Preparation of suspension concentrates

Several interfacial aspects must be considered when dealing with agrochemical formulations (i) Both equilibrium and dynamic aspects of adsorption of surfactants at the air/liquid interface. These aspects determine spray formation (spray droplet spectrum), impaction and adhesion of droplets on leaf surfaces as well as the various wetting and spreading phenomena, (ii) Adsorption of surfactants at the oil/water interface which determines emulsion formation and their stability. This subject is also important when dealing with microemulsions, (ill) Adsorption of surfactants and polymers at the solid/liquid interface. This is important when dealing with dispersion of agrochemical powders in liquids, preparation of suspension concentrates and their stabilization. 

Preparation of suspension concentrates and the rofe of surfactants/ dispersing agents... 

Vallea, E. and Mocquot, G. 1968. Preparation of a concentrated suspension of thermophilic lactic acid bacteria for use in cheesemaking. Lait 48, 631-643. (French)... 

Surfactants play a major role in the preparation of suspensions of polymer particles by heterogeneous nucleation. In emulsion polymerization, the monomer is emulsified in a nonsolvent (usually water) using a surfactant, whereas the initiator is dissolved in the continuous phase. The role of surfactants in this process is obvious since nucleation may occur in the swollen surfactant micelle. Indeed, the number of particles formed and their size depend on the nature of surfactant and its concentration (which determines the number of micelles formed). 

Pivinsky Yu.E., Bevz V.A., Mityakin P.L. The basic principles of the preparation of high-concentrated suspensions of quartz sand. Ogneupory 1979 3 46-51. 

Gelatin capsules are manufactured by a dipping pro-cess. The process starts by the preparation of a concentrated solution of gelatin or other suitable polymer in hot demineralized water. This solution is subjected to a low pressure to remove entrapped air bubbles. Small aliquots of this solution are (20-30 L) are taken. To this are added colorants, either solutions of soluble dyes or suspensions of pigments, preservatives, process aids, such as disodium lauryl sulfate solution, and water to adjust the viscosity. The final solution has a concentration of 25-30 wt%o of gelatin. This solution is then delivered to the capsule-manufacturing machine. 

The drug concentration in a parenteral suspension can influence the plasma concentration profile. When different concentrations of amoxicillin (100 and 200mg/ml) in aqueous suspensions of amoxicillin trihydrate were administered intramuscularly at the same site and same dose level (lOmg/kg) to horses, the preparation of lower concentration (10%) provided relatively better absorption and a more consistent plasma concentration profile. Intramuscular injection of amoxicillin trihydrate (15% in a mixed oil base) in the neck (10 cm behind the ear) of pigs produced two peaks, 1.7 and 0.8pg/ml at 1.3 and 6.6 h, respectively, rather than a single peak in the plasma concentration profile and an eight-fold longer mean residence time of the antibiotic than a preparation of the same... 

Steric repulsion results from the presence of adsorbed layers of surfactants and/or polymers. The use of natural and synthetic polymers (referred to as polymeric surfactants) for stabilization of suspension concentrates and emulsions (EW s) plays an important role in agrochemical formulations. Polymers are particularly important for preparation of concentrated dispersions, i.e. at high volume fraction ( j of the disperse phase,... 

Urea processes provide an aqueous solution containing 70—87% urea. This solution can be used directiy for nitrogen-fertilizer suspensions or solutions such as urea—ammonium nitrate solution, which has grown ia popularity recentiy (18). Urea solution can be concentrated by evaporation or crystallization for the preparation of granular compound fertilizers and other products. Concentrated urea is sohdified ia essentially pure form as prills, granules, flakes, or crystals. SoHd urea can be shipped, stored, distributed, and used mote economically than ia solution. Furthermore, ia the soHd form, urea is more stable and biuret formation less likely. 

Because the regions of the alimentary tract vary widely ia pH and chemical composition, many different commercial formulations of barium sulfate are available. The final preparations of varyiag viscosity, density, and formulation stabiUty levels are controlled by the different size, shape, uniformity and concentration of barium sulfate particles and the presence of additives. The most important additives are suspending and dispersiag agents used to maintain the suspension stabiUty. Commercial preparations of barium sulfate iaclude bulk and unit-dose powders and suspensions and principal manufacturers are E-Z-EM (Westbury, New York), Lafayette-Pharmacol, Inc. (Lafayette, Indiana), and Picker International, Inc. (Cleveland, Ohio). 

