RSC ADVANCES, cilt.6, ss.39188-39197, 2016 (SCI İndekslerine Giren Dergi)
This paper describes optimization of LC-MS/MS conditions to develop a method for selective and sensitive determination of estrogens, namely: estradiol (E2), estrone (E1), estriol (E3), and synthetic estrogen as ethinyl estradiol (EE2) by using statistical experimental design methods. The optimization studies were conducted in three stages: (i) determination of minimum alkaline volume ratio (0-17% NH4OH at 0.2 M) in mobile phase to maximize peak area by single factor experimental design; (ii) optimization of LC elution conditions including flow rate, acetonitrile concentration in standard and in mobile phase by Box-Behnken response surface method (RSM), and (iii) optimization of LC-MS/MS conditions for seven factors to maximize peak areas by Box-Behnken RSM. NH4OH volume ratio significantly affected the peak area and it was maximized at 3-5% volume ratio. Predicted optimal LC elution conditions were % ACN(standard): 28, % ACN(mobile): 44 and flow rate of 137 mu L min(-1). The optimum instrumental conditions were determined as sheath gas pressure: 33 arbitrary unit (Arb), ion sweep gas pressure: 0.4 Arb, aux gas pressure: 17 Arb, capillary temperature: 254 degrees C, vaporizer temperature: 352 degrees C, collision gas pressure: 1.9 mTorr, and spray voltage: 2740 V. Optimization provided substantial improvements in peak symmetry and resolution factor and a 20-25 times peak signal gain with respect to the instrumental self-optimized condition at detection limits of ng L-1 levels were achieved. The lower detection limits were obtained by coupling the method with a SPE procedure for attaining high pre-concentration factors. The signal enhancement was about three orders of magnitude, which constitutes a remarkable sensitivity of the method.