Hydrocarbon-free zero air for high-temperature combustion, nitrogen carrier gas for NDIR detection, and ultra-pure water for blank preparation — on-site generation ensures accurate, low-level total organic carbon measurement without cylinder contamination.
Total organic carbon analyzers convert organic compounds to CO₂ for measurement. The accuracy of that measurement depends entirely on the purity of the gases and water used in the process.
In combustion TOC analyzers, the sample is injected onto a catalyst bed heated to 680–900 °C in a stream of purified air. All organic carbon is oxidized to CO₂. Hydrocarbon contamination in the air creates a false-positive carbon signal.
Carrier gas transports the CO₂ produced during oxidation to the NDIR detector. In some methods, nitrogen also serves as sparge gas to purge inorganic carbon (IC) as CO₂ from the acidified sample before TOC measurement.
TOC analyzers measuring ppb-level organic carbon require blank water with documented ultra-low TOC (<5 ppb). Bottled reagent water degrades after opening. On-site purification delivers fresh, low-TOC water on demand.
Combustion TOC analyzers work by oxidizing all organic carbon to CO₂ and measuring the CO₂ with an NDIR detector. The combustion gas (purified air) provides the oxygen needed for oxidation and carries the resulting CO₂ to the detector.
Any hydrocarbon in the air becomes CO₂ in the detector. If your combustion air contains 0.5 ppm methane, that methane is oxidized in the furnace and measured as additional CO₂ — creating a persistent positive bias that elevates your blank values, raises your detection limit, and can cause low-level samples to read high.
This is not a baseline offset you can subtract. Unlike a stable electronic offset, hydrocarbon contamination in air varies with ambient conditions, cylinder age, and regulator contamination. The variability makes software correction unreliable, especially for measurements below 100 ppb C.
A catalytic oxidation zero air generator delivers <0.05 ppm THC consistently, reducing the air-contributed carbon background to a level that is negligible even for ultra-low-level TOC methods like USP <643> pharmaceutical water testing.
USP <643> requires TOC measurement of purified water at ≤500 ppb C. At these levels, a zero air generator is not optional — it is essential for reliable, compliant measurement. The ZA Total paired with an HLP UV water purifier provides a complete, validated gas + water supply for pharmaceutical TOC testing.
Carrier gas: After combustion, the resulting CO₂ is swept from the furnace to the NDIR detector by a stream of carrier gas. This gas must be CO₂-free to avoid contributing to the measured signal. High-purity nitrogen from a PSA generator meets this requirement with documented low CO₂ content.
Sparge gas: In the NPOC (non-purgeable organic carbon) method — the most common TOC measurement approach — the sample is first acidified to convert all inorganic carbon (carbonates, bicarbonates) to CO₂, then purged with a stream of nitrogen or zero air. This sparge step removes IC so it does not interfere with the subsequent TOC measurement.
Which gas to use? Some TOC analyzers use the same gas for both combustion and carrier (zero air serves both roles). Others use zero air for combustion and nitrogen for carrier/sparge. Check your instrument manual — we can supply either or both from on-site generators.
Shimadzu TOC-L uses purified air for both combustion and carrier. Analytik Jena multi N/C uses synthetic air or nitrogen. Sievers/SUEZ M-series uses no combustion gas (UV/persulfate oxidation). We will match the right generators to your specific instrument requirements.
TOC analyzers measuring at the ppb level are only as accurate as their blank water. If your blank water contains 20 ppb organic carbon, you cannot reliably measure a sample at 30 ppb — the signal-to-blank ratio is too low for meaningful quantitation.
Bottled reagent water degrades. Even high-quality bottled HPLC-grade water absorbs CO₂ and leaches organic compounds from the plastic bottle within hours of opening. Water that was 3 ppb TOC when sealed can reach 20–50 ppb after a day on the bench. On-site purification delivers fresh, low-TOC water on demand — never stored, never exposed, never degraded.
The HLP UV advantage: The HLP Series with UV sterilization (254 nm) photo-oxidizes trace organics in the purified water, delivering Type I water with TOC consistently below 5–10 ppb. This is adequate for routine TOC measurement and many pharmaceutical water-testing applications.
Quick reference for gas and water requirements by TOC oxidation method.
| TOC Method | Combustion Gas | Carrier / Sparge | Water | Recommended Generator(s) |
|---|---|---|---|---|
| High-Temp Combustion MOST COMMON | Zero Air (100–250 mL/min) | Same (Zero Air) | Type I (UV) | ZA Total + HLP UV |
| High-Temp Combustion (N₂ carrier) | Zero Air (100–250 mL/min) | N₂ (100–200 mL/min) | Type I (UV) | ZA Total + NG EOLO + HLP UV |
| UV / Persulfate Oxidation | — (no combustion) | N₂ sparge (100 mL/min) | Type I (UV) | NG EOLO 500 + HLP UV |
| UV Only (online) | — | — | Type I (UV) | HLP UV |
| Pharma Water (USP <643>) | Zero Air | Zero Air / N₂ | Type I (UV) | ZA Total + HLP UV |
| 2+ TOC Analyzers | Zero Air (200–500 mL/min) | N₂ (200–400 mL/min) | Type I (UV) | ZA Total + NG EOLO 1300 + HLP UV |
TOC labs that switch from cylinder supply to on-site generation consistently see immediate improvements in data quality and operational efficiency.
Catalytic oxidation zero air delivers <0.05 ppm THC — reducing the air-contributed carbon background to levels negligible even for ppb-level TOC methods.
Cleaner gases + fresher blank water = lower baseline noise = lower detection limits. Labs routinely report 2–3x improvement in TOC detection limits after switching.
Generator specifications provide documented, traceable purity data for your quality system and SOPs. No reliance on cylinder certificates that may not reflect delivered purity.
TOC analyzers often run continuous online monitoring or long automated batch sequences. An on-site generator never runs out mid-sequence.
TOC gas consumption is modest but continuous. Over time, the cumulative cost of zero air and nitrogen cylinders, rental, and delivery adds up. A generator pays for itself in 12–24 months.
For pharmaceutical labs, documented gas and water purity from a generator simplifies USP <643> compliance and audit readiness versus managing cylinder COAs and expiration tracking.
Our zero air generators, nitrogen generators, and water purifiers support every TOC platform from every major manufacturer.
TOC-L series (CSH/CPH). TOC-V series. TNM-L total nitrogen. High-temp catalytic combustion at 680°C. Purified air for combustion + carrier.
multi N/C 2100S, multi N/C pharma. High-temp combustion up to 950°C. Synthetic air or nitrogen carrier gas configurations.
vario TOC cube, acquray TOC. Combustion and wet-chemical oxidation modes. Zero air and nitrogen gas supply compatible.
Sievers M500, M9, InnovOx. UV/persulfate and supercritical water oxidation. Nitrogen sparge gas. Online and laboratory models.
Lotix, Torch, Fusion UV/Persulfate TOC. Nitrogen sparge gas for IC removal. Pharma water compliance models.
QbD1200, BioTector B7000i online TOC. Process and laboratory analyzers. Continuous monitoring with on-site gas supply.
5000TOCi online analyzers for pharma water systems. USP <643> compliance. Continuous monitoring with generator gas supply.
Central gas and water supply for labs running multiple TOC analyzers. One generator set feeds your entire TOC operation.
Tell us which TOC analyzer you run, your oxidation method, and your target detection limits. We will recommend the right combination of gas generators and water purification to optimize your results.