Category:Analysis of dyes by LC/DAD/MAS
For many years now, one of the primary techniques for identification of natural and synthetic dyestuffs used in cultural artifacts has been high performance liquid chromatography (HPLC or LC). In earlier years, most analyses were carried our using a photodiode array detector (DAD), while in recent years, the use of LC/DAD combined with a mass spectrometer (MS) has become more and more common (LC/DAD/MS). There are many variations in sample preparation techniques, LC instrumentation and operating parameters, ionization techniques and types of mass spectrometers (and their operating parameters). The results produced by one lab using one instrumental setup and group of procedures can differ in some respects from those produced by another lab using different equipment and procedures, and thus similar samples analyzed by various setups are included.
The purpose of this database is to collect data from LC/DAD/MS analyses of actual samples from artifacts and standard dye materials. Each record represents one sample. The record includes information on the sample source, interpretation of the results, the sample preparation procedure, and details of the analytical technique. Images of the chromatograms are included, both DAD signals (at one or more different wavelengths of absorption) and MS (possibly including total ion chromatograms, base peak chromatograms, or extracted ion chromatograms). A table of specific compounds identified in the sample includes common name of the compound, retention time during the analysis, molecular weight (or major ion, if a fragment), and major UV/visible absorbance wavelengths. Finally, images of spectra are included. These include UV/visible absorption spectra of individual compounds and mass spectra. In general, mass spectra that only show the molecular ion will not be included. Spectra that contain collision-induced fragments in addition to the molecular ion, or MS/MS spectra, if acquired, will be included when possible. Many analyses often include small, unidentified peaks. These generally will not be discussed in the analysis record, but users should consult the original data source for full discussion.
This database also includes a compound index, which lists every compound that has been identified in at least one chromatogram currently included in the database, along with the molecular weight, or major ion if the molecular ion is usually not observed, and positions of major UV/visible absorption bands for the compound. These positions can vary somewhat depending on instrumental conditions, and as many bands are broad, users should consult the actual spectra in specific records. Individual compounds may be searched for, and results will indicate all samples in which the compound was identified.