heating element1102may comprise a heating element1102with a higher wattage rating than the required wattage to heat the GC column GC1from the lowest predicted ambient temperature202to the highest GC target temperature206. Such a design allows the heating element1102to provide the heat required for the sensor at a lower current and heating element1102temperature than a minimally specified heating element would. Such a design minimizes the potential for heat spikes and non-uniformity throughout the GC column GC1.

The apparatus1100may further comprise insulation1104between the heating element and the GC column GC1. The insulation1104further reduces the occurrence of temperature variability induced in the GC column GC1by the heating element1102.

FIG. 12Ais a schematic block diagram illustrating one embodiment1200of slot1204machined into the sensor body1202for packing a preconcentration material in accordance with the present invention. The slot1204may be machined vertically into the sensor body1202and the apparatus1200may be packed vertically. Further, the slot1204may comprise a slot machined into the sensor body1202, with a tube inserted into the slot, wherein the apparatus1200is packed into the tube.

Referring toFIG. 12B, the slot may be packed by inserting a slurry comprising microspheres and adhesive to form a uniformly porous plug1206at a first end of the slot1204, and packing in the preconcentration material1208. The apparatus1200may be completed by inserting a slurry to form a uniformly porous plug1206at a second end of the slot1204. Referring toFIG. 12C, it may be desirable to offset the preconcentration material1208from the adhesive slurry1206. Therefore, the apparatus1200ofFIG. 12Cshows the preconcentration material1208separated from the adhesive slurry1206by a pair of offset rods1210configured to offset the preconcentration material1208the desired distance.

The adhesive slurry may comprise glass microspheres. The adhesive may comprise an epoxy glue comprising 10% or less by weight of the slurry. The glass-glue mixture provides a consistent pressure drop once evenly mixed.

FIG. 13is an illustration of sampling data1300shown in constant time, in accordance with the present invention. The example data labeled Chem1may be a typical elution peak for a relatively fast-eluting chemical, and the example data labeled Chem2may be a typical elution peak for a relatively slow-eluting chemical. Note that the time scale forFIG. 13is relative only, and that the differences between the fast-eluting and slow-eluting chemicals are compressed to demonstrate the similarity effect and relative peak shapes. In practice, chemicals with elution peak widths that vary as much as those shown inFIG. 13will often, but not necessarily, exhibit much greater separation in the time axis.

The fast eluting chemical may comprise a sharp peak as shown, and a relatively small number of sample points. The slow eluting chemical may comprise a flattened peak as shown, and a relatively large number of sample points. The area under the peaks is similar in the examples, as evidenced by the similar final values of the integration curves, indicating that these two chemicals were in the sample at approximately the same concentrations. The differences in the peak widths and the number of samples in each peak may complicate the use of a modified Z-transform in analyzing GC sensor102signals.

FIG. 14is an illustration of sampling data1400shown in constant log time, in accordance with the present invention. For purposes of illustration, the same example data fromFIG. 13is shown inFIG. 14, and therefore the time axis differences between the fast and slow eluting chemicals may likewise be compressed inFIG. 14. The fast eluting chemical may comprise a sharp peak as shown. The slow eluting chemical may comprise a similarly shaped peak in constant log time. The peaks for the fast and slow eluting chemicals inFIG. 14may exhibit similar numbers of sample points within each peak. Note that the integral curves inFIG. 14are generated with a rectangular estimate, and that close observation of the integral curves inFIG. 14illustrates that although the fast and slow eluting chemicals had the same area under the curve in constant time sampling, they are not at exactly the same area under the curve in constant log-time sampling, although the introduced error is small.

FIG. 15is an illustration of sampling data adjusted with a plurality of noise suppression methods in accordance with the present invention. The first data set1502may show a data set adjusted by a first noise suppression method, the second data set1504may show a data set adjusted by a second noise suppression method, and the third data set1506may show a data set adjusted by a third noise suppression method. In one embodiment, the noise-filtering module116may label a peak at about15time units as data because this peak occurs in all three sets1502,1504,1506. The noise-filtering module116may label peaks at about 45, 65, 75, 90, and 130 time units as noise because these peaks appear on only some of the sets1502,1504,1506. Further, the noise-filtering module116may label a peak at about115time units as data because this peak occurs in all three data sets1502,1504,1506. The noise suppression methods may be noise suppression wavelets.

FIG. 16is a schematic flow diagram illustrating one embodiment of a method1600to manufacture a GC column GC1, GC2in accordance with the present invention. The method1600may be performed with a torsion spring making machine configured to manage materials of the diameter of the GC column GC1, GC2. The method1600may begin with bending1602a tube of slightly longer than the desired GC column length into a GC column GC1, GC2. Then, the tube may be crimped1604at the ends to facilitate maintaining tube cleanliness during storage1606and/or transport1606of the column GC1, GC2. Then method1600may continue with a practitioner cutting1608off the ends of the column GC1, GC2and installing1610the column GC1, GC2into a GC sensor102.

