An analytical method using salting‐out assisted liquid–liquid extraction to quantify ceftriaxone from micro volumes of human serum

Ceftriaxone (CTRX) is a commonly used cephalosporin antibiotic. It is suggested that monitoring plasma/serum concentrations is helpful for its safe use. This study aimed to develop and validate an analytical method for measuring CTRX concentrations in human serum according to International Conference on Harmonization guideline M10. Ten microliters of serum sample was purified using a salting‐out assisted liquid–liquid extraction procedure with magnesium sulfate. The upper layer was then diluted threefold and analyzed using a liquid chromatography–tandem mass spectrometry‐based method with a total run time of 12 min. The linear calibration curve was obtained over the concentration range 5–500 μg/ml. The within‐run accuracy varied from 0.2 to 6.5%, and the precision was ≤8.0%. The between‐run accuracy and precision ranged from 0.7% to 5.6% and ≤6.4%, respectively. Significant carryover was resolved by injecting four blanks after high‐concentration CTRX samples. The recovery rates from spiked serum at low and high concentrations were 44.4 and 43.4%, respectively. Other factors, including selectivity, matrix effects, stability, dilution integrity and reinjection reproducibility also met the acceptance criteria. Serum concentrations in 14 samples obtained from two participants receiving 2 g/day of CTRX were successfully determined using this method.