Development of a Portable LED-Based 8-Channel Reflective Colorimeter and Its Application to Simple Determination of Hexacyanoferrate (II) in Common Salts

摘要

A portable LED-based 8-channel reflective colorimeter has been developed. It has eight LEDs whose wavelengths are 430, 470, 525, 565, 590, 635, 660, and 740 nm, respectively, and their light emissions are merged by means of plastic-core fiber optics and led to the surface of a solid sample vertically. Each LED is turned on and off sequentially and the light reflected by the sample is detected by a photo-diode mounted at 45° with respect to both the sample surface and the light source. Another photodiode is mounted behind the LEDs and used to correct the fluctuation of LED emission. The Kubelka-Munk function (K-M) for each LED is calculated by an embedded controller and displayed on a liquid crystal display (LCD). This colorimeter is applied to the sensitive determination of hexacyanoferrate (II) in common salts. Hexacyanoferrate (II) reacts with iron (II) sulfate and they produce iron (II,III) hexacyanoferrate (II,III) complex (Prussian blue dye). Then the precipitate is filtered by membrane filter and its K-M at 635 nm measured for the construction of a calibration curve. The obtained calibration curve is linear, between 2.5 and 30 ug of sodium hexacyanoferrate (II), and the detection limit is 0.6 ug (calculated from 3 s of determination results for 2.5 pg hexacyanoferrate(II), n = 5). Recovery tests are performed with the commercial common salt sample spiked with 1.25 and 10 μg g~(-1) of hexacyanoferrate (II), and the results are from 96 to 113%.