Abstract:
A highly sensitive fluid composition analyzer where a fluid may be placed in contact with a very small area on a material sensitized to change color in the presence of a specific type of compound, to be impinged with light. The light reflected, transmitted and/or scattered by the material may serve as input for the analyzer electronics. The fluid may be pre-concentrated prior to being brought in contact with the material. The area on the material may be a spot having an outside dimension of less than one millimeter.

Description:
BACKGROUND 
       [0001]    The invention pertains to sensors and particularly fluid composition sensors. More particularly, the invention pertains to sensitive fluid composition analyzers. 
       SUMMARY 
       [0002]    The invention is a highly sensitive analyzer where a fluid may be placed in a very small area on a fluid-composition-sensitive material to be impinged with light and detected for analysis. The fluid may be pre-concentrated prior to being placed on the material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1   a  is a diagram of a fluid-composition-sensitive-paper holder having a gas inlet and outlet, an optical input channel and an optical readout; 
           [0004]      FIG. 1   b  is a diagram of an analyzer assembly incorporating the holder in  FIG. 1   a;    
           [0005]      FIG. 1   c  depicts a short piece of a paper tape which may be used in the assembly in  FIG. 1   b;    
           [0006]      FIGS. 2   a  and  2   b  are diagrams of side and perspective views, respectively, of a micro-spot paper tape analyzer module; 
           [0007]      FIG. 3  is a diagram of a magnified portion of the micro-spot paper tape analyzer assembly or system; 
           [0008]      FIGS. 4   a  and  4   b  show a fabricated micro-spot paper tape assembly; 
           [0009]      FIG. 5   a  is a graph of the spectral change of material paper after exposure to a fluid, which causes the material to change in color, as indicated by intensity counts versus wavelength in nanometers; 
           [0010]      FIG. 5   b  is a graph of a drop in a photo detector light signal from paper  11  versus time of exposure of the paper to analyte and its associated change in color; 
           [0011]      FIG. 6   a  is a diagram of a two-valve sensor system having an absorber as pre-concentrator analyte modulator arrangement with a reservoir; 
           [0012]      FIG. 6   b  is a diagram of the two-valve sensor system having the absorber/pre-concentrator analyte modulator arrangement with a reservoir having a long tubular shape; 
           [0013]      FIG. 7   a  is a diagram of a one-valve version of the sensor system in  FIG. 6   b;    
           [0014]      FIG. 7   b  is a diagram of a sensor system like that of  FIG. 7   a  in which the reservoir and valve has been replaced by a rapidly heatable reservoir; 
           [0015]      FIG. 8  shows experimental data of an FID signal in microamps versus time in seconds, demonstrating several pre-concentration cycles with an absorber film inside a 10-cm capillary; 
           [0016]      FIGS. 9 and 10  are experimental data of retention time of ammonia in air, measured in millivolts from an electrochemical cell, while keeping track of flow and capillary temperature; and 
           [0017]      FIGS. 11-14  show an illustrative example of a pre-concentrator which may be used as an analyte modulator for the present sensor system. 
       
    
    
     DESCRIPTION 
       [0018]    Industrial toxic gas monitors as used, for example, in semiconductor processing, should be sensitive (ppb level) and specific. Traditional NDIR analyzers are unwieldy (with meter-long path lengths) if they are to reliably achieve ppb-level sensitivities. Typical GCs and MSs can not achieve such sensitivities. Therefore, a family of analyzers based on color-changing reactions on paper (as with litmus paper) have been offered and accepted in the market for their reliable performance. However, the servicing and material cost of such reagent-bearing paper is a burden that many present customers would rather avoid if a reliable alternative can be found. In addition, some analytes such as GeH 4  (Germane), are “slow”, i.e., take too much time to be detected at the desired level. 
         [0019]    A solution to these shortcomings may be a combination of the following: 1) Make the sample-paper interaction spot very small, so that the use of costly reagent paper is very low, but the mass flux of sample fluid transferred to the spot area, and therefore its speed of detection are large; 2) Preconcentrate the analyte(s) of interest, so that the time needed for detection becomes one in an acceptable range, which is equivalent to an increase in sensitivity; 3) Make the spot size so small that a micro-fabricated adsorber, such as a PHASED chip or the like, can provide the needed analyte preconcentration, and thus minimize the electric power needed for preconcentrator operation; and 4) Reduce preconcentrator action for other analytes to prevent swamping of the detector. 
