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Handbook of Size Exclusion Chromatography and Related ...

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oversimplified approach. It seems that too many scientists consider the SEC<br />

method in its present stage <strong>of</strong> development a“concluded story” which enables<br />

sufficiently exact molecular characterization <strong>of</strong> synthetic polymers <strong>and</strong> does not<br />

needanyfurtherimprovements.Asresult,thesectionsonbulk<strong>and</strong>HPLCmethods<br />

for polymer characterization practically disappeared from the program <strong>of</strong> many<br />

broad-scope international symposia on polymers (see for example, Brisbane<br />

IUPAC Macro Symposium 1998). Besides the limited intrinsic accuracy <strong>of</strong> SEC<br />

even in the case <strong>of</strong> homopolymers, as demonstrated by aseries <strong>of</strong> IUPAC round<br />

robin tests (96), the possible influence <strong>of</strong> interfering macromolecular admixtures<br />

ontheSECdataforcomplexpolymersystemsrepresentsanotherreasontodevelop<br />

more advanced methods for molecular characterization <strong>of</strong> complex polymers.<br />

The most straightforward way to avoid negative effects <strong>of</strong> interfering<br />

polymeradmixturesistheirremovalfromtheanalyzedmixture.Inmanycasesthis<br />

can be done by utilizing differences in enthalpic interactivities <strong>of</strong> analyte <strong>and</strong><br />

admixture in the HPLC system. As aresult we arrive at aspecial case <strong>of</strong> aquasi<br />

two-dimensional HPLC arrangement in which the only role <strong>of</strong> the first separation<br />

system is purification <strong>of</strong> the analyte from unwanted macromolecular admixtures.<br />

If, however, the resulting purified analyte is acomplex polymer system one will<br />

needalso toengage atrue2D-HPLC methodfor itscharacterization <strong>and</strong>weagain<br />

arrive at aquasi three-dimensional HPLC.<br />

The elegant method for sample purification renders the full retention<br />

approach,amainlyfulladsorptionprocedure.Theinterferingadmixtureistrapped<br />

either within the interactive SEC column (97) or within an extra full retention<br />

guardcolumnintheapparatussimilartoafullretention–elutioninstrument(Sec.7,<br />

Fig. 16). The full adsorption approach is very efficient in the case <strong>of</strong> admixtures<br />

that are more polar than the macromolecules <strong>of</strong> analyte. Nonpolar admixtures can<br />

be better removed under application <strong>of</strong> enthalpic partition <strong>and</strong> phase separation<br />

retention mechanisms. After its saturation the guard column is regenerated by<br />

appropriate displacing liquid.<br />

Itis,however,possiblealsotoapplyareversedapproach.Analyteistrapped<br />

within the full retention precolumn while admixtures are eluted. In the next step,<br />

analyte is displaced into the analytical HPLC or 2D-HPLC system(s).<br />

The HPLC-like procedures <strong>of</strong> sample purifications are used in many<br />

industrial analytical laboratories. Unfortunately, their results remain largely<br />

unpublished.<br />

9 SAMPLE TRANSFER BETWEEN FIRSTAND SECOND<br />

DIMENSION SEPARATION SYSTEMS<br />

Defined reintroduction <strong>of</strong> eluent from the first dimension separation column into<br />

the second dimension column is an important condition for unambiguous<br />

© 2004 by Marcel Dekker, Inc.

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