#92 - Metamerism – Part 2

Last time, the topic of metamerism as related to the coatings industry was discussed. We don’t really have any issues with metamerism in manufacturing gas analyzers, but the whole idea reminded me of some challenges that we do face in the analysis of atmospheric gases.

Analytical Interference

Various methodologies lend themselves to analysis of different gases. Some methods are more or less specific than others, and there is usually no ‘magic bullet’ sensor/detector for any one gas.

Hydrogen – At Nova, we offer analysis of percent hydrogen by thermalconductivity detector. Hydrogen has a high degree of thermalconductivity, and this property can be used to measure it. However, other gases also have various degrees of thermalconductivity. The presence of several other gases in a mixture can interfere with the effectiveness of a thermalconductivity measurement. For hydrogen applications, we need to know what other gases are in the sample and the low/normal/high levels of each.

Methane & Hydrocarbons – At Nova, we offer infra-red analysis of hydrocarbons. The most common infrared analysis requested of us is methane. If the sample contains methane and enough other mixed hydrocarbons, some of the non-methane constituents will also produce a response on the infra-red detector. This is because many hydrocarbons have similar or overlapping IR spectra.

The methane reading may be compromised to an unknown degree by the non-methane hydrocarbons. For methane applications, we need to know what other gases are in the sample and the low/normal/high levels of each. We may be able to offer a methane-specific detector. In some cases, we may be able to compensate for the problem using certain calibration gas blends. Sometimes we can ignore the whole problem if the effects are not sufficient to be of concern to the end-user.

Electrochemical Sensors – At Nova, we offer analysis of various gases, including oxygen, using an electrochemical sensor. Electrochemical sensors are reactive by nature and are frequently affected by gases other the one of interest. For example, the gases carbon monoxide and hydrogen will often provoke a strong response on the same electrochemical detector. For electrochemical applications, we need to know what other gases are in the sample.

All of this really isn’t metamerism, but the ideas and potential consequences do bear some similarities. When discussing your analytical needs with Nova, we may request that you fill out an Application Questionnaire. This form is intended to assist you to provide us with critical data that may influence the type of equipment that is feasible in your application.

Nova Application Questionnaire
http://www.nova-gas.com/appq.html

For information on these and other gas analyzer systems, give Mike or Dave at Nova a call, or send us an e-mail.
1-800-295-3771
sales at nova-gas dot com
websales at nova-gas dot com
http://www.nova-gas.com/
https://twitter.com/NOVAGAS
http://www.linkedin.com/company/nova-analytical-systems-inc-
http://www.tenovagroup.com/

IR Spectrum:

NIST Chemistry WebBook (http://webbook.nist.gov/chemistry); COBLENTZ SOCIETY; Collection (C) 2009 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

-