CE‐ESI‐MS of biological anions in plastic capillaries at high pH

Abstract

In this study, the potential of poly(methylmethacrylate) (PMMA, Plexiglas) and polyether ether ketone (PEEK) tubing for CE-ESI-MS separations of anions at high pH values was examined. A set of model compounds of biological interest was used to investigate the main operational parameters for CE-ESI-MS, such as the sheath-flow interface design, the polarity of the ionization voltage, the use of ammonia-based separation electrolytes, and the sheath liquid composition. Optimum separations and detection sensitivities in negative ESI mode were obtained using a running electrolyte of 75 mM of ammonia at pH 11 and a sheath liquid of 60:40 v/v or 75:25 v/v isopropanol/water with 0.5% v/v of ammonia. At these experimental conditions, PMMA and PEEK capillaries show good hydrolytic stabilities and lower EOF values than fused-silica columns. Better separation resolutions were obtained with PMMA capillary, but this plastic rapidly swelled and bled because of its limited chemical resistance to the sheath liquid. PMMA columns equipped with a fused-silica tip were used for a safer exposure to the sheath liquid, but the inner surface of the fused-silica tips had limited stability at pH 11. On the other hand, good separations and reproducibility on migration times and peak areas were obtained using PEEK capillaries without capillary column deterioration.

Capillary Electrophoresis in Bioanalysis

“…A solution to this problem is to use poly(methyl methacrylate) and polyether ether ketone capillaries instead of modified fusedsilica capillaries (63). Using these plastic capillaries, common biological anions have been separated and electrosprayed at a high pH (i.e., pH 11).…”

Development of a capillary electrophoresis‐mass spectrometry method using polymer capillaries for metabolomic analysis of yeast

“…It could not be explain only the destacking of the sample zone caused by a complex matrix of high ionic strength. From our results and the peak shape of AMP obtained in the previous paper [17], the possibility of nonspecific interactions between a phosphoric group and the capillary wall of a polymer capillary cannot be ruled out. We also tried the CE-MS separation using a 150 mM ammonium hydrogencarbonate buffer (pH 8.5) as the electrolyte, but the current drop and disruption often occurred because the EOF was increased rather than the counter flow with a constant pressure at 6.9 kPa (1 psi) during the CE separation.…”

“…In our preliminary experiments, no elution, band-broadening, and/or asymmetric peaks were observed for several metabolites. The potential of polymer capillary for CE-MS separations of anionic metabolites at high pH values has been developed elsewhere [17], but this report has analyzed only a few analytes. Therefore, in the present study, an analytical method for metabolic analysis has been developed using an inert polymer capillary made of PEEK and PTFE.…”

“…Because the detection of sample components is usually "on-column" through a window in the capillary, an interface has been developed to prevent the above problem [20]. Unlike UV/LIF detection, however, the detection window on the capillary is dispensable for end-capillary detection, such as inductively coupled plasma atomic emission [12] and condensation nucleation light scattering detection [14], and is also not required for CE-MS [17].…”

“…Some hydrophobic materials, such as PTFE [11][12][13], poly(ether etherketone) (PEEK) [14][15][16][17], poly(methyl methacrylate) [15,17], polypropylene [18], and fluorinated ethylene propylene [19], have been used for CE capillaries. In the use of these polymer capillaries the main problem encountered is high background absorbance values in the low UV region [15].…”