There is provided a delta-sigma AD converter including a first integrator, a second integrator located on an output side of the first integrator, a quantizer located on an output side of the second integrator, and a first current DA converter receiving an output of the quantizer and providing a negative feedback signal to an input side of the quantizer. The water-sensitive polymer is a copolymer polymerized from one or more alkylene oxide monomers and one or more epoxy-functional monomers. The method involves the use of a catalytic amount of a hindered cyclic oxammonium compounds as a primary oxidant and chlorine dioxide as a secondary oxidant in an aqueous environment. Where a message received at the server is sent in reply to an earlier message it carries the reference of the earlier message.