High performance liquid chromatography-mass spectrometric analysis of sulphonated dyes and intermediates

This paper reports our results in the analysis of polysulphonated anionic d yes and their intermediates using highperformance liquid chromatography-mas s spectrometry (HPLC-MS). Negative-ion electrospray ionization is the most suitable ionization technique for the molecular mass determination of polys ulphonated dyes or other dyes carrying a negative charge. From the series o f [M-xH](x-) ions and their sodiated adducts [M-(x + y)H + yNa](x-), the mo lecular mass and the number of sulphonic and carboxylic groups can be deter mined. The mobile phase should be compatible with the mass spectrometric de tection, which rules out non-volatile tetraalkylammonium salts usually used as ion-pair mobile phase additives for the HPLC of sulphonated compounds. Some mono- and disulphonated dyes and intermediates can be separated with a queous-organic mobile phases containing 5 mM ammonium acetate, which is the most suitable additive as far as compatibility with MS detection is concer ned. However, the retention of compounds with two or more sulphonic groups is too low for a successful separation both with this mobile phase additive and with ion-pair additives with short alkyl chains. The dihexylammonium. acetate ion-pairing reagent offers a reasonable compromise in terms of suff icient volatility and adequate retention and separation selectivity for the HPLC-MS analysis of polysulphonated dyes. (C) 2001 Elsevier Science B.V. A ll rights reserved.