         [0020]    Building on an established paper tape approach (e.g., dry reagent embedded in porous paper changes color upon contact with specific air-borne analyte), an original size of the exposed paper tape spot of about 3 to 4 mm outside dimension (OD) may be reduced by about 42 times to about 0.15 mm or so OD, to permit use of a much smaller sample gas flow. The dimension of spot  18 , whether circular or not, should not be much less than 0.1 mm OD in order not to become of the same order of magnitude as the pores or fibers of the paper or reagent host material. The small flow because of the small spot may enable preconcentration of the analyte with little power consumption (during the adsorber heating period). 
         [0021]    The system may consist of “channeling” just a pre-concentrated sample towards the paper tape spot, (by splitting a flow from an adsorber into a low-analyte and a high-analyte stream) thus resulting in a reduced paper tape sampling time and/or improved sensitivity to the selected preconcentrated analyte. Furthermore, the system may also feature a low-cost and reliable design of such “channeling,” based on the action of valve-less, thermal gas expansion and contraction. 
         [0022]    The system may be based on principles of gas adsorption, and gas expansion/contraction. Specific adsorber materials for selected analytes may be known from gas chromatography. 
         [0023]    The system may provide a near-term solution to the problem faced to modernize the typical chemical cassette analyzers, versus the longer-term solution of analyzing the color change of liquid reagent droplets directly. The present system may lead to a reduction in the amount of the used reagent paper, faster and/or more sensitive response to selected analytes, while maintaining about the same sensitivity to other analytes. An additional benefit from this approach is that one does not necessarily block the potential use of an adsorber structure, such as PHASED instrumentation and other adsorber designs, but may make the paper tape flow compatible with it, while leveraging the low energy requirements of the adsorber. A PHASED mechanism may be noted herein and in U.S. Pat. No. 6,393,894, issued May 28, 2002, U.S. Pat. No. 7,000,452, issued Feb. 21, 2006, U.S. patent application Ser. No. 11/738,853, filed Apr. 23, 2007, and U.S. patent application Ser. No. 11/762,891, filed Jun. 14, 2007. U.S. Pat. No. 6,393,894, issued May 28, 2002, U.S. Pat. No. 7,000,452, issued Feb. 21, 2006, U.S. patent application Ser. No. 11/738,853, filed Apr. 23, 2007, and U.S. patent application Ser. No. 11/762,891, filed Jun. 14, 2007, are hereby incorporated by reference. 
         [0024]    The system may address prospective customer concerns about a slow response of paper tape to, for example, GeH 4  and the high cost of paper tape. The system may reduce the size of the exposed “spot” on the paper tape as a way to reduce the consumption and cost of the paper tape, and to augment this benefit with reducing the analysis time via the use of pre-concentrated analyte, for example, PHASED instrumentation. The smaller spot size may also enable reducing the sample flow typically used with paper tape by about a 180 times, down to ≦1 sccm, which is typical for a PHASED micro gas analyzer (MGA) flow. 
         [0025]    A paper tape-based gas sensing system may typically use a spot having an outside dimension (OD) between 2.5 mm and 4 mm. Such system may have a sample flow velocity through a paper  11  of about 9 cm/s, which can also be the flow used for the micro-spot version sensor  10  presented in  FIGS. 1   a  through  4   b , so that sample gas pressure-drop pump-load of a system  21  ( FIG. 7   b ) does not need to change with a substitution of the present sensor  10  in lieu of a previous sensor. Analyte reaction with the reagent in the paper may result in a change in color (spot  18 ), which is detected photoelectrically. Sensor system  10  may have a paper tape  11 , an LED light source  13 , a photodetector  14 , sample gas inlet  15 , a sample gas outlet  17  and a spot  18  on paper  11  ( FIG. 1   a ). 
