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Water for VOC Analysis


Water may be used to rinse the sample containers, in the various sample preparation steps, as well as in the preparation of standards and blanks for the analysis. Gas chromatography (GC) using purge and trap is often used for these analyses.

The following water contaminants may interfere with VOC analysis:

  • Organics
    Organic molecules, in particular volatile organics (VOC) present in the water used to prepare or analyze the samples may interfere with VOC analysis by contributing a high background and possibly affecting selectivity and sensitivity.
  • Chlorine
    Some VOCs, in particular aromatic compounds, may react and be degraded by chlorine.
  • Bacteria
    Bacteria may degrade some VOCs and should therefore be avoided. They may also release some small organics that may interfere with VOC analysis.

Preparing VOC-free water using an activated carbon point-of-use purifier

Ultrapure water was spiked with various VOCs at a concentration of approximately 1 ppb (1 µg/L). The water was passed through a specific activated carbon cartridge (VOC-Pak) and the concentration of each VOC was measured at the outlet of the cartridge. The VOC analysis was performed using a Purge & Trap GC-MS system.

The results are shown in the table below:

VOC tested
Challenge (ppb) (*)
Limit of quantification (ppb) (**)
Concentration after VOC-Pak (ppb) (***)
benzene
0.97
0.05
<0.05
bromodichloromethane
1.56
0.05
<0.05
bromoform
1.58
0.50
<0.50
carbon tetrachloride
1.06
0.05
<0.05
chlorobenzene
0.94
0.05
<0.05
chloroform
1.07
0.05
<0.05
dibromochloromethane
1.01
0.10
<0.10
1,2-dichlorobenzene
1.01
0.05
<0.05
1,4-dichlorobenzene
1.53
0.05
<0.05
1,2-dichloroethane
1.08
0.05
<0.05
1,1-dichloroethene
0.87
0.05
<0.05
cis-1,2-dichloroethene
0.95
0.05
<0.05
trans-1,2-dichloroethene
1.53
0.05
<0.05
1,2-dichloropropane
0.86
0.05
<0.05
cis-1,3-dichloropropene
0.97
0.04
<0.04
trans-1,3-dichloropropene
0.91
0.05
<0.05
ethylbenzene
1.09
0.05
<0.05
tetrachloroethene
1.44
0.05
<0.05
toluene
0.96
0.10
<0.10
1,1,1-trichloroethane
0.94
0.10
<0.10
1,1,2-trichloroethane
0.93
0.05
<0.05
trichloroethene
1.02
0.05
<0.05
o-xylene
0.79
0.05
<0.05
m-xylene
1.02
0.05
<0.05
p-xylene
0.94
0.05
<0.05
(*) Challenge = VOC concentration in feed water upstream of the VOC-Pak cartridge
(**) Limit of quantification of the VOCs measured by GC-MS
(***) Concentration of VOCs downstream of the VOC-Pak

Conclusion

Ultrapure water should be used for VOC analysis. Using the VOC-Pak cartridge at the point of use of the water purification system (producing water with a resistivity of 18.2 MΩ.cm at 25 °C and TOC < 5 ppb) can ensure that the VOCs listed in the table are below the analytical quantification limits listed.

     
 

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