High-performance liquid chromatography mass spectrometry method for quantifying dissolved black carbon

Abstract

Dissolved black carbon (DBC) is an important component of dissolved organic matter (DOM), and it plays an essential role in global carbon cycling through its ubiquity and roles in mediating biogeochemical and environmental reactions. Currently, DBC in DOM is quantified by oxidation with nitric acid to produce benzene polycarboxylic acids (BPCAs) and subsequently measured by ion-pair reverse-phase liquid (IP-RP) chromatography with photodiode array (PDA) detection. This popular method relies solely on retention times and light absorbance for analyte identification and quantitation, leading to potential errors if co-eluting and light absorbing non-BPCA compounds are present. Moreover, this method is incompatible with mass spectrometry (MS) detection due to its mobile phase composition. To address these limitations, our study evaluated an alternative MS-compatible quantification method that can be used to corroborate DBC values determined by IP-RP. This alternative method separates the target analytes using multi-mode ion exchange-reverse phase columns that elute the necessary BPCAs with MS-friendly mobile phases. We analyzed various DOM samples from different environments. Detection was performed using high-performance liquid chromatograph with both a PDA and a single quadrupole electrospray ionization mass spectrometer detector arranged in series. This MS-friendly method enabled us to identify BPCA with higher confidence relative to methods that rely solely on retention times and PDA light absorbance, while also introducing the potential for superior limits of detection relative to current methods in future studies utilizing higher sensitivity tandem MS instruments.