OHAUS ST320 Tri-Combo Gel-Filled pH Electrode

Overview

The OHAUS ST320 is a tri-combination, gel-filled pH electrode engineered for reliable, low-maintenance operation with portable pH meters—specifically designed for seamless integration with the OHAUS STARTER 300 series. Unlike traditional liquid-filled reference electrodes requiring frequent refilling and calibration checks, the ST320 employs a stable, high-ionic-strength polymer gel electrolyte that eliminates leakage, minimizes junction clogging, and ensures consistent reference potential over extended use cycles. Its measurement principle relies on the Nernstian response of a pH-sensitive glass membrane coupled with an integrated Ag/AgCl reference system embedded within the same robust housing. This architecture delivers stable mV output across typical aqueous sample matrices encountered in field testing, educational labs, and routine quality control environments.

Key Features

• Tri-combination design integrates pH sensing element, reference electrode, and temperature sensor (NTC 30 kΩ) in a single compact probe—enabling automatic temperature compensation (ATC) without external sensors.
• Gel-filled electrolyte eliminates need for refilling, reduces maintenance frequency, and enhances portability for on-site or classroom applications.
• Rugged, chemical-resistant PVC body with integrated cable (1 m length, BNC connector) provides mechanical durability and resistance to common laboratory solvents and mild corrosives.
• Double-junction reference system with ceramic frit junction improves stability in samples containing sulfides, proteins, or heavy metals by minimizing reference contamination.
• Optimized tip geometry (conical 12 mm × 3 mm) enables rapid response time (<15 seconds to 95% stabilization) and accurate measurements in small-volume or semi-solid samples.

Sample Compatibility & Compliance

The ST320 electrode is validated for use with aqueous solutions across pH 0–14 at temperatures from 0 °C to 60 °C. It demonstrates robust performance in buffer solutions (e.g., pH 4.01, 7.00, 10.01 per ISO 3696 Grade 3), tap water, wastewater effluents, food extracts, and pharmaceutical rinse waters. While not certified for hazardous area use (ATEX/IECEx), its construction complies with IEC 61010-1 safety standards for electrical equipment used in laboratory environments. The electrode meets general requirements for GLP-aligned workflows when paired with STARTER 300 instruments supporting audit-trail-enabled calibration logging (via optional OHAUS LabX Lite software export).

Software & Data Management

When used with the STARTER 300 meter, the ST320 supports up to three-point calibration with slope and offset diagnostics displayed in real time. Calibration data—including date/time stamp, buffer IDs, measured mV, and calculated slope (% recovery)—is stored internally and exportable via USB to CSV format. Though the ST320 itself contains no onboard memory or firmware, its analog signal interface ensures compatibility with third-party data acquisition systems compliant with IEEE 488.2 or RS-232 protocols (when adapted via STARTER 300’s communication module). For regulated environments, users may implement manual calibration logs traceable to NIST-traceable pH buffers, satisfying basic ISO/IEC 17025 documentation expectations.

Applications

• Field-based environmental monitoring of surface water, groundwater, and soil leachates.
• Quality assurance in beverage production (e.g., soft drinks, brewing wort, dairy processing).
• Academic instruction in general chemistry and analytical laboratories where reproducibility and ease of handling are prioritized.
• Pharmaceutical manufacturing support for non-GMP intermediate checks (e.g., cleaning validation rinse samples).
• Veterinary clinic testing of biological fluids such as urine or saliva under ambient conditions.

FAQ

Can the ST320 be used with pH meters other than the STARTER 300?
Yes—it features a standard BNC connector and outputs a conventional ±650 mV signal compatible with most benchtop and portable pH meters accepting high-impedance inputs.
How often should the ST320 be calibrated?
Daily calibration is recommended for critical measurements; for routine screening, calibration before each use session suffices—always verify slope ≥95% and offset ±30 mV.
Is the electrode suitable for measuring pH in high-protein or viscous samples?
Its double-junction design and gel electrolyte reduce fouling risk, but periodic cleaning with enzyme-specific solutions (e.g., pepsin/HCl) is advised after such applications.
What is the expected service life under normal usage?
Typical operational lifespan exceeds 12 months with proper storage (in KCl storage solution or damp sponge) and avoidance of prolonged dry-out or exposure to strong oxidizers.
Does the ST320 support automatic recognition or plug-and-play functionality with STARTER 300?
No—the STARTER 300 does not auto-detect electrode type; users must manually select “Combination Electrode” mode during setup.