Quantitative Determination of the Scattering and Absorption Coefficients from Diffuse Reflectance and Transmittance Measurements: Application to Pharmaceutical Powders

1997 ◽  
Vol 51 (3) ◽  
pp. 309-317 ◽  
Author(s):  
T. Burger ◽  
J. Kuhn ◽  
R. Caps ◽  
J. Fricke
Keyword(s):  
Particle Size ◽  
Diffuse Reflectance ◽  
Pharmaceutical Powders ◽  
Separate Determination ◽  
Absorption Coefficients ◽  
Absorption Properties ◽  
Flux Approximation ◽  
Reflectance Measurements ◽  
Made In

A measurement and data evaluation technique for the separate determination of the scattering and absorption properties of loose pharmaceutical powders is described. The equation of radiative transfer for diffuse reflectance and transmittance is analytically solved by using a three-flux approximation. Combined transmittance and reflectance measurements then allow one to derive both the scattering and the absorption coefficients. The scattering and absorption coefficients provide more information about particle size, degree of agglomeration, and chemical composition of the samples in comparison to the usual determination of only the ratio of the coefficients from diffuse reflectance measurements on optically thick samples. Furthermore, the theory of diffuse reflectance of optically thick samples according to Kubelka and Munk is compared to the three-flux approximation. The influence of the particle size on the scattering and absorption coefficient is investigated, and it is shown that the assumption of a wavelength-independent scattering coefficient, though often made in reflectance spectroscopy, is not generally valid.

NIR Radiative Transfer Investigations to Characterise Pharmaceutical Powders and Their Mixtures

1998 ◽  
Vol 6 (1) ◽  
pp. 33-40 ◽  
Author(s):  
T. Burger ◽  
J. Fricke ◽  
J. Kuhn
Keyword(s):  
Particle Size ◽  
Radiative Transfer ◽  
Absorption Coefficient ◽  
Pharmaceutical Powders ◽  
Absorption Coefficients ◽  
Hemispherical Reflectance ◽  
Flux Approximation ◽  
Particles Size Distribution ◽  
Set Up ◽  
Reflectance Measurements

A measurement and data evaluation technique to determine quantitatively and separately the scattering and absorption coefficients of disperse media has been applied to pharmaceutical powders and their mixtures. This technique uses a 3-flux approximation of the equation of radiative transfer to evaluate analytically directional-hemispherical reflectance and transmittance data with the boundary conditions adjusted to the experimental set-up in order to derive the scattering and absorption coefficient. The performance of this technique is demonstrated by applying it to a variety of pharmaceutical powders and comparing it to Kubelka–Munk's 2-flux approximation. By applying this technique, more information about the investigated powders (e.g. particle size, degree of agglomeration or chemical composition) compared to diffuse reflectance measurements on optically thick samples can be obtained. From the latter only the ratio of the scattering to the absorption coefficient is determined. Using lactose and ascorbic acid, the effects of varying particle size and particles size distribution on the scattering and absorption coefficients are shown. Additionally this technique has been applied to powder mixtures with different contents of acetylsalicylacid and microcrystalline cellulose to demonstrate the usefullness of this technique for quantitative analysis.

Determination of Particle-Size Distribution in GR-S Latexes

1954 ◽  
Vol 27 (4) ◽  
pp. 1051-1060 ◽  
Author(s):  
Alfred Nisonoff ◽  
W. E. Messer ◽  
L. H. Howland
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Light And Electron Microscopy ◽  
Wide Distribution ◽  
Plant Production ◽  
Particle Sizes ◽  
Laboratory Centrifuge ◽  
Made In

Abstract A method based on Stokes' law, involving the use of an ordinary laboratory centrifuge, is described for the determination of particle size distribution in GR-S latexes. It is shown to be valid by tests for reproducibility and by comparison with the results of light and electron microscopy. In applying the method, several unusually fluid high-solids latexes made in the pilot plant were found to be characterized by a wide distribution of particle sizes. Data on various latexes in plant production are reported.

