High performance liquid chromatography of slightly soluble brominated indigoids from Tyrian purple

• Published in: Journal of Chromatography A Vol. 1218; no. 9; pp. 1244 - 1252
• Main Authors: Nowik, W., Marcinowska, R., Kusyk, K., Cardon, D., Trojanowicz, M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 04-03-2011; Amsterdam; New York: Elsevier; Elsevier
• Subjects: 6,6′-Dibromoindigotin; Acetonitriles; Acidification; Analytical chemistry; Archaeology; Asymmetry; Bromination; Bromine - chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, High Pressure Liquid - methods; Derivatives; Exact sciences and technology; High performance liquid chromatography; High temperature liquid chromatography; Indigo Carmine; Indirubin; Indoles - chemistry; Marine; Natural dye; Other chromatographic methods; RPLC-PDA; Solubility; Solvents; Spectrophotometry, Ultraviolet; Temperature; Tyrian purple; Archaeology; Indirubin; Natural dye; 6,6′-Dibromoindigotin; High temperature liquid chromatography; Tyrian purple; RPLC-PDA; Chemical analysis; Indigoid dye; HPLC chromatography; Temperature effect; Operating conditions; Reversed phase chromatography; 6,6'-Dibromoindigotin; Diode array; Bromine Organic compounds; Ultraviolet visible spectrometry
• ISSN: 0021-9673; 1873-3778
• DOI: 10.1016/j.chroma.2011.01.004

Attempts at identification of mollusc species producing Tyrian purple from archaeological material are usually done with high performance liquid chromatography in the reversed-phase system, but the peaks obtained are often wide and asymmetric. This is due to the low solubility of the indigoids and their brominated derivatives in the mobile phase, especially 6,6′-dibromoindigotin, which is soluble in only few, particular solvents. Our study focused on improving both symmetry and peak height for more precise quantification. The influence of various factors was evaluated: stationary phase characteristics, mobile phase composition, elution gradient parameters and temperature on the peak shape of the main components of Tyrian purple. The best results were obtained using highly retentive, but moderately bonded ODS stationary phases (about 2.8
μmol
m
−2), percolated with gradient of acetonitrile with acidified aqueous mobile phases (0.1% strong acid) at elevated temperatures (70
°C). The upper quantification limit for 6,6′-dibromoindigotin was improved by over 350%, between standard and optimised systems. Using them, the detection and quantification of trace Tyrian purple components (less than 0.15%) aside from major indigoids becomes possible. Consequently, for the first time, the new analogues of brominated and unbrominated indirubins were found in the shellfish purple from
Hexaplex trunculus.