Appendix VIII G. Determination of Methanol and 2-Propanol

Examine by gas chromatography (2.2.28).

Internal standard solution Prepare a solution containing 2.5 per cent V/V of propanol R in ethanol R1.

Test solution (a) To a certain amount of the distillate add 2.0 mL of the internal standard solution; adjust the ethanol content (2.9.10) to 10.0 per cent V/V by dilution to 50 mL with water R or addition of ethanol R1.

Test solution (b) Adjust the ethanol content (2.9.10) of a certain amount of the distillate to 10.0 per cent V/V by dilution to 50 mL with water R or addition of ethanol R1.

Reference solution (a) Prepare 50 mL of a solution containing 2.0 mL of the internal standard solution, 3.0 mL of ethanol R1, 0.05 per cent V/V of 2-propanol R and sufficient anhydrous methanol R to give a total of 0.05 per cent V/V of methanol taking into account the methanol content of ethanol R1.

Reference solution (b) Prepare a 10.0 per cent V/V solution of ethanol R1 containing 0.0025 per cent V/V of each methanol R and 2-propanol 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 2 mL/min.

Split ratio 1:10.

Temperature:

Detection Flame ionisation.

Injection 1.0 µL.

System suitability:

• — propanol: there is no peak corresponding to propanol in the chromatogram obtained with test solution (b),

• — peak-to-valley ratio: minimum 15, where H_p = height above the baseline of the peak due to 2-propanol and H_v = height above the baseline of the lowest point of the curve separating this peak from the peak due to ethanol in the chromatogram obtained with the reference solution (a),

• — signal-to-noise ratio: minimum 10 for the peaks due to methanol and 2-propanol in the chromatogram obtained with reference solution (b).

The content of methanol and 2-propanol is calculated with reference to the original sample.