SOP for Preparation of a 2.5% w/v Sodium Hydroxide Solution

In short: This template describes a site-specific 2.5% w/v sodium hydroxide solution only where the approved cleaning procedure calls for it. The calculation is 25 g per litre of final solution, so 250 g is used to make a final volume of 10 L; it is not added to 10 L of water. This example does not give a drain-disposal method, and several preparation details require site confirmation.

Purpose and scope

This procedure template covers preparation and control of a 2.5% w/v sodium hydroxide (caustic soda) solution for an approved equipment-cleaning use. This example identifies the pellet section and equipment/accessories, but does not identify the site or define the surfaces, cleaning method, solution hold time, or disposal route. Complete the controlled copy for the actual site and approved cleaning procedure before use.

Example in-house criterion (not a pharmacopoeial requirement): The inherited target is 2.5% w/v. It is a site cleaning-solution target, not a concentration prescribed by the cited GMP provisions. Those provisions require suitable cleaning controls and written procedures; they do not set this solution strength.

Where equipment or utensils are used in manufacturing a U.S. drug product, 21 CFR §211.67(a)–(c) (current eCFR text up to date 15 October 2026) calls for appropriate cleaning and maintenance, written procedures and related records. India’s revised Schedule M, Part I, §§13.6 and 13.8 (G.S.R. 922(E), 2023) addresses scheduled cleaning of production equipment and selection/use of cleaning and drying equipment to avoid contamination. Neither source specifies a 2.5% sodium hydroxide solution.

Concentration calculation

For a 2.5% w/v target, use 2.5 g of sodium hydroxide per 100 mL of final solution:

Use the approved raw-material specification and site calculation procedure. Prepare to the final solution volume; adding the amount to the same volume of water does not define the same w/v concentration. Do not adjust for assay or purity unless the approved formula specifies how.

Safety and preparation

Sodium hydroxide is corrosive. International Chemical Safety Card ICSC 0360 (ILO/WHO, May 2010) reports that contact with water or moisture generates heat and instructs users to add the solid slowly to water when dissolving; it also warns against pouring water onto the solid. Follow the current supplier safety data sheet, the site’s chemical-handling procedure and task-specific risk assessment. Use only the protective equipment, ventilation, eyewash access, compatible vessel and mixing equipment approved for the site and task.

Example in-house criterion (not a pharmacopoeial requirement): If the approved cleaning procedure requires this solution, prepare only the quantity and final volume specified in that controlled procedure.

1. Check the approved cleaning procedure, raw-material identity and status, calculation, final volume, water grade, preparation record and waste route before starting.
2. Verify that the preparation area and compatible, clean vessel and mixing tool are approved for sodium hydroxide. Do not use a vessel or utensil with unknown material compatibility.
3. Measure part of the approved water volume into the vessel. Weigh the required sodium hydroxide quantity using the approved method.
4. With the required PPE and controls in place, add sodium hydroxide slowly to the water while mixing as specified by the site procedure. Do not pour water onto solid sodium hydroxide. Control the heat generated during dissolution using the approved method; do not rely on a fixed, unvalidated cooling period.
5. After dissolution and cooling to the approved condition, add the approved water to the specified final solution volume and mix as directed by the controlled method. Record the actual quantities and final volume.
6. Apply the approved label before the solution leaves the preparation area.

Labelling, use and storage

Example in-house criterion (not a pharmacopoeial requirement): Label the container with the solution name and concentration, preparation date and time, preparer’s identity, approved use, hazard information, storage condition and expiry or use-by time if one has been established. Keep the container closed and in the designated compatible storage location. Use the solution only for the equipment and cleaning step named in the approved cleaning procedure.

This example says to use freshly prepared solution only but gives no approved holding time, storage condition or reuse rule. Do not assign a shelf life or reuse solution unless the site has approved supporting evidence and a controlled instruction.

Unused solution and disposal

Do not dilute the remainder and pour it into a drain. ICSC 0360 (ILO/WHO, May 2010) advises collecting sodium hydroxide residues and disposing of them according to local regulations; it also describes the substance as potentially hazardous to the environment. Collect and manage unused solution under the site’s approved chemical-waste procedure and any applicable local authorisation. Do not neutralise or discharge it unless the authorised procedure specifically permits that method.

Records and training

Example in-house criterion (not a pharmacopoeial requirement): Record the solution name and target concentration, raw-material name and lot, raw-material quantity, water grade and amount, final solution volume, preparation date and time, preparer and checker, label or container ID, intended cleaning use, and unused-solution disposition. Train authorised personnel on this procedure and the approved chemical-safety and waste procedures.

For any batch-specific GMP records, retain the records at least one year after expiry of the respective product batch. EU GMP Volume 4, Part I, Chapter 4 (January 2011), §4.11 requires batch documentation to be kept for one year after expiry or for at least five years after Qualified Person certification, whichever is longer. Current 21 CFR §211.180(a) requires records for at least one year after the batch expiry date, subject to the regulation’s specific provisions.

Related procedures

• Equipment cleaning in the production department
• Cleaning and numbering containers and stainless-steel accessories
• Operating and cleaning a compression machine

Frequently asked questions

Does 250 g in 10 L of water make 10 L of 2.5% w/v solution?

No. A 2.5% w/v target is 2.5 g per 100 mL of final solution. For 10 L final volume, 250 g is dissolved in part of the approved water and the solution is brought to a final volume of 10 L after cooling as directed by the approved method.

Is 2.5% w/v a GMP limit for equipment cleaning?

The cited GMP provisions do not set this concentration. The 2.5% target is an example in-house criterion and must be confirmed as suitable for the specified equipment, residues and cleaning method.

Can unused solution be diluted and poured down a drain?

Do not assume so. Use the site’s authorised chemical-waste procedure and applicable local requirements; a drain instruction is not supported by a disposal endpoint or authorisation.

References

1. Ministry of Health and Family Welfare, Government of India. Drugs Rules, 1945, revised Schedule M (G.S.R. 922(E), 28 December 2023), Part I §§13.6 and 13.8. Official Gazette notification; CDSCO consolidated Drugs Rules, 1945 (September 2024).
2. United States Electronic Code of Federal Regulations. 21 CFR §211.67(a)–(c), equipment cleaning and maintenance (current eCFR text up to date 15 October 2026). Official eCFR.
3. International Labour Organization and World Health Organization. International Chemical Safety Card 0360: Sodium Hydroxide (May 2010). Official ILO/WHO card.
4. European Commission. EudraLex Volume 4, EU Guidelines for Good Manufacturing Practice, Part I, Chapter 4: Documentation (January 2011), §4.11. Official Chapter 4 PDF.
5. United States Electronic Code of Federal Regulations. 21 CFR §211.180(a), general record-retention requirements (current eCFR edition, 2026). Official eCFR.