Hanna Instruments HI98131 Portable pH/EC/TDS/°C Meter

Overview

The Hanna Instruments HI98131 is a compact, field-deployable multiparameter meter engineered for simultaneous measurement of pH, electrical conductivity (EC), total dissolved solids (TDS), and temperature in aqueous samples. It operates on potentiometric (pH) and conductometric (EC/TDS) principles: pH is determined via a glass electrode measuring hydrogen ion activity relative to a stable reference junction; EC is derived from the solution’s ability to conduct current between two stainless-steel electrodes, with TDS calculated using user-selectable conversion factors (0.5 or 0.7) based on standard calibration protocols. The instrument features automatic temperature compensation (ATC) with a programmable β coefficient of 1.9 %/°C—aligned with common electrolyte behavior in environmental and agricultural matrices—and integrates a built-in thermistor for real-time thermal correction across the full 0.0–60.0 °C operating range. Designed for rugged daily use in variable ambient conditions (0–50 °C, up to 100% RH), the HI98131 meets the functional expectations of field technicians, educators, and QA/QC personnel requiring traceable, repeatable measurements without benchtop infrastructure.

Key Features

• Simultaneous dual-line display showing primary parameter (pH, EC, or TDS) and temperature in real time, with intuitive one-touch parameter switching
• Guided on-screen calibration workflow for pH (1–2 point, auto-recognition of pH 4.01, 7.01, or 10.01 buffers) and EC/TDS (single-point, auto-detection of 1.41 mS/cm or 5.00 mS/cm standards)
• Integrated HI73127 probe assembly: replaceable polypropylene-body pH glass electrode with built-in stainless-steel EC/TDS sensor and NTC temperature thermistor—no external cables or connectors
• Battery Error Prevention System (BEPS) actively monitors voltage and halts measurement if power falls below operational threshold, preventing drift-induced inaccuracies
• Auto-off function after 8 minutes of inactivity preserves battery life (4 × 1.5 V button cells); battery replacement requires no tools and takes under 15 seconds
• Ruggedized housing (163 × 40 × 26 mm, 100 g) with IP67-rated ingress protection against dust and temporary immersion

Sample Compatibility & Compliance

The HI98131 is validated for use with freshwater, wastewater effluents, hydroponic nutrient solutions, soil extracts (1:5 or saturated paste), irrigation water, aquarium systems, and educational lab samples. Its measurement architecture complies with foundational electrochemical test methodologies referenced in ASTM D1125 (Standard Test Methods for Electrical Conductivity and Resistivity of Water) and ISO 7888 (Water Quality — Determination of Electrical Conductivity). While not certified for GLP/GMP-regulated production environments, its calibration traceability—via Hanna-certified buffer and standard solutions (e.g., HI7031, HI7039, HI5036)—supports audit-ready documentation when used within institutional QA frameworks. The device does not meet FDA 21 CFR Part 11 requirements for electronic records but supports manual logbook-based data integrity practices per ISO/IEC 17025 Clause 7.7.

Software & Data Management

The HI98131 operates as a standalone instrument with no embedded Bluetooth, USB, or cloud connectivity. All data are displayed in real time and retained only on-screen until the next measurement cycle. Users must manually record values in laboratory notebooks or spreadsheets. Calibration history—including date, standard used, and offset values—is not stored internally; however, the guided calibration interface ensures procedural consistency across operators. For laboratories requiring digital data capture, Hanna recommends pairing the HI98131 with external logging tools or upgrading to the HI98194 series, which supports RS232 output and GLP-compliant timestamped memory.

Applications

• Environmental monitoring: rapid assessment of surface water pH and salinity proxies in watershed surveys and regulatory compliance checks
• Agricultural extension: on-site verification of irrigation water quality, nutrient solution balance in greenhouses, and soil extract EC for salinity risk evaluation
• Education: undergraduate chemistry and environmental science labs where students learn fundamental electrochemical measurement concepts and calibration best practices
• Water treatment: preliminary screening of influent/effluent streams prior to advanced analysis; verification of RO pretreatment effectiveness
• Aquaculture and hydroponics: daily tracking of culture medium stability to prevent osmotic stress or pH-induced toxicity

FAQ

What calibration standards are required for routine operation?
HI98131 requires Hanna-certified pH buffers (HI5036 or HI50036) and EC standards (HI7031 for 1.41 mS/cm or HI7039 for 5.00 mS/cm). Use of non-Hanna standards may compromise accuracy due to unstated ionic composition or temperature coefficients.
Can the HI98131 measure seawater or high-salinity brines?
No. Its EC range (0.00–6.00 mS/cm) and TDS scaling (max 3999 ppm) are unsuitable for seawater (~53 mS/cm, ~35,000 ppm). For marine applications, consider the HI98194 or HI98304 series.
Is the electrode assembly replaceable in the field?
Yes. The HI73127 probe allows independent replacement of the pH sensing element while retaining the integrated EC/TDS sensor and temperature thermistor—minimizing downtime and consumable cost.
Does the meter support custom TDS conversion factors?
No. Only factory-programmed factors of 0.5 (500 ppm/mS/cm) and 0.7 (700 ppm/mS/cm) are available, aligned with common US EPA and APHA conventions for freshwater and wastewater reporting.
How often should calibration be performed?
Daily calibration is recommended for critical applications; for routine field screening, calibration before each sampling session—or at least every 2 hours of continuous use—is advised to maintain ±0.1 pH and ±2% EC accuracy specifications.