Atomic Absorption Spectroscopy Overview

Overview

This lecture covers how to use atomic absorption spectroscopy (AAS) to analyze the concentration of hard water ions—specifically calcium and magnesium—in tap water.

Atomic Absorption Spectroscopy Basics

• Atomic absorption spectroscopy (AAS) measures the concentration of elements in a sample by detecting light absorbance.
• Instruments are set up separately for calcium and magnesium analysis.
• Each element has its own lamp filled with that element's vapor.

Sample and Standard Analysis

• Standard solutions with known concentrations (2, 5, 15, 25 mg/L) are analyzed to create a calibration curve.
• Tap water samples are prepared and tested for calcium and magnesium using the respective spectrometers.
• The sample is introduced into a flame, causing atoms to excite and emit/absorb specific light.

Data Collection and Graphing

• Absorbance (y-axis) is plotted against concentration (x-axis) for standard solutions.
• The relationship between absorbance and concentration should be linear.
• Use LabQuest, Excel, or manual graphing to plot data and draw the best fit straight line.

Beer's Law and Calculations

• Beer's Law: Absorbance = ε (molar absorptivity) × b (path length in cm) × c (concentration).
• The slope of the calibration line equals ε × b (should be 1 cm).
• For unknown samples, rearrange the line equation to solve for concentration using measured absorbance.

Comparison and Reporting

• Determined concentrations for calcium and magnesium are compared to values in the lab manual's hard water data table.

Key Terms & Definitions

• Atomic Absorption Spectroscopy (AAS) — Technique to determine element concentration by measuring light absorption.
• Standard Solution — Solution with a known concentration used for calibration.
• Absorbance — Measure of the amount of light absorbed by a sample.
• Beer's Law — A linear relationship between absorbance and concentration of an absorbing species.
• Calibration Curve — Graph plotting absorbance vs. concentration for standard solutions.

Action Items / Next Steps

• Complete the pre-lab questions before starting the lab session.
• Analyze tap water and standard samples for calcium and magnesium.
• Graph and interpret your data using LabQuest, Excel, or manual methods.
• Compare your results to the hard water data table in your lab manual.