APERA INSTRUMENTS / PH8500-HF / AI5525

Strong acid and fluoride.
Start with HF-resistant glass.

The PH8500-HF pairs Apera’s portable PH8500 meter with the Swiss LabSen 833 refillable pH/temperature electrode. Apera designs the 833 for professional pH measurement of solutions containing hydrofluoric acid and other strong acids, with an HF-type glass membrane rated resistant to hydrofluoric corrosion at 1 g/L and a silver-ion-trap reference for stability and service life.

Choose AI5525 when the sample chemistry, rather than portability alone, decides the electrode. Apera lists the LabSen 833 at 0–11 pH and 0–100°C. Those are the electrode’s working limits, not the meter’s wider −2.00 to 16.00 pH display range. The HF rating is a measuring allowance with time limits, not immunity: Apera’s manual caps each HF immersion and rules out solutions at or above 0.5 mol/L.

HF-type glass for strong acids

Ordinary pH glass is attacked by hydrofluoric acid and ages quickly in strong acids. Apera specifies an HF-type membrane on the LabSen 833, rated resistant to hydrofluoric corrosion at 1 g/L. The membrane is a hemispherical bulb; it is still glass, so rinse promptly and protect it from impact.

Silver-ion-trap reference, ceramic junction

The reference system traps silver ions before they reach the ceramic junction, which Apera describes as increasing measuring stability and extending service life. The junction still needs clean samples, rinsing and wet storage.

Refillable, with a built-in temperature sensor

The 833 uses 3M KCl reference solution that you top up through the refill hole, and a 30 kΩ NTC sensor wired to a separate RCA plug. Connect both the BNC and RCA leads so the meter can display sample temperature and apply automatic compensation.

Where this configuration fits.

Use the PH8500-HF for strong acid solutions and for samples that contain limited hydrofluoric acid, measured within the electrode’s 0–11 pH and 0–100°C limits. Apera’s manual allows HF solutions up to 0.1 mol/L (about pH 2.1) for up to 3 minutes per measurement, recommends tests under 2 minutes near 0.5 mol/L, and rules out HF at or above 0.5 mol/L (pH below 1.8).

Measure HF-containing samples in a PTFE container, never glass. If the sample is strongly alkaline, compare the PH8500-SA with LabSen 843; for hot, complex or electroplating baths, the PH8500-HT with LabSen 863 is the matching configuration. Apera’s manual advises against using the 833 in strong alkaline solutions and dehydrating media such as absolute ethanol and concentrated sulfuric acid.

Calibrate below pH 7.
Then measure quickly and rinse.

Connect the electrode’s BNC plug to the pH input and the black RCA plug to the temperature input. Twist off the storage bottle cap, pull out the electrode, rinse it with distilled or deionized water and open the blue rubber plug on the refill hole so the reference solution flows smoothly.

Apera specifies at least a two-point calibration before a new electrode is used. The PH8500 always starts at 7.00 pH (6.86 pH in the NIST series). For acid work, add 4.00 pH or 1.68 pH as the second point; a three-point calibration can use 4.00 or 1.68, 7.00 and 10.01 pH. The kit supplies 4.00, 7.00 and 10.01 pH; add 1.68 pH buffer when samples sit near the bottom of the range.

For HF-containing samples, use a PTFE container, keep each immersion inside Apera’s time limits, stir to speed stabilization and rinse immediately afterward. If drift or slow response appears after a run of acid work, Apera’s manual says to soak the electrode in 3M KCl for more than half an hour and recalibrate. Hydrofluoric acid is a serious contact hazard: follow your site’s HF procedures and PPE.

Refill with 3M KCl.
Store the glass wet.

When the electrode is not in use, keep it in the storage bottle with 3M KCl soaking solution (Apera AI1107). Replace the solution if it becomes contaminated. Distilled and deionized water are rinse liquids, not storage liquids; never store the 833 in pure water.

The reference solution runs down with use. When it falls to about half the electrode height, unplug the blue rubber plug and add 3M KCl through the refill hole with a syringe or pipette. After measuring, return the electrode to its bottle, tighten the cap and close the refill hole.

Keep the BNC and RCA connectors clean and dry. Apera puts typical pH-electrode service life at 12–24 months and recommends replacement every 12–18 months; HF work consumes the membrane faster, so track how many HF tests each electrode has seen. The replacement electrode is LabSen 833, AI3177.

Read the meter.
Know what is held.

Use the physical controls for standalone measurement and calibration. The stable-reading indicator and HOLD help you read a result; a held display is not a stored record.

The PH8500 measures −2.00 to 16.00 pH at 0.01 or 0.1 pH resolution with ±0.01 pH ±1 digit accuracy, mV from −1999 to 1999, and temperature from −5 to 100°C. A calibration reminder can be set in days or hours. The meter runs on three AA batteries or 5 V USB power and carries an IP57 rating.

Build a local record.
Keep the transfer workflow clear.

The PH8500 can retain up to 500 data sets, including number, date, time, measured value, unit and temperature. M+ saves a reading manually after stability, and timed logging records automatically at the interval you set. Deleting stored data cannot be undone.

For computer work, connect the supplied USB cable and use PC-Link or the browser-based Web PC-Link on a desktop Chrome or Edge browser under Windows or Mac to download records and export them. While connected to PC-Link, new readings go to the software rather than to meter memory, so export before closing the session.

Check the electrode limits.
Then the meter’s.

Apera lists the LabSen 833 at 0–11 pH and 0–100°C, with an HF-type hemispherical membrane, ceramic junction, silver-ion-trap reference, 3M KCl electrolyte, 30 kΩ NTC temperature sensor, lead-free glass body (Ø12 × 120 mm), membrane resistance below 400 MΩ, a 1 m cable and BNC plus RCA connectors.

The meter’s automatic temperature compensation covers 0–100°C. Keep samples, buffers and the electrode within those limits, and confirm suitability with Apera’s documentation before measuring unusual chemistries.