Determination of mono- and disulphonated azo dyes by liquid chromatography–atmospheric pressure ionization mass spectrometry

Abstract

Liquid chromatography–atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) with positive (PI) and negative (NI) modes of operation and liquid chromatography–high flow pneumatically assisted electrospray (ES) mass spectrometry with negative mode were used for the determination of the disulphonated azo dyes Acid Red 1, Mordant Red 9, Acid Red 13, Acid Red 14, Acid Red 73, Acid Yellow 23, Direct Yellow 28 and Acid Blue 113 and of the monosulphonated azo dyes Mordant Yellow 8, Mordant Black 11 and Mordant Black 17. High fragmentation was observed when using APCI with losses of one or two SO3Na groups, either attached to one ring or two different rings. Losses of Na and 2Na are common to all techniques used. High flow ES was the most sensitive technique for all the dyes studied, except for Mordant Red 9, with a linear range varying from 1–3 to 700–800 ng. APCI using negative ion mode was one order of magnitude less sensitive than ES, with a linear range varying from 50–70 to 2000–3000 ng, whereas positive ion mode APCI-MS showed the poorest linear range and sensitivity. The determination of Direct Yellow 28 and Acid Blue 113 in water samples was also reported by preconcentrating 500 ml of water with solid-phase disk extraction followed by LC–high flow pneumatically assisted ES-MS.