Temperature-programmed packed-capillary liquid chromatographic separation of polystyrenes

Abstract

SummaryTemperature-programmed packed capillary liquid chromatography with UV detection has been used for the separation of a wide range of polysf,/renes. The low thermal mass of the reversed phase packed capillary columns (0.32-mm internal diameter) allowed rapid temperature programming for retention control. By the use of temperature gradients as steep as 40~ 9 min 1, rapid separations (11 minutes) of polysf,/rene standards (2000-400000) could be achieved. Furthermore, the oligomers of the polyslyrene 1000 standard were resolved using temperature programming. When replacing tetrahydrofurane with acetonitrile as mobile phase component, peak splitting within the ohgomer peaks was observed, revealing some information about the tacticify of the polysf,/rene 1000 sample.

Temperature programming in liquid chromatography

“…Thus, 200 kD polystyrenes had an adsorption enthalpy close to -120 kJ/mol [81]. The ID of the columns used in separation of polymers by temperature programming has gradually decreased from the standard dimensions via 2.1 mm [81] and further down to the packed capillaries [58]. Diastereomers of low MW polystyrenes were separated by temperature programming [58], and later even better by gradient elution [83].…”

“…With temperature programming, a rising baseline may occur due to refractive index changes and can be mathematically corrected by a commercially available software package [57] or by dual wavelength measurements and corrections [58]. In a microcell equipped with optical fibers, no dramatic change in the signal-to-noise ratio was found when the temperature was raised to 1508C [59], while significant changes were found in another study [58]. The refractive index changes can be expected to be a function of the mobile phase and the construction of the flow cell.…”

“…With narrow-bore columns, the flow splitter was removed and a smaller nebulizer allowed efficient deposition of the analytes on rotating germanium discs [58].…”

“…The ID of the columns used in separation of polymers by temperature programming has gradually decreased from the standard dimensions via 2.1 mm [81] and further down to the packed capillaries [58]. Diastereomers of low MW polystyrenes were separated by temperature programming [58], and later even better by gradient elution [83]. Due to the non-linear van't Hoff plots from deviations from the Martin rule, separation of polymers with one unit difference is only possible in the lower molecular mass range.…”

Controlling the retention in capillary LC with solvents, temperature, and electric fields

“…When temperature programming is used with UV detection, a rising baseline is often observed due to refractive index changes, but might also in some instances be due to column bleeding [85]. The rising baseline can be corrected mathematically by a commercial software package [108] or by dual wavelength measurements and corrections [133]. To obtain improved limits of detection and increased linearity, the nebulizer of the ELSD has been modified for the low flow rates used in capillary LC [122].…”