         [0026]    Sensor system  10  may be regarded as a micro-toxic gas analyzer cassette  10 .  FIG. 1   a  shows a reagent-paper holder  19 , a gas inlet  15  and outlet  17 , an optical input channel  23  and an optical readout  22 .  FIG. 1   b  shows an assembly of system  10 .  FIG. 1   a  reveals how the paper tape  11  is clamped between gas inlet  15  and outlet  17 , with an upper structure  25 , especially at the point where the light source  13  (via optical fiber or channel  23 ) illuminates the small spot  18  having an OD  81 , as shown on a paper tape  11  in  FIG. 1   c , and reflects and/or scatters light into the optical fiber or channel  22  leading to the photo detector (PD)  14 . Photo detector  14  may output signals that indicate intensity and/or color of the detected light. Detector  14  may be connected to a controller/processor  16 , which may provide further analysis of the detector signals. Light source  13  may be connected to controller/processor  16  for reasons of knowing when the source  13  is on or for controlling source  13 . Controller/processor  16  may be connected to a module  29  having an MM-interface, and so forth. 
         [0027]    Spot  18  may be referred to as a micro spot. The range of dimension  81  may be between 0.1 and 1 millimeter. A nominal size range of spot  18  may be between 100 and 250 microns. Spot  18  may be of various shapes, but likely a close-to-circular shape. 
         [0028]      FIGS. 2   a  and  2   b  are diagrams of side and perspective views, respectively, of a micro-spot paper tape analyzer module  10 , showing a structure  82  containing the structure  25 , retaining just enough space for a paper tape  11 , being clamped down by two thumb-screws  24  onto a structure  83  containing the base plate  19  for supporting the paper  11 . 
         [0029]      FIG. 3  is a diagram of a magnified part of the micro-spot paper tape analyzer assembly or system  10 , showing a critical alignment of the optical inlet  23  and outlet  22  fibers or channels over the spot  18  on the paper  11  where the sample gas is to be pumped through. The sample may be brought in through the inlet channel, tube or capillary  15 . The sample may exit the analyzer  12  via outlet channel or tube  17 . The initial portion of outlet  17  may have a diameter which is the same as the diameter  81  of spot  18 . An example diameter may be about 150 microns (0.15 mm). The diameter of a micro spot may vary from about 0.1 to 1 millimeter. At the low end of this range, the spot diameter may be commensurate to the thickness of the paper or material hosting the reagent. 
         [0030]      FIGS. 4   a  and  4   b  show a fabricated micro-spot paper tape assembly or system  10  example. The shown white-head thumbscrews clamp down the (not yet inserted) paper tape  19 . The optical fibers  22  and  23  (with cladding and outer sheath) as well as the gas inlet capillary  15  are held in place by a strip  26  of aluminum. A black knob  27  is a handle that was used to hold a plastic insert of the assembly while being machined. 
         [0031]      FIG. 5   a  is a graph  31  of the spectral change of sensitized material paper after exposure to a fluid-component, which causes the material to change in color, as indicated by intensity counts versus wavelength in nanometers. For example, graph  31  of the spectral change (intensity curve  32 ) may be of “hydride paper” after exposure to ammonia, which caused the paper to turn pink. Detection may be via a 0.6 mm optical fiber leading to an OceanOptics™ spectrometer.  FIG. 5   b  is a graph  33  of a drop in a photo detector light signal decrease with time (curve  34 ) as paper  11  is exposed to analyte and changes color. 
         [0032]      FIG. 6   a  may present an approach  70  based on the combination of a pre-concentrator (PC)  42  with a storage reservoir  43 , into which several injection pulses of PC&#39;d analyte  71  can be made. System  70  of  FIG. 6   a  may solve a problem of non-commensurate response times between PC  42  and sensor  44  by using a reservoir  43  and valves  45  and  72 .  FIG. 6   a  is a diagram of pre-concentration arrangement for a sensor  44  with large dead volumes. One may first purge reservoir  43  and sensor  44  with valves  45  and  72  having positions 1,1, respectively. Second, the reservoir  43  and sensor  44  may be evacuated with valve  45  and  72  positions, respectively, 2,3, 2,2 or 2,1. Third, the PC  42  sampling time may be taken with positions 3,2 of valves  45  and  72 , respectively. Fourth, the analyte  71  in PC  42  may be desorbed while valves  45  and  72  having positions 3,2, respectively. Fifth, a PC  42  analyte  71  pulse  41 , having a width of a delta time (At)  73 , may be injected into reservoir  43  with valves  45  and  72  having positions, respectively, 1,2 or 1,3 (for a few milliseconds). The first through fifth steps may be repeated until reservoir  43  is filled. Sixth, the analyte from reservoir  43  may be measured with positions 1,1 of valves  45  and  72 , respectively. One may continue by returning to the first step. 
