Sheathless interface to match flow rate of capillary electrophoresis with electrospray mass spectrometry using regular‐sized capillary

Abstract

RATIONALE:The flow rate match has been a great challenge when coupling capillary electrophoresis (CE) with electrospray ionization mass spectrometry (ESI-MS). Conventional CE-ESI-MS interfaces used liquid sheath flow, narrowed capillary or additional pressure to meet this requirement; sacrifice of either capillary inner diameter (i.d.) or separation efficiency is often inevitable. Thus, a regular-sized capillary-based sheathless interface would be attractive for flow rate match in CE-MS. METHODS:The regular-sized capillary-based CE-MS interface was achieved by coupling CE with induced electrospray ionization (iESI) which was stimulated by the fact that the iESI could both achieve flow rate down to 0.2 μL/min and retain ionization efficiency. The CE-iESI-MS interface was completed with an intact separation capillary, outside the outlet end of which a metal electrode was attached for the application of alternating current (ac) high voltage (HV). RESULTS: The feasibility of this CE-iESI-MS interface was demonstrated through the stable total ion chromatograms obtained by continuous CE infusion of tripropylamine with regular-sized capillaries. Tripropylamine and atenolol were separated and detected successfully in phosphate buffer solution (PBS) by CE-iESI-MS using a 50 or 75 μm i.d. capillary. Furthermore, this new interface showed a better signal-to-noise (S/N) of 3 to 7 times enhancement compared with another sheathless CE-ESI-MS interface that using one high voltage for both separation and electrospray when analyzing the mixture of tripropylamine and proline in NH 4 OAc buffer. In addition, the reproducibility of this interface gave satisfactory results with relative standard deviation (RSD) in retention time in the range between 1% and 3%. CONCLUSIONS: The novel sheathless CE-MS interface introduced here could match conventional electroosmotic flow (EOF) with electrospray which could also preserve the separation efficiency and sensitivity of CE-MS. This newly developed CE-iESI-MS interface was also demonstrated to be effective for different buffers, PBS and NH 4 OAc, without any additives such as methanol and acetic acid. Hence, we believe that this sheathless CE-MS interface could be operated with other nonvolatile and volatile buffers. Copyright © 2016 John Wiley & Sons, Ltd.The combination of capillary electrophoresis (CE) and mass spectrometry (MS) [1][2][3] has become a powerful technique for separation and detection of a broad range of compounds since it was introduced in the late 1980s. [4] To date, electrospray ionization (ESI) has been the most frequently used interface for CE-MS coupling. However, there are two major challenges when interfacing CE with ESI-MS. One is to maintain a constant electrical contact for both CE separation and the ESI process. A sheath or make-up flow [5][6][7] can be used to mix with the CE effluent at the outlet to establish the electrical contact. While for sheathless interfaces the electrical contact was established by direct application of high voltage (HV) via a conductiv...

Applications of capillary electrophoresis for biopharmaceutical product characterization

“…Although quite a few commercial interfaces have been introduced in the past, practical difficulties in coupling CE with MS still remains an issue. Several improvements in sheath flow, liquid junction, and sheathless interfaces have been reported offering improved stability and sensitivity [156][157][158][159][160]. Advances in capillary coatings were also reported with demonstrated applications of analyzing protein samples with UV and MS, for example, the use of double-layer polyvinyl alcohol (PVA) coated capillaries for better detection of glycans in a human serum sample [161,162].…”

Recent trends of capillary electrophoresis‐mass spectrometry in proteomics research

“…In contrast, the sheathless interface can significantly enhance signal/noise due to decreased analyte dilution and background noise, as the BGE is the only liquid in the system (Fonslow and Yates, ; Yin et al, ). In this configuration, the main challenge is maintaining CE flow while generating a closed electrical circuit between the CE separation and the ESI source (Fonslow and Yates, ).…”

“…This has been accomplished in two different ways. The first method includes an ESI tip coated with a highly conductive metal emitter (gold) or detachable porous emitter to transfer the high voltage to the liquid (Yin et al, ; Hocker et al, ). A second strategy includes a porous region close to the ESI tip for electrical connection through an electrolyte (Fonslow and Yates, ).…”

Revealing the potential of capillary electrophoresis/mass spectrometry: the tipping point

“…Different research groups, mainly experts in separation sciences and CE, have developed their own type of CE/MS interfaces, certainly motivated by the absence of commercial alternatives to sheath‐liquid interfaces . The various CE/MS interfaces resulting from these technical improvements can be divided in two major categories; sheath‐flow CE/nanoESI‐MS interfaces which tend to reduce to the minimum the flow rate of the sheath liquid and sheathless CE/MS interfaces that do not require a sheath liquid to enable online CE/ESI‐MS hyphenation …”