Instrument for measuring non-methane organic gases in gas samples

Abstract: An analytical system for measuring the concentration of non-methane organic gases within a test sample including methane and non-methane component groups. In one version, a dual column analysis system utilizes a metal column and a porous layer open tubular (PLOT column to separate methane and non-methane organic gases (NMOG). The metal column captures non-methane compounds which are more easily thermally trapped on the metal column, generally higher molecular weight compounds and polar molecule, which prevents these compounds from contaminating the PLOT column. In another version, the system incorporates a single trap in the form of a porous layer open tubular (PLOT) column which the sample mixture is directed through and which traps the NMOG group through adsorption. The methane group passes through the trap and is vented to atmosphere or evaluated using a detector. After trapping of the NMOG group, the flow direction through the column is reversed and the column temperature is increased to desorb the NMOG group which is evaluated using a detector such as a flame ionization detector (FID).

Description: This invention relates to an organic compound analytical instrument, and in particular, to one capable of providing a measurement of the concentration of non-methane organic gases (NMOG) in samples containing methane such as internal combustion engine exhaust gases. Those concerned with environmental emissions from sources such as internal combustion engines are often interested in quantifying the total concentration of certain compounds within the exhaust gas. In some evaluations, rather than requiring speciation of the mixture, the total concentration of NMOG emissions as a lumped parameter is desired. The distinction between methane and NMOG relates to differences in environmental impact attributed to these different groups of gases. Various techniques are currently used for determining NMOG concentrations. One approach obtains the value of NMOG as a difference in the measurements of total hydrocarbons and methane using a flame ionization detector (FID). Several problems are associated with the current test methods. As methane can be a significant proportion of exhaust composition, small errors in the measurement of either methane or total hydrocarbon levels result in large errors in the estimation of NMOG levels. In fact, it is not uncommon for this evaluation technique to result in yields of negative NMOG emissions. In addition, the current method requires large volumes of dilution air to be mixed with the exhaust gas, and samples are stored in so-called "Tedlar" sample bags before analysis. The purpose of dilution air is to prevent significant water condensation on the walls of the Tedlar bags. The use of Tedlar bags is problematic with certain compounds found in exhaust gas, and it has been found that the dilution air can have levels of NMOG exceeding that found in the raw gas under certain circumstances. The use of Tedlar bags further raises concerns with the test reliability, reproducability and stability, and provides a media for adsorption and interactions of certain compounds. Particularly in the case of oxygenated organic compounds, reactivity with the walls of the Tedlar bags is a known problem. Moreover, current processes are very time consuming to carry out, which is a particular disadvantage in engine development applications. The accuracy limitations of current procedures for NMOG determination are especially of concern in view of increasingly stringent vehicle emission requirements. Legislation by the Federal Government (Federal Clean Air Act) and the California Air Research Board (CARB) have defined further limitations on vehicle emissions to improve air quality. These new mandates require that vehicles sold must be designed to meet stringent emissions standards which are a fraction of the presently accepted levels. In addition to evaluating regulatory compliance, instruments for NMOG determination can be used by automotive manufacturers while developing their products. Other evaluation procedures have been proposed and considered for methane and NMOG measurement using a trap in which NMOG components are collected and later desorbed for evaluation using and FID. In one device, a packed column for adsorbing NMOG components is used to separate out the methane, and thereafter, the trapped NMOG is desorbed. Traps based on adsorption, however, have the disadvantage of having a long desorption time which lengthens measurement time and limits accuracy due to the difficulty in integrating the output. JP-A-6 094 698 (which is related to US-A-5,392,634) discloses a hydrocarbon analyser in accordance with the pre-characterising portion of claim 1 and which uses two absorption columns, one for trapping non-methane organic gases for desorption and measurement by one FID, and another for trapping remaining gases, such as methane and oxygen, for desorption and measurement in a second FID. The desorption and measurement phases are carried out in parallel on both columns. EP-A2-0,590,932 discloses