🧪 TOC—Total Organic Carbon
Determination of total organic carbon (TOC) in water by catalytic combustion at 680°C or wet oxidation with CO₂ detection in NDIR detector.
Overview
Total Organic Carbon (TOC) is a sum parameter describing the content of organic compounds in water, expressed as the mass of organic carbon in mg C/L. It is a universal indicator of organic pollution—it includes all dissolved and suspended organic compounds, regardless of their susceptibility to biological or chemical oxidation.
The PN-EN ISO 8245 standard provides guidelines for determining TOC and dissolved organic carbon (DOC) in various water types: drinking, groundwater, surface, marine, and wastewater. Two main methods are used: catalytic combustion at high temperature (680°C) with NDIR detection and wet oxidation (persulfate + UV) with NDIR detection.
Permissible TOC concentration in drinking water: without anomaly (Journal of Laws 2017 item 2294)—practically <5 mg C/L. Mandatory parameter in drinking water, ultrapure water (pharmaceuticals, electronics), and wastewater monitoring.
Method principle
TOC determination includes: (1) inorganic carbon (TIC) removal—sample acidification with HCl/H₃PO₄ and purging with carrier gas (O₂ or air) to expel CO₂ from dissolved carbonates/bicarbonates; (2) organic carbon oxidation—in catalytic combustion method, sample is injected into furnace with platinum catalyst at 680°C, where all organic compounds undergo complete combustion to CO₂; (3) CO₂ detection—carrier gas with CO₂ passes through NDIR (non-dispersive infrared) detector, which measures CO₂ concentration proportional to organic carbon content.
Applications
- Drinking water quality control (Journal of Laws 2017 item 2294)
- Ultrapure water monitoring (pharmaceuticals, electronics, semiconductors)
- Wastewater treatment plant efficiency control
- Surface and groundwater monitoring
- Water treatment system validation (reverse osmosis, activated carbon)
- Water for injection (WFI) purity control in pharmaceutical industry
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.004–30,000 mg C/L (depending on analyzer) |
| Detection limit | 4 µg/L (catalytic combustion, Shimadzu TOC-L) |
| Accuracy | ±2–5% (depending on method and range) |
| Methods | Catalytic combustion (680°C) or wet oxidation (UV/persulfate) |
| Detector | NDIR (non-dispersive infrared) |
| Analysis time | 3–10 minutes per sample |
Standard
- Standard number
- PN-EN 1484:1999
- Title (PL)
- Jakość wody — Wytyczne dotyczące oznaczania ogólnego węgla organicznego (OWO) i rozpuszczonego węgla organicznego (RWO)
- Title (EN)
- Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC)
Step-by-step procedure
1. Analyzer startup
Turn on TOC analyzer, combustion furnace, NDIR detector, and carrier gas flow. Wait for baseline stabilization (30–60 min).
2. Calibration
Prepare TOC standard series from KHP: 0.5; 1.0; 2.0; 5.0; 10.0 mg C/L (for drinking water). Run calibration sequence. Correlation coefficient r² > 0.999.
3. Sample preparation
For TOC—shake sample (suspended particles). For DOC—filter through 0.45 µm. Transfer to glass vials (acid-washed and rinsed with ultrapure water).
4. Acidification and purging (TIC removal)
Analyzer automatically adds H₃PO₄ and purges sample with carrier gas (sparging), removing CO₂ from carbonates and bicarbonates.
5. Combustion and detection
Sample is injected into combustion furnace (680°C, Pt catalyst). Organic compounds → CO₂. Carrier gas transports CO₂ to NDIR detector, which measures peak area.
6. Result reading
Software calculates TOC concentration based on calibration curve. Result in mg C/L. Each measurement performed in replicates (typically 3×), reporting mean and deviation.
7. Quality control
Blank (ultrapure water), CRM control sample, duplicates every 10 samples. Check repeatability (CV <5%). Vial cleanliness control.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| TOC analyzer | Shimadzu TOC-L, Analytik Jena multi N/C x300, Mettler Toledo 5000e, Sievers M9 | 80,000–250,000 PLN |
| Autosampler | Shimadzu ASI-L, Analytik Jena APG | 30,000–80,000 PLN |
| Sample vials (40 mL) | Glass vials with PTFE/silicone septa | 3–10 PLN/piece |
| Syringes for samples (optional) | Hamilton, for manual dosing | 200–800 PLN |
| Water purification system | Millipore Milli-Q, Hydrolab—water with TOC <0.05 mg/L | 20,000–60,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Phosphoric acid (H₃PO₄) 2 mol/L | 7664-38-2 | For acidifying samples to remove inorganic carbon (TIC). p.a. purity. |
| Platinum catalyst on Al₂O₃ support | — | Combustion column packing (replacement every 3000–5000 analyses). Operating temperature 680°C. |
| Organic carbon standard solution (potassium hydrogen phthalate KHP) | 877-24-7 | C₈H₅KO₄—primary standard. 2.1254 g KHP in 1 L water = 1000 mg C/L. For analyzer calibration. |
| Inorganic carbon standard solution (Na₂CO₃ + NaHCO₃) | — | Na₂CO₃ (3.497 g) + NaHCO₃ (4.412 g) in 1 L water = 1000 mg C/L TIC. For TIC calibration. |
| Carrier gas—oxygen or synthetic air | — | Purity 99.999%. Operating pressure 100–200 kPa. |
| Ultrapure water (TOC <0.05 mg/L) | — | For preparing standards and blanks. From Milli-Q or equivalent system. |
Health and safety (OHS)
- Combustion furnace (680°C)—burn risk. Do not touch heating elements.
- Phosphoric acid (H₃PO₄)—corrosive (H314). Use gloves and glasses.
- Carrier gas (pressurized oxygen)—pressure cylinder. Secure against tipping. Do not grease.
- Work with pressure cylinders—use reducer and safety valve.
- Safety glasses and lab coat required.