Densitometers reflectance mode

This experiment is based on the use of a Kontes fiber optics densitometer (K-49500) with baseline corrector and strip-chart recorder. The description given in the second paragraph of Experiment 8, Section 8 is based on the use of that equipment. Readers will have to modify their approaches to in situ densitometry based on the available instrumentation in their laboratories. In our laboratory, we no longer use the K-49500 model and do most of our lipid in situ densitometry with either a Kontes Model 800 densitometer equipped with a Hewlett-Packard Model 3992A integrator/recorder (Morris et al., 1987) or a Shimadzu CS-930 computerized TLC densitometer operated in the single-beam, reflectance mode. [See Morris et al. (1987), Park et al. (1991), and Masterson et al. (1993) for further information on the use of these instruments in lipid quantification by TLC-densitometry.]... 

A Schoeffel model SD-3000 doublebeam spectro-densitometer equipped with a high-pressure mercury-zenon lamp is used with a Schoeffel SDR 303 recorder. All measurements made at 230 nm in the reflectance mode at an attenuation output of 0.2 a.u.f.s. Peak areas determined by multiplying peak height by the peak width at half-height. Linearity noted between 1-20 g between peak area and concentration Ref... 

Optical quantitation in TLC, 273-306 assessment in QTLC, 300-305 testing and validation, 301-305 basic principles of quantitation, 274-287 discontinuum theory, 276-280 measurement of fluorescence, 281-287 densitometers, 287-291 reflectance mode, 287-288 special scanning procedures, 289-291 transmittance, 288-289 integration in QTLC, 293-300 quantitative evaluation with digital cameras, 291-293... 

For greater accuracy, the plate is scanned with a densitometer in one of the three modes—transmission, reflectance, or fluorescence. Some instruments can also provide spot areas. Four scanners are described in Beesley s review,21 and Touchstone and Sherma27 have described the use of densitometers. Accuracies are about 2 to 5%. 

Normal and reverse-phase thin-layer chromatography (TLC) chromatograms are quantitated using a dual-wavelength scanning densitometer. Trace levels of organics in a mixture are separated and detected using UV-visible, reflectance, or fluorescence modes. Hydrazine, for example, can be analyzed for trace components on polymeric materials, determined to a 50-ppb or even lower level via established official (i.e., ASTM, USP) analytical procedures. TLC plates can be scanned unattended and quantitated automatically. The technique has been found to be particularly useful for compositional analysis, since individual component spots can be collected for subsequent spectral analysis or other available analytical techniques. 

Operate the densitometer using the visible light source without a filter and the reflectance, single-beam mode, scanning with the small head (reference head). Operate the densitometer at a scanning speed of 10 cm/min and an attenuation of 10. Operate the baseline corrector with an input of 2 mV and an output of 10 mV. Set both the positive drift knob and noise suppression knob at 2. Set the recorder input at 10 mV and the chart speed at 30 cm/min. 

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