Improved pulsed discharge systems

Abstract: The discharge systems of this disclosure are useful in the chemical analysis field, including identification and quantification of gaseous impurities. The systems utilize a pair of electrodes which apply a spark across a gap between the electrodes, the spark preferably being repetitively formed. As an inert gas flows between the electrodes, the spark creates photons of energy which are emitted and are used as described. In alternate aspects, other particles are energized in the spark gap and subsequently surrender their energy. Photon emission or loss of energy assists in identification and measurement of peaks eluted from a typical gas chromatograph. The preferred inert gas is helium with or without traces of rare inert gases.

Description: BACKGROUND OF THE DISCLOSURE The discharge systems of this disclosure utilize a pair of electrodes which, in the preferred embodiment, apply a transverse spark across a gap between the electrodes, the spark preferably being repetitively formed. Bipolar or monopolar discharge can be used. An inert gas flows between the spark electrodes. The spark creates photons of energy which are emitted and are used as described. Particles are charged or energized in the spark gap and energized particles subsequently surrender energy. The inert gas is helium with traces of inert gases. The photon emission or loss of energy assists in identification and measurement of gas chromatographic column (GC hereinafter) eluted peaks from a typical GC source. Various types of discharge systems are known from a paper: Process control and quality, vol. 5, No. 2/3, December 1993, Elsevier, Amsterdam, NL, pages 193-204, XP000505400 W.E. Wentworth et al.: 'Pulsed-Discharge Helium Ionization/Electron Capture/Emission Detector of Chlorinated Compounds', from two patent documents WO 92 15874 A (Valco Instruments Company) EP-A-0 387 041 (Varian Associates), and from a paper: Analytical Chemistry, vol. 68, No. 7, April 1, 1996 pages 1233-1244 H. Cai et al: Characterization of the pulsed discharge electron capture detector. It is known from the Cai et al paper mentioned above to provide a detector to analyze a compound in a gaseous sample, comprising a closed chamber having a helium source, a flow inlet fitting body at one end of the chamber and an outlet fitting body at the other to enable helium to flow through the chamber from one end to the other, spark-forming electrodes which are spaced apart and means to provide said electrodes with a current forming a spark sufficient to arc thereacross, said spark-forming electrodes being positioned in said chamber to form a spark gap across helium flow through said chamber, means downstream in said chamber from said spark-forming electrodes to inject a gaseous flow of sample into the chamber, a bias electrode and a collector electrode in said chamber for collection of current formed as a result of the spark across the gap wherein the helium flows toward said bias and collector electrodes to enable a current to be formed indicative of the concentration of a particular sample compound in said chamber and the bias and collector electrodes are connected to a detector means to measure the concentration of the sample compound in said chamber by changing current flow. In the detector, dopant gas, mixed with helium, is supplied to the chamber, via a dopant input capillary fitted through the outlet fitting. STATEMENTS OF INVENTION The present invention is defined in claims 1 and 5. A preferred embodiment of the present invention will now be described by way of example and with reference to Figures 5 and 6. The systems described and shown in the other Figures are presented as background only. DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view through a spark operated system utilizing helium to test GC column peaks wherein an output signal is formed by ring shaped electrodes; Figure 2 is an alternate system incorporating three ring shaped electrodes with a bias voltage and further including a trace gas input; Figure 3 is an alternate structure utilizing a sample input downstream of facing electrodes and utilizing a set of spaced rings connected with selected voltages; Fig. 4 is a timing chart showing the timing sequence of coil charging circuitry for pulse formation; Fig. 5 illustrates a preferred embodiment of the present invention in which helium is mixed with rare inert gases; Fig. 6 graphs emission radiation and ionization potential; Fig. 7 shows several detector chambers provided with rare gases for analysis; Fig. 8 is an alternate system showing dopant added to the helium; Figs. 9A