Measurement of methanol, superior alcohols and ethyl acetate (Type IV)
OIV-MA-VI-19 Measurement of methanol, superior alcohols and ethyl acetate
Type IV method
- Introduction
The method described here allows to measure, at the same time, several major volatile components of vinegars. The interest of this measurement is two-fold, organoleptic and possibly toxicologic.
- Principle
Neutralization of the sample at pH 7.00 with a sodium hydroxide solution.
Measurement, via gas chromatography, of some volatile components:
- Methanol
- propan-1-ol
- butan-2-ol
- 2-methylpropan-1-ol
- butan-1-ol and 2-methylbutan-1-ol + 3-methylbutan-1-ol.
- Reagents
3.1. aqueous-alcoholic solution at 5% v/v.
3.2. in-house standard solution (4-methylpentan-2-ol).
In a 1 L volumetric flask, dissolve 1110.0 mg (to an accuracy of 0.1 mg) of 4-methylpentan2-ol into the aqueous-alcoholic solution (3.1). Make up to the mark with this solution.
3.3. reference solution
In a 1 L volumetric flask, dissolve, in the aqueous-alcoholic solution (3.1), 152.0 mg of ethyl acetate, 50.0 mg of methanol, 7.7 mg of propan-1-ol, 16.3 mg of butan-2-ol, 17.0 mg of 2-methylpropan-1-ol, 2.5 mg of butan-1-ol, 7.9 mg of 2-methylbutan-1-ol and 8.7 mg of 3-methylbutan-1-ol (to the accuracy of 0.1 mg). Make up to the mark with the solution (3.1).
3.4. reference solution added from the in-house standard solution. Add 1 ml of the solution (3.2) to 10 ml of the solution (3.3).
3.5. sodium hydroxide solution at 40% (m/v).
- Devices and utensils
Standard laboratory material, plus:
4.1. gas chromatograph with a 'split' type injector and a flame ionization detector
4.2. Supelcowax 10 glass column, 30 m long and 0.75 mm internal diameter (as an example).
- Technique
Neutralize the sample at pH 7.00 with the sodium hydroxide solution (3.5), and record the initial and final volumes.
Add 1 ml of the neutralized sample solution at 10 ml (3.2).
Inject 1 μL of each of these two solutions into the chromatograph. Temperatures of the injector and the detector are 250° C. Oven temperatures are: 6 mn at 50° C, 50° C to 70° C to 8° C/mn, 14 mn at 70° C, 70° C to 210° C to 8° C/mn and 16 mn at 210° C. The output of the vector gas (hydrogen) is 10 ml/mn.
- Results
6.1. Calculation
Taking:
- the component 1 content, in mg/L, in the reference solution (3.4)
- the in-house standard solution content, in mg/L, in the reference solution (3.4)
- the surface of the peak of component 1 of the reference solution (3.4)
- the surface of the peak of the in-house standard solution in the reference solution (3.4)
- the surface of the peak of component 1 in the neutralized sample solution plus the in-house standard solution
- the surface of the peak of the in-house standard solution in the neutralized sample solution plus the in-house standard solution
- the in-house standard solution content, in mg/L, in the neutralized sample solution plus the in-house standard solution
- f the dilution factor resulting from the neutralization of the vinegar sample.
The component i content , expressed in milligrams per L of vinegar, is given by:
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6.2. Presentation
Round results to the integer value.
- Bibliography
- Climaco, M.C., Estudo de um método de doseamento de compostos voláteis em vinagres por cromatografia em fase gasosa, Relatório dactil., Estação Vitivinícola Nacional, Dois Portos (1993). (Study of a measurement method for volatile components in vinegars with gaseous chromatography).