Rapid Microdetermination of Hydroxyproline in Biomedical Samples by Flow Injection Analysis Using Cysteine as an Antioxidant

A new practical method for the rapid microdetermination of hydroxyproline (Hyp) in biomedical samples, such as tissue and urine, in the presence of a definite amount of cysteine as antioxidant was established by means of the modified KISO method using flow injection analysis. This method uses no organic solvent and requires only 9 min for each sample, which can be injected every 3 min (about 5 h is sufficient for 100 samples). A good linear relationship (r=0.99996) was obtained between the concentration of Hyp (0–80μg/ml) and the absorbance (0–0.514). In biomedical samples (hydrolyzates of rat stomach tissue), the recoveries (94.8–103.7%) and the reproducibility (the mean of RSD; 0.484% for ten kinds of rat tissues) were satisfactory. The correlation between values from this method and from the conventional KISO method was shown to be good enough (r=0.966) for hydrolyzate samples (N=95), when a proper amount of cysteine solution was added to both the sample and standard solutions and the concentration of the oxidant was optimized to Hyp contents.