To determine the concentration of lead in a water sample using atomic absorption spectroscopy AAS , follow these steps:1. Sample preparation: Collect a representative water sample and filter it to remove any suspended particles. Acidify the sample with a few drops of concentrated nitric acid HNO3 to dissolve any precipitated lead salts and to prevent microbial growth during storage.2. Calibration: Prepare a series of standard solutions containing known concentrations of lead by diluting a certified lead standard with deionized water and appropriate matrix modifiers, if necessary. Matrix modifiers are added to improve the atomization efficiency and to minimize interferences.3. Instrument setup: Set up the atomic absorption spectrometer with a hollow cathode lamp HCL specific for lead. Adjust the wavelength to the optimal absorption line for lead usually around 283.3 nm . Set the slit width, lamp current, and other instrument parameters according to the manufacturer's recommendations.4. Measurement: Aspirate the blank, standards, and sample solutions into the nebulizer, which converts the liquid into an aerosol. The aerosol is then carried by a stream of inert gas usually argon or nitrogen into the atomizer usually a graphite furnace or a flame . The atomizer converts the aerosol into gaseous atoms of lead. These atoms absorb the light emitted by the HCL at the specific wavelength. The absorption is proportional to the concentration of lead in the solution.5. Data analysis: Measure the absorbance of the blank, standards, and sample solutions. Subtract the blank absorbance from the standards and sample absorbances. Plot the corrected absorbance values of the standards against their concentrations to create a calibration curve. Use this curve to determine the concentration of lead in the sample solution.Several factors may affect the accuracy of the measurement:1. Interferences: Spectral, chemical, and physical interferences can affect the accuracy of the measurement. Spectral interferences occur when other elements in the sample absorb light at the same wavelength as lead. Chemical interferences arise from the formation of non-volatile compounds or the alteration of the atomization process. Physical interferences result from differences in viscosity, surface tension, or refractive index between the sample and standards.2. Matrix effects: The presence of other elements or compounds in the water sample may affect the atomization efficiency or the absorption of light. Matrix matching or the use of matrix modifiers can minimize these effects.3. Instrumental drift: Changes in the instrument performance over time can lead to inaccuracies in the measurement. Regular calibration and maintenance of the instrument can help to minimize drift.4. Sample contamination: Contamination of the sample or the reagents used during sample preparation can lead to inaccurate results. Use clean glassware, high-purity reagents, and deionized water to minimize contamination.5. Human error: Errors in sample collection, preparation, or analysis can affect the accuracy of the measurement. Proper training and adherence to standard operating procedures can help to minimize human error.