Polyaniline‐coated nanoelectrospray emitters: performance characteristics in the negative ion mode

Abstract

The increasing tendency to miniaturize analytical techniques has resulted in the widespread use of nanoelectrospray ionization mass spectrometry. A new polyaniline-coated nanoelectrospray emitter has shown increasing promise as a more durable and stable alternative to traditional metal-coated emitters. In this report, the utility of polyaniline-coated nanoelectrospray emitters in the negative ion mode is investigated. Here, oligonucleotides and peptides have been ionized in the negative mode using polyaniline-coated nanoelectrospray emitters. The emitters were found to be durable for at least an hour in the negative ion mode, during which time the signal was stable. The high amount of electrical discharge usually associated with negative ion mode nanoelectrospray was not problematic with the polyaniline-coated emitters. These characteristics make possible the reliable coupling of low-flow separations to negative ion nanoelectrospray without the worry of emitter failure during the course of the experiment.

A sheathless CE/ESI‐MS interface with an ionophore membrane‐packed electro‐conduction channel

“…Negative mode ESI was first applied considering the charge status of the UA, but a stable spray was not achieved as is common in negative mode nanospray [24,32]. Upon applying positive ESI mode, however, high sensitivity detection with a well-defined peak was achieved.…”

“…Initially, the surrounding area of the emitter tip was coated with an electrically conducting material such as silver [19], graphite [20], carbon [21] or gold [22]. An electro-conducting polymer such as polyaniline was even applied [23,24]. In general, however, electrical discharges at the emitter tip often damage the coating, which shortens the lifetime of the electrical contact to less than a few days.…”

Properties of an electrospray emitter coated with material of low surface energy

“…This prevents a stable spraying of negative ions, thereby hindering their coupling to HPLC or other separation methods that require a stable operation of ESI for a longer time period. Nanoelectrospray emitters coated with polyaniline, a conductive polymer, were very recently developed and they are resistant to electrical discharge and durable for at least an hour in the negative ion mode [11]. The tips of FortisTips are electrically non-conductive.…”

Effect of ionization mode in the analysis of proteolytic protein digests

“…However, the negative ion mode is a surprisingly underutilized tool in the analysis of proteins and protein digests. In particular, nanoESI has been shown to analyze oligonucleotides and peptides of low isoelectric point using both metal [21] and polyaniline [22] coated emitters as well as fused silica capillaries [23] and a wire in a pulled capillary [24]. Fewer molecules produce negative ions [25,26] and less salt adduction is observed in the negative ion mode [27], so cleaner mass spectra result.…”

“…Fewer molecules produce negative ions [25,26] and less salt adduction is observed in the negative ion mode [27], so cleaner mass spectra result. Data has already been shown that the negative ion mode can produce less interference for peptides than the positive mode [22]. It should be expected then, that by using the negative ion mode, more information and higher quality spectra from protein digests could be obtained.…”