Percentage transmission

The absorbance and the percentage transmission of an approximately 0.1M potassium nitrate solution is measured over the wavelength range 240-360 nm at 5 nm intervals and at smaller intervals in the vicinity of the maxima or minima. Manual spectrophotometers are calibrated to read both absorbance and percentage transmission on the dial settings, whilst the automatic recording double beam spectrophotometers usually use chart paper printed with both scales. The linear conversion chart, Fig. 17.18, is useful for visualising the relationship between these two quantities. 

Infrared spectra are recorded using either or both absorbance and percentage transmission just as they are in visible/ultraviolet electronic spectra, and the Beer Lambert relationship ... 

In one method the intensity of the primary beam is diminished by several orders of magnitude through the use of a series of neutral filters, the percentage transmission of each at the wavelength X having been accurately measured. Comparison of the intensity of light scattered by the solution with the intensity of the incident beam meas-... 

Aqueous solution of a drug (0-10 milli molar) shows a percentage transmission of 50 in a 1 cm cell at 250 run. The molar absorptivity, calculated ... 

Fig. 9.—Rate of Change in Percentage Transmission (at 490 m/i) of D-Xylose, d-Glucose, D-Galacturonic acid, and 5-(Hydroxymethyl)-2-furaldehyde with Glycine, Compared with the Sugars Alone.189 [Each constituent (0.25 mole) in aqueous solution at reflux temperature (102°) --- D-xylose A-----A D-glucose O----O...

Here, /o and I denote the intensities of the incident and transmitted beams, respectively, e is the molecular absorption coefficient, and c and d are the concentration of the sample and the cell length, respectively (Fig. 1-7). In IR spectroscopy, it is customary to plot the percentage transmission (T) versus wave number (v) ... 

Piguie 20. Percentage transmission vs. reciprocal wavelength before irradiation and after ultraviolet (330 nm) irradiation of thin film of Pb(N3)2. 15% of total nitrogen content of the film removed by irradiation (after Varma et al. [ 120]). 

Figure 6.6. Frequency versus percentage transmission for three types of optical filters. A cut-in or cut-off. B bandpass. C band-rejection.

The IR absorption spectrum is the graphical representation of a measure of energy depending on a measure of wave of the involved radiation. IR practice has established the use of the wave number (reciprocal of the wave length and proportional to the frequency of the radiation) and of the percentage transmission (T%) or absorbance (A), as related to the... 

Figure 8.14 Percentage transmission versus wavelength for PLA (98% L-lactide), PS, LDPE, PET and cellophane films 1101 (Reproduced with permission from 110], Copyright 2004 Wiley-VCH, Verlag GmbH Co. KGaA, Weinheim.)...

To illustrate a typical calculation based on equation (7-10), an emulsion calibration curve is needed. Figure 7-7 is a typical calibration curve using percentage transmission as the ordinate and relative intensity as the abscissa. 

Several methods of background correction can be used. One method is to adjust the read-out circuit to read 100% transmission through the background adjacent to the analytical line. This technique basically is a correction based on percentage transmission differences of the clear emulsion and the background. It is useful at low background intensity levels but mathematically is not correct. 

A common procedure to determine absorbance is to obtain data in terms of percentage transmission. If the transmission of radiant energy through the blank is adjusted to 100% transmission, the signal, after passing through to sample, will produce a reading of less than 100%. If these conditions are met, the absorbance A is... 

The irradiance of light that emerges after passing through a solid is often recorded as percentage transmission (%T) = lOOT, where the transmittance, T, varies between 0 and 1 and is given by... 

Figure 8.5 The relationship between percentage transmission and absorbance.

All commercial instruments record on a paper chart the percentage transmission or the absorbance against wave-number or wavelength. Doublebeam instruments provide a base-line free from atmospheric water vapour and carbon dioxide absorption, and enable compensation to be made for the solvent when recording solution spectra. 

Throughout this manual the term extinction (symbol E) is employed. The extinction is defined as log 1 1 where and 1 are incident and transmitted light intensities, respectively. Spectrophotometers are calibrated directly in extinction units (also called optical density or absorbency). If the absorptiometer employed reads percentage transmission, T, calculate E as logio(100/r). The use of transmission values in absorptiometry is to be discouraged as they are rarely if ever simply related to the concentration of substance being measured. 

An assessment of spectral noise was made for data collected at both the AS-IRM and the SRC IRENI beamlines. The details of the measurements are provided in Table 15.1. root mean squared (RMS) noise was determined from 2450 to 2550 cm" for individual spectra, after converting the data from absorbance to percentage transmission. Three spectra were selected in each case. In sum, the two facilities produce similar quality spectral data for 4 X 4 pm sample-projected pixels (aperture based on RS spectromicroscopy and binned WF spectromicroscopy) measuring eight co-added scans for the AS-IRM data, and 64 co-added scans for IRENI data, the latter to overcome the noisier characteristics of the FPA detector. When collecting 64 scans at the AS-IRM beamline, the RMS noise level at 4 X 4 pm aperture and 6 cm resolution was reduced to 0.022% as expected. 

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