Separate the technical data sheet, specification and COA
A technical data sheet describes a supplier's product and may show typical values. A purchase specification identifies the requirements that are contractually binding. A certificate of analysis reports results for an identified production lot. These documents serve different purposes and should not be treated as interchangeable.
Start with the complete identity: anhydrous sodium sulfate, Na2SO4, CAS 7757-82-6, or a named hydrate where that is actually required. State whether assay is measured as received or recalculated on a dry basis. Without that basis, two apparently equal assay figures may not describe the same material.
Core chemical fields and why they matter
| Field | What to define | Why a buyer may control it |
|---|---|---|
| Na2SO4 assay | Minimum or range, basis and test method | Confirms chemical content on an agreed basis |
| Moisture or loss on drying | Maximum, temperature, time and calculation | Affects net active mass, caking and handling |
| Water-insoluble matter | Maximum and filtration method | Can affect dissolution, residues and visible defects |
| Chloride | Limit and chloride reporting convention | May matter in corrosion-sensitive or formulation-specific processes |
| Calcium and magnesium | Individual or combined limits and method | Can matter in textile baths and other water-sensitive processes |
| Iron and color-related impurities | Limit, units and method | Can be relevant to white products, glass or shade control |
| Free acid or free alkali | Limit, endpoint and reporting basis | Provides process-specific acidity or alkalinity control |
Not every application requires every test. Adding an irrelevant low limit can increase cost without reducing process risk. The responsible formulator or process owner should select the smallest set of parameters that predicts fitness for use.
Physical properties need defined methods
Whiteness, color, pH, particle-size distribution and bulk density can be important, but each result depends on a method. A particle result is incomplete without the sieve or instrument, sample preparation and reporting format. Bulk density should identify whether it is loose or tapped. A pH result needs a stated solution concentration, water quality, temperature and procedure.
Physical behavior can change with storage and packing even when the chemistry is compliant. If dust, flow, feeder calibration or dissolution is critical, qualify these properties using both laboratory measurements and a process trial.
Analytical method, units and detection limits
Write the method or an agreed equivalent beside each controlled parameter. Confirm units such as percent by mass, milligrams per kilogram or parts per million. For trace limits, the method's quantification limit must be low enough to verify compliance. A result reported as “not detected” is meaningful only with the method and detection or quantification limit.
When buyer and supplier laboratories use different methods, agree before the first shipment which method governs a dispute. Method alignment is especially important for moisture, insolubles, whiteness, trace metals and particle-size results.
Sampling and lot definition
A precise test cannot correct an unrepresentative sample. Define what constitutes a lot, how bags or bulk points are selected, how increments are combined and divided, and how samples are sealed and identified. Keep retained samples for an agreed period where commercial risk justifies it.
The COA should identify the product, lot or batch, manufacture or test date where applicable, results, limits or reference specification, units and approval. A generic COA copied from another lot is not evidence for the shipment being received.
Application-specific specification priorities
| Use | Common priorities to evaluate | Final qualification |
|---|---|---|
| Powder detergent | Assay, moisture, insolubles, whiteness, particle behavior and caking | Actual formulation and packing trial |
| Textile dyeing | Dissolution, calcium, magnesium, iron, insolubles and shade consistency | Actual fiber, dye and recipe trial |
| Glass batch | Assay, moisture, iron, chloride, particle distribution and lot consistency | Controlled batch and product-quality review |
| Other industrial process | Parameters connected to reaction, contamination and handling risk | Customer technical approval |
These are screening fields, not universal limits. The buyer should provide numeric requirements and methods rather than asking only for “detergent grade” or “glass grade.”
Incoming inspection and nonconformance
Verify packaging condition, labels, lot identity and agreed documents before use. Apply a risk-based incoming test plan and record results against the controlling specification. If a result is disputed, quarantine the material, preserve representative samples and follow the agreed retest procedure before making a release decision.
The supply agreement should address off-specification material, root-cause response and notification of changes to site, source, process, method, additive, particle form or packing. Change control protects process performance that may not be visible in a headline assay.
Frequently asked questions
Is a TDS the same as a product specification?
No. A TDS commonly describes typical product characteristics; the controlling purchase specification states the agreed acceptance limits.
What does a sodium sulfate COA prove?
It reports test results for an identified lot. It should be checked against the purchase specification and does not replace application qualification.
Should assay be reported on a dry basis?
Either dry-basis or as-received reporting can be used if clearly defined. The quotation, specification and COA must use a consistent basis.
Does every buyer need the same impurity limits?
No. Limits should be selected from actual process, product-quality and regulatory risks and verified with an appropriate method.