A New Potentiometric Ammonium Electrode for Biosensor Construction

Figures & data

Table 1 The membrane compositions of ammonium-ion selective electrodes

	Membrane composition (%)
Membrane components	I	II	III	IV
PVC	30.0	30.0	–	–
Carboxylated PVC	–	–	32.5	31.5
Palmitic acid	3.0	2.0	–	–
Nonactin	3.0	4.0	3.0	4.0
Bis-(2-ethyl)hexyl sebacate DOS	64.0	64.0	64.5	64.5

Figure 1 Calibration curve for ammonium ion. Electrode I: with 3% nonactin prepared by using PVC membrane containing palmitic acid. Electrode II: with 3% nonactin prepared by using carboxylated PVC membrane.

Figure 2 Calibration curve for ammonium sensor. Electrode IV: with 4% nonactin prepared by using PVC membrane containing palmitic acid. Electrode V: with 4% nonactin prepared by using carboxylated PVC membrane.

Table 2 Slopes and linear working ranges of the ammonium electrodes at 20 ± 1°C

Electrodes	Slope (±s)* mV/p[NH4^+]	Linear range
I	58.0 ± 0.1	1.0 × 10^−1 – 1.0 × 10^−6 M
II	54.7 ± 0.2	1.0 × 10^−1 – 1.0 × 10^−6 M
III	57.1 ± 0.1	1.0 × 10^−1 – 1.0 × 10^−6 M
IV	52.5 ± 0.1	1.0 × 10^−1 – 1.0 × 10^−6 M

*s: Standard deviation.

Figure 3 The effect of buffer concentration on ammonium-selective sensors. I and II: electrodes with 3% and 4% nonactin prepared by using PVC containing palmitic acid; III and IV: electrodes with 3% and 4% nonactin prepared by using carboxylated PVC, respectively.

Figure 4 The effect of pH on ammonium sensors. I and II: electrodes with 3% and 4% nonactin prepared by using PVC containing palmitic acid; III and IV: electrodes with 3% and 4% nonactin prepared by using carboxylated PVC, respectively.

Figure 5 The effect of temperature on ammonium-selective sensors. I and II: with 3% and 4% nonactin prepared by using PVC containing palmitic acid; III and IV: with 3% and 4% nonactinprepared by using carboxylated PVC, respectively.

Table 3 Selectivity coefficients of ammonium electrodes

	Selectivity coefficients, KNH4,X
Interference ion	I	II	III	IV
Na^+	1,7 × 10^−2	1,7 × 10^−2	1,7 × 10^−2	1,7 × 10^−2
K^+	1,0 × 10^−1	1,7 × 10^−1	1,3 × 10^−1	1,3 × 10^−1
Li^+	2,2 × 10^−2	1,8 × 10^−2	2,3 × 10^−2	1,9 × 10^−2
Ca^2+	1,5 × 10^−2	1,6 × 10^−2	2,7 × 10^−2	3,3 × 10^−2

Figure 6 Lifetime of the ammonium sensors. I and II: electrodes with 3% and 4% nonactin prepared by using PVC containing palmitic acid; III and IV: electrodes with 3% and 4% nonactin prepared by using carboxylated PVC, respectively.