How to use gas chromatography to analyze liquor

The scent of liquor is complex, and in addition to ethanol and water, there are a large number of aromatic components. What constitutes the quality style of liquor is the type of flavor component contained in the wine and its quantitative relationship. Gas chromatography can quickly and accurately measure the content of alcohols, esters, organic acids, carbon-based compounds, phenolic compounds and high-boiling compounds in liquor.

First, the packed column DNP column is used to determine the alcohol, ester and other components in the liquor (usually required by the winery, liquor)

(1) DNP column direct injection method for determination of main alcohol and ester components in liquor

Alcohols and esters in liquor are the main aroma components. The original sample is taken for chromatographic analysis, and the advantages thereof are: the operation is simple, the measurement result is high and fast; the disadvantage is that extremely small components are not easily detected.

1 sample preparation

● 2% internal standard preparation:

Pipette 2mL of the internal standard - n-butyl acetate in a 100mL volumetric flask, (since the internal standard is volatile, a small amount of alcohol can be placed in the bottle), and the volume is adjusted with 55%-60% ethanol.

● Preparation of 1-2% standard sample:

Take acetaldehyde, methanol, n-propanol, sec-butanol, acetal, n-butanol, isoamyl alcohol, (n-hexanol), (furfural), respectively, lmL, ethyl acetate, ethyl butyrate, valerate 2 mL of each of ester, ethyl lactate, ethyl hexanoate and isoamyl acetate was added to a 100 mL volumetric flask, and the volume was adjusted with 55%-60% (V/V) ethanol, and mixed to form a standard. (Add a little ethanol to the volumetric flask to prevent evaporation)

● Preparation of mixed standard:

Pipette the standard sample 10 mL and internal standard 5 mL, and dilute to 100 mL with 55%-60% (V/V) ethanol, mix well (can be dispensed) and use.

The formula for calculating the content of each component i and internal standard in the mixed standard:

Mi=ci×Vi×di×lO00

Ms=cs×Vs×ds×lO00

Where: mi / ms - the content of each component i / internal standard in the mixed standard (mg / l0OmL);

Ci/cs—concentration of the i/internal standard of each component in the mixed standard (V/V)

Vi/Vs—the volume (mL) of each component i/internal standard in the mixed standard;

Di/ds—the density (g/mL) of the i/internal standard of each component in the mixed standard;

1000—calculated as a coefficient in mg.

Example: Calculate the content of n-butanol in the mixed standard

m n-butanol = 1% × lOml × 0.809g / ml × lO00 = 80.9mg / 100ml mixed standard

Calculate the content of ethyl acetate in the mixed standard

m ethyl acetate = 2% × lOml × 0.809g / ml × lO00 = 179.6mg / 100ml mixed standard sample to calculate the internal standard - n-butyl acetate content

Ms=2%×5ml×0.882g/ml×lO00=88.2mg/100ml mixed standard

Recommendation: In the case that such conditions are not mature, you can also directly purchase the prepared mixed standard for use.

● Preparation of mixed sample of wine sample and internal standard: Add 2% internal standard 0.2mL to the wine sample, and prepare it into lOmL

The wine sample solution is mixed and ready for use.

The formula for calculating the internal standard content of the wine sample is the same as above.

Namely: ms=2%×0.2ml×0.882g/ml×lO00×100/10=35.28mg/100ml wine sample

The method of adding the internal standard directly to the wine sample:

Add 10 μL of the internal standard to the wine sample and prepare a 25 ml wine sample.

The calculation formula for the internal standard content of the wine sample:

Ms=(Vs/l00O) ×ds×lOOO×lO0/25=4×Vs×ds

Namely: ms=4×lO×0.882=35.28mg/lOOml wine sample

Where: ms—the content of the internal standard (mg/lOOml);

Vs/l000—the pure volume of the internal standard (μl is converted into a factor in ml)

Ds—the density of the internal standard (g/ml);

1000—converted to a factor in mg;

100/25—converted to a factor calculated in 100 ml.

Note: You can also add 4OμL of internal standard to 100ml of wine sample, or add 4μL of internal standard to lOml wine sample. Remember to add the amount of internal standard to be very accurate. Manufacturers with electronic balances can be added by weighing method, and the calculated value is more accurate.

2 choice of chromatographic operating conditions

Column: DNP mixed column (didecyl phthalate 20% fixative, Tween-60 70%)

Reducer, the carrier is white diatomaceous earth Chromosorb W-HP)

Stainless steel column, Φ3×2m;

Column temperature: 85 ° C ~ 105 ° C;

Vaporization chamber temperature: 130 ° C ~ 145 ° C;

Detector temperature: 130 ° C ~ 145 ° C;

Carrier gas flow rate: high purity nitrogen 25~40mL/min;

Hydrogen flow rate: 40~60mL/min;

Air flow rate: 300~600mL/min;

Injection volume: 0.4uL~luL.

3 qualitative and quantitative analysis

● Qualitative analysis: The retention time of each component was determined by standard sample, and each component in the measured wine sample was compared with the standard sample, and the same retention time was used as the main factor of qualitative.

● Quantitative analysis: calculated by internal standard method. N-butyl acetate was used as an internal standard.

A. Find the quantitative correction factor

Advanced standards give retention times and peak areas for each component. Quantitative correction factor

Calculation formula:

Fi = (As × mi) / (Ai × ms)

among them;

Ai, As-- are the peak areas of component i and internal standard s, respectively;

Mi, ms-- are the content of component i and internal standard s, respectively.

Then, according to the report of the data processor, a peak identification table is prepared, and the retention time of each component is

Inter- and content input, calculate the quantitative correction factor for each component.

