Applicability of hybrid micelle liquid chromatography for practical determination of acid dissociation constant

Figures & data

Figure 1. Sigmoid dependence of retention times of IBU and NPX on pH of the mobile phase at different molar strength of SDS (using 15% 1-propanol, keeping column temperature at 50°C), where A: 0.05 M SDS, B: 0.075 M SDS, C: 0.1 M SDS, D: 0.15 M SDS and E: 0.18 M SDS.

Figure 2. First-derivative curves for the dependence of the retention times of IBU and NPX on pH of the mobile phase at different molar strength of SDS (using 15% 1-propanol, keeping column temperature at 50°C), where A: 0.05 M SDS, B: 0.075 M SDS, C: 0.1 M SDS, D: 0.15 M SDS and E: 0.18 M SDS.

Table 1. Comparison of pKa values obtained by HMLC, reported and practical values using other methodologies.

The studied drug	NPX	IBU	BZA
Practical pKa values applying the proposed HMLC method
Effect of SDS molar strength
0.05	4.3	4	3.6
0.075	4.5	4.1	3.7
0.1	4.6	4.2	3.77
0.15	4.71	4.35	3.87
0.18	4.8	4.5	4
Effect of organic modifier ratio
7	5	4.45	3.75
10	4.8	4.25	3.7
12	4.6	4.2	3.65
15	4.5	4.1	3.55
Effect of column temperature (°C)
25			3.8
30	4	4	3.9
35	4	4.5	3.8
40	4	4.25	3.7
45	4.35	4.15
50	4.5	4.1
Reported pKa values [25]
	4.4	4.4	4.2
Practical pKa values applying other methodologies [1, 24]
	4.16–4.57	4.24–4.52	4.08–4.2

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