Analysis of metal complex azo dyes by high-performance liquid chromatography/electrospray ionization mass spectrometry and multistage mass spectrometry

Five metal complex azo compounds were analyzed using negative-ion electrosp ray ionization mass spectrometry (ESI-MS). Mass spectra of all compounds yi eld intense peaks corresponding to [M - H](-) ions without any fragmentatio n, where M denotes the neutral compound with a proton as the counterion. Un der collision induced dissociation (CID) conditions, structurally important fragment ions were studied using the ion trap analyzer with a multistage m ass spectrometry (MSn facility. Synthesized compounds with N-15 atoms in th e azo group facilitated the fragmentation pattern recognition. A reversed-p hase highperformance liquid chromatography (HPLC) method using 5 mM ammoniu m acetate in 70% aqueous acetonitrile as mobile phase was developed making possible the separation of all complex compounds tested, The lower detectio n limits of the ESI-MS method are in the range 10-20 ng of each compound. T he HPLC/ESI-MS method makes possible the monitoring of ligand exchange in a queous solutions of metal complex azo dyes, and also investigation of the s tabilities of the complexes in solution, Copyright (C) 2000 John Wiley & So ns, Ltd.