US3607096A - Alkali flame ionization detector having cap means for changing the gas flow pattern - Google Patents

Alkali flame ionization detector having cap means for changing the gas flow pattern Download PDF

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US3607096A
US3607096A US836350A US3607096DA US3607096A US 3607096 A US3607096 A US 3607096A US 836350 A US836350 A US 836350A US 3607096D A US3607096D A US 3607096DA US 3607096 A US3607096 A US 3607096A
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chimney
jet
air
current
base
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Charles H Hartmann
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CHARLES H HARTMANN
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CHARLES H HARTMANN
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
    • G01N27/626—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using heat to ionise a gas
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/17—Nitrogen containing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/18—Sulfur containing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/19—Halogen containing

Definitions

  • the present invention relates generally to thermionic detectors used in gas chromatographic analysis and in particular to such detectors equipped with a source of alkali salt adjacent the combustion region.
  • detectors known as alkali flame ionization detectors or AFID's
  • AFID's are especially useful in determining the presence and concentration of phosphorous, nitrogen-, sulfur-and chlorine-containing hydrocarbon compounds in the effluent stream from a gas chromatographic column because they exhibit enchanced sensitivity to these compounds as compared to other hydrocarbons present in the effluent stream.
  • an AF ID detector provides means for mixing the effluent gases from a chromatographic column with a combustible gas such as hydrogen and burning the mixture in the presence of one of the salts of an alkali or alkaline earth metal.
  • a pair of electrodes disposed in the vicinity of the flame are connected to a constant voltage DC source and the ionic current flowing between the electrodes is measured with an electrometer and plotted as a function of time.
  • the flame jet and electrodes are typically enclosed within a cylindrical tower or chimney which shields the combustion region from the ambient atmosphere. Air to support combustion is introduced under pressure at the base of the chimney and flows upwardly to the combustion region and out the top which is typically partially closed by a loosely fitted lid which restricts the flow of ambient air to the combustion region.
  • the flow of air within the detector can be controlled in such a way as to reduce background current and noise while enhancing sensitivity to the compounds under investigation by providing a removable sealed top for the chimney and an exhaust passage for the products of combustion and for excess air at the base of the chimney.
  • the air instead of flowing in quantity past the combustion region and out the top, diffuses from the base region of the chimney into the combustion region only in sufficient quantities to be virtually consumed by the flame. Any excess air is exhausted together with combustion products through the exhaust passage near the base of the chimney. The result is that the deleterious effects of the unrestricted upward flow of air in the prior art detectors are substantially eliminated.
  • the principal object of the present invention is to provide an improved alkali flame ionization detector having enhanced sensitivity to organic vapors of compounds of interest while substantially reducing background current and noise.
  • Another object is to control the flow of air within the chimney of such a detector in such a way that air enters the combustion region only in sufficient quantity to support combustion.
  • Another object of the present invention is to provide such a detector in which air in excess of that needed for combustion is exhausted from the chimney via a passage which is located so that currents of air adjacent the combustion region are eliminated.
  • a further object is to provide an alkali flame ionization de' tector in which air sufficient for combustion is transported to the combustion region solely by the forces of gaseous diffusion.
  • FIG. 1 is a cross-sectional view of an improved AFID incorporating the means for altering the flow pattern in accordance with the present invention.
  • FIG. 2 is a graph illustrating the effect of hydrogen flow on the performance of the AFID.
  • the improved AFID 1 includes a base 3, chimney 5 and a cap 7.
  • the base 3 and chimney 5 may be made of stainless steel while the cap 7 may be of aluminum, for example.
  • Each of these parts may be cylindrical about a vertical axis in the drawing.
  • a jet assembly 9 from which emerge the gases to be burned.
  • a connector assembly 11 provides a removable sealed coupling means for connecting the outlet end portion of a gas chromatograph column 13 in gas flow communication with jet assembly 9.
  • a collector electrode assembly 15 and an igniter-polarizing voltage electrode assembly 17 project through the wall of chimney 5 into the interior thereof.
  • Jet assembly 9 comprises a hollow jet 19 which has near the lower end a conical sealing plug 21 which is joined to jet 19 as by swagging for example.
  • Plug 21 is received in a similarly conical recess in base 3 and forced into good sealing engagement with base 3 by an externally threaded clamping nut 23.
