| HS Code | 485930 |
| Productname | EDTA 4Na |
| Chemicalname | Tetrasodium ethylenediaminetetraacetate |
| Synonyms | EDTA tetrasodium salt; tetrasodium edetate; sodium edetate; tetrasodium EDTA |
| Casnumber | 64-02-8 |
| Einecenumber | 200-573-9 |
| Molecularformula | C10H12N2Na4O8 |
| Molecularweight | 380.17 g/mol |
| Appearance | White crystalline powder |
| Color | White |
| Odor | Odorless |
| Form | Powder, granules, or aqueous solution |
| Ph | 11.0-11.5 (1% aqueous solution) |
| Watersolubility | Highly soluble in water |
| Chelatingproperty | Strong chelating agent; forms stable complexes with metal ions such as calcium, magnesium, and iron |
| Decompositiontemperature | >300 °C |
| Assay | ≥99% |
As an accredited EDTA 4Na factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | EDTA 4Na is supplied in 25 kg polyethylene-lined paper bags, securely sealed and labeled for safe chemical handling. |
| Container Loading (20′ FCL) | EDTA 4Na in 25 kg bags, palletized and securely loaded into a 20′ FCL container for safe export shipment. |
| Shipping | EDTA 4Na (tetrasodium EDTA) is generally not regulated as dangerous goods for transport. Ship in sealed, labeled containers, protected from moisture, heat, and incompatible acids or oxidizers. No special UN hazard class or placard is normally required. Always follow the SDS, carrier requirements, and local regulations. |
| Storage | Store EDTA 4Na in a cool, dry, well-ventilated area away from acids, oxidizers, and moisture. Keep containers tightly closed, labeled, and upright. Protect from direct sunlight and physical damage. Avoid dust generation and incompatible materials. Maintain segregation from strong acids to prevent heat or gas release. Use appropriate secondary containment where required. Store at ambient temperature, preferably between 15–25°C. |
| Shelf Life | EDTA 4Na has a long shelf life, typically 2–5 years if kept dry, sealed, cool, and away from moisture. |
Open recirculating cooling water systems operating at pH 7.8–8.8 with makeup water hardness between 150–450 mg/L as CaCO₃ develop calcium carbonate scale on condenser tube surfaces when the Langelier Saturation Index rises above +1.2 at bulk water temperatures above 40 °C. Tetrasodium EDTA is injected into the return header or makeup-water line at continuous residuals of 5–15 mg/L as the active chelant to keep calcium, magnesium, iron, and copper in solution and to reduce crystal growth at metal interfaces. Field observations from open-evaporative systems show that a residual below 4 mg/L allows measurable calcite deposition within 14 days when makeup iron is above 0.3 mg/L, while a residual above 25 mg/L increases chelant demand without proportional scale inhibition. The additive is not a dispersant for deposited scale; it is a threshold inhibitor and must be applied before deposition.
Compliance anchors are 21 CFR 173.310 for steam boiler water additives, NSF/ANSI/CAN 60 for potable-grade scale inhibitors, ASTM D1126-17 for total hardness, and ASTM D1068-15 for total iron. In a chelant-based steam boiler program, the product is fed at 20–80 mg/L as delivered product to the deaerator storage section or feedwater line; free chelant residual is titrated with a standard calcium chloride solution using a metallochromic indicator and maintained at 0.5–1.5 mg/L as EDTA. Overfeed above 5 mg/L free chelant is avoided because free ethylenediaminetetraacetic acid can sequester iron from magnetite passivation layers and create localized corrosion attack along heat-affected zones. The feed solution is prepared from a 20–40 wt% concentrate diluted in demineralized water at 20–30 °C; storage below 10 °C increases viscosity and has been associated with diaphragm pump fatigue in induced-draft cooling tower installations.
The downstream production process uses positive-displacement diaphragm metering pumps fitted with PVDF wetted heads and rated at 3–5 bar discharge, followed by a 12–18 element static mixer before the injection quill. In cooling towers, the injection point is placed in the return loop upstream of the chemical injection quill to avoid localized concentration at the basin wall; in steam boilers, the chelant is fed downstream of the deaerator to avoid reacting with oxygen scavenger feed lines. Terminal finished product types include liquid scale-inhibitor/chelant blends, single-drum cooling water treatments, and chelant boiler all-in-one liquid products.
