How to detect the purity of acetic acid by gas chromatography?

How to detect the purity of acetic acid by gas chromatography?

In the chemical industry, acetic acid is an important organic compound, widely used in the production of chemicals, solvents, food additives and pharmaceuticals and other fields. In order to ensure the quality and performance of acetic acid, it is very important to test its purity. Gas chromatography (Gas Chromatography, GC) is an efficient, sensitive and accurate analytical technique, which is often used to detect impurities and purity in acetic acid. This article will discuss in detail how to detect the purity of acetic acid by gas chromatography, and analyze its key steps and technical points.

1. The basic principle of gas chromatography

gas chromatography is an analytical method based on separation technology, which is mainly used to separate and detect various components in mixtures. The basic principle is to introduce the sample into the chromatographic column, and use the interaction between the mobile phase (gas) and the stationary phase to separate the components in the mixture. The separated components are sequentially passed through a detector, which transmits the signal to a recording system, resulting in a chromatogram.

In detecting the purity of acetic acid, gas chromatography judges the purity of acetic acid by analyzing impurities in the sample. If the impurity content in acetic acid is low, the area of the impurity peak on the chromatogram will be small, which indicates that the purity of acetic acid is high.

2. Steps for detecting the purity of acetic acid by gas chromatography

preparation of 2.1 samples

before the test, the acetic acid sample needs to be properly processed. Since acetic acid is a highly volatile acid, complex sample preparation steps are usually not required. In order to ensure the accuracy of the analysis, it is recommended to filter the sample to remove the insoluble substances that may exist, so as to avoid interfering with the separation effect of the chromatographic column.

Preparation of 2.2 standard curve

in order to quantitatively analyze the impurities in acetic acid, it is usually necessary to prepare a standard curve. The preparation steps of the standard curve are as follows:

1. prepare a series of standard solutions of acetic acid of known concentration, for example 0.1, 1%, 5%, 10% and 20% impurity concentration.
2. Each standard solution was injected into the gas chromatograph for analysis, and the peak area of each component was recorded.
3. The standard curve is drawn with the peak area of the impurity as the ordinate and the concentration of the impurity as the abscissa.
4. The impurity concentration in the unknown sample was quantitatively analyzed using a standard curve.

Setting of 2.3 gas chromatography conditions

in order to obtain the best separation effect, it is necessary to set appropriate gas chromatography conditions according to the nature of acetic acid and its impurities:

• column selection: Usually choose a capillary column with weaker polarity, such as HP-5 or HP-1, to ensure a good separation of acetic acid and its impurities.
• carrier gas selection: Helium or nitrogen is commonly used as the carrier gas, and the carrier gas flow rate needs to be adjusted according to the performance of the column and the nature of the sample.
• Temperature Program: Set a suitable temperature program, usually between 40°C and 200°C, to ensure complete separation of the sample.
• Detector Selection flame ionization detectors (FID) or thermal conductivity detectors (TCD) are commonly used detectors. FID is suitable for high-sensitivity detection, while TCD is suitable for detection of non-volatile substances.

2.4 sample analysis

inject the prepared acetic acid sample into the gas chromatograph, run the chromatographic procedure, and record the chromatogram. In the chromatogram, acetic acid as the main component will form a main peak, and impurities will form other peaks. Through the comparison of peak area, the content of impurities can be quantitatively analyzed, so as to judge the purity of acetic acid.

2.5 data analysis

when analyzing the gas chromatogram, it is necessary to integrate the area of the impurity peak, and then calculate the concentration of the impurity according to the standard curve. If the total content of impurities is lower than the specified purity standard, the purity of acetic acid is higher.

3. The advantages and disadvantages of gas chromatography to detect the purity of acetic acid

advantages:

• high sensitivity: Gas chromatography has extremely high sensitivity and can detect trace impurities.
• High resolution: Gas chromatography can separate complex mixtures and ensure accurate impurity analysis.
• Rapid analysis: Compared with traditional analysis methods, gas chromatography has a shorter analysis period.

Disadvantages:

• complexity gas chromatography requires high technical requirements and professional equipment operation.
• Sample pretreatment: Although the pretreatment of acetic acid samples is relatively simple, complex samples may require additional processing steps.
• higher cost: Gas chromatographs are expensive and require regular maintenance and calibration.

4. Comparison of gas chromatography with other detection methods

in addition to gas chromatography, other methods for determining the purity of acetic acid include chemical titration, infrared spectroscopy, and nuclear magnetic resonance. Compared with other methods, gas chromatography has higher sensitivity and accuracy, and is especially suitable for detecting volatile impurities.

5. Summary

gas chromatography is an efficient, sensitive and accurate detection method, which is widely used to detect the purity of acetic acid. By preparing the standard curve, setting the appropriate chromatographic conditions and analyzing the chromatogram, the impurities in acetic acid can be accurately quantitatively analyzed, so as to judge its purity. For the chemical industry, the use of gas chromatography to detect the purity of acetic acid can not only ensure product quality, but also improve production efficiency and safety. If you want to know more detailed information about gas chromatography, or encounter problems in actual operation, it is recommended to refer to the relevant technical manual or consult a professional.