  • annular recess 25 which interconnects an air flow passage 27 and a series of bores 28 equispaced around the axis of nut 23.
  • Passage 27 is connected to a source of air under pressure (not shown) in order to supply air to the interior of chimney 5 for combustion.
  • a salt cup 29 is mounted on the end of jet 19 and stored in place for example by brazing.
  • a duct 31 is aligned with the central bore in jet 19.
  • a salt of an alkali metal or alkaline earth metal 33, rubidium sulfate (Rb S0,) for example, is pressed into an annular recess in cup 29 under high pressure to form a solid block surrounding duct 31.
  • Chromatographic column 13 projects into a mixing chamber 34 and is sealingly supported concentrically therein by an internally threaded sleeve 35 and a conical plug 37.
  • a cylindrical adapter 39 is received within a counterbored recess in base 3 and may be sealed to base 3 by swagging for example.
  • a hydrogen flow passage 41 interconnects mixing chamber 34 and a source of hydrogen gas under pressure (not shown).
  • a short elbow-shaped duct 42 interconnects mixing chamber 34 and hollow jet l9.
  • Electrode assembly 17 comprises an igniter electrode 43 in the form of a coiled resistance heater element disposed adjacent the salt cup 29, a pair of insulators 45 which enclose the leads for electrode 43, a shell 47 which is fastened within an aperture in chimney for example by brazing, and a two-terminal coaxial connector 49 which is insulatingly mounted in the shell 47.
  • Collector electrode assembly is similar except that only a single insulator and lead are needed to connect to a ringshaped collector electrode 51 disposed above the jet assembly 9.
  • electrode 51 is actually disposed with the plane of the ring approximately perpendicular to the axis of symmetry of the chimney 5, it has been illustrated in the drawing as if twisted about the axis of its electrical lead in order to display the circular configuration of the electrode.
  • Cap 7 comprises a plug 53 dimensioned to fit loosely within the bore of chimney 5 and having an O-ring 55 disposed in a circumferential groove in plug 53 and providing a seal within chimney 5.
  • a rod 57 disposed, for example by press fitting, within a bore in plug 53 and a knob 59 of phenolic for example, on the end of rod 57 form a convenient handle for removal ofthe plug which becomes very hot in use.
  • gaseous samples emerge serially from column 13 into mixing chamber 34.
  • a controlled flow of hydrogen also enters chamber 34 as previously noted and flows into the annular space surrounding the portion of column 13 within chamber 34.
  • the hydrogen then flows axially within this annular space to the end of column 13 as shown by the arrows where it mixes with the effluent gaseous samples from column 13.
  • the mixture then flows through elbow-shaped duct 42, into jet 19 and emerges from the duct 31 in salt cup 29.
  • Air to support the combustion of the gaseous mixture enters through air flow passage 27, flows into annular recess and upwardly through bores 28. The air then emerges from the bores 28 as shown by the arrows into the annular space surrounding jet 19.
  • igniter electrode 43 is momentarily energized by a low voltage established between the leads from a power supply 61 to cause electrode 43 to glow producing ignition of the combustible mixture.
  • all of the air entering chimney 5 flows upwardly past the combustion region and out the open top of chimney 5 together with combustion products as in the prior art detectors such as the one shown in the aforementioned US. Pat. No. 3,423,181.
  • one or more small passages could be formed at the base of the chimney 5. If this were done, base 3 and chimney 5 could be formed as one piece, while such passages could be used to vary gas conductance by constricting or closing one or more of them.
  • base 3 and chimney 5 could be formed as one piece, while such passages could be used to vary gas conductance by constricting or closing one or more of them.
  • a pool or static mass of air is believed to exist in the regions surrounding the top of nut 23 such that as air under pressure enters this pool through bores 28, some air leaves through the above-described radial flow passage while the remaining air travels upwardly to the combustion zone above salt cup 29.
  • the partial pressure of oxygen in the region of the flame is reduced so that more air diffuses into the combustion zone from the pool of air below as shown by the arrows in the drawing.
  • the salt in salt cup 29 is heated.
  • the effluent vapors of hydrocarbon compounds burning in the presence of this heated salt mass form a conductive plasma of ions in the interelectrode space between electrodes 43 and 51.
  • the presence of these positive and negative ions in the interelectrode space lowers the resistance of this space.
  • a polarizing voltage of, for example, 300 volts DC is applied in the series circuit loop which includes power supply 61, the input of an electrometer amplifier 63, collector electrode 51, igniterpolarizing electrode 43 and the associated leads, with the igniter-polarizing electrode typically being negatively polarized, and the collector electrode being at or near ground.
  • the current which flows in the circuit is proportional to the density of ions in the interelectrode space.
  • a relatively steady background current exists in the series circuit. Since this background current contains no information about the samples of interest it is desirable to, in effect, subtract it from the current to be measured in amplifier 63 and the remaining circuitry.