Polyphosphate replacements in liquid laundry detergents require a strong chelant that remains stable at pH 8.5–10.5 and does not hydrolyze at the 40–55 °C premix temperature. Tetrasodium EDTA is used at 0.2–1.5 wt% as the 100% active chelant in heavy-duty liquid laundry detergents, at 0.5–2.0 wt% in automatic dishwashing gels, and at 0.1–0.5 wt% in hard-surface cleaners. The additive functions by sequestering residual hardness from process water before it can form calcium carbonate/anionic-surfactant precipitates in the formulation. Without this step, process water above 150 mg/L as CaCO₃ can produce a visible haze in the batch within 24 h at 25 °C; residual hardness is checked by EDTA titration before surfactant addition.
The regulatory file for European product placement is driven by Regulation (EC) No 648/2004 on detergents, supported by REACH registration for the imported salt. Finished pH is checked according to ISO 4316:1977, and the chelant level is verified by ion chromatography against an EDTA standard in the raw material QC release. During compounding, the order of addition is fixed: tetrasodium EDTA is added to the water phase at 40–55 °C before enzymes and before pH adjustment; it is mixed with a high-shear rotor-stator at 1,500–3,000 rpm until the solution is clear. Sodium hydroxide or potassium hydroxide is then metered to pH 8.5–10.5. Adding EDTA after nonionic surfactant gel phases or after enzyme slurries creates localized ionic-strength gradients that can reduce enzyme activity and produce stringy viscosity defects. Production-scale liquid detergent plants using batch mixers of 5,000–20,000 L observe batch-to-batch viscosity variation below ±10% when the chelant is dissolved before polymer thickener addition.
Terminal finished product types include concentrated liquid laundry detergent, automatic dishwashing gel, and acid-based hard-surface cleaner. The practical boundary in cationic-rich formulations is recognized: direct contact between concentrated tetrasodium EDTA and cationic surfactant streams precipitates a dense complex; separate dosing lines with water flushing are required. Formulations containing hypochlorite bleach must not use tetrasodium EDTA as the sole chelant because oxidative degradation consumes the chelant and generates low-molecular-weight nitrogen compounds.
Alkaline cotton scouring at 90–98 °C with 20–40 g/L sodium hydroxide extracts pectin and wax but also releases calcium, magnesium, and iron ions from the cotton fiber into the process bath. Without chelation these ions react with sodium carbonate or sodium silicate and deposit as hard rings on fabric, rollers, and dyeing machines. Tetrasodium EDTA is dosed at 1–3 g/L in the scouring bath and at 0.5–2.0 g/L in the subsequent hydrogen peroxide bleaching bath to suppress fiber-tenderizing catalytic decomposition of peroxide by iron and copper. Hardness consumption is first in the reaction sequence; therefore the higher end of the range is selected when incoming water hardness exceeds 100 mg/L as CaCO₃.
Compliance is evaluated against OEKO-TEX Standard 100 residual-metal limits and ZDHC Manufacturing Restricted Substances List v3.1 for textile chemical formulations; residual hydrogen peroxide is measured by AATCC TM 102. In a continuous open-width bleaching range, the chemical is mixed into the saturator with stabilizer and NaOH at pH 10.5–11.5; fabric runs at 85–95 °C with a steaming dwell of 20–40 min. Equipment such as a Benninger continuous open-width range with a 20-ton padder applies the liquor to wovens; for knits, a soft-flow jet with circulation rates of 3–5 m³/min per chamber provides homogenization. The additive is combined with sodium silicate only after dilution; direct mixing of concentrated EDTA 4Na with silicate at pH above 12.5 can precipitate calcium silicate seeds already present in the silicate drum.
Terminal product types are fully scoured and bleached woven cotton, knitted cotton, and cotton blend goods prepared for dyeing or printing. The process boundary in hard water is explicit: when incoming hardness exceeds 100 mg/L as CaCO₃, the scouring dose is raised toward the upper range because hardness consumes the chelant before fiber-extracted metals can be complexed. Wool and other protein fibers are excluded from EDTA-containing oxidative treatments because the chelant can sequester mordant metals and alter dyestuff shade reproducibility.
