Burettes: setup, titration and operational checks

When a titration result changes, immediately replacing the burette may move the problem without resolving it. The analyst needs to separate three questions: how much liquid was indicated, how much reached the receiving vessel and how that volume became the reported result.

This guide connects burette setup and operational checks with the evidence to retain. It does not replace the approved analytical procedure or complete titration method validation.

Select the type and working range

A glass burette measures using a scale and delivers by gravity; a piston burette doses through mechanical displacement. “Digital” describes a control or readout, not evidence of better performance. Even with a display, filling, leaks, the liquid path and actual transfer remain relevant.

Define the expected titrant volume, the increments needed near the endpoint, chemical compatibility and detection method. A larger capacity may avoid refilling during the analysis, but does not demonstrate fitness for very small additions. ISO 385:2005 covers glass burettes; ISO 8655-3:2022 covers piston burettes. Select the reference appropriate to the configuration.

Read the markings before reading the volume

Identify the instrument, capacity, graduation interval, declared class, reference temperature and delivery conditions. Ex/TD markings refer to delivery; In/TC to containment. These conventions are not interchangeable: liquid remaining on the walls may be accounted for in the specified use.

Distinguish delivery time from any prescribed waiting time before reading. Do not apply a number of seconds from a teaching procedure to every model. For piston burettes, also identify the units, zeroing, cumulative counting and refill handling. Read the certificate alongside its tested range and conditions: the last digit on a display does not summarise transfer uncertainty.

Prepare the liquid path

Before use, check integrity, cleanliness, stability and authorised status. Clamp glass burettes vertically using appropriate supports without overtightening the glass. Check that the titrant is compatible with the stopcock, seals and tubing. Protection, containment and disposal depend on the reagent and risk assessment.

Conditioning prevents residues of rinsing liquid or another solution from changing the titrant. Follow the applicable instructions, using identified waste vessels; do not automatically return residues to the original bottle. Check that the required tip, valves and lines are filled and free of bubbles, and that there are no leaks. NIST SOP 14 explicitly considers vertical positioning and leak checks in gravimetric burette calibration.

Make readings and increments consistent

For optical readings, bring the eye level with the meniscus to reduce parallax. The reference to read depends on the liquid and scale; apply the specified convention, particularly with coloured solutions. Record initial and final readings with digits justified by the graduation and procedure. For an ordinary scale increasing downwards, the indicated volume is the final reading minus the initial reading.

Near the endpoint, control additions, mixing and response time according to the method. Adding too quickly can overshoot the point to be detected even when the volume is read correctly. An intermediate refill requires traceable readings and addition of the delivered portions; do not rely on memory. Handle a drop remaining at the outlet according to the specified delivery technique, without adding an unauthorised rinse or blowout.

Separate volumetric error from the analytical result

A titrimetric result depends on volume, the actual titrant concentration and its chemical relationship with the analyte. Endpoint detection is another step requiring control: this is the principle outlined in the public introduction to USP 〈541〉.

The matrix guides investigation; it does not establish a cause on its own. Avoid correcting the volume to compensate for a chemical problem that remains unexplained.

Distinguish operational checks, verification and calibration

A check before use detects obvious anomalies. Verification compares measured performance with defined criteria. Calibration establishes the metrological relationship with a reference and its uncertainty; adjustment changes the instrument. None of these activities, alone, validates the analytical method.

A gravimetric test requires appropriate references and conditions: a suitable balance, known liquid and temperature, evaporation control and relevant corrections. Do not indiscriminately convert grams into millilitres. Define test points and replicates according to the applicable procedure and intended use, with criteria set before testing. Retain identification, raw data, conditions, calculations, outcome and decision. A check with water does not demonstrate every performance characteristic with every titrant.

Manage anomalies and return to use

Simulated case, without experimental data: two analysts obtain conflicting titration results despite repeatable burette readings. Volumetric verification under the specified conditions is acceptable. The investigation retains the original results and compares titrant preparation, sample preparation, mixing and endpoint criteria. The burette is not adjusted to make the assay agree. The volumetric test narrows the hypotheses; it does not automatically identify the remaining cause.

If leakage, damage or irregular behaviour is observed, identify the instrument and remove it from routine use. Cleaning and maintenance must respect materials and instructions; do not lubricate every type of stopcock or dismantle unauthorised parts. After intervention, check the affected functions, document release and assess potentially affected results.

For related operations, see the bottle-top dispenser selection criteria and selection of a pipetting principle. Explore the full Liquid Handling & Sample Preparation hub.

For the related steps, see: Serial dilutions: calculations, execution and error control.

Sources and consultation limits

ISO 385:2005 and ISO 8655-3:2022: official catalogue entries and scopes, not full texts or tolerance tables. NIST SOP 14, 2019 edition: a metrological procedure to be used within its scope. USP 〈541〉, public introductory preview dated 2024: titrimetry principles; compendial applicability requires the relevant current text. The matrix and case are original GuideGxP editorial work.