Pharmaceutical Chemistry — 02
Sampling procedure
Selecting representative intact finished-product units from the manufactured batch, and carrying them to the laboratory with identity, integrity and traceability intact.
Sampling unit
The intact finished-product container, kept sealed during collection and transport
Selection
Predetermined, justified sampling plan — stratified across the filling sequence where appropriate
Governing guidance
WHO sampling guidance (2005), WHO GPPQCL (2024), ISO 2859-1
2.1
Objective
The objective of the sampling procedure is to obtain a representative selection of finished Acetylcysteine 20% w/v Nebulising Solution units from the manufactured batch for subsequent chemical analysis. The procedure must ensure that:
- —The selected samples adequately represent the batch;
- —Sample identity is maintained;
- —Contamination is minimised;
- —Degradation is minimised;
- —The samples remain physically and chemically intact; and
- —Complete traceability is maintained from the manufactured batch to the analytical result.
WHO defines sampling as an operation intended to obtain a representative portion of a pharmaceutical product for a defined purpose using an appropriate sampling procedure (WHO, 2005).
2.2
Why the dosage form affects the sampling procedure
The physical nature of the dosage form must be considered when designing the sampling strategy. Our product is a homogeneous aqueous solution. It is therefore different from:
- —A suspension, where particles may settle;
- —An emulsion, where phases may separate;
- —A cream, where components may become non-uniform; or
- —An ointment, where the API may be distributed within a semi-solid base.
Consequently, top/middle/bottom sampling of the liquid within one container should not automatically be used for our product. The main sampling concern is instead obtaining representative finished dosage units from the batch. This is an important distinction:
Top / middle / bottom
Refers to different physical regions of a bulk material.
Beginning / middle / end
Refers to different stages or locations in the manufacturing/filling process.
For our homogeneous solution, if the filling process is being considered, units may be selected from different stages of filling to provide representation across the batch.
2.3
Sampling plan
Sampling must be based on a predefined and justified sampling plan rather than convenience. WHO guidance states that sampling plans for finished products should be based on defined sampling standards, such as ISO 2859-1, and that when physical and chemical testing is required, the sampling units should consist of whole packs. Individual packs should not be opened merely for the purpose of sampling (WHO, 2005).
Therefore, for this project, the sampling unit will be the intact finished-product container. The exact number of containers selected should be determined from the applicable sampling plan, batch size and analytical purpose.
An arbitrary statement such as “three vials must always be collected” would not be sufficiently justified because the appropriate sample number depends on the sampling design and intended testing.
2.4
Representative sampling strategy
For the proposed manufacturing process, finished units can be selected according to a predetermined plan that provides representation across the batch. Where appropriate, sampling can be stratified across the filling sequence, for example:
The purpose is to detect possible variability between units produced at different stages of the filling operation. For example, if an issue developed during part of the filling process, analysing only one conveniently selected vial could fail to identify the problem. Selecting units from different stages provides a more representative assessment of the batch.
However, the beginning/middle/end approach is a proposed project sampling strategy, not a universal requirement that applies to every acetylcysteine product. The final number and exact selection pattern should follow the predetermined sampling plan.
2.5
Sampling unit
The sampling unit is the intact finished-product container. The selected container should remain closed during collection and transport. This is particularly appropriate for chemical testing because WHO specifies that finished-product sampling units should consist of whole packs and that individual packs should not be opened merely for the purpose of obtaining a sample (WHO, 2005).
Opening the container belongs to the subsequent sample preparation procedure, where a measured aliquot can be taken under controlled laboratory conditions. This distinction prevents the sampling procedure from overlapping unnecessarily with sample preparation.
2.6
Equipment and materials
The following materials should be available:
- —Appropriate personal protective equipment (PPE)
- —Clean sampling area
- —Clean and suitable sampling equipment, where required
- —Sample labels
- —Permanent marker or validated identification system
- —Sampling record/form
- —Suitable transport container
- —Original finished-product containers
The equipment and environment should be suitable for preventing contamination and maintaining sample integrity.
2.7
Detailed sample collection procedure
Step 1
Verify product identity
Before sampling, verify: product name; dosage form; strength; batch number; manufacturing/filling information; packaging configuration; and approved sampling plan.
This prevents samples from the wrong product, strength or batch from entering the analytical process.
