The production of quality bee products,
as well as bee survival itself, depends on the health conditions of
the environment, but ironically, harmful solvents are often employed
by scientists and traders to monitor the quality of these products.
Many types of propolis have been recognized around the world, but
specific biological activities can be expected for specific types
of propolis. This work aimed to develop a new and green ultrahigh
performance liquid chromatography method for the identification of
green propolis type. The method was able to discern this type of propolis
in a set of samples from seven countries as well as to cluster these
samples by fingerprint similarity based on principal component analysis
and partial least squares–discriminant analysis. This proved
to be efficient, reproducible, and greener than methods previously
reported in the literature for similar purposes and compatible with
the cheap, largely available food grade ethanol produced from sugar
cane
Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography is introduced. Modulation optimization involved a systematic investigation of heat transfer, analyte retention, and migration velocity at a range of temperatures. Longitudinal on-column thermal modulation was realized using a set of alkylphenones and compared to a conventional valve-modulator employing sample loops. The thermal modulator showed a reduced modulation-induced pressure impact than valve modulation, resulting in reduced baseline perturbation by a factor of 6; yielding a 6-14-fold improvement in signal-to-noise. A red wine sample was analyzed to demonstrate the potential of the longitudinal on-column thermal modulator for separation of a complex sample. Discrete peaks in the second dimension using the thermal modulator were 30-55% narrower than with the valve modulator. The results shown herein demonstrate the benefits of an active focusing modulator, such as reduced detection limits and increased total peak capacity.
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