and 9B graph certain ratio measurements to determine sample identification; Fig. 10 is an alternate system showing a round chamber utilizing circular flow; Fig. 11 is an exploded view of the round chamber in Fig. 10 and electrodes in the chamber; Fig. 12 is a side view of the round chamber; and Fig. 13 shows an air analyzer. DETAILED DESCRIPTION In Fig. 1, a detector 10 uses helium from a helium source 12 regulated above atmospheric pressure flowing from right to left. A GC column 14 provides flow of solvent and eluted sample. GC column 14 connects to a sample injection tube 16 moved and clamped by an adjustment mechanism 18 to a desired location. The power supply 20 provides current for pulse forming circuit 22 . Inverter 24 forms alternating positive and negative pulses. Conductors 26 and 28 are input to a differential amplifier 30 connected to time based recorder 32. The detector 10 has an elongate cylindrical shell 34 around an elongate cylindrical sleeve 36 about passage 38. The passage 38 is between electrodes 40 and 42. The housing 34 supports fitting 44 connected with the helium source 12. Ring 48 seals the body 36. Transverse web member 50 has a central opening 52 aligned at cylindrical spacers 54, 56 and 58. Circular electrode 60 forms a full circle around passage 64. At the surface of the passage 64, an exposed metal ring 66 connects to the circular electrode 60. A second circular electrode 62 is wider than the electrode 66. Sample tube 16 is axially moved to the left or right to vary current at electrometer 30 . The sample tube 16 is inserted through the threaded detail 68 in the end fitting 70. The tube clamp and adjustment device 18 moves the sample tube 16 in and out to vary sensitivity and performance. The terminals 62 and 66 have an adjustable bias. Photon emission spectra through the passage 38 and 64 interact, and charged particles are either formed or neutralized depending on the sample material creatomh current flow at electrodes 62 and 66. Helium (slightly above atmospheric pressure) flows at about 20-120 milliliters per minute or between ten to thirty times larger than the flow from the tube 16 . An elevated temperature may keep samples in the volatile state. Spark duty cycle is in Fig. 4. At 1000 pulses per second, a pulse is 10 microseconds or less. FIGURE 2 An electron capture device (ECD). 110 has an elongate cylindrical housing 112 around cylindrical member 114 defining passage 116 . Helium source 118 connects to a fitting detail 120 in a fitting 122 . Spaced electrodes 124 and 126 terminate in parallel end faces on metal rods having a diameter of about 1/16" spaced approximately 1/16" across the passage 116 . Smaller diameterd of about 0.3 mm can be used. Larger electrodes having sharpened points transverse to the gas flow are permissible. The passage 128 is defined by a spacer ring 130. Four similar rings are separated by three rings 132 with an exposed electrode ring 134 . Rings 134 are first, second and third electrodes for operation of the ECD. The first ring has a negative 50 to 250 VDC, and -100 VDC is optimum. The next ring bias is about -5 VDC. The third ring is permitted to float. The last two rings input to an electrometer 136 to measure current output to a time based recorder 138. First and second injection tubes are concentric and move axially. Smaller tube 140 introduces a fixed flow of a trace gas 144. The second concentric tube 142 connects to the GC column 148. The tubes 140 and 142 are moved in ECD 110 and lock means 150, 152 lock the tubes at specified locations. Arrows indicate tube movement. Dopant gas and GC gas effluent are swept by the larger helium flow to the left past the electrometer electrodes to form a signal. FIGURE 3 A detector system 220 utilizes a carrier gas source 212 to provide helium and about 0.3% argon. The carrier gas inlet opening 218 connects with right end cap 222 opposite the left end cap 223. The end caps plug the tube 221. Spark gap 230 is between opposing, parallel faces on two electrodes 231 and 232 provided with a high voltage pulse. Sample gas from a source 229 is injected into the tube 221 at a port 235 from a GC column or the like. Exposed metal rings 226 are spaced along the tube 221 arranged serially downstream. Intermediate rings 226 are tied to series resistors 233 for voltage drops. Ring 227 is connected to an-electrometer 228 . Electrodes 226 are connected to series resistors 233. B + supply 234 voltage (positive or negative) attracts the desired charged particles. B + voltage is pulsed and is controlled by a timer 216 and proportioned by resistors 233. The port 236 is aligned with the port 