         [0033]    A PHASED chip may be used as a PC  42 , e.g., with its elements connected in series, as shown, to maximize the analyte concentration gain, or some elements in parallel if increasing the volume of the output pulse is also important. Alternatively, a small, heatable, stainless (or other material) tube coated or packed with Tenax™ on its internal walls of the PC  42 , may be used as a preconcentrator and modulator in  FIG. 6   a . The reservoir  43  may be fashioned as simple empty containers of volume commensurate with the dead-volume of the sensor  44 . But the containers may also feature some loose packing in a long tube that would enable the volume of the repeatedly injected analyte pulses  41  to gradually progress from an inlet  74  towards an outlet  75  in the manner of a so-called “plug-flow”, and thus reduce mixing of the injection-pulse analytes with the main carrier fluid and/or require less of a vacuum at the start of the process. In addition, another approach is that the second valve  72  (between the reservoir  43  and the sensor  44 ) may have an opening to the ambient or sample fluid, so that the fluid may be sampled by the sensor  44  directly, without the need for pre-concentration, in a situation where the analyte  71  concentrations are much higher than needed for a minimum detection limit (MDL). 
         [0034]      FIG. 6   b  shows another version of the sensor system  70  with an input sample  71  of about 10 mm 3 /sec to the modulator  42  which is connected to reservoir  43  as in  FIG. 6   a .  FIG. 6   b  shows reservoir  43  having a long tubular shape to minimize mixing of new analyte pulses with previous pulses  41 , while still facilitating an increase of sensitivity of the detector or sensor  44 , due to the increased concentration of analyte from the modulator  42 . In other words, the reservoir  43  may have the shape of a long and narrow tubing to minimize mixing of new gas with old gas. 
         [0035]      FIG. 7   a  is a diagram of an apparatus  70  having one valve and indicating how analyte pulses  41  desorbed by an adsorber  42  (e.g., PHASED) are led towards the reservoir  43  and sensor  44  by briefly switching the valve  45  from the normal valve position of 3-1 to position 3-2 and back, to have only the peaks flow through the flexible-volume reservoir  43 , when they pass that valve  45 . The total flow of 0.6 cm 3 /min being “on” all the time may be effected by pump  46  whether through the reservoir  43  and sensor  44 , or bypass line  47 . 
         [0036]      FIG. 7   b  is a diagram of a valve-less approach of a sensor system  21  in which the reservoir  43  and valve  45  have been replaced by a rapidly heatable reservoir  48 , which pulls each pre-concentrated Δt-peak  41  into a “high concentration path” by way of suitably synchronized slow heating and rapid cooling periods. An output of reservoir  48  may provide about 0.9 mm 3 /sec concentration flow through line  77  to the paper tape sensor system  10 . Bypassing input  74  of reservoir  48  may be a low concentration 9 mm3/sec flow through line  49  to pump  46  via a restriction  78 . The restriction  78  in the low-concentration bypass adjusts the flow, so that (in this example) the high-concentration flow in line  77  may be about 10 times smaller than the bypass flow in line  49 . 
         [0037]    During soaking and PC (pre-concentration) time, the reservoir  48  gas temperature may rise and expand (graph  79 ) to prevent low concentration gas from entering. As to volume (V) dynamics of reservoir  48 , a peak volume may be VΔt/10 and the reservoir volume may be VΔt. The reservoir  48  “suction” pump rate (during rapid gas cooling) may be minus 10 mm 3 /sec for a time of about 1 Δt and the “expansion” rate (slow heating) may be plus 1 mm 3 /sec for a time of about 10 Δt. 
