How many peaks has C6 in a natural gas

[BEE]

I have an agilent 7890 Gc i use for NGA, with a HP PONA column as the capillary column. My standard gas gave me a single peak as C6, but when i analyesd a gas sample, I had 4 peaks coming out around the expected retention time for C6. My question is do i sum those 4 peaks as C6 or take the highest of the peaks which happens to be the last one. Are these contaminants or isomers of C? Can anyone post me a std gas chromatogram for a natural gas?

Help my ignorance, pls. Many thanks.

[chromatographer1]

Most natural gas standards (from a quality supplier who knows what they are doing) will include a combination of C6-C8 isomers in varying amounts. This will approximate the BTU value of actual natural gas.

Thus a C6+ peak will include several peaks when a BTU analysis is performed on a std NG analyzer (Daniel Industries is a common analyzer).

While the BTU value of shorter hydrocarbons vary by a large degree, the higher hydrocarbons differ less in their BTU content, this this averaging is an accepted industry practice.

http://www2.emersonprocess.com/siteadmi ... ochure.pdf

This document contains a chromatogram (with changes in scaling for N2 and methane) of natural gas C6+ analysis.

best wishes,

Rod

[GasMan]

If you are using the standard natural gas sample supplied by Agilent, then you only have one C6 peak in the sample, N-Hexane. You are seeing other C6 isomers that are in your sample. As chromatographer1 mentions, you can sum all of these together. The other isomers that can be present are 2-Methyl pentane, 3-Methyl pentane, 2,2 Dimethyl butane and 2,3 Dimethyl butane. You might also have cyclohexane, another C6 contender.

Gasman

[BEE]

@ gasman & Rod, Thanks for your response. I have a further concren, in my quantification,what is the industry practice? Is it to sum all these isomers and call them C6 or to single out the peak which corresponds to the retention time given by the standard gas as my C6.

Looking forward to your professional advice.

Thanks in advance.

@ gasman, i did not see the standard gas chromatogram for a natural gas.


Bee