218 which also is an observation port during the spark. Photons impinge on an external spectrum analyzer 240 output to a recorder 241. Charging circuit 242 connects with a high voltage discharge circuit 243 to provide a timed pulse for firing. In FIG. 4, the top curve shows the charging pulse 244 for high voltage discharge circuit 243. That circuit forms an output 248, a pulse of short duration. Detection is delayed by a specified time 252, and then a detection enable pulse 250 is formed. Helium with a trace of argon flows into the spark gap 230 where ions and atoms are excited. Argon resonance lines are at 104.8 and 106.6 nm with corresponding energies of 11.62 and 11.83 eV. Excited argon (Ar*) from the spark gap 230 and sample compound AB from the port 235 are mixed. Possible ionization reactions are: (1) Ar*+AB=AB + +e - +Ar (2) Ar*+AB=A+B + +e - +Ar (3) Ar*+AB=AB*+Ar where AB* = AB + hγ (4) Ar* + AB=A+B*+Ar where B* = B + hγ (5) Ar* → Ar + hγ (11.62,11.83 eV) hγ + AB → AB + + e - where e - denotes a free electron, * denotes an excited state, and hγ denotes spectral emission. Equation (3) and (4) reactions form characteristic emission spectra signals for identification and quantification. Equation (1) and (2) reactions produce free electrons measured with electrometer 228 , with the measured current increasing with increasing concentration of compound AB. Ar* radiation at 11.62 and 11.83 eV will not ionize any compound with an ionization potential above 11.83 eV. Major components of air are nitrogen (15.6 eV), oxygen, (12.08 eV), water (12.6 eV), and carbon dioxide (13.8 eV). Air is not ionized and impurities (pollutants) with ionization potentials below 11.83 eV are ionized. FIGURE 5 The preferred embodiment of the invention is described with reference to Figure 5:- In monitoring for unwanted pollutants (BF 3 ) in a plant making NO 2 , it is not possible to selectively ionize impurity BF 3 without ionizing NO 2 . An atmospheric sample of air (nitrogen, oxygen, water and carbon dioxide) may mask testing by emissions from air constituents. Selective ionization of helium with less than 1.0% trace rare gas creates a relatively slow diffusing flux of metastable helium which excites the dopant rare gases argon (Ar), krypton (Kr), xenon (Xe), or neon (Ne). The helium-argon gas emission has resonance lines at 104.8 and 106.6 nm. Argon emission therefore avoids ionizing air while ionizing impurities with ionization potentials less than 11.8 eV. A helium-xenon gas has a resonance energy of 9.57 eV which selectively ionizes compounds with lower ionization potential. Likewise, helium-krypton will produce resonance energies of 10.64 and 10.03 eV. Helium-neon mixtures will produce a resonance energy of 10.97. For a mixture of BF 3 in NO 2 , helium-xenon gas is ideally suited in that the ionization potential of NO 2 is above the resonance of xenon yet the ionization potential of BF 3 is below. BF3 is selectively ionized while NO 2 is not ionized. Referring to FIG. 5, a pulsed capture detector (PCD) has cylindrical housing 312 around cylindrical member 314. Passage 316 delivers helium from a source 318 through a valve 319 and regulator 321 slightly above atmospheric pressure. The helium flow is into manifold 323 threaded to a detail 320 in a fitting body 322. Dopant Ne, Xe, Kr and Ar tanks 350, 352, 354 and 356 are connected through valves 360, 362, 364 and 366 and pressure regulators 370, 372, 374, and 376 . Valve 319 and a selected solenoid valve mix helium and rare gas Ne, Xe, Kr or Ar at the manifold 323 which flows between the electrodes 324 and 326 across the gap 325 and exposed to the spark from the DC pulse circuit 327. The flow passage 316 connects downstream with a larger axial hollow passage 328. Rings 334 and 335 are positioned axially along passage 328. Ring 334 has a bias voltage and also serves as a first terminal for the electrometer 336. The bias is about -50 VDC to -400 VDC; and -200 VDC is illustrative. The ring 335 is the second terminal for the electrometer 336 to measure current from the ionization of the trace compounds by the excited dopant. Recorder 338 forms a record of the ionization current measuring the trace compound. The injection tube 340 provides sample gas supplied from the GC column 348. The injector tube 340 is coaxially centered within the exhaust passage 344 which connects with passage 328 through a fitting 342 like the fitting 322. A smaller fitting 346 is centered in the fitting 342. Doped carrier gas flows from top to bottom while sample gas from the GC column 348 enters through the injector tubes 340. The sample and carrier gas (with