a hydrocarbon analyser in which two porous layer open tubular (PLOT) columns are arranged in series, the first of which is temperature controlled to control the timing of desorption. The first column is used to cryofocus the desired analytes, which are then released to the second column, and then to a single detector (FID). According to the present invention there is provided an analysis system for the measurement of a concentration of a gaseous sample including a non-methane organic gases group and a methane gases group including methane, comprising: a first column which selectively thermally traps the non-methane organic gases group and passes the remainder of the sample gas including the methane gases group; first detector means operatively connected to said first column for measuring the concentration of the non-methane organic gases group after it is desorbed from said first column; a second column arranged downstream of said first column for receiving the remainder of the sample gas; second detector means operatively connected to said second column for measuring a concentration of the methane gases group passed through said second column; first fluid circuit means for causing said gaseous sample to flow through said first column in a first direction; and second fluid circuit means for causing a remaining portion of said gaseous sample not trapped by said first column including the methane gases group to flow through said second column in said first direction; characterised in that: the first column is a metal column which, when at a trapping temperature, selectively thermally traps a first portion of the non-methane organic gases group and passes the remainder of the sample gas including the methane gases group and the remaining non-methane organic gases group, and at an elevated desorption temperature above said trapping temperature, causes the trapped portion of the non-methane organic gases group to be desorbed, whereby the first detector means is operative to measure the concentration of the first portion of the non-methane organic gases group after it is desorbed from the metal column; the second column is a porous layer open tubular column which, when at a trapping temperature, allows the methane gases group to pass while adsorbing the remaining portion of the non-methane organic gases group, and at an elevated desorption temperature above said trapping temperature, causes said remaining portion of the non-methane organic gases group to be desorbed; temperature control means are provided for selectively causing said metal column to be at said trapping temperature, or at said desorption temperature, said temperature control means including a heater means for effecting vaporization and desorption of said adsorbed components, said temperature control means further provided for causing said porous layer open tubular column to be at said trapping temperature, or at said desorption temperature, said temperature control means including a heater means for effecting rapid vaporization and desorption of the remaining portion of the non-methane organic gases group; the second detector means is operative to measure the concentration of non-methane organic gases group desorbed from said porous layer open tubular column at said desorption temperature; the first fluid circuit means is operative to cause said gaseous sample to flow through said metal column in said first direction while said metal column is at said trapping temperature and thereafter to cause the desorbed non-methane organic gases group to flow in a second opposite direction through said metal column when said metal column is at said elevated desorption temperature, and the second fluid circuit means is operative to cause the remaining portion of said gaseous sample not trapped by said metal column including the methane gases group and a remaining portion of the non-methane gases group to flow through said porous layer open tubular column in said first direction when said porous layer open tubular column is at said trapping temperature causing the remaining portion of the non-methane gases group to be adsorbed, and thereafter causing the desorbed remaining portion of the non-methane organic gases group to flow in the first direction through said porous layer open tubular column when at said elevated desorption temperature. Thus the present invention can provide a fast and accurate measurement of NMOG concentrations, within several seconds rather than tens of minutes as in the case of prior art devices, and without the need for sample collection bags and large volumes of dilution air. The metal column traps generally higher molecular weight material which are readily thermally trapped, and the PLOT column passes methane gases while trapping the remaining non-methane gases. As a result, water and higher boiling point molecules are trapped and prevented from contaminating the PLOT column which extends its life and reduces trapping cycle time. Both columns trap and release their respective gases in response to regulation of their temperatures. The metal column uses thermal cryofocusing to thermally trap and desorb