Analyt: Thyroxine
Matrix: Serum
Measuring Method: GC-ID/MS
Standard: Thyroxine IRMM-468
Internal Standard: ¹³C₆-L-Thyroxine in protein solution - custom synthesis
Sample Processing: Samples are spiked gravimetrically with internal standard and equilibrated, then precipitated with acetone-HCl and extracted into ethyl acetate. Derivatisation (methylation) is with methanolic-HCl-CH3COCl followed by HFBA in tetrahydrofuran and extraction into cyclohexane
Measurement: Measurement at m/z 773 and m/z 779 and m/z 970 and m/z 976