dopant) commingle. Trace compounds are ionized and electrometer 336 measures trace concentration. The carrier gas flow is substantially greater than the sample flow. The commingled and reacted sample and carrier gas is exhausted through the outlet 344. Helium and the dopant flow into the PCD through fitting 320 into the spark gap 325 where ions and atoms in the excited state are formed. The dopant "D" is energized and excited to emit photons. Using argon as an example, emission forms resonance lines at 104.8 and 106.6 nm with corresponding energies of 11.62 and 11.83 eV, respectively. Helium containing D* gas mixes with AB from the tube 340. D* emits the photon hγ D in proximity to compound AB and reactions are: (6) D*=D+hγ D (7) hγ D +AB=AB + +e - +D (8) hγ D +AB=A+B + +e - +D (9) hγ D +AB=AB*+D where AB* = AB + hγ (10) hγ D +AB=A+B*+D where B* = B + hγ where hγ D denotes photon emission of excited dopant D*. (9) and (10) reactions form specific and characteristic emission spectra, thereby enabling identification and quantification. Equations (7) and (8) describe reactions which produce free electrons measured with electrometer 336 where electron current measures with concentration of compound AB. The present invention selects the dopant D thereby allowing selected ionization of components of the sample gas. If D = Ar and D* = Ar*, then Ar* radiation is hγ Ar = 11.62 and 11.83 eV and will not ionize any compound with an ionization potential above 11.83 eV. Air is not ionized by the Ar* source while air pollutants with ionization potentials below 11.83 eV are ionized. One example comprises air with an impurity such as carbon tetrachloride (CCl 4 ). In another example, NO 2 has impurity of BF 3 . If D = Xe, Xe exhibits a resonance energy at 9.57 eV. The ionization potential of NO 2 is 9.75 eV which is above the resonance energy of Kr while the ionization potential of BF 3 is 9.25 eV which is below the resonance of Xe. BF 3 in the NO 2 is selectively ionized while N0 2 is not ionized. The electrometer 338 measures trace concentrations of BF 3 . Ar, Kr and Ne are not suitable dopants since the resonance energies are greater than the ionization potential of NO 2 ; therefore the NO 2 as well as the BF 3 would be ionized by these dopants. In the passage 328 , the radiation from the excited dopant is absorbed by the analyte, and those components with ionization potentials less than the resonance energy of the selected dopant are current detected by the collecting electrode 335 and measured by the electrometer 336. Fig. 6 shows selected ionization concepts where the axis 380 represents dopant emission radiation h γ D in electron volts (eV). The line 382 locate the Ar emissions at 11.62 and 11.83 eV. The line 386 represents the 10.97 eV emission from Ne and the line 388 represents the 9.57 eV emission from Xe. Finally, emissions 384 are 10.03 and 10.64 from Kr. Ionization potentials are depicted on the axis 390. The line 392, 394, 396 and 398 represent the ionization potentials of air constituents O, H 2 O, CO 2 and N, respectively. The ionization potential 393 of CCl 4 is 11.47 eV. NO 2 and BF 3 potentials are 395 and 397, respectively. For dopant emission photon hγ D , any element or compound which on the high energy side of hγ D (that is, to the right of the emission line in Fig. 6) is ionized while any element or compound which falls to the low energy side of hγ D (that is, on the left of the emission line) will not be ionized. Dopant gases are selected based upon two criteria which are (1) the ionization potential of the compound to be measured, and (2) the ionization potentials of other constituents not measured which generate "noise" in the measure of the compound of interest. In operation, selected dopants are introduced into the carrier gas by the solenoid valve from the reservoir of the selected dopant gas. If Xe is the dopant, solenoid valve 362 allows Xenon from the reservoir 352 to flow through the pressure regulator 372 to the manifold 323. FIGURE 7 Four detector chambers 451, 453, 455 and 457 receive GC column 448 flow from the GC conduit 472 to a valve 470 which "splits" the flow into four parts. Conduits 440 connects to four ionization detectors chambers 451 , 453, 455 and 457 . Four different carrier gas sources 450, 452, 454 and 456 flow into the detector chambers. Gas constituents are excited and commingled with the sample gas splits. The excited carrier gases ionize the sample, generating an ionization current. Mixtures of carrier and sample gas are vented from each chamber through a port 444. Ionization currents generated at chambers 451 , 453 , 455 and 457 are transferred