Tests

If necessary, cut the material to be examined into pieces of maximum dimension on a side of not greater than 1 cm.

Solution S1. Place 2.0 g in a borosilicate-glass flask with a ground-glass neck. Add 80 ml of toluene R and heat under a reflux condenser with constant agitation for 90 min. Allow to cool to 60 °C and add 120 ml of methanol R to the flask with constant stirring. Filter the solution through a sintered-glass filter (16). Rinse the flask and the filter with 25 ml of a mixture of 40 ml of toluene R and 60 ml of methanol R, add the rinsing mixture to the filtrate and dilute to 250 ml with the same mixture of solvents.

Solution S2. Use within 4 h of preparation. Place 25 g in a borosilicate-glass flask with a ground-glass neck. Add 500 ml of water for injections R and boil under a reflux condenser for 5 h. Allow to cool and decant. Reserve a portion of the solution for the test for appearance of solution S2 and filter the rest through a sintered-glass filter (16).

Appearance of solution S2. Solution S2 is clear (2.2.1) and colourless (2.2.2, Method II).

Acidity or alkalinity. To 100 ml of solution S2 add 0.15 ml of BRP indicator solution R. Not more than 1.0 ml of 0.01 M sodium hydroxide is required to change the colour of the indicator to blue. To 100 ml of solution S2 add 0.2 ml of methyl orange solution R. Not more than 1.5 ml of 0.01 M hydrochloric acid is required to reach the beginning of the colour change of the indicator from yellow to orange.

Absorbance (2.2.25). At wavelengths from 220 nm to 340 nm, the absorbance of solution S2 is not greater than 0.2.

Reducing substances. To 20 ml of solution S2 add 1 ml of dilute sulphuric acid R and 20 ml of 0.002 M potassium permanganate. Boil under a reflux condenser for 3 min and cool immediately. Add 1 g of potassium iodide R and titrate immediately with 0.01 M sodium thiosulphate, using 0.25 ml of starch solution R as indicator. Carry out a blank titration. The difference between the titration volumes is not more than 0.5 ml.

Amides and stearic acid. Examine by thin-layer chromatography (2.2.27), using 2 plates of the TLC silica gel GF254 plate R type.

Test solution. Evaporate 100 ml of solution S1 to dryness in vacuo at 45 °C. Dissolve the residue in 2 ml of acidified methylene chloride R.

Reference solution (a). Dissolve 20 mg of stearic acid CRS (plastic additive 19) in 10 ml of methylene chloride R. Reference solution (b). Dissolve 40 mg of plastic additive 20 CRS in 10 ml of methylene chloride R. Dilute 1 ml of the solution to 5 ml with methylene chloride R. Reference solution (c). Dissolve 40 mg of plastic additive 21 CRS in 10 ml of methylene chloride R. Dilute 1 ml of the solution to 5 ml with methylene chloride R. Apply separately 10 pl of each solution to the two plates. Develop the first plate over a path of 10 cm using a mixture of 25 volumes of ethanol R and 75 volumes of trimethylpentane R. Allow the plate to dry. Spray with a 2 g/l solution of dichlorophenolindophenol sodium salt R in ethanol R and heat in an oven at 120 °C for a few minutes to intensify the spots. Any spot corresponding to plastic additive 19 in the chromatogram obtained with the test solution is not more intense than the spot in the chromatogram obtained with reference solution (a).

Develop the second plate over a path of 13 cm using hexane R. Allow the plate to dry. Develop a second time over a path of 10 cm using a mixture of 5 volumes of methanol R and 95 volumes of methylene chloride R. Allow the plate to dry. Spray with a 40 g/l solution of phosphomolybdic acid R in ethanol R. Heat in an oven at 120 °C until spots appear. Any spots corresponding to plastic additive 21 or plastic additive 20 in the chromatogram obtained with the test solution are not more intense than the spots in the chromatograms obtained with reference solutions (b) and (c) respectively.

