Zheng Jack, Norton Dean, Shamsi Shahab A
Department of Chemistry, Center of Biotechnology and Drug Design, Georgia State University, Atlanta, GA 30303, USA.
Anal Chem. 2006 Feb 15;78(4):1323-30. doi: 10.1021/ac051480l.
In this study, we report a novel procedure for fabricating internally tapered capillary columns suitable for the coupling of capillary electrochromatography (CEC) to electrospray mass spectrometry (ESI-MS). The internal tapers were prepared by slowly heating the capillary end in a methane/O2 flame. Due to continuous self-shrinking of the inner channel of the capillary, the inside diameter of the opening was reduced to 7-10 microm. The procedure is easy to handle, with no requirement for expensive equipment as well as elimination of problematic grinding of the tip. Several advantages of these new internal tapers, as compared to using externally tapered columns, are described. First, the problems of poor durability and tip breakage associated with external tapering were successfully overcome with the internal taper. A comparison of the online CEC/ESI-MS between external versus internal tapers showed that the latter provides enhanced electrospray stability, resulting in significantly lower short-term noise and very short-term noise values. In turn, the more rugged design of internal tapers allows performing CEC/MS utilizing a harsh polar organic mobile phase, which was not previously successful using an external taper due to higher operating current and electrospray arcing. Next, data on the reproducibility of the internally tapered CEC/MS column using warfarin and beta-blockers as model analytes are presented. For example, when comparing the reproducibility for separation of warfarin under reversed-phase conditions, the internal taper demonstrated superior intraday % RSD (1.6-3.4) as compared to the external taper intraday % RSD (5-6). Last, the applicability of performing quantitative CEC/MS with internally tapered capillaries is demonstrated for simultaneous enantioseparation of beta-blockers. Impressive quantitative results include good linearity of calibration curves (e.g., R2 = 0.9940-0.9988) and limit of detection as low as 30 nM. The sensitive detection of a minor impurity of one enantiomer at the 0.1% level in a major chiral entity buttresses the suitability of compliance with FDA guidelines.
在本研究中，我们报告了一种制造内部呈锥形的毛细管柱的新方法，该毛细管柱适用于毛细管电色谱（CEC）与电喷雾质谱（ESI-MS）的联用。内部锥度是通过在甲烷/氧气火焰中缓慢加热毛细管末端来制备的。由于毛细管内部通道的持续自收缩，开口的内径减小到7-10微米。该方法易于操作，不需要昂贵的设备，也无需对尖端进行有问题的研磨。描述了这些新型内部锥度与使用外部锥形柱相比的几个优点。首先，内部锥度成功克服了与外部锥度相关的耐久性差和尖端破损问题。外部锥度与内部锥度的在线CEC/ESI-MS比较表明，后者提供了更高的电喷雾稳定性，导致短期噪声和超短期噪声值显著降低。反过来，内部锥度更坚固的设计允许使用苛刻的极性有机流动相进行CEC/MS，而使用外部锥度时，由于操作电流较高和电喷雾电弧现象，以前未能成功实现。接下来，给出了以华法林和β-阻滞剂作为模型分析物的内部呈锥形的CEC/MS柱的重现性数据。例如，在反相条件下比较华法林分离的重现性时，内部锥度显示出优于外部锥度的日内相对标准偏差（RSD）（1.6-3.4），而外部锥度的日内RSD为（5-6）。最后，证明了使用内部呈锥形的毛细管进行定量CEC/MS用于β-阻滞剂对映体同时分离的适用性。令人印象深刻的定量结果包括校准曲线的良好线性（例如，R2 = 0.9940-0.9988）和低至30 nM的检测限。在主要手性物质中对一种对映体的0.1%水平的次要杂质进行灵敏检测，支持了符合FDA指南的适用性。
