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ENCH 213 (25)
Lecture

# 18spectrometry5.pdf

3 Pages
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School
Queen's University
Department
Chemistry
Course
ENCH 213
Professor
Diane Beauchemin
Semester
Fall

Description
More instrumentation for spectrophotometry • optical sensors ◦ optodes ◦ waveguides ◦ surface plasmon • dealing with noise Refraction of light • when light is reflected ◦ reflection angle=incidence angle • light is refracted when it passes from a medium into another • Snell’s law: n s1nθ= nisinθ2 r ◦ n =rxfractive index of medium x ◦ θ =iicidence angle ◦ θ =rrfraction angle Refraction of light by water • when visible light passes from air into water at a 45° angle, what is the refraction angle? • the refractive index of air is close to 1.00 while that of water is 1.33. ◦ (1.00)(sin45 ) = (1.33) (sin θ ) → θ 2 32 2 o • what is the refraction angle if the light is perpendicular to the water surface? ◦ 1.00)(sin0 ) = (1.33) (sin θ ) → θ 2 0 2 o • a perpendicular ray is not refracted. sinθ r (n /1 )2sinθ i Optical fibers Protective plastic • light is carried by total internal reflection • vs electrical wires: Lowern ,2transparent ◦ immune to electrical noise High n , transparent: ◦ higher rate of data transmission 1 ◦ can handle more signals glass orpolymer • if n1/n2>1, range of θ foi which ≈ all light is reflected • critical angle: sin θ criticaln 2n 1 Optode or optrode • = Chemical sensor at the end of an optical fiber that is designed to respond to various analytes (sulfites in food, nitric oxides in cells, explosives in groundwater, etc.) • examples: ◦ end of O opto2e coated with Ru(II) complex in a layer of polymer ▪ sample as small as 100fL (100 x 10 L) -15 -18 ▪ detection limit = 10 amol O (1 amol2 10 mol) ◦ with enzyme glucose oxidase: glucose sensor ▪ detection limit = 1 fmol glucose What is an Optode? a) Adevice used to increase the number of electrons produced by a photosensitive material. (photomultiplier tube) b)A device created by placing a chemically sensitive layer at the end of an optical fiber. c) An optical device used to disperse light into its component wavelengths. (monochromator, grating
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