Sensitivity Enhancement of Thermal-Lens Spectrometry Using Laser-Induced Precipitation

Abstract

The possibility of thermal lensing of dynamically emerging light-absorbing layers at cell surfaces was investigated. Analyte accumulation at a cell surface determines long-term changes in the thermal-lens signal that was used as a source of analytical information to enhance sensitivity of thermal lensing. Considering the rate of accumulation as an additional analytical signal, we achieved a threefold decrease in the limits of detection for 4-aminoazobenzene to the level of 7 mM in a batch mode with the same level of reproducibility. The details of observed thermal-lens signal behavior in cells are discussed. The possibilities to use thermal-lens detection for 4-aminoazobenzene determination in quartz capillaries in flow mode were discussed and a drastic thermal-lens signal enhancement was discovered. The corresponding limit of detection for 4-aminoazobenzene in a flow mode is further decreased to the level of 3 mM.

Sensitivity Enhancement in Near-Field Photothermal-Lens Detection in Capillary Electrophoresis Using Laser-Induced Online Precipitation

“…These phenomena can be accounted for by laser irradiation only, not with conventional UV-Vis sources. From our point of view, upon exposure to intense UV He-Cd laser irradiation the following processes occur in a capillary: 40 (a) initial exposure induces the trans-cis isomerization of 4aab, 38,39 resulting in an easily coagulating isomer mixture; (b) the precipitation of cis-and trans-isomer mixture begins in the irradiated zone at the detection window; 25,41 and finally, (c) photoinduced dissolution of the precipitate occurs in a slow (Fig. 3, inset) or in a fast mode.…”

“…1). 38,39 In the conventional ''central'' configuration, the excitation beam passes through the capillary center. This configuration is optimal for detection in capillary electrophoresis as soon as the light path of the beam through the solution is the longest; the thermal lens formed in the capillary is symmetrical.…”

“…A detailed description of the thermo-optical elements corresponding to these configurations is given elsewhere. 38,39 Changes between the configurations are made with a single micro-screw at the detector unit (see Fig. 1).…”

“…The substances selected are 4-aminoazobenzene (4-aab) and Mordant Yellow 7 (MY7). The former is a cationic dye readily precipitating upon the absorption of laser energy 38,39 as a result of isomerization; 40 the latter is an anionic dye known to be unaltered by laser irradiation; 25,39,40 its adsorption at capillary inner surface is hardly possible.…”

Progress in Thermal Lens Spectrometry and Its Applications in Microscale Analytical Devices

“…Apart from the above methods, other possible ways for sensitivity enhancement have also been developed, such as using on-line sample preconcentration (Kitagawa et al, 2006;Otsuka, 2007), reversed micelles (Tran, 1988), crown ethers (Tran and Zhang, 1990), unique properties of water (Franko and Tran, 1989), sample matrix absorption of the probe laser beam (Grishko et al, 2002), and even the latest reported, laser-induced precipitation (Nedosekin et al, 2009). In TLS systems, there are mainly two kinds of noise sources.…”