gases, whereas the PLOT column thermally and chemically adsorbs and desorbs gases. By forward flushing the PLOT column into a detector while at a trapping temperature, the methane gas group which passes through can be evaluated using the detector, and the trapped non-methane gases adsorbed in the PLOT column can be desorbed and forward flushed from the column by increasing the column temperature. As a result, the detector produces a pair of humps, one from the methane gas group which is directly passed and the other from the adsorbed/desorbed component of the non-methane gas group. Likewise, the metal column is backflushed with a carrier gas while the column is thermally heated which desorbs the trapped component of the non-methane gas group which is then carried to a respective detector where it is evaluated. By separating the pair of "humps" measured from the PLOT column, the output of the first produced hump formed by directly passed methane gases can be integrated to quantify the methane gases passed through the PLOT column. Likewise, by integrating the non-methane gas group trapped in the metal column, and adding it to the remaining integrated output of non-methane gases trapped in the PLOT column, namely the second hump, a quantitative evaluation of the concentration of NMOG components is provided. The invention will be further described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a schematic illustration of an analysis instrument in accordance with a preferred embodiment of this invention; Figure 2 is a representative chromatogram from a detector providing a partial measurement of NMOG concentration which is trapped in a metal trap using the instrument of Figure 1; and Figure 3 is a representative chromatogram from a detector providing a measurement of methane concentration and remaining partial measurement of NMOG concentration which is trapped in a PLOT trap using the instrument of Figure 1. An analysis system in accordance with an embodiment of this invention is shown schematically in Figure 1 and is further designated by reference numeral 10. In Figure 1, solid lines interconnecting pairs of system elements indicate fluid flow conduits. Dual column analysis system 10 separates and measures concentrations of a non-methane organic gases group and a methane gases group from a gas sample utilizing a dual column trap technique. The system 10 includes a first branch 12 of fluid flow elements, generally shown on the left-hand side of Figure 1, with a second branch 16 at the right-hand side of Figure 1. A sample source 14 is included in first branch 12 where it is connected in conduit flow such that a sample is introduced into the conduit for evaluation. Typically, the sample source is an internal combustion engine such that an exhaust outlet on the engine is interconnected to first branch 12. Sample source 14 is connected to a fluid restrictor 18 which is provided to produce flow restriction through the system which adjusts fluid flow rates between various branches therethrough. A carrier gas source 20 supplying a gas such as hydrogen is connected at a first location between restrictor 18 and sample gas storage loop 22 at a tee connector 24 through an on/off valve 26, and a second location between the first and second branches 12 and 16 at a tee connector 28 through an on/off valve 30. A metal trap 32 is connected to an end of first branch 12 opposite the sample source 14. Likewise, a PLOT trap 34 is provided at one end of second branch 16 such that first and second branches 12 and 16 are joined together at tee connector 28 by joining the metal trap 32 to the plot trap 34. A detector which can be constructed in various forms but preferably is a flame ionization detector (FID) 36 is connected to first branch 12 by tee connector 40 on an opposite side of metal trap 32 from tee connector 28. A vacuum source 46 is connected to first branch 12 with an on/off valve 48 through a tee connector 50 which is provided between the sample loop 22 and tee connector 40. Furthermore, a second detector 42 which is preferably a flame ionization detector (FID) is connected to second branch 16 at an opposite end of the branch from tee connector 28 such that FID 42 is connected to PLOT trap 34 through a fluid restrictor 44. Carrier gas source 20 provides a source of hydrogen (or other) carrier gas contained in a pressurized vessel 52 whose delivery pressure is monitored and regulated by a pressure meter and delivery valve 54 either to first branch 12 through tee connector 24 when valve 26 is open, or to both the first and second branches 12 and 16 at tee connector 28 when valve 30 is open. Valves 26 and 30 are selectively opened and closed to supply a carrier gas for moving a gas sample through the fluid flow elements of the system 10. Before applying the carrier gas, a gas sample is first delivered to sample loop 22 by applying a vacuum source 46 through valve 48 while valves 26, 30 and 38 are preferably closed. Then the carrier gas is selectively applied by sequentially activating such valves which moves the gas sample through the first and second branches of system 10 for analysis. Further