Sampling of pellets

Which type of sample thief is used for sampling of pellets

Thieves are also sometimes referred to as “double-tube spears”

The angle at which the thief enters the powder bed can also influence sampling error. If a thief is inserted into the powder bed or a pellet bed vertically, it can extract samples of different particle size from those that would be obtained using the same thief inserted at an acute angle.

In addition the orientation of a chamber thief in relation to the bed (i.e. whether the chamber is at the top, the bottom or in the middle of the thief) may also influence the sampling error.

The material from which the thief is constructed, e.g. stainless steel or polypropylene, may also have an effect on sampling error due to static effects.

Sampling error can also be affected by bed depth, as the static pressure of the bulk blend forces the material into the sample chamber(s). This pressure is far greater at the bottom of a large container than it is in the middle or at the top.

Training is an essential part when you sample powders and pellets. It is also stressed by WHO and EMEA in their regulations pertaining to sampling procedures.

Its rather difficult to conclude on type of sampler needed without proper data about sample size, sample charecterestics,Pellet size, Bulk density, moisture content and place of sampling.



WHO Technical Report 929 Annexure-4 may be of a great help…

Just Browse it !

Sample Thieves

Sample thieves are the only available method for sampling bulk blenders. The two types of sample probes are side-sampling and end-sampling thieves. Side-sampling thieves contain a sample chamber within a tube. When rotated to the open position, the sample chamber aligns with the opening, thereby allowing the powder sample to flow into the cavity.

Examples of side sampling thieves include the grain thief, pocket thief, and slit thief. End-sampling thieves, also known as plug thieves, consist of a plunger inside a rod. The sample is obtained without the need for powder flow into the thief. Plug thieves cannot be used with poorly compressible powders because the sample would fall out of the tube as it is withdrawn from the powder bed. The diameter of the thief affects the tendency of samples to fall out.

Sampling bias of particulate systems by the use of sample thieves has been revealed by mixture solidification and image analysis techniques. Sampling bias is likely to occur when small samples are extracted with a thief from large volume populations for a variety of reasons, such as the following: Significant disturbances are produced during insertion of the sample thief into the static powder bed, which may result in inter particulate movement and segregation. The insertion of the thief into the powder bed may cause contamination of the lower regions with powder from the upper regions of the bed. Powder compaction during the insertion into the powder bed may inhibit powder flow into the sample chamber. Thief insertion may also cause particle attrition. The static pressure at the sampling location may affect powder flow into the sample chamber because greater pressure is observed at lower regions of the powder bed.

The flow of particles into the sample chamber of the sample thief introduces further uncertainty. Preferential segregation during thief sampling may arise due to particle size differences between drug and excipient particles as well as electrostatic properties. Larger particles (generally excipient) may preferentially flow into the cavity due to their enhanced flow properties In addition, free-flowing particles have been observed to enter the sample cavity of side-sampling probes before the thief was opened. Particles may be entrapped and cause difficulty in sample chamber closing. Particles entrapped in the space surrounding a closed sample chamber are captured when the sample chamber is opened.

The sampling technique may influence sampling bias when using sample thieves. Significant differences in the particle size distribution of sampled powders have been observed with sample depth, sample thief type, and sample chamber orientation. The angle of insertion may affect the flow dynamics of powder entering the sample chamber. Differences in powder sampling have been observed with different types of sample thieves. Tighter relative standard deviation (RSD) values have been obtained when using the plug thief compared with the use of a grain thief. However, difficulty in obtaining reproducible desired sample weights was observed for the plug thief.

For students from Pharmacutical and Biochem Engg institutes: Please read this article from your library

[COLOR=“blue”]International Journal of Pharmaceutics
Volume 155, Issue 2, 26 September 1997, Pages 153-178
Sampling practices in powder blending
Fernando J Muzzioa, , Priscilla Robinsonb, Carolyn Wightmana and Dean Bronea

“A regulatory guideline gives a basis of a method.When you have good science in your practice it serves you during regulatory inspections.Always read scientific papers and journals published.It gives you lot more flexibility at your work spot.”

True, Mr. Durga Prasad

Technical papers suggest the interpretation part from industry point of view while the guidelines are just imposing the requirements !!

Dear Mr prasad,
if we r directly sample thief is inserted to pellets possibility have broken the pellets which type of sample thief is used for sampling

One must use a proper technique during sampling.Its the angle. If you use it properly there will not be any issues that you are reffering to.

ok thanks Mr prasad

any guidlines for sampling of pellets from blender or bin.