Abstract: An ion mobility spectrometer is disclosed which includes a sample input port, an ion generator, an ionization chamber receiving and ionizing samples, an ion gate for causing the ionized samples to travel in a direction, and a drift region for receiving the directed ionized samples and for subjecting the ionized samples to an electric potential. The ionized samples then separate according to their electric charge and mass and are detected by a sensor having an output with linear, non-linear, and logarithmic characteristics. The ion mobility spectrometer further includes circuitry coupled to the sensor for linearizing the output such that the non-linear and logarithmic characteristics are linearized while preserving the linear characteristics.

Abstract: A gas injector comprises (1) a carrier gas channel through which a carrier gas can enter the injector, (2) an output channel through which the carrier gas and a gaseous sample can be injected from the device to an analytical instrument, (3) a sample gas channel capable of holding the gaseous sample, and (4) a switch structure regulating the connections among the sample gas channel, the carrier gas channel and the output channel. The injector also comprises at least a purge channel through which the carrier gas can flow across part of the device, purging therein and preventing contaminants from reaching the output channel. The gas injector provides a low baseline noise and a high signal to noise ratio when applied to a sensitive analytical instrument.

Abstract: An apparatus for and method of making a discharge ionization detector. The apparatus comprises a detector body, a detector cavity, located in the detector body and having a discharge electrode and an second discharge electrode, wherein an electric discharge runs between the second discharge electrode and the discharge electrode, and a signal electrode which attracts ionized molecules, an inlet interface, through which a discharge gas enters the detector, an analyte inlet, through which the analyte enters the detector cavity, and an outlet through which the analyte and discharge gas exit the detector body, wherein the apparatus is hermetically sealed. The apparatus is hermetically sealed by vacuum brazing the components to the detector body. The present invention can also have a detector volume as small as 10 micro-liters or less.

Abstract: Energy efficiency of a thermal zone in an analytical instrument is improved by use of an oven housing module having an enclosure body defining an oven cavity, wherein the enclosure body exhibits a size and shape sufficient to receive a component to be subjected to temperature control within a thermal zone located in the oven cavity. A temperature control assembly includes a vent assembly communicating with ambient air, a fan, and a fast cooling flap, wherein the temperature of the thermal zone may be modulated by supplementing the oven cavity air with ambient air. The fast cooling flap may be operated for opening one side of the oven cavity to ambient conditions such that ambient air may be rapidly introduced to the oven cavity and the cavity air may be rapidly exhausted from the oven cavity for rapid cooling of the thermal zone.

Abstract: A multichannel capillary column having an interior wall defining a single internal bore, wherein the interior wall defines a plurality of n channels and n ridges, wherein adjacent channels are partially separated by a respectively interposed ridge, and wherein a central, coaxial portion of the internal bore allows cross-channel fluid communication between all of the n channels.

Abstract: Linearization of an ionization detector is obtained by processing the output signal derived from the ionization detector so as to compensate for the naturally-occurring logarithmic decay of the detector response at high sample concentrations. Linearization is accomplished according to a linearizing formula:I.sub.(lin) =I[1+(I/I.sub.(dec))].sup.pwrwhere:I.sub.(lin) =linearized output signal current of the detectorI=non-linearized output signal current of the detectorI.sub.

Abstract: Apparatus for purification of a discharge gas, wherein the discharge gas is selected from a group of noble gases, and most preferably is helium or argon. The purification of the discharge gas is achieved by attraction and removal of at least one ionized contaminant in the discharge gas, wherein the contaminant exhibits an ionization potential that is less than the excitation potential of the discharge gas. A discharge gas purification system may be constructed to include a discharge ionization detector that employs a discharge chamber and discharge source for effecting a discharge to provide photons and metastables for ionization of an analyte in an adjacent ionization chamber, wherein the discharge chamber includes a bleed flow for attracting and removing ionized contaminants present in the discharge chamber.

Abstract: An ionization detector for detection of an analyte includes a source chamber having a source of ionizing particles and receiving a fluid stream of detector gas; an ionization chamber connected to the source chamber at an ionization chamber entrance therebetween so as to allow metastables and photons to be generated in the source chamber and to be transferred in the fluid stream to the ionization chamber; a signal electrode assembly located in the ionization chamber; and a signal measuring circuit for measuring ionized analyte molecules. The signal electrode assembly includes a spaced array of electrodes including a collector electrode, a first signal electrode, and a second signal electrode. The first signal electrode is situated immediately downstream from the ionization chamber entrance and substantially upstream of the collector electrode, so as to extend the detection zone to the vicinity of the ionization chamber entrance.

Abstract: Method and apparatus are disclosed for improved transfer of ionizing particles from a source chamber to a detection zone in an ionization chamber in an ionization detector. An ionization detector includes a source chamber, an inlet for introducing detector gas to the source chamber, a transitional structure including a flow guide that directs detector gas flow between the source chamber and the adjacent ionization chamber, an inlet for introducing sample gas containing an analyte into the ionization chamber, and an outlet port for exhausting the mixture of the sample gas and the detector gas. The aspect ratio of the flow guide causes the linear velocity of the detector gas stream to be highest at a throat in the flow guide and to decrease as the detector gas stream approaches a detection zone in the ionization chamber, thereby suppressing analyte diffusion from the ionization chamber through the flow guide.

