Electrochromatography Coupled to Mass Spectrometry

As a result, their intensity can be adjusted by modifying either the applied electrospray voltage or the position of the CE capillary outlet. Prior to starting a sequence, analyses have to be performed to ensure that these electric currents remain stable, otherwise, the capillary position has to be slightly adjusted to achieve good quantitative results, furthermore, the capillary current monitoring can be a diagnostic tool of the chiral selector s entrance into the nebulisation chamber. 

The choice of an appropriate sheath liquid and its flow rate is essential to achieve good performance. This choice is a compromise between separation (to maintain an efficient electrophoretic separation) and ionization performances (to assist droplet formation and spray stability). Most CE-ESI-MS applications described in the literature for the analysis of protonated compounds use a sheath liquid containing a mixture of organic solvent, water and formic or acetic acid. In method development, the impact of the nature of the sheath liquid on the expected chiral separation can be evaluated by placing it in the outlet vial. The solubility of the chiral resolving agent in the sheath liquid has to be carefully investigated to avoid its precipitation at the spray needle. 

Choosing an internal standard to correct errors due to sample preparation and injection reduced the impact of variability on the final trueness and precision of the developed method. Peak area can be corrected (peak area/migration time) to avoid the migration time drift influence, because of the temperature affecting both electro-osmosis and electrophoretic mobilities as well as buffer electrolysis, adsorption into the capillary wall and so on. 

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