The second, final part of the review. The use of ionic liquids in voltammetry and amperometry as organic electrolytes for carrying out electrochemical processes, extraction, and voltammetric analysis and for the development of composite materials and the creation of electrochemical sensors is discussed. The most important use of ionic liquids for modifying electrode membranes is considered: as an inert matrices allowing the immobilization of ionophore components and also as ionophore components of membranes of liquid-based and solid-state ion-selective electrodes.

The first part of the review presents general information and brief historical notes about ionic liquids (ILs) along with various versions of microextraction preconcentration using ILs: single-drop extraction, membrane extraction, dispersive liquid–liquid microextraction, in situ ionic liquid-based dispersive microextraction, etc. A review of papers on the extraction of metal ions and organic compounds in ILs for chemical analysis is presented. Aqueous biphasic systems based on ILs immiscible with water and salting-out agents are described; examples of such systems, their advantages, and factors affecting phase separation are considered.

New donor-acceptor 3d-transition metal complexes were synthesized and the cobalt and nickel complexes were studied by X-ray diffraction; CIF files CCDC no. 1516693 (III(Ni)) and 1516694 (III(Co)). The crystal structure details of the reactants were discussed. The proposed compounds were tested as the active components of ion selective electrode membranes for determination of thiocyanate ions. The selectivity of the SCN-SE with metal complex-based membranes depends on the ligand structure and the central metal ion type. The proposed electrode is suitable for determination of thiocyanate ions in the presence of sulfate, chloride, nitrate, nitrite, bromide, and iodide ions.

Phenoxy-substituted boron subphthalocyanine was synthesized and studied as an ionophore of plasticized polyvinyl chloride membranes of ion-selective electrodes. The electrodes exhibit reversible response to dobutamine, demonstrating the cation function, as well as reversible response to the salicylate anion. The effects of concentration of the ionophore (0.2–5 wt %) and ionic components (sodium tetraphenylborate, TPhBNa, and tributylhexadecylphosphonium bromide, TBGDPBr), including ionic liquids (ILs), such as diphenylbutylethylphosphonium bis(triflyl)imide, diphenylbutylethylphosphonium hexafluorophosphate, and 1,3-dihexadecylimidazolium chloride, as well as plasticizers, such as ortho-nitrophenyloctyl ether and diethyl sebacate, on the electrochemical characteristics of membranes were studied. For the electrode containing 2% of the phenoxy-substituted boron subphthalocyanine in dobutamine and salicylate solutions, the slopes of the electrode function were 36 ± 1 mV/dec and–46 ± 3 mV/dec and the limits of detection (LODs) were 4 × 10–5 M and 3 × 10–4 M, respectively. The addition of an ionic liquid containing the diphenylbutylethylphosphonium cation and the bis(triflyl)imide and hexaflurophosphate anions to the membrane composition had no effect on the response of membrane electrodes to both dobutamine and salicylate. The use of phenoxy-substituted boron subphthalocyanine in an amount of 2% and the TPhBNa additive significantly improved sensor characteristics: the slope of the electrode function (S) for the dobutamine-selective electrode was (54 ± 1) mV/dec and LOD was 1 × 10–5 M. Dobutamine can be determined in the presence of dopamine, adrenalin, and glucose. Electrodes based on 2% phenoxy-substituted boron subphthalocyanine and 0.5% (C16H33)2ImCl, or TBGDPBr in salicylate solutions demonstrate the slope of the electrode function close to the theoretical one and a low limit of detection: S = (–59 ± 1) mV/dec, LOD = 2 × 10–5 M and S = (–57 ± 1) mV/dec, LOD = 4 × 10–5 M, respectively. The anti-Hofmeister selectivity of sensors was observed. The electrode based on phenoxy-substituted boron subphthalocyanine and (C16H33)2ImCl was used for the assay of acetylsalicylic acid in the drug Cardiomagnyl.

The possibility of using solid-state and liquid PVC-membrane electrodes based on ionic liquids to design a potentiometric multisensor system is assessed. Ionic liquids with 1,3-dihexadecylimidazolium cation and chloride, bromide, iodide, and nitrate anions are used. The sensitivity parameters of the sensors are determined. A multisensor array is applied to detect chloride and iodide anions in the multicomponent mixture. The designed system is used to discriminate between mineral waters of different compositions by applying the method of principal component analysis (PCA).

