Maria Dolores Fernández-Ramos

Publications (2)1.49 Total impact

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

  Maria Dolores Fernández-Ramos, Magda Greluk, Alberto J Palma, Eduardo Arroyo-Guerrero, Joaquin Gómez-Sánchez, Luis Fermin Capitán-Vallvey
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  ABSTRACT: 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.
  Measurement Science and Technology 08/2008; 19(9):095204. · 1.49 Impact Factor
• Article: Microcontroller-based portable instrument for stabilised optical oxygen sensor

  Alberto J. Palma, Javier López-González, Luis J. Asensio, Maria Dolores Fernández-Ramos, Luis Fermin Capitán-Vallvey
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  ABSTRACT: A novel measurement system comprised of a portable electronic instrument with an opto-chemical sensor for atmospheric oxygen sensing is presented. Optical sensors based on luminescence quenching have been thoroughly investigated in the search for sufficient sensitivity and high stability. The dye platinum octaethylporphyrin complex immobilised in a polystyrene membrane was selected as an oxygen probe that was stabilised with the heterocyclic amine DABCO, achieving in this way a mean drift of 0.01% oxygen concentration per day. The portable instrument is based on a microcontroller. Its main features are: a single optical sensor channel, lack of optical filters, fully digital signal processing, autonomous operation with computer communication capability for reprogramming and data saving and low power consumption. The use of a digital output photodetector makes it possible to avoid analogue processing with the consequent circuitry saving and better noise immunity. The measured parameter in the transduction process is quite similar to the luminescence lifetime. The typical measurement range is from 0 to 30% oxygen and the response time is below 30 s for full range swing. Typical instrument characteristics are temperature effect correction, low drift and an accuracy of 0.5% in oxygen concentration for the collective calibration curve. Better accuracy can be obtained with individual sensor calibration. Dimensions and weight are 110 mm × 66 mm × 28 mm and 95 g (without battery), respectively. Powering it with a standard 9 V PP3 battery for more than 10 days of operation is possible.
  Sensors and Actuators B: Chemical.