SOP for Ultrasonic Water Bath: Operation, Cleaning, Calibration

In short: This example SOP explains how a Quality Control laboratory can operate, clean, maintain and calibrate an ultrasonic water bath used to dissolve samples, degas solvents and clean glassware. It is a template: the key controls are checks before use, daily water change, an up-to-date calibration of the temperature indicator and timer, and a usage record.

Note: This is an example SOP. Control names, button layout, water level, intervals and responsibilities differ between models and must be set under your own quality system and the manufacturer’s manual.

1. Objective

To define how the ultrasonic water bath is operated, cleaned, maintained and calibrated in the Quality Control laboratory.

2. Scope

This SOP applies to ultrasonic water baths in the Quality Control department at the manufacturing facility of [company name].

3. Responsibility

• Analyst / section head or designee: follows this SOP, records usage and cleaning.
• Head of Quality Control or designee: ensures implementation, calibration and training.

4. Regulatory background

• 21 CFR 211.67(a)-(c): equipment must be cleaned and maintained at suitable intervals under written procedures with defined responsibilities and schedules, and records of cleaning and maintenance must be kept.
• 21 CFR 211.160(b)(4): laboratory instruments and apparatus must be calibrated at suitable intervals under an established written program that includes directions, schedules, accuracy and precision limits and remedial action; instruments not meeting these limits must not be used.

The calibration interval in this SOP is an example in-house criterion, not a regulatory number.

5. Procedure

5.1 Checks before use

1. Confirm the bath is clean, labelled with its equipment ID and “calibrated” status (not past its due date).
2. Fill the tank with water to the level mark on the tank (some models state a minimum depth, for example 7 cm; follow your manual). Never run the bath empty.
3. Check there is no water leakage.
4. Do not place heavy objects directly on the bottom of the tank, as they can damage the transducers. Use the tray or basket supplied.
5. Keep liquid away from the controls and switches.
6. If a set temperature is needed, switch the heater on.

5.2 Operation

Controls vary by model. A typical sequence:

1. Connect the plug to a grounded (earthed) outlet and switch on. The display shows the actual temperature and the last set time.
2. Set the timer with the + and - keys (typically 1-minute steps, larger steps if the key is held). The bath stops when the timer reaches 00:00.
3. If heating is needed, press the heating key and set the temperature (the heater can only raise the water above room temperature; a typical maximum is about 80 °C, and many users work at 40-60 °C). On some models the heater starts only if the set temperature is above the actual water temperature, and does not stop automatically; switch heating off with its key when done.
4. Select the ultrasonic mode, where available:
   • Normal: continuous strong ultrasonic power.
   • Degas: intermittent operation (for example 6 seconds on, 2 seconds off) to remove dissolved air from liquids quickly.
   • Soft / sweep: slight continuous variation of frequency to reduce hot spots, dead zones and standing waves.
5. A steady “sizzling” sound during operation shows the bath is working properly.
6. After use, switch off the ultrasonic and heating functions, disconnect the plug and record the use.

Note: some models switch off after a long run (for example 8 hours) and return to standby until a key is pressed.

5.3 Cleaning and maintenance

1. Switch off and disconnect the power cable before cleaning.
2. Drain, clean the tank and replace the water daily, or sooner if the water becomes turbid (example in-house criterion).
3. Clean the outer surface with a damp lint-free cloth; do not spray liquids on controls.
4. Report faults to the section head and tag the bath “out of order” until repaired and verified.
5. Record cleaning and maintenance as required by 21 CFR 211.67(c).

5.4 Calibration

1. Calibration frequency: yearly (example in-house criterion).
2. Calibrate the temperature indicator/controller with its sensor, and the timer, using traceable standards, by an approved external party.
3. Define acceptance limits for each parameter in the calibration procedure (for example temperature and timer accuracy) from the manufacturer’s specification and the method’s needs.
4. Affix a calibration status label showing the date performed and the next due date.
5. If a result is outside the limits, take the bath out of use and assess the impact on analyses carried out since the last good calibration, under your deviation or out-of-calibration procedure.

For the general calibration framework see SOP for Calibration of Instruments and Measuring Devices (Example).

5.5 Records

Keep the usage log, cleaning and maintenance record and calibration certificates. Retain GMP records at least 1 year after the expiry date of the respective product batch (EU GMP Part I Chapter 4, 4.11; 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires.

6. Training

Trainer: Head - Quality Control. Trainees: section heads, analysts and officers.

7. Distribution

Controlled copies: Head of Department - Quality Assurance and Head of Department - Quality Control. Display copy: at the equipment location. Original: Head - Quality Assurance.

Frequently asked questions

Why change the water daily? Debris and contamination build up with use; dirty water reduces cleaning efficiency and can contaminate sample containers.

Does sonication heat my sample? Yes, the water warms during long runs. If the method is temperature sensitive, monitor the bath temperature or use cooling and note it in the record.

Do analysts need to record the time and mode? Where sonication is a method step (for example in sample preparation), record time and temperature in the analytical worksheet.

See also

• SOP for Maintenance of Laboratory Instrument
• HPLC Calibration - A Complete Guide Part 1

References

1. Equipment user manual.
2. US FDA, 21 CFR 211.67 Equipment cleaning and maintenance (eCFR, current).
3. US FDA, 21 CFR 211.160(b)(4) General requirements, laboratory controls (eCFR, current).
4. US FDA, 21 CFR 211.180(a) General requirements, records (eCFR, current).
5. European Commission, EudraLex Volume 4, Part I Chapter 4: Documentation, §4.11.