Tetrasodium Glutamate Diacetate (GLDA): Properties & Uses

Tetrasodium Glutamate Diacetate (GLDA): Structure, Properties, and Applications

1. Introduction

Chelating agents (complexing agents) are widely used in industry, medicine, and household products to bind metal ions. For decades, salts of ethylenediaminetetraacetic acid (EDTA) were the most common choice. However, it has become clear that EDTA degrades slowly in the environment, posing a risk of accumulation in aquatic ecosystems. This has driven the search for "green" chelating agents with higher biodegradability and a better environmental profile. One such compound is tetrasodium glutamate diacetate (GLDA).

2. Chemical Structure and Nomenclature

Tetrasodium glutamate diacetate is the tetrasodium salt of a glutamic acid derivative in which the nitrogen atom carries two additional acetic acid (acetate) groups. The structure can be described as L-Glutamic acid, N,N-diacetic acid, tetrasodium salt:

• Core skeleton: L-glutamic acid (a naturally occurring amino acid).

• Side chains: Two acetic acid groups attached to the amino group of glutamate (diacetate groups).

• Salts: In solution, all carboxyl groups – both those native to glutamic acid and the additional acetate fragments – are neutralised by sodium cations, forming the tetrasodium salt.

The empirical formula is C₉H₉NNa₄O₈, with a molecular weight of approximately 351.13 g/mol.

CAS number: 51981-21-6.

EC number: 257-573-7.

3. Physicochemical Properties

• Solubility: GLDA is highly soluble in water across a wide pH range, including at low pH values where many other chelates are poorly soluble.

• pH and stability: GLDA remains stable between pH 2 and 13 at room temperature. It retains its chelating ability over a broad pH range.

• Biodegradation: GLDA is classified as readily biodegradable according to OECD standards, with over 60% degradation within 28 days (OECD 301D). In some tests, degradation exceeds 80% within 28 days. About 50% of the carbon in GLDA is plant-based, and it is free from genetically modified raw materials.

• Chelating ability: GLDA forms stable complexes with divalent and trivalent metal ions, including Ca²⁺, Mg²⁺, and Fe³⁺, making it effective for binding hardness ions and heavy metals. It has a calcium chelation capacity of 186 mg/g – 18% higher than EDTA.

• Appearance: Typically supplied as a clear, colourless to yellowish liquid (40–47% aqueous solution) with a slight ammonia-like odour.

• Thermal stability: GLDA is thermally stable at 170°C for 6 hours without decomposition.

4. Mechanism of Action

Chelation occurs when functional groups (carboxylate groups and nitrogen centres) form coordinate bonds with metal cations. In the case of GLDA, the carboxyl groups of glutamic acid and the additional acetate groups "capture" the metal ion, forming a stable complex that prevents:

• Premature hydrolytic degradation of metal-sensitive solutions.

• Precipitation of insoluble salts (carbonates, sulphates, etc.).

• Unwanted redox reactions catalysed by metal ions (rust formation, fat rancidity, etc.).

• Metal-catalysed degradation and oxidation in formulated products.

5. Applications

• Cosmetics and personal care: GLDA is used in creams, lotions, shampoos, conditioners, makeup, sunscreens, and wipes to bind metal ions, enhancing product stability, efficacy, and appearance. It improves foaming and cleaning performance in shampoos and body washes, and is gentle on the skin.

• Household and industrial cleaning: Widely used in liquid detergents, dishwashing formulations, and hard surface cleaners. It improves detergency at high water hardness, boosts stain removal, and acts as a scale inhibitor at high pH. GLDA is an effective alternative to phosphates and traditional chelating agents (EDTA, NTA).

• Water treatment and industrial systems: GLDA binds hardness ions (Ca²⁺, Mg²⁺) and heavy metals, preventing scale formation (calcium/magnesium carbonates and sulphates) and corrosion in reverse osmosis systems, cooling water circuits, and boilers.

