#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.

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#90 - Metamerism – Part 1

“Metamerism” is primarily a chemistry term for a type of isomerism in which chemical compounds have the same molecular weight and identical proportions of the same elements, but have different chemical properties because of radicals of different types or in different positions. Sounds complicated, but it’s basically a reference to two chemicals that you would expect to behave the same, but don’t because of minor differences.

In the coatings industry, especially in pigmentary studies, metamerism has a somewhat different meaning, but the idea is still sort of the same. Metamerism is a term used for when two colored samples appear to match under one set of lighting and viewing conditions, but not under another set. Metameric dissimilarity may also be due to differences in observers’ color perception aside from lighting or viewing conditions.

There are instruments available that simulate
various lighting and viewing conditions to
help manage unexpected metameric effects.

I have noticed that metameric effects are often more pronounced in coating systems that do not have high opacity and where the substrate is colored (non-white), or where the system is comprised of multiple layers of varying color contribution. Coatings that incorporate different types of coloring material types also seem prone to metamerism (e.g. organic/inorganic colorants or dyes/universal colorants added post-manufacture).

An example scenario might be a manufactured article whose color is designed and agreed to under the viewing conditions at the manufacturing facility, but doesn’t match expectations when the article is completed and moved to the final location. Metamerism may be the reason. (I say ‘may be’ because a legitimate manufacturing error may also be the cause.) During my time in the coatings industry, I dealt with metamerism often enough to appreciate its potential for disruption.

At Nova, we are thankful that we do not have to worry about such aesthetic complexities in our manufacturing process. Making gas analyzers is complicated enough already. But there are a couple of phenomena in gas analysis that remind me a little of metamerism. I’ll talk about those next time.

The Nova blog appears to be about gas analyzers, and yet this post discussed a completely different subject. Literary metamerism.

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/

Pictures:

Copyright © INTEKE INSTRUMENT CO. LIMITED

http://www.inteke.com/

 

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