sampling volume guidelines


 

MEMORANDUM

 

 

To: AIR QUALITY CONSULTANTS From: John Sliwinski

OSB Lab

 

Re: Sampling Volumes Guidelines                             Date: 15 February 2002


 

 

Multisorbent and VOST Tubes

 

Suggested sampling volumes for sorbent tubes ATD-GC/MSD for a large number of proportionally represented chemicals.

 

TVOCs

SAMPLING VOLUME (L)

GC/MSD

mg/m3

FID

ppm

(Propane)

Range

Maximum

Split Maximum

0.5 1.0

0.2

20 - 30

50

None 1:1

5

2

5 - 10

20

None 1:1

15

6

5 - 10

20

1:3 1:4

25

10

5 - 10

10

1:3 1:4

100

40

1 - 3

5

1:3 1:4

500

200

0.1 0.5

1

1 1:10

 

 

It is difficult to generally predict how a sample concentration chromatographs without prior characterization. A concentration of 25mg/m3 of a single peak requires much less volume to prevent saturation than 25mg/m3 of 250 peaks that are proportionally represented.

 

Split ratios greater than 10 are not recommended due to degeneration of method accuracy and losses in overloaded tubes.

 

 

 

 

 

Charcoal Tubes

 

Charcoal tubes are used where concentrations exceed 100mg/m3 and larger sample volumes need to be taken for representative sampling. Present methods use a CS2 extraction volume of 2.0mL or 4.0mL and a standard injection of 1L. The smallest syringe that can be used is 0.5L range and can deliver 0.05L with reasonable precision.

 

TVOCs

SAMPLING VOLUME (L)

GC/MSD

mg/m3

FID

ppm

(Propane)

Range

Maximum

L

(4000 Dilution)

100

50 - 300

50 - 200

200

1

500

250 - 1500

30 - 100

200

0.5 - 1

1000

500 - 3000

30 - 50

100

0.5 1

2000

1000 - 6000

10 - 30

50

0.5 - 1

5000

2500 - 15000

5 - 30

50

0.5 1

10000

5000 - 30000

5 - 10

20

0.5 - 1

 

 

Gas Bags

 

Gases with high concentrations can be sampled with Tedlar bags where routine injections range 0.01mL to 300mL. The net concentration analyzed overlaps with the charcoal method but permits determination of low boiling fractions lost in the CS2 method. High boiling organics tend to be lost (deposited) in gas bags. Larger volumes are not usually sub-sampled due to artifacts NNDMA and Phenol leaching from bags and producing large peaks.

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