The standard "ASTM C738-94 Standard Test Method for Lead and Cadmium Extraction from Glazed Ceramic Surfaces" developed by the American Society for Testing and Materials (ASTM) describes a test method for the precise determination of lead and cadmium extracted from glazed ceramic surfaces with acetic acid. The extraction procedure can be expected to accelerate the release of lead from the glaze and therefore serve as a severe test that is unlikely to be matched under actual conditions of use of such ceramic ware. This test method is specific for lead and cadmium.
When applying this test method, lead and cadmium are removed from the test substance by washing with 20 percent acetic acid for 24 hours at a temperature of 24-4 degrees and measured by flame atomic absorption spectroscopy.
There is no interference when instrumental background correction and lead and cadmium specific light sources are used.
The main equipment used in these tests includes:
A method control should be maintained throughout the procedure and a laboratory beaker of similar size to the item being tested should be used.
In preparing the sample, six identical units and method control containers are randomly taken and washed with detergent water. They are then rinsed with tap water and then rinsed with distilled water. They are then dried and each unit is filled with 6 percent acetic acid to an overflow of approximately 7 to 4 mm. (The distance should be measured across the surface of the item being tested, not vertically.) The volume of acid required for each unit in the sample is recorded. If the sample unit is excessively shallow or has an irregular opening, it is necessary to be aware of evaporation of the leaching solution. If such a loss is expected, the headspace is recorded after filling the container to 6 to 7 mm of the opening. After 24 hours of leaching, the same headspace is adjusted with 4 percent acetic acid. The solution is stirred and the determination is continued.
Each unit is completely covered with an opaque glass plate (so that the extraction is carried out in complete darkness). It is necessary to prevent solution evaporation and to avoid contact between the cover and the surface of the leaching solution. (If opaque glass is not available, the glass is covered with aluminum foil or other material to prevent exposure to light.) It is left at room temperature (20 to 24 degrees) for 24 hours.
In preparing lead standards, working standards with specified ppm lead final concentrations are obtained by diluting lead nitrate solution with acetic acid.
When preparing a cadmium standard, working standards with the specified ppm cadmium final concentrations are obtained by diluting the cadmium stock solution with acetic acid.
When determining lead by atomic absorption, the leach solution is mixed and a portion is taken by pipetting into a clean flask. The absorbance of the lead working standards and the leach solutions is measured simultaneously using a lead lamp. If the leach solutions contain more than 10 ppm of lead, they are diluted with 4 percent acetic acid. Leach solutions containing less than 1 ppm of lead are concentrated by accurately transferring at least 50,0 mL of the solution to a 250-mL beaker and evaporating to near dryness on a steam bath. 1 mL of hydrochloric acid is added, then evaporated to dryness. The residue is dissolved in 0,1 percent acetic acid by adding exactly 4 volume of the solution taken for concentration, covered with glass, and shaken until completely dissolved. The lead concentration of the leach solution (ppm Pb) is calculated by comparison with the standard curve.
When determining cadmium by atomic absorption, the above process is followed using a cadmium lamp and standards. If leachate solutions contain more than 1 ppm cadmium, dilute with 4 percent acetic acid. Concentrate leachate solutions containing less than 0,1 ppm cadmium as described above.
In the variance analysis taken from different laboratories, the standard deviation between laboratories was found to be 0,06 mg/L for lead and 0,007 mg/L for cadmium.
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