Silver(i) ions are used for chemical ionisation in the electrospray mass spectrometric analysis of neutral metal carbonyls such as [M(3)(CO)(12)] (M = RU, OS), [Re-2(CO)(10)] or [SiFe4(CO)(16)] in a variety of solvents (MeOH, (PrOH)-O-i, THF, or MeCN-H2O).