CH INST 20/21 homework!

What are the advantages and disadvantages of decreasing the monochromator slit width

advantage: increased resolution (increase the ability to resolve closely spaced spectral peaks) disadvantage: lower signal to noise ration (smaller slit=less photons reaching the detector= lower signal to noise ratio)

What are three types of atomic spectroscopy?

atomic emission, atomic fluorescence, and atomic absorption

A hollow cathode lamp can only..

be used for analysis of the element(s) from which the cathode is made

Tungsten lamp is best source for what range of light?

320-2500 nm light

define atomic emission

Atoms are thermally promoted to the excited state through collisions in the plasma. As they return to a lower energy state, they emit photons. (No excitation source outside of the plasma is required!)

A flame can be used in both atomic absorption and atomic emission spectroscopy to atomize the sample. In which technique is a stable flame temperature more critical? Why?

it is most critical in atomic emission spectroscopy because a small fluctuation in the temperature can greatly effect the excited-state population of the atoms in the sample

For resolution = lambda/∆lambda What does each represent?

lambda is the average of the two wavelengths in question ∆lambda is their difference

What can the resolution for grating also be defined as?

nN=resolution n; diffration order N; number of grooves on the grating that are illuminated

What are advantages to using a furnace instead of a flame in atomic absorption?

-higher sensitivity because the atomized sample is in the optical path longer -a smaller sample amount is required

Describe the beam chopping method of background correction?

-uses the difference in signals when the lamp is blocked and when the lamp is not blocked to give the desired analytical signal -corrects for flame emission

What are the three methods of atomization?

1. combustion flame 2. graphite furnace 3. inductively coupled plasma

Deuterium arc lamp is best source for what range of light?

110-400 nm light

GaN based diode is best source for what range of light?

360-500 nm light

Helium-neon laser is best source for what range of light?

632.8 nm light

Draw Czerny-Turner grating monochromator and describe each component

Entrance Slit: Where polychromatic radiation from the source enters the monochromater Collimating mirror: Splits the radiation into parallel rays Reflection grating: Detracts (spread) radiation into different wavelengths Focusing mirror: It refocuses the collimated radiation Focal Plan: it is what the refocused radiation of different wavelengths is focused onto Exit Slit: It is where the monochromatic radiation leaves the monochromator

Advantage of ICP-AES (inductively coupled plasma atomic emission spectrometry) compared to atomic absorption spectrometry (AAS)

ICP-AES is lower cost

atomic absorption

The atomized sample in the flame absorbs a portion of the radiation emitted from the source, which is composed of the same element as that which is being analyzed. The amount of radiation that passes through the flame unabsorbed by the analyte is measured.

atomic fluorescence

The sample is atomized in the flame. A laser is used to promote the atoms in the flame to an excited state. As the atoms return to the ground state, they fluoresce.

Draw the schematic of a double beam spectrophotometer and define each part

reference cuvet; houses the reagent blank mirror; passes the beam to the detector Sample cuvet: holds the sample with a defined path length Amplifier: increases the detector signal for ease of display and quantitation Beam chopper: mirror that rotates to direct light to either the sample or the reference cuvet light source: proveds electromagnetic radiation in the UV, Visible, or IR region of the spectrum Detector: typically a photomultiplier tube that generates an electrical current proportional to the photon flux Scanning monochromator; wavelength selector that passes a narrow band of wavelengths to the sample by scanning through a user-defined range of selected wavelengths.

Draw the components in the single-beam spectrophotometer schematic and define each component

sample cuvet; holds the sample and has a defined path length light source; provides electromagnetic radiation in the ultraviolet (UV), visible, or infrared (IR) region of the spectrum monochromator; is typically a grating, prism, or filter that selects a narrow wavelength band of radiation and passes it to the sample Detector: It is typically a photomultiplier tube that generates an electric signal when struck by photons