How to Read a Calcium Carbonate Certificate of Analysis (CoA)
A calcium carbonate CoA can report the same purity as CaCO3, CaO or Ca, so convert before you compare (CaCO3 = CaO × 1.785 = Ca × 2.497). Read LOI and moisture as two separate losses, check the method and basis beside every line, and treat typical values as reference, not a promise.
Three certificates sit on a purchase desk. The filler supplier's says CaCO3 95%. The glass supplier's says CaO 53.2%. The feed supplier's says Ca 38%.
Which is purest? They are the same material, written three ways.
The certificate is the only document that speaks for the lot in the truck. Many buyers read only its first line.
A calcium carbonate certificate of analysis (CoA) is the test report for one lot. Read identity first: lot number, sampling date, laboratory. Then chemistry: CaCO3 or its CaO or Ca equivalent, LOI, MgO, Fe2O3, SiO2, acid insolubles, moisture; then physical lines: particle size, whiteness. No result means much without its limit, test method and basis.
This guide covers each line, the three bases, what limits promise, red flags, and CoA vs TDS vs SDS. Quicklime and hydrated lime certificates report available lime instead; see what a lime test report should cover.
What a calcium carbonate certificate of analysis shows
A calcium carbonate certificate of analysis ties test results to one lot. Before reading any number, check that it states:
- Product, grade and lot or batch number.
- Sampling point and date, and test date.
- The laboratory, and who signed.
- A specification column beside a result column.
- Method, unit and basis (dry or as received) for each line.
Without these, the numbers cannot be traced to your delivery. See also how to verify a supplier's test report.
CaCO3, CaO or Ca: how to convert between the three bases
Calcium carbonate purity is reported on three bases. Filler and water buyers read CaCO3, glass plants read calcium oxide (CaO), and feed formulators read elemental calcium (Ca).
The factors come from the molar masses listed by PubChem: CaCO3 is 100.09 and CaO is 56.08. So CaCO3 = CaO × 1.785, and CaCO3 = Ca × 2.497.
Use this table to put two certificates on one basis before comparing them.
| Reported as | Pure calcium carbonate | A 95% CaCO3 material | To get CaCO3 |
|---|---|---|---|
| CaCO3 | 100% | 95.0% | As reported |
| CaO | 56.0% | 53.2% | × 1.785 |
| Ca | 40.0% | 38.0% | × 2.497 |
| CO2 (theoretical LOI) | 44.0% | 41.8% | ÷ 0.440 |
Final specifications should always be confirmed by the buyer's technical or quality team.
Calcium oxide (CaO) here is an oxide equivalent, not quicklime. And an oxide analysis may include calcium held in silicates, so cross-check CaO against LOI or CO2.
Impurities follow the same logic. Fe × 1.430 gives Fe2O3, and Mg × 1.658 gives MgO. A limit of 0.03% is the same as 300 ppm.
LOI and moisture: two different weight losses
Loss on ignition (LOI) is the weight a dried sample loses on strong heating. IS 1760 (Part 1):1991, the Bureau of Indian Standards (BIS) method for limestone and allied materials, dries the sample at 105 ± 2 °C first. It then ignites it at 900–950 °C and finally 1,000 °C, to constant mass.
For pure calcium carbonate, LOI is the carbon dioxide driven off: 43.97% of the weight. Magnesium carbonate loses 52.2%, so dolomitic material pushes LOI up. Water held in clay, and organic matter, add to it too.
Moisture is different: free water in the material as delivered, found by drying (ASTM C25; ISO 787-2 at 105 °C).
Chemistry is often reported on the dried sample, so check the basis line. A wet lot can pass on chemistry and still deliver less calcium carbonate.
The CoA line by line
Read each row as: what is measured, why it matters, and which method should sit beside it.
| Line on the CoA | What it measures | Why it matters | Method usually named |
|---|---|---|---|
| CaCO3, CaO or Ca | Calcium on a stated basis | Calcium you receive | EDTA titration, IS 1760 (Part 3):1992; ASTM C25 |
| MgO or Mg | Magnesium, often from dolomite | Feed availability; glass limits | IS 1760 (Part 3); ASTM C25 |
| Fe2O3 or Fe | Iron | Colour in fillers and glass | Spectrophotometric, IS 1760 (Part 3); ASTM C25 |
| SiO2 | Silica, including quartz | Abrasion; glass batch | IS 1760 (Part 2):1991; ASTM C25 |
| Al2O3 | Alumina, mostly from clay | Glass and chemical limits | IS 1760 (Part 3); ASTM C25 |
| Acid insolubles | Matter acid does not dissolve | Inert load and specks | ASTM C25 insoluble matter |
| LOI | CO2, plus clay water and organics | Cross-check on carbonate content | IS 1760 (Part 1); ASTM C25 |
| Moisture | Free water, as delivered | Caking, dosing, paying for water | ASTM C25; ISO 787-2 |
| Particle size distribution (PSD): D50, top cut | Size spread | Dispersion, flow, reaction rate | ISO 13320 laser, or sedimentation |
| Residue on sieve | Oversize particles | Specks, screen blinding | ISO 787-7; ASTM C110 |
| Whiteness or brightness | Reflectance on a named scale | End-product colour | Scale named, e.g. DIN 53163 Ry; ASTM C110 dry brightness |
Final specifications should always be confirmed by the buyer's technical or quality team.
A whiteness figure without its scale and illuminant cannot be compared across suppliers.
Particle size: D50 and top cut
D50 is the median particle size: half the sample is finer. Top cut (D98 or D97) is the size that 98% or 97% of the sample is finer than.
Laser diffraction under ISO 13320:2020 reports by volume and assumes spheres; sedimentation and sieving report by mass. Compare D-values only when the method matches. To choose a grade, see which filler fineness to specify.
