AMDIS & EXCEL: A Powerful Combination for Evaluating THM-Py-GC/MS Results from European Lacquers

Abstract

ABSTRACTPyrolysis gas chromatography/mass spectrometry using tetramethylammonium hydroxide (TMAH) for thermally-assisted hydrolysis and methylation (THM-Py-GC/MS) is a powerful analytical technique for comprehensive characterization of organic materials in European lacquers. A daunting challenge, though, is systematically sorting through the vast number of chromatographic peaks in order to accurately locate marker compounds that are characteristic of lacquer artists’ materials. AMDIS (Automated Mass spectral Deconvolution and Identification System) software, developed by NIST, is proven to be capable of extracting and locating library marker compounds in highly complex GC/MS data files. An AMDIS marker compound library of more than 1400 compounds representing Asian and European lacquer and a number of other artists’ materials has been compiled from information in various publications and private communications. A customized Excel workbook was developed to semi-automatically analyse and interpret the marker compound information in the AMDIS search report, using interpretation guides based upon knowledge shared by experts in material characterization that aid in accurate identification. These software tools have been used in training workshops, organized by the Getty Conservation Institute, by scientists with varying levels of GC/MS experience to successfully identify artists’ materials in complex samples from lacquered works of art. Based upon positive feedback from the workshop participants and successful application in their laboratories, we have concluded that the tools may be considered as an Expert System for Characterization with AMDIS Plus Excel (ESCAPE). Examples will be shown for using ESCAPE to identify a wide range of natural products in samples from lacquered objects and easel paintings.