The invention relates to target-associative tags incorporating cysteamine as the target-associative moiety. The invention further relates to a method for producing a target-associative tag by addition of cysteamine as the target-associative moiety to another molecule or entity having a property or properties useful in discriminating or selecting between members of a set, where such properties could include, for example, fluorescence, mass, affinity, reactivity, size, absorbance, magnetism, subatomic spin characteristics, or an ability to associate specifically or preferentially with certain structures. The invention further relates to a method for analyzing, identifying, or purifying phosphorylated proteins or phosphorylated protein fragments using a tag having the properties of both fluorescence and affinity.