Abstract: A method evaluates a quality of a dephosphorylation reagent, the method including the steps of: providing a dephosphorylation reagent containing an alkaline phosphatase and a peptide fragment derived from the alkaline phosphatase; and evaluating the dephosphorylation reagent as having a high quality if a content ratio of the peptide fragment to the alkaline phosphatase is a predetermined reference value or less.

Abstract: A composition contains an alkaline phosphatase and first to sixth peptide fragments, wherein content ratios of the first to sixth peptide fragments to the alkaline phosphatase satisfy formulas (1) to (6), respectively: (X1/Y)×100?0.6000 (1); (X2/Y)×100?0.1800 (2); (X3/Y)×100?0.2000 (3); (X4/Y)×100?0.8000 (4); (X5/Y)×100?1.6000 (5); and (X6/Y)×100?0.3500 (6), wherein X1 to X6 represent peak area values of the first to sixth peptide fragments calculated by an automatic integration method from an extracted ion chromatogram obtained by an LC-MS/MS analysis of the composition, respectively, and Y represents a peak area value of the alkaline phosphatase calculated by an automatic integration method from a chromatogram obtained by an LC-UV analysis of the composition.

Abstract: A composition contains an alkaline phosphatase; and a peptide fragment group (A) composed of two or more peptide fragments, wherein each of the two or more peptide fragments consists of 5 to 50 consecutive amino acid residues selected from positions 501 to 578 of the amino acid sequence set forth in SEQ ID NO: 5, wherein a content ratio of the peptide fragment group (A) to the alkaline phosphatase satisfies formula (A): (XA/Y)×100?4.4000 (A), wherein XA represents a peak area value of the peptide fragment group (A) calculated by an automatic integration method from an extracted ion chromatogram obtained by an LC-MS/MS analysis of the composition, and Y represents a peak area value of the alkaline phosphatase calculated by an automatic integration method from a chromatogram obtained by an LC-UV analysis of the composition.