InLab®450 pH ElectrodeWith Redox Couple Reference Technology

Operating Instructions

METTLER TOLEDO

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METTLER TOLEDO InLab®450 pH ElectrodeWith Redox Couple Reference Technology

This METTLER TOLEDO Combination pH electrode incorporates a specialreference system whereby chemical equilibrium is controlled to thepoint that no solution or precipitation of the reference solutioncomponents occur at the reference element at temperaturesbetween 0 and 100°C. The composition of the pH internal fillsolution has also been designed so that its temperature coefficient isminimal. The net effect is to make the electrode predictable,reliable, and quick to respond at any temperature.

Required equipment & solutions

1. A pH or ion meter.2. Deionized or distilled water for solution and standard

preparation.3. Inlab®450 pH electrode (order no. 51340259).4. Reference fill solution, 3mol/L KCl (order no. 51340049).

Electrode preparation

Remove both the black protective cap covering the electrode tip and thesleeve covering the filling hole of the reference chamber to expose thefill hole. Fill the electrode with the reference filling solution* shippedwith the electrode to a level just below the fill hole. Gently shake theelectrode downward in the same manner as a clinical thermometer toremove any air bubbles which might be trapped behind the membrane.Prior to first usage, immerse the electrode in 3mol/L KCl solution for aminimum of thirty minutes (optionally overnight). The electrode is nowready for use. Connect the electrode to the meter as recommended inthe operating instructions of the meter.

Note: Never fill the electrode with filling solutions containing silver ions,as this will adversely affect the redox couple reference system.

* For measuring samples which will precipitate in the presence of chloride ions, the electrode may be filled with 1mol/L KNO3 solution (order no. 51340047).

Notes:

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Calibration / Standardization

New Inlab®450 pH electrodes are factory-tested to have an efficiencyor “slope” of > 97%. The theoretical pH response is 100% (59.16mV/pH unit), so the millivolt difference between pH 4.00 and pH 7.00certified calibration standards at 25ºC should then be 177.48 mV. A97% slope means that a new electrode will have a response of at least172.16 mV between these values. As electrodes naturally age thisefficiency deteriorates. Periodic calibration against known standards isnecessary to ensure the electrode efficiency. Most pH meters havefeatures to display the current electrode slope and protection that warnusers of a low slope (usually 90%) or prevent erroneous calibrations.

After following the calibration procedure of your meter, compare the measured pH reading of each calibration buffer to the pH valueindicated for each buffer at the actual temperature. A chart with pH atvarious temperatures is usually found on the calibration standardpackaging or label. Using a one-point standardization, proper responseis indicated if the reading is within ± 0.05 pH units from thestandardization point within 30 seconds when using certified pHbuffers. Multiple-point standardization is recommended for moreprecise measurements. To provide a linear response in the area ofinterest, use one calibration standard above and one below theexpected sample pH.

Measuring hints

- Always use fresh buffers for calibration. - Do NOT use any filling solution containing silver.- Remove fill hole cover to ensure proper flow during use.- Always rinse electrode with distilled water between measurements.- Use moderate stirring on all standards and samples.- Do NOT wipe pH glass bulb, as this may remove the hydration layer

on the pH glass and introduce polarization effects.

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SPECIFICATIONS

pH Range 0 ... 14 (Na+ < 0.1N)Temperature Range -5 ... +100°CZero Point pH 7.00Offset (assymetry potential) 0 ± 15 mVResponse Time < 20 seconds (98% response)Glass Membrane Impedance < 250 MΩ at 25°CReference Junction Impedance < 50 kΩ at 25°CBody Material Glass

Reference Electrolyte 3mol/L KCl(order no. 51340049)

Reference System Redox Couple Reference Technology

Order no. InLab®450 51340259

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TROUBLESHOOTING

Out of range reading

Interferences

Sodium ion is the primary interference for pH measurement. At pH valuesabove 13.5, the concentration of hydrogen ion is very small, and theelectrode will falsely register sodium ions as hydrogen ions.

Temperature influences

There are two temperature effects which the Inlab®450 electrode cannotcompensate for alone:- Electrode slope will change with varying temperature. However, this may be compensated for either manually, or with the use of an auto- matic temperature compensator (ATC) probe. Consult your pH meter’s instruction manual for details on using an ATC probe*.- The chemical equilibrium of buffers and samples are temperature dep- endent, and therefore, affect their pH values. By calibrating with standard buffers whose true pH values at varying temperatures are known, this error is calibrated out of the reading.

Electrode storage

The sensing bulb and reference junction must remain wet at all times toensure proper functioning of the electrode.

For short periods of time (up to one week), the electrode may be storedin electrode storage solution: 50:50 ratio mixture of 2mol/L KCl andpH 4.01 buffer.

For longer storage periods, fill the reference chamber with fill solutionand cover the fill hole.Fill the protective rubber storage cap halfway with electrode storagesolution and slide the cap up onto the body until both the glass sensorand reference junction are covered.

- Defective meter .......................................

- Electrode not plugged in properly ..............- Reference chamber not filled ....................

- Air bubbles on membrane ........................

- Electrode not in solution ..........................

Check meter with shorting plug.(see meter instruction manual).Unplug electrode and reseat.Fill reference chamber to level justbelow the fill hole.Remove air bubbles by re-dippingelectrode.Put electrode in solution.

Low slope or no slope

- Standards contaminated or incorrectly....... made- Air bubbles on membrane .......................

- Defective electrode ..................................

Prepare fresh standards.

Remove bubbles by re-dippingelectrode.Change electrode.

Drifty Readings (readings slowly moving in one direction)

- Incorrect reference filling solution .......- Clogged reference junction..............

Use recommended filling solution.Soak electrode in hot tap water.

Noisy or unstable readings (readings randomly changing)

- Defective meter ................................

- Air bubbles on membrane ................

- Meter or stirrer not grounded ..............- Defective electrode ...........................

Check meter with shorting strap(see meter instruction manual).Remove bubbles by re-dipping electrode.Ground meter or stirrer.Change electrode.

* Separate temperature probes:- NTC30kΩ order no. 51300164- Pt1000 order no. 51300165