More instrumentation for spectrophotometry
• optical sensors
◦ 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
• 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.)
◦ end of O opto2e coated with Ru(II) complex in a layer of polymer
▪ sample as small as 100fL (100 x 10 L) -15
▪ 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.
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