GAS CHROMATOGRAPHIC ANALYSIS OF AMINO ACIDS AS ETHYL CHLOROFORMATE DERIVATIVES.
MICHAEL R. SCHILLING, HERANT P. KHANJIAN, & LUIZ A. C. SOUZA
2 SCOPE OF RESEARCH
The split injection technique employed by Hušek (1991) could not be used in the analysis of paint samples from objects. Excessively high detection limits result from split injection because only a small fraction of the sample solution is transferred to the GC column (the remainder is diverted to a vent).
Much lower detection limits may be achieved using splitless injection, a technique in which nearly the entire sample is deposited into the GC column for analysis. To use splitless injection, it is necessary to reduce the initial temperature of the oven to a value below the boiling point of the solvent, modify the GC temperature program, increase the helium flow rate through the column, and use a column that is compatible with the solvent. Trial usage in our laboratory of an untested splitless injection procedure (Hušek 1991) resulted in premature failure of the OV-1701 capillary GC column, caused by stripping of the stationary phase by the chloroform and acid components of the derivatization solvent. Eventually, a satisfactory procedure was developed that exhibited the requisite sensitivity for analysis of samples from art objects without causing unnecessary damage to the capillary GC column.
The amino acid composition data appearing in this article were obtained from various sources. From a thorough study of the conservation literature, a number of references were located that contained the amino acid compositions for common proteinaceous binding media and adhesives. The data in these articles were obtained by various analytical techniques: ion chromatography (Keck and Peters 1969), high-performance liquid chromatography (Sinkai and Sugisita 1990), and elemental analysis (Bergquist 1981; Hall 1981).
To augment the existing literature data, the ECF method was used to analyze a large number of proteinaceous materials. These samples were collected from various sources for testing; the primary source was the binding media library of the Getty Conservation Institute (Stulik et al. 1991). This library consists of more than 1,550 samples of modern and historical organic binding media donated by individuals and institutions or obtained from vendors; it includes 320 proteinaceous materials. The collection exists for the purpose of advanced scientific study and is especially useful as a source of materials for research.