Membrane-based microextraction techniques in analytical chemistry: A review

The use of membrane-based sample preparation techniques in analytical chemistry has gained growing attention from the scientific community since the development of miniaturized sample preparation procedures in the 1990s. The use of membranes makes the microextraction procedures more stable, allowing the determination of analytes in complex and “dirty” samples. This review describes some characteristics of classical membrane-based microextraction techniques (membrane-protected solid-phase microextraction, hollow-fiber liquid-phase microextraction and hollow-fiber renewal liquid membrane) as well as some alternative configurations (thin film and electromembrane extraction) used successfully for the determination of different analytes in a large variety of matrices, some critical points regarding each technique are highlighted.     

Direct ionization methods in mass spectrometry: An overview

Within this paper a sub-group of ambient ionization mass spectrometry namely direct ionization mass spectrometry techniques are reviewed. They are characterized by the generation of an electrospray directly from the sample investigated. Prominent representatives include paper spray mass spectrometry, tissue spray mass spectrometry, probe electrospray ionization or thin-layer chromatography mass spectrometry. Applications of all major direct ionization techniques within different fields such as biomedical analysis, analysis of natural products, analysis of technical products and food analysis, just to name a few, are discussed and relevant parameters are listed in five Tables.     

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS.     

Recent developments in asymmetric catalytic addition to CN bonds

Methods for enantioselective C-C bond constructions via additions to imines and related compounds are reviewed, with an emphasis on the most recent efforts involving asymmetric catalysis. Selected seminal examples are provided in order to place the recent developments in context.