Natural compounds analysis using liquid and supercritical fluid chromatography hyphenated to mass spectrometry: Evaluation of a new design of atmospheric pressure ionization source

The MS hyphenation performance of UniSpray®, a new design of atmospheric pressure ionization source was evaluated in both SFC and RPLC modes. Sensitivity, stability, versatility and matrix effects offered by the UniSpray were assessed in positive and negative ionization modes and systematically compared to an electrospray source (ESI) using 120 natural compounds covering an extended chemical space. In a first instance, a multivariate approach was used to screen and optimize the UniSpray source settings to maximize detection sensitivity. The position of the source capillary against the fixed charged rod was highlighted as the major parameter affecting the detection sensitivity. The sensitivity improvement in Unispray vs. ESI strongly depends on the compounds chemical class and the chromatographic mode. For a few compounds (i.e. anabasine, theanine, caproic acid, fumaric acid and protopanaxatriol), up to a 10-fold increase in sensitivity was noticed with UniSpray. The signal stability over multiple injections was also found to be equivalent between both sources with RSD values on peak intensity lower than 14% on >100 injections, in both chromatographic modes. On complex plant extract, the matrix effects occurring from the secondary metabolites were also found to be comparable between ESI and UniSpray, at least in the positive ionization mode. However, a systematic decrease of MS signal intensity was observed in SFC mode when compounds were ionized using UniSpray in the negative ion mode.