Phenolic antioxidants. Examine by liquid chromatography (2.2.29).

Test solution (a). Evaporate 50 ml of solution S1 to dryness in vacuo at 45 °C. Dissolve the residue in 5.0 ml of a mixture of equal volumes of acetonitrile R and tetrahydrofuran R. Test solution (b). Evaporate 50 ml of solution S1 to dryness in vacuo at 45 °C. Dissolve the residue in 5.0 ml of methylene chloride R. Reference solution (a). Dissolve 25 mg of butylhydroxytoluene CRS (plastic additive 07), 40 mg of plastic additive 10 CRS, 40 mg of plastic additive 09 CRS and 40 mg of plastic additive 11 CRS in 10 ml of a mixture of equal volumes of acetonitrile R and tetrahydrofuran R. Dilute 2 ml to 50.0 ml with a mixture of equal volumes of acetonitrile R and tetrahydrofuran R. Reference solution (b). Dissolve 40 mg of plastic additive 11 CRS and 40 mg of plastic additive 12 CRS in 10 ml of methylene chloride R. Dilute 2 ml to 50.0 ml with methylene chloride R.

The chromatographic procedure may be carried out using:

- a stainless steel column 0.25 m long and 4.6 mm in internal diameter packed with octadecylsilyl silica gel for chromatography R (5 pm),

- as mobile phase at a flow rate of 1.5 ml/min one of the two following mixtures:

Mobile phase 1: 10 volumes of water R, 30 volumes of tetrahydrofuran R, 60 volumes of acetonitrile R, Mobile phase 2: 5 volumes of water R, 45 volumes of 2-propanol R, 50 volumes of methanol R,

- as detector a spectrophotometer set at 280 nm. Using mobile phase 1, inject 20 pl of test solution (a) and 20 pl of reference solution (a). The chromatogram obtained with test solution (a) shows only principal peaks corresponding to the peaks in the chromatogram obtained with reference solution (a) with a retention time greater than 2 min.

The areas of the peaks in the chromatogram obtained with test solution (a) are not greater than those of the corresponding peaks in the chromatogram obtained with reference solution (a), except for the last peak eluted in the chromatogram obtained with reference solution (a). The test is not valid unless, with mobile phase 1, the number of theoretical plates calculated for the peak corresponding to plastic additive 07 is at least 2500 and the resolution between the peaks corresponding to plastic additive 09 and plastic additive 10 is not less than 2.0. If the chromatogram obtained with test solution (a) shows a peak with the same retention time as the last antioxidant eluted from reference solution (a), use mobile phase 2 as follows.

Inject 20 pl of test solution (b) and 20 pl of reference solution (b). The chromatogram obtained with test solution (b) shows only principal peaks corresponding to the peaks in the chromatogram obtained with reference solution (b) with a retention time greater than 3 min.

The areas of the peaks in the chromatogram obtained with test solution (b) are not greater than those of the corresponding peaks in the chromatogram obtained with reference solution (b).

The test is not valid unless the resolution between the peaks corresponding to plastic additive 11 and plastic additive 12 is at least 2.0.

Substances soluble in hexane. Place 5 g in a borosilicate-glass flask with a ground-glass neck. Add 50 ml of hexane R, fit a condenser and boil under reflux on a water-bath with constant stirring for 4 h. Cool in iced-water; a gel may form. Adapt a cooling jacket filled with iced water to a sintered-glass filter (16) fitted with a device allowing pressure to be applied during filtration. Allow the filter to cool for 15 min. Filter the hexane solution applying a gauge pressure of 27 kPa and without washing the residue; the filtration time must not exceed 5 min. Evaporate 20 ml of the solution to dryness on a water-bath. Dry at 100 °C for 1 h. The mass of the residue is not greater than 40 mg (2 per cent) for copolymer to be used for containers and not greater than 0.1 g (5 per cent) for copolymer to be used for tubing.

Sulphated ash (2.4.14). Not more than 1.2 per cent, determined on 5.0 g.

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