Step 2
Review the sampling plan
The sampler should review the predetermined sampling plan before selecting any units. The plan should identify: which batch is being sampled; the number of units required; how the units will be selected; where applicable, the stages/locations from which units will be selected; the analytical tests required; and the requirements for storage and transport.
WHO guidance emphasises that sampling plans should be appropriately designed rather than based on arbitrary selection (WHO, 2005).
Step 3
Prepare the sampling area
The sampling area should be clean and organised. Unnecessary materials should be removed to minimise contamination, cross-contamination, sample mix-ups, and accidental substitution.
The sampler should also ensure that all required equipment and documentation are available before beginning.
Step 4
Wear appropriate PPE
The sampler should wear the PPE required by the laboratory or manufacturing site’s approved procedure. PPE helps protect both the product and the person performing the sampling.
Step 5
Select representative finished units
Select the required number of intact finished-product units according to the predetermined sampling plan. Where the filling process is being evaluated, the units may be distributed across different stages of the filling sequence: beginning → middle → end.
The selection must be planned rather than based on convenience.
Step 6
Inspect the selected units
Each selected unit should be examined for obvious defects before being accepted as a sample. The following should be checked: container damage; leakage; compromised closure; damaged packaging; unusual appearance; visible particulate matter; and any other evidence of compromised product integrity.
Any abnormality must be documented.
Step 7
Maintain container integrity
Selected units should remain sealed in their original containers during collection and transport. The product should not be unnecessarily transferred into another container during the sampling process.
This minimises exposure to environmental contamination and unnecessary exposure to air.
Step 8
Assign unique sample identification
Each selected sample should receive an identification that allows it to be traced to the original batch. The sample identification should link the unit to product name, strength, batch number, individual sample number, sampling date, sampling location/stage (where applicable), and sampler.
Traceability is essential because the final analytical result must be linked back to a clearly identified sample.
WHO good practices for pharmaceutical quality control laboratories emphasise documented sample identification, receipt and traceability throughout the testing process (WHO, 2024).
2.8
Sample labelling
Each selected unit should be clearly labelled or otherwise uniquely identified. The record should include, where applicable:
| Information | Purpose |
|---|---|
| Product name | Identifies the product |
| Strength | Confirms the correct formulation |
| Batch number | Links sample to manufacturing batch |
| Sample/unit number | Identifies the individual unit |
| Date and time | Establishes sampling history |
| Sampling stage/location | Establishes where the unit was selected |
| Sampler identification | Establishes responsibility |
| Storage requirements | Maintains sample integrity |
| Observations | Records abnormalities |
Clear identification prevents sample mix-ups and supports traceability.
2.9
Sample storage
The selected samples should be stored according to the established storage conditions for the final formulation. A storage condition should not be invented solely for the assignment if the final product specification has not yet established it.
The product should be protected from conditions that could alter its chemical or physical characteristics. This includes avoiding:
- —Unnecessary heat exposure;
- —Unnecessary exposure to air;
- —Inappropriate light exposure where relevant;
- —Excessive handling; and
- —Prolonged storage outside the established conditions.
This is particularly important because acetylcysteine is oxygen-sensitive (DailyMed, 2026). For a commercial acetylcysteine 20% solution, one current DailyMed presentation specifies storage at 20–25 °C before opening and refrigeration after opening, demonstrating why the storage condition should be tied to the actual product specification rather than assumed universally (DailyMed, 2026).
For our proposed product, the final storage condition should therefore be established as part of the formulation and stability specification.
2.10
Sample handling
The samples should be handled as little as reasonably possible between collection and analysis. The following principles should be followed:
- 01Keep the original container closed
- 02Avoid unnecessary exposure to air
- 03Avoid unnecessary transfer between containers
- 04Avoid excessive heat or other inappropriate environmental conditions
- 05Maintain clear sample identification
- 06Follow the established storage requirements
- 07Record any abnormal event or storage excursion
The purpose is to ensure that the sample reaching the analytical laboratory remains representative of the product that was originally manufactured.
2.11
Sample transport
During transport from the sampling site to the analytical laboratory:
- —Samples should remain securely closed;
- —Containers should be protected from physical damage;
- —Required storage conditions should be maintained;
- —Samples should remain clearly identified; and
- —Unnecessary handling should be avoided.
The transport conditions should preserve sample integrity rather than introduce changes that could affect the assay. WHO good laboratory practice guidance emphasises appropriate sample receipt, identification and control of conditions affecting sample integrity (WHO, 2024).
