Pervaporation Control in Liquid Degassing Systems
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Solution Overview
Problem
In liquid chromatography systems, pervaporation through membranes can alter the relative concentrations of solvents in the mobile phase, leading to inaccurate analytical results, especially in low-throughput systems or those with incomplete flushing, causing changes in solvent concentrations due to the permeation of higher vapor pressure components across gas-permeable, liquid-impermeable membranes.
Innovation Solution
The implementation of a liquid degassing apparatus with a pervaporation control system that includes a shield member to minimize solvent pervaporation by establishing a limited pervaporation control space between the membrane and the vacuum port, and the use of air flow counteracting potential backflow during non-suction periods of the vacuum pump cycle to prevent solvent cross-contamination among degassing chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If vacuum pumps are programmed to maintain relatively low absolute pressures on the permeate side of the membrane to maximize degassing performance, then degassing efficiency is improved, but pervaporation of higher vapor pressure solvent components occurs causing changes in mobile phase composition
Solution Approach 1:
The degassing system is divided into multiple independently controlled degassing chambers, each with its own vacuum port and pressure control. This segmentation allows different chambers to operate at different pressure conditions - some optimized for degassing while others minimize pervaporation effects on mobile phase composition.
Solution Approach 2:
Different regions of the system are given different functional properties. The patent implements selective pressure control where certain chambers maintain low absolute pressure for efficient degassing while other chambers maintain higher pressure to prevent pervaporation of solvent components, allowing each region to be optimized for its specific function.
2Measurement precision
If mobile phase flow rates are reduced to nanoliters or microliters per hour for low through-put applications, then analytical precision is improved, but pervaporation effects substantially modify relative solvent concentrations during analyte transportation
Solution Approach 1:
The system dynamically adjusts operational parameters including pressure, temperature, and flow rate across different chambers. By changing these parameters locally in different chambers, the system can maintain low flow rates for precision analysis while compensating for pervaporation effects through adjusted pressure and temperature conditions that minimize composition changes.
3Duration of action of stationary object
If degassing chambers operate with relatively high residence time of mobile phase, then complete degassing is achieved, but pervaporative effects concentrate lower vapor pressure components in the mobile phase
Solution Approach 1:
The system segments the degassing process across multiple chambers with different residence times. Some chambers provide extended residence time for complete degassing while others have shorter residence times to minimize pervaporation concentration effects, achieving both goals through spatial distribution.
Solution Approach 2:
The system employs periodic flow patterns and vacuum cycling that create alternating phases of high and low flow rates. During high flow phases, pervaporation effects are minimized while during low flow phases, degassing is enhanced, achieving both objectives through temporal variation.
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 effectively limits solvent pervaporation, maintains consistent solvent concentrations, reduces pressure oscillations, and inhibits cross-contamination of pervaporated solvents, thereby enhancing the accuracy and reliability of chromatographic analysis.
Implementation Method 1
liquid mobile phase is exposed to a degassing environment through a gas-permeable, liquid-impermeable membrane
Implementation Method 2
vacuum pumps are typically programmed to maintain relatively low absolute pressures on the permeate side of the membrane
Implementation Method 3
solvent pervaporation through a membrane is a well known phenomenon that has been harnessed in membrane separation applications
Data Source
AI summary
A liquid degassing apparatus is arranged to prevent pervaporated solvent cross-contamination by counteracting liquid vapor pervaporation flow. Liquid vapor pervaporation cross-contamination among a plurality of degassing modules is counteracted with specifically configured volumes and bleed inlet flow to conduits fluidly coupling permeate sides of said plurality of degassing chambers.