Analysis of Acidic Metabolites of Biogenic Amines in Bovine Retina and Vitreous and Aqueous Humour by Gas Chromatography-Negative Ion Chemical Ionisation Mass Spectrometry

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Abstract
Acidic metabolites of a number of biogenic amines have been identified and quantified by reaction with either acetic or propionic anhydride in the aqueous phase followed by extraction into ethyl acetate, esterification of carboxyl groups with ditrifluoromethylbenzyl bromide (DTFMBzBr), and then conversion of the remaining free hydroxyl groups to acetates. Subsequent analysis of these derivatives revealed that most (>60%) of the ion current was carried by the ion resulting from the loss of DTFMBz from the molecular ion. This made the method highly specific and practical—limits of detection were established at ∼200 pg with a potential limit of detection below the picogram level. This method establishes unequivocally that the metabolites of tyramine. dopamine, and adrenaline/noradrenaline (4‐hydroxyphenylacetic acid, 3,4‐dihydroxyphenylacetic acid, and dihydroxymandelic acid, respectively) are present in bovine retina and in vitreous and aqueous humour. In addition, high concentrations of the dopamine metabolite homovanillic acid were found in retina and vitreous, but not in aqueous humour. p‐Hydroxymandelic acid, the acidic metabolite of p‐octopamine‐p‐synephrine, was identified in vitreous and in aqueous humour.