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The purpose of this guide is to show lab professionals how to remove air bubbles in a burette quickly and verify a bubble-free titration setup for accurate results.
Why bubbles cause error
Air compresses and delays liquid flow, which shifts the endpoint volume and increases random error. Bubbles at the tip or in the stopcock create lag and spurts. Results drift high or low depending on when the bubble releases. Precision degrades.
Pre-setup checks
- Inspect the jet tip for chips or cracks. Replace if damaged.
- Verify the stopcock plug turns smoothly. Lubricate glass plugs lightly with compatible grease or use a PTFE plug in good condition.
- Confirm the delivery tube and tip are clean. No fiber or dust should be present.
- Match temperature of burette, reagent, and lab air. Large temperature gaps increase bubble formation.
- Use freshly prepared or degassed titrant for gas-releasing systems. Carbonate or peroxide formation can outgas.
Primary method: prime and flush
- Condition the burette. Rinse with 10 to 20 mL of titrant. Rotate the burette while draining to wet all internal surfaces.
- Fill above zero. Close the stopcock. Fill the burette 2 to 5 cm above the zero mark.
- Seat the stopcock. Turn the plug fully to the closed position and back once to seat seals.
- Purge the tip. Open the stopcock fully. Drain 5 to 10 mL into a waste beaker. Watch the jet. The stream must be continuous with no spurts.
- Tap out residual bubbles. Gently tap the tip with a nitrile-gloved finger or a rubber stopper while a slow stream runs. Small bubbles detach and exit.
- Refill to operating level. Close the stopcock. Refill to 0.00 to 0.10 mL above zero. Drain to the exact zero if required by your SOP.
- Verify. Open briefly and observe flow. No pause or sputter should appear. If present, repeat steps 3 to 6.
Caution: Never force air through the tip with mouth suction or squeeze bottles. This contaminates the titrant and is unsafe.
Secondary methods when bubbles persist
- Stopcock bleed technique. With the funnel attached and stopcock closed, raise the reservoir head by 10 to 20 cm. Crack the stopcock slightly until a thin stream forms. Maintain for 3 to 5 seconds to push microbubbles out of the plug channels. Then open fully for 2 to 3 seconds.
- Capillary backfill. Touch the jet tip to the liquid surface in a small waste beaker. Open the stopcock slowly so the jet remains submerged. This prevents air reentry and helps detach bubbles.
- Warm-water outer rinse for viscous titrants. For viscous or high-surface-tension solutions, briefly rinse the outside of the tip with warm water and wipe dry. Do not heat the titrant. Lower surface tension at the interface helps bubbles detach.
- Degas titrant when safe. Sonicate the titrant bottle briefly with a loosely capped lid, or apply a gentle vacuum using a trap. Avoid volatile or reactive systems unless validated.
Common root causes and fixes
| Cause | Diagnostic sign | Corrective action |
|---|---|---|
| Dry or contaminated inner wall. | Bubbles reform after one flush. | Condition with titrant. Repeat rinse until walls are uniformly wetted. |
| Leaky stopcock plug or O-rings. | Slow downward creep of meniscus with stopcock closed. | Reseat or replace plug. Replace O-rings. Verify correct grease for glass plugs. |
| Damaged jet tip. | Sideways spray or spurting stream. | Replace tip. Do not attempt to flame-polish calibrated tips. |
| Gas-releasing titrant. | Strings of microbubbles ascend during stand. | Prepare fresh titrant. Degas if validated. Minimize carbonate pickup with CO₂ barriers. |
| High surface tension or viscosity. | Persistent bead at the jet outlet. | Use capillary backfill. Maintain submerged purge during priming. |
| Temperature mismatch. | Bubbles appear after moving from cold storage to warm lab. | Equilibrate glassware and titrant to lab temperature before filling. |
Validation checklist before titration
- No visible bubbles in the barrel, stopcock, or jet tip.
- Continuous laminar stream at a steady stopcock angle.
- Stable meniscus after 60 seconds with stopcock closed.
- Consistent dispensed volume on two 10 mL trial deliveries within your RSD target.
Fast SOP you can paste into your method
# Burette Bubble-Removal SOP 1. Rinse burette twice with 10 mL titrant. Drain through jet. 2. Fill to above 0 mL. Seat stopcock by turning closed and open once. 3. Open fully. Purge 10 mL while tapping the jet tip lightly. 4. Submerge jet tip in a waste beaker. Open slowly for a thin, steady stream. 5. Close. Refill to the working level. Remove any external droplets with lint-free tissue. 6. Verify no bubbles and stable meniscus for 60 s. Repeat purge if needed. 7. Record zero and proceed with titration. Quality tips for regulated labs
- Document bubble checks in the titration worksheet as a required field.
- Train analysts to recognize sputter, pause, and side spray as failure modes.
- Standardize purge volume and verification time for method reproducibility.
- Maintain spare stopcocks and tips to avoid downtime.
FAQ
Is it acceptable to read the burette above a small trapped bubble?
No. The bubble reduces delivered volume unpredictably. Remove it before any measurement.
Can I invert the burette to chase bubbles?
No. Inversion risks breakage and contaminates the graduation scale. Use priming and tapping only.
How much purge volume is enough?
Five to ten milliliters clears most systems. Use a fixed value in your SOP and verify with a stability check.
What if bubbles keep returning during the run?
Suspect stopcock leakage or outgassing titrant. Reseat or replace the plug and prepare fresh titrant.
Does the final drop hanging at the tip matter?
Yes. Wipe external droplets consistently or deliver them into the flask per your method. Be consistent.