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

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 sorbent surface. The measurements were carried out at a wavelength of 566.1 nm yielding the largest divergence 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 lifetime are discussed in detail. The main advantages of this prototype device are sensitivity and higher selectivity over Mg(II). The proposed method has been successfully applied to the determination of Ca(II) in milk and drinking water samples.