U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



Anal. Chem. 2017, 89, pp. 10537−10546, DOI: 10.1021/acs.analchem.7b02753.


U.S. government work.


Online two-dimensional (2D) comprehensive liquid chromatography (LC × LC) has become increasingly popular. Most LC × LC separations employ one or more detectors at the outlet of the second dimension, 2D, with very short runs to avoid undersampling. We used six detectors, including dual parallel mass spectrometry (LC1MS2), for detection of the first dimension, 1D. We made an argentation (silver-ion) UHPLC column from a strong cation exchange column for 2D, coupled with UV and LC1MS2 detection. LC1MS2 in 1D combined with LC1MS2 in 2D, plus five other detectors, constituted LC2MS4 in a comprehensive LC1MS2 × LC1MS2 2D-LC separation. Electrospray ionization (ESI) high resolution accurate mass (HRAM) mass spectrometry (MS) and atmospheric pressure chemical ionization (APCI) MS were used in parallel for 1D detection, while atmospheric pressure photoionization (APPI) MS and ESI-MS were used for detection of 2D. The LC1MS2 used for 1D allowed quantification of triacylglycerol (TAG) molecular species of Parinari curatellifolia and other seed oils, while the 2D allowed isomers of TAG containing 18:3 fatty acyl chains as well as TAG regioisomers to be separated and identified. The LC1MS2 in 1D allowed identification of oxo-TAG species by HRAM MS and quantification of 806.3 ± 1.3 and 1101 ± 22 μg/g of α- and γ- tocopherols, respectively, in P. curatellifolia by APCI-MS. It is now feasible to use silver-ion UHPLC as the 2D separation in LC × LC and to use multiple mass spectrometers across both dimensions to perform conventional quantitative analysis and to take advantage of the newest LC × LC separation technology to identify isomers that are otherwise difficult to separate.