to the computer 460. Measurements processed at the computer 460 yield identity and concentrations of the sample gas. Results from the computer go to a recorder 438. The number of detectors can be varied. In analyzing a large number of different compounds, accuracy and precision may be maximized by using more detectors. FIGURE 8 The pulsed discharge photoionization capture detector (PDPID) has a long cylindrical housing 512 which contains a cylindrical member 514 which is axially hollow at 516. The helium source 518 flows through a valve 519 and regulator 521 to deliver helium at a pressure slightly above atmospheric. Manifold 523 via fitting 520 connects to a fitting 522 at the body 512 of the PDPID. Reservoir 566 is connected through valve 564 and pressure regulator 562 to the manifold 523. By opening valves 519 and 564, helium and dopant gas flow to the manifold 523 and into the axial passage 516 and between the electrodes 524 and 526. The electrodes 524 and 526 are about 1/16" with spaced end faces approximately 1/16" across passage 516 . Electrodes 524 and 526 are electrically insulated from the PDPID. The electrode 526 is grounded while the electrode 524 is provided with a high voltage pulse of short duration by the DC source 527. The two terminals 524 and 526 form a sharply fixed, narrowly constrained spark so that the spark does not dance around the two electrode faces, and remains a straight line. Carrier gas is introduced into the PDPID from top to bottom. Sample gas from the GC column 548 enters the passage 528 through the injector tube 540 so that sample and carrier gas excited by the spark commingle. Compounds are ionized producing a response across the exposed rings 534 and 535 input to the electrometer 536 indicative of the sample and concentration. After commingling and reacting, the mixture of sample and carrier gas is swept from the passage 528 of the PDPID and exhausted through the outlet 544. The outlet is supported in the fitting 546 in the end cap 542. The GC gas flow input is the tube 535. Helium and a dopant gas flows into the PDPID through fitting 520 into the spark gap 525 where ions and atoms in the excited state. Dopant "D" is energized and excited. The excited dopant passes from the spark gap 525 through passage 516 into the passage 528 of the PDPID. Dopant D in the excited state emits photons. Using argon as an example dopant, emission resonance lines at 104.8 and 106.6 nm have energies of 11.83 and 11.62 eV, respectively. By mixing dopant D with helium and exciting the gas at the gap 525, excited dopant D* is created. D* decays within approximately 5 microseconds after excitation. Some photons from decay pass through channel 516 into channel 528. Sample AB is injected into the channel 528 and exposed to photons h γ D resulting from the decay of D*. Flow of carrier and sample gas is from top to bottom to the outlet 544. Reactions are exemplified in Equations (1) to (10) above. Table 1 summarizes emission spectra from helium, argon and krypton doped helium. Other gas mixtures can be effectively used, and the data primarily support the examples presented. EMISSION SPECTRA FROM HELIUM AND ARGON AND KRYPTON DOPED HELIUM ACTIVE SPECIES WAVELENGTH (nm) ENERGY (eV) He 388 He 2 70-90 13.5-17.7 Ar 104.8 11.83 Ar 106.6 11.62 Kr 116.5 10.64 Kr 123.6 10.03 Ar 2 121-133.6 9.28-10.24 Kr 2 139.7-152.8 8.11-8.87 The sample gas maybe split and passed through multiple detectors. Electrometer output current with helium as a carrier gas, C He , is measured and stored within the computer 560. The electrometer outputs C He+Ar and C He+Kr from the second and third detectors, respectively, are measured simultaneously and likewise stored within the computer 5 6 0 . The ratios (11) R' Ar =C He+Ar /C He and (12) R' Kr =C He+Kr /C He are computed. The system is first "calibrated" by measuring the ratios R' Ar and R' Kr using a calibration gas comprising a known amount of benzene. All other constituents exhibit ionization potentials above the highest emission level of the carrier gas and, therefore, do not contribute to the electrometer current readings of the detectors. The ratios defined in equations (11) and (12) for benzene gas are R'' Ar and R" Kr , respectively. Ratios measured using the unknown sample, normalized to a corresponding reading for benzene of 100, are computed from the equations (13) R Ar = 100 (R' Ar /R" Ar ) and (14) R Kr = 100 (R' Kr /R" Kr ) Table 2 lists normalized ratios R Kr and R Ar for selected compounds. The tabulation is presented for illustration only. If an unknown sample gas R Ar is measured at 77.8 +/- 0.8, the designated uncertainty is