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A multi-thermal-lens approach to evaluation of multi-pass probe beam configuration in thermal lens spectrometry
Humberto Cabrera, Leja Goljat, Dorota Korte, Ernesto Marin, Mladen Franko, izvirni znanstveni članek

Opis: In this work, a recently proposed thermal lens instrument based on multi-pass probe beam concept is investigated and described as a multi-thermal-lens equivalent system. A simulation of the photothermal lens signal formation in a multi-thermal-lens equivalent configuration of the system is performed and validated by comparing the experimental signals of single, dual and ten-pass configurations to theoretically calculated values. The theoretically predicted enhancement of the signal is 9 to 10-fold for a weak thermal lens when comparing the ten-pass configuration with the conventional single-pass thermal lens system. Experimentally achieved signal enhancement in the ten-pass system is 8.3 for pure ethanol sample and between 8 and 9 for solutions with different concentrations of the Fe(II) - 1,10-Phenanthroline complex. Additionally, a value of 9.1 was calculated as the ratio of the slopes of the calibration lines obtained using the ten-pass and single-pass configurations. The achieved limit of detection for determination of Fe(II), in the ten-pass configuration, was 0.4 µgL-1, with a relative standard deviation around 4.5%, which compares favorably with previously reported results for TLS determination of Fe(II) in thin samples using low excitation power. For the multi-pass configuration the linear range of measurement is reduced when compared to the single-pass configuration. This is explained by the theoretical analysis of the photothermal signal under multi-pass condition, which shows the important contribution of the nonlinear term in the theoretical expression for the photothermal signal. The ten-pass configuration, which is presented and validated experimentally for the first time, offers important signal enhancement needed in recently developed TLS instruments with tunable, low power excitation sources.
Ključne besede: Thermal lens spectrometry, Photothermal detection, Trace determination, Chemical sensor
Objavljeno v RUNG: 10.12.2019; Ogledov: 3061; Prenosov: 0
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Photothermal lens technique: a comparison between conventional and self-mixing schemes
Humberto Cabrera, Imrana Ashraf, Fatima Matroodi, Evelio E. Ramírez-Miquet, Jehan Akbar, Jose Juan Suárez-Vargas, John Fredy Barrera Ramírez, Dorota Korte, Hanna Budasheva, Joseph J. Niemela, 2019, izvirni znanstveni članek

Opis: This work focuses on assessing the analytical capabilities of a new photothermal lens method based on the self-mixing effect to reliably measure metallic traces in water-ethanol solutions. We compare it with the conventional thermal lens scheme, considering the low detection limit and versatility. A theoretical model is presented to describe the laser power variations as a function of the photothermal parameters of the analyzed sample. The experimental results demonstrate that the laser intensity variations, induced by the external optical feedback, are governed by the photothermal lens effect. Measurements of Fe(II)-1,10-phenanthroline in water–ethanol solutions show a favourable correspondence and agreement with the theory. The low detection limits obtained by the two analytic techniques also agree very well. Nevertheless, our instrument presents advantages regarding compactness and simplicity, suggesting that this platform could be potentially useful as a robust analytical tool for metallic trace detection. In addition, calibration of the method is performed by measuring the so-called self-mixing constant.
Ključne besede: thermal lens, photothermal spectroscopy, self-mixing effect, trace detection
Objavljeno v RUNG: 05.04.2019; Ogledov: 3239; Prenosov: 0
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Determination of Trace Cr(VI) with Diphenylcarbazide by μFIA–Thermal Lens Microscopy
Tatyana Gor’kova, Michail Proskurnina, Mingqiang Liu, Mladen Franko, 2016, izvirni znanstveni članek

Opis: The optimum reaction parameters for the interaction of hexavalent chromium [Cr(VI)] with diphenylcarbazide in microfluidic chips (μFIA) with thermal-lens microscopic detection were selected. The characteristic feature of the applied flow scheme is the injection of the reagent into the stream containing the test metal, which enables in-field and real-time monitoring of Cr(VI) simply by flowing the sample continuously through the microchip. The limit of detection of Cr(VI) under the selected conditions (signal generating wavelength, 514.5 nm; excitation power, 100 mW; detection position, 10 cm downstream from the mixing zone of the microchip; flow rate 10 μL min–1; injection volume, 1.4 μL) is 15 ng mL–1 (2.9 × 10–7 mol L–1). The linear range is 40 ng mL–1 – 10 μg mL–1 with a relative standard deviation no higher than 10% in the concentration range 0.1–1 μg mL–1. The online monitoring by this scheme provides the possibility of up to 360 analyses per hour.
Ključne besede: Photothermal lensing, thermal-lens microscopic detection, microfluidic applications, μFIA, hexavalent chromium, diphenylcarbazide
Objavljeno v RUNG: 12.12.2016; Ogledov: 4345; Prenosov: 0
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