| Abstract
| - Major progress in interfacing liquid chromatography andelectron ionization mass spectrometry is presented. Theminimalism of the first prototype, called the Direct-EIinterface, has been widely refined, improved, and appliedto modern instrumentation. The simple interfacing principle is based on the straight connection between ananoHPLC system and a mass spectrometer equippedwith an EI source forming a solid and reliable unicumresembling the immediacy and straightforwardness of GC/MS. The interface shows a superior performance in theanalysis of small-medium molecular weight compounds,especially when compared to its predecessors, and aunique trait that excels particularly in the followingaspects: (1) It delivers high-quality, fully library matchable mass spectra of most sub-1 kDa molecules amenableby HPLC. (2) It is a chemical ionization free interface(unless operated intentionally) with accurate reproductionof the expected isotope ion abundances. (3) Response isnever influenced by matrix components in the sample orin the mobile phase (nonvolatile salts are also wellaccepted). A deep evaluation of these aspects is presentedand discussed in detail. Other characteristics of theinterface performance such as limits of detections, rangeof linear response, and intra- and interday signal stabilitywere also considered. The usefulness of the interface hasbeen tested in a few real-world applications where matrixcomponents played a detrimental role with other LC/MStechniques.
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