New analytical chemistry exam 2

what is so special about atomic absorption spectroscopy

very specific, measures trace metals that are not as easily excited

uses a hollow cathode lamp containing the analyte

uses a chopper

uses a nebulizer and flame 

uses a graphite furnace

In atomic absorption spectroscopy absorbances is…

proportional to the analyte concentration

what does a chopper do in AAS?

allows differentiation between light transmitted vs light emitted

what does the nebulizer and flame do in AAS?

-disperses sample

-converts metal ions into atoms in their ‘ground state’

where does the monochromator sit in relation to the sample and the photodetector in AAS?

Between the sample and the photodetector

What is the chemical interference with AAS and how is it overcome?

Phosphate interfers w/ calcium measurement, this is overcome by adding lanthium or strontium to bind the phosphate

What is so special about chemiluminescence?

there doesnt need to be a light source or monochromator, it is also proportional to its concentration

How are turbidimetry and nephelometry similar

both depend on wavelength and size (suspension)

Both are sensitive and used in immuno assays

Interference with turbidimetry and nephelometry

lipidemia, non-scratched cuvet

What does turbidimetry measure?

Decrease in light transmitted

what does nephlometry measure?

light scattered at a defined angle

Why is turbidimetry special?

it can be used to measure large macromolecules

detected at a 0* angle

Inversely related to particle concentration

In nephlometry, the bigger the particle size the…

more forward and straight the scattering of light is

what is so special about phosphorescence?

Paired electrons in triplet excited state- light emissions continue 

What is so special about luminescence ?

Best for Electron rich molecules

What is so special about reflectance spectrophotometry

inversely related to the analyte concentration

uses a flat surface

photodetector is set at a 90* angle relative to the light source

Disadvantage to fluorescence ?

quenching- sensitivity to enviromental changes like temp. and ph

Advantage to fluorescence ?

Specificity and sensitivity

What is fluorescence ?

when exposed to short wavelength, high-energy radtion, certain molecules absorb the energy and become excited, when these molecules come down from that high to their resting state, they emit longer wavelengths, lower energy radiation

-porportional to the concentration

excitation stage is first, then emission phase 

what do exit and entrance slits do in regards to the size of the slit?

narrow slits make the bandpass smaller, leading to a better resolution.

Whats do filters do?

construcive interference that occurs as light passes through a thin film

What do prisms do?

as light enters the glass at an angle, it bends b/c of the difference between the speed of light in air and in the glass

glass cuvet is used for

visible light

tungsten is used for

visible light and greater than 360nm

quarts cuvet is used for 

uv light 

deterium is used for

uv light, and greater than 165nm

What is bandpass?

defines the range of wavelengths trasnmitted through

a decrease in bandpass correlates with a higher resolution, but a lower noise-noise ratio

-requires less than 1/5 natural bandpass

what does a monochromator do?

A wavelength selector that isolates desired wavelengths & excludes others

what is diffraction grating?

Light reflected off the surface will produce constructive interference for different wavelengths at different angles of reflection

What is this?

photmultiplier tube

What is this?

Phototube

What is this?

photodiode

What is this?

Diode arrays

The 1^st  step in any spectrophotometric measurement is…

establishing the optimal absorbance wavelength (۸_max)  for the analyte

-By running a spectral absorption curve

What is this?

Diffraction grating