Q Preparation of 2-Acetyi-3-Methyi-5-(2-Oxo-2,5-Dihydro-4-Furyi)Benzo[b]Furan (3556 CB) (1) A suspension of 2 grams of the compound prepared according to (B) in 20 ml of concentrated hydrochloric acid, is heated to about 50°C, just until it dissolves. Thereafter it is heated for 2 minutes to 70°C, just until precipitation commences. The mixture is allowed to cool, diluted with water, filtered, the residue washed, dried, and sublimed at 200°C and 0.1 mm pressure, 1.4 grams of product (Yield 70%) Is obtained, MPc = 218°-221°C. A second sublimation produces a chemically pure product, MP = 221°-222°C. 

Preparation of 3-n-Butyiamino-4-Phenoxy-5-Suifamyibenzoic Acid To a suspension of 3-amino-4-phenoxv-5-sulfamylbenzoic acid (10 grams) in n-butanol (200 ml), concentrated sulfuric acid (2 ml) was added while stirring. The reaction mixture was heated under reflux under conditions in which the water formed during the reaction could be removed. IWhen, after dilution with n-butanol, the N MR-spectrum of a sample of the reaction mix-... 

Preparation of 4-Benzy/oxypheny/hydrazine 200 grams 4-benzyloxyaniline hydrochloride was suspended in a mixture of 264 ml concentrated hydrochloric acid, 528 ml water and 732 grams crushed ice. A solution of 62.4 grams sodium nitrite in 136 ml water was added below the surface of the stirred suspension at -10 2°C during 10 minutes. After stirring for 1 hour at 0°C, the suspension was treated with acid-washed charcoal and filtered. 

Preparation of J-Methy/ Lumilysergic Acid 8-Methyl Ester-10-Methyt Ether into a suspension of 10 grams of 1-methyi-iumiiysergic acid in 600 cc of absoiute methanoi a stream of anhydrous hydrogen chloride is bubbied for 1.5 hours with strong cooiing. The stream of hydrogen chloride is stopped and the mixture is aiiowed to stand for 30 minutes at 0°C, and is evaporated in vacuo to dryness. The residue is taken up with ice-cooied water made aikaiine with concentrated ammonia and extracted with chioroform. The combined chioro-form extracts are washed first with a 5% aqueous solution of sodium bicarbonate, then with water, and are thereafter dried over anhydrous sodium sulfate and finally evaporated in vacuo to dryness. 

Heller and Tabibian (13) noted that errors, due to laterally scattered light and the corona effect, as large as to cause a 30 reduction in measured turbidity, may result if instruments which are perfectly suitable for ordinary absorption measurements are used for turbidity measurements without proper modifications. To evaluate the performance of our turbidity detector, particle suspensions of various concentrations of several polystyrene latex standards were prepared. Their extinction coefficients were measured using both a bench-top UV spectrophotometer (Beckman, Model 25) and the online detector (Pharmacia). 

Still another requirement is that the concentrated form of the insecticide readily combines with various types of vehicles. At the present time, pure DDT can be dissolved only in organic solvents, and it has been necessary to provide a 50% water-dispersible DDT powder when wrater was to be used as the vehicle. With the advent of 90% water-dispersible DDT, it may be possible to utilize this material in the preparation of both water suspensions and organic solutions of the chemical. The ideal chemical in this respect would be one that could be shipped as 100% dust, and could be readily diluted with inert dust, water, and organic solvents in the field. 

Flocculating agents can be simple electrolytes that are capable of reducing the zeta potential of suspended charged particles. Examples include small concentrations (0.01-1%) of monovalent ions (e.g., sodium chloride, potassium chloride) and di- or trivalent ions (e.g., calcium salts, alums, sulfates, citrates or phosphates) [80-83], These salts are often used jointly in the formulations as pH buffers and flocculating agents. Controlled flocculation of suspensions can also be achieved by the addition of polymeric colloids or alteration of the pH of the preparation. 

Another recent innovation to improve the efficiency of polymer addition to water and derive the maximum yield from hydrophylic polymers was introduced by Briscoe(165,166). The method involved the preparation of a stabilized polymer slurry (SPS) to be added to water. Briscoe used water as the suspension liquid, usually also containing dissolved KC1 as a clay stabilizer, and formulated a package of inhibitors (borate and caustic) to prevent the polymer from hydrating until the pH was lowered. These concentrates remain in routine use today. 

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