Simultaneous LC determination of amino acids and creatine in dietary supplements

Dietary supplements are on the market, containing ingredients, which work synergistically to support the metabolic activity and energy capacity of muscle cells to help support and restore physical strength. Amino acids such as aspartate increase resistance to fatigue, thus intensifying the strength of athletes. Acetylcarnitine taurinate is a novel molecular combination of acetylcarnitine with taurine to improving energy production, stabilizing cell membranes and supporting antioxidant functions. Creatine is a nitrogeneous organic acid, which help to supply energy to muscle and is used for the treatment of muscular, neuromuscular, neurological and neurodegenerative diseases. The present communication describes the development and validation of a RP-HPLC method for the simultaneous determination of creatine, asparagine, potassium aspartate, carnosine and acetylcarnitine taurinate. The amino acids were analyzed by pre-column derivatization using the reagent DNFB (2,4-dinitrofluorobenzene). The derivatization reaction was carried out at 70°C in basic medium and the resulting DNB-amino acid derivatives (II) were monitored at λ=360 nm without any interference from the reagent. Creatine lacking of an aminic function did not react in these conditions, so it was determined directly (λ= 208 nm), simultaneously to the amino acid adducts. The chromatographic separations were performed at 33±2°C on a RP-amide C16 column and a RP C18 column using different mobile phase consisting of a mixture of triethylammonium phosphate buffer (pH 3) and acetonitrile (or methanol). The validated method showed to be useful for routine analysis of dietary supplements.