ISSN:
0935-6304
Keywords:
Addition of variances and second moments in chromato-graphy, GC, LC
;
Additivity of homogeneous column contributions
;
Additivity of extra-column contributions
;
Estimation of time constant from peak shape
;
Discontinuous plate number
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The time constant, τ, is determined from the tail of an authentic HPLC peak through a plot of In U versus time, t, according to the relation \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm In\, U} = {\rm In }\mathop {\rm U}\nolimits_{\rm o} - \frac{1}{\tau }{\rm \,t} $$\end{document} expected at low recorder deflexions, U. The value obtained, τ = 2.43 s, is one order of magnitude larger than an ordinary recorder time constant, which is quite normal for LC detectors. It agrees with the value, τ = 2.44 s, needed theoretically to distort a Gaussian-shaped peak so as to obtain the experiment-ally found second moment, σ2 = 11.13 s,2 and the experimental difference between first moment t and peak retention time tmax, t - tmax = 0.78 s. The determination is therefore regarded as a demonstration of the variance addition rule \documentclass{article}\pagestyle{empty}\begin{document}$$ \sigma ^2 = \sigma \frac{{\rm 2}}{{\rm G}} + \tau ^2 $$\end{document} where σG2 is the second moment of the non-distorted peak. The column contribution version \documentclass{article}\pagestyle{empty}\begin{document}$$ (\sigma ')^2 = \sigma \frac{2}{{\rm o}}_{{\rm (k)}} + \sigma \frac{{\rm 2}}{{\rm s}} $$\end{document} is also considered. This equation was appliied earlier to an estimation of extra-column contributions to band broadening with the aid of the “abt” concept. An explicitly k-(capacity ratio)-dependent expression for the mass exchange contribution, σG2 is derived from Golay's equation for capillary columns, but the validity of the Golay equation is under discussion.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jhrc.1240021004
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