METTLER TOLEDO LE438 Combination pH Electrode

Overview

The METTLER TOLEDO LE438 is a robust, maintenance-free combination pH electrode engineered for field-deployable and routine laboratory applications where reliability, rapid response, and stable calibration retention are critical. Designed around a proven three-in-one architecture—integrating pH-sensing glass membrane, Ag/AgCl reference system, and integrated NTC 30 kΩ temperature sensor—the LE438 eliminates the need for external temperature probes and ensures automatic, real-time temperature compensation across its full operational range of 0 °C to 80 °C. Its U-type glass membrane delivers consistent sensitivity and low drift in aqueous and mildly aggressive media, while the gel-filled reference electrolyte prevents leakage and minimizes junction clogging—key advantages for intermittent or unattended measurements in environmental monitoring, wastewater analysis, education labs, and quality control of drinking water or process streams. The electrode’s POM (polyoxymethylene) body provides mechanical resilience against impact and chemical exposure, and its compact 120 mm × 12 mm form factor facilitates immersion in narrow containers and handheld use with portable pH meters equipped with BNC or RCA inputs.

Key Features

• Integrated NTC 30 kΩ temperature sensor enabling automatic, accurate temperature compensation without auxiliary hardware
• Gel-filled Ag/AgCl reference system with polyester liquid junction—resistant to drying out and contamination, ensuring long-term stability between calibrations
• U-type pH-sensitive glass membrane optimized for fast equilibration (< 30 s typical response time) and high reproducibility across pH 0–14
• Maintenance-free design: no refilling, no electrolyte replacement, no junction cleaning required under normal use conditions
• Rugged POM housing rated for continuous immersion; resistant to common solvents, acids, and bases encountered in municipal and industrial water testing
• BNC/RCA dual-compatible connector simplifies integration with legacy and modern portable meters—including METTLER TOLEDO’s SevenGo and FiveGo series—as well as third-party data loggers and controllers

Sample Compatibility & Compliance

The LE438 is validated for direct measurement in aqueous samples including potable water, surface water, wastewater effluents, buffer solutions, and mild aqueous process streams. It is not recommended for non-aqueous solvents, highly viscous media (> 1000 mPa·s), or strong oxidizing agents (e.g., concentrated HNO₃ or bleach above 5% w/w). Its performance conforms to ISO 7027-1:2016 (for turbidity-correlated pH stability), ASTM D1293 (Standard Test Method for pH of Water), and supports GLP-compliant workflows when used with meters featuring audit-trail-capable software (e.g., METTLER TOLEDO LabX or EasyDirect pH). While the electrode itself carries no CE or FDA certification, its materials comply with EU RoHS Directive 2011/65/EU and REACH Annex XIV restrictions.

Software & Data Management

As an analog-output sensor, the LE438 interfaces directly with any pH meter supporting standard mV input and automatic temperature compensation (ATC). When paired with METTLER TOLEDO’s SevenCompact or SevenExcellence platforms, it enables full traceability: calibration history (including date, buffer values, slope, and offset), measurement metadata (operator ID, sample ID, ambient temperature), and instrument firmware version are automatically logged in accordance with 21 CFR Part 11 requirements when LabX software is deployed. Raw mV and temperature data are exportable in CSV or PDF format for LIMS integration or regulatory submission.

Applications

• Field-based environmental monitoring (rivers, lakes, groundwater wells)
• Drinking water quality verification per WHO Guidelines and national standards (e.g., EPA 150.1, GB/T 5750.4)
• Wastewater treatment plant influent/effluent pH profiling
• Academic teaching labs requiring durable, low-cost electrodes for introductory electrochemistry experiments
• In-process control of neutralization steps in food, beverage, and pharmaceutical manufacturing
• Calibration verification of benchtop pH systems using standardized buffers (pH 4.01, 7.00, 9.21)

FAQ

Is the LE438 compatible with non-METTLER TOLEDO meters?
Yes—it features industry-standard BNC/RCA analog output and requires only a meter with ATC capability and mV-to-pH conversion functionality.
What is the expected service life under regular field use?
Typical functional lifespan exceeds 18 months with daily use and proper storage in pH 4 buffer; longevity increases significantly with infrequent use and storage in KCl 3 mol/L solution.
Can the electrode be sterilized or autoclaved?
No—autoclaving exceeds its 80 °C upper temperature limit and may damage the gel electrolyte and NTC sensor.
Does it support ISE or ORP measurements?
No—the LE438 is a dedicated pH/temperature combination electrode; it lacks the internal elements required for ion-selective or redox potential detection.
How often should calibration be performed?
For GLP-compliant work, two-point calibration before each measurement session is recommended; for routine field checks, single-point verification against pH 7.00 buffer suffices if slope remains >95% and asymmetry potential is within ±30 mV.