Chemiluminescence detection of amino acids and related compounds using acidic potassium permanganate, manganese(IV) or tris(2,2′-bipyridine)ruthenium(III)

We have explored the chemiluminescence response of amino acids and related compounds (including the tripeptide glutathione, and disulfides: cystine, homocystine and glutathione disulfide) with several new adaptations of the permanganate and tris(2,2′-bipyridine)ruthenium(III) ([Ru(bipy)3]3+) reagents and a recently developed colloidal manganese(IV) system. The selectivity of the permanganate reagent can be directed towards tyrosine or thiol compounds like cysteine, homocysteine and glutathione by manipulating reaction conditions (providing limits of detection of 4 nM tyrosine and 5 nM glutathione). Colloidal Mn(IV) produced measureable responses with all analytes, but was most suitable for tryptophan, tyrosine, thiols and disulfides, including α-lipoic acid and dihydrolipoic acid, for which the limits of detection were 30 nM and 20 nM, respectively. A stabilised form of [Ru(bipy)3]3+, prepared by oxidising [Ru(bipy)3](ClO4)2 in acetonitrile, exhibited similar selectivity to that of the conventional aqueous reagent. The [Ru(bipy)3]3+ reagent was effective for the detection of secondary amino acids such as proline and hydroxyproline, as well as the disulfide, homocystine.