Abstract: Fluid purification systems employing a monolithic composite photocatalyst to remove volatile organic compounds (VOCs) and/or pathogenic organisms are disclosed. Pairing of systems tuned to abate each of these materials are discussed in different configurations such as series and parallel, as well as combining systems to target both materials simultaneously. System configurations that allow a portion of the fluid stream to be purified are also disclosed as are configurations that allow regeneration of the photocatalyst. These features may be augmented by sensors that allow closed loop control of bypass and regeneration cycles in the systems.

Abstract: In gas chromatography (GC), a sample is introduced into a flow of carrier gas and the mixture is driven through a heated GC column to acquire chromatographic data from the sample. During this time, the column is heated from an initial temperature to a final temperature. Subsequently, the column is cooled according to a cooling program. The cooling program may include a first cooling ramp, a subsequent isothermal hold, and a subsequent second cooling ramp. Alternatively, while the column is cooled down the flow of carrier gas through the column may be slowed down or ceased for a period of time, after which the flow of carrier gas through the column may be resumed at the original flow rate in preparation for processing another sample. Controlling column temperature and/or flow in this manner may be effective for reducing column bleed carryover and/or the effects thereof.

Abstract: In gas chromatography (GC), a sample is introduced into a flow of carrier gas and the mixture is driven through a heated GC column to acquire chromatographic data from the sample. During this time, the column is heated from an initial temperature to a final temperature. Subsequently, the column is cooled according to a cooling program. The cooling program may include a first cooling ramp, a subsequent isothermal hold, and a subsequent second cooling ramp. Alternatively, while the column is cooled down the flow of carrier gas through the column may be slowed down or ceased for a period of time, after which the flow of carrier gas through the column may be resumed at the original flow rate in preparation for processing another sample. Controlling column temperature and/or flow in this manner may be effective for reducing column bleed carryover and/or the effects thereof.

Abstract: An MFC includes: a proportional valve; a mass flow sensor; a first flow line connecting from an outlet of the proportional valve through the mass flow sensor to an exit line; a second flow line joining the first flow line at a first junction located upstream of the mass flow sensor and at a second junction located downstream of the mass flow sensor; a switching valve placed such that the switching valve can regulate a flow of a gas through the first flow line or the second flow line; and a control device connected to provide a feedback control loop for regulating the proportional valve based on signals measured by the mass flow sensor, wherein the control device includes a program for keeping a rate of a flow exiting the exit line substantially constant when the flow is through the second flow line.

Abstract: The present invention relates to methods and systems for controlling depressurization of a vial containing a gas sample. The disclosed systems and methods are employed during sampling and/or analysis of the gas sample. One exemplary method for controlling depressurization of a vial containing a gas sample includes establishing fluid communication between a sample loop of a head space sampling device and the head space of the vial. A sample gas pressure is established within the head space of the vial. The sample loop is connected in fluid communication with a lower pressure environment through a ventilation pathway. A ventilation valve within the ventilation pathway is used to vent gas from the vial through the sample loop to the lower pressure environment at a predetermined rate. Devices and systems for depressurizing a vial containing a gas sample at a predetermined rate are also disclosed.

Abstract: An MFC includes: a proportional valve; a mass flow sensor; a first flow line connecting from an outlet of the proportional valve through the mass flow sensor to an exit line; a second flow line joining the first flow line at a first junction located upstream of the mass flow sensor and at a second junction located downstream of the mass flow sensor; a switching valve placed such that the switching valve can regulate a flow of a gas through the first flow line or the second flow line; and a control device connected to provide a feedback control loop for regulating the proportional valve based on signals measured by the mass flow sensor, wherein the control device includes a program for keeping a rate of a flow exiting the exit line substantially constant when the flow is through the second flow line.

Abstract: The present invention relates to methods and systems for detecting leaks in a head space sampling device. One exemplary method for detecting leaks in a head space sampling device includes establishing fluid communication between a head space and a pressurization gas conduit. Gas pressure and flow rate are monitored within the pressurization gas conduit during pressurization of the head space. Changes in monitored gas pressure and flow rate are used to evaluate whether a leak exists within the head space sampling device or the vial containing the head space. One exemplary head space sampling device includes a conduit for receiving a pressurization gas, flow and pressure sensors for measuring gas flow and pressure within the conduit, a ventilation valve, a pressure valve for controlling gas flow through the conduit, and a controller for processing and controlling pressure and flow through the conduit.

Abstract: The present invention relates to methods and systems for detecting leaks in a head space sampling device. One exemplary method for detecting leaks in a head space sampling device includes establishing fluid communication between a head space and a pressurization gas conduit. Gas pressure and flow rate are monitored within the pressurization gas conduit during pressurization of the head space. Changes in monitored gas pressure and flow rate are used to evaluate whether a leak exists within the head space sampling device or the vial containing the head space. One exemplary head space sampling device includes a conduit for receiving a pressurization gas, flow and pressure sensors for measuring gas flow and pressure within the conduit, a ventilation valve, a pressure valve for controlling gas flow through the conduit, and a controller for processing and controlling pressure and flow through the conduit.

Abstract: The present invention relates to methods and systems for controlling depressurization of a vial containing a gas sample. The disclosed systems and methods are employed during sampling and/or analysis of the gas sample. One exemplary method for controlling depressurization of a vial containing a gas sample includes establishing fluid communication between a sample loop of a head space sampling device and the head space of the vial. A sample gas pressure is established within the head space of the vial. The sample loop is connected in fluid communication with a lower pressure environment through a ventilation pathway. A ventilation valve within the ventilation pathway is used to vent gas from the vial through the sample loop to the lower pressure environment at a predetermined rate. Devices and systems for depressurizing a vial containing a gas sample at a predetermined rate are also disclosed.