details of the sequential application of carrier gas source 20 and vacuum 46 will be provided below. Metal trap 32 is formed from an elongated tubular column 56 which is preferably formed from stainless steel which selectively thermally traps a portion of non-methane organic gases group (NMOG), as well as water and water vapor, while permitting the remaining portion of non-methane gases, methane, and a group of so-called permanent gases (nitrogen, oxygen, carbon dioxide) to pass through the column into the PLOT trap 34. The temperature of the metal column is regulated to effect thermal cryofocusing while at a low temperature, and to desorb the cryofocused gases at a subsequently elevated temperature. Column 56 is connected to an electric heater circuit 60, preferably a capacitive discharge heater circuit, to form a heater tube which functions to controllably regulate the temperature of metal column 56 in order to selectively thermally trap and release selective non-methane organic gases and water, as will be described in more detail. The outlet end of column 56 is connected to second branch 16 by tee connector 28. By thermally regulating the temperature of metal column 56, certain non-methane organic gases are selectively thermally trapped in the column and remaining gases are passed therethrough into PLOT trap 34. Trap 34 is formed from an elongated column of the porous layer open tubular (PLOT) type. PLOT column 62 has an inside coating of a stationary phase material such as aluminum oxide (AlO) which adsorbs a group of gases referred to as NMOG, while permitting a second group of gases including methane and so-called permanent gases (nitrogen, oxygen, carbon dioxide) to pass through the column. Other PLOT column configurations and stationary phases could also be used, including the following commercially available products: PoraPLOT Q™, PoraPLOT U™, and CarboPLOT™ columns. PLOT column 62 is surrounded by a heater tube 58 which is connected to an electric heater circuit 66, which is also preferably a capacitive discharge heater circuit, which functions to regulate temperature of column 62 such that the column temperature is rapidly decreased to absorb NMOG and increased to desorb NMOG, as will be described in more detail. First end of PLOT column 62 receives gases through tee connector 28 whereas second end of column 62 is connected through a second flame ionization detector (FID) 42 through a fluid restrictor 44. Restrictor 44 serves to control fluid flow rates through PLOT column 62 and into FID 42. Carrier gas source 20 is connected between the metal column 56 and PLOT column 62 at tee connector 28 through on/off valve 30. An example of a dual column analysis system 10 would preferably employ the following specific components and parameters for the analysis of internal combustion engine exhaust gases: ELEMENT NUMBER ELEMENT NAME SPECIFICATION/PARAMETER 18 and 44 Restrictor 0.1mm fused silica glass capillary tubing, 30cm long 20 Carrier Gas Source Hydrogen 26, 30, 38, 48 Valves Low dead-volume On/off solenoid controlled valves of the type commonly used in gas chromatography instruments 56 Metal Column Stainless Steel Tubing 62 PLOT Column 15cm long fuse silica glass capillary, 0.32mm ID with Al0 stationary phase coating 58 Heater Tube Stainless Steel Tubing 60, 66 Heater Circuit Capacitive-Discharge circuit as described in U.S. Patent No. 5,096,471, herein incorporated by reference In operation, a dual column analysis system 10 of this invention will operate in accordance with it's depiction as shown in Figure 1 and described as follows. At the beginning of an analysis procedure, exhaust gas or some other type of gas sample is delivered for evaluation from sample source 14 into sample loop 22 by opening valve 48 while valves 26, 30 and 38 are closed. As a result, a vacuum is applied from vacuum source 46 through tee connector 50 such that a gas sample is pulled through restrictor 18 where it is delivered and stored in sample loop 22. Once the gas sample is received in loop 22, valve 48 is closed which retains the gas sample in the loop. Consequently, valve 26 is opened such that carrier gas source 20 drives the gas sample into and through metal column 32 while it is thermally held at a desirable "trapping" temperature such that higher boiling point molecules namely a group of non-methane organic gases and water, are thermally trapped on the metal column where they are retained, and the remaining methane gases group, and carrier gases are passed into PLOT column 62 where the remaining non-methane organic gases are adsorbed while the PLOT column is likewise retained at a temperature for effecting chemical adsorption of the non-methane in a PLOT column. As a result, the carrier gas delivers the gas sample through metal column 56 where a portion of the non-methane organic gases are retained, and the remaining gases are passed through PLOT column 62 where the remaining portions of non-methane organic gases are also adsorbed, and finally, gases of the methane group are passed therethrough such that they flow through restrictor 44 into FID 42 where their presence is