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December 2010


benefit of the ActiPix D100 with the Agilent 7100 CE system for determination of absolute mobilities.


Figure 5. Example of experimental data and fitting for Taylor dispersion analysis. Blue and black lines are absorbance output traces for benzoate from the second and third windows, respectively. The green line the result of convoluting the blue line with a Gaussian function that has a standard deviation of 5.891 s.


The charges for lidocaine and benzoic acid were expected to be 1.0 and -1.0 respectively. Measured values of charge as reported in the last row of Table 2 are 0.86 for lidocaine and -0.86 for benzoic acid. Differences from unity are most likely due to the lack of correction for effects of ionic atmospheres on the dynamics of ionic diffusion and mobility. However, the fact that the charges for fully ionised cationic and anionic species in Table 2 are equal in magnitude is encouraging and suggests that with further refinement of non- ideality effects this method combining use of the ActiPix D100 with the Agilent 7100 CE system should yield absolute values.


Conclusions


Figure 6. Traces at second and third windows (blue and red, respectively) for 30 mbar, 10 kV; ActiPix D100 detector, 214 nm. Analyte migration order lidocaine, phenylmethanol, benzoate.


Figure 7. Measured effective mobility of A, lidocaine and B, benzoate with applied voltages of 5, 10, 15 & 20 kV plotted against dissipated power density. The fitted line extrapolated to zero gives the effective mobility at zero power. The fit assumes a mobility increase of 2% / o m W-1


C and indicates an estimated temperature increase of 10 o . C


The Paraytec ActiPix D100 detector has been used in combination with an Agilent 7100 CE system to determine diffusion coefficient, hydrodynamic radius, mobility and charge of components in a mixture of small molecules. Initial separation is carried out using pressure assisted capillary electrophoresis and measurement of diffusion coefficient and size achieved after switching to pressure driven flow. A capillary with three windows is used, with detection at the first window using the Agilent 7100 and at the second and third using the


ActiPix D100. The method has been applied to a mixture of three small molecules, lidocaine, phenylmethanol and benzoate, and shown to provide good repeatability (RSDs better than 2.5%, n=9) in diffusion coefficient and hydrodynamic radius. Charge follows by combining data on diffusion coefficient and mobility. The method could readily be applied with molecules in other classes, e.g. peptides and proteins.


Acknowledgement We wish to thank Agilent Technologies for the loan of a 7100 CE system.


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[9] T. Le Saux, H. Cottet, Anal. Chem. 80 (2008) 1829-1832. [10] F. d’Orlyé, A. Varenne, P. Gareil, J. Chromatogr. A 1204 (2008) 226–232.


[11] A.J.S. Chapman, D.M. Goodall, Chromatography Today volume 1 issue 3 (2008) 22-24.


[12] Paraytec Application Note AN015. Precision and accuracy of protein size determination using the ActiPix TDA200 Nano-Sizing System.


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[17] I.G.R. Gutz, CurTiPot freeware for pH and acid-base equilibrium calculations,


www2.iq.usp.br/docente/gutz/Curtipot_.html –


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[20] T. Hirokawa, M. Nishino, Y. Kiso, J. Chromatogr. 252 (1982) 49-65.


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