1. A. Checks to run to make sure the instrument is in good working condition: Absorbance optics: ● run an intensity wavelength scan on an empty hole at 5.9 cm, at 6.5 and 7.1 cm. Overlay the scans and make sure that a) the peak intensity at 230 nm is at least 15,000 (or clean the lamp) and make sure that intensity plots from all three positions overlay (guarantees that the optical system is properly aligned). ● check radial alignment ● check the overlayed menisci of 40-50 scans of the same sample – they should form a single sharp peak, if the meniscus shifts back and forth, the slit assembly may need to be serviced. ● Take advantage of unique absorption peaks (i.e., heme, metal in the visible) to extend concentration range with absorbance optics. Match absorbance and emission peaks. Instrumentation

3. High Concentration Interference Equilibrium: Wiener Skewing or Conc. Nonideality Instrumentation

4. Absorbance Offsets caused by an optical/electronic flaw in the instrument Instrumentation

5. Too steep gradient in early velocity scans causes optical (refractive) artifacts Instrumentation

6. Too steep gradient in early velocity scans causes optical (refractive) artifacts also in absorbance experiments, plus bad radial calibration Instrumentation

7. Leaky cell sectors – one sector bleeds into the other First Scan: Last Scan: Instrumentation

8. Gain setting change of the Photomultiplier tube when run in intensity mode and absorbance is both channels is too high. Solution: load water in reference channel or lower OD in both channels. Instrumentation