Characterisation techniques fluorescence spectroscopy

Kazarian et al. [281-283] have used various spectroscopic techniques (including FUR, time-resolved ATR-FHR, Raman, UV/VIS and fluorescence spectroscopy) to characterise polymers processed with scC02. FTIR and ATR-FTIR spectroscopy have played an important role in developing the understanding and in situ monitoring of many SCF processes, such as drying, extraction and impregnation of polymeric materials. 

The latest experiments have used tunable laser induced fluorescence techniques to monitor the CN(A 2 ) fragments produced through photodissociation of ICN by a frequency quadrupled NdrYAG laser (X = 266.2 nm) or a flash lamp (X > 220 nm) ). They each concluded that virtually all the CN(JT) fragments are formed without vibrational excitation (Nj,=o-No= i > 1.00 0.02) but that they are rotationally excited with a distriTtution characterised approximately by a rotational temperature of 3000 K. While earlier time-of-fl ht photofragment spectroscopy experiments had been rationalised by assuming that CN(A 2 ) and CN(4 II)... 

In Table 3 the orientation information which can be obtained from these various structural techniques is summarised. This table also shows the part of the molecular structure which is being characterised, and some of the theoretical and experimental limitations of each method. A further technique, that of polarised fluorescence has been added. This technique is exactly analogous in its orientation aspects to Raman spectroscopy. The distinction between the two techniques lies in the fact that in the Raman effect, the lifetime of the process is of the order of the vibrational period ( 10 s) whereas fluorescence occurs after much longer occupancy of the transition state ( 10 s). 

The particle concentration of the eluent is normally measured by means of infrared or ultraviolet photometers. Additionally, fluorescence photometer, interferometric measurements (for the refractive index), or mass-spectroscopic methods (e.g. induced coupled plasma mass spectroscopy—ICP-MS, Plathe et al. 2010) are employed. The combination of different detection systems offers an opportunity for a detailed characterisation of multi-component particle systems. Note that the classification by FFF is not ideal and the relevant material properties are not always known moreover, the calibration of FFF is rather difficult. The attribution of particle size to residence time, thus, bears some degree of uncertainty. Recent developments of FFF instrumentation, therefore, include a particle-sizing technique additional to the flow channel and the quantity measurement (usually static and dynamic light scattering, Wyatt 1998 Cho and Hackley 2010). 

FT-Raman has been used as an alternative to TG techniques to determine filler content in HDPE/ CaC03 composites and provides comparable results [400]. As most pigments (apart Ifom carbon-black) and glass are poor Raman scatterers, in principle Raman spectra are obtainable Ifom these samples without removal of the fillers or difficult sample preparation. Conventional visible Raman spectroscopy has failed in attempting to analyse dyesmffs. Conventional Raman spectra of dyed textiles tend to be dominated by the (fluorescent) spectrum of the dye [401]. Consequently, FT-Raman spectroscopy may be a more useful tool for direct observation of low levels of dyestuffs in polymeric materials. Indeed, by using NIR excitation dramatic improvements in the Raman spectra of these dyes can be achieved [392]. FT-Raman was quite useful for the discrimination of differently dyed cotton-cellulose fabrics with the bifunctional reactive dye Cibacron C, provided that the interpretation was facilitated by chemometrics [402]. Schrader et al. [403] have used FT-Raman spectra to distinguish non-destructively the main dye components in historical textiles. Bourgeois et al. [401] have successfully used FT-Raman in the characterisation of... 

---