detected and their quantity is measured. The temperature of metal column 56 is set to allow a methane group of gases and portion of the non-methane organic gases to pass through the column when thermally regulated at a trapping temperature. This group of gases will generally have smaller molecular weight, and will typically be harder to thermally cryofocus, or trap, in the metal column. As a result, the methane group of gases and the non-methane organic gases which are not trapped in metal column 56 pass through the metal column into PLOT column 62. The remaining, generally higher molecular weight, NMOG will be thermally trapped in metal column 56. As the carrier gases drive the gas sample through the metal column and into PLOT column 62, the remaining non-methane organic gases are adsorbed in the PLOT column. Accordingly, metal column 56 acts as a pre-separation column which thermally traps water, water vapor, and non-methane groups of gases which are more easily thermally trapped in the metal column. These trapped products are usually highly polar and typically comprise molecular chains of higher molecular weight which might otherwise contaminate and clog the PLOT column. By trapping these products in the metal column, it is easier to clean the PLOT column subsequent to extended use, and the life of the PLOT column is extended. In order to provide adequate pre-separation, the temperature of column 56 is preferably held at a desirable "trapping" temperature which is within a predetermined range, and which is believed to extend from ambient temperatures (e.g. 20°C) to sub-ambient temperatures down to -100°C and perhaps lower, depending on the particular configuration of system 10 and especially column 56. Where an ambient trapping temperature is used, the trapping temperature can be provided by exposing column 56 to ambient air. Where cooler trapping temperatures are needed, in order to trap a desired range of non-methane gases, a bath of cool water or a cold gas (e.g. nitrogen) can be used to cool column 56. Once the methane gas group and the remaining non-methane organic gas group which was not thermally trapped in the metal column 56 has passed through the column beyond tee connector 28, it is delivered into PLOT column 62 such that the PLOT column is held at a desirable adsorption temperature which adsorbs the remaining non-methane organic gases in the column. The methane gases group passes through the PLOT column through restrictor 44 and into FID 42 where their presence and concentration are measured and quantified. Once the methane gas group and remaining non-methane gases have passed tee connector 28, valve 30 is opened such that carrier gas source 20 is applied to tee connector 28. Valve 30 is opened in conjunction with the thermal modulation of both the metal column 56 and PLOT column 62 through respective heater circuits 60 and 66 which act on metal column 56 and heater tube 58, respectively. After operation, the tube forming column 56 and tube 58 are brought to an elevated temperature to desorb trapped gases in each respective column such that delivery of carrier gases at tee connector 28 delivers the desorbed gases in two directions through FID's 36 and 42, respectively. Upon opening valve 30, valve 38 is also opened while valves 48 and 26 remain closed. Restrictor 44 provides for a balanced split flow of carrier gases from the connector 28 into the metal column 56 and the PLOT column 62 such that thermally released gases are carried through valve 38 into FID 36 where the released NMOG concentration and quantity is measured. Likewise, carrier gases collect and deliver desorbed gases from PLOT column 62 through restrictor 44 and into FID 42 where corresponding gas concentration is measured. Dual trap analysis system 10 provides a significant improvement in that metal column 56 is preferably tailored by adjusting column lengths and temperatures to thermally trap the heaviest components of the gas sample, typically those having molecular chains with five carbons or more, and the lighter components, typically those having molecular chains with four or less carbons, travel through the metal column to the PLOT column where the remaining non-methane gas group is chemically adsorbed through thermal regulation. Furthermore, an improvement is provided by supplying carrier gas at tee connector 28 such that only metal column 56 is subject to backflush of gases during the thermal release phase. As a result, gases trapped in metal column 56 are analyzed on FID 36, while gases adsorbed and gases passed through PLOT column 62 are measured or integrated on FID 42. Since PLOT column 62 is not backflushed in this procedure, flow through the PLOT column does not change, which provides a benefit of more consistent and enhanced chemical adsorption/desorption in response to thermal regulation. Furthermore, durability of the PLOT column 62 is improved since backflushing can seriously affect the life and durability of a PLOT column. Furthermore, metal column 56 traps the generally higher molecular weight carbon chain compounds of non-methane gas, i.e., those that are more easily thermally