Scoops / Spatula
- Small containers of solid materials may be adequately sampled using a spatula or scoop.
- The samples are then blended to provide a representative sample of that container.
- If the scoop used is too small for the sizes of particle being sampled, large particles will roll off and testing bias may be introduced.
- On the other hand, if the scoop is too big, an unnecessarily large sample will be obtained for a given number of increments.
- A scoopful of sample should be taken in a single movement and transferred to the sample container.
- Avoid tapping the scoop to remove pharmaceutical product as this is likely to cause segregation of the sample.
- Dip tubes should be used for sampling liquid and topical products and should be made of an inert material, such as polypropylene or stainless steel.
- For taking samples from large tanks and storage vessels, a container in a weighted carrier can be used.
- The container is designed such that it can be opened at the required depth.
- Marks on the cord used for lowering the container can be used to determine when the correct sampling depth has been reached.
- Sample thieves should be used when taking samples from deep containers of solids.
- The plug thief typically consists of a hollow tube with an inner rod that has a tip on the end to allow the thief to enter the powder bed in the closed position.
- The geometry of this tip can inﬂuence the sample taken; pointed tips distort the powder bed less than blunt-tipped probes, thereby reducing sampling error.
- Some thieves have a locking device that allows the sample volume to be set to the required sample weight, thereby reducing the weight variation in the sample population.
- A chamber thief generally consists of two concentric tubes;
- The inner tube is solid except for the chambers in which the sample is collected.
- The outer tube is hollow with openings that can be aligned with the chambers in the inner tube.
- A well-designed thief will have a sharp end to minimize disruption to the powder bed. When it is inserted into a static powder blend, a thief will distort the bed by carrying pharmaceutical product from the upper layers of the blend to the lower layers.
- The magnitude of this distortion can depend on whether the thief is inserted into the blend with a smooth, jerky or twisting action.
- Therefore, the correct sampling procedure should be deﬁned and staff trained in using the appropriate technique.
- The Angle at which the thief enters the powder bed can also inﬂuence sampling error. If a thief is inserted into the powder 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 powder 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. It is quite possible that the same thief could extract samples of different particle size from the top or bottom of a static powder blend.
Simple Bag-Sampling Spears
- Simple bag-sampling spears are the most commonly used instruments for taking samples from bags, because they are relatively cheap, simple and quick.
- Sampling spears generally have a maximum external diameter of about 12 mm, but can be up to 25 mm in diameter.
- To obtain a good cross-sectional sample, the spear should be 40–45 cm in length. The tapered type of sampling spear penetrates bags easily.