ESI-MSn analysis of diuretic compounds: unusual mass fragmentation pathways

The analysis of diuretic compounds has become of great concern because of their extensive use both in therapy and in illicit treatments (as masking agents in sport doping and drug abuse). The variety of chemical structures of this class of drugs encouraged the development of new methods and techniques of analysis, especially as regards acidic compounds. LC/MS has so grow to be the reference technique for this kind of analysis in forensic and anti-doping confirmation purposes. Multiple stage MS permits identification of single drugs with high selectivity, but some unexpected pathways could weaken the entire process. In this work we used high resolution MS to try to explain some unusual fragmentation steps. For example, in the case of amiloride an intense product ion in MS3 analysis generates an apparent loss of 10 Da. Water complexation and successive carbon monoxide elimination can explain this uncommon behaviour, which was studied using different ion traps. Bendroflumethiazide MSn spectra show instead 3 successive HF losses, difficult to envisage in the presence of a trifluoromethyl group. Finally homolytic fragmentation with radical ion production appears not so rare as generally reported, as in the case of negative ion fragmentation of furosemide (loss of aminosulphonyl radical) or in the case of protonated positive ion of ethacrynic acid (loss of chlorine radical). Different ionization modes were studied and a tentative correlation with acidic-base properties was done. Multiple stage mass spectra of positive and negative ions were discussed.