How to Read a TiO2 Certificate of Analysis
The CoA is your evidence that the TiO2 batch matches spec. Here's how to read every line and verify quality.
Every TiO2 shipment includes a batch-specific Certificate of Analysis (CoA). The CoA is the formal quality document that certifies the specific batch meets specification. Knowing how to read it lets you verify quality at receipt and catch issues before they affect production.
Standard CoA structure:
Header section: - Product name and grade designation (e.g., "SEMITI 996, Universal Rutile Titanium Dioxide") - Batch / Lot number (unique identifier) - Production date and shipment date - Container / FIBC numbers (for traceability) - Customer reference / Order number
Chemistry section: - TiO2 content (typically ≥93.0% for rutile, ≥98% for anatase): the primary chemistry assay. Below spec indicates dilution or contamination. - Rutile content (for rutile grades, ≥98.5%): proportion of TiO2 in rutile crystal form. Anatase grades have ≥99% anatase content. - Crystal form: rutile or anatase (or specific specifications for nano). - Surface treatment composition: e.g., "Al2O3 + organic" or detailed percentages if specified.
Physical properties: - Specific gravity / density: 4.0 g/cm³ for rutile, 3.9 for anatase — should be consistent batch-to-batch. - Oil absorption: gram of oil per 100 g of TiO2. Range typically 12–25 depending on surface treatment. Higher = needs more dispersant. - Loss on ignition (LOI): heating to 800°C, percentage weight loss. Should be ≤0.50%. - pH (aqueous suspension): 6.5–8.5 typical. Acidic batches indicate surface treatment issue. - Water-soluble matter: ≤0.50% typical. Higher indicates residual processing chemicals.
Color properties: - CIE L*: lightness (97.0–98.8 range) - CIE a*: red-green (-0.5 to +0.5) - CIE b*: blue-yellow (1.0–2.5) - Whiteness Index (WI) or Yellowness Index (YI): derived color metric
These three (L*, a*, b*) tell you the color match against your reference. Major deviation (more than ±0.5 on any axis) means batch will look different in finished product.
Optical properties: - Tinting strength (Reynolds method or % vs standard): typically 1700–1950+. The functional opacity metric. - Particle size (D10, D50, D90): microns. Standard for coating-grade rutile: D50 0.25–0.30 μm. - 45 μm sieve residue: ≤0.02% typical. Higher indicates coarse particles or contamination.
Heavy metals: - Pb (lead): < 10 ppm typical (lower for premium grades) - Cd (cadmium): < 2 ppm - As (arsenic): < 3 ppm - Hg (mercury): < 1 ppm
Some CoAs also report Sb (antimony) and Ba (barium).
Functional spec (application-specific): - Thermal stability (for plastics grades): typically expressed as Δb* at 280°C or 300°C, 5 min hold - QUV gloss retention (for outdoor coatings grades): typically % retention at 2000 or 5000 hr - Photocatalytic activity (for cosmetic nano grades): % of uncoated baseline
How to use the CoA at receipt:
Step 1: Verify batch identity Check that the CoA batch number matches the actual product (bag tags, container documentation). Mismatched batches are rare but happen — flag immediately.
Step 2: Compare against your spec For each critical parameter (typically TiO2 content, tinting strength, color L*/b*), verify the batch falls within your accepted range. Specific automotive OEM specs may have tighter tolerances than the CoA's normal range.
Step 3: Compare against historical batches Look for batch-to-batch variation in critical parameters. Sudden shifts (e.g., b* jumping from 1.8 to 2.4) suggest process change at the supplier — worth investigating before scaling production.
Step 4: Archive CoA Keep the CoA on file for 2+ years. If a quality issue surfaces in finished product, you'll need the CoA to investigate.
Common CoA red flags:
1. Missing batch number or production date: indicates poor traceability; refuse acceptance 2. TiO2 content right at minimum spec (e.g., exactly 93.0%): probably means the batch was at the edge, may have actual content lower; request retest or reject 3. b* significantly higher than historical range: indicates impurity carry-through; investigate before scaling 4. Heavy metals above spec: rare but critical; reject and request replacement 5. Test methods not specified: ask supplier to clarify which methods used (GB, ISO, ASTM)
Independent verification: For critical applications, periodic third-party testing (SGS, Bureau Veritas, Intertek) of samples confirms supplier CoA accuracy. Typical cost $500–1500 per analysis. Not necessary for every shipment, but worth periodic verification.
SEMITI CoA practice: - CoA prepared for every batch - PDF emailed at shipment date - Hard copy in document pouch with B/L - All test methods explicitly listed - Historical batch data available on request - Third-party retest available on customer request