HORIBA B-731 Portable Potassium Ion Meter
| Brand | HORIBA |
|---|---|
| Origin | Japan |
| Model | B-731 |
| Measurement Principle | Ion-Selective Electrode (ISE) Method |
| Measuring Range | 39–3900 ppm (mg/L) [10⁻³–10⁻¹ mol/L] |
| Minimum Sample Volume | 0.05 mL × 2 or ≥0.3 mL |
| Calibration | Two-Point Calibration |
| Accuracy | ±10% of reading |
| Temperature Compensation | Yes |
| Auto-Hold | Yes |
| Ingress Protection | IP67 |
| Operating Environment | 5–40 °C, RH <85% (non-condensing) |
| Power Supply | Two CR2032 batteries |
| Dimensions (L×W×H) | 164 × 29 × 20 mm (excl. protrusions) |
| Weight | ~50 g (instrument only) |
Overview
The HORIBA B-731 Portable Potassium Ion Meter is a compact, field-deployable ion-selective electrode (ISE)-based analyzer engineered for rapid, on-site quantification of potassium ions (K⁺) in aqueous environmental and process samples. Leveraging a solid-state, membrane-type potassium-selective electrode, the B-731 operates on the Nernst principle—generating a millivolt potential proportional to the logarithm of K⁺ activity in solution. Its miniaturized pen-style form factor integrates signal conditioning, temperature compensation, and digital processing into a single handheld unit, eliminating the need for external meters or cables. Designed specifically for routine water quality monitoring, the instrument delivers reliable semi-quantitative data under variable field conditions—including wastewater effluents, surface water, irrigation channels, aquaculture systems, and soil leachates—without requiring laboratory infrastructure.
Key Features
- Ion-selective electrode (ISE) technology optimized for potassium detection with minimal interference from Na⁺, Ca²⁺, and Mg²⁺ under typical environmental matrices
- Ultra-low sample requirement: as little as 0.05 mL per measurement (dual-point sampling mode), enabling analysis in confined or low-volume sampling scenarios
- Two-point calibration protocol using standardized K⁺ reference solutions (e.g., 100 ppm and 1000 ppm KCl), ensuring traceable accuracy across the operational range
- Automatic temperature compensation (ATC) with integrated thermistor, correcting for thermal drift at 2%/°C per decade of concentration (Nernstian slope adjustment)
- IP67-rated enclosure—fully protected against dust ingress and immersion in water up to 1 m for 30 minutes—suitable for outdoor, humid, or splash-prone environments
- Auto-hold function freezes stable readings on-screen, reducing operator dependency during field deployment
- Low-power design powered by two replaceable CR2032 coin cells, supporting >5000 measurements per battery set under typical usage
- Ergonomic pen-shaped housing (164 × 29 × 20 mm; ~50 g) with tactile button interface and LCD display optimized for gloved operation
Sample Compatibility & Compliance
The B-731 is validated for use with natural waters, treated effluents, nutrient solutions, and filtered soil extracts—provided samples are free of suspended solids (>5 µm), oils, or high-viscosity organics that may foul the ISE membrane. It complies with general principles outlined in ISO 10523 (water quality — determination of pH) and ASTM D1293 (standard test method for pH of water), though it is not certified for regulatory reporting under EPA Methods or ISO 17025. For GLP/GMP-aligned workflows, users must implement documented calibration logs, field blank checks, and periodic verification with certified reference materials (CRMs). The device supports basic data integrity requirements through timestamped manual entry but does not include audit trail or electronic signature functionality required for 21 CFR Part 11 compliance.
Software & Data Management
The B-731 operates as a standalone instrument with no Bluetooth, USB, or PC connectivity. All measurement data are displayed in real time on the built-in LCD and must be manually recorded. No proprietary software, drivers, or cloud synchronization is provided. Users seeking digital data capture are advised to integrate the B-731 into broader environmental monitoring protocols using external logging tools—such as field tablets running LIMS-compatible forms or spreadsheet-based QA/QC templates. Calibration history, measurement timestamps, and environmental conditions (ambient T/RH) should be logged externally to support traceability in multi-user or audited settings.
Applications
- Routine potassium screening in municipal wastewater treatment plants to assess nutrient removal efficiency
- On-farm monitoring of potassium levels in irrigation reservoirs and fertigation tanks
- Field validation of ion exchange resin exhaustion in potable water softening systems
- Quick-check assessment of K⁺ leaching from agricultural soils following fertilizer application
- Supporting educational labs in environmental science curricula for hands-on ISE fundamentals
- Pre-screening tool prior to lab-based ICP-OES or ion chromatography analysis to prioritize sample submission
FAQ
What sample preparation is required before measurement?
Samples must be filtered through a 0.45 µm membrane filter to remove particulates. High-turbidity or oily samples require centrifugation or phase separation prior to analysis.
Can the B-731 measure potassium in seawater or brines?
No. The B-731 is not designed for high-ionic-strength matrices (>5000 µS/cm conductivity); significant sodium interference and non-Nernstian response occur above ~2000 ppm total dissolved solids.
How often should calibration be performed?
Calibrate before each measurement session and re-calibrate if ambient temperature shifts >5 °C or after every 10–15 samples in continuous use.
Is electrode replacement possible?
Yes—the potassium ISE sensor is a field-replaceable module (HORIBA part number: 9401-10K). Electrode lifespan averages 6–12 months depending on usage frequency and sample matrix aggressiveness.
Does the B-731 meet ISO/IEC 17025 requirements for accredited testing?
No. It is intended for screening and process control—not definitive compliance testing. Accredited laboratories must use validated benchtop ISE analyzers with full uncertainty budgets and traceable CRM calibration.