         [0038]    It may be said that the valves can be absent in the system  21  of  FIG. 7   b  since, in lieu of valve  45  and reservoir  43  of  FIG. 7   a , there is a reservoir  48 , V, which is a heatable version with a similar long and narrow tube, which can be operated (by cooling and heating) to draw the modulator gas pulse  41  into the reservoir  48  when rapidly cooled, and slowly heated to expand the gas to match the sample flow rate to the pump  46 , and have a substantially zero flow rate input from the modulator or pre-concentrator  42  during the time when the modulator is in its adsorption period or mode. 
         [0039]    Again, during soaking and PC time, the gas temperature in volume, V (reservoir  48 ), may rise (graph  79 ) and expand to prevent low concentration gas to enter. When the analyte peak passes the “T”, the gas is allowed to rapidly cool and contract, thereby drawing or pulling the peak  41  into V  48 . The average flow rates may be 0.9 mm 3 /sec of high concentration gas in line  77  and 9 mm 3 /sec of low concentration gas in bypass line  49 , as indicated, and represent a PC gain of analyte concentration of ten times. The total flow of the sample  71  at the input of the pre-concentrator or modulator  42  may be approximately 0.6 cm 3 /min or 10 mm 3 /sec. 
         [0040]    To achieve such or similar concentration gains, the “duty cycle” (cold/hot time ratio) of the adsorber  42  needs to equal that gain, and be supported by analyte “breakthrough” times that are greater than the chosen “cold” adsorbing time. A low concentration bypass  49  may be between the input of volume  48  and the input of pump  46 . In the present example with a time ratio (which correlates with the concentration gain) of 10/1, the flow ratio bypass/high-concentration may also be at the value of 10/1, as indicated in  FIG. 7   b.    
         [0041]    In sum, the reservoir in  FIG. 7   a  is filled with concentrated analyte via a conventional valve  45  may switch the flow of the analyte peak  41 . The  FIG. 7   b  shows a way of accomplishing the same thing, i.e., directing the flow of the analyte peak  41 , but using thermal gas expansion pulses, as used with thermal micro-pumps. 
         [0042]    Aspects of the present system  21  with the sensor  10  may include splitting the flow from an adsorber device  42  into a “low-analyte” concentration or waste stream and an “enriched analyte” stream. The enriched stream may be channeled towards a sensor (EC or paper tape  10 ) in order to generate a stronger sensor signal, and to achieve a more rapid sensor response. The split flow may be used with an integrating sensor, such as the paper tape sensor system  10 . The size of the paper spot may be reduced so much (a reduction of about 42 times in the diameter, to about 0.1 to 0.3 mm) in that sufficient flow can be provided by a micro gas chromatography (GC) adsorber, such as PHASED  42 , and the concentration of analyte in the flow stream can be (2 to 10 times) more concentrated or enriched. 
         [0043]    One or two valves 3-way valves may be used. The second valve may be located upstream of the sensor  44  to enable exposing the sensor to “zero analyte” condition. The second valve is shown in  FIGS. 6   a  and  6   b  but not in  FIGS. 7   a  and  7   b . The 3-way valve  45  may be replaced with a heatable gas channel or volume  48 , which can control the gas temperature to rapidly cool and contract, thereby pulling the desorbed peak towards the sensor stream, and slowly expand to provide the flow towards the sensor  10  and prevent “low-analyte” gas to enter this stream. The adsorber film or packing material may be selected to favor one analyte over others and thus make the sensor more sensitive to that specific analyte. Control of the sample stream valve may be set in such a way that it either maximizes the sensitivity of the sensor  44  or  10 , or reduces its sensitivity (to prevent swamping) if the analyte concentration is too high. 
