title: Note: Investigation of a null measurement of optical absorbance using a pulse width modulated light-emitting diode.
abstract: We examined the possibility of making a null measurement of optical absorbance by using pulse-width modulation to control the intensity of a light-emitting diode (LED). This type of measurement is intriguing because the instrumental sources of noise are different from those in the traditional absorbance measurement. Our experiment employed phototransistor detectors and a RC integrator to measure the amount of light being transmitted. However, instead of measuring the ratio of the detector voltages for a blank and sample, we measured the ratio of the LED duty cycles required to give the same detector voltage for a blank and a sample. Using this method, it is presumed that the same amount of light reaches the detector during measurement of the blank and sample.
authors.affiliation: Department of Chemistry, University of Scranton, Scranton, Pennsylvania 18510, USA. rusakd2@scranton.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Rusak
authors.forename: Ernest A
authors.initials: EA
authors.lastname: Kawka
authors.forename: E Brady
authors.initials: EB
authors.lastname: Trexler
mesh_terms: D000042:Absorption; D000818:Animals; D004529:Egg White / Q000737:chemistry; D008027:Light; D055096:Optical Devices; D055095:Optics and Photonics / Q000295:instrumentation* / Q000379:methods*; D012394:Rosaniline Dyes / Q000737:chemistry
chemical_list: D012394:Rosaniline Dyes; C048139:Coomassie blue