Purity is the content of active ingredients in the original drug, expressed in percentage. Purity is the main index of the quality of the raw material. The higher the percentage of active ingredients, the better the quality. The quality standard of pesticide raw materials published by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) should be more than 90%. In China's pesticide quality standard, the purity of the original drug can also reach above 90%. The impurities in pesticides with low purity are high, and the excessive impurities in pesticides have the following harms: (1) they may cause pesticide damage to crops. In 2000, the rice seedlings in Meihekou, Jilin were exposed to pesticide poisoning, resulting in the death of rice seedlings. The safety of rice seedlings was not good. According to the preliminary study, the cause of the pesticide damage is that the contents of impurities JP-003 and JP-004 in bensulfuron-methyl exceed the standard. (2) more impurities will increase the toxicity of the original drug to humans. For example, the LD50 of pure methamidophos was 30 mg/kg in rats, while the LD50 of 50% methamidophos EC produced by some domestic manufacturers was 13.6 mg/kg in rats, indicating that the toxicity was increased because the content of five impurities in methamidophos crude oil was higher, and the toxicity of these impurities was higher than that of pure methamidophos. (3) The impurities in the original medicine all lose the original accuracy of the chemical analysis method for calculating the content of the active ingredient by the amount of the molecule containing an element or an atom group. Because impurities also contain the same elements or atomic groups as the effective components, the results of determination are deviated, and the real content of the effective components in the original medicine and its preparations can not be reflected. (4) The impurities in the original medicine also bring difficulties to the processing powder, because the existence of impurities makes the solidification point of the original medicine drop, not easy to crush. (5) The impurities of the original drug can reduce the stability of the effective ingredients, and with the use of pesticides, impurities into the environment, causing pollution. Therefore, we should improve the purity and reduce the content of impurities as much as possible.
PH is not only the quality index of the original drug, but also the quality index of the preparation. Acidity and basicity refer to the amount of free acids or bases in pesticides and their preparations, or the concentration of hydrogen ions. The purpose of limiting acidity and basicity is to reduce the decomposition of effective components in pesticides and pesticides during storage and to prevent the change of physical properties of pesticides and the occurrence of pesticide hazards when they are used. It can also be used as a reference for evaluating the corrosiveness of pesticides to packaging materials. The quality standard of FAO for the acidity and basicity of the original medicine and preparation is expressed by acidity (percentage of H2SO4 content) or alkalinity (percentage of NaOH content). The general requirement for the raw powder is < 0.1%~0.2%. The acidity and basicity of the raw powder and preparation are sometimes expressed by PH value. China's pesticide regulations are expressed in terms of acidity or alkalinity, and most of the formulations are expressed in terms of pH.
Three. Moisture content
Water content is both the original and the quality index of the preparation. The purpose of limiting the moisture content of raw pesticide powder is to reduce the decomposition of active ingredients and maintain chemical stability. For powders and wettable powders, limiting the moisture content can keep the preparation in a good dispersion state, spraying can be well dispersed to the leaf surface. In the pesticide quality standard issued by FAO after 1971, there are water content indexes for the original pesticide, emulsifiable powder and some soluble powder, while there is no water content index for the powder and wettable powder. China's requirement for moisture content of powder is not more than 1.5%. But because of the different kinds of fillers used in powder processing, their water absorption performance is different, some fillers have strong water absorption, even if the moisture content is higher, it does not affect the dispersibility of powder; some fillers have weak water absorption performance, even if the moisture content is not too high, it will also affect the dispersibility of powder, so controlling the moisture content to ensure the powder The method of dispersing agent is unreliable. It is more effective to control the dispersibility of powder by the fluidity index of powder than by controlling the water content. There is no fluidity index in the quality standard of powdered pesticide preparations in China, but the dispersibility is controlled by limiting water content.
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