• Textile and leather industries: Used to chelate iron and other metal ions that affect dyeing uniformity or leather tanning quality, improving colour evenness and preventing defects.

• Environmental remediation: GLDA is effective for removing heavy metals (e.g., cadmium, copper, lead) from contaminated soils and sediments, offering a biodegradable alternative to EDTA for phytoremediation applications.

• Agriculture and animal feed: Studied as a feed additive to improve trace mineral bioavailability in livestock.

• Oil and gas: GLDA has been shown to be a robust chelator for calcium and iron ions under highly acidic conditions (pH 1–3) typical of oil and gas production.

6. Environmental Profile

GLDA offers significant environmental advantages over traditional chelating agents:

• Readily biodegradable: over 60% degradation within 28 days (OECD 301D); some studies report over 80% degradation.

• Ultimately biodegradable: converted completely to CO₂ and H₂O.

• Low ecotoxicity: Exhibits low toxicity to aquatic organisms and does not accumulate in food chains.

• Renewable source: Derived from natural amino acids and plant-based carbon (approximately 50% plant-derived carbon).

• EPA recognition: GLDA meets the U.S. EPA Design for the Environment program requirements and is listed on CleanGredients.

• Ecolabel compliance: Approved for COSMOS, Ecocert, and EU Ecolabel certification.

7. Safety and Toxicology

• Acute toxicity: Low acute oral and dermal toxicity.

• Skin and eye irritation: At typical use concentrations (cosmetics, household products), GLDA rarely causes irritation.

• Repeat-dose toxicity: Very slight nephrotoxicity was noted at very high doses (1000 mg/kg bw/day) in animal studies.

• Regulatory status: GLDA does not require dangerous goods labelling and is recognised as safe by numerous international institutions. The Cosmetic Ingredient Review (CIR) Expert Panel has confirmed its safety in cosmetics.

• Precautions: As with all chemicals, standard industrial hygiene practices (gloves, safety goggles, adequate ventilation) are recommended when handling concentrated material.

8. Advantages Over Traditional Chelating Agents

Compared to traditional chelating agents such as EDTA, GLDA offers several key advantages:

• Biodegradability: GLDA is readily biodegradable (over 60% in 28 days), whereas EDTA is poorly biodegradable (less than 10% in 28 days).

• Solubility at low pH: GLDA has high solubility across a wide pH range, including low pH values, while EDTA has very low solubility at low pH.

• Metal chelation: GLDA is effective for Ca²⁺, Mg²⁺, Fe³⁺, and heavy metals, with 18% higher calcium chelation capacity than EDTA.

• Environmental impact: GLDA has low ecotoxicity and contains plant-based carbon, whereas EDTA persists in aquatic environments.

• Regulatory status: GLDA is listed with EPA DfE and CleanGredients and approved for EU Ecolabel, COSMOS, and Ecocert, while EDTA is subject to increasing restrictions.

9. Storage and Handling

• GLDA is typically supplied as a 40–47% aqueous solution.

• Store in tightly sealed containers at room temperature, in a dry place away from direct sunlight.

• Avoid contact with strong oxidising agents.

• Use standard personal protective equipment (gloves, safety goggles) when handling concentrated solutions.

• Shelf life: typically 12–24 months under recommended storage conditions.

10. Conclusion

Tetrasodium glutamate diacetate (GLDA) is a next-generation chelating agent that successfully competes with traditional complexing agents such as EDTA and NTA. Its key advantages include:

• High metal-binding efficiency across a broad pH range, including under highly acidic conditions.

• Superior environmental safety – readily biodegradable, low ecotoxicity, and derived from renewable plant sources.

• Wide applicability – from cosmetics and detergents to industrial water treatment, textile processing, oil and gas, and environmental remediation.

• Good safety profile – low irritation potential and favourable toxicology.

The transition to GLDA as a replacement for less sustainable chelating agents helps reduce anthropogenic environmental impact and enables the development of greener, more sustainable products that meet modern ecological standards.