The Senior Director of Gas Analysis R&D at TFS, took the theme of ’Improved efficiency in bulk & specialty gas analysis using ultra-sensitive FTIR’, highlighting not only new corporate solutions but how its product range allows for routine impurity measurements from low PPB (parts per billion) to mid PPT (parts per trillion) range.
Bulk and specialty gases require highly accurate gas concentration monitoring to meet stringent purity and blend requirements.
Spartz began the presentation by highlighting the compact and lightweight benefits of the 75lb TS Max-iR FTIR Gas Analyzer. Featuring a 5U rack-mounted design, one of its main benefits is it is designed to run for more than 10 years with minimal maintenance, and the spectrometer has a single crystal beamsplitter which allows high thermal stability.
Thermo Fisher MAX-iR FTIR Gas Analyzer
Additionally, instead of using a helium neon laser, it uses a VCSEL Diode Laser, which is ideal for process and environmental applications.
The system comes with DTGS (room temp) detector which can measure the full infra-red spectrum, although it’s in the tens of ppb range. To go lower, you would use an MCT or InAs which are thermo electrically cooled. They are coupled with optical band pass or long pass filters to get the highest signal to noise and lowest detection levels.
“With these configurations we’ve demonstrated sensitivities three orders of magnitude lower, in the tens of parts per trillion,” he said. A gas cell can be run from vacuum to 10 atmospheres – they can be changed while doing measurements – and a 10cm cell is under development.
The next slide highlighted the StarBoost Technology, which enables ultra-low measurements. A very high D* detector is coupled with an optical filter, which removes all the frequencies that are not of interest. “We can turn the gain up and gain even more signal to noise,” he added.
Spartz said FTIRs are ideal in that we want the detector noise to be the largest noise source. Instead of having an enhancement of 3.5, it can be 30 times.
”If I was to try and generate the same signal to noise with just the detector, it would require the square of that enhancement. So if I want to look for three, four or five compounds, I can put a number of different filters in and get high signal to noise in a very fast amount of time.”
A slide highlighted specific features, such as the black box (IR source) and small spectrometer. No adjustments are required. The light beam passes through the gas cell 48 times and exits at the bottom, and then strikes the detector. Up to four different beams can be put in the beam at any one time.
Martin Sparz, Senior Director of Gas Analysis R&D at TFS
Data shown in the webinar was collected with a Broad Band Optical Filter, in a sense the ‘least sensitive’ mode. A gas company asked for a gage R&R carbon dioxide (CO2) in bulk hydrogen (H2) and included CO, CH4 and THC. Spartz said, “Even in this fairly insensitive configuration, we could probably get down to 1PPB fairly easily,” he said.
Many applications also run out five atmospheres, and to get to the lowest levels, it would use a narrow band filter. Those two elements would provide 25% enhancement on this data.
The next slide illustrated the challenges with FTIRs, notably their instability. If you’re trying to measure very small peaks, any drift to the baseline can make it very different to see. “So we’ve come up with a technology called AutoReference, which allows us to remove the baseline drift and reduce any zero drift in the measurement,” he said.
One major benefit of AutoRef – Igram Processing Method is that it combines high resolution and low resolution, which eliminates baseline drift and bias drift in low level measurements.
Another slide illustrated the importance of pressure modulation with bulk gas impurity analysis (CO in N2). Among the four panels, the lower right panel showed the ‘single reconstruction’, where the analysis is occurring. A narrow band optical filter showed descent from 150PPTRN to zero.
”As it turns out, this system was only assembled for a couple of hours – and CO2 was coming out of the optics. But it shows how quickly we can do these measurements with this type of technology.”
Another graph measured CH4 in Bulk N2, comparing Long pass and Band pass filters. ”Each molecule will be different, but in all cases we see an enhancement going from a Long pass to Band pass filter. In some cases it’s five, 10 or 20 times enhancement.”
Most customers want Thermo Fisher Scientific to measure multiple gas streams, so it has designed an eight-channel High Purity Multiplexer.
It provides a continuous flow on channels and has a ‘Double block and bleed’ design which prevents cross-contamination. The whole system is controlled by a PLC, and uses a precise Digital MFC which controls flow rates into the instrument.
Spartz said, “We tie everything together using our MAX-Acquisition Software. When we build a system for any application we use a product configuration, and we can configure it to run our equipment or other equipment that the customer may want. The big thing about the software is the workflow, which controls the entire sequence of events.”
Customers can receive export daily concentration data to Microsoft Excel reporting templates and export alarms, for hardware and gases. The Optional factory interface module (FIM) provides flexibility, using either analogue or digital communication.