Aplicaciones analíticas de la reacción entre el azul Nilo y el anión hipofosfito. Determinación cinética de poladío y oro

In a 0.75 M sulphuric acid médium, the oxazinic dyestuff Nile Blue (C.L 51180) is not reduced by HzPO; (0,1 M) at appreciable rate. Palla used for the kinetic determination of the metalHc ion (0.30-2.50 p.p.m.). The reaction is followed spectrophotomietrically measuring the decrease of the absorbance due to Nile Blue at 640 nm. Variables that influence the heterogeneous catalytic process and the effect of some foreign ions are studied. As a consequence a new kinetic method for Au(III) determination is also presented. It is based on the apparition of an induction period in the reaction between Nile Blue and hypophosphite catalysed by Pd(II). The length of the induction period is proportional to the Au(III) concentration in the 0.40-2.00 p.p.m. range. In the prssence of a fixed amount of Au(III) the method is applicable for the kinetic determination of Pd{II) (0.20-2.50 p.p.m.) because 'the length of the induction period decreases wben increases the Pd/Au ratio.En medio 0,75 M en ácido sulfúrico, el colorante oxazínico azul Nilo (I.C. 51180) no es reducido por el hipofosfito 0,1 M, al misnos a velocidad apreciable. El Pd(II) ejerce sobre la reacción anterior un efecto catalítico que puede emplearse para su determinación cinética (0,30-2,50 p.p.m.)- La reacción se sigue por vía espectrofotométrica midiendo a 640 nm la disminución de la absorbancia debida al Eizul Nilo. Se estudian las variables que afectan al proceso catalítico heterogéneo y el efecto ¿3 diversos iones. Como consecuencia se presenta también un nuevo método cinético para la determinación de Au(III) basado en que la presencia de este ion provoca la aparición de un período de inducción en la reacción entre el azul Nilo y el hipofosfito catalizada por el Pd(II). La duración del período de inducción es proporcional a la concentración de Au(III) en el intervalo 0,40-2,00 p.p.m. En presencia de una cantidad fija de Au(III) el método es aplicable a la determinación cinética de Pd(II) (0,2-2,5 p.p.m.) ya que la duración del período de inducción disminuye cuando aumenta la relación Pd/Au

Head-space gas chromatography coupled to mass spectrometry for the assessment of the contamination of mayonnaise by yeasts

Head-space (HS) gas chromatography (GC) coupled to mass spectrometry (MS) is proposed for the assessment of the contamination of mayonnaise as an alternative to plate counting, which is the technique commonly used for evaluating microbial contamination. More specifically, this method was applied in the detection of Candida metapsilosis and Zygosaccharomyces bailii, both of great importance in term of food spoilage since they are resistant to many of the common methods of food preservation. Different chemometric models were investigated using the data obtained by GC-MS (m/z profile, area of the chromatographic peaks and entire chromatographic profile), in order to obtain the highest classification success. The best results were obtained using the chromatographic profile (success rate of 92%). Contaminated samples could also be classified according to the concentration of yeast, obtaining a success rate of 87.5%. Finally, a chemometric model was constructed in an attempt to differentiate between strains