ISO 17025 Sampling Requirements: How to Build a Compliant Sampling Plan

ISO 17025 sampling requirements define how you select, collect, and prepare samples when your lab controls the sampling step. You must use a documented sampling method and plan that produce representative samples and support valid test or calibration results. When sampling goes wrong, even a strong quality management system cannot protect your data.

Sampling matters because it sits at the start of conformity assessment. ISO 17025 expects you to manage sampling with the same care as testing, including traceability, records, and risk control. These requirements link closely to management requirements, structural requirements, and impartiality and confidentiality, and they align well with ISO 9001 principles used in many quality manuals.

The rules apply when you or your lab act as the sampler, not when a customer or third party fully controls that work. Knowing where responsibility starts and ends helps you avoid nonconformities and protect confidence in your results. A clear sampling plan also makes audits smoother and strengthens your overall quality management approach.

Key Takeaways

• Sampling under ISO 17025 must be planned, documented, and controlled.
• Requirements apply when your lab is responsible for sampling activities.
• Strong sampling supports traceability, impartiality, and reliable results.

Video Walkthrough: ISO 17025 Sampling Requirements (Clause 7.3)

Watch the video below for a concise overview of ISO 17025 Clause 7.3. I’ll walk you through how to build a compliant sampling plan, develop an effective sampling SOP, and manage sampling records and chain-of-custody documentation to meet auditor expectations.

Why Sampling Matters So Much Under ISO 17025

Sampling shapes the quality of every test result you report. If you collect a poor sample, even the best method and equipment cannot fix the error. ISO 17025 treats sampling as a core activity because it directly affects result validity.

You often work with large or mixed materials. You test only a small portion. That portion must reflect the whole. ISO 17025 expects you to control this risk through clear sampling plans and methods.

For testing and calibration laboratories, sampling defines trust. Clients and regulators rely on your results to make decisions. When sampling fails, results can mislead and cause disputes or rework.

Sampling also affects consistency across testing and calibration labs. Standard methods help you produce repeatable results across sites, staff, and time. This control supports fair comparisons and audits.

If you’d like a deeper look at how sampling fits into the bigger picture of valid results, my article on Ensuring the Validity of Results ISO 17025 walks through the broader controls in Clause 7.7 that your sampling plan should support.

• Result validity: Representative samples support accurate results
• Risk control: Planned sampling reduces bias and contamination
• Compliance: Documented methods meet audit and accreditation needs
• Traceability: Clear records link results back to the sample source

Common sampling risks and controls:

Risk	Control
Contamination	Clean tools and proper handling
Bias	Random or stratified selection
Degradation	Correct storage and transport
Inconsistency	Written plans at the sampling site

When ISO 17025 Sampling Requirements Apply (And When They Don’t)

ISO 17025 sampling requirements apply only when you are responsible for sampling. This includes cases where your lab collects samples in the field or defines how sampling must occur before testing or calibration.

If you control sampling, ISO 17025 expects you to use a documented method. You must define how you select samples, follow a sampling plan, and prepare samples for testing. These duties link directly to 7.1 review of requests, where you confirm that sampling needs, methods, and responsibilities are clear before you accept the work.

Sampling requirements also apply when you subcontract sampling but still retain responsibility. In this case, you must ensure the method meets ISO 17025 and suits the test purpose.

ISO 17025 sampling requirements do not apply when the customer supplies samples and controls how they were collected. You still need to assess sample condition and suitability, but you do not need an accredited sampling method.

The table below shows when the requirements apply:

Situation	Sampling Requirements Apply?
You collect samples	Yes
You design the sampling plan	Yes
Customer collects samples	No
Sampling done outside your control	No

During 7.1 review of requests, you must record who is responsible for sampling. Clear agreement at this stage helps avoid disputes, invalid results, and nonconformities during audits.

Overview Of ISO 17025 Sampling Requirements

ISO/IEC 17025 sets clear rules for how you plan, perform, and control sampling. The ISO/IEC 17025:2017 version places sampling within Clause 7, which defines the core process requirements for laboratories.

Sampling doesn’t stand alone—it’s part of the broader process requirements in Clause 7. If you want the full context, my ISO 17025 Clause 7 Process Requirements Explained article walks through how sampling, handling, testing, and reporting all link together.

You must treat sampling as a controlled activity, not a casual task. When sampling affects test or calibration results, the ISO/IEC 17025 standard requires you to define methods, responsibilities, and records. This applies whether you sample raw materials, finished products, or calibration items.

Your sampling methods must suit the intended use of the results. You need to validate methods when standard methods do not exist or when you modify them. Method validation helps you show that your approach produces reliable data under real conditions.

