3 Reasons why syringes are the preferred sample collection vessel for tests of pH, dissolved oxygen & carbon dioxide

 

TIME

Dwell time between sample collection and analysis allows for the production or consumption of gases by the cells in the sample. As cells consume O2 and produce CO2 during sample preparation, pH will shift from actual conditions in the vessel yielding a misleading result.

Collecting the sample directly in the syringe allows for quick dispensing into analyzer insteading of aliquoting volumes from a larger collection vessel.

 

DEGASSING

All plastics allow some gas transmission. Syringes are constructed of thick walled rigid plastic so the transmission rate is slowed. Degassing occurs where the fluid is in contact with the plastic. Cylinders, like a syringe, provide the greatest volume with the lowest surface area and thus the lowest O2 and CO2 transfer.

 

BOUND OXYGEN

Oxygen in air binds to the plastic of a sample collection vessel prior to collecting the sample. Most cell cultures have a much lower O2 saturation rate (20% to 50%) than is found in air. When fluid enters the sample collection vessel oxygen moves from higher to lower concentration and the O2 saturation level can be artificially inflated in the sample collected. Collection vessels with lower surface areas will contribute less oxygen.

 

The surface area and construction of the syringe effects sample accuracy. The table below demonstrates constancy of surface area of syringes compared to sampling bags.

 

Table 1: Liquid Volume and Surface Area

 

 

10mL Syringe

50mL Bag

Volume of Liquid Analyzed

 

Surface Area cm3

Surface Area to Volume

Surface Area cm3

Surface Area to Volume

1

 

3.08

3.08

424

424.00

2

 

6.16

3.08

424

212.00

3

 

9.24

3.08

424

141.33

4

 

12.33

3.08

424

106.00

5

 

15.41

3.08

424

84.80

6

 

18.49

3.08

424

70.67

7

 

21.57

3.08

424

60.57

8

 

24.65

3.08

424

53.00

9

 

27.73

3.08

424

47.11

10

 

30.82

3.08

424

42.40

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