From 1950 to 1992, advances in AUC were developed largely by academic labs and commercialized by Beckman Instruments (now Beckman Coulter Inc.). The current analytical ultracentrifuge, the XLI, was developed in the mid-1980s by retro-fitting an existing high-speed preparative centrifuge with absorbance and interference optics (Giebeler 1992; Yphantis et al. 1994). Since 1992, only one new optical system, the fluorescence optics (Schmidt and Riesner 1992; MacGregor et al. 2004; MacGregor 2000; Kroe and Laue 2009) has been commercialized and no improvements to the existing optical systems have been commercialized. Alternative base instruments have been commercially available that are less versatile than the XLI due to their lower maximum rotor speeds (LumiSizer by LUM GmbH: 6,000 rpm; BI XDC by Brookhaven Instruments: 10,000 rpm; DC24000 by CPS instruments: 24,000 rpm) and unconventional sample holders (monosector cells or discs instead of multisector cells). While these machines marginally qualify as analytical centrifuges, they clearly demonstrate the expansion potential for innovative AUC designs, such as one-shot detection of concentration profiles (LumiSizer) or non-optical detection by X-ray absorption (XDC).