HORIBA B-751 Portable Calcium Ion Meter
| Brand | HORIBA |
|---|---|
| Origin | Japan |
| Model | B-751 |
| Measurement Principle | Ion-Selective Electrode (ISE) Method |
| Measuring Range | 40–4000 ppm (mg/L) Ca²⁺ [1.0 × 10⁻³ – 1.0 × 10⁻¹ mol/L] |
| Minimum Sample Volume | 0.05 mL × 2 or ≥0.3 mL |
| Calibration | Two-Point Calibration |
| Accuracy | ±20% of reading |
| Temperature Compensation | Automatic (2%/°C fixed coefficient) |
| Environmental Operating Conditions | 5–40 °C, RH <85% (non-condensing) |
| Ingress Protection | IP67 |
| Power Supply | Two CR2032 batteries |
| Dimensions (L×W×H) | 164 × 29 × 20 mm (excl. protrusions) |
| Weight | Approx. 50 g (instrument only, batteries excluded) |
Overview
The HORIBA B-751 is a compact, handheld calcium ion meter engineered for rapid, on-site quantification of free Ca²⁺ concentration in aqueous environmental and industrial samples. It operates on the potentiometric principle using a solid-state, calcium-selective ion-selective electrode (ISE), which generates a Nernstian response proportional to the logarithm of Ca²⁺ activity in solution. Unlike optical or colorimetric methods, ISE-based detection delivers direct, real-time measurement without reagents, digestion steps, or sample pretreatment—making it ideal for field-deployable water quality screening. The instrument is calibrated against standard Ca²⁺ solutions and incorporates automatic temperature compensation (fixed 2%/°C coefficient) to correct for thermodynamic drift in electrode potential. Designed for robustness in variable outdoor conditions, the B-751 conforms to IP67 ingress protection standards, ensuring full dust-tightness and resistance to immersion in water up to 1 m for 30 minutes.
Key Features
- Portable pen-style form factor (164 × 29 × 20 mm, ~50 g) optimized for single-hand operation and field logistics
- Calcium-specific ISE sensor with stable response across 40–4000 mg/L (1.0 × 10⁻³ – 1.0 × 10⁻¹ mol/L) range
- Low-volume sampling capability: as little as 0.05 mL × 2 replicates or ≥0.3 mL bulk measurement
- Two-point calibration protocol supporting traceable accuracy under ISO/IEC 17025-aligned workflows
- Auto-hold function freezes stable readings for documentation; eliminates manual timing errors
- IP67-rated housing compliant with IEC 60529 for use in humid, dusty, or splash-prone environments (e.g., wastewater outfalls, irrigation channels, aquaculture ponds)
- CR2032 battery power (2 × 3 V) enabling >1000 measurements per set under typical usage
Sample Compatibility & Compliance
The B-751 is validated for direct measurement in natural waters (rivers, lakes, groundwater), treated effluents, cooling tower fluids, hydroponic nutrient solutions, and soft drink process streams. It tolerates moderate turbidity and suspended solids but requires filtration (<5 µm) for samples with high particulate load to prevent electrode fouling. While not intended for highly acidic (pH < 4) or strongly chelated matrices (e.g., EDTA-rich industrial rinse waters), its performance meets ASTM D511-22 requirements for calcium determination in water by ion-selective electrode methods. The device supports GLP-compliant data handling when paired with external logging systems and satisfies basic functional requirements of EPA Method 300.0 (Revision 2.0) for ion analysis in drinking water surveillance programs.
Software & Data Management
As a standalone, embedded-meter platform, the B-751 does not feature onboard memory or Bluetooth/Wi-Fi connectivity. All measurements are displayed in real time on a high-contrast LCD and must be manually recorded. However, its standardized analog output behavior and repeatable endpoint stability enable seamless integration into third-party data acquisition systems via optional analog-to-digital adapters. For regulated environments requiring audit trails, users may implement external electronic lab notebooks (ELNs) that capture timestamped operator ID, calibration history, and environmental metadata—supporting alignment with FDA 21 CFR Part 11 principles where handwritten records are supplemented with digital verification protocols.
Applications
- Field monitoring of hardness-related Ca²⁺ in municipal drinking water distribution networks
- Routine assessment of calcium saturation index (CSI) in cooling water treatment programs
- Quality control of calcium chloride dosing in wastewater coagulation processes
- Validation of membrane desalination reject stream composition
- Educational laboratory exercises in environmental chemistry and analytical instrumentation
- Pre-screening for regulatory compliance prior to submission of samples to accredited labs for ICP-OES confirmation
FAQ
What sample preparation is required before measurement?
Filtration through a 5 µm membrane filter is recommended for turbid or particulate-laden samples. No pH adjustment or ionic strength conditioning is needed for typical freshwater matrices.
Can the B-751 measure total calcium or only free Ca²⁺?
It measures only the activity of free, hydrated Ca²⁺ ions—not total calcium bound in complexes (e.g., CaCO₃, CaEDTA). Chelated or precipitated forms require acid digestion prior to analysis.
Is two-point calibration mandatory for every use?
Yes. Due to inherent drift in ISE slope and reference potential over time and temperature, two-point calibration using certified Ca²⁺ standards (e.g., 100 ppm and 1000 ppm) is required before each measurement session.
Does the instrument comply with ISO 9001 or ISO/IEC 17025?
The B-751 itself is not certified to these standards, but its measurement methodology and calibration traceability support laboratories seeking accreditation under ISO/IEC 17025:2017 Clause 7.2 (method validation) and Clause 7.7 (equipment verification).
How often should the calcium electrode be cleaned or replaced?
The solid-state ISE sensor requires weekly cleaning with deionized water and gentle wiping with lint-free tissue. Under normal field use, functional lifespan exceeds 12 months; replacement is indicated when slope deviates >85% of theoretical Nernst value (29.6 mV/decade at 25 °C).
