Deionized water — water with dissolved minerals and salts removed — is the workhorse of laboratory water purification. DI systems use ion-exchange resins to swap dissolved cations and anions for hydrogen and hydroxyl ions, producing water with resistivity from 1 to 18.2 MΩ·cm depending on configuration.
How DI Water Systems Work
Ion-exchange deionization uses two types of resin:
- Cation resin — removes positively charged ions (calcium, magnesium, sodium, potassium) and replaces them with hydrogen (H⁺)
- Anion resin — removes negatively charged ions (chloride, sulfate, bicarbonate, silica) and replaces them with hydroxyl (OH⁻)
- Mixed-bed resin — combines both resins in a single cartridge for higher purity in a single pass
The result: H⁺ + OH⁻ = H₂O. Pure water.
DI System Types
Cartridge DI Systems
Compact, bench-top units ideal for labs consuming 10–50 liters per day:
- Plug-and-play — connects to any standard faucet or water line
- Disposable or refillable cartridges
- Built-in resistivity meters for real-time water quality monitoring
- Low maintenance — swap the cartridge when quality drops
Multi-Bed / Dual-Bed DI Systems
Higher-capacity systems for labs that need 50–500+ liters per day:
- Separate cation and anion tanks for maximum capacity
- Service-deionization options — we swap the tanks, you focus on science
- Regenerable or single-use cartridges depending on your preference
RO/DI Combination Systems
The gold standard for most labs. Reverse osmosis removes 95% of contaminants first, then DI polishing takes water to 18.2 MΩ·cm:
- DI cartridges last 5–10x longer because RO does the heavy lifting
- Produces ASTM Type I water from any municipal water source
- Ideal for HPLC, ICP-MS, and trace analysis
- Lower long-term cost per liter than DI alone
DI Water Quality Grades
| Grade | Resistivity | Applications |
|---|---|---|
| Type I (Ultrapure) | 18.2 MΩ·cm | HPLC mobile phase, ICP-MS, cell culture, PCR |
| Type II (Analytical) | 1–15 MΩ·cm | Buffer prep, reagent dilution, spectrophotometry |
| Type III (Primary) | 0.05–1 MΩ·cm | Rinsing, autoclaves, feed water for Type I systems |
DI vs. Distilled Water — Which Do You Need?
| Factor | DI Water | Distilled Water |
|---|---|---|
| Ion removal | Excellent (18.2 MΩ·cm) | Good (1–5 MΩ·cm) |
| Organic removal | Limited (needs carbon pre-filter) | Excellent (boiling removes organics) |
| Energy cost | Low (no heating) | High (requires boiling) |
| Output rate | High (on demand) | Slow (1–12 L/hr) |
| Best for | High-volume, ion-sensitive work | Low-volume, organic-sensitive work |
Related Water Purification Pages
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