5 Hidden Specs in a Korean COA That Separate Premium Toothpaste Silica from Commodity Grade

You do not need to be a chemist to read a silica Certificate of Analysis. But you do need to know which numbers matter. When a Korean toothpaste manufacturer sends back a Chinese supplier's COA with revision requests, they are not being difficult. They are filtering for a specific kind of product — the kind that does not cause formulation failures, consumer complaints, or regulatory problems 18 months after production.

Here are the five specs on a Korean-bound COA that tell you whether you are looking at premium toothpaste-grade precipitated silica or commodity material in a nice bag.

1. Loss on Drying at 145°C — Not 105°C

What it says on the COA: "Loss on Drying (145°C, 4 h): ≤5.0%"

What most Chinese suppliers show: "Loss on Drying (105°C): ≤8.0–10.0%"

The temperature is not a typo. It is the single fastest way to distinguish USP-NF-grade silica from domestic-grade material. At 105°C, you are measuring free moisture. At 145°C, you are measuring free moisture plus bound water and surface hydroxyl groups that affect how the silica interacts with humectants (sorbitol, glycerin) and thickeners in the toothpaste base.

Why Korean buyers care: toothpaste sits on a shelf for 2–3 years. Silica with high bound-moisture release can cause tube corrosion, cap rusting, viscosity drift, and phase separation. A 145°C LOD under 5% means the silica is stable in the formulation over its full shelf life.

Red flag: If a supplier's COA lists LOD at 105°C but not 145°C, they have likely never run the USP test. Ask for a 145°C/4 h result before you commit to a container.

2. Chloride Under 0.1%

What it says on the COA: "Chloride: <0.1%"

What QB/T 2346 allows: "Chloride: ≤0.3%"

Precipitated silica is made by reacting sodium silicate with sulfuric acid. Sodium chloride is a residual byproduct. At 0.3%, chloride is harmless on paper. In a toothpaste tube, it is a different story.

Chloride accelerates corrosion of aluminum tube linings and metal dispensing components. It can produce a faint salty off-note that is invisible in a lab test but obvious to a consumer brushing their teeth. It can also interact with sodium monofluorophosphate, reducing available fluoride over time.

Korean brands — especially those selling premium sensitive and children's toothpaste — specify <0.1% chloride because they have already learned these lessons the hard way. Getting there requires extra washing stages that commodity producers skip to save cost.

3. Sulfate Under 0.5% — Listed Separately

What it says on the COA: "Sulfate: <0.5%"

What QB/T 2346 shows: "Total Salts (as Na₂SO₄ + NaCl): ≤2.0%"

This is the most deceptive line on a Chinese COA. "Total salts ≤2.0%" sounds fine until you realize it lumps sulfate and chloride together. A product could have 1.8% sulfate and 0.1% chloride and still pass — but that 1.8% sulfate will cause real problems:

• Transparency loss: In gel toothpastes, dissolved sulfate affects refractive index matching, turning a crystal-clear gel hazy
• Taste: Sodium sulfate has a bitter, medicinal note at high concentrations
• Fluoride interaction: Sulfate ions compete with fluoride in the formulation matrix
• Tube corrosion: Sulfate is even more aggressive than chloride toward unlined aluminum

Korean buyers demand sulfate as a separate line item at <0.5%. If your supplier only reports total salts, you are flying blind.

4. pH 6.0–8.0 — The Window That Protects Fluoride

What it says on the COA: "pH (5% slurry): 6.0–8.0"

What QB/T 2346 allows: 5.5–8.5 depending on grade

Toothpaste pH matters more than most formulators realize. Below pH 6.0, sodium monofluorophosphate can hydrolyze, reducing bioavailable fluoride. Above pH 8.0, the formulation can irritate sensitive oral mucosa and interact with acidic flavor compounds. The 6.0–8.0 window is the sweet spot for fluoride stability, consumer comfort, and flavor integrity.

Hitting 6.0–8.0 is not difficult for a single batch. Hitting it every batch — with a standard deviation under 0.3 — requires closed-loop pH control during precipitation and final rinse. Commodity producers often run pH anywhere from 5.5 to 8.5 and let the COA reflect whatever comes out.

5. Mercury at ≤1 ppm — The Test Most Suppliers Do Not Run

What it says on the Korean spec: "Mercury: ≤1.0 ppm"

What QB/T 2346 requires: Nothing. Mercury is not listed.

The Korean Food Additives Code mandates a mercury limit of 1 ppm for silicon dioxide. Most Chinese COAs do not include mercury at all because the domestic standard does not require it. This creates a dangerous gap: a shipment can be 100% QB/T 2346-compliant and still be rejected at Korean customs for missing mercury data.

For context, mercury enters silica through trace contamination in sodium silicate feedstock (particularly if the silicate is derived from mineral sources with cinnabar or other Hg-bearing impurities). Reputable suppliers test every batch or at a validated frequency using ICP-MS or direct mercury analysis. If your supplier cannot show you a mercury test report with a detection limit below 1 ppm, they are not ready for the Korean market.

Bonus: The Standard Line on the COA

Look at the "Standard" field on the COA. A commodity product reads: "QB/T 2346-2015". A Korean-ready product reads: "USP-NF, QB/T 2346-2015" — and sometimes adds the Korean Food Additives Code.

That one line tells you the supplier has been audited by international buyers, has adjusted their process to meet pharmacopeial specs, and is not guessing about what your customer wants.

How to Use This Checklist

Before approving any silica shipment for Korea, pull the COA and check these five lines:

1. Loss on drying at 145°C, 4 h — ≤5.0%?
2. Chloride — <0.1%?
3. Sulfate — separately listed, <0.5%?
4. pH (5% slurry) — 6.0–8.0?
5. Mercury — tested, ≤1 ppm?

If any line is missing or outside the limit, the silica is commodity grade — regardless of what the supplier's website says. Premium toothpaste silica is not defined by price or brand name. It is defined by these five numbers, and they are either on the COA or they are not.

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