Gunshot Residue Analysis You are provided with cotton balls that were used to swab 2 suspect’s hands for the presence of gunshot residue. Determine, by atomic absorption spectroscopy, if either of the 2 have fired a gun recently. To do this you will first extract the lead residue off of the cotton ball and then you will run the lead samples and a lead positive sample and a blank to determine if there is lead in the residue from the suspect’s hands. Extraction/Sample Prep: 1.) Use tweezers or forceps to remove the cotton ball from its container and place it into a plastic centrifuge tube. Add 10 mL of 1% nitric acid and shake well. Continue shaking occasionally for 10 minutes. 2.) Remove the supernatant (the liquid in the tube) with a transfer pipet and place it into a labeled 25 mL volumetric flask. 3.) Add 1 mL of Ammonium dihydrogen phosphate solution. 4.) Dilute the contents of the flask with 1% nitric acid. 5.) Label the flask(s) as unknowns (1,2). Positive and negative control samples: 1.) Add 1 mL of lead standard to a 25 mL volumetric flask. 2.) Add 1 mL of Ammonium dihydrogen phosphate solution. 3.) Dilute the contents of the flask with 1% nitric acid. 4.) Label the flask as positive control #1 5.) Add 0.5 mL of lead standard to a 25 mL volumetric flask. 6.) Add 1 mL of Ammonium dihydrogen phosphate solution. 7.) Dilute the contents of the flask with 1% nitric acid. 8.) Label the flask as positive control #2 9.) Add 1 mL of Ammonium dihydrogen phosphate solution. 10.) Dilute the contents of the flask with 1% nitric acid. 11.) Label the flask as negative control.

The instructor will show you how to run the Atomic Absorption spectrometer and collect the data. Were any of the swab samples positive for lead?