Description
Temperature responsive liquid chromatography (TRLC) is a green HPLC mode that uses only water as mobile phase. TRLC is beneficial compared to other temperature based LC-approaches as larger changes in retention and selectivity can be obtained over moderate temperature variations (e.g. between 5 and 55°C). This circumvents the drawbacks observed with high temperature HPLC in terms of analyte and stationary phase stability. To perform separation in gradient mode, this however requires to vary the whole column temperature in a short time span (5-60 minutes). The difficulty in operating temperature responsive stationary phases in traditional column formats (i.e. normal and narrow bore column with an ID between 4.6 and 1mm) is the large thermal mass of the stationary phase support (often silica particles) and especially the column wall (stainless steel or PEEK columns). Whereas the temperature of the mobile phase can easily be tuned by changing the inlet temperature of the mobile phase, the stationary phase and the column wall require a much larger heat flux to obtain the desired variation in temperature in time and space. Similarly to mobile phase gradients, the ideal gradient not only induces a gradual change in retention with time, but also creates a retention gradient along to column length from weakly retained at the front to strongly near the end to obtain a peak compression effect during elution, improving the separation resolution. In the case of a TRLC column, this means that the temperature at the front of the column should be lower than that at the back, creating a positive temperature gradient and negative retention gradient along the column.There are two main methods to change the column temperature, either by changing the temperature of the incoming mobile phase, or by changing the temperature at the external surface of the column wall. The former method is however limited in maximum amount of heat that can be added to or removed from the column due the flow rate and heat capacity of the incoming liquid. The advantage of this approach is however that the desired positive axial temperature gradient is established. Externally supplying the heat using e.g. a forced air oven or water bath allows for much larger heat fluxes, but will heat up the column uniformly along its length. In addition, both techniques will result in the presence of radial gradient of temperature and retention in the column, resulting in additional band broadening.
The goal of this theoretical investigation is to evaluate the possibilities and limitations of different heating methods and column materials for TRLC separations. The different configurations are compared using numerical simulations from a perspective of heating rate, axial and radial temperature gradients and band broadening. It was found that neither heating method can achieve the desired operating conditions by itself and that a combination of both is required to achieve the optimal temperature profiles. Nevertheless, the formation of radial temperature gradients is inevitable and will negatively impact the separation performance in TRLC.
| Periode | 10 okt. 2024 |
|---|---|
| Evenementstitel | 34th International Symposium on Chromatography (ISC 2024) |
| Evenementstype | Conference |
| Locatie | Liverpool, United KingdomToon op kaart |
| Mate van erkenning | International |