Comparison of the Performance of Two Sample Thieves for the Determination of the Content Uniformity of a Powder Blend

Abstract

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.

Monitoring Powder Blend Homogeneity Using Light-Induced Fluorescence

“…Powder blend sampling techniques are widely recognized as a potential source of error in assessments of blend homogeneity. The correct choice of blend thief and associated sampling technique is critical to acquiring representative blend uniformity data (13,14). Compared to LIF data acquisition, the more complex HPLC sample preparation, analysis methodology, and lack of replicates could have also contributed to observed high %RSD.…”

Composite method to quantify powder flow as a screening method in early tablet or capsule formulation development

“…Sampling devices and techniques are critical to the procurement of representative blend samples. Garcia et al have compared the performance of two sample thieves (plug and grain) to determine content uniformity of a powder blend [8]. Relative standard deviations for blend samples taken with the plug thief were approximately half of those obtained using the grain thief.…”

Particulate Analysis – Particle Size

“…This method should therefore be avoided during product development and quality control. The use of a sample thief will avoid the problems associated with particle segregation since the sample is taken from inside the powdered bed but the sample thief is still considered to be an inferior technique (Berman et al 1996;Garcia et al 1998). The very act of inserting the sample thief into the powder bed must disturb the powder to some extent, potentially changing its packing and altering the powder surrounding the outer walls of the thief.…”