Precipitate formation Storage stability

Solvents are important ingredients of emulsifiable concentrates and of solution formulations. When the formulation is to be used on crops, it is critical that the solvent be nonphytotoxic. The solvent must have a high level of solvent power if an EC is being formulated. Because most toxicants are insoluble in water, the solvent must also be water insoluble. Otherwise, when the EC is added to water in the spray tank, the solvent will mix with the water and leave the toxicant behind as a crystalline precipitate. The carrying power of the solvent, i.e., the amount of pesticide it will hold in solution, is important in the storage stability of formulations. If near its saturation point at ordinary temperatures, it may exceed this at low temperature with the result that solvent and pesticide may separate, causing crystal formation and phase separation (Terriere, 1982). 

Thus potential gum is determined by the accelerated gum test (ASTM D-873, IP 138), which is used as a safeguard of storage stability and can be used to predict the potential for gum formation during prolonged storage. In this test, the gasoline is heated for 16 h with oxygen under pressure in a bomb at 100°C (212°F). After this time, both the gum content and the solids precipitated are measured. 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

A minimum temperature of 88°C is required for paste storage of thermally oxidized starch in order to prevent retrogradation. Various retrogradation control agents have been recommended for stabilizing. The addition of 0.5 to 1.0% calcium stearate prevents the build up of viscosity, but could actually lead to the precipitation of amylose due to gradual stearate dissolution (ionization) and complex formation with... 

The stability of the distillate fuels in storage is influenced to a considerable degree by compounds of sulfur and nitrogen that may be present. Thus, sludge formation has been found to be promoted by disulfides, polysulfides, and thiophenol (327), as well as by pyrroles (328). Furthermore, the precipitates that form are much enriched in both sulfur and nitrogen. Pyrrole-type compounds have been identified among the nitrogen compounds in catalytically cracked gas oil (281,329) if present in appreciable amounts, their removal may be necessary (328). 

Characterization of aluminum chlorohydrate has revealed a predominance (about 88%) of Ai polymer with the balance being monomers and smaller polycations (20). The highly charged Al 3 surrounded by Q counterions is self-stabilized by repulsion forces, preventing association and subsequent aluminum hydroxide precipitation (21). Thus, aluminum chlorohydrate solutions remain clear and free of precipitate after years of storage at room temperature. Aqueous dilution or an increase in pH to 5—6, however, results in rapid degradation and formation of gibbsite [14762-49-3] an insoluble aluminum hydroxide polymorph (8). 

The presence of water can affect compound stability in several different ways. Water can participate or catalyze degradation reactions in solid or DMSO solution format. Additionally, in solid-state storage, water absorption can alter the morphology of the sample and the mobility of the molecules in the sample and therel y affect the rate of degradation or compound loss. In liquid storage, the presence of water can change the solubihty of compounds in DMSO and, depending on the nature and concentration of the analyte in solution, cause compound precipitation. 

---