Application of electrospray ionization-mass spectrometry to screen extractants for determination of insulin in an emulsion system by HPLC-UV

Soybean lecithin and phenol intensely interfered in the determination of insulin with HPLC-UV in an emulsion system which was developed for transmucosal delivery. Thus, in this study electrospray ionization mass spectrometry (ESI-MS) with ion trap detection was applied to screen extractants to remove soybean lecithin and phenol in an insulin-loaded emulsion system (IES). The results showed that n-pentanol was a suited extractant to meet the measurement requests because a large quantity of soybean lecithin and phenol were removed simultaneously, and there appeared no interferences brought by n-pentanol in insulin measurement. The analytical method was assessed by the criteria including linearity (linearity range: 1.05-7.34 U/mL and correlation coefficient: 0.99936), accuracy (recoveries: 98.1-102.5%), within-day precision (R.S.D.: 0.5%, n = 6), LOD (0.01 U/mL), and LOQ (0.03 U/mL), and exhibited high sensitivity and specificity, and considerable accuracy and precision on the determination of insulin in the emulsion system. The application of this method had been successfully performed to study the storage conditions of IES, and the results indicated that insulin in IES would be stable at 4 °C in light proof condition, which was significant for further pharmaceutical research.