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

Abstract

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.

Determination of resin acid composition in rosin samples using cyclodextrin-modified capillary electrophoresis

“…There have been reports of many different analytical techniques used for the characterization of rosins, including GC , pyrolysis‐GC–MS , CE , HPLC , TLC , supercritical fluid chromatography , and micro‐Raman spectroscopy . GC is the first reported and most common method used for determining resin acids.…”

“…Few studies described in the literature apply CE methods to rosin sample analysis. While comparing CE and GC for the separation of binders in museum objects, Dell'Moura et al analyzed a rosin sample using a buffer containing cyclodextrins (CDs) . Six acid peaks were identified in the rosin electropherogram; however, none were quantified.…”

“…The resin acids present in rosins have also been analyzed by various methods such as CE, HPLC and GC–MS in matrices other than rosins, e.g. paint varnish . Luong et al developed what they report to be the first application of CE to the analysis of resin acids in pulp mill effluents and compared it to their HPLC method .…”