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- Posts: 105
- Joined: Sat Feb 02, 2008 12:35 am
Recently we ran into linearity problems when analyze VOCs in soil.
Our system is composed of:
* A GC/MS - DB624 column
<< split 4:1,
<<4.8 ml/min He,
<<35°C init. temp.
<< 1.2kV
<< total flow 24 ml/min
* Atomx purge and trap unit, running in soil mode with the default soil method:
<< Valve temp = 140°C
<< Transfer line = 140°C
<< Sample vial = 40°C
<< Soil valve = 100°C
<< Standby flow = 10ml/min
<<water added = 10mL
<< stirring bar speed = medium.
<<purge time = 11 min
<<purge flow = 40ml/min
<<trap temp = 20°C ( 250°C when desorbing)
<<condensate trap = 20°C
<<dry purge time = 2min
<<dry purge flow = 100 ml/min
<<dry purge temp = 20°C.
* Consider this:
<< We inject 2uL of methanolic standards directly into the GC injection port, 1,2,4,16 & 32 mg/L, linearity....OK.
<<We purge water standards ( Atomx in water mode, 5mL fritted sparger) of 0.2; 1; 2; 5 & 10 ug/L, linearity....OK.
<<Our soil technique is: Add 5mL of water to a 40mL VOA amber vial, then we add a stirring bar.
After that, we inject quickly (under the water level) one vial at a time: 50, 80, 100, 150 & 200 ng from a methanolic standard. Linearity...too bad.
For instance:
Toluene
50ng = 43K area counts
80ng = 47K
100ng = 193K
150ng = 256K
200ng = 189K
Any help would be appreciated.
Best regards.