FIG. 17is a schematic flow diagram illustrating one embodiment of a method1700to utilize an internal standard chemical in a GC sensor102in accordance with the present invention. The method1700may begin with packing1702a preconcentration material1208into a GC sensor. The preconcentration material1208may comprise a known material, for example Tenax, that releases a known byproduct at a set temperature. The method1700may proceed with heating1704the preconcentration material1208to a specified temperature at which the known byproduct is released. The controller104may then track1706the elution of the known byproduct, and compare1708the elution time to a known standard elution time according to the temperature of the GC columns GC1, GC2.

FIG. 18is a schematic flow diagram illustrating one embodiment of a method1800to pack a preconcentration material1208in accordance with the present invention. The method1800may begin with a practitioner mixing1802a microsphere-adhesive slurry and placing1804some of the slurry at one end of a slot1204. The practioner may then insert1806an offset rod into the slot to position a preconcentration material in the slot1204. The practitioner may then pack1808a preconcentration material into the slot, and insert1810another offset rod into the slot. The practitioner may then fill the slot1204with microsphere-adhesive slurry to complete the packing of the preconcentration material.

FIG. 19is a schematic flow diagram illustrating one embodiment of a method1900to control the temperature of a GC column GC1, GC2in accordance with the present invention. The method1900may begin1902with the controller storing1902a set of elution versus temperature data for a number of chemicals of interest. The temperature control module106may be configured to detect1904the ambient temperature202, and to select1906a target temperature206for the GC column(s) based on the ambient temperature202and the elution versus temperature data204. The temperature control module106may be further configured to heat1908the GC column(s) GC1, GC2to the target temperature206.

FIG. 20is a schematic flow diagram illustrating one embodiment of a similarity sequencing sample data acquisition method2000in accordance with the present invention. The method2000may begin with the similarity sequencing module112determining2002whether a variable time step sampling rate is available. Where variable time step sampling is available, the similarity sequencing module112may collect2004data in a constant log-time step, wherein each data point proceeds at the time value t, where:
t=A*ek*sEquation 3.

In Equation 2, s is the sample number to be taken, and t is the normal time at which the sample is taken. The value k determines the distance between sample increments, while the value A is used to define the time at which the first sample is taken. For example, the value k may be 0.2, and A may be 1. In the example, the first sample is taken at approximately 1.22 seconds, the second sample at 1.49 seconds, and another sample is taken at each 0.2 log-seconds. In the example, the 20thsample would be taken at about 54.6 seconds.

Where variable time step sampling is not available, the similarity sequencing module112may collect2010data in a constant normal-time step, and process2012the data to simulate constant log-time steps.

The method2000may proceed with the similarity sequencing module112storing2006the sample data, and the controller104may make2008the stored data available to a signal processing algorithm on the signal processing module114.

FIG. 21is a schematic flow diagram illustrating one embodiment of a method2100for analyzing sampling data in accordance with the present invention. The method2100may begin with the signal processing module114receiving2102sample data216which may be sequenced by the similarity sequencing module112. The signal processing module114may receive2104a system characterization which may comprise a Z-transform transfer function of the system100. The signal processing module114may deconvolute2106the sample data216with the largest polynomial division that does not produce a negative response and induce instability. The signal processing module114may then determine the input signal according to Equation 2.

FIG. 22is a schematic flow diagram illustrating one embodiment of a method2200for identifying data peaks and noise peaks in a set of sampling data216in accordance with the present invention. The method2200may begin with the noise filtering module116receiving sample data216. The noise filtering module116may then apply2204a plurality of noise suppression wavelets222to the sample data216. The noise filtering module116may then generate2206a set of data peaks, and identify2208shifting peaks as noise, and stable peaks as signal or data.

FIG. 23is a schematic flow diagram illustrating one embodiment of a method2300for low cost high resolution chemical detection in accordance with the present invention. Some steps of the method2300may be implemented by a controller104. The method2300includes providing2302a first outer sealing body1008and a second outer sealing body1010. The method2300further includes etching2304a plurality of flow channels into the first outer sealing body1008and a second outer sealing body1010. The method2300continues with providing2306a first GC column GC1and a second GC column GC2and further providing2308a valve408that switches between a first flow regime and a second flow regime. The method2300includes operating2310the valve in the first flow regime by flowing a sample through the first and second GC columns GC1, GC2, and operating2312the valve in the second flow regime by flowing a sample through the second GC column GC2without flowing the sample through the first GC column GC1.

The method2300further includes flowing2314an intake air stream through a preconcentration tube402in a first direction to concentrate chemicals on the tube402, and flowing2316the intake air stream through the preconcentration tube402in a second direction to deliver a concentrated sample to a GC unit308. The method2300may further include heating2318the preconcentration tube402to a specified temperature, thereby releasing a known chemical from preconcentration material in the preconcentration tube402, and detecting elution of the known chemical from the GC unit308. The method2300may further include providing a detector circuit316interposed between the first and second outer bodies1008,1010, providing a detector circuit seal, and further providing a pressure equalizing channel from a sample channel to the detector circuit316.