trapped in the metal column 56, such that they do not enter PLOT column 62 which makes clean-up of the PLOT column easier. Water is also prevented from entering PLOT column 62 as it is thermally trapped in the metal column 56. Additionally, use of the two column system allows for application of carrier gases through tee connector 28 in order to backflush of metal column 56 even before separation is completed in PLOT column 62. As a result, this system provides further advantages in speed when separating gases. Once the methane gas group and the remaining non-methane gas group have passed through metal column 56 into PLOT column 34, carrier gas is supplied from source 20 to the tee connector 28 by opening valve 30, while valve 26 and 48 are closed, and valve 38 is opened. This action produces a split flow of carrier gas at tee connector 28 in which a fraction of the carrier gas backflushes through metal column 56 and a remaining portion continues to flow forward through PLOT column 62 through restrictor 44 and into FID 42 where its presence is detected and a quantitative measurement is provided. Figure 2 provides a representative output from FID 36 where the area under the curve can be integrated to obtain a measure of the concentration of the first part of the non-methane organic gas group trapped by metal column 56. Such gas group is backflushed through the metal column 56 where it is measured by FID 36. The balance of carrier gas received from carrier source 20 flows forward through PLOT column 62 while the PLOT column is held at a desirable thermally regulated desorption temperature such that a chemical desorption releases previously adsorbed non-methane gases from the PLOT column which are now carried through restrictor 44 and which are delivered through FID 42 where their presence is detected and a quantitative measurement is provided. Figure 3 provides a representative output from FID 42 which comprises a pair of humps. The first hump results from methane which was directly passed through PLOT column 62 and the second hump represents non-methane organic gases which were adsorbed and desorbed in the PLOT column which delayed their being directly delivered to FID 42. By integrating the area under each hump, a measure of the concentration of the methane gases passed through PLOT column 62 can be obtained by measuring the area under the first hump, and the remaining measure of concentration of the non-methane gas group can be further obtained by measuring the area under the second hump. By adding the area of the hump obtained from FID 36 as shown in Figure 2, with the area of the second hump in Figure 3, the total amount of non-methane organic gases (NMOG) can be quantified and obtained. Simultaneous with opening of valve 30, both heater circuits 60 and 66 are activated, causing the temperature of the tube forming column 56 and heater tube 58 to increase rapidly which subsequently increases the temperatures of metal column 56 and PLOT column 62 which causes the previously trapped and adsorbed gas in each column to be thermally released and desorbed, respectively, where they are subsequently both picked up by the carrier gas and delivered to FID 36 and FID 42, respectively. By opening valve 38, the portion of the NMOG components which are released from metal column 56 pass through FID 36 where they are detected and quantified by integrating their resulting output as depicted in Figure 2. Figure 2 provides a representative output of the desorbed component of NMOG group measured by FID 36. The flow of carrier gases backward through metal column 56 also provides a backflushing which clears the column for subsequent sample evaluation. The forward flow of carrier gas through PLOT column 62 flushes desorbed remaining non-methane organic gases from the PLOT column which carries them through restrictor 44 through FID 42 for analysis and quantitative measurement. After methane and non-methane gases have been integrated at FID's 36 and 42, valves 26, 30, 38 and 48 are closed, which prepares the system 10 for receiving a new gas sample which is introduced from sample source 14 by opening valve 48. It is to be understood that further variations of the preceding preferred embodiment will provide a device which functions essentially the same but with slightly modified structure. For example, FID 36 can be eliminated and tee connector 40 can be ported through valve 38 with a line which connects between PLOT trap 34 and fluid restrictor 44 such that valve 38 is opened during backflush of the metal trap 32 where the desorbed component of non-methane gases are analyzed with FID 42. Typically, such a modification would produce an output from FID 42 with three separate humps such that the first hump quantifies the component of methane gases present in a gas sample, and the remaining pair of humps quantify the component of non-methane gases present. In operation, it is preferable to provide a carrier gas velocity which is at least 100cm per/sec., a PLOT column and metal column having a combined maximum length of 30cm, and a heating rate up to 100,000°C/sec. Furthermore, it is desirable to produce