1. Lead Sensor Development Our Lady of the Lake University 411 S.W. 24 th Street San Antonio, Texas 78207 Elizabeth Walther Directed by Dr. Charles A. Smith
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4. In order to develop a lead sensing pad a chemical reaction is needed. The chemical reaction chosen is: The lead sulfide precipitate has a black color and should be easily seen on a white pad. The sulfide is in several forms in solution related by the below equilibria: It is assumed from these equilibria that the reaction may proceed most efficiently at pH above 12.9 since sulfur will mostly be in the form of S -2 . Chemistry of lead sensing pad
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8. Equal volumes of different concentrations of lead were placed on a surface and allowed to dry over night. The following day 30% sodium sulfide solution was placed on the pad and rubbed over each dried lead solution for thirty seconds. Method Development: color of wipe at different concentrations 10 ppm 50 ppm 100 ppm 1000 ppm Resulting Color on Wipe Concentration of Lead (Pb)
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11. Standard Addition Technique and Relations The concentration of analyte in the sample, Cx , is determined by the below equation: where b is the y-intercept, m is the slope, Cs is the concentration of stock solution added to each addition flask and Vx is the volume of original solution placed in each addition flask. The weight percent is then calculated by dividing the mass of analyte determined through standard addition divided by the orignal mass of the entire sample digested.
12. The presence of lead in samples was verified using the atomic absorption spectrometer. Standard addition plots were prepared and calculations performed. Weight percent of lead in digested old green paint=0.19% Weight percent of lead in digested old black paint =0.79% The Standard Addition Technique of Lead-based Paint m=0.79 b=0.149 COR=0.9 Volume of stock added Signal m =1.01 b=0.04 COR=0.99 Volume of stock added Signal
![Lead in our environment… ,[object Object],The paint on the painted sample in the photo was made during the 1950s. Paint made before 1978 contains unhealthy levels of lead. The pad in the photo was coated with a solution of sodium sulfide and rubbed on the paint. A resulting dark patch can be seen indicating the presence of lead in the paint.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)