Sodium Thiosulfate Specifications: How to Read a COA

Sodium thiosulfate specifications define the quality limits a product must meet, while a Certificate of Analysis, or COA, shows the actual results for a production batch.

Before ordering, buyers should confirm the product form and CAS number, then review purity, pH, water-insoluble matter, sodium sulfide and iron. The agreed specification and batch COA should be used together when evaluating the product.

Aozun Chemical lists industrial-grade sodium thiosulfate pentahydrate with a minimum purity of 98.0%.

Which Sodium Thiosulfate Specifications Matter Most?

The most important parameters depend on the intended application, but industrial buyers usually need to check the following:

Checking purity alone is not enough. Two products with the same assay may still have different impurity limits, particle sizes or testing conditions.

Specification Sheet, COA, TDS and SDS: What Is the Difference?

These documents serve different purposes and should not be treated as interchangeable.

A specification sheet may remain unchanged for many batches. A COA should identify a specific batch and report its actual test results.

For bulk purchasing, buyers should request the latest specification before ordering and confirm that a batch COA will be provided with the shipment.

How to Read a Sodium Thiosulfate COA

1. Confirm the Product Form and Identity

First check the product name, molecular formula and CAS number.

Sodium thiosulfate pentahydrate is identified by:

• Formula: Na₂S₂O₃·5H₂O

• CAS number: 10102-17-7

• Molecular weight: 248.18

Anhydrous sodium thiosulfate has a different CAS number and molecular weight. The two forms should not be compared or substituted on an equal-weight basis without adjusting the process.

2. Compare the Result with the Specification Limit

A COA normally includes three pieces of information:

• Test item

• Specification limit

• Actual batch result

“Min” means the result must not be lower than the stated value. “Max” means it must not exceed that value.

For example, if the purity requirement is 98.0% minimum, a result of 98.5% meets the requirement. If water-insoluble matter is limited to 0.03% maximum, the batch result must be 0.03% or lower.

3. Check the Testing Conditions

Some results can vary depending on the test conditions.

For pH, buyers should confirm the solution concentration, test temperature and method when these details are important to the application. Results produced under different conditions may not be directly comparable.

The same principle applies to particle size and solution appearance. The acceptance method should be agreed upon before the order is confirmed.

4. Review the Batch Information

A useful COA should include information such as:

• Product name

• Batch or lot number

• Production or testing date

• Test results

• Quality approval

The batch number on the COA should match the product or packaging information supplied with the shipment.

Example: Aozun’s Listed Industrial Specification

Aozun Chemical currently lists the following specification for its industrial-grade sodium thiosulfate pentahydrate:

These values are supplier specification limits rather than guaranteed results for every batch. The actual figures should be checked on the relevant batch COA.

Buyers with a specific testing method or stricter limit should state the requirement in the RFQ.

Which Parameters Matter for Different Applications?

Different applications may place greater importance on different quality indicators.

An industrial-grade product should not automatically be treated as food, pharmaceutical, reagent or photographic grade. Buyers should confirm the required standard for their own application.

Common Mistakes When Comparing Specifications

Industrial buyers should avoid these common purchasing mistakes:

• Comparing pentahydrate with anhydrous sodium thiosulfate

• Looking only at purity and ignoring impurities

• Comparing pH results measured under different conditions

• Treating a general specification sheet as a batch COA

• Accepting a COA without checking the batch number

• Comparing quotations with different packaging or Incoterms

• Assuming one industrial specification is suitable for every application

Clear requirements at the inquiry stage reduce technical disagreements and unnecessary follow-up.

What to Include in a Sodium Thiosulfate RFQ

To receive an accurate quotation, buyers usually only need to provide:

• Required product form or grade

• Intended application

• Order quantity

• Preferred packaging

• Destination port or delivery location

• Required delivery date, if applicable

If you have specific purity, impurity limits or document requirements, please include them in the inquiry. Otherwise, the supplier can recommend a suitable specification based on the application.

Providing this information helps the supplier confirm product suitability and prepare a more accurate quotation.

Frequently Asked Questions

Is a specification sheet the same as a COA?

No. A specification sheet defines the acceptable quality limits. A COA reports the actual test results for a specific production batch.

Can pentahydrate and anhydrous sodium thiosulfate use the same specification?

No. They have different formulas, molecular weights and active content. The required form should be stated clearly on the inquiry and purchase order.

Why should the pH test method be confirmed?

The reported pH may depend on solution concentration, water quality, temperature and testing method. Buyers with a strict pH requirement should define the test conditions.

Request a Specification and Batch COA

Aozun Chemical supplies industrial-grade sodium thiosulfate pentahydrate for international industrial buyers.

Products are tested before shipment, and a COA is issued for quality verification. To receive an accurate quotation, please provide your required specification, application, quantity, packaging, destination port and preferred Incoterm.

View the sodium thiosulfate product page or contact Aozun Chemical to request the latest specification, sample, COA and quotation.