The LC-NMR/MS setup was first introduced by Bruker BioSpin in 1999. An LC-NMR system including a Bruker Peak Sampling Unit (BPSU-36) was coupled with a Bruker Daltonics esquire series ion trap mass spectrometer via a Bruker NMR-MS interface (BNMI). Nowadays mostly maXis / micrOTOF time-of-flight mass spectrometers are used in hyphenated systems.
The time-of-flight mass spectrometers provides the exact mass of the analyzed sample and therefore access to the sum formula. This, together with the NMR spectrum for the compound, often already provides the answer to your questions.
The mass spectrometers and the controlling software are completely integrated into the LC-NMR setup. During chromatographic separation the mass spectrometer provides the mass spectra of the eluted peaks. Likewise they allow HyStar™ to trigger collection of chromatographic peaks into loops (LC-NMR), or SPE cartridges (LC-SPE™ NMR) based on mass chromatograms.
The relatively new technique of LC-SPE NMR and mass spectroscopy go especially well together. The SPE as interface between LC and NMR allows the usage of completely non-deuterated solvents during the chromatographic separation, and thus simplifies the acquired MS spectra. Sample enrichment through repeated chromatographic runs requires highly reliable peak detection. This peak detection is accomplished much easier through the use of highly sensitive mass chromatograms, then with UV chromatograms.