Chemstation training : help with overlapping peaks

[catnip]

Hi,
I am new to this forum. Not sure if this is the correct place to post. Does anyone know where I could get good online training for Chemstation? Learn how to develope methods, trouble shoot, ect? I just got a 7890A GC and 5975C Mass spec in my lab and I have gone as far as I can go on my own learning. Yea, I'm definitely missing something. Have some peaks overlapping, and then some peaks eluding at 18~24min when the RT should be 5~8min. Using 5ms column: 30m x 250um x 0.25um. Thank you in advance for your help.

[tom jupille]

If your problem is overlapping peaks and / or incorrect retention times, then learning more about chemstation won't help. You can't compute your way around bad chromatography.

If you post details about your method (analytes, column, temperature program, flow, etc.), there are many GC gurus here who can help.

[catnip]

Hi Thank you. Here is the method information below. I am evaulating fragrance mixture samples. Let me know if you need any other info:

Column is an hp 5ms: 30m x 0.25mm x 0.25um
Carrier: Helium
Mode: split
Inlet heater: 250c
Injection volume: 1uL
Head pressure: 7.6522 psi
Total Flow: 53 ml/min
Septum Purge flow: 2ml/min
Split ratio: 50:1
Split flow: 50ml/min

Oven program
Initial: 50c
Pressure: 7.6522 psi
Flow: 1ml/min
Ave velocity: 36.445 cm/sec
Hold up time: 1.3719
Flow program: off 1ml/min for 0 min
Outlet pressure psi: 0
Ambient psi: 14.696
Initial: final temp 50c / final time 0.085
Ramp: 10.607c min / final temp 275c / final time 21.128
Run time: 42.425

Tune file: atune.u
Acquisition mode: scan

Solvent delay: 1.5 min
EMV relative voltage: 106
Resulting EM Voltage: 1706

Scan perameters
Mass: 40.0~500.0
Threshhold: 150
Samples: 3 A/D samples 8
Plot 2 mass: 40.0~500.0

MS Source: 230c max 250c
MS Quad: 150c max 200c

[DSP007]

Hi, brand new!

It is best to completely separate the peaks. But the plant extracts contain many substances that are not always possible.
Use the manual partitioning. Icon-two hump camel and the like between the vertical bar.

[Peter Apps]

Hi catnip

The method that you have is pretty much a standard generic one - the only thing that I would change would be to decrease the oven prgramme rate to 5C/min.

With complex natural samples you will always get peak overlaps - the trick is to get the peaks that you are interested in separated enough to measure what you need to measure. The most powerful way of moving peaks around is to use columns with different stationary phases - but as you get better separation for one set of peaks you will get other peaks that start to overlap.

Your unexpected retention times may be due to the MS library search mis-identifying the peaks; many terpenes (which are the mojor components of essential oils) have spectra that are very similar. You can check this by injecting a pure sample of the compound that you are looking for instead of locating it on a chromatogram from an oil on the basis of MS identifications.

And I'll unreservedly support what Tom said - this is about columns, gas flows, temperatures, inlets and injections, etc etc, not about software.

Peter