How do I calculate the assay of Hexane, if my sample has four hexane-isomers?
By Mr. PererÍ on Monday, December 16, 2002 - 02:21 pm:
Can I considerate that the Assay of the hexane-isomer 1 is proportional to its area percent?
I do not have Standard of Hexane-isomers.
By Rod on Monday, December 16, 2002 - 04:36 pm:
If you can measure all the components of sample and all the components are C6 hexenes and hexanes then the error introduced by FID detection is quite small, especially if the sample you are assaying is > 90% pure.
The short answer is that C6s have about the same response to a FID and to a large degree a TCD. There should also be similiar responses to a pulsed Ionization Detector as well.
The danger is that there may be dimers present (C12s) or other peaks not seen in your analysis.
By Anonymous on Monday, December 16, 2002 - 10:12 pm:
can anybody name the possible isomers of hexane
By john b on Tuesday, December 17, 2002 - 01:15 am:
I think the problem is naming it hexane, does not Mr P. mean C6 compounds? For example: n-hexane vs a branched C6 compound? n-hexane and cyclo-hexane are not true isomers. Molecular formulas are different.
By Mr PererÍ on Tuesday, December 17, 2002 - 03:13 am:
Tank you for your important observations!
The retention time of hexane dimers (C12s) will be very diferent. The molecular sample of thse molecules increase the RT. But do you have a reference (or experience) about it? Because I do not included this question in my considerations.
But Mr John B
Tank you for your consideration about my problem. I agree with you, but:
Will be the retention time of Cyclo-hexane equal to Hexane?
I do not have Cyclo-hexane in my Lab, but chromatograms obtained with same chromatographic method have very different retention times between n-Hexane and Cyclo-hexane (5 min and 10 min, respectivally). But I agree that must to analyse my sample on CG-Headspace-MS for elucidate the Mass spectrum of the hexane-isomers of my sample. Or buy Cyclo-hexane reagent for my Lab.
By Anonymous on Tuesday, December 17, 2002 - 05:25 am:
The major c6 isomers are dimethylbutane, methylpentane, methylcyclopentane,n-hexane, cyclohexane.
By john b on Wednesday, December 18, 2002 - 01:02 am:
I repeat cyclohexane is NOT an isomer of hexane
example C6H12 is not equal to C6H14. There are
5 Isomers of Hexane - C6H14.
By vloet jos on Wednesday, December 18, 2002 - 06:03 am:
I often have to determine hexane technical grade.
One of the peaks has indeed the same retention time as cyclohexane. Cyclohexane has almost the same response as n-hexane (headspace/FID). The response of the isomers is also comparable with the response of n-hexane.
For quantitatation I mostly use hexane technical grade (the same batch which is used in production if available) as reference standard. If not available I summarize all peaks and calculate to the response of n-hexane. In a headspace / FID system the accuracy is very good (recovery 99-101 %).
By Mr PererÍ on Wednesday, December 18, 2002 - 11:40 am:
I am very happy with your informations.
Maybe I considerate:
Hexane / tr (min) / Area%
1 / 4.0 / 22
2 / 4.9 / 45
3 / 5.5 / 27
4 / 6.2 / 5
So if my solution of Hexane Reference Standard is
at 200 ppm:
1 200x22% = 44 ppm
2 200x45% = 90 ppm
3 200x27% = 54 ppm
4 200x5% = 10 ppm
Is this procedure aceptable?
By Anonymous on Wednesday, December 18, 2002 - 11:30 pm:
we are following the same at our lab.
By jos vloet on Thursday, December 19, 2002 - 04:49 am:
It is okť.
My data system first adds up the areas and subsequently calculates the content in ppm, this gives the same result.
By Mr PererÍ on Thursday, December 19, 2002 - 06:23 am:
Rod, Anon, Job and Jos
Tank you for important help.
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