  • a bucking current source 65 passes an adjustable current through the input of amplifier 63 in opposition to the main current flowing from the interelectrode space. Source 65 can be adjusted to null any background current so that only current indicative of a sample gas will be registered.
  • a range switch 71 which may consist of a bank of selectable feedback resistors, is connected from output to input of amplifier 63 in order to adjust the amplifier again.
  • FIG. 2 a graph summarizing performance factors and illustrating the optimization of operating conditions is shown.
  • the AFID used to 12 this data was as shown in FIG. 1 and had the following approximate dimensions: Chimney 5 height2 inches; inside noise, of chimney 5-seveneighths inch; height of collector electrode 51 above top of salt cup 29five-eighths inch; loop diameter of collector electrode 5l--one-fourth inch; distance from top of salt cup 29 to top of base 3-eleven-sixteenths inch.
  • the ignitor electrode 43 was held at a potential of 300 volts below collector electrode 51 potential and the salt used in salt cup 29 was Rb S0,.
  • the carrier gas flowing through column 13 was helium.
  • the solid line of FIG. 2 indicates that background current reached a maximum of somewhat more than 5X10 amps at approximately 43 ml./min. of hydrogen. Since high background currents correspond to rapid consumption of alkali salt and to excessive noise, operation of the detector at 43 ml./min. of hydrogen is plainly undesirable in this case.
  • the response curve which is plotted only qualitatively with respect to the ordinate scale passes through a maximum at about the same hydrogen flow of 42-43 ml./min.
  • response which may be measured in coulombs of electric charge crossing the interelectrode space per gram of sample which, when burned, produces this charge transfer, does not take into account the noise level.
  • FIG. 2 shows that sensitivity, which may be defined as the minimum sample flow rate in grams per second which can be reliably detected, reaches a maximum at approximately 37 mL/min. of hydrogen. At this hydrogen flow, background current is only 50 percent of the maximum value.
  • sensitivity which may be defined as the minimum sample flow rate in grams per second which can be reliably detected, reaches a maximum at approximately 37 mL/min. of hydrogen.
  • background current is only 50 percent of the maximum value.
  • Qualitatively similar results have been produced using a variety of AFlDs constructed according to FIG. 1 although the optimum air and hydrogen flows have been found to vary slightly according to the fit of the chimney 5 to the base 3 and the exact positioning of the electrodes.
  • the procedure for establishing optimum operating conditions is to choose an air flow in the range of 200 to 270 ml./min. and to scan hydrogen fiow in step changes from 85 to 20 ml./min. to produce a curve of background current similar to FIG. 2.
  • the hydrogen flow should then be set at
  • the performance of the AFlD according to FIG. 1 has been evaluated using as alkali salts KBr, RbBr, CsBr, K 50, and Rb,SO Each required different H and air flows for optimum performance.
  • the AFID exhibited very high sensitivity to nitrogenand phosphorous-containing hydrocarbon compounds compared to other hydrocarbon compounds i.e. the selectivity for the nitrogen and phosphorous compounds was excellent such that they could be reliably detected and quantified even in the presence of other hydrocarbon compounds in the effluent gases from the column.
  • the AFlD also exhibited good selectivity for sulfurand chlorine-containing compounds.
  • a chromatographic detector for analyzing the gaseous components in the effluent gas emerging from a chromatographic column comprising in combination: an enclosure defining at one end thereof an open portion; a cap means for sealingly closing said open portion; a hollow jet member extending into said enclosure from one wall thereof, said jet member having an open end within said enclosure; said enclosure defining a first gas flow passage in communication with said jet and with the exterior of said enclosure for connection to said chromatographic column; means in communication with said passage for mixing said effluent gases with a combustible gas to form a combustible mixture; said enclosure defining a second gas flow passage therethroug'h for conducting an oxygen-containing gas mixture to the interior of said envelope from a source of said oxygen-containing gas mixture; means disposed adjacent said open end of said jet member for producing ions in response to the combustion of said combustible gas mixture; said enclosure defining a third gas flow passage extending from the exterior of said enclosure to portrons of the interior of said enclosure distal said open portion thereof for
  • a detector according to claim 1 wherein said enclosure includes a base portion defining on one surface thereof a recess, and a chimney portion having one end thereof received in nesting relation within said recess and wherein said third gas flow passage is defined between the mating surfaces of said base portion and said chimney portion.
  • a detector according to claim 1 wherein said cap means comprises a plug dimensioned to be insertable within said open portion of said enclosure and having a resilient gasket extending around the periphery thereof.
  • one of said electrodes incorporates means for igniting said combustible gas mixture.
  • said means for producing ions comprises a cup member surrounding said open end of said jet member, said cup member containing an alkali salt.