         [0044]    Advantages of the present analyzer over other chemical cassette analyzers may include faster and/or more sensitive (about 10 times) detection of analytes. This improvement of speed and/or sensitivity may be accomplished with an added selectivity feature (besides the one associated with the semi-specific chemistry of the paper tape) provided by the chosen nature of the adsorber (polar or non-polar; favoring small or large molecules . . . ) film/packing materials. Paper tape  11  consumption and cost may be reduced by about 40 times. Sample gas stream control may be provided that can either use one  45  or two conventional valves or a more reliable valve-less approach  48  to accomplish the sample gas stream splitting function. 
         [0045]    From the flow rates needed for a chemical cassette analyzer (180 cm 3 /min for 6 min to sense GeH4 at the needed concentration), 10 times that amount may be needed to pre-concentrate with a gain of 10 times. That could correspond to 1800 PHASED chips working in parallel at 1 cm 3 /min each, while drawing a 10 times higher mass flow. However, a reduction the paper spot area by 1800 times or the diameter by 42 times (i.e., a 150 micron diameter), a PHASED-pumped and 10 times-concentrated flow of 0.1 cm 3 /min over the smaller diameter, with the same mass flux as before, should increase the response by 10 times (i.e., shorter time or greater sensitivity). The sample velocity through the old conventional paper may be about 180/60 cm 3 /s/(π(0.25*2.54)̂2/4)=9.5 cm/s. The velocity of the present paper  11  may be about 0.1/60 cm 3 /min/(π0.015̂2/4)=9.5 cm/s, i.e., can be pumped with the same pump. 
         [0046]    A test with the assembly  10  of  FIGS. 5   a  and  5   b , with its role as the “paper tape sensor” in  FIGS. 7   a  and  7   b , may be conducted with a sample of about 75 ppm of ammonia in air, which can result in measurable decay of scattered light intensity, as predicted. The light may be from a He—Ne laser. 
         [0047]      FIG. 8  and graph  51  shows some elements of the reduction to practice of the present system, such as an ability to generate analyte concentration pulses  52  of amplitude greater than the concentration in the sample gas, for undecane as analyte. Graph  53  of  FIG. 9  shows results with ammonia (=analyte) adsorbed/desorbed in a heatable, short stainless steel capillary. 
         [0048]      FIG. 8  shows the graph  51  of an FID (spectrometer, flame ionization detection) signal in microamps versus time in seconds. Graph  51  reveals a generation of analyte concentration pulses or modulation  52 , using a 10 cm/100 μm/400 nm DB-5-coated capillary, and a 64 ppm undecane(=analyte)-in-air sample gas flowing at 129.4 cm/s, leading to a 56 sec breakthrough time. The heater on and off periods are indicated by lines  53 . The dashed lines mark the FID signal position for sample gas with the input analyte concentration of 64 ppm and with ˜0 ppm, right after desorption, for a time needed to readsorb analyte into the DB-5 coat. 
         [0049]      FIG. 9  shows a graph  53  of flow in sccm (cubic centimeters per minute at standard temperature and pressure (stp)), EC (electrochemical) sensor output in millivolts and capillary temperature in degrees C. versus time in minutes. Graph  53  reveals an adsorption and breakthrough of NH 3  in a 28.5 cm/0.53 mm ID (inside diameter) SS (stainless steel) capillary packed with Hayesep “P” μspheres. The measured breakthrough time  54  shown as 2.4 min between the start of NH 3  in flow  55  and EC output signal  56 . Curve  57  represents the flow and curve  58  represents the T capillary in degrees C. With the used flow of about 1.3 sccm and “flow-through” time of 0.019 min (assuming a conservative void fraction of as much as 40 percent), the breakthrough occurs only after 124 “sample gas changes.” The NH 3  concentration may be about 60 ppm, but its value may not necessarily influence the above breakthrough time. As intended, this breakthrough time appears larger than the 60 to 100 sec response time of an EC cell, and much larger than PHASED breakthrough times. 
