Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev
Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev
Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev
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EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS<br />
As a general guideline, the amount of sample loaded onto the<br />
normal phase fl ash column should be 5%-10% of the column size. Factors<br />
affecting the capacity of the column include compounds, sample matrix,<br />
concentration of reaction products <strong>and</strong> elution solvent used.<br />
12.6 Elution<br />
12.6.1 Step Gradient Elution<br />
Step gradients provide controlled elution with discrete changes<br />
in eluent strength. Each step is optimized to elute only those components<br />
that are soluble in that eluent. This technique can be applied to both off-line<br />
<strong>and</strong> on-line fl ash chromatography.<br />
1. Use TLC to determine a suitable solvent strength to elute<br />
the components at discrete intervals, choosing different solvent<br />
mixtures that elute each component separately with an<br />
R f of 0.2-0.5.<br />
2. Calculate the volume of solvent required to elute each component<br />
using CV=1/R f . Values of CV <strong>for</strong> different column sizes<br />
are listed in Table 3.<br />
3. Apply between 2 <strong>and</strong> 5 CV of solvent <strong>for</strong> each step, starting<br />
with the solvent with weakest strength.<br />
4. Collect the eluent from each step in a separate vessel.<br />
12.6.2 Linear Gradient Elution<br />
Liner gradients are a quick way of separating complex mixture,<br />
reducing the complexity of the subsequent purifi cation of the fractions collected.<br />
This technique is suitable <strong>for</strong> on-line fl ash chromatography.<br />
1. Use TLC to fi nd both the weakest <strong>and</strong> strongest elution<br />
solvent. The weak solvent (solvent A) should give retention<br />
of the majority of components (R f 0.5).<br />
2. Run a gradient starting with 100% solvent A <strong>and</strong> ending with<br />
100% solvent B.<br />
3. Collect the eluent at regular intervals.<br />
Automated fl ash chromatography instrumentation such as the<br />
FlashMaster II <strong>and</strong> Solo systems can monitor the signal from a UV detector,<br />
<strong>and</strong> collect only the fractions of eluent carrying the compounds of interest.<br />
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