The use of electrospray mass spectrometry (ES/MS) for the differential detection of some steroids as calix-[n]-arene sulphonate complexes

Non-covalent inclusion complexes formed between three p-sulphonato-calix-[n]-arenes ( 1 n = 4, 2 n = 6 and 3 n = 8) and three steroids ( progesterone, testosterone and oestradiol) have been studied by electrospray mass spectrometry (ES/MS). Mass spectrometric titration experiments have demonstrated differences with regard to selectivity of each p-sulphonato-calix[n]-arene against the steroids. p-sulphonato-calix-[ 8]-arene interacts more strongly with oestradiol and p-sulphonatocalix[ 6]-arene with progesterone. Studies in which different orifice voltages were applied show that all oestradiol complexes are reduced in signal intensity at 50 V as compared to 20 V, whereas the intensities observed for the testosterone and progesterone complexes do not vary with voltage. Competition experiments confirm the selectivity of the complexation.