Supercritical Fluid Chromatography as an Alternative Tool for the Qualitative and Quantitative Analysis of Metarhizium brunneum Metabolites from Culture Broth.

A fast and selective ultrahigh-performance supercritical fluid chromatography photodiode array detector method was established for the qualitative and quantitative analysis of destruxins, cyclic hexadepsipeptides, from fungal culture broth samples. Prior to analysis, sample purification was carried out using an off-line solid-phase extraction protocol on a reversed-phase material in order to remove unwanted matrix constituents. For separation, detection, and identification, an ultrahigh-performance supercritical fluid chromatography photodiode array detector system hyphenated to a triple quadrupole mass spectrometer was utilized. Analyses were performed on an Acquity ethylene bridged hybrid 2-ethylpyridine sub 2 µm particle size column with CO2 and an acidified (0.02% trifluor acetic acid) modifier mixture of methanol/acetonitrile (8/2 v/v) serving as mobile phase. For the optimal separation of destruxins, the amount of the modifier was increased in a 10 min linear gradient from 2% to 20%, and the column outlet pressure and temperature was set at 140 bars and 60 °C, respectively. Seventeen analytes were separated within an elution window of 4 minutes. Five destruxin congeners (destruxin A, destruxin B, destruxin D, destruxin E, and destruxin E-diol) were identified using reference material. Additionally, eight analytes were tentatively assigned as known destruxins by the evaluation of mass spectrometry data performed as multiple reaction monitoring experiments in the positive electrospray ionization mode.