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- Posts: 4
- Joined: Thu Aug 10, 2017 3:35 pm
Is it possible that liquid and gas calibration of a species yield the same area and residence time, using GC?
I have a Shimadzu GC 2014 with capillary column in my lab. The main objective is to use the GC to quantify concentration of hydrocarbon products of the thermal decomposition of jet fuels.
In the past, I have calibrated the GC with C1 to C4 species, using calibration gas standards (mainly purchased from Airgas or Air Liquide). My next step is to calibrate bigger hydrocarbon species (C5 and up). However, these species are rarely available in gas form. Thus, I need to calibrate using liquid standards.
My first attempt was to use a 1000-ppm mixture of benzene in methanol because I have a gas standard bottle for benzene. Here is how I made the solution:
The mole fraction of benzene is
x = 1000 moles of benzene/ 1,000,000 total moles
I converted moles to masses by using the corresponding molar mass
x = 78,110 g of benzene/(32,007,960 g of methanol + 78,110 g of benzene)
I reduced the ratio to
x = 0.122 g of benzene/(50 g of methanol + 0.122 g of benzene)
Then, I made the solution accordingly.
I used split injection method. However, the liquid sample gave an area that was 3 times higher than the gas sample did. And the residence time shifted earlier than the gas sample.
The gas standard bottle is of 1000 ppm benzene in balance of nitrogen.
Could anyone please help explain why I cannot obtain similar results for both gas and liquid samples?
Many thanks,
Khanh