Suitable Gas Sensor for Organic Vapour - non-catalytic since no oxygen present

I agree. Looking strictly at the business aspects of this problem, it looks like this may be either a cost that cannot be cut or a frivolous expenditure. The facts that an "off the shelf" technique exists for any process that fits all but the cost criteria indicates to me that this is an esoteric concern. One possible business solution is to contract out to a consulting firm to bring their expensive equipment and technical knowledge to measure this process once for a certified analysis. A drawback of this approach is that continuous monitoring will not be possible. IMHO the main advantage of contracting an outside firm will be that this will bring certification of the results.

Type your requirements here: Search GlobalSpec

Absorption spectrum analysis might fit your criteria but without knowing anything about the suspected volatile gas it is impossible to say if an infrared frequency range will be sufficient. Forget about using a monotonic LED source, you need a spectrum.

I can see from replies that I need to be more specific. The particular configuration of the gas stream is necessary as part of a novel process still under development. The sensor is required for monitoring of process conditions, where online measurement of solvent vapour concentration is targeted. Specifically, this is not a measurement of air quality for ventilation. I mentioned the tgs sensor only for illustration. The solvent is isopropyl acetone. It saturates at 2% in air. I need to measure from 0 to saturation, for proper process control. Thanks again

<...measure from 0 to saturation, for proper process control...>

Given that the set point is somewhere in the 0-2vol% range, what does the control system modulate in order to sustain the setpoint?

What is so critical about the process that a steady-state solvent concentration needs to be maintained? What is it that presents a varying concentration that needs to be modulated?

At what temperature and pressure?

Flowrates?

If it is a solvent, then it should be flamable.

If it is flamable:

A standard catalytic sensor can be used, although it will quickly consume itself; this won't work.

A standard IR sensor CAN be used as it will not consume itself, and won't need regular calibration. Any Combustible Gas Detector can be calibrated to any combustible gas using a K factor. Standard output is 4-20ma, giving you process control input.

The original poster stated that oxygen was absent, though. so any measurement derived from the prospect of combustion is therefore a non-starter.

You are correct, I missed that.

Very simple: (1) Use a thermal conductivity detector and linearize the response between values of "0%", and "100%" saturation at a reference temperature. The problem is process will probably never be "exactly" at the reference temperature. Vapor pressure of organic vapor is strongly dependent on temperature.

Less simple: (2) Infrared analysis does appear to be a viable option, and there are process instruments which might suffice for this, but you must configure a gas cell (longer path length) most likely. Another option is laser scattering if that molecule exhibits Raman bands (usually a result of a totally symmetric vibration quantum state, as in methane).

@PWSlack: Your questions are what our development should hopefully clarify :)

I am hoping to find what is mentioned in the title of this post: a sensor which can report the concentration of solvent in a given volume of nitrogen gas. This is necessary to find out which process conditions are optimal.

The flow rates are small. I need to maintain a certain concentration for a time, then it will change from that. Hence, the sensor should give a variable output proportional to concentration. I think of it as a relative humidity sensor, but sensitive to solvent instead of H2O.

PWSlack, your questions are reasonable, but way ahead of the curve. I simply need a "concentration-meter," sensitive to the solvent, and which works in nitrogen instead of air.

Thanks again.

Tobacco industry, right?

Tobacco? No, that wouldn't work, tobacco is a poor sensor and doesn't have a good interface.

Limit the cost by renting the device or maybe you could contact an instrument manufacturer and get on their field BETA equipment testing program.

Contact IOMEGA and if they can't provide a solution they will point you in the right direction.

Hi SHOCKHISCAN,

I made a search for IOMEGA, but only turned up the data storage Company. Could I ask you to send me a link? Thanks

Don't have the exact answer to your question but may I suggest that you do a search at TI.com for "chemical sensor". They have descriptions of the units that they make and also the circuitry for the electronics to make them able to work. I received some samples but haven't had the time to experiment with them. I was hoping to work-up a wireless continuous monitoring of carbon monoxide device. The literature for the sensors makes them look quite interesting with a possible wide range of applications.

Wife is a teacher home for summer vacation therefore the "honey-do list" increases exponentially during the summer! Very little time for "intelligent" play things.

Good Luck, Old Salt

Hi old salt,

best lead so far, thanks. I am checking the website now, they have several nice sensors, that may indeed turn out useful.

I will return when I have figured out if the lead actually led anywhere.

thanks

Hi all,

Inow have two contenders fulfilling the requirement of existence. Availability (at least to me) still has no solution:

1) A good while back, I found the Micronas platform:

http://www.micronas.com/de/products/gas-sensors/gas-86xyb

one of these also includes VOC sensing. It is based on a floating gate, where the potential changes due to absorption (not combustion) of gas molecules.

Further, it has the added advantage of being available in a USB stick demonstrator platform. However, my country's distributor says they are focussing on big clients, and don't want to defocus by selling the USB stick with sensor to me. So...

2) From old salt's lead, I was able to locate a sensor based on a principle I was hoping to implement earlier, but couldn't find the part for. The idea is that VOC and many other molecules absorb in the IR range, so a simple IR emitter-sensor setup will detect a signal. Obviously, cross-talk between chemical species will be impossible to separate, but I don't believe I have to worry about this in my setup:

http://www.ti.com/product/lmp91051

The sensor is known as an NDIR Gas Sensor. This package also provides reference and temperature, for drift compensation.

My question now boils down to:

Does anybody know of a finished product out there based on NDIR?

I would prefer a developed package, as all I want is to log the concentration of solvent in vapour.

thanks again

Still there is needed more information. When you state solvent in vapor, this could be slightly misleading, then NDIR (non-dispersive infrared) may not in fact work. You may need at least to discriminate by known published IR absorption data for the solvent (MIBK??), and then obtain a suitable infrared band pass filter (these can be found with not as much difficulty as once was). This would produce a much more selective and sensitive instrument.

Since you are dealing with MIBK (methyl isobutyl ketone, sic isopropylacetone), there are specific regulations dealing with emissions of this compound. IF this is an environmental cleanup, your best bet might well be to assure compliance by going with periodic gas sampling (or even better some form of automatic gas sampling), then having the sample analyzed by GC-MS by an accredited laboratory.

IF this instrument is intended to be a screening tool for various areas, then you need something that gives you a field instrument, then maybe your other ideas will at least give you an "indication".