Preparation,stability and acidity of difluoromethylene bis phosphonic acid

Hydrolysis of difluoromethylene phosphonate esters quantitatively yields difluoromethylene $\text{bis}$ phosphonic acid as a dihydrate. $\text{In vacuo}$ drying leads to either the monohydrate or the anhydrous acid. Titration of either the free acid or its disodium salt and computer fit of the data gives all four pKas. The disodium salt and the free acid are thermally stable, and the disodium salt is extremely stable even to strong base.     

Enzyme electrode for the determination of salicylate

Salicylate hydorxylase is used with a carbon dioxide sensor for the determination of salicylate in aqueous solution and pooled serum. The enzyme is physically entrapped with a dialysis membrance at the sensing tip of the carbon dioxide electrode. The enzyme catalyses the stoichiometric formation of catechol and carbon dioxide from salicylate and reduced pyridine nucleotide in the presence of flavin adenine dinucleotide as a specific cofactor. The carbon dioxide is detected by the sensor and related to the concentration of salicylate via a calibration curve. The method compares favorably with the spectrophotometric method for assay of salicylate. Although suitable for salicylate concentrations in the range of 5–300 μg ml^?1, its response below 5 μg ml^?1 is limited by the detection limit of the carbon dioxide sensor.     

Amperometric determination of sulfite with sulfite oxidase immobilized at a platinum electrode surface

Sulfite oxidase is immobilized on collagen membrane at the surface of a platinum electrode and catalyzes the oxidation of sulfite to sulfate with stoichiometric production of hydrogen peroxide. The hydrogen peroxide is detected amperometically at the platinum electrode at an applied potential of 700 mV. The system responds linearly to sulfite in the range 1–150 μM, with a detection limit of 0.2 μM. The enzyme retains over 95% of its activity for three weeks if stored at ?20° C when the probe is not in use.     

Comparative study of potentiometric and amperometric tissue-based electrodes for oxalate

Acetone-precipitated pulp from banana skins is physicall entrapped at the tip of a carbon dioxide gas-sensor and on a hydrogen peroxide sensor probe to determine oxalate potentiometrically and amperometrically in aqueous solution and inurine. The enzyme present in the tissue is oxalate oxidase. The potentiometric response has a slope of 47–50 mV/decade for 1 × 10^?4 M–2 × 10^?3 M oxalate with a detection limit of 2 × 10^?5 M. The amperometric response is linear for 2 × 10^t-5–3 × 10^?4 M oxalate with a dectection limit of 2 × 10^?6 M. Average recoveries of oxalate added to aqueous samples were 96.2% and 98.0%, and average relative standrd deviations were 3.8% and 3.6% for the potentiometric and amperometric systems, respectively. Oxalate was determined in six control urine samples, with relative errors of about 2.5%, by both electrode systems after a simple clean-up.