Abstract: Method and apparatus for purification of a discharge gas, wherein the discharge gas is selected from a group of noble gases, and most preferably is helium or argon. The purification of the discharge gas is achieved by attraction and removal of at least one ionized contaminant in the discharge gas, wherein the contaminant exhibits an ionization potential that is less than the excitation potential of the discharge gas. A discharge gas purification system may be constructed to include a discharge chamber, an inlet for supplying a pressurized flow of discharge gas into the discharge chamber, a discharge device for effecting a discharge in the discharge chamber to effect ionization of a contaminant in the discharge gas, and a bleed flow device located with respect to the discharge and to the discharge cathode for electrically attracting and removing a bleed flow of the discharge gas in the discharge chamber. A disproportionate amount of the ionized contaminants thus created are captured in the bleed flow.

Abstract: An ionization detector having an upper ionization chamber, a lower ionization chamber, and a radioactive source located in the upper ionization chamber but shielded from the lower ionization chamber by a barrier. A substantially constant fluid stream of detector gas is supplied to the upper ionization chamber so as to fill the upper ionization. The radioactive particle emitter is disposed on the periphery of the interior of the upper ionization chamber so as to generate a constant supply of alpha particles into the internal volume defined by the upper ionization chamber. The interaction of the alpha particles and the detector gas generates metastables and photons as the alpha particles traverse a portion of the volume in the upper ionization chamber. The lower ionization chamber is coupled to the upper ionization chamber so as to receive the detector gas flow and the metastables.

Abstract: In a discharge ionization detector, a method and apparatus are disclosed for increasing the transfer of photons and metastables from a discharge chamber to a ionization chamber, while effecting ion discrimination of the ionic current with respect to a signal cathode, thereby reducing the effect of ionic current in the signal output. Preferred embodiments of the invention include a discharge source located in a discharge chamber, means for introducing discharge gas flow into the discharge chamber, a flow guide that directs discharge gas flow between the discharge chamber and an adjacent ionization chamber, and inlet port for introducing a flow of sample gas containing an analyte into the ionization chamber and an outlet port for exhausting the sample gas and the discharge gas. A plurality of apertures in the flow guide are situated proximate the discharge source so as to promote the rapid and efficient transfer of photons and metastables from the discharge source into the ionization chamber.

Abstract: Electron capture detector for use with an effluent stream from a gas chromatograph includes an ionization cell and a sample inlet system connected to the ionization cell for providing an effluent fluid having a sample concentration therein. In the preferred constant-current, variable frequency mode of operation, a cell current is measured and compared to the reference current. The pulse rate is then adjusted to maintain a constant cell current. The pulse rate is converted to a voltage, processed according to a novel linearization formula, and recorded. The ionization cell includes a radioactive ionization source and the ionization cell defines an optimized cell volume in which the electron capture reaction is forced to occur according to a concentration mode of operation. Improved sensitivity in the electron capture detector may be achieved by restricting the effective radioactivity in the ionization cell to be in the range of 0.5 to 3 milliCuries, and preferably in the range of 1 to 2 milliCuries.

Abstract: Electron capture detector for use with an effluent stream from a gas chromatograph includes an ionization chamber and a sample inlet system connected to the ionization chamber wherein the sample inlet system effects uniform fluid mixture of the effluent fluid and a make-up gas prior to entry of the fluid mixture into the ionization chamber. A preferred mixing device includes a column liner having a flow acceleration region wherein a localized reduction in the internal diameter of the liner causes momentary turbulence of the fluid mixture.

Abstract: Electron capture detector for use with an effluent stream from a gas chromatograph includes an electron source means and an adjacent ionization chamber in which electron capture takes place. The active region of the ionization chamber is disposed to receive free electrons and a flow of purge gas. The detector has an inlet port for receiving a sample gas as well as an outlet port for exhausting the sample gas and the purge gas. A collector electrode in the detection chamber is biased so as to collect the free electrons in the absence of electrophilic substance. Electrophilic substances in the detector will reduce the flow of electrons to the collector and generate an ionic current. An insulative member in the form of a flow guide may be located at the portion of the anode so as to permit pulsing of free electrons to the anode but substantially block the ionic current, i.e., to discriminate between the free electrons and the ionic current.

Abstract: The invention is a method and apparatus for significantly improving the performance of a reciprocating pump by delivering the pumping fluid at a desired pressure and flow rate with minimal flow fluctuations. The compressibility of the pumping fluid directly effects volumetric flow rate and mass flow rate. The method includes the step of sensing various pump parameters related to said compressibility and adjusting the pumping speed to make appropriate accommodations. In particular, the compressibility of the pumping fluid is effected by the adiabatic heating of the pumping fluid during compression, variations in pumping fluid density, leaks in the check valves of cylinder/piston seals and the primary and secondary switching losses in the fluid flow occurring when the primary and secondary pistons reverse direction.

Abstract: A method and apparatus for sensing the mass flow of a fluid and for generating an output signal representative of the sensed mass flow are shown to include a conduit formed from resistive material, a voltage source connected to a first point on the conduit, for providing a voltage to the first point in response to a control signal, a differential amplifier wherein the output of the amplifier is representative of the difference in voltage between a second point on the conduit and a third point on the conduit, and a controller for generating the control signal so that the voltage provided to the first point is regulated in relation to the flow of fluid through the conduit. In an especially preferred embodiment the resistive material is Nickel-52. In a further embodiment, the controller generates the control signal so that the voltage applied to the first point is regulated to maintain the average resistance of the conduit at a desired value. In one embodiment, the desired value is a constant value.