Effects of nebulizing and drying gas flow on capillary electrophoresis/mass spectrometry

Abstract

This study was focused on examining the influence of gas flow parameters on capillary electrophoresis/mass spectrometry (CE /MS) performance using sheath-liquid CE /MS interfaces. The effects of nebulizing and drying gas velocity and drying gas temperature on CE separation and MS detection sensitivity were systematically determined. Nebulizing gas velocity was observed to be a critical parameter in the optimization of CE /MS method, since it affected both MS detection sensitivity, and also CE separation efficiency for one interface design tested. Better detection sensitivity was obtained when the nebulizing gas velocity was increased. However, high velocity of the nebulizing gas flow can cause a hydrodynamic bulk flow inside the CE capillary, thus clearly increasing the apparent mobility and decreasing the resolution obtained for the compounds studied. Increasing the drying gas velocity or temperature did not affect the apparent mobility or the separation efficiency and the temperature could be increased to achieve the optimal detection sensitivity in the CE /MS analysis. For comparison, the effects of nebulizing gas flow were studied using a different design of the coaxial sheath-liquid CE /MS interface, and in this case better detection sensitivity but no effect on CE separation efficiency was observed with increased nebulizing gas velocity. These different effects of nebulizing gas flow on the CE bulk flow were concluded to result from pressure differences at the tip of the CE capillaries for the different CE /MS interface arrangements. It is therefore recommended that the cross-sectional dimensions of the fused-silica and steel capillaries, and the gas streamlines, should be optimized when CE /MS interfaces are built. Moreover, the effect of gas flow on CE separation should be studied when optimizing the CE /MS operation parameters.

Capillary electrophoresis – mass spectrometry: 15 years of developments and applications

“…Increasing the content of volatile solvent also has this effect. The sheath gas may increase the speed of the solution in the capillary by suction effect [119] and thus reduce analysis time. We showed that this effect is dependent on the speed of the buffer (pH-dependency).…”

Quantitation in capillary electrophoresis-mass spectrometry

“…Using this approach RSD% values down to 7.8% (n = 101) for the analyte used to optimize the system without application of an internal standard could be achieved [4]. The nebulizer gas pressure has a strong influence on detection time because of the suction effect [35]. Thus, low values should be applied in order to achieve stable conditions, e.g., by preventing of air entrance into the capillary during the injection process and to avoid the loss of separation.…”

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

“…ESI is the method of choice for producing gas phase ions from solution because it is a very soft ionization method and is useful for the ionization of larger molecules or biomolecules. ESI-MS can be used for the analysis of complex mixtures [1][2][3][4][5] and is commonly used to couple separation techniques, such as high performance liquid chromatography (HPLC) [6][7][8][9], capillary electrophoresis (CE) [10][11][12][13][14][15][16][17][18][19][20][21], or microchannel electrophoresis (ME) [22][23][24][25][26][27][28][29] with MS. Many sample introduction methods, particularly those that employ separations, rely on pressure driven flow for sample introduction.…”

“…For optimal sample utilization, determination of the parameters that provide the highest signal intensity is crucial. Many previous studies have been performed to optimize different parameters that affect the ESI signal, like sheath flow [10,12,20], nebulizing gas [13,16], buffer systems [20,30], and ESI voltage [31,32]. Likewise, ESI emitters have been extensively studied because the characteristics of the emitter, such as the emitter i.d., the surface area of the emitter orifice, and the hydrophobicity, have a great impact on the observed ESI signal; in addition to influencing the working parameters of the system, such as flow rate or ESI voltage [33].…”