# Ammonium persulfate

Chemical identity, supplied grades, property bases, and source limits for ammonium peroxydisulfate.

Reviewed: 2026-10-30

Tags: chemicals, oxidants, persulfates

## Identity and related salts

Evonik lists **1.98 g/cm³ crystal density** and **1.05 g/cm³ loose bulk density** for its ammonium persulfate. The latter includes interparticle space. Ammonium persulfate, or APS, is ammonium peroxydisulfate, (NH₄)₂S₂O₈, CAS 7727-54-0, EC 231-786-5, 228.20 g/mol. [Sigma-Aldrich product 248614](https://www.sigmaaldrich.com/US/en/product/sigald/248614)

The formula contains two ammonium ions per peroxydisulfate ion. Commercial assays and impurities have their own reporting bases.

Sodium and potassium persulfates contain the same peroxodisulfate anion with different cations. United Initiators lists Na₂S₂O₈ and K₂S₂O₈ separately from APS. Its CAROAT potassium monopersulfate belongs to the peroxymonosulfuric-acid family. These names do not denote interchangeable substances or equal masses of active material. [United Initiators persulfate brochure, revision 2.0, pages 4–6](https://www.united-initiators.com/-/media/files/download-center/new-brochures/2025/united_initiators_persulfates.ashx)

## Supplied grades and assay

Sigma-Aldrich 248614 is an ACS reagent with assay ≥98.0%, supplied as chunks, granules, powder, or crystals. Its specification also names insolubles, titratable acid, ignition residue, and trace contaminants. An assay threshold alone does not describe those other attributes. [Sigma-Aldrich product properties](https://www.sigmaaldrich.com/US/en/product/sigald/248614)

United Initiators distinguishes APS from silica-containing APS-3 and APS-5F. Its Pullach-site table gives APS specified purity ≥99.0% and typical purity 99.9%. Active oxygen is specified ≥6.94% and typical 7.00%. The table footnotes distinguish technically specified values from typical results. Those APS entries are not specifications for every derivative. [United Initiators brochure, pages 4–5 and footnotes](https://www.united-initiators.com/-/media/files/download-center/new-brochures/2025/united_initiators_persulfates.ashx)

San Yuan separately specifies purity ≥99.0%, active oxygen ≥6.94%, and moisture ≤0.04% for its white crystalline product. These are supplier-specific limits, not a universal APS specification. [San Yuan ammonium persulfate specifications](https://www.sanyuanchemical.com/en/product/ammonium-persulfate)

The United Initiators US SDS lists ≤100% ammonium persulphate by mass, with actual concentration withheld as a trade secret. This is not a 100% assay. [APS US SDS, version 2.2, section 3](https://www.united-initiators.com/files/APS/United_Initiators_APS_MSDS_US_EN.pdf)

Synthesis of these sources distinguishes identity, product specification, typical analysis, and a lot-specific certificate of analysis. None of the cited general documents establishes the composition or measured assay of an unidentified lot.

## Active oxygen basis

Active oxygen is an oxidation-equivalent quantity, rather than the mass of all eight oxygen atoms in the formula. Evonik's assay equations use different factors for active oxygen and ammonium persulfate. Their ratio implies approximately 7.0% active oxygen for pure APS. [Evonik technical brochure, pages 13–14](https://www.evonik.com/content/dam/evonik/documents/Evonik_Persulfates_Technical_Information_Brochure_EN_Asset_2237848.pdf.coredownload.pdf)

The distinction is chemical and analytical. An active-oxygen percentage is not a prediction of reaction rate, selectivity, or useful oxidant consumption in a particular formulation.

## Physical properties and their bases

| Property | Source value and scope |
| --- | --- |
| Crystal density | Evonik gives 1.98 g/cm³ for crystalline monoclinic APS. The table does not state a measurement temperature. |
| Loose bulk density | Evonik gives 1.05 g/cm³. This is a powder-bed quantity, distinct from crystal density. |
| Water solubility at 25 °C | Evonik gives 85 g APS per 100 g water. |
| Water solubility at 50 °C | Evonik gives 116 g APS per 100 g water. |

The table summarizes [Evonik's physical-property and maximum-solubility tables, page 8](https://www.evonik.com/content/dam/evonik/documents/Evonik_Persulfates_Technical_Information_Brochure_EN_Asset_2237848.pdf.coredownload.pdf).

Derived solely from the mass basis, 85 g per 100 g water corresponds to 85 ÷ 185 × 100 ≈45.9% APS by total mass. It does not mean 85% by mass or 850 g per litre of final solution. Conversion to a final-solution volume basis additionally requires solution density.

The US SDS gives solubility as 850 g/L at 25 °C without defining the litre basis. Its bulk density of 1,100 kg/m³ at 20 °C equals 1.10 g/cm³. That differs from Evonik's loose-bulk value, with different product and test descriptions. [United Initiators US SDS, section 9](https://www.united-initiators.com/files/APS/United_Initiators_APS_MSDS_US_EN.pdf)

## Decomposition and hazard classification

The US SDS states that APS decomposes below its melting point, without a melting-point value. Its OSHA Hazard Communication classification includes oxidizing solid category 3, oral acute toxicity category 4, skin irritation category 2, eye irritation category 2A, respiratory and skin sensitization category 1, and respiratory single-exposure target-organ toxicity category 3. These classifications concern the supplied product in the US context. [United Initiators APS US SDS, sections 2 and 9](https://www.united-initiators.com/files/APS/United_Initiators_APS_MSDS_US_EN.pdf)

A decomposition entry cannot be treated as a reversible solid-to-liquid transition. Hazard classification also does not establish a manufacturing process's oxidation performance or material compatibility.

## Source scope and remaining limits

The United Initiators brochure identifies revision 2.0 but shows no issue date. Its website path contains 2025, which is not a stated document revision date. The cited US SDS is version 2.2, revised October 16, 2025. The Evonik brochure and supplier product pages provide no explicit revision identifier in the cited material. The pages and PDFs were consulted October 30, 2026 PDT.

This reference covers chemical identity and selected solid-product properties. It does not establish a complete formulation, current lot quality, substitution equivalence, application performance, or customer capability. Regional SDS versions and additive-containing grades remain separate evidence contexts. [Surface-finishing processes](../../processes/finishing/index.md) provides broader manufacturing context.