Pesticide

Application of Differential Scanning Calorimetry (DSC) in the Pesticide Industry

Differential scanning calorimetry (DSC) analyzes the phase transition behavior of materials by measuring changes in heat flow during programmed temperature control, whether endothermic or exothermic. For pesticides, physical or chemical changes such as melting, crystallization, decomposition, and oxidation occur during heating or cooling. These changes are accompanied by the absorption or release of heat. DSC can accurately measure these heat flow changes to obtain relevant thermal performance paramet...

Thermal performance parameters of pesticides, such as melting point, glass transition temperature, and thermal decomposition temperature, are important indicators of their thermal stability, purity, and crystallization properties. For example, the melting point can reflect the purity of a pesticide, as highly pure pesticides generally have sharper melting peaks. The glass transition temperature is closely related to storage stability and processing performance. The thermal decomposition temperature can...

Measuring Instrument
- Model: DSC600 Differential Scanning Calorimeter
- Brand: ThermCon Scientific

Sample Preparation
- Sampling requirements: Take about 5–20 mg of pesticide sample, ensuring uniformity and avoiding contamination. For solid pesticide samples, grind into fine powder as much as possible to ensure uniform heat conduction. For liquid pesticide samples, use a well-sealed container to prevent evaporation.
- Pretreatment: If the pesticide sample contains moisture or volatile solvents, it should be dried at low temperature first to eliminate their influence on the experimental results. For some pesticide samples requiring elimination of thermal history, a heating–cooling cycle may be carried out, e.g., heating to a certain temperature at 10 ℃/min and then cooling.

Instrument Calibration
Use standard substances (e.g., indium, tin) to calibrate the temperature and heat flow signals of the DSC. The melting points and enthalpy values of standard substances are known. By measuring their DSC curves, the instrument’s temperature and heat flow can be calibrated to ensure accuracy.
Ensure nitrogen or inert gas protection (50–100 mL/min) to prevent oxidation reactions of pesticide samples during testing, which could affect results.

Experimental Parameter Settings
- Temperature range: 30–350 ℃
Set according to the nature of the pesticide sample and the expected thermal transition temperature. Generally, the starting temperature should be below the expected transition, and the end temperature above its decomposition point.
- Heating rate: 10 ℃/min
A too high rate may cause peak temperature shifts and lower resolution, while too low a rate prolongs the experiment. The heating rate should be chosen appropriately.
- Nitrogen protection: 50 mL/min

- Repetitive testing: Each group of samples should undergo at least 2–3 parallel tests to verify reproducibility and reliability of data.

Measurement Results and Analysis
- Melting peak: The melting peak temperature was 132 ℃, indicating the pesticide begins melting at this temperature.
- Thermal decomposition: The decomposition temperature was 142 ℃, showing that the pesticide exhibits good thermal stability below 250 ℃.
- Glass transition temperature: Analysis of the DSC curve also revealed a glass transition temperature, providing a basis for studying physical states and performance changes.

Curve analysis:
- Melting peak identification: The onset point is where the baseline starts deviating, indicating the start of melting. The peak value corresponds to the pesticide’s melting point. The endpoint marks complete melting.
- Thermal decomposition analysis: The exothermic peak position and area indicate decomposition onset temperature, rate, and enthalpy. This allows evaluation of pesticide stability at high temperatures.
- Glass transition analysis: Appears as a step-like baseline change. The onset, midpoint, and endpoint provide the glass transition temperature range. Below Tg, pesticides remain in a glassy, stable state; above Tg, flowability increases, potentially affecting performance and quality.

Common Problems and Solutions
1. Baseline drift or high noise
- Cause: Excessive sample amount, unstable gas flow.
- Solution: Reduce sample to 5–10 mg, calibrate gas flow for stability.

2. Large deviation from literature values
- Cause: Batch differences, additives (adjuvants, solvents), inaccurate calibration, or abnormal instrument condition.
- Solution: Compare with literature data of samples from the same source, recalibrate the instrument, check sensor sensitivity and furnace sealing.

3. Thermal decomposition interfering with melting peak
- Cause: Some pesticide samples decompose before melting.
- Solution: Use inert gas (e.g., nitrogen) to reduce oxidation risk. Apply fast heating (e.g., 20 ℃/min) to shorten residence time at high temperatures.

Conclusion
Differential scanning calorimetry provides an efficient and sensitive method for characterizing the thermal performance of pesticide samples. By standardizing sample preparation, optimizing test parameters, and analyzing data appropriately, key thermodynamic parameters of pesticides can be accurately obtained. This provides theoretical support for pesticide research, production, storage, and use.

In the pesticide field, DSC technology has broad application prospects. It can help researchers better understand pesticide properties and behavior, thereby promoting the development of the pesticide industry.