Summary. An improved ion-pairing reversed-phase high-performance liquid chromatography method coupled with evaporative light scattering detection (HPLC-ELSD) was developed to determine spectinomycin and its related substances in commercial samples. The method was validated in accordance with International Conference on Harmonization (ICH) guidelines. The specificity of the HPLC-ELSD method was similar to that of the European Pharmacopoeia (Ph. Eur.) method, and repeatability and robustness were markedly improved relative to other reported methods due to our empirical evaluation of separation columns. Indeed, it is a more specific assay of spectinomycin than traditional microbiological techniques. The HPLC-ELSD method was used to evaluate the impurity profiles of eight compounds in seven spectinomycin batches from five different companies. Liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) was employed to characterize the structures of these compounds. Though the HPLC-ELSD method was not as sensitive as the Ph. Eur. method, its limit of quantitation (LOQ) (0.16%) was lower than the disregard limit (0.3%) described by the Ph. Eur. 7.0. This suggests that the HPLC-ELSD method is appropriate for routine analysis of spectinomycin and its related substances.

A novel and robust two‐dimensional liquid chromatography with ultraviolet detection method (2D‐LC–UV) was developed and validated for high‐throughput determination of the concentrations of valproic acid (VPA) in human plasma. This 2D‐LC system was composed of a first‐dimensional LC column, a second‐dimensional LC column and an intermediate transfer column. The sample was directly injected into the 2D‐LC system after an easy protein precipitation treatment. After online preconcentration and primary separation by the first‐dimensional column, the target was captured by an intermediate column and then transferred to second‐dimensional column for analysis. The system transferred the target through “central cutting” mode whereby the drug peak was not subject to interference from the matrix. The analysis cycle time was completed within 7.0 min. Compared with other methods that have been developed, the analysis time was reduced and the operation was much easier without any derivatization. The calibration curve was linear over the 5.90–188.94 μg/ml range for the VPA concentrations. The intra‐day and inter‐day precisions were <5.6%. The recoveries were in the range from 95.2 to 98.0%. This method appears to be sensitive, precise, rapid and low‐cost for the quantification of VPA in serum sample.

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