Abstract
Abstract part I:
Investigation of the effect of column temperature in capillary reversed phase high performance liquid chromatography of proteins
The effect of column temperature on separation of proteins in reversed phases capillary LC has been investigated in the range of 25ºC-125ºC. Five proteins have been used as models to study changes in retention time and recovery using a 150 x 0.3 mm PLRP-S column and a water/Acn mobile phase gradient. Generally, the retention time decreases as the temperature increases. No significant reduction in recovery was found below 100ºC.
Furthermore, the proteins were heated prior to injection to cause denaturation, and the effect of denaturation was measured. All model proteins but one showed reduced recovery after being heated to 75ºC and 100ºC for one hour. In no case could renaturation be observed after cooling the proteins for 24 hours. Instead, the recovery of some proteins tended to decrease even more after this “storage”.
It has also been investigated how protein denaturation is influenced by the time period the proteins are exposed to high temperature (residence time). Increased column residence time did not result in more denaturation below 100ºC during a measurement period of 60 minutes. At 100ºC, a significant decrease in recovery was observed for most proteins when exceeding 30 minutes additional residence time on the column.
Additionally, separation of two and three proteins using temperature gradient as an alternative to mobile phase gradient has been investigated. Satisfying separation was accomplished using both mobile phase and temperature gradient without any significant difference in recovery between the modes.
Furthermore, the use of temperature to aid separation of complex mixtures has been investigated on a monolithical 60 x 0.180 mm column. A mobile phase gradient that almost separated a mixture of ten proteins at 30ºC was carried out under different temperature conditions, flow rates, and with or without a preheater to heat the mobile phase prior to the column to investigate if the separation could be improved. Complete separation of all the proteins was not achieved, but the effect of temperature was clearly seen by comparing the chromatograms generated under different conditions.
Abstract part II:
Fractionation and separation of basic plasma proteins using two-dimensional liquid chromatography
In this study, a method for on-line two-dimensional separation of basic proteins in plasma was investigated. The proteins were separated according to their pI value using a strong anion exchange column. Selected fractions were further separated according to hydrophobicity using a PLRP column.
The on-line two-dimensional system failed. Large interfering peaks appeared during the second dimension. Mobile phase components and the trap columns were pointed out as the source of the interferences, but no strategy was developed to deal with the problem.
An alternative off-line system was developed. The method was tested once without providing satisfying separation and was rejected because it was a labour and time consuming method, involving several manual steps.