Comparative study of the zero-crossing, ratio spectra derivative and partial least-squares methods applied to the simultaneous determination of atrazine and its degradation product desethylatrazin-2-hydroxy in ground waters.

The application of the ratio spectra derivative and partial least-squares methods to the simultaneous determination of atrazine and its degradation product desethylatrazin-2-hydroxy is presented. When the different methods are applied to the determination of these products in ground waters, PLS method gives the best results due to the presence of interfering substances with overlapping spectra.

On the determination of the free concentration of ligands.

Working with a sufficient excess of any of the protonated forms of a ligand is shown to guarantee the validity of the determination of its free concentration when calculated by disregarding complexing effect. This result significantly extends the possibilities of studying the stability constants of co-ordination systems.

Complexation equilibria between niobium(V) and 4-(4'H-1',2',4'-triazolyl-3'-azo)-2-methylresorcinol Extraction-spectrophotometric determination of niobium in pyrochlore-bearing rocks.

The complexation equilibria between niobium(V) and 4-(1'H-1',2',4'-triazolyl-3'-azo)-2-methylresorcinol has been studied by spectrophotometric methods and graphical and numerical calculation methods. The 1:2 Nb:R complex species formed at pH 6.2 ( = 2.