Preparation of Sample—
From a homogeneous plastic specimen, use a portion, for each 20.0 mL of extracting medium, equivalent to 120 cm
2 total surface area (both sides combined), and subdivide into strips approximately 3 mm in width and as near to 5 cm in length as is practical. Transfer the subdivided
Sample to a glass-stoppered, 250-mL graduated cylinder of Type I glass, and add about 150 mL of
Purified Water. Agitate for about 30 seconds, drain off and discard the liquid, and repeat with a second washing.
Transfer the prepared
Sample to a suitable extraction flask, and add the required amount of
Extracting Medium. Extract by heating in a water bath at the temperature specified for the
Extracting Medium for 24 hours. Cool, but not below 20
. Pipet 20 mL of the extract of the prepared
Sample into a suitable container. Use this portion in the test for
Buffering Capacity. Immediately decant the remaining extract into a suitably cleansed container, and seal.
Blank—
Use
Purified Water where a blank is specified in the following tests.
NONVOLATILE RESIDUE—
Transfer, in suitable portions, 50.0 mL of the extract of the prepared
Sample to a suitable, tared crucible (preferably a fused-silica crucible that has been acid-cleaned), and evaporate the volatile matter on a steam bath. Similarly evaporate 50.0 mL of the
Blank in a second crucible.
[NOTE—If an oily residue is expected, inspect the crucible repeatedly during the evaporation and drying period, and reduce the amount of heat if the oil tends to creep along the walls of the crucible.
] Dry at 105
for 1 hour: the difference between the amounts obtained from the
Sample and the
Blank does not exceed 15 mg.
RESIDUE ON IGNITION 
281
—
[NOTE—It is not necessary to perform this test when the
Nonvolatile Residue test result does not exceed 5 mg.
] Proceed with the
Nonvolatile Residue obtained from the
Sample and from the
Blank, using, if necessary, additional sulfuric acid but adding the same amount of sulfuric acid to each crucible: the difference between the amounts of residue on ignition obtained from the
Sample and the
Blank does not exceed 5 mg.
HEAVY METALS—
Pipet 20 mL of the extract of the prepared
Sample, filtered if necessary, into one of two matched 50-mL color-comparison tubes. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH paper as external indicator, dilute with water to about 35 mL, and mix.
Into the second color-comparison tube pipet 2 mL of
Standard Lead Solution (see
Heavy Metals 231), and add 20 mL of the
Blank. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH paper as external indicator, dilute with water to about 35 mL, and mix. To each tube add 1.2 mL of thioacetamide-glycerin base TS and 2 mL of
pH 3.5 Acetate Buffer (see
Heavy Metals 231), dilute with water to 50 mL, and mix: any brown color produced within 10 minutes in the tube containing the extract of the prepared
Sample does not exceed that in the tube containing the
Standard Lead Solution, both tubes being viewed downward over a white surface (1 ppm in extract).
BUFFERING CAPACITY—
Titrate the previously collected 20-mL portion of the extract of the prepared Sample potentiometrically to a pH of 7.0, using either 0.010 N hydrochloric acid or 0.010 N sodium hydroxide, as required. Treat a 20.0-mL portion of the Blank similarly: if the same titrant was required for both Sample and Blank, the difference between the two volumes is not greater than 10.0 mL; and if acid was required for either the Sample or the Blank and alkali for the other, the total of the two volumes required is not greater than 10.0 mL.
