A fused silica micro-electrospray tip with an electrically floating metal wire insert to achieve more stable electrospray ionization

Abstract

A new electrospray tip with a wire insert was tested and compared with the conventional bare fused silica capillary tip. The new tip combined the approach of conventional fused silica spray tips with those containing metal wires. Here, we used a floating wire so that the tips could be prepared and replaced more easily. With the conventional tip, the electrospray process became unstable and the spray current fluctuated significantly in the presence of an air bubble. When the wire-inserted tip was used under the same conditions, much less signal deterioration occurred. The superior performance of this tip over the conventional tip was attributable to its enhanced electric conduction. [4,5], and petroleum samples [6,7]. Electric energy clearly plays an important role in the ESI process, and the electrostatic field distribution at the emitter is crucial to improving ESI efficiency and stability. The electrostatic field distribution can be even more important for the micro-spray ESI [8,9] because it is often carried out without the assistance of drying and/or nebulization gas. For this reason, many studies have been devoted to improving spray tip architecture and subsequent field distribution. Spray tips made of bare fused silica [8,10] The spray tips can be divided into two main categories according to their electric conductivity: those made of a conducting material like stainless steel, and those made of a nonconducting material such as bare fused silica. The electric conduction behaviors of these two types of spray tips have been investigated thoroughly [18]. The solution resistance (R s ) was found to be a significant factor for nonconducting tips, resulting in a large drop in iR s of the applied voltage, especially when remote electric contact was made [18]. This means that the performance of nonconducting tips can be more dependent on solution conductivity than that of conducting tips. However, nonconducting tips are used more widely, presumably because they are cheaper, easier to make and replace, and have a wide range of internal diameters available. Many attempts have been made to improve the electrical conductivity of silica tips, e.g., metal-coated tips [12,13,19]. However, metalcoated tips lack long-term stability and may have a risk for particulate contamination [13,19,20]. Another way to enhance conductivity has involved dipping a metal wire into the solution inside of the capillary as a conducting electrode [21][22][23]. Fong and Chan showed that the placement of a very fine gold-plated tungsten wire (about 10 m) through a glass tip helped to maintain stable ESI for over 3 h at a low flow rate (ϳ25 nL/min) [22]. The inserted wire played an important role in stabilizing the nanospray by providing electrical contact.In this work, a new nano-electrospray tip with a floating metal wire was demonstrated. Unlike previous attempts from other groups [21][22][23], the wire was not connected directly to a power supply, so that it could be easily prepared and replaced. The electric conduction was made to a metal...

Proteomic Analysis of Protein Expression Affected by Peroxiredoxin V Knock-Down in Hypoxic Kidney

“…For long-term ionization stability, a newly developed spray tip was used as previously reported. 25 Tryptic digested peptides (5 µL) were loaded onto the enrichment column with mobile phase A containing 3% acetonitrile in water with 0.1% formic acid. A step gradient was used at flow rate of 300 nL/min.…”

“…The separations were performed on a 75 μm × 250 mm nano-ACQUITY UPLC 1.7 μm BEH300 C18 RP column and a 180 μm × 20 mm Symmetry C18 RP 5 μm enrichment column using a nano-ACQUITY Ultra Performance LC Chromatography System (Waters Corporation, Miliford, MA). For long-term ionization stability, a newly developed spray tip was used as previously reported …”