Towards smaller and faster gas chromatography-mass spectrometry systems for field chemical detection

Gas chromatography-mass spectrometry (GC-MS) is already an important laboratory method, but new sampling techniques and column heating approaches will expand and improve its usefulness for detection and identification of unknown chemicals in field settings. In order to demonstrate commercially-available technical advances for both sampling and column heating, we used solid phase microextraction (SPME) sampling of both water and air systems, followed by immediate analysis with a resistively heated analytical column and mass spectrometric detection. High-concern compounds ranging from 140 to 466 amu were analyzed to show the applicability of these techniques to emergency situations impacting public health. A field portable (about 35 kg) GC-MS system was used for analysis of water samples with a resistively heated analytical column externally mounted as a retrofit using the air bath oven of the original instrument design to heat transfer lines. The system used to analyze air samples included a laboratory mass spectrometer with a dedicated resistive column heating arrangement (no legacy air bath column oven). The combined sampling and analysis time was less than 10 min for both air and water sample types. By combining dedicated resistive column heating with smaller mass spectrometry systems designed specificallyfor use in the field, substantially smaller high performance field-portable instrumentation will be possible.     

Correlating the Surface Basicity of Metal Oxides with Photocatalytic Hydroxylation of Boronic Acids to Alcohols

Photoredox catalysis provides opportunities in harnessing clean and green resources such as sunlight and O₂, while the acid and base surface sites of metal oxides are critical for industrial catalysis such as oil cracking. The contribution of metal oxide surfaces towards photocatalytic aerobic reactions was elucidated, as demonstrated through the hydroxylation of boronic acids to alcohols. The strength and proximity of the surface base sites appeared to be two key factors in driving the reaction; basic and amphoteric oxides such as MgO, TiO₂, ZnO, and Al₂O₃ enabled high alcohol yields, while acidic oxides such as SiO₂ and B₂O₃ gave only low yields. The reaction is tunable to different irradiation sources by merely selecting photosensitizers of compatible excitation wavelengths. Such surface complexation mechanisms between reactants and earth abundant materials can be effectively utilized to achieve a wider range of photoredox reactions.     

Intensity models and transition probabilities for credit card loan delinquencies

We estimate the probability of delinquency and default for a sample of credit card loans using intensity models, via semi-parametric multiplicative hazard models with time-varying covariates. It is the first time these models, previously applied for the estimation of rating transitions, are used on retail loans. Four states are defined in this non-homogenous Markov chain: up-to-date, one month in arrears, two months in arrears, and default; where transitions between states are affected by individual characteristics of the debtor at application and their repayment behaviour since. These intensity estimations allow for insights into the factors that affect movements towards (and recovery from) delinquency, and into default (or not). Results indicate that different types of debtors behave differently while in different states. The probabilities estimated for each type of transition are then used to make out-of-sample predictions over a specified period of time.     

Recent Advances in Chiral Guanidine‐Catalyzed Enantioselective Reactions

Chiral guanidines have been widely used as Brønsted base catalysts and phase transfer catalysts in enantioselective reactions. Due to their amendable structure and powerful catalytic ability, they have attracted much interest. Several new catalysts containing a guanidinium moiety have been reported over the past decade and many promising outcomes have been achieved. This article illustrates the progress of chiral guanidine catalysis in asymmetric synthesis from 2009 to 2018. It is an update of a review of the same title published in 2009.     

Synthesis of the benzothiophen analogue of biphenylene by fvp

Extrusion of dinitrogen from the cinnoline (2) by flash vacuum pyrolysis (FVP) gave the benzothiophen analogue of biphenylene (3), which is more stable than the corresponding thiophen derivative.     

Remazol‐Catalyzed Hydroperoxyarylation of Styrenes

A mild photocatalytic hydroperoxyarylation of styrenes has been developed, in which a novel photocatalyst, remazol brilliant blue R (RBBR), is employed at low catalytic loading (1 mol %). The operationally easy procedure uses air as the dioxygen source. Simple mono‐substituted styrenes react with aryl hydrazines in moderate‐to‐good yields. RBBR is proposed to act as a photosensitizer for the generation of singlet oxygen.     

Numerical study on effects of check valve closure flow conditions on pressure surges in pumping station with air entrainment

This paper proposes a numerical procedure to better compute the characteristics of pressure surges when check valves close under different flow conditions in a pumping station. Studies have shown that the effects of check valve closure on the pressure transients are predominantly dependent on the magnitude and gradient of the flow velocities immediately downstream of the check valve at the instant of valve closure. Through the present study, it was noted that the transient flow velocities near the check valve of a fluid system are also dependent on the characteristics of the air entrained into the fluid system. An improved numerical computational procedure for the fluid system with air entrainment under different transient conditions downstream of the check valve is also proposed in this paper. With a fluid system operating within the critical range of air entrainment values, the present analysis showed that there is a possibility of ‘high pressure surges’ when the check valves were closed at flow rates other than the positive flow conditions. This phenomenon was confirmed through field observations. This study thus concludes that a detailed numerical transient analysis of the fluid system, with various assumed amounts of entrained air, is necessary whenever there is the possibility of air entrainment into the fluid system, and that the flow conditions at the instant of check valve closure need to be modelled. Copyright © 2001 John Wiley & Sons, Ltd.