powder sampling

Question 1

why do we powder sample?

Answer 1

• To determine particle size distribution or drug content uniformity
• Not practical to test entire bulk of a powder

Question 2

what do you consider before conducting a powder sampling?

Answer 2

• Nature of the powder –physical properties e.g. packing, flow properties, tendency to segregate, friability
• Quantity of powder and sample size
• Associated assay technique
• Convenience
• Degree of precision required
• Avoidance of bias e.g. selection of sample does not affect the selection of another sample.

Question 3

what do you consider in your sampling programme?

Answer 3

• How many samples to represent the bulk? •Sample size?•Analysis? e.g. pool samples or analyse individually
• Method of sampling
• Probability or non-probability sampling?

Question 4

what are the rules of sampling?

Answer 4

Powder should be sampled in motion
Whole stream should be taken for many short increments of time, rather than part of the stream being taken for the whole of the time

Question 5

what are the two types of sampling programmes?

Answer 5

• Non-probability –judgment sampling. Samples chosen using expertise of operator –obtained from experience but may contain a bias. Done when probability sampling too difficult.
• Probability sampling –more complex but give more representative results. Random, stratified, systematic and cluster sampling.

Question 6

what do you consider about the sample size?

Answer 6

Heterogeneity: need larger sample size/number of samples to study more diverse product
•Desired precision: need larger sample size/number of samples to get smaller error
•Nature of analysis: complex multivariate statistics need larger number of samples
•Accuracy of sample depends upon number of samples/sample size, not ratio of sample to population

Question 7

what does random sampling entail?

Answer 7

Each unit has equal chance of being sampled
•e.g. formulated powder packed into small bottles, a batch of 10,000. Each bottle given a number and a random number generator selects 10 bottles from the run. Analyse entire content of bottle. •Alternatively samples could be extracted at random time points during filling.

Question 8

what does stratified sampling entail?

Answer 8

• Selecting units deliberately from various locations within a lot or batch or from various phases or periods of a process
• i.e. dividing the powder into different subsets and subset random sampling each
• Stratified sampling of the blend and dosage units specifically targets locations either in the blender or throughout operations, which have a higher risk of producing failing content uniformity results
• Every nthsample chosen during a production run. •Time not important, just the position

Question 9

what kind of powder does stratified sampling only work for?

Answer 9

•Only works for homogeneous powder

Question 10

what is cluster sampling?

Answer 10

• Powder/product divided into smaller clusters
• Clusters then chosen at random for analysis
• High error if clusters are different to each other

Question 11

what are the types of ways of obtaining powder samples?

Answer 11

•Static sampling (not in motion, so not as effective as dynamic sampling)•Scooping•Thieving•Cone and quartering•Dynamic sampling•Chute sampling•Spin riffling

Question 12

what is scooping?

Answer 12

• Plunge a scoop into a powder bulk
• Easiest method and provides the greatest errors. Not usually recommended
• Surface may not represent the bulk
• Chemical degredationof surface, segregation (upper layers have greater proportion of coarser particles)

Question 13

what is sample thief

Answer 13

•Device plunged into a powder bulk•Sample chamber opened and closed by operator•Retrieves small aliquots of powder•Improvement over scooping but thief may disturb blend, damage particles and compress powder.

Question 14

what is cone and quartering?

Answer 14

•Pour a cone of powder, as even as possible•Divide into quarters, then two opposite quarters are discarded•Remaining quarters are recombined and process repeated until desired sample size•Care –segregation when pouring –finer particles in centre.

Question 15

what does the spinning riffler do?

Answer 15

• Powder flows from hopper into rotating sample vessels i.e. must be relatively free flowing
• The stream is cut into small portions
• Need fast rotation compared to feed rate to reduce effects of segregation
• Samples may be analysed separately or subdivdedby selecting opposite vessels and repeating the process