[Determination of sulfur amino acids in feedstuffs by high performance liquid chromatography coupled with pre-column...

A method of quantitative analysis of sulfur amino acids in feedstuffs by high performance liquid chromatography coupled with pre-column derivatization was developed. Before the feedstuffs were hydrolyzed under acidic condition, the cystine and methionine in the feedstuffs were oxidized to cysteic acid and methionine sulfone respectively by performic acid, and then derivatized by 2,4-dinitrofluorobenzene. The separation was performed on an Elite AAK C18 column (250 mm x 4.6 mm, 5 microm) by the gradient elution of 0.05 mol/L sodium acetate and acetonitrile-water (50: 50, v/v) as the mobile phase with a flow rate of 1.2 mL/min at 31 degrees C. The detection wavelength was set at 360 nm. The linearities of cystine and methionine were good in the ranges of 0.4 - 16.0 mg/L and 0.7 - 29.6 mg/L with the correlation coefficients of 0.999 9 and 0.999 8, respectively. The quantification limits (S/N = 10) were 2.6 microg/kg, 3.1 microg/kg, and the recoveries were 100.28% - 102.00% and 105.72% - 107.89%, respectively. The method can be adapted to the accurate quantification of the sulfur amino acids in feedstuffs.