The Measurement of Double Decay Rates in Small Enclosures Containing Highly Absorbent Samples

1994 ◽  
Vol 1 (4) ◽  
pp. 287-297
Author(s):  
M.J. Greaves ◽  
J.L. Homer
Keyword(s):  
Decay Rate ◽  
Three Dimensional ◽  
Sound Field ◽  
Decay Rates ◽  
Experimental Results ◽  
Common Method ◽  
Absorption Coefficients ◽  
Absorption Properties ◽  
Absorbent Material ◽  
Made In

One common method of obtaining the absorption properties of a sample of material is to measure the decay of sound in an enclosure partially lined with the sample. In order to infer absorption coefficients from decay rate measurements, it is assumed that the sound field in the enclosure is diffuse. When measurements are made in enclosures which are small compared with wavelength, and contain non-uniform absorption, the diffuse field may no longer be three-dimensional in nature. Descriptions are given of measurements made in a small rectangular enclosure with one surface lined with highly absorbent material, and the results presented. Predictions are made of the decay rates in this situation and compared with the experimental results. Finally, the different field states present during the decay are explored.

scholarly journals Determination of mean particle size by diffuse reflectance Foruier transform spectrometry.

1990 ◽  
Vol 27 (6) ◽  
pp. 383-387 ◽  
Author(s):  
Akira TSUGE ◽  
Yoshinori UWAMINO ◽  
Toshio ISHIZUKA ◽  
Kazuo SUZUKI
Keyword(s):  
Particle Size ◽  
Diffuse Reflectance ◽  
Mean Particle Size

Diffuse Reflectance and Transmittance Spectroscopy for the Quantitative Determination of Scattering and Absorption Coefficients in Quantitative Powder Analysis

1997 ◽  
Vol 51 (9) ◽  
pp. 1323-1329 ◽  
Author(s):  
T. Burger ◽  
H. J. Ploss ◽  
J. Kuhn ◽  
S. Ebel ◽  
J. Fricke
Keyword(s):  
Absorption Coefficient ◽  
Diffuse Reflectance ◽  
Scatter Correction ◽  
Least Squares Regression ◽  
Absorption Coefficients ◽  
Component Mixture ◽  
Hemispherical Reflectance ◽  
Flux Approximation ◽  
Nonlinear Relation ◽  
Powder Analysis

A three-flux approximation of the equation of radiative transfer is used to separately determine the effective specific scattering and absorption coefficients of powder mixtures from hemispherical reflectance and transmittance measurements. For a two-component mixture of lactose and paracetamol, it is demonstrated how the knowledge of the separately known scattering coefficient can be used to improve partial least-squares regression (PLS) calibrations of diffuse reflectance data pretreated by multiplicative scatter correction (MSC). Furthermore it is shown that the measured specific absorption coefficient of the investigated mixtures is not generally a linear function of the constituents concentration, a result which might be caused by the mixing procedure of the samples. With the use of the absorption coefficient, it is demonstrated that artificial neural networks are superior to PLS calibrations when modeling a nonlinear relation.

scholarly journals Determination of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy

2008 ◽  
Vol 33 (4) ◽  
pp. 7-12 ◽  
Author(s):  
M. A. Gotardo ◽  
R. Sequinel ◽  
L. Pezza ◽  
H. R. Pezza
Keyword(s):  
Diffuse Reflectance ◽  
Diffuse Reflectance Spectroscopy ◽  
Limit Of Detection ◽  
Pharmaceutical Formulations ◽  
Reflectance Spectroscopy ◽  
Reaction Conditions ◽  
British Pharmacopoeia ◽  
Reflectance Measurements ◽  
Good Agreement

A simple analytical method for quantification of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy is described. The method is based on the reaction, on the filter paper surface, between the drug and p-chloranil producing a colored compound. The best reaction conditions were obtained with 20 µL of atenolol solution and 20 µL of p-chloranil. All reflectance measurements were carried out at 550 nm and the linear range was from 1.13x10-2 to 7.88x10-2 mol L-1 (r = 0.9992). The limit of detection was 2.80 x 10-3 mol L-1. The proposed method was successfully applied to analysis of different commercial brands of pharmaceutical formulations and the results obtained by the proposed method were in good agreement with those obtained using the British Pharmacopoeia method.

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