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US836350A 1969-06-25 1969-06-25 Alkali flame ionization detector having cap means for changing the gas flow pattern Expired - Lifetime US3607096A (en)

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4038864A (en) * 1974-10-15 1977-08-02 State Board Of Higher Education For And On Behalf Of The University Of Oregon Hydrocarbon measurement
US4129418A (en) * 1978-02-21 1978-12-12 General Electric Company Discriminating halogen sensor
US4182740A (en) * 1976-03-01 1980-01-08 Varian Associates, Inc. Flame ionization detector
US4202666A (en) * 1978-02-24 1980-05-13 Tracor, Inc. Method and apparatus for preventing the destruction of an alkali source of a nitrogen-phosphorous detector
US4311664A (en) * 1976-12-08 1982-01-19 Wojskowy Instytut Chemii I Radiometrii Flame-photometric detector burner of gas chromatograph
US4420565A (en) * 1980-12-31 1983-12-13 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations
US4555488A (en) * 1982-03-01 1985-11-26 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations using organonitrogen tracers
US4555489A (en) * 1982-03-01 1985-11-26 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations using organosulfur tracers
US4744954A (en) * 1986-07-11 1988-05-17 Allied-Signal Inc. Amperometric gas sensor containing a solid electrolyte
US4839143A (en) * 1985-02-15 1989-06-13 Allied-Signal Inc. Selective ionization of gas constituents using electrolytic reactions
WO1998005956A1 (de) * 1995-01-26 1998-02-12 Preussag Wasser Und Rohrtechnik Gmbh Ionisationsdetektor für die gaschromatographie
US6309604B1 (en) * 1998-01-22 2001-10-30 Proengin S.A. Apparatus combining spectrophotometry and flame ionisation detection for analysing a gas composition

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3423181A (en) * 1966-06-06 1969-01-21 Varian Associates Thermionic detector for gas chromatography

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3423181A (en) * 1966-06-06 1969-01-21 Varian Associates Thermionic detector for gas chromatography

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4038864A (en) * 1974-10-15 1977-08-02 State Board Of Higher Education For And On Behalf Of The University Of Oregon Hydrocarbon measurement
US4182740A (en) * 1976-03-01 1980-01-08 Varian Associates, Inc. Flame ionization detector
US4311664A (en) * 1976-12-08 1982-01-19 Wojskowy Instytut Chemii I Radiometrii Flame-photometric detector burner of gas chromatograph
US4129418A (en) * 1978-02-21 1978-12-12 General Electric Company Discriminating halogen sensor
US4202666A (en) * 1978-02-24 1980-05-13 Tracor, Inc. Method and apparatus for preventing the destruction of an alkali source of a nitrogen-phosphorous detector
US4420565A (en) * 1980-12-31 1983-12-13 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations
US4555488A (en) * 1982-03-01 1985-11-26 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations using organonitrogen tracers
US4555489A (en) * 1982-03-01 1985-11-26 Mobil Oil Corporation Method for determining flow patterns in subterranean petroleum and mineral containing formations using organosulfur tracers
US4839143A (en) * 1985-02-15 1989-06-13 Allied-Signal Inc. Selective ionization of gas constituents using electrolytic reactions
US4744954A (en) * 1986-07-11 1988-05-17 Allied-Signal Inc. Amperometric gas sensor containing a solid electrolyte
WO1998005956A1 (de) * 1995-01-26 1998-02-12 Preussag Wasser Und Rohrtechnik Gmbh Ionisationsdetektor für die gaschromatographie
US6309604B1 (en) * 1998-01-22 2001-10-30 Proengin S.A. Apparatus combining spectrophotometry and flame ionisation detection for analysing a gas composition

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