A new 3, 6, 9-trioxadecylamide of monensin A (M-AM4) has been synthesised and its ability to form complexes with Li+, Na+ and K+ cations has been studied by ESI mass spectrometry, 1H and 13C NMR, FT-IR spectroscopy and PM5 semiempirical method. The ESI MS data indicate that M-AM4 forms complexes with Li+, Na+ and K+ of exclusively 1: 1 stoichiometry which are stable up to cv= 70V. The formation of the M-AM4–Na+ is strongly favoured. ...