Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine the concentration of metal elements in samples by measuring the absorption of light by free atoms in the gas phase.

Key Principles:
1. Atomization Process: The sample is converted into free atoms using a flame, graphite furnace, or hydride generation system.
2. Absorption of Light: A hollow cathode lamp (HCL) or electrodeless discharge lamp (EDL) emits light at a specific wavelength corresponding to the target metal.
3. Beer-Lambert Law: The amount of light absorbed is directly proportional to the concentration of the analyte in the sample.
4. Monochromator & Detector: A monochromator isolates the specific wavelength of light absorbed, and a detector measures the intensity reduction.

Interferences in AAS can affect the accuracy and precision of metal concentration measurements. These interferences can be classified into several categories:

Types of Interferences:
1. Spectral Interference: Overlapping absorption lines from other elements or molecular species (e.g., oxides).
2. Chemical Interference: Reactions in the flame or furnace that prevent atomization (e.g., phosphate or sulfate forming stable compounds with metal ions).
3. Ionization Interference: High temperatures causing partial ionization of atoms, reducing absorbance.
4. Matrix Interference: Complex sample matrices affecting signal response due to variations in viscosity, surface tension, or composition.

Minimization Strategies:
1. Using background correction methods (e.g., deuterium lamp or Zeeman effect correction).
2. Adding chemical modifiers (e.g., releasing agents or ionization buffers).
3. Matrix-matching standards and using standard addition methods for calibration.

Sample preparation is a critical step in AAS analysis to ensure that metals are fully solubilized and free of interferences.

Quantitative analysis in AAS involves determining the exact concentration of metal ions in a sample.

i. Key Steps in Quantitative Analysis:
1. Instrument Calibration: Establishing a standard calibration curve.
2. Sample Measurement: Recording absorbance values for unknown samples.
3. Data Processing: Applying Beer-Lambert law to determine concentrations.

ii. Standard Calibration Curve
A standard calibration curve is essential for accurate quantification in AAS.

Procedure:
i. Prepare Standard Solutions with known metal concentrations.
ii. Measure Absorbance of each standard using AAS.
iii. Plot Absorbance vs. Concentration to obtain a linear calibration curve.
iv. Determine Sample Concentration by comparing absorbance with the calibration curve.

iii. Limit of Detection (LOD):
- The lowest concentration of an analyte that can be detected but not necessarily quantified.

iv. Limit of Quantification (LOQ):
- The lowest concentration that can be reliably quantified with accuracy and precision.

The assessment consists of multiple-choice questions (MCQs) including calculation-based problems, covering fundamental principles, components, atomization processes, sample preparation, and quantitative analysis in AAS.