attributed to random errors. In Table 2, the compounds C 3 H 7 NO 2 (R Ar = 78.3) and CH 3 CHO (R Ar = 77.9) and 1-pentene (R Ar = 77.6) all fall within the uncertainty of +/- 0.8. With only two detectors, the unknown compound could not be uniquely identified from ionization detection measurements. Assume that R Kr is 37.4 +/- 0.4. From Table 2, only 1-pentene is within the range of values of R Ar and RKr since the tabulated values of R Kr for C 3 H 7 NO 2 and CH 3 CHO are 0.74 and 43.4, respectively. The unknown compound is, therefore, identified as 1-pentene. The concentration of 1-pentene is from C Ar or C Kr standardized with a calibration gas containing 1-pentene. Computations are performed in real time with the computer 560. The identification analysis is depicted graphically in Fig. 9A. R Ar is plotted on the axis 584 and R Kr is plotted on the axis 582. Corresponding "coordinates" for 1-pentene, C 3 H 7 NO 2 and CH 3 CHO, with expected systematic uncertainties for each value, are taken from Table 2 and depicted as circles 572, 574 and 570 , respectively. Should R Ar and R Kr plot within any circle of uncertainty, the unknown compound is thereby identified. In the previously discussed example, the measured values of R Ar and R Kr plot within the circle 572 and therefore the unknown compound is identified as 1-pentene. NORMALIZED RESPONSE RATIOS R Ar AND R Kr FOR SELECTED COMPOUNDS COMPOUND R Ar . R Kr . CS 2 204.0 38.3 1-hexene 81.7 41.8 C 3 H 7 NO 2 78.3 0.74 CH 3 CHO 77.9 43.4 1-pentene 77.6 37.4 2-methyl-1-pentene 76.0 35.3 heptane 76.0 4.58 1-butene 70.5 24.3 butane 62.4 1.13 n-C 3 H 7 OH 60.9 10.2 As a second example, assume that R Ar is measured to be 76.8 +/- 1.0 and R Kr is measured to be 36.0 +/- 2.0. The illustrative uncertainties are greater that usual. From Table 2, it is not possible to define uniquely the unknown compound as 1-pentene or 2-methyl-1-pentene since both fall within the uncertainty ranges. An additional detector with gas dopant helps so that the normalized ratio from this detector, denoted as "R X ", delineates between the two compounds in question. The data using four detectors (which yields three ratios) is depicted graphically in Fig. 9B . Coordinates representing 1-pentene and 2-methyl-1-pentene, with spheres representing the systematic uncertainty of the system, are depicted as 592 and 590, respectively. R Kr and R Ar are plotted along the axes denoted by the numerals 582 and 584, respectively. The ratio from the additional detector, R X , is plotted along the axis denoted by 586 and is in arbitrary units. Hypothetical values for R X 1-pentene and 2-methyl-1-pentene, (for purposes of illustration), are denoted by the numerals 596 and 595, respectively. Should values of R Ar , R Kr and R X for an unknown plot within the sphere of uncertainty for either compound, the unknown compound is identified. The graphical interpretation is presented only for purposes of illustration and is easily adapted for computer interpretation. FIGURE 10 The circular detection system 620 utilizes a carrier gas source 612 connected to the detector valve 613. The circular detector 620 in a representative GC system utilizes a sample source 611 connected with the loading valve 613. They provide a carrier gas flow to a GC column 615. System timer 616 controls operation. Compounds supplied with the flowing carrier gas flow through the valve 613 to the GC column 615. There is a tangential inlet port 618 to the detector interior to sustain rotational motion and discharge through a vent port 619. The collecting electrode terminal 621 is connected to the electrometer 628. The terminal 621 connects with one ring electrode while the terminal 622 connects with a bias electrode. A B+ supply 634 provides power. One output from the B+ supply 634 is to the timer 616 and to a charging circuit 642. The charging circuit operates with a high voltage discharge circuit 643 to form an output pulse having a controlled polarity, controlled width and, specified current flow. This is input at a first terminal 624 opposite a ground terminal 625. The terminals 624 and 625 provide the DC spark in the detector 620. One of the two terminals is hollow for delivery of helium from a helium source 626. A window 627 passes light to be emitted from the spark, and observed by a spectrum analyzer 640. The analyzer 640 provides an output signal to the recorder 641. Helium is delivered at the center of the detector 620 through the hollow electrode 624 from the reservoir 626. Dopant may be optionally introduced from the reservoir 626' into the helium flow. The detector housing 620 has two cylindrical shell