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Mass spectrometers are sensitive tools used to identify and quantify both small and large analytes using the mass-to-charge ratios ( m/ z) of ions generated by electrospray ionization (ESI) or other methods. Ionization typically generates protonated or deprotonated forms of the analytes or adducts with adventitious metal ions derived from the spray solvent. The formation of a variety of ionized forms of the analyte as well as the presence of cluster ions complicates the data and can have deleterious effects on the performance of the mass spectrometer, especially under high salt or buffer conditions. To address this, a method involving a dual-electrode nano-electrospray source has been implemented to rapidly and temporarily desalt the spray solution of interfering cationic and anionic species using electrophoretic transport from the spray tip. Peptides, proteins, and pharmaceutical drugs all showed improved results after the desalting process as measured by the quality of the mass spectra and the limits of detection achieved. Importantly ordinary phosphate buffers could be used to record protein mass spectra by nano-ESI.

A rapid method is described for quantification of six illegal colorants in beverages, i.e., soft beverages, energy beverages, alcoholic beverages, teas, and fruit juices. Paper spray (PS) ionization combined with tandem mass spectrometry (MS/MS) allowed detection of particular dyes in times of less than 1 min per sample. Samples where diluted in methanol and isotopically-labeled internal standards were utilized to obtain linear responses over ranges of two or three orders of magnitude. The LODs were below 1.5 ng mL−1 and LOQs were below 5 ng mL−1. Quality control experiments gave accuracies that ranged between 80% and 120%. Matrix effects were evaluated for different samples but had little effect given the use of the dilution method.

In this work, an electro-kinetic assisted electrospray ionization (EK-ESI) source is proposed and characterized. In EK-ESI, an additional auxiliary electric field is introduced in the liquid flow of a nano-ESI. While traveling forward in the electrospray flow, charged analytes also experience a reverse electric field, which pushes them backwards. As a result, analytes could be separated preliminarily based on their electrophoretic mobility during the electrospray process. Experiments show that EK-ESI can reduce charge competition effects in the ESI source and increase biomolecule detection sensitivities. It was also found that EK-ESI effectively ionizes proteins in a relatively mild solvent condition, which does not require the addition of acids or salt buffers into the solvent. As a proof-of-concept study, a very rough separation effect was observed in this study, further experiments and theoretical study will be carried out to enhance its performances.