Abstract: Diaza-18-crown-6 compounds of the formula I: ##STR1## wherein X is a phenol, naphthol or quinolinol moiety selected from those of the formulae: ##STR2## R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are independently selected from hydrogen, halo, cyano, nitro, (C.sub.1 -C.sub.6) alkyl, (C.sub.2 -C.sub.8) acyl, acetamido, mercapto, alkyl or arylsulfonyl, trifluoromethyl, aryl, and substituted aryl wherein the aryl moiety is selected from phenyl and naphthyl and the aryl substituent is selected from halo, cyano, nitro, (C.sub.1 -C.sub.6) alkyl, (C.sub.2 -C.sub.8) acyl, phenyl, acetamido, mercapto, alkyl or arylsulfonyl and trifluoromethyl; provided that when R.sub.1, R.sub.2, R.sub.3 and R.sub.5 are hydrogen and X is phenol, R.sub.4 is not nitro; and provided that when X is phenol and R.sub.5 is hydrogen, R.sub.1 (or R.sub.2) and R.sub.4 are not both nitro.

Abstract: A dry immunoassay analytical element, for assaying a ligand, comprising in the following order:(a) a layer containing a labeled ligand;(b) a spreading layer;(c) a receptor layer containing a fixed concentration of an immobilized receptor for the labeled ligand and the receptor is i) covalently bonded to polymeric beads having a diameter in the range of 0.1 to 5 .mu.m and ii) dispersed in a polymeric binder and(d) a support;characterized in that the spreading layer contains a water soluble polymer containing vanadium IV (V.sup.+4) ions.