Simultaneous Determination of Two-Component Mixtures and pHs by Dual-Wavelength Thermal Lens Spectrometry

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Abstract
The recently developed dual-wavelength thermal lens spectrometer, which is capable of simultaneously measuring thermal lens signals at two different wavelengths, has been used to simultaneously determine two-component samples and solution pHs. Compared to conventional absorption spectrophotometry, this dual-wavelength technique offers advantages that include fast data acquisition and higher sensitivity. With the use of 20-mW excitation beams, the limits of detection for the simultaneous determination of ferroin and iron(II) bipyridyl complexes mixtures are estimated to be 3.6 × 10−9 M and 8.4 × 10−9 M, respectively. In addition, the high monochromaticity of the laser makes this technique uniquely suited for the simultaneous determination of two-component samples whose absorption bandwidths are too narrow to be determined by the conventional spectrophotometric method. The limits of detection for the Er3+ and Nd3+ ions in the two-component mixtures are estimated to be 8.9 × 10−4 M and 7.6 × 10−5 M, respectively. Solution pHs have also been sensitively and accurately determined by using this technique to measure the concentrations of the protonated and deprotonated forms of an indicator. Similar to the two-component sample determination, this thermal lens technique is superior to the conventional spectrophotometric method because it is fast, has relatively higher sensitivity, and allows an indicator to be used over a wider pH range. Solution pHs, ranging from 2 to 9, have been determined accurately with this technique, with the use of such indicators as phenol red, methyl orange, and thymol blue, whose concentrations can be as low as 10−9 M.