ISO 17025 also requires control of facilities and environmental conditions during sampling. You must manage factors like temperature, humidity, and contamination risks. These controls help protect sample integrity from collection through transport.

You must maintain clear records for each sampling activity. Records typically include:

• Sampling plan and method
• Location, date, and time
• Sampler identity and competence
• Handling and storage details

When applicable, you should use certified reference materials to support traceability and confidence in results. This aligns sampling with broader ISO 17025 process requirements and supports consistent laboratory performance.

Step-By-Step: How To Build A Compliant Sampling Plan

You build a compliant sampling plan by setting clear goals, defining what you sample, and using controlled methods. ISO/IEC 17025 clause 7.3 sampling expects written plans, valid sampling methods, and proper sample handling that protects result quality.

Define The Objective And Scope

Start by stating why you sample and how the results will support testing or calibration. Link the objective to a clear decision, such as product release, compliance checks, or trend monitoring.

Define the scope in plain terms. Specify the material, product, or location you will sample. State where sampling occurs and when it applies.

Document limits and exclusions. For example, note if the plan applies only to routine samples or excludes customer‑supplied items.

Include at minimum:

• Purpose of sampling
• Applicable tests or calibrations
• Regulatory or customer requirements

Describe The Population And Sampling Units

Define the population you want to represent. This may include a batch, lot, area, container set, or time period.

Break the population into sampling units. A unit could be one container, one location, one tablet, or one time‑based grab sample.

Describe key traits that affect variability. These may include size, layout, storage conditions, or production stages.

Use simple diagrams or tables when helpful.

Element	Example
Population	5,000 kg raw material lot
Sampling unit	One sealed bag
Total units	100 bags

Choose An Appropriate Sampling Strategy

Select a sampling strategy that matches the objective and risk. ISO 17025 expects you to justify your approach.

• Random sampling to reduce bias
• Systematic sampling at set intervals
• Stratified sampling when groups differ
• Judgmental sampling with documented reasoning

Avoid convenience sampling unless justified. Explain why the chosen method controls known risks.

If a standard method applies, reference it. If you use a lab‑developed method, document how it ensures valid results.

Determine Sample Size And Frequency

Define how many samples you collect and how often. Base this on variability, risk, and decision impact.

Use statistics when possible. Consider historical data, process stability, and acceptance criteria.

Explain sampling frequency in clear terms. For example, sample per batch, per shift, or per delivery.

Document rules for increased or reduced sampling. Triggers may include failures, changes, or complaints.

Record:

• Number of samples
• Sampling intervals
• Conditions that change frequency

Define Sampling Procedures And Techniques

Write step‑by‑step instructions for how you collect samples. Keep language simple and precise.

Include tools, equipment, and materials used. Specify cleaning steps to avoid contamination.

Describe the exact technique, such as grab, composite, or incremental sampling. Note any environmental controls needed.

Address deviations. State how staff must record and report any changes to the sampling plan.

Procedures must stay available at the sampling site, as required by 7.3 sampling.

Include Handling, Preservation, And Transport

Protect the sample from damage, loss, or change. This is a core part of compliant sample handling.

Define how you label samples. Include ID, date, time, sampler, and conditions.

Describe preservation steps, such as cooling, drying, or chemical treatment. State time limits before testing.

Cover transport and storage. Specify containers, temperature ranges, and security controls.

Stage	Key Controls
Storage	Temperature and light limits
Transport	Sealed containers
Holding time	Maximum allowed duration

Clarify Roles, Responsibilities, And Competence

Assign clear responsibility for each sampling task. Name roles, not just job titles.

Define who can sample, who reviews records, and who approves changes to the sampling plan.

Confirm competence. Staff must receive training on sampling methods, equipment use, and safety.

Keep training and authorization records. ISO 17025 expects proof of competence for sampling work.

State who handles nonconforming sampling events and customer communication.

Writing Sampling Procedures That Meet ISO 17025

You need sampling procedures that give repeatable results and support valid test and calibration work. A clear sampling SOP links field work to technical records, test reports, and calibration results without gaps.

What A Sampling SOP Should Include

Your sampling SOP must clearly define who samples, what they sample, and how they sample. State the scope, sample types, and sampling locations. Identify trained staff and list the equipment they use, including any equipment calibration requirements.

Describe the sampling method in clear steps. Cover sample selection, sample size, and any controls used to prevent contamination or mix-ups. If conditions affect results, record them.

Explain how you label, store, and transport samples. These steps protect sample integrity and support valid reporting of results. Define what records you keep, such as field notes, chain-of-custody forms, and technical records.