portions. One shell portion 629 incorporates a circular protruding lip which enables the shell half 629 to join with a second shell portion 631 . The shell portions 629 and 631 join with an overlapping lip arrangement so that a chamber 632 is formed. The collecting electrode 621 is connected to a ring 633 while the similar ring 635 is the bias electrode. The housing portions 629 and 631 are formed of a material which is not an electrical conductor. In Fig. 12, the shell portion 629 is provided with a tangentially located inlet passage 618 to introduce gas flow at the interior tangential edge of the cylindrical chamber. The port 619 is a vent located radially inwardly. FIGURE 13 The numeral 710 identifies the gas sampling apparatus formed of an insulating material. The body 710 is divided into two chambers by the partition or "window" 740 forming the upper spark chamber 712 which is leak proof to the surrounding atmosphere and a lower sample chamber. Two round and equal diameter electrodes. 714 and 716 protrude inwardly from the body 710 of the detector. The spark gap 715 within the spark chamber 712 has an insulating material at the faces of the electrodes 714 and 716 sufficiently thick to physically isolate the electrodes from the environs of the interior of spark chamber 712 yet sufficiently thin to allow the generation of a pulsed DC spark across the spark gap 715. Electrode 716 is electrically connected to B+voltage power supply 720 while the electrode 714 is grounded at 722 . The voltage applied to the electrode pair is timed by a clock 738. The spark chamber 712 is filled with helium and a trace of krypton. Sample gas enters the sample chamber through a port 726 and exits the chamber through the port 728 . A small pump delivers sample gas. The sample chamber contains circular electrodes 730 and 732 recessed within the chamber walls and exposed to the interior of the chamber. Electrode 732 is grounded at 734. The electrode 730 is connected to an amplifier 737 and then to the recording device 736. A clock 738 controls the applied positive or negative voltage and times the recorder. The electrode 732 has the requisite voltage to attract desired charged particles within sample chamber. The window 740 separating the spark chamber 712 and the sample chamber is a thin membrane of magnesium fluoride (MgF 2 ) or lithium fluoride (LiF). The material and dimensions are selected so that photoemissions at the desired energy levels experience minimal absorption entering into the sample chamber. The discharge heats the gas in the spark gap 715. Heated relatively buoyant gas in the spark path rises in the closed spark chamber 712 where it is cooled by mingling with cooler gas. Simultaneously, cooler gas replaces the heated gas at the spark gap 715. The net result is circulation within the closed spark chamber 712 as depicted by the broken lines 718. Convective circulation constantly supplies "fresh" gas to the spark gap 715. Krypton in the excited state emits photons at 116.5 and 123.6 nanometers (nm) with corresponding energies of 10.03 and 10.64 electron volts (eV), respectively. This radiation passes through the window membrane 740 and into the sample chamber where it interacts with the sample gas. Each spark creates a fresh supply of Kr* which, in turn, decays to the ground state by the emission of 10.03 eV and 10.64 eV photons. The spark generation system in cooperation with the helium-krypton gas mixture acts as a self replenishing source of 10.03 eV and 10.64 eV radiation. Sample flow is preferably continuous although discrete samples may be taken. In air monitoring, small concentrations of pollutant compounds AB and air are exposed to the photon flux of energies 10.03 and 10.64 eV from the spark chamber 712 through window membrane 740. This photon flux ionizes the compound AB. Free electrons are collected at the electrode 730 which is at a positive potential. Electrode 732 is at ground to retard ionic recombination and to repel electrons. The free electron current from the electrode 730 is recorded by the recorder 736 with the current proportional to the concentration of AB. Electron current is, therefore, an analytical measure of concentration. Recall that Kr* emits radiation at 10.03 and 10.64 eV. This radiation will not ionise any compound with an ionisation potential above 10.64 eV. Major constituents of air are not ionised by the emissions from Kr*, but impurities in the air sample (pollutants with ionisation potentials below 10.64 eV) will be ionised. While the foregoing describes an embodiment of the present invention, the scope is determined by the appended claims.

