Chromatography Forum

Hi all,

I am working on leaf wax composition. These are the parameters/features I used on GC-MS:

Machine: Agilent 8890 GC 7010B Triple Quadrupole GC/MS
Column: 30 m x 250 μm x 0.25 μm DB1-MS
Carrier gas: Helium
Flow rate: 1 ml/min
One microliter of the sample was injected into the column at an initial oven temperature of 50 °C for 2 minutes, then increased for 1 minute at 40 °C/min to 200 °C and then raised for 10 minutes at 3 °C/min to 320 °C.

I cannot define the compounds that have more than 33-carbon because the spectra are not good enough after the peak belonging to a 33-carbon compound. The leaf I use has 44, 46, and 48-carbon wax esters (I could see them in FID).
I need to define the compounds between 33 - 44 carbon chemicals. In order to see clear peaks after 33-carbon compounds, I have tried wax ester methods; however, still I cannot see chemicals with longer than 33-carbon chains.

The adjusted parameters for wax esters:

Transfer line temperature: 310 C
MS ion source: 220 C
Scan range: 40-850
Scan time: 720 ms
Solvent delay: 5 min
Injector temp: 325 C
Splitless mode with 2 min splitless time
One microliter of the sample was injected into the column at an initial oven temperature of 50 °C for 3 minutes, then increased for 1 minute at 50 °C/min to 180 °C and then raised for 10 minutes at 3 °C/min to 320 °C.

Could you please advise me what I should change/edit/remove to be able to see peaks of the compounds with more than 33-carbon and define them?

Thanks in advance!

We used GC-FID for waxes in products such as candles. We used a specialty thin-phase high-temperature nonpolar capillary designed for big molecules, typically coated with metal instead of polyimide so it could handle higher oven temperatures.

We could get GC over carbon waxes larger than you state. We bought pure C28 wax and used that to assign identities.

Thank you for your reply.

Some papers about waxes mention that they used high temperatures like you said, around 350 C for their methods, However, my column's max temperature is 340, and I usually put around 325 at maximum to avoid damaging the column. I should check if we have that kind of column for higher temperatures.

Best.

Some papers about waxes mention that they used high temperatures like you said, around 350 C for their methods, However, my column's max temperature is 340, and I usually put around 325 at maximum to avoid damaging the column. I should check if we have that kind of column for higher temperatures.

Your boss needs to obtain the correct tools for you. THAT'S his job.

The most informative GC-MS for wax analysis is GC-MS with Cold EI
It can analyze up to C74 (mass 1050 limit of Agilent 5977) and provide good peak shapes and molecular ion and fragment ions (plus elemental formula)
One example is described in http://blog.avivanalytical.com/2012/10/ ... ables.html
You can write me is such analysis is essential
Aviv Amirav
amirav@tau.ac.il

The most informative GC-MS for wax analysis is GC-MS with Cold EI
It can analyze up to C74 (mass 1050 limit of Agilent 5977) and provide good peak shapes and molecular ion and fragment ions (plus elemental formula)
One example is described in http://blog.avivanalytical.com/2012/10/ ... ables.html
You can write me is such analysis is essential
Aviv Amirav
amirav@tau.ac.il

Hi Dr. Amirav,

Thank you for your reply!
I don't have time to do the GC-MS tests again as I am writing my master's thesis these days. Besides, I'm afraid we do not have that column in my lab inventory. I will check the Cold EI system in detail later for further analysis.

Best,
Melike