What ≥ and ≤ commit a supplier to
A minimum (≥) or maximum (≤) is a promise about every lot, at the stated method, basis and sampling point. A typical value is not a promise; see typical values versus guaranteed specifications.
Three details make it enforceable.
The method. ASTM C25 says its classical gravimetric and volumetric methods are typically required for referee analyses where the specification is contractual. Name a referee method in your purchase specification.
The rounding. IS 2, the BIS rules for rounding off numerical values, says that where prescribed limits apply, rounding should go in one direction only. A 94.96% result against a 95% minimum should not be rounded up into compliance.
The laboratory. ISO/IEC 17025:2017 sets the competence requirements for laboratories. In India, NABL accredits laboratories to it for a stated scope, so check that your test is in that scope.
Red flags you can check with a calculator
Most of these can be checked before the lot is unloaded.
| What you see | Why it matters | What to ask for |
|---|---|---|
| No lot number, or a test date that does not fit the dispatch | May not describe your lot | A certificate for this lot |
| Only a "typical" column | Typical values are not a promise | Limits with results beside them |
| No method, basis or unit | Results cannot be compared | Method, unit and basis |
| CaCO3 and CaO that disagree at × 1.785 | Calcium in silicates, or an arithmetic error | The LOI or CO2 result |
| Oxides plus LOI far from 100% | Something unreported or miscalculated | The full analysis |
| LOI well above 44% on a high-purity calcite claim | Magnesium carbonate, clay or organics | MgO and acid insolubles |
| Iron in ppm with no method named | IS 1760 (Part 3):1992 iron method covers 0.2–2% Fe2O3 | The method and its working range |
CoA, TDS and SDS: which document answers which question
Ask for all three; each answers a different question.
| Document | Answers | Tied to a lot? | Numbers shown |
|---|---|---|---|
| Certificate of analysis (CoA) | Did this lot meet the specification? | Yes | Results against limits |
| Technical data sheet (TDS) | What is this grade, and how does it usually perform? | No | Typical values |
| Safety data sheet (SDS, formerly MSDS) | How do we handle, store and respond safely? | No | Hazard and handling data in 16 sections |
A TDS usually gives typical values and leaves suitability to the user. The SDS follows the 16-section format that OSHA's guidance aligns with the UN Globally Harmonized System (GHS).
Where Dr. Lime fits
Dr. Lime's product pages publish specification limits on the basis each industry reads.
CaSure Powder, for feed, is specified at Ca ≥ 38%. CalFill, for fillers, is specified at CaCO3 ≥ 95%. Glass Pure, for float glass, is specified at CaO ≥ 53%.
The material comes from a single-source deposit and is processed at Dr. Lime's ISO 9001:2015-certified plant in Nagaur, Rajasthan, which has its own laboratory. Particle size distribution is measured by volume using laser analysis, with lot-level traceability.
A certificate of analysis and safety data sheet are available on request from the Dr. Lime technical team. The team can also share specifications and arrange samples.
Read the basis before the number
Most arguments over a certificate are about basis, method or sampling point, not chemistry. Put two certificates on the same basis, check the method beside each line, and the numbers start to mean something.
A certificate does not tell you how pure a material is. It tells you how pure one lot was, on a stated basis, by a stated method.
FAQs
What is a certificate of analysis for calcium carbonate?
A calcium carbonate certificate of analysis (CoA) is the test report for one production lot. It lists each parameter, such as CaCO3, MgO, Fe2O3, acid insolubles, LOI, moisture and particle size, with its specification limit, measured result and test method. It should name the lot, the sampling and test dates and the laboratory, so the results can be traced to a delivery.
How do you convert CaO to CaCO3?
Multiply CaO by 1.785 to get the calcium carbonate equivalent, because the molar mass of CaCO3 (100.09) is 1.785 times that of CaO (56.08). A CaO result of 53.2% equals about 95% CaCO3. To convert elemental calcium, multiply Ca by 2.497. The conversion assumes all the calcium is present as carbonate, so cross-check it against LOI or CO2.
What does LOI mean on a calcium carbonate CoA?
LOI, or loss on ignition, is the weight a dried sample loses when heated to about 1,000 °C. For calcium carbonate it is mostly carbon dioxide, and pure calcium carbonate loses 43.97% of its weight. Higher values can point to magnesium carbonate, clay or organic matter. LOI is not moisture, which is free water measured separately by drying.
What is the difference between a CoA, a TDS and an SDS or MSDS?
A certificate of analysis (CoA) reports test results for one lot against its specification. A technical data sheet (TDS) describes a grade with typical values and is not tied to a lot. A safety data sheet (SDS, formerly MSDS) covers hazards, handling, storage and emergency measures in a 16-section format. Buyers need all three, for different decisions.
Is a typical analysis the same as a guaranteed specification?
No. A typical analysis is a representative or average result, and it is not a promise for any one lot. A guaranteed specification is a minimum or maximum that every lot must meet by the stated method. Purchase specifications should be written in limits, with typical values kept for reference.
Should the laboratory that issues a CoA be NABL accredited?
Not always. Many lot-release certificates come from the producer's own laboratory, working under its quality system. ISO/IEC 17025 sets the competence requirements for laboratories, and in India NABL accredits laboratories to it for a stated scope of tests. For qualification trials and disputes, an independent laboratory accredited for that specific test is the stronger referee.
Does Dr. Lime provide a certificate of analysis with its calcium carbonate products?
Dr. Lime publishes specification limits on each product page, and a certificate of analysis and safety data sheet are available on request from the Dr. Lime technical team. Each product page states its limits on the basis its industry uses, such as Ca for feed, CaCO3 for fillers and CaO for glass.
