Unit 1: Analytical Techniques Flashcards
Q: What is mass spectrometry?
A: A technique involving ionisation, separation, and detection of ions to determine isotopic composition.
Q: What information does a mass spectrum provide?
Relative atomic mass
Isotopic composition
Percentage abundance of isotopes
Booklet:
It can be used to determine the isotpic compositon of elements or to examine the structure of organic molecules
Q: What is the difference between absorption and emission spectra?
A: - Absorption spectrum: Electrons absorb energy and move to higher levels.
Emission spectrum: Electrons release energy as they return to lower levels.
Q: How do flame tests and atomic absorption spectroscopy (AAS) work?
A: They rely on electron transitions between energy levels to identify elements and measure ion concentrations.
Q: What does the hydrogen emission spectrum indicate?
A: - Evidence for discrete energy levels (Bohr model)
Convergence of levels at higher energy
What does a mass spectrometer consist of
anionisation chamber,astrong electromagnet and adetector.
A sample is vaporized, ionized by high-energy electrons, and accelerated through a magnetic field. Heavier ions are deflected less, traveling in a wider curve, while lighter ions are deflected more, following a tighter curve. More highly charged ions are also deflected more.
Q: How does AAS compare to the flame test?
Both involve excitation of electrons.
The flame test is qualitative, while AAS is quantitative and can determine metal ion concentrations.
Q: What is the role of the hollow cathode lamp in AAS?
A: It emits light of specific frequencies that match the absorption wavelengths of the target metal ions.
Q: What is the relationship between absorbance and concentration in AAS?
A: The amount of light absorbed is proportional to the concentration of the metal ion in solution.
Q: What is the purpose of an AAS calibration curve?
A: To determine unknown concentrations of metal ions by comparing their absorbance to a standard curve.
Q: What are the steps for using an AAS calibration curve?
Create a calibration curve using known concentrations.
Measure the absorbance of the unknown sample.
Use the graph to determine the concentration by matching absorbance values.
Account for dilution if necessary.
Q: Why is a calibration curve needed in AAS?
A: Because absorbance values must be compared to known standards to quantify the concentration of metal ions.
Q: What units are commonly used for concentration in AAS?
A: mg/L or ppm (parts per million).
Q: What is the ground state of an atom?
A: The lowest energy state where all electrons are in their normal orbitals.
Q: What happens when an atom absorbs energy?
A: Electrons jump to a higher energy level, putting the atom in an excited state.
Q: How do excited electrons return to the ground state?
A: They release energy in the form of light (photon emission), producing an emission spectrum.
Q: How does the energy of emitted light relate to its color?
Violet = Highest energy
Red = Lowest energy
Q: What is the difference between absorption and emission spectra?
A: - Absorption spectrum: Dark lines where light is absorbed.
Emission spectrum: Bright lines where light is emitted.
What is AAS
Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine the concentration of specific metal elements in a sample by measuring the amount of light absorbed by free atoms in the gaseous state.
Advantages and disadvantages of MS
✅ Advantages:
High Sensitivity – Detects very low concentrations.
Precision – Accurate mass measurements.
Versatile – Analyzes a wide range of substances.
Quantitative & Qualitative – Provides both structural and concentration data.
Rapid – Quick results, often in minutes.
❌ Disadvantages:
Expensive – High cost for equipment and maintenance.
Complex – Requires skilled operators.
Destructive – Consumes samples during analysis.
Sample Prep Needed – Some samples require extensive preparation.
Advantages and disadvantages of AAS
Advantages:
High Sensitivity & Accuracy – Detects trace metals (ppm/ppb).
Fast & Cost-Effective – Quick analysis, lower cost than ICP-MS.
Reliable & Widely Used – Minimal sample prep, used in various fields.
❌ Disadvantages:
Metal-Specific – Only detects metals, not non-metals.
Single-Element Analysis – Slower for multi-element testing.
Interference Issues – Matrix effects can affect accuracy.
Destructive & Skill-Dependent – Consumes samples; requires trained users.
Flame test colours: Lithium
Red
Flame test colours: Potassium
Lilac
Flame test colours: Sodium
Yellow
Flame test colours: Calcium
Orange-Red
Flame test colours: Copper
Green
Flame test colours: Barium
Blue-Green
Key point for understanding atomic absorption spectroscopy
that light withspecific frequencies areabsorbed by different metals when they are vaporised
Parts of AAS
Light Source – A hollow cathode lamp that emits specific wavelengths for the element being analyzed.
Atomizer – Converts the sample into free atoms (usually a flame or graphite furnace).
Monochromator – Selects the specific wavelength of light absorbed by the element of interest.
Detector – Measures the amount of light absorbed by the sample.
Signal Processor – Converts the detector’s output into a readable data format for analysis.
