Analytical labs burn through nitrogen cylinders quietly but relentlessly — and pay for it in rental fees, handling injuries and 3 a.m. changeovers when an overnight GC run is on the line. A lab nitrogen generator ends all of that. The only real question is specifying it correctly: which purity, which flow, and one unit or several. Here is the practical answer, instrument by instrument.
Purity & Flow Requirements by Instrument
| Application | Purity | Typical flow |
|---|---|---|
| GC carrier gas (capillary) | 99.999% (N2.0) | 0.3–1.5 L/min per GC |
| GC detector make-up (FID etc.) | 99.999% | 0.3–0.5 L/min |
| LC-MS nebulizer + drying | 99.5–99.9% | 10–35 L/min |
| TGA / FTIR purge | 99.5–99.99% | 5–20 L/min |
| Sample evaporation / blowdown | 99.5% | 5–20 L/min |
| Glove box (with purifier) | 99.999% | per box spec |
Two rules simplify everything: carrier gas wants 5.0-grade and nothing less; nebulizer, purge and evaporation duties are happy at 99.5–99.9%. Never overspecify the second group — purity you do not need is capacity and money you waste.
PSA vs Membrane in the Lab
| PSA | Membrane | |
|---|---|---|
| Purity ceiling | 99.999% (5N) | ≈ 99.5% |
| Best for | GC carrier gas, glove boxes | LC-MS nebulizer, evaporation |
| Noise / size | Cabinet, < 60 dB(A) | Smaller, quieter still |
| Air compressor needed | Yes (built-in or house air) | Yes (higher volume) |
Many labs end up with a two-unit setup: one PSA unit feeding the GCs, one membrane unit for the "bulk" consumers. It sounds like more equipment; in practice it costs less than one oversized PSA unit trying to serve both grades.
A Worked Sizing Example
Three GCs (1 L/min each), two LC-MS systems (25 L/min each) and a blowdown station (10 L/min): total peak demand ≈ 68 L/min ≈ 4.1 Nm³/h. Add 30% headroom and a small buffer tank → a 5–6 Nm³/h generator covers the whole lab, supplied through a simple manifold with individual shut-offs per instrument.
Installation Notes Engineers Actually Care About
- Noise: modern cabinets run below ~60 dB(A) — fine inside the lab, or install in the service corridor with a line through the wall
- Ventilation: small rooms should vent normally; an O₂ monitor is cheap insurance in any room smaller than ~30 m³
- Air supply: oil-free compressor or oil-lubricated + carbon filter; the lab generator inherits whatever air you feed it
- Safety & logistics: no more cylinder trolleys through corridors, no more weekend changeovers guarding an overnight run