Studies on nessler's reagent and nessler's precipitate part II

The composition of the precipitate formed when the Nessler's reagent is treated with ammonia, is assumed as NH_n-1Hg₂I_n, aq. and has been studied potentiometrically from iodine-hypoiodite-system. It has been observed that the value of n depends on the concentrations of [HgI₄]^-2 and OH^- ions as well as on the amount of ammonia added and it may vary from 1 to 3. The colour of the precipitate deepens from brown to chocolate as the value of n increases.     

Sensitized schiff's reagent as an acid-base indicator

The sensitized Schiff's reagent has been used as an indicator in the neutralization of strong acids by means of strong or weak bases. (1) Since the acid to alkali transition is much sharper than the reverse process, the titration is best done by adding alkali to the acid. (2) The results are compared with those of titrations using methyl orange as indicator. (3) The end-point is very sharp with sensitized Schiff's reagent, the transition taking place from a dull red colour to an abrupt rise in intensity. (4) Acids which are comparable in strengths or weaker than H₂SO₃ cannot be titrated with this reagent as indicator.     

Spectrophotometric study of the compounds obtained with schiff's reagent and acetaldehyde

Five different compounds have been identified spectrophotometrically in the reaction between acetaldehyde and Schiff's reagent.It has been found that, with a small amount of acetaldehyde, a complex with only one molecule of acetaldehyde for every molecule of the reagent is formed. This shows the peak at 545 mμ.With excess of acetaldehyde, the complex contains two molecules of aldehyde per molecule of Schiffs reagent, corresponding to the peak at 555 mμ. After standing for some time, the solution containing this compound, gradually shows the presence of three new compounds, having peaks at 525 mμ, 575 mμ and 615 mμ. The former results from the interaction of two molecules of acetaldehyde and a molecule of fuchsin derived from Schiff's reagent itself. The other two are formed when the former loses one and two water molecules, respectively.     

Spectrophotometric method for the estimation of ammonium acetate with sensitized schiff's reagent

A spectrophotometric method has been described for the estimation of ammonium acetate with the help of sensitized Schiff's reagent. 1) Ammonium acetate restores the colour of fuchsin from the Schiff's reagent as shown by the same absorption maxima at 535 mμ of the coloured compound and fuchsin. 2) Standard curves of optical density versus concentration of ammonium acetate with different sets of sensitized Schiff's reagent having varying SO₂ contents have been presented. 3) There is a limit of ammonium acetate concentration beyond which the sensitivity considerably decreases. 4) Appropriate amounts of acetone along with a particular set of sensitized Schiff's reagent make the latter useful for different sensitive ranges of concentrations of ammonium acetate. 5) The method may be extended in its scope for the estimation of ammonium salts of other organic acids which are weaker than H₂SO₂.     

Fenton’s reagent for kinetic determinations

The use of the Fenton’s reagent (FR) (a mixture of H₂O₂ and Fe²⁺) for the kinetic determination of individual chemical species is proposed. The possibilities of the reagent arise from the oxidant power of intermediate species generated during the slow oxidation of Fe²⁺ by H₂O₂, but very few analytical applications of the reagent can be found. The oxidation of organic compounds (known as the Fenton reaction) is in fact an induced chain reaction that proceeds to an extension which is influenced by the reaction conditions. Experimental design has been used for optimization thinking of the analytical application. The pesticide atrazine has been used as analyte to test the analytical possibilities of the FR. Partial least squares regression (PLS), applied to reaction profiles between 206 and 270 nm, was used as algorithm to make the calibration model. Atrazine concentrations ranging from 0.46 to 13.4×10⁻⁵ M have been used for calibration, and mean errors under 2.5% both for calibration and validation have been found. Other classical methods of calibration such as those using absolute values of absorbance, initial rates, etc. gave poor results in the cases considered. According to the study of interferences, the main drawback of the reagent is the lack of selectivity, but some possible ways of improving it are discussed. The method was applied for the determination of atrazine in several commercial atrazine-based pesticide preparations. In general, good results were obtained when compared with those found by gas-liquid chromatography as a reference. Recovery studies also gave satisfactory results.     

Spectrophotometric method for the determination of the relative strengths of organic acids with sensitized schiff's reagent

1. Ammonium salts of the weak acids, oxalic, citric, taitaric, formic, lactic, succinic. acetic, n-butyric and propionic bring colour to sensitized Schiffs reagent. The intensity of the colour thus produced stands in inverse relationship with the dissociation constants of these acids and hence of their strengths. The intensity of colour is dependent on the concentration of the ammonium salts and hence the concent ration of the latter was adjusted to a suitable value, keeping in mind the range of the sensitivity of the reagent itself. 2. The colour produced by the different salts is the same as that of the solution. The probable mechanism appears to be that the ammonium salts react with SO₂ which displaces the acids from the salts. The greater the displacement the greater the intensity of colour and the weaker the acid.