28.02.2013 Views

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

fractionation rather than analysis <strong>of</strong> the MW distribution, injection <strong>of</strong> a<br />

concentrated solution has an edge. HOPC uses this principle.<br />

3 HOPC SYSTEMS<br />

At this moment, commercial HOPC systems are not available. Fortunately, <strong>of</strong>f-theshelf<br />

HPLC components can be assembled to construct an HOPC system, except<br />

for the columns (1–10). A typical system consists <strong>of</strong> an HPLC pump, a column,<br />

<strong>and</strong> a fraction collector. Two parts <strong>of</strong> Fig. 3 illustrate different injection methods.<br />

Figure 3a shows the injection <strong>of</strong> a concentrated solution by using an injection<br />

valve equipped with a sample loop <strong>of</strong> a large volume (2–4mL for a column <strong>of</strong><br />

3:9 300 mm), swept by an HPLC pump <strong>of</strong> any type. The sample loop needs to<br />

have a large interior diameter to minimize the backpressure. In Fig. 3b, a simple<br />

HPLC pump directly injects the viscous solution through a pump head into the<br />

column. In the latter, a tubing <strong>of</strong> minimal length should connect the outlet check<br />

valve <strong>of</strong> the pump <strong>and</strong> the inlet end fitting <strong>of</strong> the column, bypassing a pulse<br />

damper, a pressure transducer, <strong>and</strong> other auxiliary components. A single-head<br />

pump will be preferred.<br />

A detector may be connected to the column outlet. Upon detection <strong>of</strong> the<br />

first polymer, the eluent should be diverted to the fraction collector to avoid<br />

damage to the flow cell in the detector <strong>and</strong> to minimize b<strong>and</strong> broadening in the<br />

fluid path between the column <strong>and</strong> the fraction collector. Any SEC detector can be<br />

used, but dropping the eluent into a solvent that does not dissolve the polymer<br />

<strong>and</strong> mixes with the eluent <strong>and</strong> visually inspecting the drops may be<br />

sufficient; precipitation signals the first polymer. If such a solvent is not readily<br />

available, dropping the eluent into the mobile phase solvent may be a good<br />

alternative. Because the polymer concentration in the eluent shoots up as the<br />

polymer enters, the human eye will detect spatial fluctuations <strong>of</strong> the refractive<br />

index to signal the first polymer.<br />

Figure 3 HOPC systems: (a) a polymer solution is injected into the sample loop, <strong>and</strong><br />

then into the column, (b) the solution passes through the pump head.<br />

© 2004 by Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!