DTPA acid (diethylenetriaminepentaacetic acid, CAS 67-43-6) is a synthetic aminopolycarboxylic acid and one of the most powerful chelating agents available for industrial applications. With five carboxylic acid groups and three nitrogen atoms, DTPA forms exceptionally stable complexes with a broad range of metal ions — particularly rare earth elements, actinides, and heavy metals. This makes it invaluable across nuclear processing, pharmaceutical manufacturing, textile dyeing, pulp and paper, and water treatment industries.
DTPA is closely related to DTPA Fe (iron-DTPA chelate used in agriculture), but the free acid form has distinct industrial applications that differ substantially from its agricultural chelate derivatives.
DTPA Acid: Key Properties
- CAS: 67-43-6
- Molecular formula: C₁₄H₂₃N₃O₁₀
- Molecular weight: 393.35 g/mol
- Appearance: White crystalline powder
- Purity (industrial grade): 98% min
- Solubility: Sparingly soluble in water (pH-dependent); freely soluble in dilute alkali
- pKa values: pKa1 1.8, pKa2 2.6, pKa3 4.4, pKa4 8.6, pKa5 10.5
DTPA forms 1:1 complexes with metal ions. Conditional stability constants (log K) for key metals include: Fe³⁺ (28.0), Cu²⁺ (21.4), Zn²⁺ (18.4), Mn²⁺ (15.6), and Ca²⁺ (10.7). These high stability constants mean DTPA can maintain metal chelation even in the presence of competing ligands and across a wide pH range.
Key Industrial Applications of DTPA Acid
1. Pulp and Paper Bleaching
DTPA is widely used in the pulp and paper industry as a chelating agent during peroxide bleaching of mechanical and chemical pulp. Heavy metal ions (Fe, Mn, Cu) catalyze the decomposition of hydrogen peroxide, reducing bleaching efficiency and brightening yield. Adding DTPA before the peroxide stage sequesters these metals, protecting the peroxide and achieving higher brightness. This is one of the largest volume applications of DTPA globally.
2. Nuclear Medicine and Radiopharmaceuticals
DTPA is approved by the US FDA and used in nuclear medicine as a radiopharmaceutical chelating agent. ⁹⁹ᵐTc-DTPA (technetium-99m labeled DTPA) is used for kidney function studies (renal scintigraphy), brain imaging, and lung ventilation scans. DTPA also functions as a decorporation agent — it forms stable complexes with internalized radionuclides (plutonium, americium, curium) and is approved as an antidote for internal contamination by transuranic elements (Ca-DTPA and Zn-DTPA injections).
3. Textile Dyeing and Finishing
In textile processing, trace metal ions in water or on fabric can cause uneven dyeing, color fading, and fabric degradation. DTPA sequesters these interfering metals during pre-treatment, dyeing, and peroxide bleaching stages — ensuring consistent color uptake and protecting fabric from oxidative damage. It is particularly important in cotton processing where iron contamination from water or equipment is common.
4. Detergents and Industrial Cleaning
DTPA is used as a sequestrant in industrial and institutional cleaning formulations to prevent scale formation and inactivate metal catalysts. In phosphate-free detergent formulations, DTPA replaces STPP (sodium tripolyphosphate) as a water softener and scale inhibitor. It is also used in CIP (clean-in-place) systems for food and beverage processing equipment to remove mineral deposits.
5. Photography and Imaging
DTPA and its salts are used in photographic bleach-fix (blix) solutions to chelate iron(III) as Fe-DTPA, which serves as the oxidizing agent for silver halide removal during film and paper processing. Fe(III)-DTPA offers better biodegradability than ferricyanide-based bleaches and is preferred in modern photographic processing chemistry.
DTPA Acid vs EDTA: How Do They Compare?
| Property | DTPA Acid | EDTA Acid |
|---|---|---|
| CAS | 67-43-6 | 60-00-4 |
| MW (g/mol) | 393.35 | 292.24 |
| Chelating sites | 8 (5 carboxyl + 3 N) | 6 (4 carboxyl + 2 N) |
| Log K (Fe³⁺) | 28.0 | 25.1 |
| Log K (Cu²⁺) | 21.4 | 18.8 |
| pH stability range | Wider (2–12) | Good (4–10) |
| Cost | Higher | Lower |
| Best for | Strong chelation, nuclear, pharma | General chelation, agriculture |
DTPA forms stronger metal complexes than EDTA acid due to its additional chelating sites. For applications requiring maximum metal binding strength — particularly with rare earth elements, actinides, or in competitive metal environments — DTPA is the preferred choice despite its higher cost.
Packaging and Supply
Hainan Unifarm Chemical supplies industrial-grade DTPA acid (98% min) in 25 kg sealed polyethylene bags. FCL and LCL shipments are available to all major ports. We provide COA, MSDS, and all required export documentation. For agricultural chelate applications, we also supply DTPA Fe chelated iron for use as a micronutrient fertilizer.