Determination of available lysine in infant milk formulae by high-performance liquid chromatography.
A high-performance liquid chromatography (HPLC) method to determine available lysine is proposed. Available lysine was measured by an optimised fluorodinitrobenzene method on the basis of the reactivity of the free epsilon-amino group of the lysine. The classical acid hydrolysis has been improved and shortened from the usual time of 12 h to 2 h 30 min using an oil bath. Optimal resolution and quantitation of Nn-dinitrophenyllysine was obtained with a Nova-Pak C18 column using an isocratic elution with 35% methanol and 65% 0.01 M sodium acetate buffer (pH 4.5) and a flow-rate of 1 ml/min. Satisfactory results were obtained for the reliability of the method in terms of linearity from 0.1 to 5.0 mg/l of lysine-free base, precision (R.S.D. values between 4.3% and 7.8%), recovery (91.5%) and sensitivity (detection limit of 0.02 mg/l). The proposed method has also been checked for lack of interferences from other dinitrophenyl-amino acids.
Albalá-Hurtado
S
S
Unitat de Nutruió i Bromatologia, Facultat de Farmàcia, Universitat de Barcelona, Spain.
Bover-Cid
S
S
Izquierdo-Pulido
M
M
Veciana-Nogués
M T
MT
Vidal-Carou
M C
MC
D000143:Acids / Q000737:chemistry; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006801:Humans; D006868:Hydrolysis; D007223:Infant; D007225:Infant Food / Q000032:analysis*; D008239:Lysine / Q000032:analysis*; D008892:Milk / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors
D000143:Acids; D008239:Lysine