Analytical & Bioanalytical Electrochemistry
Volume:1 Issue: 2, Jun 2009

The use of the recently synthesized pyridine-containing thia-aza macrocycle 2,8-dithia-5-aza-2,6-pyridinophane as an anion receptor in a PVC-membrane based ionselective electrode was studied. The sensor showed selectivity towards perchlorate anions with a linear working range of 2.1×10-7 to 1.3×10-1 M. The characteristic response of the membrane-based perchlorate-selective electrode and the selectivity coefficients towards common diverse ions using dibuthyl phthalate (DBP) as plasticizer were also determined. The proposed electrode showed a near-Nernstian slope with detection limit of 2.0×10-7 M (20 ppb) and was used successfully to determine the perchlorate concentration in drinking water.

The array of chemiresistors coupled with a preconcentrator unit was developed and its recognition capability for benzene, chloroform and carbon tetrachloride was investigated. Some potential polymers were chosen from numerous available polymers according to interaction parameters of polymers and vapors of interest. Principal component analysis (PCA) showed that three of seven polymers could have enough ability to recognize different gas classes. By using hierarchical cluster analysis (HCA) the tested polymers were categorized into three main groups with respect to their recognition ability. Precisely evaluation of obtained results from PCA and HCA showed that the array containing polymers of 75% pheny125% methylpolysiloxane (OV25), poly (epichlorohydrin) (PECH) and poly bis(cyanopropyl)- siloxane (SXCN) were the most proper design for recognition of analytes of interest. The fabricated EN was used successively for target vapors recognition in their different concentrations.

Quantum-chemical calculations {DFT(B3LYP)/6-311+G**} were performed for all possible nine tautomers of neutral purine (P) and its charged radicals, cation (P+•) and anion (P-•), which may be formed in the presence of oxidizing or reducing agents. Comparison of the stabilities orders for the neutral and charged forms shows evidently that one-electron oxidation (P − e → P+•) has no important effect on the tautomeric preferences. The NH tautomer containing the moving proton at the N9 atom predominates for P+• (99.3%) as for P (99.8%). Dramatical changes take place for P-•. One-electron reduction (P + e → P-•) favors the C atoms for the moving proton, particularly at the 6- (72.8%), 8- (26.2%) and 2-position (0.1%), and also the N3 atom (0.9%). Preference of the CH tautomers in the tautomeric mixture of P-• may partially explain synthesis and degradation reactions of purine derivatives.

A polymeric membrane based lanthanum selective electrode was developed using N,N'-1,3-phenylenedimaleimide. The best performance was recorded with a membrane composition of PVC: DBP: Ionophore: NaTPB as 33: 64: 2: 1 (w/w %). The Nernstian slope calculated from the calibration curve for La3+ sensor was 18.1 mV decade-1. The detection limit of the sensor was 3.16×10-9 M, in the linear concentration range of 1.0×10-2-1.0×10-8 M. Selectivity coefficients were calculated using Matched Potential Method. The interaction mechanism of the ionophore with different cations was estimated quantitatively by complex formation constant Kf values and qualitatively by FTIR spectroscopy and UV-Vis. spectrophotometry. The electrode was successfully applied to determine the fluoride content in the mouthwash and toothpaste sample.

Electrocatalytic effect of Alizarine complexon as a homogenous mediator at 0.1 M concentration of phosphate buffer (pH=6.0) is used for the determination of hydroxylamine. The kintic parameters such as rate constant of the electrochemical reaction (k) and electron transfer coefficient (α) were determined by cyclic voltammetry technique. Also, the linear range and detection limit for hydroxylamine were determined by differential pulse voltammetry (DPV) and linear sweep voltammetry (LSV) techniques. The linear range and detection limit of hydroxylamine were 0.050-6.000 μM (with two linear segments) and 0.028 μM respectively, by DPV. The nanomolar detection limit obtained by DPV. The independency of these methods from the interferences, and its ability at removing the effect of most cationic interferences easily are the features of the technique. The described method is simple, sensitive and nonexpensive. The application of this method in measurement of hydroxylamine in real sample is considered in this paper.