igh-precision interferometer Interference optics can detect solutes that have no convenient absorbance signal and have a higher precision than the absorbance optics. The XLI interferometer has a sensitivity of approximately 3.25 fringe mg−1 ml−1 and a precision of ±0.01 fringe (Yphantis et al. 1994). Changes to the source and detector will improve the sensitivity more than twofold and the precision more than 100-fold (see detector shown in Fig. 4). The changes will extend the useful concentration range for interference detection by two orders of magnitude, making it useful for characterizing trace quantities of materials and high-affinity interactions (Howlett et al. 2006).
Fig. 4 Advances for Rayleigh Interference optics: a high-precision Rayleigh interference optical system mounted on an Xl ultracentrifuge (Laserarm from Spin Analytical); b large format interference camera from Philips (3,000 × 2,000 pixels); c data quality from the stock Beckman Coulter interference camera; d data quality from a large format Philips camera (1,024 × 2,048 pixels); e comparison of data quality as the residual noise from ten successive scans taken approximately 1 min apart. The residuals were calculated using WinMatch (available from http://www.rasmb.org) to optimize the fringe displacements. In c the residuals from the large format camera (rms 0.00017 fringe) are superimposed on those from the stock camera (camera rms 0.009). The increased number of fringes provided by the large format camera reduces the magnitude of the residuals over 50-fold, thus making it possible to acquire data at lower concentrations and improving the precision of analysis. Additional improvements can be expected from the Philips or any other large format CCD camera. Data supplied courtesy of David Yphantis and Jeff Lary
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