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Handbook of Size Exclusion Chromatography and Related ...

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The st<strong>and</strong>ard deviations for the molar mass results are in the order <strong>of</strong> 0.5%<br />

RSD for this HighSpeed separation. They are similar to analyses using<br />

conventional columns on good instrumentation. It has been shown that not the<br />

column but the instrument determines result precision (11). In particular, in<br />

HighSpeed separations, the pumps must be able to deliver constant flowat higher<br />

flow rates <strong>and</strong> with high precision.<br />

4.2.2 Accuracy <strong>of</strong> HighSpeed Columns<br />

Correct molar mass results are very important <strong>and</strong> they should not be<br />

compromised even in HighSpeed applications. PSS checked the absolute<br />

accuracy <strong>of</strong> molar masses using various narrow <strong>and</strong> broad st<strong>and</strong>ards in various<br />

solvents<strong>and</strong>comparedmeasuredmolarmassaverageswiththeacceptedvalues<strong>of</strong><br />

the polymer st<strong>and</strong>ards.<br />

Table 4compares results <strong>of</strong> 10 repeats <strong>of</strong> abroad polystyrene st<strong>and</strong>ard with<br />

the measured molar mass averages <strong>and</strong> their st<strong>and</strong>ard deviation. The accuracy <strong>of</strong><br />

the HighSpeed results is excellent, while the st<strong>and</strong>ard deviation is similar to<br />

normal SEC separations. RSD values will depend directly on the maintenance<br />

status <strong>of</strong> the instrumentation. Different instruments have shown different RSD<br />

levelswhilethemolarmassaverageshavebeenveryclosetothosereportedforthe<br />

reference st<strong>and</strong>ard.<br />

Similar results have been reported by Alden (15) <strong>and</strong> Nielson (private<br />

communication), whoinvestigated theaccuracy<strong>and</strong> precision <strong>of</strong> polystyrene runs<br />

using short columns (6 150 mm) on an optimized SEC system (Fig. 14).<br />

4.2.3 Saving Time with HighSpeed SEC Columns<br />

HighSpeedSECiscertainlynicetohave,buthowmuchcanbegainedwithrespect<br />

to time <strong>and</strong> money? Analysing the analytical process shows that calibration,<br />

validationruns,<strong>and</strong>samplerunsareareaswherethePSSHighSpeedSECcolumn<br />

concept must show its validity.<br />

Typical conventional calibrations require a minimum <strong>of</strong> 10 calibration<br />

points. Also typical are SEC run times <strong>of</strong> 40 to 60 min (3 to 4columns per<br />

instrument) for high-quality analyses. Please note that these conditions are very<br />

close to the requirements <strong>of</strong> the international (ISO 13885, Ref. 9) <strong>and</strong> national<br />

Table 4 Accuracy <strong>of</strong> HighSpeed Separation for Polystyrene Reference St<strong>and</strong>ard<br />

Mn %SD Mw %SD Mp %SD<br />

Reference polymer 47,500 n/a 93,300 n/a 85,300 n/a<br />

HighSpeed results 47,200 5.2 93,100 3.0 85,200 1.1<br />

n/a, not applicable.<br />

© 2004 by Marcel Dekker, Inc.

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