(par' a fin).
» Paraffin is a purified mixture of solid saturated hydrocarbons obtained from petroleum. It may contain suitable antioxidants.
Packaging and storage Preserve in light-resistant, well-closed containers, and avoid exposure to excessive heat.
Labeling Label it to indicate the name and quantity of any antioxidants.
USP Reference standards 11
USP Naphthalene RS
USP Paraffin RS
A: Infrared Absorption 197, using a thin film of melted test specimen. [noteEnsure complete melting to avoid doublet peaks that may be observed at wavenumbers at about 1460 cm-1 and 730 cm-1. ]
B: It meets the requirements of the test for Congealing range.
Congealing range 651: between 47 and 65.
Acidity Introduce 15 g into a suitable separator, add 30 mL of boiling water, and shake vigorously for about 1 minute. Allow to cool, and draw off the separated water. To 10 mL of the filtrated aqueous layer add 0.1 mL of phenolphthalein TS: the solution does not produce a pink color. Not more than 1.0 mL of 0.01 M sodium hydroxide is subsequently required to change the color of the indicator to pink.
Alkalinity To an additional 10 mL of the filtrated aqueous layer obtained from the test for Acidity add 0.1 mL of methyl red TS 2: the solution produces a yellow color. Not more than 0.5 mL of 0.01 M hydrochloric acid is subsequently required to change the color of the indicator to red.
Readily carbonizable substances 271 Use a clean, dry, heat-resistant, glass-stoppered test tube, 140 ± 2 mm in length with an outside diameter between 14.5 and 15.0 mm and calibrated at the 5- and 10-mL liquid levels. The capacity of the tube with stopper inserted is between 13.6 and 15.6 mL.* Place in the test tube 5 mL of Paraffin at a temperature just above the melting point, add 5 mL of sulfuric acid containing 94.5% to 94.9% of H2SO4, and heat in a water bath at 70 for 10 minutes. When 5 minutes have elapsed, and at each successive minute thereafter, remove the tube from the bath, place a finger over the stopper, and give the tube three vigorous vertical shakes over an amplitude of about 12 cm, returning the tube to the bath within 3 seconds after the time when it was removed therefrom. At the end of 10 minutes from the time the tube was placed in the bath, the acid (lower layer) has no more color than a mixture of 3 mL of ferric chloride CS, 1.5 mL of cobaltous chloride CS, and 0.50 mL of cupric sulfate CS, overlaid with 5 mL of mineral oil. If the sulfuric acid remains dispersed in the molten paraffin, the color of the emulsion is not darker than that of the standard mixture when shaken vigorously.
Limit of polycyclic aromatic hydrocarbons
Dimethyl sulfoxide Use spectrophotometric grade dimethyl sulfoxide.
Standard solution Dissolve a quantity of USP Naphthalene RS, accurately weighed, in Dimethyl sulfoxide, and dilute quantitatively and stepwise with Dimethyl sulfoxide to obtain a solution having a concentration of 7.0 µg per mL. Determine the absorbance of this solution in a 1-cm cell at the wavelength of maximum absorbance at about 278 nm, using Dimethyl sulfoxide as the blank.
Procedure Dissolve 0.50 g of Paraffin, accurately weighed, in 25 mL of n-heptane, place in a 125-mL separator with unlubricated ground-glass parts (stopper, stopcock), and mix. Add 5.0 mL of Dimethyl sulfoxide, and shake the mixture vigorously for 1 minute. Allow to stand until two clear layers are formed. Transfer the lower layer to another 125-mL separator, add 2 mL of n-heptane, and shake the mixture vigorously. Allow to stand until two clear layers are formed. Separate the lower layer, and determine its absorbance in a 1-cm cell, in the range of 265 nm to 350 nm, using as the blank Dimethyl sulfoxide that previously has been shaken vigorously for 1 minute with n-heptane in the ratio of 5 mL of Dimethyl sulfoxide to 25 mL of n-heptane. The absorbance at any wavelength in the specified range is not greater than one-third of the absorbance, at 278 nm, of the Standard solution.
Limit of sulfur compounds To 4.0 g of Paraffin add 2 mL of dehydrated alcohol, and then add 2 drops of a clear saturated solution of lead (II) oxide in sodium hydroxide solution (1 in 5). Heat the mixture at 70 for 10 minutes with frequent shaking, and cool. No dark brown color develops.
* A suitable test tube is available from Kimble Kontes. Item number: 34-19426. Description: Nessler Tube. Contact: phone 800-682-6644, fax 856-692-6644, e-mail email@example.com.
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USP35NF30 Page 1885Pharmacopeial Forum: Volume No. 33(5) Page 972