Analysis of anka pigments by liquid chromatography with diode array detection and tandem mass spectrometry

Anka is with Monascus sp. fermented rice, which shows a purplish red color. On rice grains Monascus purpureus DSM 1379 synthesized four anka pigments. Through extraction of anka with n-hexane and methanol in succession and through repeated crystallizations from absolute ethanol anka pigments were crystallized into two fractions: orange anka pigments (rubropunctatin and monascorubrin) and yellow anka pigments (monascin and ankaflavin). The treatment of two orange anka pigments with aqueous ammonia solution gave red nitrogen analogues (rubropunctatamine and monascorubramine). The above six pigments were separated into each pigment by two dimensional thin layer chromatography (TLC) or high performance liquid chromatography (HPLC). HPLC-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS-MS) and direct probe mass spectrometry (MS) were used to identify these pigments. HPLC-diode array detector (HPLC-DAD) was used to determine UV-VIS spectra of pigments. Pigments were analyzed with HPLC under the following conditions: C-18 column, acetonitrile/water (80:20, v/v), 0.5 mL min(-1), 233 nm.