Liquid chromatographic separation and detection of n-methylamino acids using mobile phases containing copper(II) ions

The chromatographic separation of N-methylamino acids can be accomplished using a reversed-phase column with an aqueous mobile phase containing copper ions. The N-methylamino acid-Cu complex absorbs UV radiation with λ_max around 235 nm. Thus copperions ifluence the retention times and allows the detection of the above solutes. Unsubstituted amino acids also absorb radiation at 235 nm. The molar absorptivities of the two types of solutes seem to be of the same order of magnitude and the detection limits are therefore also close. The method can be utilized in the simultaneous analysis of amino acids and their N-methyl derivatives. Although the method cannot compete with the sensitivity of amino acid analysers, its simplicity and its detection limits make it useful in such research fields as peptide synthesis.