ABSTRACT: We employed a cyanopropylsilane column Zorbax SB-CN (150 x 3.0 mm x 3.5 um, Agilent technologies, Santa Clara, USA) for optimizing the separation conditions.
We use two gradient methods, one of 30 minutes for optimizing TTX retention, and another of 20 minutes shortening the re-equilibration time. For both cases, the mobile phases were A (5 mM formic acid and 5 mM ammonium formate in Milli-Q water) and B (ACN, 5 mM formic acid, 5 mM ammonium formate) at a flow rate of 0.2 mL/min and 45ºC. First gradient elution started to 80%B for 3 min, then decreased to 70%B at 4 min, then to 65%B at 4.5 min, 60%B at 6 min, and maintained for 4 min and thereafter returned back to starting conditions in 15 min and finally 5 min of re-equilibration time was applied. Total run time was 30 min. Second gradient started to 80%B, then decreased to 70%B at 3 min, then to 60%B at 4 min, 55%B at 4.5 min, then increased again to 60%B at 6 min, 70%B at 7 min, and thereafter returned back to starting conditions in 13 min. Total run time was 20 min. MS spectra of both methods were acquired in positive ion mode in the range of 20–400 m/z and a scan rate of 6 scan/min.
10 uL of the TTX 10 ppm solution or from samples of frog extracts were analyzed using an HPLC1260 system coupled to a Q-TOF 6520 (Agilent Technologies, Santa Clara, CA, USA). The Q-TOF mass spectrometer was operated in positive electrospray ionization (ESI) mode in separate runs, employing a full scan mode in the mass range from 20 to 400 m/z and a scan rate of 6.0 scan/s. The mass spectrometer source conditions consisted of gas heater of 350 C, a nebulizer gas flow rate of 13 L/min, a pressure of 45 psi, a capillary voltage of 3500V, fragmentor to 120 V, skimmer voltage of 75 V and octupole RF of 750 V. A constant mass correction was performed during all analysis using an Agilent Standard mix (Agilent Technologies, Santa Clara, USA) with two reference masses: m/z 121.0509 (C5H4N4) and m/z 922.0098 (C18H18O6N3P3F24).
Mabel Gonzalez 