Cobalt(II) porphyrazine is synthesized and studied as an active component of a polyvinyl chloride plasticized membrane ion-selective electrodes (ISEs). It is established that regardless of their structure, ISEs are sensitive to iodide. The introduction to the ISE of an ionic additive, ionic liquid 1,3-dihexadecylimidazolium chloride, significantly improves the electrochemical characteristics: the slope of the electrode function reaches −(57 ± 1) mV/dec, c min = 8.3 × 10–6 M. Solid-state screen-printed electrodes the surfaces of which are modified by a 1: 4 mixture of cobalt(II) porphyrazine and ionic liquid 1,3-dihexadecylimidazolium chloride demonstrate satisfactory electrochemical characteristics: the slope of the electrode function is −(56 ± 4) mV/dec and c min = 2.5 × 10–5 M. The potentiometric selectivity of the ISEs for iodide is studied. It is found that the effect of lipophilic interfering ions is significantly lower for solid state ISEs than for plasticized membrane electrodes.

An ion-selective electrode based on tetraoctylammonium N-lauroyl sarcosinate ionic liquid, which is solid at room temperature, is responsive to anionic forms of amino acids. Preconditioning in copper sulfate solution and the introduction of more high-melting and hydrophobic ionic liquid (1,3-dihexade-cylimidasolium bromide) allowed the limit of detecting phenylalanine to be lowered by several times (c min = 2.7 × 10–5 M) and significantly improves the service life of the ion-selective electrode. The possibility was shown for using two ionic liquids for designing ISE with one of them that serves as an inert solid matrix for immobilizing the second one, which in turn ensured the analyte binding and the generation of a potentiometric signal.

In this study screen-printed solid-state electrodes using low-melting ionic liquids with cation of 1,3-dihexadecylimidazolium and such anions as chloride, iodide, and thiocyanate were developed. Potentiometric response and electrochemical characteristics of ion-selective electrodes in KCl, KI, and KSCN solutions were studied. All sensors exhibited sensitivity toward the corresponding anions, the slopes close to Nernstian ones, low detection limits (3.0∙10−6M for SCN−), and high selectivity in the presence of the extraneous anions. Operation time of the sensors was not less than one year. The applicability of the developed electrodes for the potentiometric determination of iodide in pharmaceuticals and thiocyanate in human saliva was demonstrated.

Nickel(II), manganese(III), and magnesium(II) porphyrazines are synthesized and investigated as active electrode components of polyvinyl chloride plasticized membranes for ion-selective electrodes ( ISE ). The potentiometric response of membranes based on metalloporphyrazines doped with 1,3-dihexadecylimidazolium chloride (ionic additive) relative to benzylpenicillin and iodide anions is studied. It is found that the introduction of the ionic additive significantly improves the electrochemical characteristics of the ISE: the slope of the electrode function in benzylpenicillinate solutions is (58 ± 7) mV/dec and c min = 7 × 10 −5 M, and in iodide solutions, (55 ± 2) mV/dec and c min = 6 × 10 −6 M. It is shown that the ISE based on manganese(III) porphyrazine with an ionic additive can be used to determine iodide in Iodinol preparation.

To improve the electrochemical performance of solid-state printed electrodes, reduced graphene oxide is used as an intermediate layer (mediator) between the surface layer of a current collector and the ionophore layer. A graphene oxide film was deposited onto the surface of printed electrodes by drop-casting, followed by reduction and electrochemical deposition. An ionic liquid 1,3-dihexadecylimidazolium bromide served as ionophore. The effect of reduced graphene oxide on the characteristics of the ion-selective electrode is studied, and it is shown that the sensors electrochemically modified with reduced graphene oxide have the best performance. These sensors exhibit a stable, well-reproducible response to bromide ions with the slope of the electrode function close to the Nernstian value (−60.7 ± 0.7 mV/dec) and a low detection limit of 3.6 × 10−6 M. The response time for all of the electrodes does not exceed 15 s even in dilute solutions.