Thyroxine
| 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 |