Capillary Electrophoresis as Analytical Method for the Characterisation of Natural Diterpenoid Resins in Artistic and Historic Works: A Comparison with Gas Chromatography

Abstract

We have applied capillary electrophoresis to separate and detect the characteristic main components of diterpenoic resins applied as binders in museum objects, i.e. the abietane and pimarane acids and larixol acetate. Under the influence of the applied high voltage of 15000 V these analytes move in a narrow separation capillary with 50 m inner diameter. This open tube has 48.5 cm total length, with 40.0 cm distance to the detector. Electrophoretic migration is supported (and, in case of the electrically neutral larixol acetate, enabled) by charged additives to the running buffer, which form ionic complexes with the analytes. The separated analytes are detected within less than 15 min by their UV absorbance measured at characteristic wavelengths of 200, 250 and 270 nm. In contrast to chromatographic methods, no derivatisation is needed. As in gas chromatography, identification of the resins is carried out by the peak patterns based on the resin composition. From the comparison with established GC methodology for the analysis of resins it can be concluded that the analytical performance parameters of the capillary electrophoretic method in terms of resolution and analysis time are comparable to those from gas chromatography, whereas the detection limit is higher in general. However, sample pretreatment is simpler for capillary electrophoresis; it consists only in the dissolution of the sample in methanol.