Method and system for generating vapors of liquid solutions
Inventors
Field, Christopher • Terray, Alexander V • Hart, Sean J • Rogers, Duane A. • Lubrano, Adam • Malito, Michael P.
Assignees
Publication Number
US-9597700-B2
Publication Date
2017-03-21
Expiration Date
2033-06-25
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Abstract
A method and system for generating vapors of liquid solutions where a pneumatically modulated liquid delivery system maintains a defined flow rate for a liquid solution. The pneumatically modulated liquid delivery system includes a flow meter configured to measure a flow rate for the liquid solution flowing from a pressure vessel; a microcontroller configured to determine a pressure necessary to achieve the defined flow rate; and an electronic pressure control unit configured to adjust the pressure inside the pressure vessel. The system includes a nebulizer coupled to the pneumatically modulated liquid delivery system configured to receive the liquid solution from the pneumatically modulated liquid delivery system at the defined flow rate and configured to generate an aerosol of the liquid solution. A heat tube can vaporize the aerosol generated by the nebulizer.
Core Innovation
The invention relates to a method and system for generating vapors of liquid solutions, particularly low volatility compounds, by maintaining a defined, pulse-free flow rate using a pneumatically modulated liquid delivery system (PMLDS) coupled to a nebulizer. The PMLDS uses a closed-loop feedback mechanism where a flow meter measures the flow rate of liquid from a pressurized vessel, a microcontroller calculates the necessary pressure to maintain the target flow rate using a control algorithm, and an electronic pressure control unit adjusts the pressure within the vessel. The nebulizer receives the liquid at the defined flow rate to generate an aerosol, which is then vaporized in a heated tube.
The problem addressed by the invention is the difficulty in producing a stable, pulse-free liquid flow at low flow rates (less than 100 μL/min) with existing syringe or other liquid pumps, which generate oscillations due to mechanical operations such as stepper motors. These oscillations cause fluctuations in trace vapor concentrations, particularly problematic for low volatility compounds like explosives, affecting the accuracy and reliability of analytical instrumentation calibration. Existing nebulizers calibrated for self-aspiration also suffer issues related to tip fouling, viscosity changes, and environmental factors, compromising stable vapor generation.
The invention solves this problem by employing a pneumatically modulated liquid delivery system operating as a closed-loop feedback control system using real-time flow measurement and microcontroller-controlled pressure adjustment. This allows maintenance of a continuous, pulse-free and stable liquid flow over several hours, independent of changing conditions such as liquid volume, temperature, tubing diameter, and liquid viscosity. The system couples this stable liquid delivery with a nebulizer that generates fine aerosol droplets, which are efficiently vaporized in a heated tube to produce consistent and trace concentration vapor streams suitable for calibration and verification of sensitive detection instruments.
Claims Coverage
The patent includes one independent method claim outlining the inventive process for generating vapors from liquid solutions using a pneumatically modulated liquid delivery system combined with nebulizing and vaporizing steps.
Maintaining a defined liquid flow rate with a pneumatically modulated delivery system
Maintaining a constant flow rate of liquid solution by measuring flow rate from a pressure vessel with a flow meter, determining required pressure using a microcontroller, and adjusting pressure inside the pressure vessel with an electronic pressure control unit.
Delivering liquid to a nebulizer to generate aerosol
Delivering the liquid solution at the defined flow rate to a nebulizer that generates an aerosol from the liquid solution.
Vaporizing aerosol in a heated tube
Vaporizing the aerosol generated by the nebulizer in a heated tube to produce vapors.
Using a closed-loop feedback system for flow rate maintenance
Performing the flow rate maintenance continuously in a closed-loop feedback system, with a microcontroller recording measured flow rate and calculating pressure necessary to achieve the defined flow rate using a control algorithm such as PID.
Generating aerosol with high-velocity sheath gas over a capillary orifice
Generating the aerosol by passing a high-velocity sheath gas over the orifice of a liquid-filled capillary containing the liquid solution.
The independent claim covers a novel method for generating vapors by maintaining a stable, defined liquid flow via a pneumatically modulated delivery system with feedback control, coupling it to a nebulizer for aerosol generation, and vaporizing the aerosol within a heated tube to reliably produce stable vapor streams.
Stated Advantages
Provides a more stable, consistent liquid flow rate to the nebulizer without pulse or flow oscillations.
Enables generation of stable vapor streams of trace (sub parts-per-billion) low-volatility compounds.
Achieves high vaporization efficiency with minimal sample consumption, allowing smaller sample volumes and less solvent loading.
Allows reliable generation of parts-per-trillion level vapor concentrations for compounds with vastly different vapor pressures.
System adjusts for environmental and operational changes automatically without user interaction.
Documented Applications
Generation of stable vapors of low volatility compounds such as explosives (e.g., TNT, RDX, PETN) for calibration and verification of analytical instrumentation like inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (OES).
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