Mercury selective electrodes using dimethylsulphoxide carrier

Mercury [II] ion-selective PVC membrane sensor based on dimethylsulphoxide [DMSO] as a novel oxygen and sulfur containing sensing material was successfully developed. This reagent has the advantage of low cost and simple chemical material. Dioctylphthalate [DOP] solvent could be selected from different solvents used. DOP was found to play an important role in directing selectivity. A sodium tetraphenylborate [NaTPB] as a lipophilic salt and KCI solution of 10[-1] M as an inner solution also have been chosen. The sensor exhibited a good linear response of 30 +/- 0.2 mV per decade within the concentration range 10[-8] - 10[-2] and detection limit 0.9 x 10[-8] mol 1[-1] Hg [II]. Also, it showed good selectivity and fast response for mercury [II] ion with relation to some alkali, alkaline earth, transition and heavy metal ions. DMSO-based sensor was suitable for aqueous solutions of pH range 1.5 to 4.0. Moreover, it can be used for three months without any considerable divergence in potential. The formation constant of ionophore complex with Hg [II] ion was calculated by using segmented sandwich membrane method. The proposed sensor was applied as an indicator electrode for potentiometric titration of Hg [II] ion with EDTA solution, as well as with I[-], OH[-] and IO3[-] ions. In addition, the solubility products for the previous ions were determined

Polarographic behaviour of mononitrophenols in aqueous buffered solutions

The electroreduction of o-m- and p- nitrophenol has been extensively studied using the dropping mercury electrode. It was shown that in acid media, nitrophenols generally produce along two polarographic steps. The first is usually well-defined, and is attributed to the reduction of the nitro group to the corresponding hydroxylamine via a four-electron process. The second step usually somewhat drawn-out, is ascribed to further reduction to the amine via a two-electron transfer process. In alkaline media, on the other hand, the three isomers, are reduced quite differently

Effect of proton donors and proton acceptor on the Polarographic reduction waves of o-,m- and p- nitrophenol in methanolic media

The polarographic behaviour of o, m- and p-nitrophenol is studied in methanolic solutions. Due to the poor proton availability of this medium reduction of part of the depolarizer proceeds with the uptake of the necessary protons from the other part. The anions thus formed are reduced along a second, more negative wave. This conclusion was supported through study on the effect of addition of acid proton donors [mono-and poly percent weak and strong acids], basic proton donors [e.g. [NH4]2CO3] or proton acceptor [e.g. NaOH]. The results were interpreted on the basis of Ruetschi and Trumpier's theory of H[+] ion impoverishment in the reduction layer. In presence of sodium hydroxide, reduction occurs in a single wave, at negative potentials, due to the ionization of the phenolic groups of the depolarizers. The difference in the behaviour of the three isomers is discussed