In rinse-off and leave-on personal care formulations, tetrasodium EDTA is used to control the pro-oxidant effect of trace iron and copper introduced by tap water and botanical extracts. The addition ratio in finished products is commonly 0.05–0.2 wt% for leave-on emulsions and 0.1–0.5 wt% for rinse-off shampoos and body washes as 100% active ingredient. Above these ranges, the chelant does not improve oxidative stability further and may reduce the rheological benefits of cationic conditioning polymers by forming coacervates. The CIR Expert Panel safety assessment gives a frame for maximum use; published data for this specific configuration is limited at additive concentrations above 0.5 wt%, so each new formulation is bench-screened.
Regulatory compliance is anchored to Regulation (EC) No 1223/2009 for cosmetic products and ISO 22716:2007 for manufacturing GMP. In production, tetrasodium EDTA is dissolved in the water phase at 40–60 °C before the addition of polymers and before pH adjustment. A vacuum emulsifier operating at −0.08 MPa internal pressure with anchor stirring at 30–60 rpm and a rotor-stator homogenizer at 2,500–3,500 rpm is standard for oil-in-water creams. The chelant is added before sodium hydroxide neutralization of carbomer to prevent local pH shock that could destabilize the dispersion. In batch records, the dissolution time is recorded until visual clarity is achieved; residual undissolved chelant particles later appear as white specks in the cooled cream.
Terminal finished product types include anti-oxidant serums, body washes, daily-use shampoos, and moisturizing creams. The operational boundary in cationic formulations is clear: when cationic guar or polyquaternium-10 is present at a level above 0.2 wt%, the anionic chelant may induce coacervation, observed as a cloudy phase or stringy precipitate. Bench screening should include storage at 45 °C for 4 weeks and freeze-thaw cycling at −10 °C to 25 °C for three cycles.
Mechanical and chemi-thermomechanical pulp mills run alkaline hydrogen peroxide stages at pH 10.5–11.5 and 80–90 °C where ferric and manganese ions catalyze peroxide decomposition and reduce brightness gain. Tetrasodium EDTA is applied in a chelation stage before bleaching at 0.2–0.6 wt% on oven-dry pulp; this dosage removes transition metals from the pulp-water suspension and gives a brightness preservation benefit in the subsequent peroxide stage. The peroxide stage itself uses 2–5 wt% hydrogen peroxide and 2–4 wt% sodium hydroxide on oven-dry pulp. In mill-scale observations, manganese concentrations above 10 mg/kg in unbleached pulp can reduce final brightness by 2–4 points unless the Q-stage chelant dose is raised within the specified window.
Brightness output is measured by ISO 2470-2; process water hardness and metal content are checked before the Q-stage to adjust chelant dose. Downstream production equipment consists of a medium-consistency chelation tower at 10–14% consistency, pH 4.5–5.5, temperature 70–80 °C, and retention time 30–60 min. After chelation, the pulp is sent to a double-wire press to reach 30–35% consistency, then diluted and transferred to a high-consistency peroxide bleach tower with an upstream steam mixer. Overdosing above 1.0 wt% on oven-dry pulp can impart a yellow tint in some kraft pulps if washing after bleaching is insufficient, because the remaining iron-EDTA complex remains in the sheet. The chelation stage must remain acidic; at pH above 5.5, the EDTA-metal complexes partially dissociate and iron is redeposited onto fines, causing dark speck formation in the finished board.
Terminal finished product types are bleached softwood and hardwood CTMP and TMP for tissue, folding boxboard, and coated basepaper. The additive is not a replacement for silicate stabilization in all grades; in tissue lines with closed water loops, the chelant can accumulate and must be purged by fresh water replacement to prevent brightness loss from metal-chelate carryover.
Downhole mineral scale removal in carbonate and sulfate-prone wells uses tetrasodium EDTA as a non-acid chelant dissolver at 5–15 wt% active in workover or stimulation fluids. The additive dissolves calcium carbonate and calcium sulfate at bottomhole temperatures between 60–120 °C by forming stable water-soluble calcium chelates; unlike hydrochloric acid, it does not produce rapid CO₂ liberation or severe tubing corrosion. Evaluation for a candidate well is performed by NACE TM0374 scale dissolver screening protocols before field deployment. The dissolution rate is strongly temperature-dependent: at bottomhole temperatures below 60 °C, carbonate dissolution may require extended shut-in times above 24 h, increasing operational cost.
