Sometimes, off-line is the way to go
The size range accessible to DLS increases greatly when flow is not present. Incorporated into the DAWN, the WyattQELS can be installed at any of the 18 scattering angles supported by the read head, in order to optimize batch measurements of mixed nanoparticle sizes.
Among other applications, batch DLS is very useful in examining rates of aggregation or dissociation, when the time scales are on the order of a minute or longer (limited primarily by the time it takes to mix a sample and place it in the detector). It also excels at analyzing conformation as a function of temperature and solution properties.
Batch measurements may be performed by injecting sample into the flow cell ("microbatch") or by replacing the flow cell with a scintillation vial. The number and range of useful angles varies with the sample cell geometry.
DAWN or miniDAWN?
The DAWN HELEOS II can be ordered with precise temperature control capabilities with its on-board Peltier heating/cooling accessory. This feature is particularly useful for QELS measurements, where studies may examine particle sizes as a function of temperature.
Incorporated into the miniDAWN TREOS, the WyattQELS module can only be installed at 90°. This limits somewhat the ability to measure complex samples with both soluble and colloidal components.
The WyattQELS may also be used in a DAWN or miniDAWN in batch mode with special 10 µL cuvettes. Even using such small volumes, simultaneous measurements of molar mass are always available.