Atomic absorption spectroscopy AAS is a widely used analytical technique for the quantitative determination of heavy metals like lead, mercury, and arsenic in water samples. The process involves the absorption of light by free atoms in the gaseous state. Here's a step-by-step guide on how to accurately quantify the concentration of heavy metals in a water sample using AAS:1. Sample preparation: Collect a representative water sample and filter it to remove any suspended particles. Acidify the sample using concentrated nitric acid HNO3 to prevent the precipitation of metal ions and preserve the sample.2. Digestion: In some cases, it may be necessary to perform a digestion step to convert the heavy metals into a soluble form. This can be done using a mixture of concentrated acids, such as nitric acid and hydrochloric acid, and heating the sample to break down complex organic materials.3. Calibration: Prepare a series of standard solutions containing known concentrations of the heavy metals of interest. These standards will be used to create a calibration curve, which will help determine the concentration of heavy metals in the water sample.4. Atomization: Introduce the water sample and the standard solutions into the AAS instrument using a suitable atomization technique, such as flame atomization or graphite furnace atomization. The atomization process converts the metal ions in the sample into free atoms in the gaseous state.5. Measurement: The AAS instrument irradiates the atomized sample with light of a specific wavelength, which is characteristic of the heavy metal being analyzed. The free atoms in the gaseous state absorb this light, and the amount of absorbed light is proportional to the concentration of the heavy metal in the sample.6. Data analysis: Compare the absorbance values of the water sample to the calibration curve generated from the standard solutions. This will allow you to accurately quantify the concentration of heavy metals in the water sample.7. Regulatory guidelines: Compare the measured concentrations of heavy metals in the water sample to the regulatory guidelines for safe drinking water. In the United States, the Environmental Protection Agency EPA sets the maximum contaminant levels MCLs for various heavy metals in drinking water. For example, the MCL for lead is 15 ppb parts per billion , for mercury is 2 ppb, and for arsenic is 10 ppb. If the concentrations of heavy metals in the water sample are below these limits, the sample is considered safe for consumption according to the regulatory guidelines.By following these steps, you can accurately quantify the concentration of heavy metals in a water sample using atomic absorption spectroscopy and determine if the sample is safe for consumption according to regulatory guidelines.