Compliance is governed by NACE TM0374 for scale dissolver efficacy and by operator-specific well-return fluid disposal limits; the material is not acidizing-grade and is not a replacement for high-pH finishing fluids without compatibility testing. Field process begins by diluting the 20–40 wt% concentrate to the designed concentration in filtered produced water or 2% KCl brine. The fluid is then bullheaded through coiled tubing at 0.5–1.0 bbl/min or spotted across the perforated interval. Shut-in time is 6–24 h; after flowback, the spent chelant is analyzed for residual calcium to determine dissolution completion. For barium sulfate, published data for this specific configuration is limited; laboratory screening is required because dissolution rates are significantly lower than for calcium carbonate.
Terminal finished product types are liquid scale dissolver concentrates, chelant pills for completion operations, and brine additives for iron control during workover. The main operational boundary is brine compatibility: in high-density calcium chloride or calcium bromide completion brines, tetrasodium EDTA may precipitate calcium chelate solids; it must not be added as a concentrate directly to calcium-based brines without forced mixing and jar testing. Fluid returns are checked for pH and residual chelant before discharge because the high chemical oxygen demand of spent chelant can exceed surface water permit limits.
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Tetrasodium ethylenediaminetetraacetate (EDTA 4Na, CAS 64-02-8, C10H12N2Na4O8·xH2O, anhydrous molecular weight 380.17 g/mol) is supplied as a white crystalline powder, fine granular, and low-dust granular forms. The product is manufactured in technical, low-ammonia, photographic/electronics, and food/pharmaceutical grades. A 1% w/w aqueous solution of a standard industrial grade has a pH of 10.5–11.5 at 25 °C, and the calcium chelation value ranges from 220 to 260 mg CaCO3/g depending on hydration state and assay.
Typical commercial forms include anhydrous powder with assay 99.0–100.5% on the anhydrous basis, low-dust granules screened to 95% between 20 and 80 mesh, low-ammonia grade with ammonia below 0.01%, and food/pharmaceutical grade meeting the current FCC or USP-NF monograph. The tetrasodium form is selected where concentrated alkaline liquid stability, high cold-water solubility, and minimal acidification of the end formulation are required.
Ethylenediaminetetraacetate acts as a hexadentate chelant that forms 1:1 molar complexes with divalent and trivalent metal ions. Published conditional stability constants at 25 °C and 0.1 M ionic strength are approximately log K 10.7 for Ca2+, 25.1 for Fe3+, and 18.8 for Cu2+. The selectivity order Fe3+ > Cu2+ > Zn2+ > Fe2+ > Ca2+ > Mg2+ is pH-dependent. In alkaline process streams, carbonate and hydroxide ligands compete with EDTA, but the thermodynamic and kinetic preference for transition metals remains sufficient to suppress precipitation at practical addition levels.
In boiler feed water and industrial water treatment, the dose is calculated from stoichiometric calcium hardness. At a chelation value of 220 mg CaCO3/g, 1 m3 of water containing 100 mg/L CaCO3 requires approximately 0.45 g of EDTA 4Na. The solid is typically pre-dissolved in softened water and metered into the feed line with a diaphragm pump to avoid localized pH depression and precipitation.
For mixed-metal systems, the practical dose cannot be derived from calcium hardness alone. Iron and copper consume chelation capacity preferentially, and the total chelant demand is best determined by jar testing against inductively coupled plasma analysis of residual soluble metal. This analytical approach follows the digestion and detection principles of ISO 11885 for dissolved metal fractions in process water.
In dairy and beverage clean-in-place skids, tetrasodium EDTA is combined with sodium hydroxide at 1.0–2.0 wt% NaOH and 0.2–0.5 wt% EDTA 4Na at 70–80 °C for 15–30 min to remove calcium phosphate and casein films from stainless steel plate heat exchangers and spray-ball circuits. Production-scale observations indicate that low-dust granular EDTA 4Na added ahead of the recirculating eductor prevents the blinding of 150 µm bag filters that can occur when standard powder is dumped into a surfactant-rich path. The tetrasodium salt contributes less to acid-neutralizing capacity loss than EDTA acid, preserving alkalinity for saponification of fatty soils.
An operational limitation in closed loops is the slow attack of concentrated alkaline EDTA solutions on aluminum fittings above 60 °C; aluminum components should be isolated or the exposure time minimized. The product also has no significant foam control or surface-wetting properties and must be paired with a surfactant package rather than used alone for fatty soil removal.
When the same clean-in-place line handles protein-rich fouling, EDTA 4Na is often introduced after the initial caustic circulation and before the acid rinse. This sequence avoids unnecessary loss of chelation capacity to bulk calcium carbonate scale and directs the product toward colloidal calcium phosphate and iron-bound protein films.