Address how sampling data links to test reports, calibration certificates, and calibration results. This link shows traceability during audits.

Example Structure For A Sampling SOP

A simple structure helps you stay compliant and consistent. Use clear sections and short instructions.

SOP Section	Purpose
Scope and purpose	Defines when and why you apply the procedure
Roles and responsibilities	Assigns sampling and review duties
Equipment and calibration	Lists tools and equipment calibration needs
Sampling method	Describes step-by-step sampling procedures
Sample handling	Covers labeling, storage, and transport
Records and reports	Links data to test reports and technical records

Add references to related procedures, such as reporting of results or equipment calibration. Keep forms and templates attached or linked.

Sampling Records, Traceability, And Chain Of Custody

Accurate sampling records support traceability, protect data integrity, and meet ISO 17025 Clause 7.5 technical records requirements. Clear documentation and controlled custody reduce the risk of sample mix-ups, data loss, and invalid results.

For more on how your sampling records tie into the bigger traceability picture, see Measurement Traceability in ISO 17025, where I explain how sample origin, time of collection, and conditions feed into trustworthy measurement results.

Essential Data To Capture On Sampling Forms

You must record enough detail to trace each sample from collection to final result. Sampling forms should link the sample to the test request, method, and reported data without gaps.

Key data to capture includes:

• Unique sample ID and client reference
• Sampling date, time, and location
• Sampler name and authorization
• Sampling method and equipment used
• Environmental conditions, when relevant
• Sample quantity, container type, and preservatives
• Any deviations from the sampling plan

These records support traceability and help with the evaluation of measurement uncertainty. Sampling conditions can affect results, so you need to document them clearly. If you use a laboratory information management system (LIMS), enter data promptly and restrict edits. This protects recordkeeping and maintains data integrity during audits.

Chain Of Custody And Sample Integrity

Chain of custody shows who controlled the sample at every step. You must document each transfer from collection through testing and storage. This prevents disputes and supports result validity.

A clear chain of custody record should show:

• Date and time of each handoff
• Names and signatures of responsible staff
• Storage conditions during transport and holding
• Seal numbers or tamper evidence, if used

Once the sample enters your laboratory, you are responsible for maintaining custody. Store samples under defined conditions and track movements in your LIMS or controlled logs. Any break in custody or improper handling can affect traceability and measurement uncertainty.

Validating And Reviewing Sampling Plans And Methods

You must confirm that your sampling plan produces reliable results and supports valid test decisions. This requires careful method selection, proof of performance, and regular review. Your approach must also link sampling to measurement uncertainty and decision rules used for reporting results.

Standard Methods Vs In-House Sampling Methods

You should use standard sampling methods when they fit your scope and sample type. These methods often include defined procedures, acceptance criteria, and known performance limits. You still need to verify that the method works under your actual conditions, staff skills, and equipment.

You must validate in-house sampling methods before use. Validation should show that the method meets its intended purpose and supports accurate testing. Focus on factors such as consistency, bias, and sample handling effects.

Key validation checks may include:

• Sample selection logic and coverage
• Repeatability of the sampling process
• Impact on measurement uncertainty
• Links to metrological traceability

You should document all validation results and approvals.

Assessing Representativeness And Fitness For Purpose

You must ensure that samples represent the material, site, or batch being tested. Poor sampling can increase the uncertainty of measurement, even when the test method performs well. You should assess how sampling affects result reliability and decision-making.

Fitness for purpose depends on the test objective. Regulatory testing, trend monitoring, and conformity assessment may require different sampling rigor. You should align sampling detail with your decision rules and risk level.

Important factors to review include:

• Sampling location and frequency
• Sample size and homogeneity
• Environmental and handling controls
• Contribution to 7.6 evaluation of measurement uncertainty

You should record assumptions and known limitations.

Reviewing And Updating The Sampling Plan

You must review your sampling plan at defined intervals and after any change. Triggers include new matrices, method updates, customer requirements, or unexpected results. Reviews help confirm continued suitability and control risk.

You should evaluate:

• Sampling errors or nonconformities
• Feedback from test results and audits
• Changes affecting method selection or uncertainty
• Ongoing validity of validation data

You must update the plan when evidence shows reduced effectiveness. All revisions should remain controlled, approved, and communicated to staff to ensure consistent sampling practice.

Risk-Based Thinking Applied To Sampling

Risk-based thinking under ISO/IEC 17025 requires you to control sampling conditions that can affect test results. You focus on risks that threaten technical competence, traceability, and valid data. You also show how you review and adjust sampling during management review to support laboratory accreditation.

