Paraffin

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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CAS RN®: 8002-74-2.

1 DEFINITION

Paraffin is a purified mixture of solid saturated hydrocarbons obtained from petroleum. It may contain suitable antioxidants.

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F (CN 1-May-2020)

Sample: Use a thin lm of melted specimen.

Analysis: Ensure complete melting to avoid doublet peaks that may be observed at wavenumbers at about 1460 and 730 cm⁻¹.

Acceptance criteria: Meets the requirements

B. It meets the requirements in Specic Tests for Congealing Temperature 〈651〉.

3 IMPURITIES

3.1 Limit of Sulfur Compounds

Sample: 4.0 g

Analysis: To the Sample add 2 mL of dehydrated alcohol, and add 2 drops of a clear saturated solution of lead(II) oxide in sodium hydroxide solution (200 mg/mL). Heat the mixture at 70° for 10 min with frequent shaking, and cool.

Acceptance criteria: No dark brown color develops.

3.2 Limit of Polycyclic Aromatic Hydrocarbons

Dimethyl sulfoxide: Use spectrophotometric grade dimethyl sulfoxide.

Standard solution: 7.0 µg/mL of USP Naphthalene RS in Dimethyl sulfoxide. Determine the absorbance of this solution at 278 nm using Dimethyl sulfoxide as the blank.

Sample: 0.50 g

Instrumental conditions

(See Ultraviolet-Visible Spectroscopy 〈857〉.)

Mode: UV

Wavelength range: 260–350 nm

Cell: 1 cm

Analysis: Dissolve the Sample 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 min. 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 using as the blank Dimethyl sulfoxide that previously has been shaken vigorously for 1 min with n-heptane in the ratio of 5 mL of Dimethyl sulfoxide to 25 mL of n-heptane.

Acceptance criteria: 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.

4 SPECIFIC TESTS

Congealing Temperature 〈651〉: 47°–65°

4.1 Acidity

Sample: 15 g

Analysis: Introduce the Sample into a suitable separator, add 30 mL of boiling water, and shake vigorously for about 1 min. Allow to cool, and draw off the separated water. To 10 mL of the filtered aqueous layer add 0.1 mL of phenolphthalein TS.

Acceptance criteria: The solution does not produce a pink color. NMT 1.0 mL of 0.01 M sodium hydroxide is subsequently required to change the color of the indicator to pink.

4.2 Alkalinity

Sample: 10 mL of the filtered aqueous layer obtained from the test for Acidity

Analysis: To the Sample add 0.1 mL of methyl red TS2.

Acceptance criteria: The solution produces a yellow color. NMT 0.5 mL of 0.01 M hydrochloric acid is subsequently required to change the color of the indicator to red.

4.3 Readily Carbonizable Substances 〈271〉

Standard solution: A mix 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

Sample: 5 mL, at a temperature just above the melting point

Analysis: 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 the stopper inserted is between 13.6 and 15.6 mL.1Place the Sample in the test tube, add 5 mL of sulfuric acid (94.5%–94.9% of H₂SO₄), and heat in a water bath at 70° for 10 min. When 5 min have elapsed, and at each successive min 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 s after the time when it was removed therefrom.

Acceptance criteria: At the end of 10 min from the time the tube was placed in the bath, the acid (lower layer) has no more color than the Standard solution. If the sulfuric acid remains dispersed in the molten Paraffin, the color of the emulsion is not darker than that of the Standard solution when shaken vigorously.

5 ADDITIONAL REQUIREMENTS

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

1 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 customglass@kimkon.com.