SOP on Inspection and Maintenance of Desiccator

In short: This example SOP explains how QC staff inspect and maintain desiccators: drying and replacing silica gel, keeping the lid sealed, checking the indicator colour and tagging each desiccator. Drying temperature and change frequency shown are example in-house criteria; set your own.

This is an illustrative template for a QC laboratory. Temperatures, times and frequencies are example in-house criteria and must be set in your own approved procedure, based on the silica gel supplier’s instructions and your use.

1. Objective

To lay down a procedure for the inspection and maintenance of desiccators.

2. Scope

This SOP applies to desiccators used in the Quality Control laboratory of the pharmaceutical manufacturing facility.

3. Responsibility

QC analyst: inspects the desiccator, changes the silica gel and updates the tag.
Head of QC: ensures implementation of this SOP.

4. Procedure

4.1 Preparing the silica gel

On receipt, dry the silica gel in an oven. Example in-house criterion: 105 °C for 3 hours.
Keep the dried silica gel in an oven or in an airtight container so it does not take up moisture again. Take out only the quantity needed.
Fill the dried silica gel into the desiccator for use.

4.2 Maintenance

For a glass desiccator, apply a thin layer of silicone grease to the ground-glass rim of the lower part and the lid so the seal is airtight. Wipe off excess.
Keep the desiccator closed at all times, opening it only briefly to place or remove items, so that moisture does not enter.
Change the silica gel at a fixed frequency. Example in-house criterion: every 15 days.
Inspect the silica gel visually at each use. If you use indicator silica gel, the colour change shows it has absorbed moisture (for example, blue to pink for cobalt chloride-type indicator; some suppliers now sell cobalt-free indicator gel with a different colour change, so use the guide for your product). Change the silica gel as soon as the colour change appears, even if the scheduled date has not arrived. Follow the supplier’s colour guide for your product.
Check the lid, rim, plate and body for cracks or chips before each use. Do not use a damaged glass desiccator (risk of implosion and injury); withdraw it and report it to the QC head.
Clean the desiccator inside and outside, and let it dry fully, whenever the silica gel is changed.

4.3 Status tag

Attach a tag to each desiccator showing: desiccator number, date the silica gel was changed and the next due date (see Annexure I, status label for silica gel). Update the tag at every change.

4.4 Records

Record the silica gel drying and change, with date and analyst signature, in the laboratory equipment or desiccator logbook. Keep logbooks at least 1 year after the expiry date of the respective product batch they support (EU GMP Part I, Chapter 4, §4.11; 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires. Laboratory records, including calibration records for laboratory instruments, are covered by 21 CFR 211.194.

5. Training

As per the SOP on employee training.

6. Distribution

As per the SOP on SOP preparation and control.

7. Annexure

Annexure I: Status label for silica gel (desiccator number, date of change, next due date, changed by).

Frequently asked questions

Why dry silica gel before putting it in a desiccator? Silica gel that has already absorbed moisture cannot protect samples. Drying drives off the water so the gel can absorb moisture again.

What does the colour change mean? For indicator silica gel it signals that the gel is saturated with moisture and has to be dried or replaced. The exact colours depend on the product, so follow the supplier’s guide.

Why apply grease to the rim? A thin layer fills the microscopic gaps between ground-glass surfaces, so the desiccator closes airtight.

References

US FDA, 21 CFR 211.67 (equipment cleaning and maintenance), 211.180(a) and 211.194 (laboratory records).
European Commission, EudraLex Volume 4, EU GMP Part I, Chapter 4 “Documentation”, §4.11.