Identifying Sampling Risks

You identify sampling risks by looking at where errors can enter before testing starts. These risks often affect laboratory competence more than instrument issues.

Common sampling risk areas include:

Risk area	What can go wrong	Why it matters
Sampling location	Non-representative site	Results do not reflect reality
Method selection	Wrong or outdated method	Data becomes invalid
Personnel	Poor training or bias	Loss of impartiality
Environment	Temperature or contamination	Sample integrity changes
Transport and storage	Delays or poor containers	Sample degrades

You document these risks as part of your risk management process. Accreditation bodies such as IAS, CLAS, NABL, and ILAC expect you to show awareness, not perfection. During management reviews, you revisit sampling risks and note trends, complaints, or audit findings that affect iso 17025 accreditation.

For more detailed guidance on how accreditation bodies assess sampling activities, including when sampling is accredited as a standalone activity, see the document Principles for the Assessment and Accreditation of Sampling Methods.
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Using Risk To Design And Adjust The Plan

You use risk-based thinking to design a sampling plan that fits the sample type and use of results. Higher risk samples need tighter controls and clearer instructions.

You may adjust your plan by:

• Increasing sample numbers for variable materials
• Adding field blanks or duplicates
• Narrowing time windows for collection
• Assigning only qualified staff

You record these decisions and link them to risk level. When conditions change, such as new sites or clients, you update the plan instead of starting over.

Common Sampling Nonconformities (And How To Avoid Them)

Sampling nonconformities often start before testing begins. You may collect samples without a defined plan, or staff may not follow the approved method. These issues can affect the validity of results and lead to nonconforming work.

A frequent finding involves poor sample identification and traceability. Labels may lack dates, locations, or sampler names. You can avoid this by using controlled labels and requiring checks at the time of collection.

Another common issue is weak control of sampling conditions. You may fail to record temperature, time, or handling steps. These gaps reduce confidence in results. Simple quality control measures, such as required field logs, help prevent this.

Changes made during sampling also cause problems. Staff may adjust locations or methods without approval. When this happens, you must treat the activity as nonconforming work and assess the impact on results.

The table below shows typical issues and practical controls:

Common issue	How you avoid it
No sampling plan	Approve and control plans before use
Incomplete records	Use required field checklists
Untrained samplers	Document competence and refresher training
Unapproved changes	Enforce change and deviation review

When a sampling error occurs, you need timely corrective actions. Identify the root cause, fix the process, and confirm the action works. Avoid closing actions without verification.

Sampling problems can also trigger 7.9 complaints. Clients may question representativeness or handling. You should link complaint reviews to sampling records and use them to improve your process.

When Customers Or Third Parties Do The Sampling

You still hold responsibility for the test results, even when you do not take the samples yourself. You must control how sampling affects result quality through clear agreements, records, and reporting.

Clarifying Responsibilities In Contract Review

You must define sampling responsibilities during contract review before you accept the work. State clearly whether you, the customer, or a third party performs the sampling.

Document any limits on your responsibility when others collect samples. Confirm whether the sampling method meets your test requirements and supports valid results.

Focus on these points during review:

• Who performs the sampling
• Which sampling method is used
• How samples get identified, stored, and transported
• What risks sampling may add to results

If the sampling method does not meet your needs, you must inform the customer. Record any agreed limits in the contract. Use proficiency testing and trend reviews to check whether external sampling affects result consistency.

What To Record On Test Reports

Your test report must state that the customer or a third party performed the sampling. This disclosure supports transparency and protects result interpretation.

Include clear sampling-related details when they affect results:

• Sampler identity or organization
• Sampling date and location
• Sampling method or reference
• Known deviations or missing controls

When sampling falls outside your control, add a note that results relate only to the item received. Do not imply responsibility for sampling quality you did not manage.

If sampling conditions may affect uncertainty or validity, reflect this in your report. Keep report language factual, clear, and limited to verified information.

Tools And Templates To Help You Build A Sampling Plan

You can reduce risk and rework by using the right tools when you design your sampling plan. Templates, training, and audits help you keep sampling consistent, documented, and aligned with ISO 17025.

Using Templates To Save Time

Audit-ready templates help you build a sampling plan that meets ISO 17025 without starting from scratch. You use them to define who samples, what you sample, and how you control conditions at the sampling site.

Good templates prompt you to document key items, such as:

• Sampling method and justification
• Sample size and selection rules
• Environmental conditions and controls
• Equipment used and calibration status
• Chain of custody and labeling steps

You still need to adapt each template to your scope. Do not copy text without review. Make sure the plan matches your test methods, risks, and customer needs.

