ANKOM RF - Manual (Page 46)

Operator’s Manual
pg. 46
Rev F 8/29/14
Appendix D – Conversion of Pressure to Gas Production
Calculation of Gas Produced in ml at 39°C with pressure measured in psi
The ANKOM
RF
Gas Production System is configurable to allow for gas pressure measurements in either psi or
mbar units. For the purposes of this discussion, we will refer to gas pressure measurements in psi.
The gas pressure measured during your study can be converted to moles of gas produced using the ‘ideal’ gas
law, and then converted to milliliters
(ml) of gas produced using Avogadro’s law.
‘Ideal’ gas law
n = p (V/ RT)
Where: n = gas produced in moles (mol)
p = pressure in kilopascal (kPa)
V = head-space volume in the Glass Bottle in Liters (L)
T = temperature in Kelvin (K)
R = gas constant (8.314472 L·kPa·K -1 ·mol -1 )
Avogadro’s law
Using Avogadro’s Law, at atmospheric pressure measured in psi (1 psi = 6.894757293 kilopascal) 1 mole will
occupy 22.4 L at 273.15°K and 101.325 kPa (standard conditions). Therefore, gas measured in moles can be
converted to gas measured in ml
as follows:
gas produced in ml = n x 22.4 x 1000
ANKOM
RF
Gas Production System – Glass Bottle Volume Capacity
The actual volume capacity of each glass bottle is greater than its rated volume capacity. Therefore, use the
following Actual Volume Capacity for the specific bottle used in your study.
Rated Volume Capacity (ml) Actual Volume Capacity (ml)
250 310
500 620
1000 1140
1800 1870
Example
The Cumulative Pressure measured by the ANKOM RF Gas Production System is 10 psi at 39°C.
The Glass Bottle in the study is rated at 250 ml (actual volume capacity is 310 ml).
The sample/solution/buffer uses 150 ml of the Glass Bottle.
The head-space volume in the Glass Bottle is 310 ml - 150 ml = 160 ml = 0.16 L.
p = 10 psi x 6.894757293 kPa = 68.94757293 kPa
V = 0.16 L
R = 8.314472 L·kPa·K
-1 ·mol -1
T = 273°K + 39°C = 312°K
n = p (V/ RT)
n = 68.94757293 kPa x [0.16 L / (8.314472 L·kPa·K
-1 ·mol -1 x 312°K)]
n = 0.004252553 mol
gas produced in ml = 0.004252553 mol x 22.4 L/mol x 1000 ml/L
gas produced in ml = 95.25717874 ml