WHAT IT IS
Fraction collection in liquid chromatography (LC) is the process of capturing separated peaks from the column outlet into containers for further use. Instead of sending the effluent only to the detector or waste, a fraction collector diverts selected parts of the chromatogram into vials, tubes, or plates. Key performance parameters are collection accuracy — how precisely the system captures target peaks — and collector capacity, which defines how many fractions can be stored.
HOW IT WORKS
The fraction collector is connected downstream of the column and detector. Peaks are directed into containers either by time programming, detector signal thresholds, or software-controlled windows.
Accuracy - The system must compensate for delay between detector signal and fraction valve switching. This is managed using delay calibration or an in-line sensor that measures flow and adjusts timing.
Calibration - Retention time and flow path delay are calibrated so that collected fractions correspond exactly to detected peaks.
Capacity - Vials, tubes, or well plates are arranged in racks. Capacity determines how many fractions can be collected during a run or sequence.
KEY FEATURES
Fraction Accuracy: Controlled by delay volume calibration and optional sensors that synchronize valve switching.
Programmable Triggers: Collection can be based on time windows, detector response, or manual selection.
Formats: Compatible with vials, tubes, or multi-well plates (24–384 wells).
Capacity: Ranges from a few dozen vials to several hundred fractions, depending on rack and plate configuration.
Scalability: Used across semi-preparative and preparative LC systems with variable flow rates and fraction sizes.
IMPACT ON PERFORMANCE
Purity: Accurate timing ensures that only the desired peak is collected, reducing cross-contamination.
Recovery: Correct delay calibration prevents sample loss at the start or end of fractions.
Throughput: Large-capacity collectors support extended runs and unattended operation.
Flexibility: Ability to use different container types adapts collection to downstream analysis or storage needs.
Efficiency: Automated fraction collection replaces manual switching, saving time and reducing error.
CHALLENGES AND LIMITATIONS
Delay Calibration: Misalignment between detector signal and collection timing reduces fraction purity.
Carryover Risk: Incomplete valve switching or rinsing can contaminate adjacent fractions.
Capacity Limits: Small collectors restrict run length or require operator intervention.
Container Choice: Well plates increase throughput but limit fraction volume; large vials handle more sample but reduce number of fractions.
System Cost and Complexity: Advanced collectors with sensors and large racks increase instrument expense and footprint.