The calculated P values using one-way ANOVA statistical analysis of the results obtained from the optimization study.

Parameter	P value
	Ion exchanger	Plasticizer	Ionophore	Conditioning time	Conditioning solution concentration	Membrane thickness
Slope	<0.0001	<0.0001	<0.0001	0.8058	<0.0001	<0.0001
LOQ	NA	<0.0001	<0.0001	0.6739	<0.0001	<0.0001
r	<0.0001	<0.0001	0.0004	0.3531	<0.0001	<0.0001