Highly sensitive spectrofluorimetric determination of L-cysteine based on inhibition of hemoglobin

A highly sensitive spectrofluorimetric method for the determination of L-cysteine based on its inhibitory action on hemoglobin (Hb) activity was developed. The optimal conditions were studied. A linear calibration graph was obtained over the range 2.00 x 10(-7)-1.50 x 10(-6) mol l(-1) for L-cysteine. The relative standard derivation was 1.30% at L-cysteine concentration of 8.00 x 10(-7) mol l(-1) (n=11). Further experimental results revealed that the inhibition of L-cysteine on this system was of the competitive type. The method was applied to determine L-cysteine in protein hydrolysate and cystine electrolyte samples with satisfactory results.