Flow Cell Capillary Refractive Index Matching
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Solution Overview
Problem
In absorbance detectors, the photorefractive effect causes fluctuations in baseline measurement data due to refractive index changes in sample liquids, especially in gradient analysis, as light is introduced and extracted through capillary ends held by resin ferrules, leading to coupling losses and mismatched transmission NA.
Innovation Solution
A flow cell design with a glass capillary and resin holding members with refractive indices between 1.31 and 1.40, and an incident NA of 0.22 or less, where light is directly introduced and extracted through window members, minimizing contact with ferrules and maintaining consistent reflectance across different sample liquids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If light waveguides such as optical fibers are used to introduce light into or lead light out from the flow cell, then light can be transmitted through the capillary, but coupling loss and mismatching of transmission NA occur, greatly reducing the amount of light
Solution Approach 1:
The invention extracts and eliminates the light waveguide component from the system. Instead of using optical fibers to couple light into the capillary, the design allows light to directly enter the capillary from the light source, removing the coupling interface that causes loss and NA mismatching.
Solution Approach 2:
The capillary serves multiple functions: it acts as both the flow cell for liquid chromatography and the light guide for optical detection. By making the capillary itself the light-guiding element rather than requiring a separate waveguide, the system achieves multi-functionality and eliminates coupling losses.
2Loss of energy
If light is directly condensed at the end through which light is introduced into the capillary and emitted as it is from the other end, then coupling loss is reduced, but the photorefractive effect causes baseline fluctuations due to refractive index changes in sample liquids
Solution Approach 1:
The invention introduces an intermediary substance (refractive index matching liquid or coating) at the interface between the holding member and the capillary. This intermediary has a refractive index that matches both the holding member material and the capillary material, eliminating reflections and the photorefractive effect at the coupling interface.
Solution Approach 2:
The invention changes the refractive index parameter of the holding member or interface material to match that of the capillary. By adjusting this optical parameter, the system eliminates the refractive index mismatch that causes the photorefractive effect, thereby stabilizing the baseline while maintaining direct light coupling.
3Reliability
If resin ferrules are used to hold the capillary ends for liquid tightness, then the capillary can be securely mounted, but the interface between ferrules and capillary causes reflectance changes due to refractive index differences
Solution Approach 1:
The invention uses an intermediary material (refractive index matching liquid or coating) at the interface between the resin ferrule and the capillary. This intermediary eliminates the optical discontinuity caused by the refractive index mismatch between the resin and glass, preventing reflectance changes while maintaining the mechanical liquid-tight connection.
Solution Approach 2:
The invention modifies the refractive index parameter of the interface between the holding member and capillary by using matching materials or coatings. This parameter change eliminates the optical reflection problem while preserving the mechanical function of the resin ferrule for secure mounting and liquid tightness.
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 design suppresses the photorefractive effect, ensuring stable baseline measurements and eliminating the need for light waveguides, allowing for precise absorbance measurements without fluctuations during gradient analysis.
Implementation Method 1
a linear capillary is used as the cell in such a manner that light enters through one end side of the capillary in the direction in which the capillary extends so as to be totally reflected from the outer or inner wall of the capillary and transmitted to the other end side of the capillary
Implementation Method 2
the refractive index of the above-described holding member made of a resin in a portion that makes contact with the outer surface of the capillary in all or part of a region through which the above-described light for measurement passes through the capillary is 1.31 or less or 1.40 or greater
Data Source
AI summary
A flow cell includes holding members for holding two ends of a capillary. A refractive index of holding members is 1.31 or less or 1.40 or greater at least in portions through which the holding members make contact with an outer surface of the capillary. A numerical aperture of light for measurement that enters from a light source into the capillary is 0.22 or less so that reflectance of portions through which the holding members make contact with the capillary is constant even when sample liquid that flows through the capillary is converted to water and acetonitrile.