The use of one-shot sensors with a dedicated portable electronic radiometer for nitrate measurements in aqueous solutions

A simplified procedure for the in situ determination of nitrate in waters is presented based on ionophore-chromoionophore one-shot sensors measured in a simple form by a portable radiometer designed by us. The colour change in the sensing film is detected by measuring the transmitted intensity with a solid state radiometer. A light-emitting diode (LED), with a dominant wavelength of 660 nm, was used as the illumination source. Negative feedback for LED bias and thermal correction were included to improve system stability. The procedure is based on the use of one-shot sensors pretreated with NaOH and the measurement of an absorbance ratio as analytical parameter. The one-shot sensors are used directly without any prior conditioning and the absorbance is measured with the portable radiometer before and after equilibration with the sample. The results obtained show that the procedure has good sensitivity with a range between 0.002 and 1000 mM using a sigmoidal calibration function, and a precision around 4% expressed as the logarithm of the nitrate concentration. The performance of the optical one-shot sensor was tested for the analysis of nitrate in different types of natural water (tap, river, well and sea), validating the results against a reference procedure.