Weakly acidic azo dye; originally introduced as a fat stain in 1896. Prepn: R. Nietzki, Ber. 13, 1838 (1880); Colour Index vol. 4 (3rd ed., 1971) p 4227. Description: H. J. Conn's Biological Stains, R. D. Lillie, Ed. (Williams & Wilkins, Baltimore, 9th ed., 1977) pp 168-169, 576. HPLC determn in cosmetics: J. W. Wegener et al., Chromatographia 24, 865 (1987); LC/electrospray-MS determn as environmental contaminant: H.-Y. Lin, R. D. Voyksner, Anal. Chem. 65, 451 (1993). Use as biological stain: W. Frisch-Niggemeyer, J. Virol. Methods 5, 135 (1982); A. Kishida et al., J. Controlled Release 13, 83 (1990). Structure effects on dye adsorption: H. L. Needles et al., Colourage Annu. 1995, 115.