Fig. 3.

Product ion spectra of the 3-OH steroids. The precursor ions are [M+⁷Li]⁺ (A) and [M+⁶Li]⁺ (B). The mobile phase consisted of solvent A [0.2 mM LiCl in deionized water (A, B) and 0.1% FA in deionized water (C)] and solvent B (MeOH). 1, 16-OH-E1; 2, 7-OH-DHEA; 3, TH-COR; 4, 11-OH-An; 5, THB; 6, 17-OH-P5. The amount of steroid injected was: 16-OH-E1 and 7-OH-DHEA, 1 ng; TH-COR and THB, 1 ng for A and B and 20 ng for C; 11-OH-An and 17-OH-P5, 20 ng. The analytes were introduced through a two-way valve directly to the mass spectrometer in 20% of solvent B. The m/z of the product ions in each spectrum reflected the ion forms assigned to the structures. The red ions represent the precursor ions for the product ion scan. The blue ions represent the product ions used for the quantitative analysis by MRM.