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5.15 DETERMINATION OF METHANOL AND 2-PROPANOL

 ​           Carry out the determination as described in the “Gas Chromatography” (Appendix 3.4), using the following solutions.

 ​           Internal Standard Solution Prepare a solution con taining 2.5 per cent v/v of 1-propanol in ethanol.

 ​           Test Solution (a) To a certain amount of the distillate add 2.0 ml of Internal standard solution; adjust the ethanol content (Appendix 6.5) to 10.0 per cent v/v by dilution to 50 ml with water or addition of ethanol.

 ​           Test Solution (b) Adjust the ethanol content (Appendix 6.5) of a certain amount of the distillate to 10.0 per cent v/v by dilution to 50 ml with water or addition of ethanol.

 ​           Reference Solution (a) Prepare 50 ml of a solution containing 2.0 ml of Internal standard solution, 3.0 ml of ethanol, 0.05 per cent v/v of 2-propanol and sufficient anhydrous methanol to give a total of 0.05 per cent v/v of methanol taking into account the methanol content of ethanol.

 ​           Reference Solution (b) Prepare a 10.0 per cent v/v solution of ethanol containing 0.0025 per cent v/v of  each methanol and 2-propanol.

 ​           Chromatographic system The chromatographic procedure may be carried out using (a) a fused silica column (30 m × 0.53 mm) packed with 7 per cent cyanopropyl-7 per cent phenyl-86 per cent methylpolysiloxane (film thickness 3 μm) and maintained at 35º for 0 to 5 minutes and at 35º to 85º for 5 to 15 minutes, with the inlet port at 250º, the split ratio at 1:10, (b) helium as the carrier gas at a flow rate of 2 ml per minute, the split ratio at 1:10 and (c) a flame ionization detector maintained at 250º.

 ​           Separately inject 1.0 μl of each solution and calculate the content of methanol and 2-propanol with reference to the original substance.

 ​           System suitability

 ​           1-PROPANOL There is no peak corresponding to 1-propanol in the chromatogram obtained from 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 from Reference solution (a),

 ​           SIGNAL-TO-NOISE RATIO Minimum 10 for the peaks due to methanol and 2-propanol in the chromatogram obtained from Reference solution (b).v