Tributyl Phosphate

Edition: BP 2025 (Ph. Eur. 11.6 update)

(Tri-n-butyl Phosphate, Ph. Eur. monograph 1682)

C₁₂H₂₇O₄P      266.3     126-73-8

Action and use

Excipient.

Ph Eur

CHARACTERS

Appearance

Clear, colourless or pale yellow liquid.

Solubility

Slightly soluble in water, miscible with ethanol (96 per cent).

bp

About 289 °C, with decomposition.

IDENTIFICATION

Infrared absorption spectrophotometry (2.2.24).

Comparison tri-n-butyl phosphate CRS.

TESTS

Appearance

The substance to be examined is clear (2.2.1) and not more intensely coloured than reference solution Y6 (2.2.2, Method II).

Acidity

Dissolve 50 mL in 50 mL of ethanol (96 per cent) R previously adjusted with 0.02 M potassium hydroxide or 0.02 M hydrochloric acid to a bluish-green colour, using 0.5 mL of bromothymol blue solution R1 as indicator. Titrate with 0.02 M potassium hydroxide to the initial bluish-green coloration. Not more than 0.8 mL of 0.02 M potassium hydroxide is required.

Related substances

Gas chromatography (2.2.28): use the normalisation procedure.

Test solution   The substance to be examined.

Reference solution   Dissolve 10 mg of the substance to be examined and 10 mg of methyl myristate R in methylene chloride R and dilute to 10 mL with the same solvent.

Column:

— material: fused silica;

— size: l = 30 m, Ø = 0.32 mm;

— stationary phase: methylpolysiloxane R (5 μm).

Carrier gas   helium for chromatography R.

Linear velocity   32 cm/s.

Split ratio   65:1.

Temperature:

— column: 250 °C;

— injection port and detector: 250 °C.

Detection   Flame ionisation.

Injection   1 μL.

Run time   Twice the retention time of tri-n-butyl phosphate.

System suitability   Reference solution:

— resolution: minimum 10 between the peaks due to tri-n-butyl phosphate and methyl myristate.

Limits:

— any impurity: for each impurity, maximum 0.3 per cent;

— total: maximum 0.5 per cent;

— disregard limit: 0.01 per cent.

Chlorides (2.4.4)

Maximum 200 ppm.

Dissolve 0.25 g in 15 mL of ethanol (70 per cent V/V) R. The solution complies with the test. Prepare the reference solution using 10 mL of chloride standard solution (5 ppm Cl) R and 5 mL of anhydrous ethanol R.

Water (2.5.32)

Maximum 0.1 per cent, determined on 1.0 g.

STORAGE

Protected from light.

IMPURITIES

A. dibutyl hydrogen phosphate,

B. butyl dihydrogen phosphate,

C. H₃C-[CH₂]₃-OH: butan-1-ol,

D. dibutyl methyl phosphate,

E. dibutyl ethyl phosphate,

F. dibutyl propyl phosphate,

G. dibutyl 2-methylpropyl phosphate,

H. dibutyl pentyl phosphate,

Ph Eur