Ultraviolet detector response of glycine and alanine homopeptides: Some specific features in capillary electrophoresis Original Research Article

UV absorbance of a single peptide bond contribution at 200 nm to the overall optical density of the solute was evaluated with two sets of model peptides composed of either 1–14 glycine or alanine residues. It was documented that in capillary electrophoresis using 57 cm (50 cm to the detector) ×75 μm i.d. capillary and 25 mmol l phosphate buffer pH 2.5 containing or devoid of 0.35% hydroxypropyl-methylcellulose (HPMC), the detectorʹs response per peptide bond drops down in peptides containing five glycine or alanine residues. This limiting absorbance value was shown to increase again with the increasing length of the peptide chain reaching either a constant value (glycine and alanine peptides) run in the absence of HPMC at elevated (50°C) temperature or exhibiting a second stepped drop with alanine peptides run at 25°C or in the presence of the polymeric sugar in the background electrolyte. The reasons of this hypochromic effect are discussed.