Analysis of drying oils used as binding media for objects of art by capillary electrophoresis with indirect UV and conductivity detection.
Capillary electrophoresis (CE) was applied to analyse the long-chain fatty acid composition of vegetable oils, and their degradation products formed upon ageing when drying oils are used as binding media. The analytes were detected with contactless conductivity detection (CCD) and indirect UV absorption, both detectors positioned on-line at the separation capillary. The long-chain fatty acids were resolved in a background electrolyte (BGE) consisting of phosphate buffer (pH = 6.86, 15 mM) containing 4 mM sodium dodecylbenzensulfonate, 10 mM Brij 35, 2% (v/v) 1-octanol and 45% (v/v) acetonitrile. As in this system dicarboxylic analytes, the products of oxidative degradation of unsaturated fatty acids, cannot be determined, a suitable background electrolyte was developed by the aid of computer simulation program PeakMaster. It makes use of a 10 mM salicylic acid, 20 mM histidine buffer, pH 5.85, which combines buffering ability with the optical properties obligatory for indirect UV detection. This buffer avoids system eigenpeaks, which are often impairing the separation efficiency of the system. Separation of the dicarboxylic analytes was further improved by a counter-directed electroosmotic flow (EOF), obtained by dynamically coating the capillary wall with 0.2 mM cetyltrimethylammonium bromide. Long-chain fatty acids and their decomposition products could be determined in recent and aged samples of drying oils, respectively, and in samples taken from two paintings of the 19th century.
Surowiec
Izabella
I
Institute for Analytical Chemistry, University of Vienna, Währingerstrasse 38, A 1090 Vienna, Austria.
Kaml
Isabella
I
Kenndler
Ernst
E
D001154:Art; D003998:Dicarboxylic Acids / Q000032:analysis; D019075:Electrophoresis, Capillary / Q000379:methods*; D005227:Fatty Acids / Q000032:analysis; D009821:Oils / Q000032:analysis*; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet
D003998:Dicarboxylic Acids; D005227:Fatty Acids; D009821:Oils