Version control matters. You should track approvals, changes, and issue dates so staff always use the current plan during sampling.

Training And Internal Audits Focused On Sampling

Training turns a written sampling plan into consistent practice. You should train staff on how to follow the plan, how to record results, and how to handle deviations in the field.

Focus training on real sampling tasks, not theory. Cover site access, contamination risks, and sample transport. Keep records of training and competence.

Internal audit activities help you confirm that sampling matches your documented plan. During an internal audit, check:

• Actual sampling steps versus the plan
• Completeness of sampling records
• Handling of nonconforming samples

Use audit findings to update templates, retrain staff, or improve controls.

Next Steps – Strengthen Your Sampling Plan

Review Your Current Sampling Practices

Start with a gap analysis of your current sampling activities against ISO 17025 requirements. Compare what you do in practice with what your documented sampling plan states.

Focus on these core areas:

• Sampling plan: Defines purpose, method, locations, and sample size.
• Sampling method: Uses valid and suitable techniques for the material.
• Staff competence: Confirms training and authorization for sampling tasks.
• Sample handling: Controls labeling, storage, transport, and preservation.

Check if your records show consistent use of the plan. Look for missing details, unclear steps, or outdated methods.

Update documents to match real practices. If conditions change at the sampling site, record how you address them. Clear and current records support traceability and audit readiness.

Get Help If You’re Unsure

Seek support if you cannot confirm that your sampling meets ISO 17025 expectations. Unclear methods or weak records can affect result validity.

You can get help through:

• Internal technical experts who know your materials and processes.
• External consultants with ISO 17025 sampling experience.
• Accreditation bodies or guidance documents that clarify sampling controls.

Ask for a targeted review of your sampling plan and methods. Focus on risks that affect sample representativeness.

Training also helps. Make sure staff understand why each step matters, not just how to perform it. Clear guidance and skilled staff reduce errors during sample collection and handling.

Frequently Asked Questions

ISO 17025 sets clear rules for how you plan, perform, and record sampling. These rules focus on control, traceability, and proof that your samples support valid test or calibration results.

What are the key elements of an acceptable sampling procedure according to ISO 17025?

You must define the sampling method, location, and conditions before you start. The procedure needs clear steps that staff can follow without guesswork.

You also need controls for sample identification, handling, and storage. These controls protect the sample from damage, mix-ups, or contamination.

How does ISO 17025 define the criteria for sampling adequacy and representativeness?

You must show that the sample reflects the item, batch, or environment being tested. The sampling method needs to match the purpose of the test or calibration.

You must record factors that affect representativeness, such as location, time, and environmental conditions. If limits exist, you must state them clearly in your records and reports.

What does Clause 7.1 of ISO 17025:2017 specify about sampling?

Clause 7.1 requires you to review sampling requests before accepting the work. You must confirm that you have the competence, methods, and resources to perform the sampling.

You must also agree on responsibilities with the client. This includes who performs sampling and how results will be reported.

Can you outline the procedural requirements for sampling under ISO 17025?

You must follow documented sampling procedures whenever sampling affects result validity. These procedures must describe how you select samples and control conditions.

You must identify samples clearly and track them from collection to testing. You also need to record any deviations from the procedure.

What documentation is necessary to meet ISO 17025 standards for sampling?

You must keep sampling procedures, plans, and records. Records need details such as date, location, method, and sampler identity.

You must also document sample condition on receipt and any issues found. These records support traceability and audit review.

How are sampling plans developed and implemented to comply with ISO 17025 guidelines?

You develop sampling plans based on the test purpose and sample type. The plan defines selection criteria, quantity, and acceptance limits.

You must train staff to follow the plan as written. You also review and update the plan when conditions, methods, or risks change.

Conclusion

You play a direct role in meeting ISO 17025 sampling requirements when you plan, perform, and record sampling work. Your sampling choices shape test results before any analysis begins.

You need a documented sampling plan when you collect samples. Keep the plan available at the sampling site, and make sure staff follow it without guesswork.

You must control key factors that affect sample quality. These include contamination risks, sample stability, storage conditions, and transport time.

You should use statistical methods when practical. Random or stratified sampling helps you collect samples that represent the full batch and reduce bias.

Strong sampling practices support audits, customer trust, and regulatory reviews. Clear records help you explain how and why you collected each sample.

Focus on these actions in daily work:

• Train staff on approved sampling methods
• Use clean, suitable tools and containers
• Label samples clearly and completely
• Record conditions, dates, and deviations

When you treat sampling as a controlled laboratory activity, you protect the validity of every test that follows.