Headspace Sampling via Inert Gas Dilution and Pressure Control
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Solution Overview
Problem
Conventional methods for preparing samples in chromatographic analysis systems, particularly gas-chromatographic analysis from a vial's headspace, face issues such as pressure-dependent sample quantity, valve contamination, and condensation problems during discharge, leading to inconsistent results and potential valve damage.
Innovation Solution
The method involves maintaining the inert gas feed line open during pressure discharge, using a proportional valve and pressure sensor to adjust pressure precisely, and employing an on/off valve with a flow sensor to control the discharge, while diluting the sample with pure gas to prevent condensation, and using a trap to reduce contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a proportional valve is used to control the residual pressure in the loop, then the analytical result becomes independent from atmospheric pressure, but the valve can be damaged or polluted by the sample crossing it
Solution Approach 1:
The patent introduces an intermediary substance (inert gas) that flows through the proportional valve instead of the sample. The sample is redirected through a separate path containing the on/off valve, while the inert gas continues to pass through the proportional valve to maintain pressure control. This mediator protects the sensitive proportional valve from sample contamination while preserving its pressure control function.
Solution Approach 2:
The patent divides the gas flow path into separate segments: one segment carries the sample through the on/off valve and loop, while another segment carries inert gas through the proportional valve. This segmentation allows each valve to handle only the type of fluid it is designed for, with the proportional valve handling only inert gas and the on/off valve handling the sample.
2Object-affected harmful factors
If the discharge duct is heated to prevent condensation, then condensation and valve malfunction are avoided, but major costs and special high-temperature resistant valves are required
Solution Approach 1:
The patent changes the composition parameter of the gas in the discharge duct by continuously introducing inert gas. This parameter change prevents condensation through dilution of the sample components, eliminating the need for thermal parameter changes (heating) or special high-temperature resistant materials.
Solution Approach 2:
Inert gas acts as an intermediary substance introduced into the discharge duct to prevent condensation. Instead of using heat as the protective mechanism, the inert gas physically dilutes the sample components, preventing them from reaching saturation and condensing on the valve surfaces.
3Object-affected harmful factors
If a filter is added on the discharge duct to avoid condensation, then valve malfunction is prevented, but an undesired volume is added on the line
Solution Approach 1:
The patent changes the compositional parameter of the gas mixture in the discharge duct by adding inert gas. This prevents condensation through dilution without requiring physical filtration, thereby avoiding the addition of filter volumes to the discharge duct system.
4Device complexity
If an on/off valve with calibrated flow limiter is used to control residual pressure, then the system is simpler, but the control is approximate and insufficient
Solution Approach 1:
The patent merges two pressure control mechanisms: the on/off valve with flow limiter provides baseline pressure control, while the continuously operating proportional valve provides fine-tuned adjustment. The inert gas flow through the proportional valve allows precise control of the residual pressure in the loop, combining the simplicity of on/off control with the precision of proportional control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures consistent sample quantity, reduces valve contamination, and prevents condensation, maintaining analytical precision and system accuracy without the need for expensive high-temperature valves or additional volume from filters.
Implementation Method 1
the feed line of inert gas is still kept open feeding the gas, according to the invention, together with the sample, to the discharge line
Implementation Method 2
a proportional valve and pressure sensor to adjust pressure precisely
Implementation Method 3
the part of sample exceeding the volume of the loop, when reaches the colder area of the discharge path, where the discharge valve is placed, it can condense
Data Source
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AI summary
The invention concerns a method for preparing a sample to be introduced in a chromatographic analysis system from the headspace of a vial, by introducing a pressurized inert gas in said headspace, controlling the pressure or flow, and subsequently by discharging said pressure from the headspace through a loop having constant volume and through a discharge duct provided with a valve, the discharge duct branching with respect to the feed duct. To eliminate the drawbacks of the known methods, during the step of discharging the pressure, the feed duct is kept open and the pressure in said loop is controlled by detecting the feed and/or discharge pressure.