Thermal lens spectroscopy

Abbreviations AOD, Acousto-optical deflection BCB, bisbenzyocyclobutadiene CCD, indirect contact conductivity detection CL, chemiluminescence ECD, electron capture detector FCS, fluorescence correlation spectroscopy FRET, fluorescence resonance energy transfer ICCD, integrated contact conductivity detection GMR, giant magnetoresistive LED-CFD, light emitting diode confocal fluorescence detector LIF, laser-induced fluorescence LOD, limit of detection MALDI, matrix-assisted laser desorption ionization PDMS, poly(dimethylsiloxane) PMMA, poly(methylmetha-crylate) SPR, surface plasmon resonance SVD, sinusoidal voltammetric detection TLS, thermal lens spectroscopy. 

Hattori, A., Yamaguchi, H., Yamaguchi, J., Matsuoka, Y., Kanki, S., Fukuzawa, T., Miwa, T., Totama, M., Tokeshi, M., Kitamori, T., Practical studies on compact photo-thermal lens spectroscopy detection system with micro chemical chip. Micro Total Analysis Systems 2003, Proceedings 7th pTAS Symposium, Squaw Valley, CA, Oct. 5-9, 2003, 359-362. 

Replacement of the conventional incoherent light source with a laser has allowed CD measurements to be made on extremely small samples, such as those encountered in capillary electrophoresis. In addition, the unique spatial properties of the laser are utilized to advantage in thermal lens spectroscopy. TL detection of CD, either via a single beam, or a differentially configured arrangement, has demonstrated significant improvements in the measurement SNR. Application to HPLC detection, or time-resolved studies, are currently under investigation. 

Allonas, X., Ley, C., Bibaut, C., Jacques, P., Fouassier, J. P, Investigation of the Triplet Quantum Yield of Thioxanthone by Time resolved Thermal Lens Spectroscopy Solvent and Population Lens Effects, Chem. Phys. Lett. 2000, 322, 483 490. 

K. L. Jansen and J. M. Harris, Double-Beam Thermal Lens Spectroscopy. Anal. Chem., 57 (1985) 2434. 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

During the last 30 years the development of laser technology has opened up new possibilities in analytical spectroscopy, both by improvements in traditional analytical techniques, such as absorption and fluorescence or optoacoustic spectroscopy, and by the introduction of new techniques such as multistep photoionization spectroscopy. thermal lens spectroscopy, and site-selection spectroscopy. 

Thermal lens spectroscopy (TLS) is another laser-based technique, associated with dissipation of absorbed laser energy followed by the formation of temperature gradients in a medium. It was observed for the first time in 1964 when a 1-cm Brewster cell containing benzene was placed inside the resonator of a cw He-Ne laser. Contrary to the expected behavior, the laser intensity began to fluctuate and in a few seconds, when the steady state was reached, the beam diameter at the resonator mirrors had increased. The benzene cell acted as a spherical negative lens with a focal length of ca. 1 m. 

Thermal lens microscopy (TLM) is a type of photothermal spectroscopy. TLM depends on the coaxial focusing of the excitation and probe laser beams (see Figure 7.20). Which is achieved using the chromatic aberration of a microscopic objective lens [731]. The excitation beam can be provided by a YAG laser (532 nm) [846,1021] or an Ar ion laser (514.5 nm [846] or 488 nm [732]).The probe beam can be provided by a He-Ne laser (632.8 nm) [846,1021], After optical excitation of the analyte molecules, radiationless relaxation of the analytes occurs,... 

We have developed a novel ultrasensitive detection method, thermal lens microscopy (TLM), for nonfluorescent species [13]. TLM is photothermal spectroscopy under an optical microscope. Our thermal lens microscope (TLM) has a dual-beam configuration excitation and probe beams [13]. The wavelength of the excitation beam is selected to coincide with an absorption band of the target molecule and that of the probe beam is chosen to be where the sample solution (both solvent and solute) has no absorption. For example, in determination of methyl red dye in water, cyclohexane, and n-octanol, a 514-nm emission line of an argon-ion laser and a 633-nm emission line of a helium-neon laser were used as excitation and probe beams, respectively [21], Figure 4 shows the configuration and principle of TLM [13]. The excitation beam was modulated at 1 kHz by an optical chopper. After the beam diameters were expanded, the excitation and probe beams were made coaxial by a dichroic mirror just before they were introduced into an objective lens whose magnification and numerical aper-... 

A treatment for analysing the excitation and fluorescence multiwavelength polarized decay surfaces has been given for the case of a mixture of noninteracting species. An improved model for analysis of fluorescence anisotropy measurements has been presented. Limitations to the use of intense excitation pulses in fluorescence and thermal lens spectrophotometers are discussed in terms of optical saturation. Such artefacts can be eliminated by reference to the fluorescence quantum yield of Rhodamine 6G. A model has been given to describe spectral diffusion in time-resolved hole-burning spectroscopy. ... 

Both molecular and atomic detectors have been used in combination with SCF extractors for monitoring purposes. Thus, the techniques used in combination with SFE are infrared spectroscopy, spectrophotometry, fluorescence spectrometry, thermal lens spectrometry, atomic absorption and atomic emission spectroscopies, mass spectrometry, nuclear magnetic resonance spectroscopy, voltammetry, and piezoelectric measurements. 

A comprehensive review of hole burning spectroscopy of species in glasses has been prepared by Haarer and Silbey. Electric field effects on the spectral holes for perylene in Shpol skii matrices in n-heptane provide a useful extension of this technique . The limitations of the thermal lens method for the measurement of fluorescence yields have been examined and discussed . It is pointed out that the... 

The overall diagram of evolution of the excited states and reactive intermediates of a photoinitiating system working through its triplet state can be depicted in Scheme 10.2 [249]. Various time resolved laser techniques (absorption spectroscopy in the nanosecond and picosecond timescales), photothermal methods (thermal lens spectrometry and laser-induced photocalorimetry), photoconductivity, laser-induced step scan FTIR vibrational spectroscopy, CIDEP-ESR and CIDNP-NMR) as well as quantum mechanical calculations (performed at high level of theory) provide unique kinetic and thermodynamical data on the processes that govern the overall efficiency of PIS. 

Rapid improvements of the DL characteristics make these devices very attractive for absorption spectrometry not only of gas species (atomic or molecular) but also of liquid and condensed-phase samples. Much attention is now focused on using NlR-DLs for molecular fluorescence spectrometry, Raman spectroscopy, thermal lens spectrometry, medical diagnostics, development of fiber. sensors. and so on. 

One approach towards such a system was accomplished by the synthesis and examination of (S)-l,T-binaphthyl-2,2 -diyl bis[4-(l,l-dicyano-l,8a-dihydro-(8aS)-azu-len-2-yl)]-benzoate (30a), monitoring its photochromic behavior by UV/Vis and CD spectroscopy. After irradiation of a solution of 30a in acetonitrile for 15.5 min, fundamentally altering its spectral properties, subsequent thermal relaxation in the dark for 12h resulted in complete restoration of the UV/Vis and CD spectra. This is a first step towards a powerful DHA/VHF-based information storage system controlled by asymmetric induction. Further investigations are underway. 

Figure 7.9. Thermal stabilities of eye lens crystallins of differently thermally adapted vertebrates. The temperature (°C) at which 50% loss of secondary structure occurred, as measured using CD spectroscopy, is given as a function of the maximal body temperature of each species. Species (1) Pagothenia borchgrevinki (Antarctic fish), (2) Coryphaenoides armatus (deep-sea fish), (3) Coryphaen-oides rupestris (deep-sea fish),...

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