Effects of reducing reagents and temperature on conversion of nitrite and nitrate to nitric oxide and detection of NO by chemiluminescence

To measure the concentration of nitrites and nitrates by chemiluminescence, we examined the efficiency of five reducing agents [V(III), Mo(VI) + Fe(II), NaI, Ti(III), and Cr(III)] to reduce nitrite (NO2−) and (or) nitrate (NO3−) to nitric oxide (NO). The effect of each reducing agent on the conversion of different amounts of NO2− and (or) NO3−(100–500 pmol, representing concentrations of 0.4 to 2 μmolar) to NO was determined at 20 °C for NO2− and at 80 °C for NO3−. The effect of temperature from 20 to 90 °C on the conversion of a fixed amount of NO2− or NO3− (400 pmol or 1.6 μmolar) to NO was also determined. These five reducing agents are similarly efficient for the conversion of NO2− to NO at 20 °C. V(III) and Mo(VI) + Fe(II) can completely reduce NO3− to NO at 80 °C. NaI and Cr(III) were unable to convert NO3− to NO. Increased temperature facilitated the conversion of NO3− to NO, rather than that of NO2− to NO. We evaluated the recovery of NO2− and NO3− from plasmas of pig and of dog. Recovery from plasma of both animals was reproducible and near quantitative.

Vanadium compounds in reductimetric titrations-II Standardisation of vanadium(II) sulphate with common oxidising agents and determination of binary mixtures

Methods for the standardisation of vanadium(II) sulphate are described. With weak oxidising agents, e.g., Fe(III)/Fe(II) in phosphoric acid, vanadium(II) undergoes a one-electron change, which is satisfactorily indicated by Neutral Red, Phenosafranine or Safranine T, or by potentiometry. Stronger oxidising agents oxidise vanadium(II) to vanadium(IV); Variamine Blue, Methylene Blue, o-dianisidine, cacotheline, ferroin, bis(alpha,alpha'-bipyridyl)iron(II) and ammonium molybdate are satisfactory indicators. Binary mixtures of oxidising agents can be determined.