The experimentally optimised M2S parameters summarised in table I indicate that similar estimates are obtained for the majority of the other pH values. The only exception is the pH region 2 < pH < 7, where we were unable to observe any singlet-filtered signal components, presumably due to short T 2 values associated with the exchange broadening at intermediate pH which is readily visible in figure . The short T 2 values cause strong signal losses during the M2S/S2M pulse schemes.