[Establishment and international comparison of reference methods for glycated hemoglobin].

To promote the standardization and harmonization of glycated hemoglobin A1c （HbA1c） testing results in medical laboratories across Beijing， we established a reference method for HbA1c. This method participated in the International Comparison Program for HbA1c Reference Laboratories organized by the European Reference Laboratory Network for HbA1c to validate its accuracy. The experimental samples consisted of HbA1c network reference laboratory proficiency testing samples imported annually from the Netherlands， including six calibrators （A-F）， ten intercomparison samples， several quality control materials， and additional auxiliary samples with International Federation of Clinical Chemistry and Laboratory Medicine （IFCC）-assigned values. The pre-treatment process involved digesting samples with protein endopeptidase Glu-C. The experimental samples were removed from the -80 ℃ freezer and allowed to reach room temperature. Subsequently， 50 μL of Glu-C （mass concentration： 200 μg/mL） was added to each sample vial at a ratio of total hemoglobin to enzyme of 1 mg∶0.01 mg. The volume was then adjusted to a final volume of 500 μL with ammonium acetate solution （50 mmol/L， pH 4.3）. After thorough mixing， the samples were incubated at 37 ℃ for 18-20 h. Using mobile phases of methanol and 0.1% formic acid aqueous solution under gradient elution conditions， the detection of HbA1c in international samples was performed via high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS）. A gradient elution mode was employed for liquid chromatography separation using a Shimadzu C18 column （50 mm×3 mm， 2.2 μm）. The injector temperature was maintained at 4-8 ℃， with a column temperature of 30 ℃. The flow rate was kept constant at 0.6 mL/min， with an injection volume of 5 μL and a total run time of 8 min. The MS detection was performed using electrospray ionization （ESI） in positive ion mode with multiple reaction monitoring （MRM）. The monitored ion pairs for the precursor and product ions of non-glycated and glycated N-terminal hexapeptides are