Chromatography and atomic absorption spectrometry for the assessment of heavy metal distribution among amino acids used in parenteral nutrition formulations-studies with cadmium and lead.

The distribution of Cd (II) and Pb (II) among amino acids in parenteral nutrition formulations was investigated by coupling ion-chromatography (HPLC/IC) and electrothermal atomic absorption spectrometry. The methodology was based on ion-exchange separation and fluorimetric amino acid detection after post-column derivatization. Cd (II) and Pb (II) were assayed in 500-µL fractions of the column effluent. The distribution of Cd (II) and Pb (II) in alanine (Ala), aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), histidine (His), methionine (Met), phenylalanine (Phe), serine (Ser), and threonine (Thr) were analyzed by monitoring changes in the concentration of free amino acids by HPLC/IC. The results indicated that Cd (II) and Pb (II) were distributed according to the following trend: Gly-Cd > Gly-Pb > Ala-Cd > Ala-Pb > His-Cd ∼ His-Pb > Thr-Cd > Thr-Pb > Phe-Cd ∼ Phe-Pb ∼ Asp-Cd ∼ Asp-Pb ∼ Met-Cd ∼ Met-Pb ∼ Glu-Cd ∼ Glu-Pb > Ser-Cd ∼ Ser-Pb. The effects of amino acid concentration and stability constants of amino acid-metal complexes are discussed.