Additional questions 6. Give an estimate of the upper and lower limits of the FMN concentration that can be measured by (a) UV-vis spectrophotometry and (b) fluorescence. 7. What factors determine the upper and lower limits for detection of FMN by light absorption? 8. What factors determine the lower limit for detection of FMN by fluorescence? What factor commonly determines the upper detection limit, above which fluorescence intensity does not increase linearly with concentration