From the perspective of pesticide formulation process, how to improve the physicochemical properties of water suspension?

Pesticide water suspension as agrochemicals directly into agricultural production, with labor-saving and refinement characteristics, so the quality control link in the processing and production process is very important, so as to ensure that good quality and excellent performance of the product into the market, play an important role in agricultural production. The quality control of pesticide water suspension mainly includes the following aspects[6]:

1. Active ingredient content

Pesticide water suspension active ingredient content of 5%-80%, most of the 40%-60%, through the nature of the active ingredient to determine the appropriate analytical methods, such as gas chromatography and high-performance liquid chromatography, then analyze the formulation content.

2. pH

Pesticide water suspension pH determination can be used as the basis for the adjustment of the acidic and alkaline conditions required by the original drug, so as to ensure that the pesticide water suspension in the two-year storage period stable non-decomposition or less decomposition. Specifically, there are two methods:

1) pH test paper determination Using a wide range of pH test paper and precision pH test paper for direct determination, the method is simple and intuitive, but can only provide a range of acidity and alkalinity, accuracy is not high.2) Acidometer determination Weigh 0.5g of water suspension samples in 100ml beaker, diluted with 50ml deionized water, mixed evenly, and then use the acidometer according to the instructions for determination.

3. Particle size determination

The average particle size of 2-4μm, the national standard: the use of sieve analysis, ≥ 90% of the requirements of 75μm sieve, ≥ 95% of the 44μm sieve, and now generally use a laser particle size analyzer to determine.

4. Suspension rate determination

Suspension rate refers to a certain height of the liquid column after standing for a specified period of time, the percentage of the active ingredient in suspension, is an important pesticide water suspension of a comprehensive quality indicators.

Provision: in the two-year storage period, the suspension rate of not less than 90%. At the same time requires: 1) sample weight of about 1-2g, accurate to 0.0002g; 2) using 342mg / l of standard hard water dilution; 3) in a constant temperature water bath at 30 ± 1 ℃ in the static temperature of 1h.

Specific methods: deionized water to formulate a known concentration of the suspension, placed in a prescribed cylinder at a constant temperature after a certain period of time after the removal of the upper layer of 9/10 of the suspension, the determination of the bottom 1/10 suspension of the effective rate. Bottom 1/10 of the suspension of the content of active ingredients, so that the upper 9/10 suspension can be calculated in the content of active ingredients.

5. Pouring

Pouring is actually a water suspension viscosity range of regulations, different varieties of different requirements, the general viscosity of 300-1000cp pouring test are qualified. Specific method is to be placed in the container of the sample placed for a certain period of time, according to the specified procedures for pouring, determine the amount of specimens retained in the container, the container will be rinsed with water, and then determine the amount of specimens in the container.

Steps are as follows: mix a sufficient amount of the sample, take a part of it in time and inject it into a weighed cylinder (500±2ml), fill it up to 8/10 of the cylinder, cover it with a tight stopper, weigh it and let it stand for 24h. Open the stopper, tilt the cylinder at 45° and maintain it for 60s, then invert the cylinder, maintain it for 60s, and weigh it again. Fill the measuring cylinder with water (20°C) equal to 80% of the volume of the cylinder and close the stopper tightly. After inverting the measuring cylinder up and down 10 times, weigh for the third time after proceeding as described above. The residual rate after dumping is not more than 8%, and the residual rate after washing is not more than 1% is qualified. Pouring retention percentage X2-1 according to the formula ① washing residual percentage X2-2 calculated according to the formula ②:

X2-1% = 100 × (m2-m0)/(m1-m0) ①

X2-2% = 100 × (m3-m0)/(m1-m0) ②

The formula m0-cylinder mass; m1-cylinder and the mass of the specimen; m2- Mass of the measuring cylinder after pouring; m3-Mass of the measuring cylinder after washing.

6. Dispersion stability

In the 250ml cylinder, fill 249ml tap water, use a syringe to suck up 1ml water suspension sample, from the distance of 5cm from the surface of the cylinder into the water, observe the dispersion, according to the dispersion can be divided into excellent, good, bad three levels:

Excellent level: in the water is cloudy and automatically dispersed, no visible particles sinking;

Good level: in the water is cloudy and automatically dispersed, no visible particles;

Good level: in the water is cloudy and automatic dispersion, no visible particles sinking;

Good grade: automatically dispersed in water, with particles sinking, can be slowly dispersed or dispersed after slight shaking;

Inferior grade: can not be automatically dispersed in water, particles or flocculent sinking, can only be dispersed after strong shaking.

7. Centrifugal stability

In 5ml tapered glass test tube with scale, accurately inject 5ml of water suspension samples, and then put the tube into the centrifuge, centrifuged at 3000r/min for 0.5h, observation and recording of water precipitation and precipitation. According to the percentage of water precipitation and precipitation volume, the grading is as follows:

1) Grading according to the amount of precipitation volume

Excellent grade: no precipitation or precipitation volume <1%; good grade: precipitation volume <5%; poor grade: precipitation volume >5%.

2) Grading by water precipitation

Excellent grade: no water precipitation or volume of water precipitation <1%; good grade: volume of water precipitation <5%; poor grade: volume of water precipitation >5%.

8. Thermal storage stability

Take 10ml sample sealed in an ampoule, stored at 54 ± 2 ℃ for two weeks, respectively, to detect the appearance, mobility, dispersion, particle size, active ingredient content and suspension rate of the indicators such as whether the change. If the indicators before and after storage is the same or slight changes (changes should be within the allowable range), it is considered that the hot storage qualified, the results are equivalent to two years at room temperature products qualified.

9. Low-temperature stability

Take 10ml sample sealed in an ampoule, cold storage at -25 ℃ for 24h, observe the freezing situation, and then left to melt at room temperature, respectively, to detect the appearance, mobility, dispersion, particle size, active ingredient content and suspension rate of the indicators of whether the change. If the indicators before and after storage is the same or slight changes (changes should be within the allowable range), it is considered cold storage qualified, the results are equivalent to two years of room temperature storage products qualified.