Recent applications of retention modelling in liquid chromatography (2015–2020) are comprehensively reviewed. The fundamentals of the field, which date back much longer, are summarized. Retention modeling is used in retention‐mechanism studies, for determining physical parameters, such as lipophilicity, and for various more‐practical purposes, including method development and optimization, method transfer, and stationary‐phase characterization and comparison. The review focusses on the effects of mobile‐phase composition on retention, but other variables and novel models to describe their effects are also considered. The five most‐common models are addressed in detail, i.e. the log‐linear (linear‐solvent‐strength) model, the quadratic model, the log–log (adsorption) model, the mixed‐mode model, and the Neue–Kuss model. Isocratic and gradient‐elution methods are considered for determining model parameters and the evaluation and validation of fitted models is discussed. Strategies in which retention models are applied for developing and optimizing one‐ and two‐dimensional liquid chromatographic separations are discussed. The review culminates in some overall conclusions and several concrete recommendations.
Unbiased characterization
of dyes and their degradation products
in cultural-heritage objects requires an analytical method which provides
universal separation power regardless of dye classes. Dyes are small
molecules that vary widely in chemical structure and properties, which
renders their characterization by a single method challenging. We
have developed a comprehensive two-dimensional liquid chromatography
method hyphenated with mass spectrometry and UV–vis detection.
We use stationary-phase-assisted modulation to enhance the method
in terms of detection limits and solvent compatibility and to reduce
the analysis time. The PIOTR program was used to optimize an assembly
of shifting second-dimension gradients, which resulted in a high degree
of orthogonality (80% in terms of the asterisk concept). The resulting
method is universally applicable to all classes of dyes extracted
from cultural-heritage objects. Thanks to the high peak capacity and
orthogonality, dye components can be separated from chemically similar
impurities and degradation products, providing a detailed fingerprint
of the dyes mixture in a specific sample. The method was applied to
a number of challenging dye extracts from 17th- and 19th-century cultural-heritage
objects.
Photodegradation greatly affects everyday life. It poses
challenges
when food deteriorates or when objects of cultural heritage fade,
but it can also create opportunities applied in advanced oxidation
processes in water purification. Studying photodegradation, however,
can be difficult because of the time needed for degradation, the inaccessibility
of pure compounds, and the need to handle samples manually. A novel
light-exposure cell, based on liquid-core-waveguide (LCW) technology,
was embedded in a multiple-heart-cut two-dimensional liquid chromatography
system by coupling the LCW cell to the multiple-heart-cut valve. The
sample was flushed from the heart-cut loops into the cell by an isocratic
pump. Samples were then irradiated using different time intervals
and subsequently transferred by the same isocratic pump to a second-dimension
sample loop. The mixture containing the transformation products was
then subjected to the second-dimension separation. In the current
setup, about 30–40% of the selected fraction was transferred.
Multiple degradation products could be monitored. Degradation was
found to be faster when a smaller sample amount was introduced (0.3
μg as compared to 1.5 μg). The system was tested with
three applications, that is, fuchsin, a 19th-century synthetic organic
colorant, annatto, a lipophilic food dye, and vitamin B complex.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.