| Chemical identity | Silicotungstic acid hydrate; heteropoly acid containing silicon, tungsten, hydrogen, oxygen, and water of crystallization | Formula reported as H4SiW12O40·xH2O, with the hydration state clearly stated | Certificate of Analysis, product specification, and identity testing by FTIR, Raman, or equivalent validated technique | 10% |
| CAS and traceability | Consistent chemical identification throughout the quotation, label, SDS, CoA, and shipping documents | CAS 12027-38-2 stated where applicable; batch number and manufacturing date included | Lot-specific CoA, container label, SDS, batch genealogy, and retention-sample policy | 8% |
| Assay or active content | High and reproducible silicotungstic acid content suitable for the intended application | Preferred commercial benchmark: ≥98.0% on the supplier’s declared basis; basis must identify whether results are as-received or dry basis | Validated titration, gravimetric, elemental, or chromatographic method described on the CoA | 18% |
| Tungsten content | Tungsten level consistent with the stated heteropoly-acid composition | Lot-to-lot result within the agreed specification range; a nominal anhydrous composition corresponds to approximately 76.7% elemental tungsten by mass | ICP-OES, ICP-MS, XRF, or another validated elemental method | 12% |
| Hydration and loss on drying | Controlled water content because hydrate level affects assay calculations, mass balance, and catalytic performance | Declared range established by application testing; moisture result reported for every batch | Karl Fischer titration, thermogravimetric analysis, or validated loss-on-drying method | 12% |
| Elemental impurities | Low levels of lead, arsenic, mercury, cadmium, and other application-relevant metals | Limits agreed according to the end use, local regulations, and customer risk assessment; results reported in mg/kg | ICP-MS or ICP-OES test report from a competent laboratory, preferably operating to ISO/IEC 17025 principles | 10% |
| Insoluble matter | Minimal undissolved residue to protect filtration systems and maintain process consistency | Preferred benchmark: ≤0.5% unless a tighter application-specific limit is required | Defined dissolution, filtration, drying, and gravimetric residue procedure | 6% |
| Chloride and sulfate | Controlled residual inorganic ions that may affect corrosion, downstream reactions, or catalyst performance | Each impurity limit defined in the purchase specification; typical screening target is ≤0.10% for each ion | Ion chromatography, validated wet chemistry, or equivalent analytical method | 6% |
| Physical form and particle size | Uniform crystals or powder with acceptable flowability and dissolution behavior | Appearance: white to pale yellow or greenish crystalline material; particle-size range agreed before ordering | Visual inspection, sieve analysis, laser diffraction, and application dissolution test | 5% |
| Packaging and moisture protection | Packaging must prevent moisture uptake, contamination, and leakage during storage and transport | Sealed inner liner with chemically compatible outer container; net weight, lot number, hazard labeling, and storage conditions shown | Packaging inspection, transport simulation where required, and incoming-goods checklist | 5% |
| Documentation and regulatory support | Complete and consistent technical, safety, and regulatory documentation | Current SDS aligned with applicable GHS requirements, specification sheet, lot-specific CoA, and transport classification information | Document review before approval; confirm regional requirements such as REACH or other applicable chemical regulations | 5% |
| Batch consistency and change control | Stable quality across repeated deliveries and controlled notification of process or raw-material changes | Historical data for at least three representative lots; advance notification for specification, process, site, or packaging changes | Supplier questionnaire, sample qualification, trend review, and quality agreement | 3% |