Magnetoelastic Resonance Detection of Calcium Oxalate Precipitation in Low Concentration Solutions

Abstract

A magnetoelastic resonance sensor of composition Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73</sub> Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> is used to monitor the precipitation reaction of calcium oxalate (CaC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) by measuring the changes in its resonance frequency, caused by the mass increase on its surface, during the precipitation process. Numerical fittings of the resonance curves were performed in order to improve the detection resolution. With respect to previous works on the monitoring of this precipitation reaction, this work explores the limit of detection of the technique, and the ability of the numerical fittings to improve the quality of the signals measured and the parameters that are extracted from them. For this purpose, the monitoring of the precipitation reactions when using reagents (oxalic acid and calcium chloride) of concentrations 1, 3, 5, and 10 mM were studied. The results show that the sensor is capable of tracking the precipitation reaction of solutions of concentration as low as 1 mM (the solubility limit of calcium oxalate is about 0.1 mM), with the sensor being able to resolve a mass of precipitate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu \text{g}$ </tex-math></inline-formula> .