Atmospheric Pressure Photoionization for Enhanced Compatibility in On-Line Micellar Electrokinetic Chromatography−Mass Spectrometry

Abstract

Atmospheric pressure photoionization (APPI) is presented as a novel means for the combination of micellar electrokinetic chromatography (MEKC) and mass spectrometry (MS). The on-line coupling is achieved using an adapted sheath flow interface installed on an orthogonal APPI source. Acetone or toluene is added as dopant to the sheath liquid to enhance analyte photoionization. It is demonstrated that with APPI signal suppression and interferences by the surfactant sodium dodecyl sulfate (SDS) and nonvolatile buffers can be circumvented. This implies that MEKC conditions can be selected independently from MS detection. Moreover, it is shown that both polar and apolar compounds can be photoionized, thereby also facilitating the analysis of compounds that are not amenable to electrospray ionization. Consequently, the MEKC-APPI-MS system can provide effective separation and detection of compounds of diverse character in one run using background electrolytes containing up to 50 mM SDS. Concentration limits of detection derived from extracted-ion traces (full scan mode) of test compounds were approximately 1 microg/mL, and the detection sensitivity remained unaffected during 1 day of continuous use. Overall, the system features are very favorable for applications such as drug impurity profiling as is illustrated by the analysis of mebeverine and related compounds (both charged and neutral) at the 0.25% (w/w) level.

Coupling CE with atmospheric pressure photoionization MS for pharmaceutical basic compounds: Optimization of operating parameters

“…Best responses in APPI were achieved with a SheaF around 50 mL/min. This high SheaF ensured stable spray and best ionization conditions and was in agreement with previous studies where a high SheaF was also selected [43,44]. It must be noted that the optimal value in ESI is quite lower (about 3-5 mL/min).…”

“…The APPI configuration, now commercially available from Agilent [47], was recently investigated by Mol et al [44] and the authors confirmed that a wider choice of CE electrolytes (buffer and additives) could be used for both polar and nonpolar compounds [44]. The study also demonstrated the possiblity to work with micellar EKC (MEKC) and MS [43]. It was concluded that SDS had no negative effect on photoionization efficiency and APPI might provide a good solution for MEKC-MS.…”

“…To our knowledge, a few publications have been dedicated to CE-APPI/MS [43][44][45][46] with experiments achieved on a conventional CE-MS system. To adapt the APPI interface, a spacer was positioned between the nebulizer and the vaporizer.…”

Capillary electrophoresis-atmospheric pressure chemical ionization-mass spectrometry using an orthogonal interface: Set-up and system parameters

“…Owing to its capability to form both even-and odd-electron ions, the latter technique was found suitable for ionization of both polar and apolar compounds. Furthermore, APPI appeared to be unaffected by the BGE composition, and even enabled the coupling of micellar electrokinetic chromatography (MEKC) and microemulsion electrokinetic chromatography (MEEKC) with MS [10,11].…”

Highly sensitive determination of dialkyl phosphinate acids in environmental samples by ion chromatography tandem mass spectrometry

“…Therefore, AS11-HC column was selected as the separation column in this experiment. It is reported that the sensitivity can be increased by introducing an organic modifier to enhance the ionization process during ESI [23][24][25][26]. Therefore, the flow rate of methanol with a post-column addition was optimized.…”