2.12
Prevention of contamination
Contamination can introduce substances into the sample that were not originally part of the formulation. This could produce additional chromatographic responses or interfere with acetylcysteine quantification. Contamination is minimised by:
- —Maintaining a clean sampling area;
- —Using clean and appropriate equipment;
- —Using appropriate PPE;
- —Avoiding unnecessary opening of containers;
- —Avoiding contact between the product and inappropriate surfaces;
- —Keeping samples properly sealed;
- —Maintaining correct sample identification; and
- —Following the predetermined sampling procedure.
WHO sampling guidance specifically emphasises precautions to prevent contamination and deterioration during pharmaceutical sampling (WHO, 2005).
2.13
Prevention of degradation
The sampling procedure must also prevent chemical degradation of acetylcysteine before analysis. This is important because the assay is intended to determine the amount of intact acetylcysteine in the finished product.
If the sample were allowed to degrade between collection and analysis, the analytical result could reflect the condition of the sample after poor handling rather than the condition of the manufactured batch. Acetylcysteine is described as oxygen-sensitive, making protection against unnecessary oxidative exposure particularly relevant (DailyMed, 2026). Therefore:
2.14
Sample receipt in the laboratory
When the samples arrive at the analytical laboratory, the receiving personnel should verify:
- 01Product identity
- 02Strength
- 03Batch number
- 04Sample identification
- 05Number of units received
- 06Container integrity
- 07Condition of the samples
- 08Relevant storage/transport information
- 09Any discrepancies between the received samples and the sampling record
The condition of the sample should be documented. If a container is damaged, incorrectly labelled, leaking, or otherwise compromised, the laboratory should document the issue and determine whether the sample remains suitable for testing according to the applicable laboratory procedure.
WHO good practices require procedures for delivery and receipt of samples and appropriate sample identification and records (WHO, 2024).
2.15
Why samples should not automatically be pooled
The selected finished-product units should not automatically be combined into one composite sample. If the purpose is to assess variability between individual units, analysing units separately provides more information. For example:
- —Unit A could have a slightly lower assay value.
- —Unit B could have a slightly higher assay value.
- —Pooling A and B could produce an average value that appears acceptable.
The average result could therefore hide variation between individual units. Consequently, where the analytical objective includes assessment of unit-to-unit consistency, individual units should be retained for individual analysis.
The final decision regarding individual versus composite analysis should be determined by the analytical objective and approved sampling plan.
2.16
Sampling and sample preparation are different stages
This distinction is important for the assignment.
Sampling answers
Which product units do we select from the manufactured batch?
Sample preparation answers
What do we do to the selected unit before injecting it into the HPLC column?
Therefore, during the sampling procedure, the selected unit remains sealed until it is required for controlled laboratory preparation. This creates a clear analytical workflow:
2.17
Summary of the sampling procedure
| Parameter | Proposed approach | Rationale |
|---|---|---|
| Product sampled | Finished acetylcysteine 20% w/v nebulising solution | Represents the final dosage form |
| Dosage form | Homogeneous aqueous solution | No routine top/middle/bottom sampling of the liquid is required |
| Sampling unit | Intact finished-product container | Maintains product integrity |
| Sampling plan | Predetermined and justified | Prevents convenience sampling |
| Batch representation | Units selected across the batch/filling sequence where appropriate | Detects possible between-unit variation |
| Number of units | Determined by the sampling plan | Avoids an arbitrary sample number |
| Container status | Sealed during collection and transport | Minimises contamination and degradation |
| Identification | Unique sample identification | Ensures traceability |
| Storage | According to established product specification | Maintains sample integrity |
| Transport | Controlled and documented | Prevents deterioration and mix-up |
| Inspection | Visual examination of container/product integrity | Identifies compromised samples |
| Documentation | Complete sampling record | Supports traceability and reproducibility |
| Subsequent procedure | Sample preparation | Separate from sampling |
Overall analytical rationale
The selected sample is the finished Acetylcysteine 20% w/v nebulising solution, not the raw API. Its homogeneous aqueous nature means that the major sampling concern is obtaining representative finished-product units rather than correcting for physical separation within a container.
The chemical characteristics of acetylcysteine, particularly its oxygen sensitivity, mean that the selected samples must be handled in a manner that preserves their chemical integrity. The presence of excipients and potential degradation products means that the subsequent HPLC method must demonstrate appropriate specificity.
The sampling procedure therefore provides the foundation for the subsequent analytical stages: