Rapid Determination of Calcium in Milk and Water Samples by Reflectance Spectroscopy

Abstract

Reflectance spectroscopy (RS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of calcium. In this analytical technique, the analyte in complex samples is extracted onto a solid sorbent matrix loaded with glyoxal bis (2-hydroxyanil (GBHA) and then quantified directly on the sor-bent surface. The measurements were carried out at a wavelength of 566.1 nm yielding the largest diver-gence of reflectance spectra before and after reaction with the analyte element. The optimum response was obtained in 0.2 mol⋅L –1 NaOH solution, and the response time of the sensor was about 5 min, depending on the concentration of Ca(II). The calibration curve of Ca(II) was found to be linear on semi-logarithmic scale within the concentration range of 0.3 -40 mg⋅L –1 , with a LOD of 0.15 mg⋅L –1 in the low concentration range. The sensor response from different sensors (n = 5) gave an R.S.D. of 1.4% at 10 mg⋅L –1 Ca(II). The response characteristics of the sensor including dynamic range, reversibility, reproducibility, response time and life-time are discussed in detail. The main advantages of this prototype device are sensitivity and higher selectiv-ity over Mg(II). The proposed method has been successfully applied to the determination of Ca(II) in milk and drinking water samples.