a FID signal output with humps having a base width, or base bandwidth, with a maximum of 10 milliseconds. Such a pulse requires rapid desorption from the PLOT column which can only be produced by rapidly thermally decreasing the temperature of a column. A wider pulse tends to be more difficult to integrate, especially with small sample sizes detected by the FID such that overlap may exist between the methane and non-methane components of gas as detected by the FID. Alternatively, tee connector 28 can be formed within the PLOT column 34 along the PLOT column 62 as shown by tee connector 28' which is connected to valve 30 by a dash line indicating an alternative fluid flow element. Such an alternative arrangement for the tee connector 28' allows for backflushing of at least a portion of the PLOT column, and where tee connector 28' is provided downstream of the PLOT column, for complete backflushing of the PLOT column. In this case, the metal column 32 generally traps components which might contaminate the PLOT column 34, yet still provides for at least partial backflushing of the PLOT column in order to clean those contaminants not trapped in the metal column 32. As alternatively depicted in FIG. 1, tee connector 28' is positioned a distance A downstream of the inlet to the PLOT column 34, and a distance B from the downstream end of the PLOT column 34.

Claims: An analysis system (10) for the measurement of a concentration of a gaseous sample including a non-methane organic gases group and a methane gases group including methane, comprising: a first column (56) which selectively thermally traps the non-methane organic gases group and passes the remainder of the sample gas including the methane gases group; first detector means (36) operatively connected to said first column (56) for measuring the concentration of the non-methane organic gases group after it is desorbed from said first column (56); a second column (62) arranged downstream of said first column (56) for receiving the remainder of the sample gas; second detector means (42) operatively connected to said second column (62) for measuring a concentration of the methane gases group passed through said second column (62); first fluid circuit means (18, 20, 24, 26) for causing said gaseous sample to flow through said first column (56) in a first direction; and second fluid circuit means (20, 28) for causing a remaining portion of said gaseous sample not trapped by said first column (56) including the methane gases group to flow through said second column (62) in said first direction; characterised in that: the first column (56) is a metal column which, when at a trapping temperature, selectively thermally traps a first portion of the non-methane organic gases group and passes the remainder of the sample gas including the methane gases group and the remaining non-methane organic gases group, and at an elevated desorption temperature above said trapping temperature, causes the trapped portion of the non-methane organic gases group to be desorbed, whereby the first detector means (36) is operative to measure the concentration of the first portion of the non-methane organic gases group after it is desorbed from the metal column (56); the second column (62) is a porous layer open tubular column which, when at a trapping temperature, allows the methane gases group to pass while adsorbing the remaining portion of the non-methane organic gases group, and at an elevated desorption temperature above said trapping temperature, causes said remaining portion of the non-methane organic gases group to be desorbed; temperature control means (58, 60, 66) are provided for selectively causing said metal column (56) to be at said trapping temperature, or at said desorption temperature, said temperature control means (58, 60, 66) including a heater means (60) for effecting vaporization and desorption of said adsorbed components, said temperature control means (58, 60, 66) further provided for causing said porous layer open tubular column (62) to be at said trapping temperature, or at said desorption temperature, said temperature control means (58, 60, 66) including a heater means (66) for effecting rapid vaporization and desorption of the remaining portion of the non-methane organic gases group; the second detector means (42) is operative to measure the concentration of non-methane organic gases group desorbed from said porous layer open tubular column (62) at said desorption temperature; the first fluid circuit means (18, 20, 24, 26) is operative to cause said gaseous sample to flow through said metal column (56) in said first direction while said metal column (56) is at said trapping temperature and thereafter to cause the desorbed non-methane organic gases group to flow in a second opposite direction through said metal column (56) when said metal column (56) is at said elevated desorption temperature, and the second fluid circuit means (20, 28) is operative to cause the remaining portion of said gaseous sample not trapped by said metal column (56) including the methane gases group and a remaining portion of the non-methane gases group to