Peak tailing problem

[envirochem]

Hi all,

I try to analysis PAH in water with GC-MS and my problem, peak come with tailing. Some peaks (almost all) come with tail like on picture. I dont understand where is the problem, I changed many things (column cutting, changed injector temperature etc.) but it doesnt work. My conditions;

İnj Temp: 260 °C
İnj Vol: 2uL pulsed splittless 30psi until 3 mins
70ml/min at 4mins
Constant Flow 1mL/min
Oven: 50 °C hold 1 min, 15°C/min to 100 °C, 10°C/min to 210 °C and hold 1 min, 8°C/min to 310 °C and hold 8 mins
MS source temp: 300 °C
MS quad temp: 180 °C
Transfer line temp (Aux temp): 320 °C




Whats the reason and how can I solve it? any idea?

thanks

[scottythree]

I think your peak tailing looks fine but you have a bit of peak front going on. Is this the first time you have run this method or have you performed this method several times without this issue? Have you run a blank and is it clean?

[Peter Apps]

Your picture does not show the retention times - if time increases to the left then this looks like sorption in the inlet. If time increases to the right it might be overloading (although the tial is not really the right shape for that).

Is this a standard or a sample ? How much PAH is in each peak ?

Peter

[envirochem]

Scotty;

Its not first time, I try to find right condition for this analysis but all peaks better when I first run and column was new..My column isnt old too much, may be 3-4 month and not too much used..I use blank every time start and end of sequence..

Peter;

Method run time is 44 mins and actually this kind peaks in the middle of the run..Peaks On the picture almost 17-19 mins..This is mixture PAHs and include 17 PAHs..I try to calibration but my linearity among 0,993 - 0,998. Not bad but not good also..I think peak tail reason for that..

[Peter Apps]

Scotty;

Its not first time, I try to find right condition for this analysis but all peaks better when I first run and column was new..My column isnt old too much, may be 3-4 month and not too much used..I use blank every time start and end of sequence..

Peter;

Method run time is 44 mins and actually this kind peaks in the middle of the run..Peaks On the picture almost 17-19 mins..This is mixture PAHs and include 17 PAHs..I try to calibration but my linearity among 0,993 - 0,998. Not bad but not good also..I think peak tail reason for that..

I need to know whether the tail on the peak is on the front of the peak or on the back of the peak, because front-tailing and back-tailing have different causes. That is why I asked about which way the time scale runs on your picture. The total run time is not relevant. Also I need to know the quantity of PAH in each peak (in nanograms) not the number of PAHs in your mixture.

If the peak shape has deteriorated as the column ages then it suggests that column deterioration might be the cause. Does cleaning the inlet and putting in a new liner make any difference ?

Peter

[envirochem]

Peter,

the tail on the front of the peak..and my calibration range start 0,1 mg/L to 1,0 mg/L..
I didnt clear inlet or change liner yet.

[Peter Apps]

Peter,

the tail on the front of the peak..and my calibration range start 0,1 mg/L to 1,0 mg/L.. so yoou have 2 ng per peak at the top of the calibration. Yes ? This is not enough to cause overloading
I didnt clear inlet or change liner yet.

You need to do inlet maintenance, and then report back to us

There may also be solvent effects - what is the sample/standard dissolved in ?

Peter

[envirochem]

Peter

I dissolved my standard mix in 1/1 Acetone:Dichloromethane..
standard mix originally solve in Dichloromethane..But its volatile than Acetone, and I want to equalize volitale and mix Acetone and Dichloromethane..

[Peter Apps]

Peter

I dissolved my standard mix in 1/1 Acetone:Dichloromethane..
standard mix originally solve in Dichloromethane..But its volatile than Acetone, and I want to equalize volitale and mix Acetone and Dichloromethane..

The mixed solvent might be the problem - what happens if you use only dichloromethane ?

Peter

[envirochem]

Peter

I dissolved my standard mix in 1/1 Acetone:Dichloromethane..
standard mix originally solve in Dichloromethane..But its volatile than Acetone, and I want to equalize volitale and mix Acetone and Dichloromethane..

The mixed solvent might be the problem - what happens if you use only dichloromethane ?

Peter

Actually nothing change but I choose acetone or acetonitrile when I prepare my calibration standards.
Bcz dichloromethane more fluidly than these solvents, cause low viscosity..I cant take true value with pipette when I use dichloromethane.

[Peter Apps]

So if it not the mixed solvent that is causing the peak distortion, the next step is to do inlet maintenance.

Peter