Solvent Gradient Delivery with Pre-Formed Mixing for Nano-LC
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Solution Overview
Problem
Nano-flow liquid chromatography systems face challenges in maintaining gradient consistency due to thermal drift and noise in nano-scale flow transducers, leading to composition errors and instability, especially at high pressures, which complicates the delivery of solvents and affects the accuracy of chromatographic separations.
Innovation Solution
A feed-forward control strategy combined with closed-loop feedback control is implemented to compensate for fluid compressibility, using a system with separate aqueous and organic pumps and transducers, and a storage capillary for gradient formation at low pressure, allowing for orthogonal gradient formation and delivery, reducing thermal sensitivity and noise impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If nano-scale flow transducers are used to deliver mobile phase at high pressure, then the chromatographic separation precision is improved, but the thermal drift and noise of the transducer cause composition errors and reduce measurement accuracy
Solution Approach 1:
The system divides the gradient delivery function into two independent segments: a gradient pump that forms the gradient at low pressure, and a delivery pump that transports the pre-formed gradient to the column at high pressure. This segmentation isolates the gradient formation process from high-pressure thermal effects, eliminating transducer drift while maintaining separation precision.
Solution Approach 2:
The gradient is pre-formed in advance by the gradient pump under low-pressure conditions where transducers operate accurately, then stored and subsequently delivered by the delivery pump. This preliminary formation of the gradient before high-pressure delivery eliminates thermal drift effects during the critical gradient formation phase.
2Reliability
If the flow transducer operates at high pressure to maintain fluid integrity, then the delivery reliability is improved, but the transducer noise and limited dynamic range increase composition errors
Solution Approach 1:
The system separates flow measurement functions into two distinct transducers: one for the gradient pump operating at low pressure with accurate measurement capability, and another for the delivery pump monitoring high-pressure flow. This allows each transducer to operate within its optimal measurement range without compromise.
Solution Approach 2:
The pre-gradient storage chamber acts as an intermediary between gradient formation and high-pressure delivery. It decouples the low-pressure gradient formation process from high-pressure delivery, allowing accurate flow measurement during formation while maintaining fluid integrity during delivery through the delivery pump.
3Measurement precision
If thermal compensation schemes are added to correct transducer drift, then the composition accuracy is improved, but the system complexity increases
Solution Approach 1:
The gradient is pre-formed under low-pressure conditions where thermal drift is minimal, eliminating the need for complex real-time thermal compensation during gradient delivery. The preliminary formation occurs in a thermally stable environment, providing accurate gradients without additional compensation hardware.
Solution Approach 2:
By separating gradient formation from high-pressure delivery into distinct operational phases handled by different pumps, the system avoids the need for complex thermal compensation during the critical delivery phase, simplifying the overall system architecture.
4Productivity
If gradient formation is performed at high pressure to maintain fluid integrity, then the delivery efficiency is improved, but the thermal effects and noise during gradient formation reduce mixture consistency
Solution Approach 1:
The system separates gradient formation and delivery into two independent functions performed by different pumps at different pressure levels. The gradient pump forms the gradient at low pressure ensuring mixture consistency, while the delivery pump efficiently transports the pre-formed gradient at high pressure to the column.
Solution Approach 2:
The gradient is pre-formed in advance under low-pressure conditions with stable temperature and accurate flow control, then delivered efficiently to the column. This preliminary formation ensures mixture consistency is established before high-pressure delivery begins.
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 improves the accuracy and consistency of solvent delivery, reduces thermal fluctuations, and simplifies system complexity by eliminating the need for extensive dynamic range extension of flow transducers, enhancing the reliability and efficiency of chromatographic separations.
Implementation Method 1
an open-loop feed forward mode to generate anticipatory control signals based on a parameter of stored energy of the system, wherein the anticipatory control signal calculates a compression flow based on a ratio of compressibility between the aqeous output and the organic output
Implementation Method 2
a storage capillary for gradient formation at low pressure, allowing for orthogonal gradient formation and delivery
Implementation Method 3
using a system with separate aqueous and organic pumps and transducers
Data Source
AI summary
A solvent delivery subsystem for a chromatography device performs relatively low pressure, high flow mixing of solvents to form a gradient and subsequent high pressure, low flow delivery of the gradient to the separation column. The mixing of the gradient is independent and does not interfere with the gradient delivery. To form the gradient, the outputs of an aqueous pump and an organic pump are mixed to fill a storage capillary while a downstream point from the storage capillary is vented to atmosphere. After gradient formation, the vent to atmosphere is closed, the solvent delivery system rises to high pressure, and only the aqueous pump runs for gradient delivery. To maintain integrity of the fluid stream, the solvent delivery system uses feed forward compensation and controls at least one parameter selected from the group consisting of pressure and flow in the conduit means to follow a gradual ramp.