Passage VI

Eating chips of lead-based paint is a cause of lead poi­soning in children. According to the law, paint is considered lead-based if the lead content exceeds 0.5% by weight. Atomic-absorption spectroscopy (AAS) is used to determine the lead content of paint. Samples containing lead in solution are vaporized in a flame, and light of a single wavelength characteristic of lead is shone through the flame. The absorbance measures the amount of light absorbed by the lead in the flame. The following experi­ments were done using AAS.

Experiment 1

Solutions with known concentrations of lead were prepared and their absorbances were measured (see Figure 1).

Experiment 2

Paint chips were collected from interior walls and exterior walls and from outdoor furniture at House A. built in 1945. The paint chips from a given location were pow­dered. Then 100 mg samples of the powder were treated with nitric acid and heated for at least 30 minutes to convert all of the lead to soluble lead nitrate. The solutions were evaporated to a dry powder, then dissolved in hydrochloric acid and diluted to 100 mL with H₂O. The absorbances were treasured and the lead concentrations were determined using the data in Figure 1. The % lead (average weight percent of lead in the paint) at the location was then calculated. The same analysis was performed at House B, built in 1990 (see Table 1).