ARTICLE pubs.acs.org/ac
Characterization of Column Packing Materials in High-Performance Liquid Chromatography by Charge-Detection Quadrupole Ion Trap Mass Spectrometry Caiqiao Xiong,† Xiaoyu Zhou,† Rui Chen,† Yiming Zhang,† Wen-Ping Peng,^ Zongxiu Nie,†,§,* Huan-Cheng Chang,|| Huwei Liu,‡ and Yi Chen†,§ †
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Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, China; Beijing National Laboratory for Molecular Sciences, Beijing 100190, Beijing, China ‡ College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China § Beijing Center for Mass Spectrometry, Beijing 100190, China ^ Department of Physics, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan ABSTRACT: This article reports an application of chargedetection quadrupole ion trap mass spectrometry (CD-ITMS) to characterize the column packing materials in high-performance liquid chromatography (HPLC). Both the mean mass and the mass distribution of the packing materials are obtained and used to calculate the specific surface area of unbonded silica, the carbon load of the bonded silica, and their particle size distributions. The obtained specific surface areas and carbon loads are consistent with those measured independently by nitrogen sorption and elemental analysis respectively, whereas the derived size distributions show better resolution than that measured by a laser particle size analyzer. Furthermore, we evaluate the uniformity of particle size, which is the key parameter for column efficiency of the liquid chromatography by analyzing the mass distribution of the packing materials at the top and bottom of the column. A broader mass distribution, which yields decreased column efficiency, is observed for the column top because of the excessive use of the column. Our results suggest that CD-ITMS can serve as an alternative means for the characterization of the packing materials in HPLC and is potentially useful for column quality control.
’ INTRODUCTION With the development of soft ionization methods such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), mass spectrometry becomes increasingly important among analytical methods.1,2 However, its application is hindered in analysis of macromolecules and synthetic polymers with mass greater than 5 MDa. 3 Such ultrahigh mass particles play important roles in nature such as interstellar dusts, aerosols, biological cells, and so forth. Therefore, the studies on these particles are not only interesting but also of high significance. To solve this problem, the charge-detection quadrupole ion trap mass spectrometry (CD-ITMS) has been developed.410 By taking advantages of the laser-induced acoustic desorption (LIAD) ion source, quadrupole ion trap (QIT) mass analyzer and charge detector, CD-ITMS can be used for rapid detection of particles with micrometer sizes. The mass-to-charge ratio (m/Ze) and the absolute number of charges (Z) can be measured independently by the QIT and charge detector, respectively. The masses and mass distributions of polystyrene spheres and different types of cells has been determined,47 and a mass resolution of ca. 100 and mass accuracy of ca. 1% have been r 2011 American Chemical Society
achieved.8 Recently, a miniature CD-ITMS has been used as a platform for portable mass spectrometer under the rough vacuum of ca. 50 mTorr.9 Besides, CD-ITMS has been successfully used for the quantitative measurement of nano/microparticle endocytosis.10 Cells taken up nano/microparticles are observed to have higher m/Ze values. By comparing the mean cell masses before and after the incubation of gold nanoparticles, the quantity of gold nanoparticles uptaken by cells is determined according to the mass deviations, and the results are proved by the inductively coupled plasma mass spectrometry (ICP-MS) method. Most importantly, CD-ITMS can be used to determine the number of nanoparticles taken up into each individual cell (including the mean and the deviation), whereas ICP-MS provides only a mean uptake for all cells. Furthermore, CDITMS can be used to measure the cellular uptake not only of metal nanoparticles but also of nonmetal nano/microparticles. The silica packing materials, a nonmetal material, on which surface alkyl chains are grafted are the most popular stationary Received: April 14, 2011 Accepted: May 25, 2011 Published: May 25, 2011 5400
dx.doi.org/10.1021/ac200966m | Anal. Chem. 2011, 83, 5400–5406
Analytical Chemistry phase used in high-performance liquid chromatography (HPLC). They are always porous particles with a diameter ranging from 3 to 10 μm.11,12 In recent years, small particles (