flow through said porous layer open tubular column (62) in said first direction when said porous layer open tubular column is at said trapping temperature causing the remaining portion of the non-methane gases group to be adsorbed, and thereafter causing the desorbed remaining portion of the non-methane organic gases group to flow in the first direction through said porous layer open tubular column (62) when at said elevated desorption temperature. An analysis system according to claim 1 further comprising: first valve means (24) within said first fluid circuit means (18, 20, 24, 26) for causing the gaseous sample to pass into said metal column (56) from said first fluid circuit means (18, 20, 24, 26) toward said second fluid circuit means (20, 28) in the first flow direction when said metal column (56) is at said trapping temperature causing the first portion of the non-methane gases group to be trapped, and thereafter causing the desorbed first portion of the non-methane organic gases group to flow through said metal column (56) toward said first fluid circuit means (18, 20, 24, 26) in a second opposite direction when said metal column (56) is at said desorption temperature, causing the first portion of the non-methane organic gases group to pass through said first detector means (36) where said concentration is measured; and second valve means (28) within said second fluid circuit (20, 28) for causing the remaining portion of said gaseous sample not trapped by said metal column (56) to pass into said porous layer open tubular column (62) from said second fluid circuit means (20, 28) in a first flow direction when said porous layer open tubular column (62) is at said trapping temperature causing the remaining portion of the non-methane gases group to be adsorbed, and thereafter causing the desorbed remaining non-methane gases group to flow through said porous layer open tubular column (62) in said first direction toward said second detector means (42) when said porous layer open tubular column (62) is at said desorption temperature, causing the non-methane organic gases group to pass through said second detector means (42) where said concentration is measured; wherein the remaining portion of said gaseous sample not adsorbed by said porous layer open tubular column (62) including the methane gases group flows through said porous layer open tubular column (62) into said second detector means (42) prior to the desorption phase where it is measured. An analysis system according to claim 1 or 2 further comprising a vacuum source (46) in fluid communication with said first fluid circuit means (18, 20, 24, 26) and a sample loop (22) provided within said first fluid circuit means (18, 20, 24, 26), said sample loop (22) provided between said vacuum source (46) and said source of sample gas (14) wherein vacuum valve means (48) are further provided for opening said vacuum source (46) in fluid communication with said first fluid circuit means (18, 20, 24, 26) to draw a gaseous sample into said sample loop, wherein said valve means (48) are thereby closed upon delivery of the gaseous sample into said sample loop (22) for later displacement therefrom by a carrier gas therethrough. An analysis system according to claim 1, 2 or 3 wherein said first detector means (36) comprises a first flame ionization detector receiving the first portion of the non-methane organic gases group passing from said metal column (56) in said second direction. An analysis system according to claim 4 wherein said second detector means (42) comprises a second flame ionization detector receiving the methane organic gases group passed through the porous layer open tubular column (62), when at a trapping temperature, where its concentration is measured during a first period, and further receiving the remaining portion of the non-methane organic gases group desorbed from the porous layer open tubular column (62) during a second period. An analysis system according to any one of claims 1 to 5 wherein said temperature control means (58, 60, 66) includes an electrical resistance heater responsive to control commands for thermal regulating the temperature of said metal column (56) between a trapping and desorption temperature. An analysis system according to any one of claims 1 to 6 wherein said temperature control means (58, 60, 66) includes an electrical resistance heater (58) responsive to control commands for thermal regulating the temperature of said porous layer open tubular column (62) between an adsorption and desorption temperature. An analysis system according to any one of the preceding claims wherein said metal column (56) and said porous layer open tubular column (62) have a maximum combined length of 30 centimetres, and the remaining non-methane organic gases group desorbed from said porous layer open tubular column (62) are displaced therethrough in such first direction by a carrier gas having a minimum velocity of 100 centimetres per second.

Inventors: KLEMP MARK ALLEN, KLEMP, MARK ALLEN
Applicants: CHROMATOFAST INC, CHROMATOFAST
Application year: 1995
Main classification: G01N30
IPC codes: G01N30, G01N33