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Silica has been widely used as HPLC column packing material. However, the fact that base can attack the silanol and dissolve the silica embarrasses the utilization of silica stationary phase in high pH mobile phases (pH >8). In our previous research, the use of porous spherical silicon oxynitride (sph-SiON) material from high temperature nitridation of silica microspheres as stationary phase for HPLC has been explored, and the sph-SiON is stable to alkaline mobile phases and demonstrates excellent separation of a variety of polar compounds in hydrophilic interaction liquid chromatography (HILIC) mode. Herein, the degree of nitridation was studied as a function of temperature of nitridation at 750-1 050 degrees C, yielding the silicon oxynitride with 0.40%-12.0% (mass fraction) nitrogen from elemental analysis. At the temperature of 1 050 degrees C, the nitrogen content increased from 12.0% to 24.5% with the nitridation time increasing from 20 h to 120 h. The sph-SiON is stable when disposed in different pH aqueous solutions for one week. The sph-SiON material can be modified to give hydrophobic surface through the reaction of surface Si-NHx with dimethyloctadecylchlorosilane. Elemental analysis and 13C cross-polarization magic-angle spinning (CP/MAS) NMR spectrum of C18-sph-SiON prove the integration of C18 alkyl groups attached onto the sph-SiON surface. The chromatographic evaluation of C18-sph-SiON in reversed-phase separation mode was performed with alkylbenzenes as hydrophobic probes. Three alkylbenzene compounds can be separated and retained well on C18-sph-SiON even in the mobile phase of methanol/H2O (70/30, v/v) with 78 507 plates/m, and an excellent tailing factor (0.95) can be obtained for ethylbenzene. In comparison with C18-SiO2, C18-sph-SiON shows distinct differences with respect to different classes of analytes, i. e. neutral analyte naphthalene, acidic analyte ibuprofen, and basic analyte amitriptyline.

A high performance liquid chromatographic (HPLC) method was established to determine the Huperzine A in the extract of Huperzia serrata. After extracted by methanol/ water/formic acid (10/90/0.2, v/v/v), the sample was filtered for HPLC analysis. The separation was performed on an XCharge C18 column (150 mm x 4.6 mm, 5 microm) by gradient elution with water (containing 0.1% (v/v) trifluoroacetic acid) and acetonitrile (containing 0.09% (v/v) trifluoroacetic acid) as the mobile phases. Rapid separation was achieved within 10 min at a flow rate of 2 mL/min with ultraviolet absorption detection at a wavelength of 310 nm. Under the optimized conditions, good linearity was obtained in the range of 2. 12 - 106 mg/L with the correlation coefficient (R2) of about 0.999 9. The average recovery was 102.34% with the relative standard deviation (RSD) of 0.46%. The intraday and interday precisions were all below 2%. The results demonstrate that this method is simple, rapid and accurate with good reproducibility, and can be used to evaluate the quality of Huperzia serrata.