The fluoride ion-selective electrode in flow injection analysis

Integrated, paper-based potentiometric electronic tongue for the analysis of beer and wine

The following manuscript details the stages of construction of a novel paper-based electronic tongue with an integrated Ag/AgCl reference, which can operate using a minimal amount of sample (40 μL). First, we optimized the fabrication procedure of silver electrodes, testing a set of different methodologies (electroless plating, use of silver nanoparticles and commercial silver paints). Later a novel, integrated electronic tongue system was assembled with the use of readily available materials such as paper, wax, lamination sheets, bleach etc. New system was thoroughly characterized and the ion-selective potentiometric sensors presented performance close to theoretical. An electronic tongue, composed of electrodes sensitive to sodium, calcium, ammonia and a cross-sensitive, anion-selective electrode was used to analyze 34 beer samples (12 types, 19 brands). This system was able to discriminate beers from different brands, and types, indicate presence of stabilizers and antioxidants, dyes or even unmalted cereals and carbohydrates added to the fermentation wort. Samples could be classified by type of fermentation (low, high) and system was able to predict pH and in part also alcohol content of tested beers. In the next step sample volume was minimalized by the use of paper sample pads and measurement in flow conditions. In order to test the impact of this advancement a four electrode system, with cross-sensitive (anion-selective, cation-selective, Ca(2+)/Mg(2+), K(+)/Na(+)) electrodes was applied for the analysis of 11 types of wine (4 types of grapes, red/white, 3 countries). Proposed matrix was able to group wines produced from different varieties of grapes (Chardonnay, Americanas, Malbec, Merlot) using only 40 μL of sample. Apart from that, storage stability studies were performed using a multimeter, therefore showing that not only fabrication but also detection can be accomplished by means of off-the-shelf components. This manuscript not only describes new paper-based, potentiometric sensors but also according to our knowledge is the first description of an electrochemical paper-based electronic tongue with integrated reference.

BF3/MCM-41 as nano structured solid acid catalyst for the synthesis of 3-iminoaryl-imidazo[1,2-a]pyridines

Multi-component reaction of various types of aldehydes, 2-aminopyridines and trimethylsilyl cyanide was carried out in the presence of MCM-41 supported boron trifluoride (BF₃/MCM-41) as a nanostructured solid acid catalyst for the synthesis of 3-iminoaryl-imidazo[1,2-a]pyridine derivatives.

Spectrophotometric determination of fluoride in dosage forms and dental preparations

The method is based upon the reaction between fluoride ions and the coloured complex of Fe(III) with methyl salicylate to form the stable, colourless hexaflouride complex of iron. The conditions of the method (pH, time and combination ratio) were studied and a standard curve was obtained for 0.01-0.08 mg NaF ml-1, at 525 nm. A study was conducted on interference with complexing anions of Fe(III), cations that react with fluoride ions and with common ingredients of dosage forms and dental preparations. The method was validated and the results showed good precision (100.16 +/- = 2.33%) comparable with that of other analytical methods. Good results were obtained in the spectrophotometric determination of fluoride ions in a stomatological gel and in a toothpaste.