Chromatograph Autosampler Liquid-Contact Detection for Air-Free Sampling
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Solution Overview
Problem
Chromatography systems face challenges in accurately determining the amount of sample in a container, leading to potential air injection into the analysis flow path, which can degrade the separation column, and wastage of remaining sample due to incomplete suction.
Innovation Solution
An autosampler equipped with a sensor circuit that outputs different signals based on needle contact with liquid or air, a liquid-contacting detector to identify the needle's state, and an empty container determiner to stop suction when the needle transitions from liquid to air, ensuring accurate sample detection and prevention of air injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitance sensor is used to detect the liquid level of a sample, then the liquid level can be detected, but the cross sectional area of the sample container must be known and uniform to calculate an accurate amount of sample
Solution Approach 1:
The patent replaces the capacitance sensor-based liquid level detection system with a pressure sensor-based system. The pressure sensor detects the weight of the sample container, directly providing information about the sample amount without requiring knowledge of the container's cross-sectional area or liquid level calculations. This substitution eliminates the need for uniform container geometry and enables accurate sample amount measurement for containers of any shape.
2Ease of operation
If the autosampler continues suction without knowing the sample amount, then the sampling process is simple, but air may be injected into the analysis flow path causing cracks in the separation column filler
Solution Approach 1:
The patent implements a feedback mechanism where the pressure sensor continuously monitors the sample container weight during the suction process. When the weight indicates that the sample has been completely suctioned, the system automatically stops the suction operation. This feedback-based control prevents air from being sucked into the analysis flow path, thereby protecting the separation column from damage while maintaining operational simplicity.
3Reliability
If the autosampler stops suction early without accurate sample amount knowledge, then air injection is prevented, but remaining sample is wasted
Solution Approach 1:
The pressure sensor provides continuous feedback on the sample container weight, allowing the system to determine the exact moment when all sample has been suctioned. This enables the autosampler to continue suction until the very end of the sample supply, maximizing sample utilization while preventing air injection. The feedback mechanism ensures that suction stops only when the container is truly empty, eliminating both sample wastage and air injection risks.
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
Enables automatic and accurate determination of sample presence, preventing air injection into the separation column and minimizing sample wastage by stopping suction when the container is empty, thus maintaining column integrity and optimizing sample usage.
Implementation Method 1
a sensor circuit that is electrically conducted to the needle and outputs different levels of signals when a tip of the needle is in contact with liquid and when the tip of the needle is not in contact with liquid
Data Source
AI summary
In a sucking operation, predetermined amount of a sample is sucked by using a needle from a sample container in which the sample to be analyzed is contained. A sensor circuit, which is electrically conducted to the needle, outputs different levels of signals when a tip of the needle is in contact with liquid and when the tip of the needle is not in contact with liquid. A liquid-contacting detector detects whether the tip of the needle is in air or in liquid by comparing a sensor signal value obtained from a signal output from the sensor circuit during the sucking operation with a preset threshold value. An empty container determiner determines that the sample container is empty when the liquid-contacting determiner detects a change during the sucking operation that the tip of the needle is changed from being in liquid to being in air.