Appendix VIII G. Determination of Methanol and Propan-2-ol

(Ph. Eur. method 2.9.11)

Method A

Head-space gas chromatography (2.2.28).

Internal standard solution Dilute 1.0 mL of propanol R1 to 100.0 mL with water R. Dilute 1.0 mL of the solution to 20.0 mL with water R.

Test solution Mix 1.0 mL of the internal standard solution and 4.0 mL of the preparation to be examined and dilute to 20.0 mL with water R.

Reference solution (a) Mix 1.0 mL of methanol R2 and 1.0 mL of 2-propanol R2 and dilute to 100.0 mL with water R. Dilute 1.0 mL of the solution to 20.0 mL with water R.

Reference solution (b) Dilute 5.0 mL of anhydrous ethanol R to 100.0 mL with water R. Dilute 25.0 mL of the solution to 100.0 mL with water R. Dilute 1.0 mL of this solution to 20.0 mL with water R.

Reference solution (c) Mix 1.0 mL of the internal standard solution, 2.0 mL of reference solution (a) and 2.0 mL of reference solution (b) and dilute to 20.0 mL with water R.

Column:

— material: fused silica;

— size: l = 30 m, Ø = 0.53 mm;

— stationary phase: poly[(cyanopropyl)(phenyl)][dimethyl]siloxane R (film thickness 3 µm).

Carrier gas helium for chromatography R.

Flow rate 3 mL/min.

Split ratio 1:50.

Static head-space conditions that may be used:

— equilibration temperature: 85 °C;

— equilibration time: 20 min.

Temperature:

Detection Flame ionisation.

Injection 1.0 mL of the gaseous phase of the test solution and reference solution (c), at least 3 times.

Elution order Methanol, ethanol, 2-propanol, 1-propanol.

Relative retention With reference to ethanol (retention time = about 5.3 min): methanol = about 0.8; 2-propanol = about 1.2; 1-propanol = about 1.6.

System suitability: reference solution (c):

— resolution: minimum 5 between the peaks due to methanol and ethanol.

Calculate the methanol content in per cent V/V using the following expression:

A₁	=	area of the peak due to methanol in the chromatogram obtained with the test solution;
A₂	=	area of the peak due to methanol in the chromatogram obtained with reference solution (c);
I₁	=	area of the peak due to the internal standard in the chromatogram obtained with the test solution;
I₂	=	area of the peak due to the internal standard in the chromatogram obtained with reference solution (c).

Calculate the 2-propanol content in per cent V/V using the following expression:

A₃	=	area of the peak due to 2-propanol in the chromatogram obtained with the test solution;
A₄	=	area of the peak due to 2-propanol in the chromatogram obtained with reference solution (c);
I₁	=	area of the peak due to the internal standard in the chromatogram obtained with the test solution;
I₂	=	area of the peak due to the internal standard in the chromatogram obtained with reference solution (c).

Method B

Gas chromatography (2.2.28).

Internal standard solution Dilute 1.0 mL of propanol R1 to 100.0 mL with water R.