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Questions and Answers
What is the typical source of UV light in analytical methods?
Which factor primarily contributes to the loss of linearity in spectrophotometric measurements?
Which type of filter is best suited for measuring stray light?
What does the entrance slit do in spectrophotometric analysis?
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In relation to reflectance photometry, which principle is used to measure the intensity of light reflected from a sample?
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Which of the following contributes to absorbance error in spectrophotometric analysis?
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What is the primary characteristic of the exit slit in spectrophotometry?
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Which light source is most commonly used in atomic absorption spectrophotometry?
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What is the primary use of an atomizer in Atomic Absorption Spectrophotometry?
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Which component is NOT necessary for a chemiluminescent immunoassay analyzer?
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In flameless Atomic Absorption Spectrophotometry, what is the primary energy source used to dissociate chemical bonds?
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Which principle does Fluorometry rely on for measuring light intensity?
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What is the role of the primary monochromator in Fluorometry?
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Which element is NOT typically measured using Atomic Absorption Spectrophotometry?
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In turbidimetry, what is primarily measured?
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What does light intensity of atoms that are emitting depend on?
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What is the advantage of using a square cuvette over a round cuvette?
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Which material is most commonly used for cuvettes intended for UV radiation?
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What does Beer's law state about the relationship between the concentration of an unknown substance and the light absorbed?
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If a solution shows an absorbance of 2.0 at 650 nm, what is its transmittance?
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What is a major reason for discarding scratched optical surfaces in cuvettes?
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What might cause consistent absorbance readings when using freshly prepared standards and reagents?
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Which is the least expensive method for isolating specific wavelengths of light?
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Which equation represents the relationship between absorbance (A) and transmittance (T)?
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Study Notes
Light/Radiant Source
- Polychromatic light sources include tungsten light bulbs, tungsten/tungsten iodide lamps, and hollow cathode lamps.
- Hollow cathode lamps are commonly used in Atomic Absorption Spectroscopy (AAS).
- Deuterium discharge lamps and mercury arc lamps are the most commonly used sources of UV light.
Entrance Slit
- Minimizes unwanted stray light.
- Stray light is the MOST COMMON cause of LOSS OF LINEARITY, especially when a substance with a narrow natural bandpass is scanned.
- Causes of stray light include deteriorated optics, second-order spectra, light dispersed by a darkened enveloped, and extraneous room light.
- Sharp cutoff filters are best for measuring stray light.
- Neutral density filters and dichromate solution verify absorbance accuracy on linearity.
Exit Slit
- Controls bandpass/bandwidth.
- A narrower bandpass leads to better photometric resolution.
- The exit slit allows +/- 5 nm in a wavelength of 500 nm (495-505).
Atomic Absorption Spectrophotometry (AAS)
- Measures light absorbed by atoms dissociated by heat.
- Used to measure unexcited trace metals such as calcium, copper, magnesium, lead, aluminum, lithium, and zinc.
- Atomizers convert ions to atoms, often through a nebulizer or a flame/graphite furnace.
- Flameless AAS uses electricity to break chemical bonds instead of flame.
- A graphite cylinder holds the sample, and electricity passes through it to evaporate the sample.
Chemiluminescence
- Light is produced from a chemical or electrochemical reaction.
- This process does not involve excitation radiation, and no monochromator is required.
- Oxidation reactions of luminol, acridinium esters, and dioxetane (Ruthenium-included) are common in chemiluminescence.
- Chemiluminescence is more sensitive than Fluorometry.
- Enzymes (bioluminescence) can enhance chemiluminescence.
Fluorometry/Molecular Luminescence Spectrophotometry
- Measures the amount of light emitted by a molecule after excitation by electromagnetic radiation.
- Requires a primary and secondary monochromator.
- The primary monochromator isolates the wavelength for excitation (non-fluorescence).
- The cuvette (absorption cell/analytical cell/sample cell) holds the solution.
Turbidimetry
- Measures light blocked by a particle in a solution.
- Used for measuring abundant large particles.
- Like spectrophotometer, the detector is behind the cuvette/sample cell.
- Square cuvettes offer an advantage over round cuvettes.
- Etched, scratched optical surfaces are discarded.
- Alumina silica is the most commonly used material for cuvettes.
- Glass cuvettes are used for the visible range, but they absorb UV light.
- Quartz cuvettes are used for UV radiation.
- Beer's law states that an unknown substance's concentration is directly proportional to the absorbed light and inversely proportional to the transmitted light.
- Concentration is directly proportional to absorbance.
- Absorbance and transmittance are inversely proportional.
- Formulas:
- A = 2.0 – log%T
- A = log 1/T
- A = -log T
- A solution having a transmittance of 1.0%T will have an absorbance of A = 2.0 – log 1.0 = 2.
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Description
This quiz covers essential concepts of light sources and slits used in Atomic Absorption Spectroscopy (AAS). Topics include the types of polychromatic light sources, the impact of entrance and exit slits on photometric resolution and stray light. Dive into the principles that affect absorbance accuracy and linearity in spectroscopic analysis.
