Sampling thieves’ used

Regardless of the method of evaluating the solids mixture, the sampling procedure is vital. Often a sampling thief, or other special device, is used to remove samples from the mixture without excessive disturbance of the batch. If an easier method of sampling is obvious and will bring less contamination to the batch, it should be used. 

Manual sampling should be carried out by grounded personnel, preferably using grounded metal equipment such as a metal sample thief bonded to the tank via metal cord. A satisfactory alternative is to place one or more glass sample bottles in a grounded metal cage (5-S.4.2). 

This is almost impossible to do satisfactorily because of the major segregation in the filling and vibrations in transport. Sampling should not be carried out in the top 30 cm to avoid the segregation in the surface layer that will have occurred as a result of vibration. When removing the samples, no surfaces on which particles can slide should be introduced. This can be achieved using a sample thief. ... 

Guidelines are to sample from a moving stream of powder and to sample the whole of the stream for many equal periods of time. This ensures that all parts of the powder are equally accessible and this maximizes accuracy.f The sample thief does not meet these criteria and therefore should not be used. Despite being popular, it suffers from many disadvantages, which lead to bias and error. Most other methods are immediately ruled out as suitable if these guidelines are followed. 

In Wargo s study, five blends of identical composition were subjected to different mixing times, 1, 5, 10, 15, and 20 min, respectively. At the specified time, the blender was stopped and samples equivalent to one to three dosage units, 200-600 mg, were removed from ten different powder bed locations using a sample thief. In the second part of this study, a single formulation was mixed for 30 min during which time six unit-dose samples were thieved from the blender at 2-min time intervals. In both experiments, powder samples were transferred to tared borosilicate sample vials and the sample... 

The removal of small samples without too much disturbance of the mixture was possible, via the very useful sampling thief which Coulson and Maitra devised. 

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