Analysis of ergosteroids

Glycerophosphocholine molecular species profiling in the biological tissue using UPLC/MS/MS

“…4B shows, the signal intensity of the [M+Na] + ion was significantly elevated when the ACN/MeOH ratio changed from 100/0 to 70/30-60/40, followed by a trend that moderately increased with a further increase in the MeOH ratio. The MeOH mobile phase system favored the formation of the sodium adduct when compared to the ACN system in the determination of steroids [32,33]. Perhaps this was due to ACNs lower dielectric constant and/or more complete solvation with the sodium ion via the cyanide functional group, which can reduce the availability of sodium ions for adduct formation.…”

Sensitivity enhancement in liquid chromatography/atmospheric pressure ionization mass spectrometry using derivatization and mobile phase additives

“…They found the response of steroids increased several fold when adding these acids at very low concentrations, the order being: formic acid (50-200 ppm, v/v) > acetic acid (100-500 ppm) > trifluoroacetic acid (5-20 ppm). The signal response for several of the ergosteroids increased more than 10-fold at TFA concentrations about 10 ppm [56]. The addition of formic acid allowed the signal of cholesterol acetate to increase more than 20-fold and made it possible to analyze the compound at the subnanogram level.…”

“…Sensitivity of detection therefore was not improved due to the formation of mixture adducts of [M + Na] + and other [M + Me] + . Marwah found that Ag + could suppress the formation of other metal adduct ions and formed an intense Ag adduct with the analyte androst-5-ene-3␤,17␤-diol [56]. Because higher voltage was needed to form fragment ions, the baseline noise was decreased and resulted in further improvement of detection.…”

Use of trifluoroacetic acid to quantify small, polar compounds in rat plasma during discovery-phase pharmacokinetic evaluation

“…Ion-pairing was investigated to see if it would improve retention and peak shape sufficiently to provide an adequate LOQ [14]. Volatility was an important parameter to consider, since MS detection was going to be used, and better ionization could counter any suppression [15][16][17]. One concern was the established fact that TFA could mask the protonated sample cations from the ESI-MS electric fields by rendering them neutral [18].…”