Aolong Chemical

12 November 2026

Pure sodium acetate trihydrate contains about 39.7% water of crystallization by mass. So 100 kg of pure trihydrate provides about 60.3 kg of sodium acetate as CH₃COONa. For a production batch, check the form, the basis of the assay and the actual lot results before working out the weight to add. [1] [2]

The key figures are on the certificate of analysis (COA). A dry-basis assay describes the dried sample. The weight on the plant scale includes the material as supplied, with its water. Putting both forms on the same basis makes it possible to compare quotes, check a delivery or update a batch sheet.

What is the difference between anhydrous sodium acetate and trihydrate?

Each formula unit of the trihydrate contains one unit of sodium acetate and three water molecules. That water is part of the crystal structure, so it is called water of crystallization. The anhydrous form has no water in its crystal formula. A commercial anhydrous batch can still pick up moisture during storage or handling. [1] [2] [4]

The 39.72% is calculated as (136.08 − 82.03) ÷ 136.08 × 100. For pure material, 1.000 kg of anhydrous sodium acetate and about 1.659 kg of trihydrate supply the same amount of CH₃COONa. This ratio is useful for an early estimate. Use the lot results when setting a production weight. [1] [2] [4]

Anhydrous sodium acetate can absorb water from the air. Trihydrate can lose crystal water in warm, dry air. Both forms can appear as powders. Ask for the full form name and formula when a quote describes the material simply as powder or granules. Both forms also share the same additive number under JECFA (INS 262(i)) and the EU (E 262(i)). [1] [2] [3]

Why can both forms show the same assay on the COA?

Assay is the amount of sodium acetate reported by the test. On a dry basis, the result is expressed as CH₃COONa per unit mass of dried material. On an as-supplied basis, it is expressed per unit mass of the material received. For a trihydrate lot, the two numbers can be far apart because drying removes a large part of the original sample mass. [1] [2]

China’s GB 30603-2014 and the FAO/WHO JECFA specification set a minimum assay of 98.5% after drying for both forms. The EU specification for E 262(i) gives the same minimum on an anhydrous basis. These three texts list loss on drying of up to 2.0% for the anhydrous form and 36.0–42.0% for the trihydrate, using 120 °C for four hours. Use the form and the method stated in the agreed specification when checking those limits. [1] [2] [3]

Loss on drying (LOD) is the change in sample mass under the stated drying conditions. The loss can include water and any other material driven off by the test. The 39.72% above comes from the pure crystal formula. The LOD on a COA comes from a test on a lot. If a recipe needs the actual water content, ask for a water test suited to that purpose. [1] [2] [5]

When reviewing a certificate, check which column gives the specification limit and which gives the result for the lot. For an anhydrous grade, the LOD limit might read “≤ 2.0%.” The measured result for a lot might read “0.50%.” Use the limit to check acceptance and the measured result to calculate how much to weigh. If the reported LOD falls outside the range for the declared form, ask the lab to check the sample and the test method before using the result.

How do you convert the COA result to an as-supplied value?

When the COA gives a dry-basis assay as CH₃COONa, use the lot’s LOD that matches the drying basis of the assay. The JECFA method, for example, runs the assay on the dried sample from the LOD test. Use the two measured results from the same lot and enter percentages as fractions in the calculation. [1] [2]

As-supplied CH₃COONa fraction = dry-basis assay fraction × (1 − LOD fraction)

If the COA already states an as-supplied assay expressed as CH₃COONa, use that value directly. If it gives an as-supplied result expressed as CH₃COONa·3H₂O, confirm that basis with the laboratory and multiply the stated fraction by 82.03 ÷ 136.08. When a COA simply says “Assay 99.5%,” ask for both the chemical formula used to report the result and the basis of the sample weight.

How much material should you weigh?

First find how much CH₃COONa the batch needs. If the batch sheet names a weight of a particular grade, multiply that weight by the grade’s as-supplied fraction to find the amount it delivers. If the sheet already gives a target weight of CH₃COONa, use that target directly.

Product to weigh (kg) = target CH₃COONa (kg) ÷ as-supplied CH₃COONa fraction

Example with two COAs

The values below are for illustration. Both lots have the same dry-basis assay. The different LOD results give different amounts of sodium acetate in each kilogram of material on the scale.

Suppose an existing batch sheet calls for 100.0 kg of Lot A. It delivers 100.0 × 0.990025 = 99.0025 kg of CH₃COONa. To deliver the same amount with Lot B, divide 99.0025 by 0.599985. The result is about 165.0 kg of Lot B.

If the batch sheet calls for 100.0 kg of CH₃COONa itself, the Lot B weight is 100.0 ÷ 0.599985, or about 166.7 kg. The difference comes from what the original 100.0 kg means. Keep the calculated fractions through the steps and round the final weight to suit the scale.

The calculation can also change between two lots of the same form. If the next trihydrate lot has the same 99.50% dry-basis assay and an LOD of 41.0%, each 100 kg provides about 58.7 kg of CH₃COONa. Both LOD values fall within the stated range. Each 100 kg of the new lot supplies about 1.3 kg less CH₃COONa than Lot B. [1] [2] [3]

Example for a solution made by weight

A 100 kg solution at 10.0% CH₃COONa by weight needs 10.0 kg of CH₃COONa. Using Lot B, weigh about 16.67 kg of trihydrate product and add water to reach 100 kg total. For a batch made with only this product and water, that is about 83.33 kg of added water. The full weight of the trihydrate product counts towards the final batch weight, including the water it brings in.

What should you check when changing forms on the line?

For a solution, check the final batch weight and concentration against the recipe. If the recipe has a separate limit for total water, use a suitable water result to check that limit. For a dry mix, check whether the new weight changes the mixer load, feeder settings or the spread of the ingredient across the batch.

Keep containers closed between uses and take a sample that represents the material to be weighed. If an open bag has been held in conditions that could change its water content, ask quality control to confirm its condition before applying the earlier COA values. [2] [3]

What should purchasing, quality and production check?

1. Purchasing. Specify the hydrate form, grade and assay basis on the order. If comparing prices by sodium acetate content, divide each delivered price per kilogram of product by its as-supplied CH₃COONa fraction.
2. Quality. Match the COA to the label and lot number. Record the measured assay, the reporting basis and the test method for LOD. Check each value against the specification for that form.
3. Production. Write down whether the target is a product weight or a weight of CH₃COONa. Multiply the proposed product weight by the new lot’s as-supplied fraction to check that it delivers the target.

Keep the lot numbers and the calculation on the batch sheet. That gives the next operator the same starting figures and shows which weight was used to reach the target.

References

[1] China’s National Health Commission · GB 30603-2014, Food Additive Sodium Acetate, Table 2 and Annex A.3

[2] FAO/WHO JECFA · Sodium Acetate, INS 262(i), specification and assay method

[3] EUR-Lex · Commission Regulation (EU) No 231/2012, E 262(i), consolidated text of 18 August 2026, pp. 74–75

[4] USP–NF · Sodium Acetate monograph preview, formula weights and CAS numbers

[5] USP–NF · General Chapter 〈731〉, Loss on Drying, preview