PubMed · 8232029
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J M Potter. 1993-11-01. Basic pharmacology.. https://doi.org/10.5694/j.1326-5377.1993.tb138042.x
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The effects of sample presentation on near-infrared (NIR) reflectance spectra were examined. Using a Foss NIRSystems Rapid Content Analyzer, which uses sample cups for sample presentation, four important parameters were identified: cup diameter, sample thickness, cup material and packing method. Below a critical diameter of 20 mm, which is dependent on the detector geometry, the spectra became increasingly distorted (i.e., changes in spectral intensities and spectral shape, shifts in peak positions and occurrence of Wood's peak). The minimum sample thickness not to cause spectral distortion was dependent on the physical and chemical nature of the substance. A thickness > or = 10 mm was found to be adequate for most pharmaceutical excipients. The method of packing was also important. Tapping a powdered sample sometimes caused significant changes (P < 0.05) in the spectral absorbance values compared with simply pouring the sample into the sample cup. Standard sample cups made from quartz were to be preferred owing to their lack of background absorptivity. However, the two commercially available flat based vials examined, which were made from soda glass and clear neutral glass, proved to be as suitable for all except applications of the most exacting nature. The spectral distortions resulting from variations in cup diameter, sample thickness and cup material were also shown to alter significantly the values of two commonly used identification algorithms, correlation coefficient (< 0.95) and maximum distance (> 3.0 standard deviation distance), sufficiently to cause misidentifications.
The objective of this study was to compare the performance of two sample thieves (plug and grain) to determine the content uniformity of a powder blend. The powder blend was prepared by mixing 2% drug substance with the remaining excipients in a tumble blender for 30 min. Samples were taken at 10 locations in the blender using both thieves. The performance of each sample thief was assessed based on the respective content uniformity values and relative standard deviations obtained for each device, as well as the content uniformity values reported following analysis of the resulting compressed tablets. The relative standard deviation values for blend samples taken with the plug thief were approximately half of those obtained using the grain thief. The superior performance of the plug thief in this study is attributed to the static charge acquired by the microcrystalline cellulose, which leads to poor flow characteristics. This impeded the flow of the blend into the sample chamber of the grain thief resulting in segregation and variable content uniformity results. The plug thief, which does not require powder flow to obtain a sample, performs better for this formulation. The selection of a sampling thief should be assessed on a case-by-case basis. Superior performance is expected for the plug thief when poor flowing, compressible blends are sampled.
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