Aquacyanocobalt(III)-Cobyrinate as a Key Compound in NO2-Sensitive Polymeric Liquid Membranes

Abstract

Recently, an NO2-sensitive polymeric optode membrane based on an aquacyanocobalt(III)-cobyrinate derivative and a phenoxazine derivative has been introduced. 1 Optical microsensors based on this layer have been produced, characterized and shown to be suitable for application in fire detectors, exhibiting a detection limit of 15 ppb NO2. 2In this study the reaction mechanism which occurs within the NO2-sensitive membrane was investigated in detail. Reactions occurring within the membrane were characterized by determining the reaction products and by modifying the composition of the membrane.Since the polymer membrane only reflects the true situation in equilibrium with NO2 pressure, NMR and MS experiments were not feasible. Therefore, non-destructive investigations had to be performed on-line, during exposure to NO2. A suitable technique would be ATR FT-IR. However, using a commercial device it was found that the method is not sensitive enough to monitor species of interest within a polymeric membrane. In various experiments, though, it was possible to obtain the necessary information with UV/VIS-spectroscopy due to the fact that both membrane compounds are optically active.In sensor technology, the interactions between the interfering species and the sensitive layer have to be studied to specify the selectivity. Unlike sensor schemes which are based only on unspecific acid/base reactions, the sensing scheme proposed here comprises a selective step. The interaction of SO2 with the sensor membrane was investigated and compared with respect to the unique affinity of aquacyanocobalt(III)-cobyrinate for nitrogen dioxide, to characterize the proposed reaction mechanism. Experimental Membrane preparation and reagentsThe NO2-selective liquid polymeric membrane used in this study incorporated 0.13 to 2 weight% of aquacyanocobalt(III)-hepta(2-phenylethyl)cobyrinate perchlorate (nitrite-ionophore I, Fluka Chemie AG, Buchs). The chromoionophores used were ETH 5418 ([11-[(1-butylpentyl)oxy]-11-oxoundecyl-4-{[9-(dimethylamino)-5H-benzo[a]phenoxazine-5-ylidene]amino}-benzenate]) and ETH 7058 (2′,4′,5′,7′-tetraiodofluorescein octadecyl ester) in a concentration of 100 to 400 mol% relative to the cobalt complex. Poly(vinylchloride) (PVC) and DOS (bis(2-ethylhexyl)sebacate) as a plasticizer (Fluka Chemie AG, Buchs) were used as the matrix in a ratio of 1:2.ETH 7058 was synthesized from erythrosin extra bluish (Fluka) and 1-bromooctadecane (Fluka) and purified. 3 The product was further purified with flash chromatography (silica gel 60) using CH2Cl2/acetone/triethylamine (20/5/1) as the eluent. The fraction was treated with 0.01 M HCl and shaken. The organic phase was separated and washed three times with doubly distilled water and dried over MgSO4. After filtration and evaporation of the solvents, the precipitate was dissolved in chloroform and converted into potassium salt by exposure to 0.01 M KOH. Then, the organic phase was dried with MgSO4 and evaporated. The indicator salt obtained was dried at high vacuum.The synthesis of ...

Novel optical NO2-selective sensor based on phthalocyaninato-iron(II) incorporated into a nanostructured matrix

“…The chemical interaction between the specific gas molecule and the selective indicator compound are detected by a change in the optical absorption or emission spectrum. Organometallic complexes which react directly with the target gas are generally more attractive than recognition principles linked to chromoionophores [3,6] since the organometallic complex is generally more stable than the dye. Since, the solubility of a metal complexe within the matrix might be a critical factor, it was proposed to immobilize OMCs to gas permeable support [7].…”

“…However, only a few investigations into the interactions of NO 2 with metal atoms have been reported [8]. In account of transmission measurement in the visible spectrum, an adequate conjugated -system similar to that of the corrin macrocycle is preferred [3,6,7]. Typical representatives of this class of compounds are phthalocyanines (Pc) [7,9].…”