Unit 2

• a spectroscopy is a spectroscopic technique that is used for measuring the absorption as it interacts with the sample. The radiation could be a function of either frequency or wavelength -related to the absorption spectrum because the sample used to interacts with electro magnitude radiation (EMR) in the form of photons from the radiating field

To the frequencies of light transmitted with dark bands when the electrons absorb energy in the ground state to reach higher energy states

Differs depending on frequency and this variation is the absorption spectrum

Interaction of EMR in the form of photons with matter

• transmission of radiation i n matter can babe viewed as a momentary retention of the radiant energy by atoms, ions or molecules followed by reemission of the radiation in all directions as the particles return to their original electronic state • types: —Rayleigh scatter —Tyndall effect — Raman scatter

• light scatter by molecules or aggregates of particles with dimensions significantly smaller than the wavelength of the radiation • examples: blue color of sky

• occurs with particles of colloidal dimensions • can be seen with the naked eye

• involves absorption of photons producing vibrational excitation • always varies from the excitation energy by a constant energy difference

• ultraviolet or visible light

• percent transmittance versus concentration • absorbance versus concentration

• states that for parallel monochromatic radiation that passes through an absorber material of constant concentration, the radian power decreases logarithmaically as the light path increases arithmetically

• that for monochromatic radiation that passes through an absorber of constant concentration, there is logarithmic decrease in the radiant power as the light path increases arithmetically

• based on previous work by Lambert, Beer discovered that for monochromatic radiation, absorbance is directly proportional to the light path, b, through the medium and the concentration , c, of the absorbing species —> the work culminated in the Beer-Lambert law, or simple beers law • concentration of the analyte in solution can be determind by several different methods based on the Beer-Lambert law

A = log1/T = log100%/%T = log100-log%T A= 2 - log(v10)%T

At= a x Ct x b As = a x Cs x b • At = absorbance of test • As = absorbance of standard • Ct = concentration of test analyte • Cs = concentration of standard

• Stable source of radiant energy • A device that isolates a specific region of the electromagnetic spectrum • A sample holder • a photo detector • A read-out device

• provide polychromatic light • must generate sufficient radiant energy or power to measure the analyte of interest • two type: —> continuum —> line

• emits radiation that changes in intensity vertically slowly as a function of wavelength

• emit a limited number of discrete lines or bands of radiation

• spectroscope modified for selective transmission of a narrow band of the spectrum • quality of a monochromator is described by: —> normal wavelength —> Effective bandwidth —> Bandpass —> Filters

• wavelength in nanometers at peak light transmittance

• range of wavelengths at a point halfway between the baseline and the peak

• total range of wavelengths transmitted

• absorption filter • interference filters