On-line preconcentration and quantitative analysis of peptide hormone of brain and intestine using on-column transient isotachophoresis coupled with capillary electrophoresis/electrospray ionization mass spectrometry

On-Line Solid-Phase Extraction Capillary Electrophoresis Mass Spectrometry for Preconcentration and Clean-Up of Peptides and Proteins

One of the major drawbacks of capillary electrophoresis (CE) and other microscale separation techniques, for the analysis of low abundant peptides and proteins in complex samples, are the poor concentration limits of detection. Several strategies have been developed to improve CE sensitivity. Here, we describe an on-line solid-phase extraction capillary electrophoresis mass spectrometry method with a commercial C18 sorbent for clean-up and preconcentration of neuropeptides from highly diluted biological samples.

Transient isotachophoresis focusing of DNA and DNA-protein complexes is essentially enhanced by spontaneously dissolved aerial carbon dioxide in electrolytes

The formation of a highly adapted high-E zone is critical to isotachophoresis separation and focusing. Recently, we discovered that the high-E zone is present only in a small portion of electrophoresis channel in the presence of EOF (Liu, S. Q. et al. J. Am. Chem. Soc. 2013, 135, 4644-4647). Accordingly, a much narrower high-E zone is presumably present in t-ITP. If so, it is hard to achieve efficient t-ITP focusing. Indeed, by online coupling t-ITP with CE-LIF immunoassay, the immunocomplexes of carcinogenic BPDE-dG adducts are not efficiently focused using a freshly prepared background electrolyte. Intriguingly, we observed that 20-day stored background electrolyte displays a 10-fold better focusing efficiency. We hypothesize that the unexpected phenomenon is associated with the dissolution of aerial carbon dioxide, which is mainly converted to ionic HCO3(-) in the weak alkaline background electrolyte. Consequently, HCO3(-) of high electrophoretic mobility will be continuously injected into the capillary along with the background electrolyte and act as an alternative leading ion to improve the focusing. By addition of dry ice (without causing significant pH decrease, ΔpH < 0.4) to freshly prepared background electrolytes, we immediately observed the enhanced focusing of immunocomplexes of the DNA adducts. NH4HCO3 and Na2CO3, included in the background electrolyte, also improve the focusing efficiency and reproducibility. All these consistently support our hypothesis. To understand the underlying mechanism, an advanced CE-SMFI was exploited to monitor in real time the motion of single DNA molecules and the E change throughout t-ITP. We uncovered that t-ITP can induce a local high-E zone, but the presence of HCO3(-) in the background electrolyte could greatly increase the E value in the high-E zone, which allows more DNA molecules to rapidly move backward and to be efficiently stacked at LE/TE boundary. This study provides new insight into nonuniform electric field-induced electrophoresis focusing.

Performance and attributes of liquid chromatography-mass spectrometry with targeted charge separation in quantitative analysis of therapeutic peptides

Herein we describe a new method, targeted enhanced multiply charged scans (tEMC), for the quantification of therapeutic peptides in tandem mass spectrometry on the linear ion trap mass spectrometer. Therapeutic peptides with chain lengths between eight and 39 amino acid residues and charge states from 2+ to 6+ were used to evaluate and illustrate the method which relies on the ability to separate ions trapped in a linear ion trap according to their charges. In particular, interference from singly charged ions on multiply charged ions can be effectively minimized. The method requires optimization of relatively few parameters, the most important of which being the exit lens barrier (EXB) voltage, thereby offering substantial time saving in a high-throughput quantification environment that currently relies on selected reaction monitoring.

Recent advances in CE-MS: Synergy of wet chemistry and instrumentation innovations

CE with MS detection is a hyphenated technique which greatly improves the ability of CE to deal with real samples, especially with those coming from biology and medicine, where the target analytes are present as trace amounts in very complex matrices. CE-MS is now almost a routine technique performed on commercially available instruments. It faces currently a tremendous development of the technique itself as well as of its wide application area. Great interest in CE-MS is reflected in the scientific literature by many original research articles and also by numerous reviews. The review presented here has a general scope and belongs to a series of regularly published reviews on the topic. It covers the literature from the last 2 years, since January 2008 till June 2010. It brings a critical selection of related literature sorted into groups reflecting the main topics of actual scientific interest: (i) innovations in CE-ESI-MS, (ii) use of alternative interfaces, and (iii) ways to enhance sensitivity. Special attention is paid to novel electrolyte systems amenable to CE-MS including nonvolatile BGEs, to advanced CE separation principles such as MEKC, MEEKC, chiral CE, and to the use of preconcentration techniques.