Direct Optical Evaluation Using Instruments

Unhke visual evaluation of a chromatograms before derivatization, which can only give quahtative or semiquantitative results, direct optical evaluation using instruments enables quantitative results to be obtained. For this, a traditional TLC scanner, diode-array scanner or video equipment, either alone or in combination with a flat-bed scanner, is used. Quantitative evaluation with these instruments is described in more detail in Sections 1.2-1 A. However, the limits of this book would be exceeded if we gave a detailed description of all the commercially available equipment that can be used to quantify substances on TLC plates. Training in the use of TLC scanners can be obtained in company seminars (e.g. CAMAG) and detailed instructions are provided by the manufacturer when the equipment is purchased. 

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Practical Tip for prewashing if the signal/noise ratio is too low (see Section 5.2 Direct Optical Evaluation Using Instruments ), the blank chromatography method should be given preference. 

Eqs. (4.140) and (4.150)-(4.152) are used to evaluate the response of the model composites in cyclic loading and the displacements 6 and 8, can be expressed as a function of the alternating stress, Aff, and the number of cycles, N. In experiments, degradation of the interface properties, e.g., the coefficient of friction, p or A(= 2pjfc/a), can also be expressed in terms of the cyclic loading parameters, Aoptical methods (with a microscope) or by means of more complicated instruments (see for example Naaman et al. (1992)) in fiber pull-out. Alternatively, they can be directly determined from the load and load-point displacement records in the case of fiber push-out. 

Horiba Jobin Yvon has an interesting portable instrument on the market called SkinScan (Figure 8.8). It is an in-vivo, fibre optic spectrofluorometer designed specifically to acquire fluorescence measurements directly from skin or hair. The fibre optic bundle transmits UV-NIR radiation to the sample and then collects the resulting fluorescence. Results are used to investigate the age and health of skin, and to evaluate sunscreens and cosmetics among other applications. 

The Finnigan LTQ linear ion trap mass spectrometer equipped with the vMALDI source (ThermoFisher, San Jose, CA, USA) was used for all imaging mass spectrometry experiments. The instrument has been described in detail previously (6), but briefly, the source consists of a N2 laser (337 nm) directed to the vacuum chamber using fiber optics. The laser spot size for these experiments was 120 xm. The spot size was evaluated by ablating a small piece of photosensitive paper and then measuring the size of the ablated area with a microscope. The source is maintained at a pressure of 0.17 Torr using N2. 

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