Soluble Liquid Formulation Agrochemical: SL and SG Guide

Soluble Liquid Formulation Agrochemical Basics: SL, SP and SG Compared

The formulation code tells the user how a product behaves in the spray tank, so the first decision is whether the active should stay dissolved. CropLife's formulation catalogue defines a soluble concentrate (SL) as a clear to opalescent liquid applied as a solution after dilution in water, and it allows water-insoluble formulants. A water soluble powder (SP) and a water soluble granule (SG) are solids applied as a true solution after dissolution in water, and both can contain insoluble inert ingredients. The FAO/WHO specification manual adds that an SL carries the active ingredient dissolved in suitable solvents and must be free from visible suspended matter and sediment.

Few actives suit these types. University of Florida extension guidance notes that few pesticides come as soluble powders because few active ingredients are readily soluble in water. A patent on soluble granules states the condition more precisely: the pesticide must be water soluble at the concentration at which it is employed.

Keeping the active in solution is mostly a solvent and surfactant problem, which is where SL design begins.

SL Agrochemical Solubility: Salts, Co-Solvents and Solubilisers

An SL has to hold the active in solution at concentrate strength through cold nights, and again after dilution. There are two broad routes. Either the active is itself a water-soluble salt, or it is dissolved in solvents with solubilising surfactants that keep it in solution when water arrives. A surfactant supplier's formulation guide shows one worked example of each.

In its glyphosate example the acid active is neutralised with an amine in water to form the soluble salt. A built-in wetting surfactant, an antifoam and propylene glycol as antifreeze complete the concentrate. In its triazole fungicide example the water-insoluble active is dissolved in an alcohol solvent and a paraffinic co-solvent, with a non-ionic solubiliser and a little water. Treat both as one supplier's illustrations rather than a standard recipe.

The order of addition differs between the routes. In the salt route, the guide charges water and base, adds the acid active gradually and neutralises with warming. It then adds the surfactant, antifreeze and antifoam, cools the batch and filters out impurities from the technical material. In the solvent route it dissolves the active in the solvents first and adds the solubiliser last. A water-based SL also carries a controlled pH, which is why the FAO/WHO template includes an acidity, alkalinity or pH range clause.

A recipe is only as good as the tests it passes, and the FAO/WHO specification sets those out.

FAO/WHO Specification Tests for Soluble Liquid Formulations

The FAO/WHO specification manual gives a reference template for an SL. Its clauses define what a buyer or regulator can reasonably test: content, impurities, acidity or pH, dilution behaviour, foam and storage. Each clause has an aim written into the manual, which turns the list into a design brief for the formulator. The table follows the SL template.

Two notes in the template deserve attention. The dilution test concentration should correspond to the highest rate of use recommended by the supplier. The foam test also uses the highest recommended rate, in CIPAC standard water D at 25 ± 5 °C. For storage, the manual's general rule is that average active content should not fall below 95 percent of the initial value. Our guide to emulsifiable concentrate formulation shows how the same storage tests apply when the solvent is water-immiscible.

Passing the laboratory tests still leaves the farmer's water, which no specification controls.

Spray Water Quality: Hardness, pH and Weak-Acid Actives

A soluble formulation meets the farmer's water as soon as it enters the tank, and that water is rarely pure. Dissolved minerals, suspended solids and pH can all change how a dissolved active behaves. University of Florida extension guidance rates water below 60 mg/L calcium carbonate as soft and water above 180 mg/L as very hard. These ranges frame the compatibility questions that a formulator has to anticipate.

These effects sit on the use side, but they shape formulation work. The FAO/WHO dilution test fixes a defined CIPAC standard water, so results can be compared between laboratories and batches. Field waters vary far more than any standard water, which is why the technical sheet should state the water-quality limits that the test data support. Our agro chemicals technology and formulations guide places these questions within the wider formulation toolkit.

The same dissolving behaviour is what a soluble granule must deliver from a solid.

Soluble Granule SG Formulation: Granule Design, Processing and Tests

A soluble granule trades the liquid's handling problems for a solid's. The FAO/WHO template describes granules of the technical active with suitable carriers and formulants. They must be homogeneous, free from extraneous matter and hard lumps, free flowing and nearly dust free. The active has to be soluble in water, and insoluble carriers must not interfere with the dissolution test.

The patent cited earlier gives a complete route. It blends a water-soluble pesticide with a water-soluble filler, adds water, extrudes the wet blend through a die and dries the granules. It names lactose, sucrose and glucose as preferred fillers, with wetting and dispersing surfactants and a defoamer as optional components. The patent argues that an SG gives easier handling and lower eye irritation than the corresponding liquid. Treat that as one patent's view and verify it for your own active.

Our guide to wettable powder and water-dispersible granule formulation compares fluid-bed, spray-drying and extrusion routes for granules that disperse. An SG differs because anything in the carrier system that does not dissolve has to pass the dissolution test.

Dust is a safety property as much as a handling one. The manual's stated aim for the dustiness clause is to restrict dust that granules can liberate into the air. For attrition resistance, the aim is to avoid dust and fines generated in handling and transport.

Choosing between the liquid and the granule then comes down to handling, storage and market.

Choosing SL or SG: Handling, Storage and Registration

Both forms deliver the same true solution in the tank, so the right one depends on the active, the market and the supply chain. An SL is simple to dose and make, but it carries the cold-storage and solvent questions. An SG avoids liquid handling but adds dust, attrition and granule-processing questions. CropLife's catalogue states that more than one formulation type can apply in individual cases and that the most appropriate one should be chosen.

1. Measure solubility — at the concentrate strength and at the spray strength, in more than one water.
2. Check stability in solution — the 54 °C test asks whether active content holds when the active sits dissolved for weeks.
3. Test cold behaviour — screen liquids at 0 °C early.
4. Test the dust and attrition profile — screen granules before scale-up.
5. Compare supply chains — weigh liquid logistics against solid logistics for the target market.

In India, pesticide formulations are registered through the Central Insecticides Board and Registration Committee under the Insecticides Act, 1968. The PPQS website publishes the list of registered products. This article covers formulation science only and gives no crop doses, label claims or registration advice for a specific active ingredient. A formulation consultant supports the technical work behind a filing, but the registration decision belongs to the authority.

Working With an Agrochemical Formulation Consultant

Soluble formulations look simple because nothing needs suspending or emulsifying, yet their failures arrive late and cost more. An agrochemical formulation consultant screens solvents, surfactants and carriers against the active's solubility and stability before the first pilot batch. Agrochemical product development services extend that work to specification drafting, stability studies and registration documents. A contract formulation agrochemical manufacturer then carries the validated process into production.

1. Characterise the active — solubility, pH sensitivity, hydrolysis and thermal stability.
2. Choose the route — salt-type SL, solvent-type SL, SG or SP.
3. Screen the system — solvents, surfactants, carriers, antifreeze and antifoam.
4. Run the specification tests — dilution, cold, heat, foam, dissolution and dust.
5. Check spray water behaviour — standard waters and representative field waters.
6. Plan stability and registration — study design and dossier needs.
7. Scale up and transfer — move the process to a qualified manufacturer with quality limits defined.

Our agro chemicals range shows where soluble formulations sit among the other types. Entrepreneurs planning a plant will find the practical route in our guide to starting an agrochemical formulation business. For contrast with suspension types, see our guide to suspension concentrate formulation. Global Formulation provides solvent and surfactant screening, SL and SG specification testing, stability planning and transfer support for agrochemical manufacturers. Active loadings, co-formulant ratios and dose recommendations stay outside this guide by design.