The equation below represents how the conductance of a sensor changes with respect to a change in carbon dioxide level:
$$\text{Conductance} = A + Bx - Bx e^{-Ct}$$
where $A,B,C$ are constants, $x$ is the concentration and $t$ is the time.
Question is how to represent this formula using a transfer function so that a change in conductance can be observed due to a change in concentration?
The only thing I can say is that the transfer function is the ratio between the output and the input in a system. This mean if you call $\rho$ the conductance and $x$ the concentration, you have: $$H(s)=\frac{\rho(s)}{x(s)}$$ So you get: $$H(s)=\frac{As+AC+BCx}{xs(s+C)}$$ considering you did the Laplace transform respect to the time $t$. If you have an input $x(t)$, your output will be: $$\rho(s)=H(s)x(s)$$