Improving the selectivity and sensitivity for quantifying 8-α-hydroxy-mutilin in rabbit tissues by using basic mobile phases and negative ionization

Simultaneous quantification of candesartan and irbesartan in rabbit eye tissues by liquid chromatography–tandem mass spectrometry

“…al., ; Tan et. al., ) . Accordingly, a quadratic calibration model with a weighting factor of 1/ x 2 was adopted to achieve better accuracy of quantification (Tan et al, ; Tan et al, ; Tan et al, ).…”

“…al., ) . Accordingly, a quadratic calibration model with a weighting factor of 1/ x 2 was adopted to achieve better accuracy of quantification (Tan et al, ; Tan et al, ; Tan et al, ). A representative calibration curve for candesartan is: y = 5.8235 × 10 −10 x 2 + 3.0564 × 10 −4 x – 2.399 × 10 −3 , where y and x represent analyte/IS peak area ratio and analyte concentration, respectively.…”

“…The method validation was conducted according to a validation protocol that was drafted mainly based on European Medicines Agency () and US Food and Drug Administration, ). Additionally, the particular challenges and characteristics of tissue sample analyses were also taken into consideration during the preparation of the validation protocol (Tan et al, ). The validated concentration ranges were 0.1–100 ng/ml for candesartan and 0.25–250 ng/ml for irbesartan in tissue homogenate, which were equivalent to the concentration ranges of 2–2000 and 5–5000 ng/g in tissues, respectively (1 g of tissue was approximated as 1 ml when it was homogenized in 19 ml of homogenization solution).…”

Use of high‐pH (basic/alkaline) mobile phases for LC–MS or LC–MS/MS bioanalysis

“…When the commonly used acidic mobile phase was adopted, no product ions could be found, which led to the use of a pseudo multiple‐reaction monitoring (MRM) transition (from protonated molecular ion to protonated molecular ion, m/z 337 → 337; De Baere, Devreese, Maes, et al, ). By using a high‐pH mobile phase and electrospray negative ionization, we, for the first time, found a true MRM transition for 8‐ α ‐hydroxy‐mutilin, m/z 335 → 179 (Tan, Gu, et al, ). In comparison with the previously published methods using the pseudo MRM transition (De Baere, Devreese, Maes, et al, ), the selectivity and sensitivity were significantly improved (Figure ).…”

“…Apart from basic compounds, acids (Svahn & Björklund, ; X.‐M. Xu, Cai, Zhang, Ren, & Han, ), neutral compounds (Tan et al, ; Tan, Gu, et al, ; Hirabayashi, Sugimoto, Matsumoto, Amano, & Moriwaki, ; Rainville et al, ; Svahn & Björklund, ), and peptides (Oe et al, ) can all benefit from the use of high‐pH mobile phases. Sometimes a basic mobile phase is the only option.…”