## 1. Determination of Acidity

### 1.1 Reagents and Solutions

a) Sodium hydroxide standard titration solution: 0.1mol/L.

b) Bromothymol blue indicator: 1g/L (ethanol solution).

### 1.2 Analysis

Weigh about 1g of the sample (accurate to 0.0002g) and place it in a 250ml Erlenmeyer flask pre-placed with 20ml of water. Add 3-4 drops of bromothymol blue indicator. Titrate with 0.1 mol/L sodium hydroxide standard solution until slightly blue.

### 1.3 Results

The acidity of glyoxal (in terms of acetic acid) is calculated in terms of mass fraction ω1%, and the number is expressed in %, which is calculated by the following formula:

where:

V——the value of the volume of sodium hydroxide standard titrant consumed by the sample, unit (ml);

C——the exact value of the concentration of sodium hydroxide standard titrant, unit (mol/L);

m——the value of the mass of the sample, in grams (g);

M – the value of the molar mass of acetic acid. The unit is grams per mole (g/mol) (M-60).

### 1.4 Allowable Error

Take the arithmetic mean of the parallel measurement results as the measurement result. The absolute deviation of parallel determination is not more than 0.05%.

## 2. Determination of Content

### 2.1 Method Principle

40% acetaldehyde reacts in potassium hydroxide medium to generate methyl glycolate. Excess potassium hydroxide was neutralized and titrated with a standard hydrochloric acid solution.

### 2.2 Reagents and Solutions

a) Potassium hydroxide solution: 1.5mol/L.

b) Standard titration solution of hydrochloric acid: 0.5mol/L.

### 2.3 Analysis

In the conical flask for measuring acidity in 1.1, accurately add 10ml of 1.5mol/L potassium hydroxide solution. Shake well for 15min. Titrate with 0.5mol/L hydrochloric acid standard solution until the solution changes from blue to yellow. At the same time do a blank test.

### 2.4 Results

The glyoxal content is calculated in mass fraction ω2, and the number is expressed in %, which is calculated by the following formula:

where:

V0——the volume value of the standard titrant of hydrochloric acid consumed in the blank test, in milliliters (ml);

V1——the volume value of the standard titrant of hydrochloric acid consumed in the measurement, the unit is milliliter (ml);

C——The standard value of the concentration of the standard hydrochloric acid titrant, the unit is moles per liter (mol/L);

m——the value of the mass of the sample, in grams (g);

M—the value of the molar mass of glyoxal, in grams per mole (g/mol) (M=58.04).

### 2.5 Allowable Error

Take the arithmetic mean of the parallel measurement results as the measurement result. The absolute deviation of parallel determination is not more than 0.2%.