Principles and Practical Aspects of Preparative Liquid Chromatography

3.5.7 Collecting fractions
using multiple detector
configurations
3.6 Recovery
collection
When multiple detectors are configured in a purification system, fraction
triggering has to be set up properly and several ways of decision making
are possible. A universal interface box can pick up signals from a variety
of detectors. Fractions can be collected when either one or more detectors
recognize an eluting peak. Boolean AND/OR logic is available for this step.
The objective of any purification task is to collect all compounds of interest
based on identification by retention time, UV signal intensity at a specific
wavelength, or abundance of target mass. There can be several possible
reasons for the compounds of interest not being collected:
• Improper fraction collection settings, for example,
target mass, or lower and upper threshold
• Lack of ionization in the mass-selective detector
• Improper selection of methods such as in
a walk-up environment
• Mechanical failure or software error
To avoid complete loss of a sample, more and more purification systems
are equipped with sample recovery locations or dedicated recovery
fraction collectors connected to the waste line of the primary fraction
collector, see Figure 3.45. For each sample there should preferably be
a separate container available to collect what is expected to be waste.
The recovery position together with the sample information must be
reported. This ensures you are able to return the entire sample back to
whoever submitted the sample for purification.
Fractions
Recovery
Figure 3.45 Recovery collection – the volume of solvent not collected
by the main fraction collector is captured by the recovery collector.
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