Abstract: Methods and system for sub-ambient pressure control for column head pressure in gas chromatography (GC) systems. The GC system includes an inlet and a capillary column connected to the inlet. The inlet includes a valve that regulates an inlet pressure and pressure sensor that measures the inlet pressure and outputs a signal that indicates a measured inlet pressure. The GC system also includes an inlet-pressure set-point that can be set to a negative pressure set-point representing a pressure below ambient pressure, the negative pressure set-point driving the valve to change the inlet pressure until the measured inlet pressure equals the negative pressure set-point.

Abstract: An oven for a chromatograph is shown in which an oven vent is located with respect to an oven fan assembly and an oven vent assembly. In certain operating conditions, the oven fan assembly and the oven vent assembly are controlled by a computer to cause an exchange of cavity air and ambient air to decrease the level of concentration of combustible gases present in the oven.

Abstract: An analytical instrument preferably in the form of a chromatograph includes a computer, a pneumatic controller responsive to the computer, and planar manifold assembly. The planar manifold assembly includes one or more fluid-handling functional devices that may be surface mounted to a planar manifold. The fluid-handling functional device may be constructed as a valve, operable in response to a control signal from pneumatic controller for controlling fluid flow in selected fluid flow paths in the chromatograph, or as a sensor, a fluid regulator, a fluid flow input or output line, or the like.

Abstract: An oven for a chromatograph is shown in which an oven vent is located with respect to an oven fan assembly and an oven vent assembly. In certain operating conditions, the oven fan assembly and the oven vent assembly are controlled by a computer to cause an exchange of cavity air and ambient air to decrease the level of concentration of combustible gases present in the oven.

Abstract: An improved pneumatic control system suitable for use in providing servo control of one or more active devices in an analytical instrument includes a series pass element that effects partial regulation of an unregulated voltage to remove any high frequency supply voltage variations (including but not limited to a ripple component), but need not regulate the low frequency voltage variations, the effects of which are compensated by a loop gain compensation scheme operable in a servo control loop. A digital signal processor employed in the servo control loop uses a voltage sense signal representative of the regulated supply line voltage to generate a correcting term for use in a proportional integral derivative (PID) control algorithm operating in control loop firmware. The correcting term causes an inverse proportional change in the control loop gain.

Abstract: A frequency response of a pneumatic system used to control a gas chromatograph may be determined by applying a loop-closed direct method. The loop-closed direct method can be used to describe a frequency response of a time-invariant, linear system and predicting the system stability for any input signal. The transfer function which describes the frequency response is used by a microprocessor to control the physical parameters of the pneumatic system in terms of pressure and flow.

Abstract: An analytical instrument preferably in the form of a chromatograph includes a computer, a pneumatic controller responsive to the computer, and planar manifold assembly. The planar manifold assembly includes one or more fluid-handling functional devices that may be surface mounted to a planar manifold. The fluid-handling functional device may be constructed as a valve, operable in response to a control signal from pneumatic controller for controlling fluid flow in selected fluid flow paths in the chromatograph, or as a sensor, a fluid regulator, a fluid flow input or output line, or the like.

Abstract: A method and apparatus for correcting flow and pressure sensor drift in a gas chromatograph. At a convenient time when the chromatograph is not being used for analysis, the input valves controlling the input into the chromatograph are shut, reducing internal flow to zero. The indicated rate of flow is then measured using the flow sensor. If the value measured by the flow sensor during this test is different than the originally calibrated offset by some predetermined amount, then the newly measured value replaces the stored offset value. In a chromatograph where some minimum internal gas or liquid flow is necessary to prevent contamination of the instrument, a three-way valve can direct liquid or gas flow away from the flow sensor during this calibration run without eliminating internal flow through the chromatograph. To calibrate the pressure sensor, the pressure sensor is vented to ambient air pressure and its reading at that pressure is then used as an offset during later sample analysis.

Abstract: Chromatographic system includes a split/splitless injection port operatively connected to an inlet line for receiving the regulated carrier gas flow, a separation column for receiving at least a portion of the mixture as a column flow, and a split vent line and a septum purge line for outputting respectively a split flow and a septum purge flow. A forward device driver operatively connected to a respective fluid controller controls fluid flow in the inlet line and a back device driver operatively connected to a respective fluid controller controls fluid pressure in the split line. A setpoint controller provides first and second setpoint control output values to a configuration module, which selectably configures the provision of each of the first and second setpoint control output values to a selected one of the forward and back device drivers according to the selection of a split or splitless injection mode.

Abstract: Apparatus and method are provided for controlling at least one physicochemical property of carrier fluids and/or support fluids provided to chromatographic detectors by determining a physicochemical property of the one or both fluids and controlling that property using interactive feedback loops.

Abstract: An improved method for coating multi-piece explosion-proof housings with a corrosion-resistant material which permits assembly and disassembly without interference with the corrosion-proofing function of the coating is disclosed. The method features assembly of the portions of the housing together with spacer means and dipping or otherwise coating the housing portions with a corrosion-resistant material. The spacer is formed in order to cause seal members to be formed directly in the coating which are brought into compression with one another upon subsequent assembly of the housing without the spacer so that an effective seal is provided.