Tiêu đề ANALYTIC TECHNIQUES AND AUTOMATION.pdf ✅

JION DIMSON, RMT, MSMLS 2 According to Beer’s Law, absorbance is directly proportional to concentration: A = abc Where: a = molar absorptivity b = path length c = concentration of solution Spectrophotometry • Involves measurement of light transmitted by a solution to determine the concentration of the light-absorbing substances in the solution • Single Beam Spectrophotometer o It is the simplest types of absorption spectrometer o It is designed to make one measurement at a time at one specified wavelength o The absorption maximum of the analyte must be known in advance when a single-beam instrument is used. • Double Beam Spectrophotometer o It is an instrument that splits the monochromatic light into two components o One beam passes thru out the sample, and the other thru a reference solution of blank o The additional beam corrects for variation in the light source intensity o The absorbance of the sample can be recorded directly as the electrical output of the sample beam • Types o Double beam in space – uses 2 photodetectors, for the sample beam and reference beam o Double beam in time – uses one photodetector and alternately passes the monochromatic light thru the sample cuvet and then reference cuvet using a chopper (rotating sector mirror) • Components of Spectrophotometers 1. Light Source 2. Entrance Slit 3. Monochromator 4. Exit Slit 5. Sample Cell 6. Photodetector 1. Light Source • It provides polychromatic light and must generate sufficient radiant energy or power to measure the analyte of interest. • An intense beam of light is directed thru the monochromator and the sample • To give accurate absorbance measurements thru out its absorbance range, its response to change in light intensity must be linear. o Types 1. Continuum source – emits radiation that changes in intensity; widely used in the lab. • Tungsten light bulb – commonly used light source in the visible and near infrared region