Multidimensional Gas Chromatography of Organosulfur Compounds in Coffee and Structure-Odor Analysis of 2-Methyltetrahydrothiophen-3-one.

Organosulfur compounds (OSCs) in coffee remain challenging to analyze by conventional gas chromatography (GC) due to their low concentrations amid coffee's complex matrix and susceptibility to chiral-odor influences. In this study, multidimensional GC (MDGC) methods were developed to profile OSCs in coffee. Conventional GC was compared to comprehensive GC (GC×GC) for untargeted OSC analysis in eight specialty coffees, and GC×GC was found to improve the fingerprinting of OSCs in coffee (50 vs 16 OSCs identified).

Recent advances in analytical strategies for coffee volatile studies: Opportunities and challenges.

Coffee has attracted significant research interest owing to its complex volatile composition and aroma, which imparts a pleasant sensorial experience that remains challenging to analyse and interpret. This review summarises analytical challenges associated with coffee's volatile and matrix complexity, and recent developments in instrumental techniques to resolve them. The benefits of state-of-the-art analytical techniques applied to coffee volatile analysis from experimental design to sample preparation, separation, detection, and data analysis are evaluated.

Combination of solid phase microextraction and low energy electron ionisation gas chromatography-quadrupole time-of-flight mass spectrometry to meet the challenges of flavour analysis.

The flavour analysis of volatile compounds remains challenging not only because of their diversity in properties and dynamic range, but also due to the high background noise from food matrix constituents. To improve sensitivity and specificity for a multiclass range of compounds, a combination of solid phase micro-extraction (SPME) devices and low energy electron ionisation (LE-EI) was proposed for the analysis of 36 volatile compounds, using coffee as a model matrix. From a pre-evaluation of devices and extraction modes, the combined use of direct immersion-stir bar sorptive extraction and headspace-thin-film SPME (SBSE-TFSPME) was selected to increase compound recovery, and further optimised for extraction temperature (88 °C) and time (110 min).

Effect of solid-state fungal fermentation on the non-volatiles content and volatiles composition of Coffea canephora (Robusta) coffee beans.

In this study, the effects of fungal fermentation on green canephora coffee beans were evaluated by observing the changes to selected non-volatile parameters before roasting, and subsequently the volatile profile after roasting. Solid-state fermentation (SSF) by Aspergillus spp. and Mucor spp.

Improved detection of key odourants in Arabica coffee using gas chromatography-olfactometry in combination with low energy electron ionisation gas chromatography-quadrupole time-of-flight mass spectrometry.

Four Arabica coffees (Brazil, Colombia, Ethiopia, and Guatemala) yield highly variant odours, attesting to the complexities of coffee aroma that command advanced analytical tools. In this study, their volatiles were extracted using solvent-assisted flavour evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). Due to matrix complexity, some trace odourants were detected in SAFE extracts by aroma extract dilution analysis (AEDA) but remained difficult to quantify by gas chromatography-mass spectrometry (GC-MS).

Ultrafast charge carrier recombination and trapping in hematite photoanodes under applied bias.

Transient absorption spectroscopy on subpicosecond to second time scales is used to investigate photogenerated charge carrier recombination in Si-doped nanostructured hematite (α-Fe2O3) photoanodes as a function of applied bias. For unbiased hematite, this recombination exhibits a 50% decay time of ~6 ps, ~10(3) times faster than that of TiO2 under comparable conditions. Anodic bias significantly retards hematite recombination dynamics, and causes the appearance of electron trapping on ps-μs time scales.

Back electron-hole recombination in hematite photoanodes for water splitting.

The kinetic competition between electron-hole recombination and water oxidation is a key consideration for the development of efficient photoanodes for solar driven water splitting. In this study, we employed three complementary techniques, transient absorption spectroscopy (TAS), transient photocurrent spectroscopy (TPC), and electrochemical impedance spectroscopy (EIS), to address this issue for one of the most widely studied photoanode systems: nanostructured hematite thin films. For the first time, we show a quantitative agreement between all three techniques.

Identifying champion nanostructures for solar water-splitting.

Charge transport in nanoparticle-based materials underlies many emerging energy-conversion technologies, yet assessing the impact of nanometre-scale structure on charge transport across micrometre-scale distances remains a challenge. Here we develop an approach for correlating the spatial distribution of crystalline and current-carrying domains in entire nanoparticle aggregates. We apply this approach to nanoparticle-based α-Fe₂O₃ electrodes that are of interest in solar-to-hydrogen energy conversion.

Transparent, conducting Nb:SnO2 for host-guest photoelectrochemistry.

Many candidate materials for photoelectrochemical water splitting will be better employed by decoupling optical absorption from carrier transport. A promising strategy is to use multiple thin absorber layers supported on transparent, conducting materials; however there are limited such materials that are both pH stable and depositable on arbitrary high surface area substrates. Here we present the first 3D porous niobium doped tin oxide (NTO) electrodes fabricated by atomic layer deposition.

A Ga2O3 underlayer as an isomorphic template for ultrathin hematite films toward efficient photoelectrochemical water splitting.

Hematite photoanodes for photoelectrochemical (PEC) water splitting are often fabricated as extremely-thin films to minimize charge recombination because of the short diffusion lengths of photoexcited carriers. However, poor crystallinity caused by structural interaction with a substrate negates the potential of ultrathin hematite photoanodes. This study demonstrates that ultrathin Ga2O3 underlayers, which were deposited on conducting substrates prior to hematite layers by atomic layer deposition, served as an isomorphic (corundum-type) structural template for ultrathin hematite and improved the photocurrent onset of PEC water splitting by 0.