Chromatographic Sample Injection Dilution via Segmented Plugs
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Solution Overview
Problem
Large volume sample injections in liquid chromatography systems often result in peak broadening and breakthrough due to strong solvents, which hinder analysis sensitivity and lead to operator errors and sample loss when attempting to dilute or change solvents.
Innovation Solution
A method and apparatus that inject incremental volumes of sample and mobile phase alternately into the chromatographic system flow, achieving a controlled dilution ratio through proportional incremental volumes and durations, with optional gradient mobile phase introduction post-injection, to maintain peak integrity and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large volume of sample is injected into the mobile phase, then the sensitivity of analysis is improved, but peak broadening and breakthrough occur due to strong solvent effects
Solution Approach 1:
The large volume sample injection is segmented into multiple smaller incremental injections. Instead of injecting the entire sample volume at once, the system divides it into sequential portions, each followed by mobile phase injections. This segmentation prevents the strong solvent effect from overwhelming the column in a single injection, thereby maintaining peak shape integrity while still achieving the desired sensitivity through cumulative analyte loading.
Solution Approach 2:
The method performs preliminary dilution of the sample by alternating incremental sample injections with incremental mobile phase injections before the actual chromatographic separation. This preliminary action reduces the strong solvent concentration in the injected sample, preventing peak broadening and breakthrough during separation, while still delivering sufficient analyte mass to the column for sensitive detection.
2Manufacturing precision
If a smaller volume of sample is used to avoid peak broadening, then peak shape is maintained, but sensitivity of analysis decreases
Solution Approach 1:
The system maintains continuous useful action by repeatedly injecting incremental sample volumes followed by mobile phase volumes over multiple cycles. Rather than relying on a single small injection that would maintain peak shape but provide insufficient analyte mass, the continuous sequence of alternating injections accumulates analyte on the column while keeping each individual injection small enough to preserve peak shape integrity.
3Manufacturing precision
If the sample is diluted offline or evaporated and reconstituted, then the strong solvent effect is reduced, but operator error and sample loss increase
Solution Approach 1:
The system performs the dilution function automatically through the alternating injection sequence without requiring manual sample preparation. The chromatographic system itself serves the dilution function by injecting mobile phase alternately with sample increments, eliminating the need for operator-performed offline dilution or evaporation steps and thereby improving reliability and reducing operator error.
4Manufacturing precision
If incremental volumes of sample and mobile phase are injected alternately, then the sample is diluted maintaining peak sharpness, but the injection process complexity increases
Solution Approach 1:
The injection process follows a periodic pattern of alternating sample and mobile phase injections. This periodic action simplifies control compared to continuous variable adjustments, as the system simply cycles through a predetermined sequence of sample injection followed by mobile phase injection multiple times. The regularity of the periodic pattern makes the process easier to control and reproduce while achieving the desired dilution and peak sharpness.
Data Source
AI summary
Described are a method and apparatus for diluting a chromatographic sample. The method includes repeating an alternating acquisition of sample fluidic plugs each having an incremental volume of sample and diluent fluidic plugs each having an incremental volume of diluent to obtain a stack of alternating sample and diluent fluidic plugs. The stack is inserted into a flow of a mobile phase in a chromatography system. Alternatively, the method includes repeating the steps of injecting an incremental volume of sample into a chromatographic system flow and providing an incremental volume of mobile phase into the chromatographic system flow. In either implementation, the dilution ratio of the sample equals the sum of the incremental volumes of the sample and the diluent or mobile phase divided by the sum of the incremental volumes of the sample.