The relevant industrial specifications are assay, chelation value, pH, moisture, insoluble matter, chloride, sulfate, and trace heavy metals. For food/pharmaceutical grade, release limits are aligned with the FCC monograph or USP-NF sodium edetate monograph. Analytical verification typically employs complexometric titration for assay and chelation value, ICP-MS or ICP-OES per ISO 11885 for heavy metals, and Karl Fischer titration for moisture.
| Parameter | Technical powder | Low-dust granular | Food/pharmaceutical grade |
|---|---|---|---|
| Assay on anhydrous basis | 99.0–100.5% | 99.0–100.5% | 99.0–100.5% |
| pH, 1% solution, 25 °C | 10.5–11.5 | 10.5–11.5 | 10.5–11.5 |
| Calcium chelation value | 220–263 mg CaCO3/g | 220–240 mg CaCO3/g | 220–263 mg CaCO3/g |
| Moisture | ≤0.5% | ≤0.5% | ≤0.5% |
| Water insoluble matter | ≤0.005% | ≤0.005% | ≤0.005% |
| Lead | ≤2 mg/kg | ≤2 mg/kg | ≤1 mg/kg |
| Arsenic | ≤1 mg/kg | ≤1 mg/kg | ≤1 mg/kg |
| Particle size | 95% through 100 mesh | 95% between 20 and 80 mesh | 95% through 100 mesh |
| Bulk density | 0.55–0.75 g/cm3 | 0.70–0.85 g/cm3 | 0.55–0.75 g/cm3 |
Hygroscopicity is a storage constraint. At relative humidity above 60%, anhydrous powder can absorb moisture rapidly and form lumps; low-dust granular grades are less hygroscopic but should be kept in closed silos fitted with desiccant vents. The powder is not classified as readily biodegradable under OECD 301B; documented mineralization in standard activated sludge within 28 days is often below 20%. Discharge to surface water should follow local permits and, where required, oxidative pre-treatment.
The product should not be stored in contact with strong oxidizing agents, particularly sodium hypochlorite solutions, because EDTA slowly degrades with loss of chelation value. Closed storage containers should be grounded during pneumatic transfer where fine powder fractions are present, and the material should be pre-dried at 60–80 °C if exposed above the recommended humidity threshold before precision gravimetric dosing.
Disodium EDTA is often used at neutral or mildly acidic pH, but in built alkaline detergent systems its solubility and phase stability are lower than those of the tetrasodium salt. EDTA 4Na adds four sodium counterions per molecule, raising electrolyte content but keeping the pH above 10; this supports nonionic and anionic surfactant systems where free acid or disodium additions would force a pH correction with additional alkali. In concentrated liquids containing sodium carbonate, sodium silicate, or citrate, the tetrasodium form reduces the risk of gelation and phase separation during high-shear mixing at low temperature.
Differences from other aminocarboxylates are application-specific. DTPA 5Na has higher denticity and stronger Fe3+ and Ba2+ binding, but its higher molecular weight and lower calcium chelation per gram can require larger doses for simple hardness control. NTA 3Na has higher calcium chelation per unit mass, but its regulatory status restricts use in many detergent markets. GLDA and MGDA offer improved biodegradability but may require higher dosing for high-hardness process water or specific temperature conditions.
| Property | EDTA acid | EDTA 2Na | EDTA 4Na | DTPA 5Na | NTA 3Na |
|---|---|---|---|---|---|
| CAS | 60-00-4 | 6381-92-6 | 64-02-8 | 140-01-2 | 5064-31-3 |
| Molecular weight | 292.24 g/mol | 372.24 g/mol | 380.17 g/mol | 503.25 g/mol | 257.08 g/mol |
| pH, 1% solution, 25 °C | 2.5–3.0 | 4.3–4.7 | 10.5–11.5 | 11.0–12.0 | 10.5–11.0 |
| Solubility at 25 °C | 0.05 g/100 mL | 10 g/100 mL | 100 g/100 mL | 45 g/100 mL | 50 g/100 mL |
| Calcium chelation value | 342 mg CaCO3/g | 269 mg CaCO3/g | 263 mg CaCO3/g | 199 mg CaCO3/g | 389 mg CaCO3/g |
| Primary limitation | very low solubility | acidic pH and lower solubility | not readily biodegradable | higher molecular weight dose | regulatory restrictions |
Values are rounded from manufacturer technical bulletins and reference texts; hydration state changes molecular weight and chelation capacity. The effective binding capacity is pH- and ionic-strength-dependent and must be verified by jar tests and water analysis for each concentrated builder system.
