Teledyne Tekmar Versa - Mass Balance Equation Restated; Sampling

Versa User Manual www.teledynetekmar.com
Mass Balance Equation Restated
M
O
= M
G
+ M
M
M
O
= C
O
*
V
M
M
G
= C
G
*
V
G
M
M
= C
M
*
V
M
C
O
*
V
M
= (C
G
*
V
G
) + (C
M
*
V
M
)
C
O
*
V
M
= (C
G
*
V
G
) + (K
*
C
G
*
V
M
)
C
O
= ((C
G
*
V
G
) / V
M
)+ ((K
*
C
G
*
V
M
) / V
M
)
C
O
= ((C
G
*
V
G
) / V
M
)+ K
*
C
G
C
O
= C
G
((V
G
/ V
M
)+ K)
V
G
/ V
M
= Phase Ratio
The system’s sensitivity for an individual compound is directly aected by two factors, the partition coecient and
the phase ratio (Volume of the Gas phase vs. Volume of the Matrix). The K value can be improved by changing the
matrix conditions forcing more compound into the gas phase thus allowing more mass to be transferred on-column.
In situations where the K value is low, the phase ratio can dominate the bottom term of the concentration equation
making it possible to change the concentration in the gas phase by decreasing the gas volume in the vial. This will
result in a denser mass or higher concentration in the gas phase for injection.
Sampling
Once the vial has reached equilibrium the sample is ready to be prepared for injection. The vial is raised onto a needle
and a small amount of gas is added to the vial to pressurize it prior to sampling. Once the vial is pressurized, a solenoid
valve is opened to allow sample gas to ow through a 6-port valve and loop. The solenoid valve is then closed and the
sample gas volume is trapped in the loop.
Since the sample is a gas, it is compressible thus sensitivity is directly aected by the Universal Gas Law.
PV=nRT
P = Pressure
V = Volume
n = Number of Moles
R = Universal Gas Constant
T = Temperature
The Universal Gas Law states that the number of moles in a system is a function of the temperature, pressure and
volume of that system. The number of moles is equal to the mass in this gas system.
n= PV /RT
Introduction • Page 1-6