FTIR Gas Analyzer with Heated Multipass Cell

What is the FTIR Gas Analyzer with Heated Multipass Cell?

An FTIR gas analyzer draws sample gas through a heated multipass cell with path lengths of 2–10 m and identifies and quantifies many species at once. It is used for stack emissions, process gas and ambient air monitoring with ppb to percent detection ranges.

Overview

The FTIR gas analyzer couples an FTIR spectrometer to a multipass gas cell, typically a White or Herriott design with a gold-coated mirror set folding the beam to a 2–10 m path length in a volume of 0.2–2 L. The cell and sample line are heated to 180 °C to prevent condensation of water, acids and semi-volatile organics. A quantitative spectral method fits reference spectra of up to 50 gases simultaneously, such as CO, CO2, NO, NO2, SO2, HCl, NH3, CH4 and H2O, with detection limits from 0.1 to 1 ppm depending on species. Resolution of 0.5 to 2 cm-1 resolves rotational structure for accurate quantification. Response times of 10–60 seconds, sample pressure and temperature sensors, and automated zero and span checks support emissions reporting. Calibration gases and reference libraries must be managed and traceable.

How does it work?

An FTIR spectrometer directs broadband infrared radiation from a globar or ceramic source into a Michelson interferometer, where a beam splitter divides it between a fixed mirror and a moving mirror. The recombined beam produces an interferogram that varies with mirror displacement. The interferogram passes through or reflects from the sample, is recorded by a DTGS or cooled MCT detector, and is converted to a spectrum by a Fourier transform. Multiplexing allows all frequencies to be measured simultaneously, giving the Fellgett advantage, and the circular aperture gives the Jacquinot advantage in throughput. A helium-neon laser tracks mirror position to give wavenumber accuracy of 0.01 cm-1. Sampling accessories include attenuated total reflection crystals, transmission holders, diffuse reflectance cells and gas cells, allowing solids, liquids, films and gases to be analyzed with minimal preparation.

What are the key features?

• Heated gold-coated multipass cell prevents condensation and reaches 2–10 m path.
• Simultaneous quantification of up to 50 gas species from a single spectrum.
• Sample line heated to 180 °C transports water-soluble and sticky compounds.
• Resolution of 0.5 to 2 cm-1 resolves rotational structure of gas bands.
• Automated zero and span checks support continuous emissions monitoring.
• Sample pressure and temperature sensors correct for gas density changes.

What are the technical specifications?

A typical ftir gas analyzer with heated multipass cell configuration offers spectral range of 4500–900 cm-1, resolution of 0.5–2 cm-1 selectable, gas cell path length of 2–10 m (multipass), cell volume of 0.2–2 L, cell temperature of Up to 180 °C and detection limit (typical) of 0.1–1 ppm (species dependent). Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The FTIR Gas Analyzer with Heated Multipass Cell is used in stack and emission monitoring, process gas analysis, engine exhaust testing, workplace and ambient air studies and greenhouse gas research. Across the wider FTIR class, laboratories also deploy it for polymer and plastics identification, forensic trace evidence analysis and contaminant and failure analysis.

Which standards and certifications apply?

Relevant standards and methods include ASTM E1421, ASTM E168, ASTM E1252, ISO 10640, USP <854>, Ph. Eur. 2.2.24 and GB/T 6040. Certification candidates for this model are CE, MCERTS and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Place the spectrometer on a stable, vibration-free bench with controlled humidity, since KBr optics are hygroscopic and water vapor interferes with spectra. Keep desiccant in the interferometer compartment or use a dry air or nitrogen purge. Collect a fresh background before each sample and clean the ATR crystal with isopropanol or a suitable solvent between measurements. Verify wavenumber accuracy with a polystyrene film and photometric performance with standard checks such as signal-to-noise and energy throughput. Replace the IR source and desiccant cartridges as recommended. Laser and MCT detector cooling with liquid nitrogen require trained handling. For regulated use, implement IQ/OQ/PQ and software with audit trails.

How do I select the right FTIR Gas Analyzer with Heated Multipass Cell?

Select an FTIR gas analyzer for multi-component gas measurements in emission or process streams where water and corrosive species are present. It is not needed for single-gas monitoring where NDIR is sufficient. In an RFQ, specify target gases and ranges, path length, heating, response time, calibration gas plan and regulatory approvals.

How does it compare with other FTIR variants?

Choose an FTIR instrument by spectral resolution, sensitivity, sampling method and intended environment. Routine identification of polymers and organics is well served by a benchtop unit with 4 cm-1 resolution, a DTGS detector and a diamond ATR accessory. Research requiring 0.1 cm-1 resolution, step-scan time resolution or far-IR coverage needs a research-grade interferometer with optional MCT detectors. Microscopic contaminants below 50 µm require an FTIR microscope with mapping. Field identification of unknown chemicals favors a ruggedized handheld unit, and emissions or atmospheric work needs a gas analyzer with a heated multipass cell. Evaluate signal-to-noise ratio, library availability, purge requirements, accessory flexibility and software features for regulated laboratories.