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

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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.

Keywords: Dual wavelength; Thermal lensing; Two-component mixtures; pH determination

Document Type: Research Article


Affiliations: Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233

Publication date: May 1, 1989

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