以矽膠層析管含微量胺鹽修飾劑水性移動相之高效液相層析法分析鹼性 藥品
利用高效液相層析法，以矽膠層析管 (silica column) 含微量三乙基胺 ( 低於 0.07%, v/v) 及醋酸 ( 低 於 0.05%, v/v) 之移動相，可以有效分析定量鹼性藥品。本方法可充分改善以矽膠層析管，含緩衝鹽 類高 pH 值移動相或以逆向層析管之離子配對技術法分析時，分析時間冗長、波峰拖尾，不對稱及 移動相配製、層析管及管道清洗費時之缺點。
本研究結果顯示，本方法層析機轉以陽離子交換為主，同時伴隨著疏水基間之交互作用。 pKa 值較 高，或屬四級氨之鹼性藥品，具有較長之滯留時間；藥品化學結構引起之立體障礙會降低滯留時間。
移動相中醋酸添加量增加，會降低鹼性藥品滯留時間；三乙基胺添加量增加雖可提升矽醇基解離程 度，使鹼性藥品獲得較好之滯留，但經氫離子結合之三乙基胺具有正電荷，會與鹼性藥品競爭解離 之矽醇基，使鹼性藥品滯留時間隨三乙基胺添加量之增加降低。移動相含高比例之有機相或水相或 以氰甲烷取代
甲醇均可獲得較長之滯留時間。
應用本法分析美國藥典第 24 版所收載 7 種含有 imidazoline 衍生成分之眼藥水或噴鼻液製劑，結果 顯示可以充分改善該藥典所用的偶離子配對法 (pair-ion chromatography method) 、酸性陽離子交換 法 ( acidic cation exchange method) 或呈色法 (colorimetric method) 繁複費時之缺點；對於含 dextrome thorphan HBr, methylphedrine HCl, chlorpheniramine maleate, noscapine HCl 等感冒製劑、含 ipratropiu m HBr 之氣喘吸入劑等或用於鹼性藥品製劑間生體可用率或相等性研究之分析定量，亦均顯示本方 法之精密度及準確度良好，同時具有方便、省時之優點。研究中以市售藥品，比較四種不同品牌矽 膠層析管分析效能，並以對照標準品建立兩百種藥品之 k’ (Capacity factor) 值，可供產官學界參考 應用。
本研究提供精確、便捷之方法，不但可改善逆向層析法分析鹼性藥品之缺點，且可提升分析效率，
同時又可節省分析成本。
High-performance Liquid Chromatographic Analysis of Basic Compounds on Silica Column with Aqueous Eluent Containing
Trace Amount of Amine Modifiers
A high-performance liquid chromatography (HPLC) method using silica column eluted with aqueous solvent mobile phase co ntaining triethylamine (lower than 0.07%, v/v) and acetic acid (lower than 0.05%, v/v) was developed for determination of bas ic compounds in pharmaceutical preparations. The key advantages of this method are not only to reduce the timing required fo r analysis, mobile phase preparation, cleansing of column and instrument tubing, but also to reduce the occurrence of peak tail ing and asymmetry
The result of this study indicates that the key mechanism of this method is cation exchange, accompanying with the hydropho bic interaction. The higher the pKa value of drugs, the longer the retention time. In addition, the retention time is longer as we ll when those basic compounds belong to the quaternary amine. Nevertheless, steric hindrance caused by chemical structure re duces the retention time. The increase of acetic acid in mobile phase also helps to shorten the retention time. Theoretically, the greater partial ionization of silanol caused by the increase of triethyamine helps to retain basic drugs. However, the protoned t riethylamine that is positive charge competes for —SiO- group with basic compounds. The competition results in the reductio n of retention time of these compounds. On the other hand, the retention time is longer under the circumstance of either the pr oportion of organic or aqueous solvent in mobile phase is high, or acetonitrile replaces methanol.
This study performs significant improvement in the complexity and time consuming resulted from pair-ion chromatography, a cidic cation exchange and colorimetric methods applied in USP XXIV, for the analysis of 7 eye drops and nasal spray prepara tions containing imidazoline derivatives. This method also demonstrates the great precision and accuracy in either the qualitati ve and quantitative tests of marketed pharmaceutical products containing dextromethorphan HBr, methylphedrine HCl, chlorp heniramine maleate, noscapine HCl and ipratropium bromide or the analysis of bioavailability and bioequivalency for basic co mpounds. In this study, four different brands of silica columns are also compared to determine the analytical capability. Mean while, the k’ (Capacity factor) values of two hundred drugs are established for reference.
