spectrophotometer lab exam

spectrophotometer

a machine that measures the amount of light absorbed by a sample

weeks

in old times how long it takes for a result to come out?

25%

what is the percentage that of the accuracy of results in older times?

Scientist Arnold J. Beckman and his colleagues

who invented spectrophotometer?

1940, national technogies laboratory

when and where was spectrophotomer invented?

Beer’s law, beer lamberts law

States that the concentration of the unknown substance is directly proportional to the absorbed light (absorbance or optical density) and inversely proportional to the amount of transmitted light (% transmittance)

light source

Provides radiant energy in the form of visible or non-visible light that may pass through the monochromator.

 

light source

The light of proper wavelength will be made incident on the analytical cell.

tungsten iodine lamp, quarts halide lamp, deuterium discharge lamp, infrared energy source, mercury vapor lamp, hallow cathode lamp

what are the types of light source?

tungsten iodine lamp

Produces energy wavelength from 340 to 700 nm (visible region).

tungsten iodine lamp

it is used for moderately diluted solution

quartz halide lamp

Contains small amounts of halogen such as iodine to prevent the decomposition of the vaporized tungsten from the very hot filament.

deuterium discharge lamp

Provides energy source with high output in the UV range (down to 165 nm)

deuterium discharge lamp

are more stable and generates continuous or discontinuous spectral.

infrared energy source

used above 800 nm

merst glower

an electrically heated rod of rare earth element oxides

globar

uses silicon carbide

merst glower, globar

what are the examples of infrared energy source?

mercury vapor lamp

Exits narrow bands of energy at well defined places in the spectrum (UV and visible)

hallow cathode lamp

Consists of a gas-tight chamber containing anode, a cylindrical cathode, and inert gas such as helium and argon.

entrance slit

Minimizes unwanted or stray light and prevents the entrance of scattered light into the monochromator system

 

stray light

refers to any wavelength outside the band transmitted by the monochromator, it causes absorbance error

stray light

limits the maximum absorbance that a spectrophotometer can achieve.

stray light

is the most common cause of loss linearity at high-analyte concentration.

monochromator

Isolate specific wavelength of light

monochromator light

light radiation of a single wavelength

prism, gratings, filters

what are the types of monochromators?

prism

Wedge-shaped pieces of glass, quarts, NaCl, or some other material that allows transmission of light

prism

Disperse white light into a continuous spectrum of colors based on variation of refractive index for different wavelength

prism

Can be rotated, allowing only the desired wavelength to pass through an exit slit

gratings

Has small grooves cut at such an angle that each groove behave like a very small prism

gratings

Separates white light into various color component

gratings

Based on the principle that wavelengths are bent as they pass a sharp corner

colored filters

Made of glass that absorb some portion of the electromagnetic spectrum and transmit others

colored filters

Light energy is absorb by dye compounds on the glass and is dissipated as heat

colored filters

Band pass in 35 to 50 nm or more

interference filter

Utilizes the wave character of light to enhance the intensity of the desired wavelength by constructive interference and reflection

interference filter

Band pass is 10 to 20 nm

produces linear spectrum therefore maintaining and constant band pass which is simple, can be used in the regions of spectrum where light energy is absorbed by glass prism

what is the advantage of gratings over prism?

exit slit

It controls the width of light beam (bandpass)

exit slit

Spectral purity of the spectrophotometer is reflected by the bandpass, the narrower the bandpass, the greater the resolution.

 

bandpass

allows only a narrow fraction of the spectrum to reach the sample cuvette

bandpass

the range of wavelengths between the points at which transmittance is one half peak transmittance

exit slit

Accurate absorbance measurement requires a bandpass <1/5 the natural bandpass of the spectrophotometer.

 

degree of wavelength isolation

is a function of the type of device used and the width or entrance and exit slit

exit slit

The degree of wavelength isolation is a function of the type of device used and the width or entrance and exit slit

analytical cell

what is the other term for cuvette?

cuvette

Used to hold the solution in the instrument whose concentration is to be measured.

glass, quartz, plastic

what is cuvette made of?

borosilicate glass cuvette, quarts or plastic, alumina silica glass

what are the types of cuvette?

borosilicate glass cuvette

for solution that do not etch glass

quartz or plastic

does not absorb UV radiation at wavelength below 320 nm

alumina silica glass

good for 340 nm and above (visible)

photodetectors

Electron tube amplifying a current that can convert transmitted energy into an equivalent amount of electrical or photoelectric energy

barrier layer cell, phototube, photomultiplier, photodiode

what are the kinds of photodetectors

barrier layer cell

Simpliest detector, least expensive; temperature sensitive

barrier layer cell

Composed of selenium on a plate of iron covered with transparent layer of silver

barrie layer cell

It requires an external voltage source but utilized internal electron transfer for current production – low internal resistance

barier layer cell

It is used in filter photometers with a wide bandpass

photocell, photovoltaic cell

what is the other term for barrier layer cell?

phototube

It contains cathode and anode enclosed in a glass case.

phototube

It has a photosensitive material that gives off electron when light energy strikes it.

phototube

It requires external voltage for operation.

photoemissive tube

what is the other term for phototube?

photomultiplier

Most common type – measures visible and UV regions

photomultiplier

Excellent sensitivity and rapid response – detects very low levels of light

photomultiplier

Detects and amplifies radiant energy

photomultiplier

It should never be exposed to room light because it will burn out

pm tube

what is the other term for photomultiplier?

photodiode

Not as sensitive as PM; excellent linearity

photodiode

Measures light at a multitude of wavelengths

photodiode

It detects less amount of light

meter

simplest method id displaying output of the detection system

read out device

what is the other term for meter?

detection of impurities, characterization of proteins, detection of functional groups

give some applications of spectrophotometer