Mass Spectrometric analysis of Urine. (A) The negative ion fast atom bombardment ionization mass spectrum of the urine from patient 1. (B) GC-MS analysis of the methyl ester-trimethylsilyl ether derivatives of bile acids in the urine of patient 1 identified with a mutation in the AKR1D1 gene and undergoing bile acid therapy with ursodeoxycholic acid. The following compounds were identified from their mass spectra and retention indices: 1. cholesterol; 2. 3a,7a,12a-trihydroxy-5a-cholanoic and 3b-hydroxy-5-cholenoic acids; 3. unknown; 4. unknown; 5. 3a,6a-dihydroxy-5b-cholanoic; 6. 3a,7b-dihydroxy-5b-cholanoic (UDCA); 7. 3,7-dihydroxy-cholanoic isomer; 8. 3-oxo-7a-hydroxy-4-cholenoic; 9. oxo-dihydroxy-cholanoic; 10. trihydroxy-cholanoic; 11. impurity; 12; dihydroxy-cholanoic acid; 13. 3-oxo-7a,12a-dihydroxy-4-cholenoic; 14. 1b,3a,7a-trihydroxy-cholanoic; 15. 3a,6b,7b-trihydroxy-5b-cholanoic; 16. 3a,4b,12a-trihydroxy-cholanoic; i.s. 1. internal standard, coprostanol; i.s. 2 internal standard, nordeoxycholic acid.