         [0050]      FIG. 10  is a graph  61  of flow in sccm, output in millivolts and capillary temperature in degrees C. versus time in minutes. Graph  61  reveals the generation of analyte (NH3) concentration pulses or modulation, with a 28.5 cm/0.53 mm ID SS capillary packed with Hayesep “P” μspheres. Shown are three sensor output pulses  62 ,  63  and  64 . Pulse  62  reveals desorbed impurities in bottled air (to which the EC sensor is sensitive to), after sampling and soaking bottled air for only 45 seconds. Pulse  63  reveals desorbed NH 3 , after sampling and soaking dilute NH 3 -in-air for 45 seconds, and then switching back to air. Pulse  64  reveals desorbed NH 3 , after sampling and soaking dilute NH 3 -in-air for 90 seconds, and then switching back to air. These results appear to verify that such adsorber increases pulse amplitude with soak time, as expected. Air flow  65  was maintained at about 1.2 sccm. Also shown is column or capillary temperature 66 in degrees C. 
         [0051]    A further approach of an analyte micro-modulator may also be described herein. In  FIG. 11 , a portion of a fluid analyzer (i.e., PHASED) may be used for an analyte modulator  42  in conjunction with the sensor system  21  which can include a channel or channels for a flow of a sample along a membrane that supports heaters and a stationary phase for sample analysis. The channel or channels may be an integral part of the micro fluid analyzer. The analyzer may have the pre-concentrator (PC)  101  (i.e., like that of PC  42 ) and chromatographic separator (CS)  102  which incorporates the channel or channels.  FIG. 11  is a system view of an example fluid analyzer which may be a phased heater array structure for enhanced detection (PHASED) micro gas analyzer (MGA)  110 . It reveals certain details of the micro gas apparatus  110  which may encompass the specially designed channel described herein. The PHASED MGA  110 , and variants of it, may be used for various fluid chromatography applications. 
         [0052]    Sample stream  111  may enter input port  112  to the first leg of a differential thermal-conductivity detector (TCD) (or other device)  115 . A pump  116  may effect a flow of fluid  111  through the apparatus  110  via tube  117 , though pump  116  may be a thermal pump or be replaced by a thermal pump. There may be additional pumps, and various tube or plumbing arrangements or configurations for system  110  in  FIG. 11 . Fluid  111  may be moved through a TCD  115 , concentrator  101 , flow sensor  122 , separator  102  and TCD  118 . Controller  119  may manage the fluid flow, and the activities of concentrator  101  and separator  102 . Controller  119  may be connected to TCD  115 , concentrator  101 , flow sensor  122 , separator  102 , TCD  118 , and pump  116 . The pump  116  may be a thermal pump or be replaced with a thermal pump integrated in the concentrator  101  or separator  102 . Data from detectors  115  and  118 , and sensor  122  may be sent to controller  119 , which in turn may process the data. The term “fluid” used herein may refer to a gas or a liquid, or both. 
         [0053]      FIG. 12  is a schematic diagram of part of the sensor apparatus  110  representing a portion of concentrator  101  and/or separator  102  in  FIG. 11 . This part of sensor apparatus  110  may include a substrate or holder  124  and controller  119 . Controller  119  may or may not be incorporated into substrate  124 . Substrate  124  may have a number of thin film heater elements  125 ,  126 ,  127 , and  128  positioned thereon. While only four heater elements are shown, any number of heater elements may be provided, for instance, between two and one thousand, but typically in the 20-100 range. Heater elements  125 ,  126 ,  127 , and  128  may be fabricated of any suitable electrical conductor, stable metal, alloy film, or other material. Heater elements  125 ,  126 ,  127 , and  128  may be provided on a thin, low-thermal mass, low-in-plane thermal conduction, membrane or support member  124 , as shown in  FIGS. 12 and 13 . 
         [0054]    Substrate  130  may have a well-defined single-channel phased heater mechanism  131  having a channel  132  for receiving the sample fluid stream  111 , as shown in  FIG. 13 . The channels may be fabricated by selectively etching silicon channel wafer substrate  130  near support member  124 . The channel may include an entry port  133  and an exhaust port  134 . 
