To determine the concentration of lead Pb in a water sample collected from a local stream using atomic absorption spectroscopy AAS , we will follow these steps:1. Collection and preparation of the water sample2. Calibration of the atomic absorption spectrometer3. Analysis of the water sample4. Calculation of the lead concentrationStep 1: Collection and preparation of the water sampleCollect a representative water sample from the local stream. The sample should be collected in a clean, acid-washed polyethylene bottle. To minimize contamination, rinse the bottle three times with the water to be sampled before filling it. Preserve the sample by adding 2 mL of concentrated nitric acid HNO3 per liter of sample. This will help to dissolve any lead particulates and prevent any microbial activity that could alter the lead concentration. Store the sample in a cool, dark place until analysis.Step 2: Calibration of the atomic absorption spectrometerPrepare a series of lead standard solutions with known concentrations, e.g., 0, 1, 5, 10, and 20 g/L micrograms per liter by diluting a lead stock solution with deionized water. Analyze each standard solution using the AAS and record the absorbance values. Plot a calibration curve by graphing the absorbance values y-axis against the lead concentrations x-axis . The calibration curve will be used to determine the concentration of lead in the water sample.Step 3: Analysis of the water sampleFilter the water sample using a 0.45 m membrane filter to remove any suspended particulates. Dilute the filtered sample, if necessary, to bring the lead concentration within the range of the calibration curve. Analyze the diluted sample using the AAS and record the absorbance value.Step 4: Calculation of the lead concentrationUsing the absorbance value obtained for the water sample, determine the lead concentration from the calibration curve. If the sample was diluted, multiply the concentration obtained from the calibration curve by the dilution factor to obtain the lead concentration in the original water sample. Report the lead concentration in g/L micrograms per liter or ppb parts per billion .Example:Suppose the absorbance value for the water sample was 0.150, and the calibration curve equation is y = 0.010x, where y is the absorbance and x is the lead concentration in g/L. If the sample was diluted 10 times before analysis, the calculation would be as follows:0.150 = 0.010xx = 0.150 / 0.010x = 15 g/L concentration in the diluted sample Lead concentration in the original water sample = 15 g/L * 10 dilution factor = 150 g/LIn conclusion, the concentration of lead Pb in the water sample collected from the local stream is 150 g/L or 150 ppb.