Claims: A detector to analyze compounds in gaseous sample, comprising a closed chamber (316, 318) having a helium source (318), a flow inlet fitting body (322) at one end of the chamber and an outlet fitting body (342) at the other end of said chamber to enable helium to flow through the chamber from one end to the other, spark-forming electrodes (324, 326) which are spaced apart and means (327) to provide said electrodes with a current forming a spark sufficient to arc thereacross, said spark-forming electrodes being positioned in said chamber to form a spark gap across helium flow through said chamber, means (340) downstream in said chamber from said spark-forming electrodes to inject a gaseous flow of sample into the chamber, a bias electrode (334) and a collector electrode (335) in said chamber for collection of current formed as a result of the spark across the gap wherein the helium flows toward said bias and collector electrodes to enable a current to be formed indicative of the concentration of a particular sample compound in said chamber and the bias and collector electrodes are connected to a detector means (336) to measure the concentration of the sample compound in said chamber by changing current flow, said detector also comprising a plurality of dopant gas sources (350, 352, 354, 356) and a mixer (323), arranged such that helium from said helium source and a selected one of said dopant gases are admixed prior to flowing into said chamber, the gases of said dopant gas source being neon, argon, krypton and xenon. A detector according to claim 1 wherein said mixer is a manifold (323), said detector also comprising a pressure regulator (321) and valve (319) for supplying helium at a controlled rate to said manifold, said gas sources comprise a plurality of reservoirs (350, 352, 354, 356), pressure regulators (370, 372, 374, 376) and valves (360, 362, 364, 366) for supplying a selected dopant at a controlled rate to said manifold, and means (320) for introducing into said chamber said helium and said selected dopant which are commingled within said manifold thereby forming said carrier gas. A detector according to claim 2 wherein said chamber (316, 328) forms an elongated helium gas flow passage and said passage directs helium flow to said electrodes (324, 326) and also directs photon emissions from said spark to interact with said one or more dopant gases to form an electrical current. The detector according to any preceding claim 3 provided with an electrometer detector means (336) cooperating with a recorder (338) to quantitatively measure said current generated within the chamber (308). A method of analysing compounds in a gaseous sample, comprising the steps of creating a flow of carrier gas through a chamber from one end to the other for exposure to DC current across the chamber, energising at least one component of said carrier gas to an excited metastable state as a result of exposure to said DC current, subsequently commingling a gaseous flow of sample with said carrier gas, forming charged particles in the sample as a result of ionizing radiation emitted in the decay of said excited component of said carrier gas wherein the charged particles are formed from said sample compounds, measuring said charged particles and selectively identifying compounds in said sample utilising said measurements, and selecting and supplying one gas dopant to the chamber, the DC current energising the inert gas to an excited metastable state, the dopant being energised to an excited state as a result of the decay of said metastable inert gas, and the charged particles formed as a result of ionising radiation emitted by the decay of said energised dopant component of said carrier gas in said chamber, said dopant being selected to selectively ionise compound in said sample, wherein said carrier gas is helium supplied from a helium source (318) a plurality of dopant gas sources (350, 352, 354, 356) comprising sources of neon, argon, krypton and xenon, and a mixer (323) are provided, and the helium and a selected dopant gases are admixed in said mixer before flowing into said chamber. A method according to claim 5 comprising the additional step of observing spark caused emissions in said chamber to analyze said sample compounds, said observation being effected with an electrometer. A method according to claim 5 or claim 6 wherein said dopant gas is selected such that the resonance energy of the dopant is greater than the ionisation energy of compounds in said sample to be measured and is less than the ionisation energy of compounds in the sample gas which are not to be measured. A method according to any one of claims 5 to 7 wherein said mixer is a manifold.

Inventors: STEARNS STANLEY D, WENTWORTH WAYNE E, STEARNS, STANLEY D., WENTWORTH, WAYNE E.
Applicants: VALCO INSTR CO INC, VALCO INSTRUMENTS COMPANY, INC.
Application year: 1995
Main classification: G01N30
IPC codes: G01N30, G01N27