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C30F Analytical Chemistry Experiments
Pb lead in old paint

Determination of lead in paint scrapings

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Pb in Paint

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Determination of lead in paints
To collect and analyse samples of paints for lead content.


Introduction

Lead compounds have been used in paints as pigments, anti-corrosive ingredients, or drying agents. Consequently, our surroundings contain a great deal of lead in paints used for metal protection, decorative finishes, or to accelerate the drying of spray paints.
Problems of lead intoxication can arise, particularly in children, if peeling or chipping paint films are ingested, usually by the habit refered to as pica (1), which is the tendency to place foreign objects in one's mouth by instinct. Lead in paints, particularly in schools and houses with young children,is of great concern since the effects of lead poisoning increases inversely with age (1). The effects of lead poisoning include decreased neuromuscular activity, retarded mental development, reduced ability to learn, and at the other extreme, death (2).
The aims of this experiment are to investigate the levels of lead in paints in buildings or structures to which young children are exposed.The risk of exposure can then be assessed, and recommendations made on further action.

Experimental

1. Sample Collection

Use a sharp stainless steel knife or spatula and a clean dustpan or sheet to collect samples. After locating suitable sites,scrape about 20 g of paint film that is peeling or cracking from an area approx. 1.5 to 2 square meters. Transfer to a clean sheet of aluminium foil, seal, label and note the foll. details:
(i) Paint samples
(ii) Color of paint
(iii) Age of paint film
(iv) Single or multiple layers of film
(v) Surface from which taken (wood, metal, glass etc...) and approx. area sampled.

2. Sample preparation for analysis

(i) Dry each sample at 130° in an oven for at least one hour.
(ii) Cool, grind finely in a mortar, and shake through sieve provided (note mesh size used)
(iii) Weigh triplicate aliquots of each paint (~0.2g) into boiling tube, and add 10ml conc. nitric acid. Allow to predigest at room temperature for 10 - 12 hours.
(iv) Digest at 130° for 1 hour, cool, dilute with 10ml distilled water. Filter through Whatman #1 filter paper into 100 ml volumetric flasks, and make up to mark with distilled water washings of residues.
(v) Make appropriate dilutions of sample. See Demonstrator or Technician.

3. Lead determination

(i) Set up atomic absorption spectrometer with hollow cathode lamp set at 283.3 nm for air acetylene flame mode of analysis.
(ii) Prepare 25 ml volume of lead standards from the 100 ppm stock provided, namely:
0.5, 1.0, 2.0, 4.0, 8.0, and 10 ppm.
(iii) Run standards and samples.
(iv) Prepare a calibration curve and determine sample concentrations, and express as % by weight.

4. Discussion

(1) Comment on the method of sample collection and preparation used, with reference to problems experienced. Suggest methods of overcoming such problems.
(ii) Discuss the values obtained for your paint samples, and possible problems of exposure to young children. What advice would you give on this matter?

5. References

(1) Boecix, R.L. (1986) Lead poisoning in Children. Anal. Chem. 58, 275-281.
(2) Centers fof Disease Control (1991). Preventing Lead Poisoning in Young Children. USDHSS, USA.



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