In high-shear liquid detergent skids, the tetrasodium salt is normally added to the water phase before surfactants. A recirculating eductor with a venturi at 1500–3000 L/min and a side-entry agitator in a 10,000 L batch tank provides sufficient dispersion. Production logs show that reverse addition, where EDTA 4Na is dumped after concentrated nonionic surfactant, can create localized gel particles that blind 150 µm in-line filters and require batch rework.
In continuous cotton bleaching ranges, residual iron and manganese ions catalyze hydrogen peroxide decomposition, causing pinhole damage and reduced whiteness. A dosage of 0.2–0.5 g/L EDTA 4Na in the alkaline peroxide liquor stabilizes the bath by sequestering Fe3+ and Mn2+. Production-scale pad-steam ranges running at 90–95 °C for 20–30 min commonly maintain peroxide residuals above 80% when EDTA is present in the saturator liquor, whereas uncontrolled metal contamination can consume 30–50% of the peroxide before the fabric exits the steamer. This behavior is reported in textile auxiliary technical literature and is consistent with the known transition-metal catalysis of hydrogen peroxide decomposition.
The product is pre-dissolved in the chemical mixing tank before addition to the saturator to avoid local supersaturation and fabric spotting. In jig and jet dyeing machines, tetrasodium EDTA is used at 0.1–0.3 g/L to complex hardness ions and prevent the formation of metal-dye complexes that cause dull shade and unlevel dyeing. The tetrasodium form is preferred in peroxide bleaching because it does not lower the bath pH as much as disodium EDTA and supplies sodium ions that help maintain alkali reserves.
However, EDTA 4Na does not replace sodium silicate as a corrosion-inhibiting and peroxide-protective colloid in all formulations. Silicate-free systems require a separate stabilizer or a blended chelant/stabilizer package. Published data for very low-silicate peroxide bleaching at high metal contamination is limited; the most reliable control strategy remains removing metal-laden fibers from the system, avoiding iron piping, and using a combination of silicate and chelant rather than chelant alone.
In produced-water squeeze applications, tetrasodium EDTA is injected as a neutralized or mildly alkaline solution to bind Ca2+ and Fe2+, but its barium selectivity is lower than DTPA 5Na. For barium sulfate scale, DTPA is generally preferred because its published Ba2+ stability constant is approximately log K 8.6 to 8.8, compared with 7.8 for EDTA. Field data from oilfield service bulletins indicate that EDTA 4Na is effective for calcium carbonate and iron sulfide dissolution at near-neutral to mildly alkaline pH, but barite dissolution is slow and highly temperature-dependent.
In acidizing operations, EDTA 4Na is not added directly to concentrated hydrochloric acid because the acid converts it to the acid form with reduced solubility. Iron-control packages in acid systems commonly use acid-compatible chelants or blends of citric acid, acetic acid, and EDTA acid. The tetrasodium salt is instead applied in pre-flushes, post-flushes, or scale-squeeze treatments where the pH is deliberately held above 7 to prevent acid gas evolution and formation damage.
For high-salinity brines above 100 g/L total dissolved solids, published data for EDTA 4Na loading limits is limited; competitive complexation with sodium and magnesium can reduce effective calcium binding, and squeeze design should be based on core-flood testing rather than bottle tests alone.
For food-processing equipment and pharmaceutical contact applications, only grades meeting the relevant FCC or USP-NF monograph are used. The USP-NF sodium edetate monograph typically employs complexometric titration with 0.05 M zinc sulfate after addition of ammonium hydroxide buffer and a suitable indicator such as Eriochrome black T. Heavy metals are controlled by color comparison or by ICP-MS; modern laboratories often apply ISO 17294-2 for trace element quantification in pharmaceutical-grade material.
Regulatory status differs by jurisdiction. FDA 21 CFR 172.120 and 21 CFR 172.135 list calcium disodium EDTA and disodium EDTA as direct food additives; tetrasodium EDTA may be used as a processing aid or in boiler water additives under local approvals, but it is not accepted as a direct food additive in every market. Formulators must confirm the intended use against the current regional food-additive regulation and not rely on an industrial-grade certificate of analysis for food-contact or pharmaceutical cleaning.
