cysteine by gc/ms
Posted: Thu Sep 17, 2009 10:03 pm
I am working on a method: analysis the N (O, S)-ethoxycarbonyl ethyl ester derivative (C2H5OOCSCH2C(HNCOOC2H5)COOC2H5)of cysteine (HO2CCH(NH2)CH2SH) by Saturn2000 GC/MS.
The derivatization procedure is as following:
100ul of cysteine std solution, add 50ul ethyl chloroformate, add 200ul ethanol: pyridine (4:1) and mixed for 5s. The derivatives were extracted with 1000ul chloroform. 1ul from chloroform layer was injected into GC/MS
GC/MS conditions:
The column: DB-5MS 25m x0.20mm
Carrier gas: helium, 1ml/min
Injector: 250°C
Oven temp: 100C to 240°C at 25°C /min
Transfer line temp: 250°C
Trap temp: 150°C
Manifold Temp: 40°C
My problem is the reproducibility. First inject I get 450000 area counts. Then I will get only 110000, 64000, and 28000; soon I cannot see any of peaks. After I clean the ion trap. I can my peaks again.
What do you think the problem is? Any temperature zone set wrong?
The derivatization procedure is as following:
100ul of cysteine std solution, add 50ul ethyl chloroformate, add 200ul ethanol: pyridine (4:1) and mixed for 5s. The derivatives were extracted with 1000ul chloroform. 1ul from chloroform layer was injected into GC/MS
GC/MS conditions:
The column: DB-5MS 25m x0.20mm
Carrier gas: helium, 1ml/min
Injector: 250°C
Oven temp: 100C to 240°C at 25°C /min
Transfer line temp: 250°C
Trap temp: 150°C
Manifold Temp: 40°C
My problem is the reproducibility. First inject I get 450000 area counts. Then I will get only 110000, 64000, and 28000; soon I cannot see any of peaks. After I clean the ion trap. I can my peaks again.
What do you think the problem is? Any temperature zone set wrong?