UV/VIS Spectroscopy Overview

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Questions and Answers

Which component of an ICP-OES system disperses emitted radiation into different directions?

  • Torch
  • Polychromator (correct)
  • Nebulizer
  • Detector

A monochromator is capable of analyzing multiple wavelengths simultaneously.

False (B)

What gas is used to create the plasma in an ICP-OES?

Argon

The _____ is responsible for introducing a liquid sample into the ICP-OES system.

<p>Nebulizer</p> Signup and view all the answers

Match the detector types with their features:

<p>Photomultiplier tubes = Measures light intensity Laser induced fluorescence = Uses lasers for detection Charge-coupled device (CCD) = Captures image and spectrum Mass spectrometer = Analyzes ions based on mass-to-charge ratio</p> Signup and view all the answers

Which light source is commonly used in Atomic Absorption Spectroscopy (AAS)?

<p>Hollow Cathode Lamp (C)</p> Signup and view all the answers

Flame Emission Spectroscopy (FES) is more sensitive than Atomic Absorption Spectroscopy (AAS).

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of nebulization in sample introduction?

<p>To transform the liquid sample into a fine mist.</p> Signup and view all the answers

The ________ is responsible for providing the required heat to atomize the sample in AAS.

<p>Flame and Burner</p> Signup and view all the answers

What is a limitation of Atomic Absorption Spectroscopy (AAS)?

<p>It only provides quantitative analysis. (B)</p> Signup and view all the answers

Flame Nebulization involves mixing the sample mist with air and combusting it with _____ gas.

<p>fuel</p> Signup and view all the answers

Match the detector types with their characteristics:

<p>Flame Spectroscopy = Simple and cost-effective for visible light Atomic Absorption Spectroscopy = Highly sensitive for trace amounts Graphite Furnace Atomization = Improved sensitivity for trace detection Flame Nebulization = Uses a burner and flame to atomize</p> Signup and view all the answers

Name one alternative to the Hollow Cathode Lamp for light sources.

<p>Electrodeless Discharge Lamps (EDL)</p> Signup and view all the answers

What is the primary purpose of a monochromator in analytical chemistry?

<p>To select a specific wavelength of light (D)</p> Signup and view all the answers

The presence of anions in a sample can lead to anionic interference that improves the detection of the analyte.

<p>False (B)</p> Signup and view all the answers

What type of detector is often used in analytical instruments due to its sensitivity in detecting low light intensities?

<p>Photomultiplier tubes</p> Signup and view all the answers

A ______ flame can achieve higher temperatures than an air/acetylene flame.

<p>nitrous oxide</p> Signup and view all the answers

Match the following types of interference with their causes:

<p>Ionization = High temperatures causing partial ionization Viscosity = High viscosity leading to incomplete atomization Anionic Interference = Presence of phosphate ions complexing with analyte Spectral Interference = Overlapping absorption or emission lines</p> Signup and view all the answers

What effect does ionization have on measurement sensitivity?

<p>Decreases sensitivity (B)</p> Signup and view all the answers

A detector measures light intensity after it has been directly sourced from the flame.

<p>True (A)</p> Signup and view all the answers

Name a treatment method used to correct for viscosity interference in samples.

<p>Advanced instruments like double-beam spectrometers or background correction methods.</p> Signup and view all the answers

Flashcards

ICP-OES Principle

ICP-OES uses an argon plasma to excite atoms. Excited atoms emit specific wavelengths (light) which identify the elements. The light intensity relates to the element's concentration.

ICP-OES Nebulizer

The nebulizer turns liquid samples into a mist to enter the plasma.

ICP-OES Torch Function

The torch converts argon gas into a plasma using radio waves, to excite the sample's atoms.

ICP-OES Polychromator

The polychromator separates the light from the plasma into various wavelengths (colors of light).

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ICP-OES High Sensitivity

ICP-OES can detect very low amounts of elements (ppm, ppb, ppt).

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Atomic Absorption Spectroscopy (AAS)

A technique that measures the absorption of light by atoms in a sample, used for detecting trace elements.

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Flame Emission Spectroscopy (FES)

A technique that measures the emission of light by atoms when heated, used for analyzing elements that emit visible light.

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Hollow Cathode Lamp

A light source in AAS that emits specific wavelengths of light corresponding to the element being analyzed.

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Nebulization

The process of transforming a liquid sample into a fine mist for introduction into a flame or furnace.

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Graphite Furnace Atomization

A sample introduction method in AAS that uses a graphite tube to atomize the sample at high temperatures, increasing sensitivity.

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Trace Element Detection

Identifying very small amounts of elements in a sample.

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Quantitative Analysis

Measuring the amount of a substance in a sample.

