APERA INSTRUMENTS / PH820 / AI531

A finer pH display, with separate control of temperature sensing

PH820 combines selectable 0.001 pH resolution with a refillable LabSen 211 glass electrode and a separate MP500 temperature probe. Its five-point calibration capability, slope feedback and clear status display suit laboratory methods that need a more detailed pH reading and deliberate electrode care.

For general aqueous laboratory pH work where finer display resolution and a refillable reference are useful. Instrument accuracy is specified as ±0.002 pH ±1 digit; this is not an unconditional accuracy guarantee for every sample.

A precision meter is one part of the method

PH820’s specified instrument accuracy is ±0.002 pH ±1 digit across its -2.000 to 19.999 pH display range. Resolution is selectable down to 0.001 pH. Achieving useful sample results also requires suitable buffers, a clean electrode, thermal equilibration and a controlled procedure; extra digits alone do not establish measurement uncertainty.

Two probes with different jobs

LabSen 211 is a pH-only electrode connected by BNC. MP500 is a separate stainless-steel temperature probe with an RCA plug and 30 kΩ thermistor. Place both in the same solution for automatic temperature compensation. The phrase combination electrode refers to pH measuring and reference elements, not a built-in temperature sensor.

Refillable reference and a glass sensing tip

LabSen 211 uses an S-type hemispherical membrane, a ceramic junction and a long-life reference system. The manufacturer’s reference graphic identifies AgCl, meaning silver chloride, inside the reference assembly. The blue inner gel and the outer 3M KCl refill solution have different roles. The glass remains fragile and the reference requires maintenance.

Choose the calibration mode deliberately

The instrument offers one to three points in 3P mode and one to five in 5P mode. USA and NIST series are supported; the manual also describes a separate one- or two-point custom calibration mode. Selecting five-point capability does not add two extra buffers to the supplied three-bottle kit.

Status information beside the result

The LCD combines the reading with temperature, stability, calibration and storage indicators. ATC identifies automatic compensation; MTC identifies manual input. M+ indicates saving and RM indicates recall. The stable-reading icon and optional auto-lock help standardize when you record a result, but neither proves that an unsuitable sample is being measured correctly.

Know what this configuration supplies.

General aqueous laboratory samples

Use the supplied LabSen 211 for compatible water-based solutions and routine laboratory analysis with a defined method. Its 0 to 14 pH electrode range is narrower than the meter display range. Select a specialty electrode for strongly aggressive or unusual matrices.

TRIS-buffer work

The exact LabSen 211 instructions state compatibility with TRIS buffers. Keep reference electrolyte at the recommended level and open the refill plug while measuring. Compatibility does not remove the need for clean junctions, fresh calibration buffers and a documented temperature procedure.

Beverage method development

The series manual lists LabSen 211 among electrodes for beverage, beer and wine analysis. Control sample preparation, temperature and cleaning between runs. Do not extend that recommendation to puncturing solids, thick dairy products or oily emulsions without an application-specific electrode and validated method.

Calibrate the electrode and measure temperature in the same solution

Connect LabSen 211 to the pH BNC input and MP500 to the temperature RCA input. Remove the storage bottle carefully, rinse the sensing end, and open the blue refill plug so reference electrolyte can flow. Support both probes with the holder without pressing their tips against the vessel. The probe manual requires at least two calibration points when connecting a new electrode.

Use fresh portions of appropriate buffer in clean vessels, not the stock bottles. Rinse between solutions, remove excess rinse water without rubbing the sensing glass, and allow the electrode and solution to reach a stable temperature. A buffer’s actual pH changes with temperature; select the correct buffer series rather than treating every bottle labelled neutral as interchangeable.

Select USA or NIST buffers and the required 3P or 5P mode before calibration. In the standard three-point sequence, begin at pH 7.00, then use 4.00 and 10.01 as appropriate. Wait for recognition and a stable indication before confirming. Extra pH 1.68 and 12.45 buffers are not part of the listed starter set.

For samples, immerse both probes adequately and let them equilibrate together. Brief gentle movement can release bubbles; then allow the reading to settle. Temperature compensation corrects the pH electrode’s response, not the sample’s own temperature-dependent chemistry. The manual’s custom-buffer procedure requires calibration and measurement at the same temperature, so use it only within an established method.

Manage the refillable reference, not just the outside of the probe

When the reference solution falls to about half the electrode height, replenish it with 3M KCl, AI1107, through the refill opening using a clean pipette or syringe. Do not confuse this outer reference solution with the sealed blue inner gel. Close the refill plug after use, and return the electrode to its storage bottle.

Soak the sensing end in 3M KCl storage solution, replacing contaminated liquid. Never store the electrode in distilled or deionized water. Rinse with purified water before and after testing. For persistent deposits, the exact probe manual describes Apera AI1166 cleaner followed by KCl conditioning and recalibration; choose cleaning compatible with the sample residue.

Avoid prolonged exposure to strong acids, strong alkalis and dehydrating media. The LabSen manual lists -5 to 100°C, while the US probe page gives an inconsistent lower-limit conversion; confirm any subzero application. Keep connectors dry and protect the glass from impact. IP54 protects the meter against splashes and dust, not immersion.

Read the display. Check the measurement mode.

Use the physical controls for measurement, calibration and the documented record functions. Check units, temperature, calibration indicators and the selected parameter before assigning a result to a sample. Screen values in photographs are illustrative, not sample results. The model-specific record and output workflow is explained below.

Use calibration solutions and settings appropriate to the parameter and fitted electrode. Temperature compensation does not make different sample temperatures, preparation methods or chemistry equivalent. Follow the model-specific meter and electrode instructions before extending the method to a new sample.