Capillary electrophoresis coupled to negative mode electrospray ionization-mass spectrometry using an electrokinetically-pumped nanospray interface with primary amines grafted to the interior of a glass emitter

Abstract

We demonstrate an electrokinetically pumped sheath flow nanospray interface for capillary electrophoresis coupled to negative mode electrospray mass spectrometry. In this interface, application of an electric field generates electro-osmotic flow at the interior of a glass emitter that is pulled to a 10–20 micrometer inner diameter orifice. Electro-osmotic flow pumps liquid around the distal tip of the separation capillary, ensheathing analyte into the electrospray electrolyte. In negative ion mode, negative potential applied to an untreated glass emitter drives sheath flow away from the emitter orifice, decreasing the stability and efficiency of the spray. In this manuscript, we treat a portion of the interior of the electrospray emitter with 3-aminopropyltrimethoxysilane, which grafts primary amines to the interior. The amines take on a positive charge, which reverses electro-osmosis and generates stable sheath flow to the emitter orifice under negative potential. Negative mode operation is demonstrated by analyzing a metabolite extract from stage 1 Xenopus laevis embryos. Production of the treated emitters was quite reproducible. We evaluated the performance of three emitters using a set of amino acids; the relative standard deviation in peak intensity was 7% for the most intense component.

Recent advances in capillary electrophoresis‐mass spectrometry: Instrumentation, methodology and applications

“…Sarver et al. modified the nanoSL interface developed by Dovichis group (commercialized by CMP Scientific) in order to perform ESI in negative ionization mode . They obtained stable spray conditions by using 10 mM ammonium acetate in 70% methanol as sheath liquid and coating of the emitter with 3‐aminopropyltrimethoxysilane to reverse the EOF in the used glass emitter.…”

Profiling nucleotides in low numbers of mammalian cells by sheathless CE–MS in positive ion mode: Circumventing corona discharge

“…Recently, Sarver et al. also reported on the detrimental effect of corona discharge when using borosilicate emitters in an electrokinetic sheath‐liquid interface for coupling CE to MS in negative ion mode . Though, corona discharge could be attenuated in our previously developed CE‐MS method for anionic metabolic profiling, the employed low‐pH separation conditions were not optimal for profiling acidic compounds, especially for the analysis of nucleoside triphosphates, such as ATP, GTP, and UTP, which were not detected.…”

On‐line capillary electrophoresis/laser‐induced fluorescence/mass spectrometry analysis of glycans labeled with Teal™ fluorescent dye using an electrokinetic sheath liquid pump‐based nanospray ion source

“…Although high reactivity and separation efficiency of the Teal™ dye in CE/LIF assays have been reported earlier, MS detection of Teal‐labeled glycans is highly desirable to generate accurate identification and minimize peak assignment ambiguity. The CE/MS method that we adopted for the analysis of Teal‐labeled glycans uses an electrokinetically pumped nanospray sheath liquid CE/MS interface design (Figure S1, supporting information) . The analytes are injected into the separation capillary from the capillary inlet, which is placed inside the CE system.…”

“…However, soon it was realized that the BGE of 0.7 M ammonia, 0.1 M ɛ‐aminocaprioic acid, 70% methanol as previously reported generated very high mass spectrometry background, preventing effective glycan identification. Taking into consideration that the previously reported CE/MS work was carried out using a much higher sheath liquid flow than that on the EMASS‐II ion source, it was decided to remove ɛ‐aminocaprioic acid from the formulation, and only use ammonium hydroxide and methanol in the BGE buffer. Figure shows the CE/MS result of a mixture of Teal‐A2F and unlabeled A2F using 0.5 M ammonium hydroxide, 50% methanol.…”