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Sample Matrix

The materials surrounding the element of interest in a sample that can interfere with analysis.

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Flame Atomization

Uses a flame (usually air/acetylene) to heat a sample to its atomic state for analysis.

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Monochromator Function

Isolates a specific wavelength of light (color).

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Ionization Interference

High flame temperatures cause elements to become ions, reducing free atoms for accurate measurement.

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Ionization Suppressors

Added to flames to prevent ionization errors and improve sensitivity.

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Viscosity Interference

High sample viscosity in methods like graphite furnaces can cause incomplete atomization, leading to background interference.

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Spectral Interference

Overlapping absorption/emission lines from sample components or instrument parts, creates wrong readings.

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Anionic Interference

Anions in the sample can complex with the analyte, affecting accurate measurements.

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Detector Function

Measures the intensity of light after it passes through the flame, indicating element concentration

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Study Notes

Electromagnetic Radiation (EMR)

  • EMR is radiant energy released through electromagnetic processes
  • Covers a range of frequencies called the electromagnetic spectrum
  • UV/VIS spectroscopy uses specific parts of the spectrum (UV: 200-400nm; Visible: 400-700nm) to analyze matter

Spectroscopy vs. Spectrometry

  • Spectroscopy studies the interaction between matter and radiated energy
  • Spectrometry is the quantitative measurement of the spectrum (light intensity vs. wavelength)
  • Spectrophotometry measures how much light is reflected or transmitted by a sample at different wavelengths

Principle of UV/VIS Spectroscopy

  • UV/VIS spectroscopy measures the absorbance of ultraviolet (UV, 185-400 nm) and visible (VIS, 400-700 nm) light by a sample
  • Light passing through the sample is partly absorbed; remaining light is transmitted
  • Each compound absorbs light at a specific wavelength (the analytical wavelength), revealing its concentration and composition
  • Absorption is due to electron excitation in chromophores (molecular regions) from a lower to a higher energy state
  • Absorbance (A) follows the Beer-Lambert law: absorbance is proportional to the concentration of absorbing species in the sample

How UV/VIS Spectroscopy Works

  • Radiation passes through a solution; bonding electrons become excited
  • Excited electrons occupy a higher quantum state, absorbing some energy from the radiation
  • The lower the electron's energy in the bonds, the longer the wavelength of absorbed energy
  • Transmitted light is measured; unabsorbed light passes through the sample solution

Interactions of UV/VIS Radiation with Chromophores

  • Chromophores are functional groups within molecules responsible for light absorption
  • These groups have specific energy gaps between orbitals that align with visible light
  • Alternating double bonds affect color by absorbing specific wavelengths and transmitting others
  • Isolated chromophores absorb at specific wavelengths
  • Conjugated chromophores absorb at longer wavelengths (bathochromic shift) and are more intense (hyperchromic effect)
  • Examples of chromophores include the amine group (-NH2) and the nitro group (-NO2)

General Applications of UV/VIS Spectroscopy

  • Quantitative Analysis: Determines compound concentration using Beer-Lambert law
  • Qualitative Analysis: Identifies compounds based on their absorption spectrum
  • Monitoring Reactions: Tracks changes in absorbance over time to study reaction kinetics
  • Purity Testing: Detects impurities in pharmaceuticals, chemicals, and biological samples

Strengths and Limitations of UV/VIS Spectroscopy

  • Strengths*
  • Non-destructive and simple to use
  • Quick, providing fast results
  • Can be used for qualitative and quantitative analysis
  • Inexpensive compared to other advanced techniques (NMR, MS)
  • Limitations*
  • Limited structural information (can only determine chromophore presence)
  • Spectral overlap in mixtures can complicate analysis
  • Requires samples to have chromophores for light absorption

Instrumentation Components

  • Light Source (UV/VIS): Deuterium (UV) or Tungsten (Visible) lamp
  • Monochromator: Disperses light into its component wavelengths
  • Slits: Control beam width - narrow for higher resolution but reduced light intensity)
  • Optics: Lenses/mirrors (often achromatic) to focus light onto/from the sample
  • Sample Cells: Quartz (UV) or glass (visible) - cuvettes for samples
  • Detector: Photomultiplier tubes (PMTs), or photodiode arrays (PDAs) to convert light into an electrical signal (higher sensitivity preferred)

Light Intensity and Beer-Lambert Law

  • Transmission (T): Ratio of transmitted light intensity to incident light intensity
  • Absorbance (A): Logarithmic measure of light absorbed by the sample (A = -logT)
  • Beer-Lambert Law: Relates absorbance to concentration and path length (A = εcl, where ε = molar absorptivity, c = concentration, l = path length)

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