The effect of nucleotides in newborn is determinant in this first stage of life, and their correct level in breastmilk is vital. We have designed a new method for the assay of nucleotides in milk by capillary electrophoresis (CE) after acid hydrolysis. Breastmilk samples were collected from healthy mothers (ages, 25-35 years) of one month lactation, and stored at -20°C. The duplicated samples were dissociated by acid hydrolysis (HClO4) and filtered through 45 mm pore size Millex filters before assay by CE on a P/ACE System 5510 (Beckman Coulter), with a silica capillary, alkaline separation system, and UV detection in the range 190-300 nm. The method gave good recoveries of 5´-mononucleotides. Under the conditions used, the actual CE analysis time was less than 20 minutes.

The physiologically and nutritionally important nucleotides were detected at concentrations of 387 mg/100ml for UMP-5P, 385.3 mg/100ml for AMP-5P, 67 mg/100ml for CMP-5P, 172 mg/100ml for TMP-5P and 315 mg/100ml for GMP-5P. Nucleotides are a significant nutrient in infant growth, and capillary electrophoresis is a sensitive and efficient tool for the assay of nucleotides with a purine or pyrimidine base in breastmilk.

These data will serve to perfect commercial infant formula milks, and bring them closer to the reference standard represented by breastmilk.