Determinacion espectrofotometrica de fosforo por medio de adicion de estandar

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  • Publicado : 2 de junio de 2011
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ABSTRACT
The phosphorus present as phosphate in food, called reagent reacts with ammonium molybdate and ammonium metavanadate which produces a yellow compound called ammonium fosfomolibdovanadato.The amount of compound formed is directly proportional to the amount of phosphorus present in the sample. Measuring the amount of fosfomolibdovanadato formed was measured in a spectrophotometercalibrated at a wavelength of 400 nanometers.
In this identification interfere appreciable concentrations of Fe (III), silicate and arsenate, among other species. That is, these species absorb light at thewavelength used (400 nm, absorption of the complex). To eliminate this interference will prepare a blank (no phosphate), whose absorbance is subtracted from the rest of the samples. Additionally, itis possible that the absorbance of the complex is affected by matrix effects.
The matrix can enhance or attenuate the light absorbance of the complex, which can lead to erroneous results. To minimizethis effect, we apply the standard additions method, which involves the addition of increasing amounts of the analyte of interest (phosphate in our case) to a fixed amount of sample. This procedure ismore effective than an external calibration (calibration curve with standard solutions) if the parent interferes with detection.


INTRODUCCION
El método alternativo de adiciones estándarconsiste en añadir sobre la muestra problema cantidades crecientes conocidas de analito. De esta manera, todas las medidas se realizan sobre la misma matriz. Al representar la señal experimental frente a laconcentración de analito añadida resulta una recta a partir de cuya pendiente y ordenada en el origen se obtiene la concentración de la muestra problema. En el intervalo de respuesta lineal la señalS es proporcional a la concentración del analito.
S= a (Ca + Cx)
Donde Ca= concentración problema
Cx= concentración añadida
S= a (Ca + Cx) = ax + b
Recta de calibrado y= ax + b
Y=S; x= Cs; b=...
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