Miniaturized photothermal sensors as analytical tools for detection of very small volumes in chemical process control

Abstract

The application of photothermal interferometry and near-field thermal lensing as analytical tools in liquids is described. Using the transverse setup, the smallest detection volumes are achieved. The setups of both sensor systems are miniaturized, so adjustment and external influences are minimized. The sensitivities of both systems are demonstrated with the textile dye Reactive Red as an analyte. © 1997 Society of Photo-Optical Instrumentation Engineers.Subject terms: photoacoustic and photothermal science and engineering; photothermal interferometry; thermal lens; photothermal effect; trace analysis; white light source; lasers; microinterferometer.Paper PPS-14

Optimization of Instrumental Parameters of a Near-Field Thermal-Lens Detector for Capillary Electrophoresis

“…10), which was also described in other papers concerning thermal-lens detection in capillaries. 5,14,16 The experimental results strongly confirm these considerations. The dependence of the thermal-lens signal on the flow velocity in the capillary within the range of 0-25 cm/min (achieved with a phosphate separation buffer, pH 7, by voltage variation) for a solution of Alizarin Yellow GG (a capillary completely filled with the solution of interest) shows that for all chopper frequencies used, the corresponding curves show a maximum.…”

“…The advantages of the crossed-beam optical scheme from the viewpoint of the small-volume detection have been considered previously. 1,16 As reported, 5,14,19 the near-field configuration (Fresnel diffraction conditions) is better suited to the thermal-lens detection in capillaries because the edge effects caused by the interference of the probe beam on the capillary walls (diffraction pattern) are significantly reduced in this case. As a result, the measurement reproducibility increases significantly.…”

“…Thermo-optical Element in the Capillary. It was previously found by Faubel and his collaborators 4,5,14 that the medium chopper frequencies (20-100 Hz) are well suited for near-field in-capillary detection, and thus the design of the instrument allows the change in the chopper frequency in a range of 40-95 Hz. Thus, contrary to the study in Ref.…”

“…Thermal lensing is one of the promising detection techniques toward this aim as it shows 100-to 1000-fold lower limits of detection compared to conventional spectrophotometry 1 and can be implemented in microanalysis. 2 There are numerous examples of both the development of thermal-lens detectors [3][4][5][6] and their CE applications for the analysis of real samples with the determination of such analytes as amino acids, [7][8][9] food preservatives, 10 pesticides, 11 and drugs and their metabolites. [12][13][14] However, only a few of them are fully devoted to thermal-lens-spectrometry-CE as a hyphenated method.…”

“…The advantages of crossed-beam thermal-lens spectrometry in capillary electrophoresis are the following: it is more preferable for smaller detection volume (the detection volume is well defined and restricted to the intersection of the probe and excitation beams, which can be very low) and easier spatial separation (separate focusing) of both beams. [3][4][5][6][7]15,16 We focused on the principal features of thermal-lens detection, namely the geometry of the optical scheme and the chopper frequency in a CE detection in 75 m capillaries most commonly used in analytical CE applications. Also, for the optimization of these instrumental parameters, we considered temperature changes in the capillary during the heating and cooling processes taking place in thermal-lens measurements and thus, the thermooptical element bloomed in the capillary, which were previously not estimated under these conditions.…”