         [0055]    The sensor apparatus  110  may also include a number of interactive elements inside channel  132  so that they are exposed to the streaming sample fluid  111 . Each of the interactive elements may be positioned adjacent, i.e., for closest possible contact, to a corresponding heater element. For example, in  FIG. 13 , interactive elements  135 ,  136 ,  137 , and  138  may be provided on a surface of support member  124  in channel  132 , and be adjacent to heater elements  125 ,  126 ,  127 , and  128 , respectively. There may be other channels with additional interactive film elements which are not shown in the present illustrative example. The interactive elements may be formed from any number of films commonly used in liquid or gas chromatography. Furthermore, the above interactive substances may be modified by suitable dopants to achieve varying degrees of polarity and/or hydrophobicity, to achieve optimal adsorption and/or separation of targeted analytes. 
         [0056]    Controller  119  may be electrically connected to each of the heater elements  125 ,  126 ,  127 ,  128 , and detectors  115  and  118  as shown in  FIG. 12 . Controller  119  may energize heater elements  125 ,  126 ,  127  and  128  in a time phased sequence (see bottom of  FIG. 14 ) such that each of the corresponding interactive elements  135 ,  136 ,  137 , and  138  become heated and desorb selected constituents into a streaming sample fluid  111  at about the time when an upstream concentration pulse, produced by one or more upstream interactive elements, reaches the interactive element. Any number of interactive elements may be used to achieve the desired concentration of constituent gases in the concentration pulse. The resulting concentration pulse may be provided to detector  118 , for detection and analysis. 
         [0057]      FIG. 14  is a graph showing illustrative relative heater temperatures, along with corresponding analyte concentration pulses produced at each heater element. As indicated above, controller  119  may energize heater elements  125 ,  126 ,  127  and  128  in a time phased sequence with voltage signals  150 . Time phased heater relative temperatures for heater elements  125 ,  126 ,  127 , and  128  may be shown by temperature profiles or lines  151 ,  152 ,  153 , and  154 , respectively. 
         [0058]    In the example shown, controller  119  ( FIG. 12 ) may first energize first heater element  125  to increase its temperature as shown at line  151  of  FIG. 14 . Since first heater element  125  is thermally coupled to first interactive element  135  (FIG.  13 ), the first interactive element desorbs selected constituents into the streaming sample fluid  111  to produce a first concentration pulse  161  ( FIG. 14 ) at the heater element  125 , if no other heater elements were to be pulsed. The streaming sample fluid  111  carries the first concentration pulse  161  downstream toward second heater element  126 , as shown by arrow  162 . 
         [0059]    Controller  119  may next energize second heater element  126  to increase its temperature as shown at line  152 , starting at or before the energy pulse on element  125  has been stopped. Since second heater element  126  is thermally coupled to second interactive element  136 , the second interactive element also desorbs selected constituents into streaming sample fluid  111  to produce a second concentration pulse. Controller  119  may energize second heater element  126  such that the second concentration pulse substantially overlaps first concentration pulse  161  to produce a higher concentration pulse  163 , as shown in  FIG. 14 . The streaming sample fluid  111  may carry the larger concentration pulse  163  downstream toward third heater element  127 , as shown by arrow  164 . 
         [0060]    Controller  119  may then energize third heater element  127  to increase its temperature as shown at line  153  in  FIG. 14 . Since third heater element  127  is thermally coupled to third interactive element  137 , third interactive element  137  may desorb selected constituents into the streaming sample fluid to produce a third concentration pulse. Controller  119  may energize third heater element  127  such that the third concentration pulse substantially overlaps larger concentration pulse  163  provided by first and second heater elements  125  and  126  to produce an even larger concentration pulse  165 . The streaming sample fluid  111  carries this larger concentration pulse  165  downstream toward an “Nth” heater element  128 , as shown by arrow  166 . 
         [0061]    Controller  119  may then energize “N-th” heater element  128  to increase its temperature as shown at line  154 . Since “N-th” heater element  128  is thermally coupled to an “N-th” interactive element  138 , “N-th” interactive element  138  may desorb selected constituents into streaming sample fluid  111  to produce an “N-th” concentration pulse. Controller  119  may energize “N-th” heater element  128  such that the “N-th” concentration pulse substantially overlaps larger concentration pulse  165  provided by the previous N- 1  interactive elements. The streaming sample fluid may carry the resultant “N-th” concentration pulse  167  to either a separator  102  or a detector  118 . 
         [0062]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0063]    Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.