Highly selective potentiometric and colorimetric determinations of cobalt (II) ion using thiazole based ligands

New PVC-membrane electrodes were prepared by using 2-((thiazol-2-ylimino)methyl)phenol (L1) and 2-((thiazol-2-ylamino)methyl)phenol (L2) and explored as Co(II) selective electrodes. The effect of various plasticizers and anion excluder was studied in detail and improved performance was observed. It was found that the electrode based on L1 shows better response characteristics in comparison to L2. Optimum performance was observed for the membrane electrode having a composition of L1:NaTPB:DBP:PVC ≡ 2:8:78:62 (w/w, mg). The performance of PME based on L1 was compared with that of CGE. The electrodes exhibit Nernstian slope for Co(II) ions with a limit of detection of 6.91 × 10− 7 mol L− 1 for PME and 7.94 × 10− 8 mol L− 1 for CGE. The response time for PME and CGE was found to be 15 s and 12 s respectively. The potentiometric responses are independent in the pH range 3.0–9.0 for CGE. The CGE could be used for a period of 90 days. The CGE was used as an indicator electrode in potentiometric titration of EDTA with Co2 + ion. Further the selectivity of the L1 and L2 was also confirmed by the UV–vis and colorimetric studies and found that L1 is more selective for Co(II) ion.