B. Calculate the content of alcohol ester in the wine sample

According to the formula: fi = (As × mi) / (Ai × ms)

Derived: mi = (As × fi) / (Ai × ms)

among them:

Ai, As-- are the peak areas of component i and internal standard s, respectively;

Fi—the quantitative correction factor for component i;

Ms--content of internal standard in wine sample (mg/100ml)

(ms=4×lO×0.882=35.28 mg/100ml wine sample)

4 List of relative retention times and parameters of main alcohols and esters on DNP columns in liquor:

supplement:

● Preparation of DNP column:

Fixing liquid ratio and coating DNP=M×0.2

Tween-60=M×O.07

Where: M is the carrier mass (g)

Using acetone as a solvent, the mixed fixing solution is dissolved and poured into a weighed carrier, and the solution is required to have a slight excess after inhaling the carrier. Evaporate to dryness in a water bath, dry in an oven at 1O5 ° C for 1.2 hours, and cool for use.

● Aging of DNP columns

The purpose of column aging is to remove low-boiling impurities and low-molecular fixatives, and to have a redistribution process of the fixative on the surface of the support to make it uniform and firm. When aging, the outlet of the column should not be connected to the detector, and the carrier gas is aged.

Aging method for DNP column:

1 constant temperature aging method: with a column temperature of 1OO ° C, 1/4 aging of normal flow at low carrier gas flow for 24h.

2 rapid aging method: set the initial temperature of the column 50 ° C, constant temperature lOmin, increase to 115 ° C at 5 ° C / min, constant temperature 60 min and then cool to 50 ° C, repeated aging once.

(2) Analysis of fusel oil

Fusel oils include n-propanol, isobutanol, and isoamyl alcohol. Liquor health indicators stipulate: fusel oil = isobutanol + isoamyl alcohol, as measured by p-dimethylaminobenzaldehyde colorimetric method, n-propanol does not develop color, isobutanol and isoamyl alcohol do not show color the same. According to the standard, isobutanol in the mixed standard: isoamyl alcohol = 1:4 does not meet the actual ratio in the wine, so there will be defects in the standard series and the wine color tone are not exactly the same and difficult to compare. Gas chromatography can accurately quantify the content of isobutanol and isoamyl alcohol, and the results are more accurate and reliable.

(III) Rapid determination of ethyl hexanoate and ethyl lactate

The content of ethyl hexanoate in Luzhou-flavor liquor is a key indicator that directly affects children from alcohol. In the production control of Luzhou-flavor liquor factory, sometimes the whole component of the wine is not needed, as long as the content of the flavor component of the main ethyl hexanoate and the ratio of other flavor components, especially ethyl lactate, are known. Need a quick measurement method.

Analytical method:

DNP column + Tween 60 column was used to raise the column temperature to 12O °C. At this time, the peak of ethyl hexanoate was as short as ten minutes. Since the separation of butyl acetate and isoamyl alcohol decreased, it was not suitable. The standard (internal standard directly affects the quantitative accuracy of each component, should be completely separated from other components), and isoamyl acetate is used as an internal standard, which peaks before ethyl lactate.

It is worth noting that after the column temperature is increased, the previously separated furfural and hexanol are separated, but the order of peaks changes, and hexanol peaks before furfural.

(IV) Determination of ethyl propionate

In most wines, the amount of acetal is much greater than ethyl propionate. However, the content of ethyl propionate in some wines can not be ignored. Because ethyl propionate and acetal are superposed on the DNP column, the inorganic acid is added to the wine sample to pre-treat the acetal to alcohol and acetaldehyde, while the ethyl propionate is unchanged, and then the DNP column is used. After analyzing the hydrolyzed wine sample, the content of ethyl propionate can be measured;

Acetal hydrolysis:

CH3CH(C2H5O)2+H2O hydrolysis 2C2H5OH+CH3CHO

1 chromatographic conditions

Same as the previous DNP analysis conditions.

2 quantitative analysis

Calculated using the internal standard method. N-butyl acetate was used as an internal standard.

A. Determination of quantitative correction factor for ethyl propionate

Accurately absorb 2 mL of ethyl propionate and add it to a 100 mL volumetric flask for 60% (VW)

The ethanol solution was made up to a 2% standard solution.

Accurately absorb 2% of ethyl propionate standard solution and 2% of internal standard solution, 0.1 mL each in a 10 mL volumetric flask, and make up to volume with 60% (V/V) ethanol solution for injection analysis.

Formula for calculating the quantitative correction factor of ethyl propionate:

Fethyl propionate = As × m propionate / A propionate × ms

=As×dethyl propionate/ethyl propionate×ds

among them:

A propionate ethyl ester, As-- is the peak area of ​​component i and internal standard s, respectively;

d propionate ethyl ester, ds-- is the density of component i and internal standard s, respectively.

B. Calculate the content of ethyl propionate in the wine sample

Accurately take 5ml of wine sample into lOml volumetric flask, add 2 drops of 1:3 hydrochloric acid solution, dilute with distilled water, let stand for 1h at room temperature, then add 0.1ml of internal standard solution, and analyze by injection.

According to the formula: f ethyl propionate = As × m propionate / A propionate × ms

Derived: m propionate = As × f propionate / A propionate × ms

among them:

A propionate ethyl ester, As-- is the peak area of ​​ethyl propionate and internal standard s, respectively;

a quantitative correction factor for ethyl propionate-ethyl propionate;

Ms--content of internal standard in wine sample (mg/1OOml)

(ms=2%×0.882×O.1×1000× (10O/5)=35.28mg/lOOml)

C. Calculate the content of acetal in the wine sample

m acetal = acetal content measured by direct injection method - m propionate ethyl ester x f acetal / f propionate ethyl ester

YT-68

YT-68

YT-68

Shenzhen Sunshine Technology Co.,Ltd , https://www.yatwinsz.com