Understanding ISO/IEC 17025:2017 Clause 7.3.1 – Sampling

Ensuring Validity and Reliability in Food Testing Labs

In the field of laboratory testing, sampling is a critical step that directly affects the validity and reliability of test results of the products. Clause 7.3 of ISO/IEC 17025:2017 focuses on the laboratory's responsibilities when it is involved in the sampling of materials, or products prior to testing.

This clause is important in food testing laboratories, where sampling errors can lead or cause to misleading test results, regulatory non-compliance, or even public health risks. A well-designed and statistically sound sampling process is essential to producing accurate, repeatable, and representative results.

What Clause 7.3.1 Requires

Clause 7.3.1 states:

“The laboratory shall have a sampling plan and method when it carries out sampling of substances, materials or products for subsequent testing or calibration. The sampling method shall address the factors to be controlled to ensure the validity of subsequent testing or calibration results. The sampling plan and method shall be available at the site where sampling is undertaken. Sampling plans shall, whenever reasonable, be based on appropriate statistical methods.”

Break this clause into more understandable :

1. The Laboratory Must Have a Sampling Plan and Method

This means that if the laboratory is responsible for collecting samples for testing (e.g., pesticide residue in vegetables, aflatoxin in spices, contaminants in milk or microbiology analysis, it must have a documented sampling plan and procedure. This plan should specify:

• What is being sampled (e.g., 50 kg of rice)

• How the sample will be taken (e.g., stratified sampling from different bags)

• What tools will be used (e.g., sample thief, sterile containers)

• Sample size and handling requirements

• Calculation/ statistics method

• Precautionary measure

2. Sampling Must Address Factors That Impact Validity

Sampling plans must control variables that can affect the integrity of the test results. For example:

• Contamination prevention: Avoiding contamination during sample collection

• Homogeneity: Ensuring that samples are representative of the entire batch/lot

• Timing: Sampling at the right time to ensure sample stability

• Storage and transport: Maintaining sample integrity during the transport (e.g., cold chain)

In food testing, these factors are crucial. A pesticide sample that degrades due to heat during transport may result in false negatives results, misleading customers or regulators.

3. Sampling Plan Must Be Available at the Site

The sampling plan and method must be physically or digitally accessible at the sampling location. This ensures that sampler or field personnel follow the correct procedures without relying on memory. Many accredited food labs use sampling checklists, mobile apps, or SOPs in the field. It is essential that procedure for the sampling must be available at the sampling site.

4. Use of Statistical Methods

Wherever practical, sampling plans should be based on statistical principles. This ensures the sample size and method are appropriate to produce representative and unbiased data. Examples include:

• Random sampling to avoid bias

• Stratified sampling in heterogeneous lots

• Lot sampling formulas (e.g., as per Codex, or ISO standards)

Using statistical sampling also strengthens the lab’s results, especially during audits, disputes, or regulatory inspections.

Example: Food Testing Lab Sampling for Pesticide Residue

A food testing laboratory receives a request to test 10 tons of apples for pesticide residue as per FSSAI norms. The apples are stored in 100 crates at a warehouse.

The lab prepares a sampling plan as follows:

• Objective: Collect a representative composite sample of 1 kg

• Sampling method: Use stratified random sampling – select 20 crates randomly, and take 50 g from each

• Tools: Clean stainless-steel scoops and sterile zip-lock bags

• Control measures:

a) Use gloves and masks to prevent contamination

b) Store the composite sample in a refrigerated container below 4°C

c) Label with date, time, lot number, and sampler initials

• Statistical basis: Based on ISO 7002:1986 and Codex guidelines

This plan ensures that the 1 kg sample tested at the lab is representative of the full 10-ton lot.

Why Clause 7.3.1 important in Food Testing

Regulatory Compliance

Food safety authorities like FSSAI, APEDA,IOPEPC and EIC require that sampling follow documented protocols. Failure to meet this requirement may invalidate test results.

Customer Trust

Clients rely on labs to provide accurate test reports. If the sample isn’t taken properly, even the most precise lab instruments won’t give reliable results.

How to Implement Clause 7.3.1

1. Develop sampling SOPs for all major commodities: grains, fruits, spices, milk, etc.

2. Train field personnel on proper sampling techniques, hygiene, and documentation.

3. Use sampling kits with all tools and materials needed.

4. Maintain records of each sampling activity including conditions, observations, and deviations.

5. Review and update plans regularly based on feedback, changes in standards, or incidents.