The fundamental requirement for a column compartment for liquid chromatography applications is the ability to maintain the preset temperature as precisely as possible. However, for obtaining good measurement results, temperature stability is more important than the temperature accuracy. The advanced electronic circuitry of the column compartment enables the column compartment to maintain the temperature with a precision of ±0.1 °C.
The thermo-optimized design of the column compartment reduces the time required to equilibrate the temperature between the column and the eluent.
Thermoelectric elements heat up or cool down the components in the column chamber. An active or a passive pre-heater can be installed to adapt the eluent to the column temperature, before the eluent enters the column. This avoids temperature gradients in the first part of the column and a loss of separation performance.
VH-C10 only:
In addition, a post-column cooler can be installed to cool down the eluate before it flows into the detector. Post-column cooling minimizes the detector noise and optimizes the detection results.
Thermostatting Modes
The column compartment supports the following thermostatting modes for column thermostatting:
Still air mode
In still air mode, the column warms up over the total length of the column.
The temperature in the interior of the column is the same as in the outer areas.
The eluent and sample travel through the interior of the column with the same speed as they travel through the outer areas (no flow concentration).
In still air mode there is less fronting and tailing of peaks.
Forced air mode
In forced air mode, the column surface is held at the preset temperature over the total length of the column.
The temperature in the interior of the column is higher than in the outer areas.
The eluent and sample travel faster through the interior of the column than they travel through the outer areas (flow concentration).
These factors lead to broader peaks and may impair the separation performance.
The pictures show the thermal distribution inside the column for the two modes:
No. | Description |
---|---|
1 | Direction of flow through the column |
2 | Flow profile |
3 | Same temperature on the column surface |
4 | Temperature increase on the column in the direction of flow |
The eluent travelling through the column generates friction in the column, with the flow rate determining the amount of friction. Friction leads to self-heating of the column. This effect is particularly pronounced with the high flow rates in UHPLC applications because the higher the flow rate is the more friction is generated and the more the column heats up.