Phosphorescence spectroscopy instrumentation

UV/VIS absorption spectroscopy, pioneered by Beckman (1941), is one of the oldest and most widely used instrumental techniques, despite being regarded by some analysts as obsolete. Recently there has been a renaissance in UV spectroscopy with many new techniques, instruments and data processing methods [8]. Modem highest specification UV/VIS absorption and fluores-cence/phosphorescence spectrometer instruments extend their wavelength region from the far UV (175 nm) into the NIR region (1100 nm). Small footprint UV/VIS spectrometers (200-1100 nm) are now available. Paul [9] has traced the history of UV/VIS instrumental developments. 

Fluorescence spectroscopy forms the majority of luminescence analyses. However, the recent developments in instrumentation and room-temperature phosphorescence techniques have given rise to practical and fundamental advances which should increase the use of phosphorescence spectroscopy. The sensitivity of phosphorescence is comparable to that of fluorescence and complements the latter by offering a wider range of molecules for study. 

Luminescence spectroscopy may be divided into two major areas fluorescence spectroscopy and phosphorescence spectroscopy. The differences between the two are based mostly on the time frames on which the phenomena of fluorescence and phosphorescence occur, phosphorescence decaying much more slowly (often taking several seconds) than fluorescence subsequent to excitation. Slight differences between the instrumentation used to observe fluorescence and that to observe phosphorescence take advantage of the temporal distinction between the two luminescence phenomena. Chemiluminescence is a form of fluorescence differing only in the fact that a chemical reaction as opposed to incident light generates the excited state. 

The basic design of instrumentation for monitoring molecular fluorescence and molecular phosphorescence is similar to that found for other spectroscopies. The most significant differences are discussed in the following sections. 

Instrumentation for fluorescence spectroscopy has been reviewed [8]. For standards in fluorescence spectroscopy, see Miller [138]. Fluorescence detection in HPLC has recently been reviewed [137], Phosphorescence detection of polymer/additive extracts is not being practised. 

In these sensors, the intrinsic absorption of the analyte is measured directly. No indicator chemistry is involved. Thus, it is more a kind of remote spectroscopy, except that the instrument comes to the sample (rather than the sample to the instrument or cuvette). Numerous geometries have been designed for plain fiber chemical sensors, all kinds of spectroscopies (from IR to mid-IR and visible to the UV from Raman to light scatter, and from fluorescence and phosphorescence intensity to the respective decay times) have been exploited, and more sophisticated methods including evanescent wave spectroscopy and surface plasmon resonance have been applied. 

Spectroscopy, annual reviews of new analytical instrumentation from the Pittsbuigh Conference on Analytical Chemistry and Applied Spectroscopy. Analytical Chemisty, "Fundamental Reviews" (June 1994, June 1996), analytical applications of infrared, ultraviolet, atomic absorption, emission, Raman, fluorescence, phosphorescence, rhemilnminescence, and x-ray spectroscopy. 

See alsa Bioassays Overview. Chemiluminescence Overview. Derivatization of Analytes. DNA Sequencing. Enzymes immobilized Enzymes. Flow Injection Analysis Detection Techniques. Fluorescence Overview. Immunoassays Oven/iew. Luminescence Overview. Molecularly Imprinted Polymers. Optical Spectroscopy Detection Devices. Phosphorescence Principles and Instrumentation. Sensors Photometric. 

Chemical imaging is described, including confocal Raman imaging. UV and visible spectroscopy includes innovations such as flow-through sample holders and fiber-optic probes, as well as instruments for analysis of submicroliter volumes and nondestructive analysis for nucleic acid and protein determinations. UV absorption spectral interpretation for organic molecules is covered in depth. Applications described include nucleic acid and protein measurements, spectrophotometric titrations, and new applications in forensic chemistry. Nephelometry, turbidimetry, fluorescence, and phosphorescence are described in detail, including instrumentation and applications. The measurement of color using the CIE system is described with examples. 

In luminescence spectroscopy the emission of the luminophore is monitored. There are two different types of luminescence spectra that can be recorded with modern spectrofluorometers, emission and excitation spectra. Note that although the name implies that these instruments measure only fluorescence, spectrofluorometers can also measure phosphorescence, especially when special accessories are added. Spectrofluorometers contain both an excitation monochromator and an emission monochromator. In emission spectra, the excitation wavelength is fixed and the emission monochromator is scanned. The excitation is usually fixed at a wavelength at which the sample has significant absorbance. In excitation spectra, on the other hand, the emission wavelength is fixed and the excitation monochromator is scanned. The emission is normally fixed at a... 

---