Sensitive method of quantifying low molecular weight peptides

LC-MS/MS was performed by focusing on a method of protein removal with TCA as a pretreatment method. The results of the measurements of PTH analogues and CNP-22 in plasma were compared between the case of performing LC-MS/MS after the treatment of protein removal with TCA and the case of employing other methods of protein removal. The method of protein removal with TCA showed a much higher recovery rate compared with the other pretreatment methods. Further, by combining SRM measurement using an inmonium ion derived from a single amino acid with a product ion, sensitive measurement could be realized. From the results of validation of this method, it was shown that the method of the invention has high sensitivity as well as sufficient reproducibility and accuracy. The method of the invention can also be applied to disease diagnosis and pharmacokinetic studies.