Scheme for Determination of Methanol Content in Liquor by Gas Chromatography

Beijing Huasheng Spectrum Instrument Co., Ltd.

First, the purpose of the experiment

1.

Master the principles and methods of quantitative analysis using the external standard method.

2.

Learn about gas chromatograph hydrogen flame ion detector

FID

Performance and method of operation.

3.

Understand the application of gas chromatography in product quality control.

4.

An analytical method for determining the methanol content by gas chromatography.

Second, the experimental principle

In the process of brewing liquor, methanol is inevitably produced. Methanol is a colorless, transparent, highly volatile liquid that is harmful to humans. Methanol is oxidized to formaldehyde and formic acid in the human body, which is highly toxic and has serious damage to the nervous system, especially the optic nerve.

5 g

Serious poisoning will occur, exceeding

12. 5 g

It may lead to death. In the fermentation process of liquor, it is difficult to completely separate methanol and ethanol. Therefore, the state has strict regulations on the methanol content of liquor. According to national standards (

GB10343-89

), the methanol content of edible alcohol should be lower than

0.1g

•

L-1 (

Gifted class

)

or

0.6 g

•

L-1

(normal level).

Gas chromatography is an efficient, fast and sensitive separation analysis technology with excellent separation efficiency. After a mixture sample is quantitatively introduced into a suitable chromatographic system, the sample is vaporized and then enters the column under the mobile phase. The components in the sample have different forces in the column and the stationary phase due to their different properties, resulting in different The migration speed in the column is different, and the components in the mixture are separated from the column to be separated. The separated components enter the detector, which converts the concentration or mass signal of the substance into an electrical signal and outputs it to a recorder or display to obtain a chromatogram. The retention value can be used to determine the peak height or peak area to be quantified.

The external standard method is to prepare a series of different standard solutions with pure components or standard solutions of known concentration under certain operating conditions, and accurately inject according to the peak area (or peak height) of the components in the chromatogram. The component content is used as a standard curve. Under the same operating conditions, the corresponding content is determined from the standard curve based on the peak area (or peak height) of the sample. Gas chromatography can be used to separate and detect the methanol content in liquor. Under the same operating conditions, the same amount of sample and methanol-containing standard sample are separately chromatographed. The retention time can be used to determine whether the sample contains methanol. The peak area of ​​the methanol peak in the sample and the standard sample determines the methanol content of the sample.

Third, instruments and reagents

1.

instrument:

Gas Chromatograph

, hydrogen flame detector (

FID

), chromatography workstation, capillary column,

10μL

Micro syringe

1

support,

100mL

Volumetric flask

1

only,

25mL

Volumetric flask

5

only,

5mL

Pipette

1

only.

2.

Reagent

:

Methanol (chromatographic alcohol),

60%

Aqueous ethanol solution (without methanol). take

1

μ

L

Inject no methanol peak.

Fourth, the experimental steps

1.

Column preparation

The inner diameter is

0.32mm

Long

30m

Liquid film thickness

0.5μm

The quartz capillary column is installed and debugged normally.

2.

Chromatographic operating conditions: detector

FID

Inlet temperature

180

°C; detector temperature

200

°C; column temperature

50

°C.

3.

Preparation of methanol standard solution

100mL

a small amount in the volumetric flask

60%

Ethanol solution

,

Then weigh accurately on the electronic balance

0.5000g

Chromatography of methanol in this volumetric flask

,

Last use

60%

Constant volume of ethanol solution

,

This solution is

5g/L

Methanol stock solution.

Accurately absorb standard methanol stock solution

1.0

,

2.0

,

3.0

,

4.0

,

5.0mL,

Placed separately

5

One

25mL

Volumetric flask

,

use

60%

Diluted ethanol to the scale

,

Mix and get separately

0.2

,

0.4

,

0.6

,

0.8

,

1.0 mg/mL

Methanol standard solution series

,

.

4.

Gas chromatography method

(

1

) Turn on the gas generator and confirm that the on/off valves on the purifier are in the fully open position (

ON

), wait until the pressure of nitrogen, hydrogen, and air reaches the corresponding value (about

30-40min

), turn on the instrument power switch, enter the workstation, set the inlet temperature

180

°C, detector temperature

200

°C, column temperature

50

°C. Click on the corresponding detector signal channel (

FID

:

1

Channel), and other instruments are stable.

(

2

Ignition: Check the detector temperature. After the detector temperature reaches the set value, confirm that the air and hydrogen valves of the corresponding detector on the gas pavement on the right side of the instrument are in the fully open position. Press the ignition key to confirm that the detector fire used is lit (see if there is water vapor generation and baseline changes). After the baseline level, the samples were injected in turn.

(

3

After the experiment is finished, the hydrogen generator should be turned off first, and then the oven temperature is set to

30

Degree, the injector and detector are turned off, the temperature is lowered, and the oven temperature is lower than

50

Below °C to exit the software, turn off the instrument power switch, turn off the gas generator.

4.

Production of standard working curves

Draw with a micro syringe

1μL

Each chromatographic grade of methanol was injected into the chromatograph to obtain a chromatogram, and the retention time was used as a control to determine the methanol peak.

Establish a new method (area external standard method) in the chromatographic workstation under defined chromatographic conditions

,

Accurately take the syringe from low to high

1

μ

L

Standard use of liquid for analysis

,

Each concentration point is analyzed by a chromatograph

3

Times, measured their peak area

,

The result is the average peak area of ​​methanol as the ordinate.

Y

, methanol concentration is the abscissa

x

, draw a standard working curve, get linear equations and correlation coefficients.

5.

Determination of methanol content in liquor samples

Under the same chromatographic conditions

,

draw

1μL

Liquor samples were analyzed and the results were directly calculated by the chromatography workstation. Sample repeat measurement

3

Times

,

take the average

,

The content of methanol in the liquor sample can be obtained.