OHAUS ST400 Portable pH Meter
| Brand | OHAUS |
|---|---|
| Origin | Jiangsu, China |
| Manufacturer Type | Manufacturer |
| Regional Classification | Domestic (China) |
| Model | ST400 |
| Instrument Type | Portable |
| Parameter Types | Multi-parameter (pH + Temperature) |
| Measurement Accuracy | ±0.01 pH |
| Measurement Range | -2.00 to 16.00 pH |
| Resolution | 0.01 pH |
| Accuracy | ±0.01 pH |
| Calibration Standard | International Buffer Solutions (pH 4.01, 7.00, 10.01) |
| IP Rating | IP67 (Instrument & Electrode) |
| Battery | Rechargeable Li-ion, up to 40 h continuous operation |
| Data Storage | 1000 measurement records |
| Interface | Micro-USB for data export |
Overview
The OHAUS ST400 Portable pH Meter is a field-deployable electrochemical instrument engineered for high-reproducibility pH and temperature measurements in uncontrolled or dynamic environments. Based on potentiometric principle—measuring the voltage difference between a pH-sensitive glass electrode and a stable reference electrode—the ST400 delivers calibrated, Nernstian response across its full operational range of −2.00 to 16.00 pH. Its design prioritizes ruggedness without compromising metrological integrity: the instrument conforms to IEC 60529 IP67 specifications for both housing and integrated electrode assembly, ensuring dust-tightness and submersion resistance up to 1 m for 30 minutes. This makes it suitable for direct immersion in lakes, rivers, wastewater channels, agricultural runoff, and industrial effluent streams—environments where conventional benchtop meters would be impractical or vulnerable to contamination and mechanical stress.
Key Features
- IP67-rated dual protection: Fully sealed meter body and matching IP67-certified combination pH/temperature electrode eliminate ingress of water, dust, or particulates during extended outdoor use.
- Long-duration power architecture: Integrated rechargeable lithium-ion battery supports up to 40 hours of continuous operation on a single charge; rated for ≥300 charge cycles with minimal capacity degradation.
- High-contrast graphical LCD display: 128 × 64 pixel monochrome screen presents real-time pH value, temperature reading, electrode status (e.g., slope %, offset mV), calibration progress, and battery level—all simultaneously and legibly under ambient sunlight or low-light conditions.
- Intuitive guided calibration workflow: Supports 1–3 point calibration using internationally recognized standard buffers (pH 4.01, 7.00, 10.01 at 25 °C); automatic temperature compensation (ATC) enabled via built-in NTC thermistor in the electrode.
- Robust data management: Internal memory stores up to 1000 timestamped measurement records, each including pH value, temperature, date/time stamp, and calibration ID. No proprietary software required for retrieval.
Sample Compatibility & Compliance
The ST400 is validated for aqueous and semi-aqueous samples with conductivity ≥50 µS/cm and total dissolved solids (TDS) ≤10,000 ppm. It is not recommended for non-aqueous solvents, highly viscous slurries, or samples containing high concentrations of fluoride, hydrofluoric acid, or strong oxidizers that may degrade the glass membrane. The instrument complies with CE marking requirements under the EU Electromagnetic Compatibility Directive 2014/30/EU and Low Voltage Directive 2014/35/EU. While not certified to ISO/IEC 17025 as a standalone testing device, its calibration traceability aligns with NIST-traceable pH buffer standards, supporting GLP-compliant field documentation when used with defined SOPs.
Software & Data Management
Data export is performed via micro-USB interface using standard CDC ACM serial protocol—no drivers required on Windows 10/11, macOS 12+, or Linux kernel ≥5.4. Exported files are plain-text CSV format (UTF-8 encoded), containing columns: Timestamp (YYYY-MM-DD HH:MM:SS), pH, Temperature (°C), Electrode Slope (%), Offset (mV), Calibration Date, and User ID (if assigned). Audit trail functionality is maintained through immutable internal timestamps and sequential record indexing. Though the ST400 does not implement FDA 21 CFR Part 11 electronic signature controls, its deterministic logging behavior supports retrospective verification in regulated environmental monitoring programs under EPA Method 150.1 or ISO 10523.
Applications
- Environmental field monitoring: Real-time pH profiling of freshwater ecosystems, wetland restoration sites, and stormwater outfalls.
- Wastewater treatment: In-situ verification of neutralization efficiency across influent, aeration, and effluent stages.
- Agricultural water quality assessment: Irrigation source screening for alkalinity-related soil salinization risk.
- Education and outreach: Undergraduate lab exercises in analytical chemistry and environmental science requiring portable, student-safe instrumentation.
- Industrial process spot-checking: Batch verification in food processing, beverage production, and pharmaceutical water systems prior to distribution.
FAQ
What calibration buffers are supported?
The ST400 accepts standard pH 4.01, 7.00, and 10.01 buffers certified to ISO 3696 Grade 3 water purity; custom buffer values are not programmable.
Can the electrode be replaced independently?
Yes—the ST400 uses a standardized BNC connector and compatible OHAUS-recommended refillable combination electrodes (e.g., ST300 series), enabling field replacement without instrument recalibration.
Is temperature measurement independent of pH sensing?
No—temperature is measured via an integrated NTC thermistor within the same electrode body; ATC is applied automatically during pH calculation per the Nernst equation.
Does the ST400 support GLP/GMP audit trails?
It maintains immutable timestamps and sequential record IDs but lacks user authentication, electronic signatures, or change logs required for full 21 CFR Part 11 compliance.
How often should the electrode be cleaned and stored?
Rinse with deionized water after each use; store immersed in 3 M KCl solution. Clean with mild detergent for organic fouling or 0.1 M HCl for inorganic deposits—avoid abrasives or alcohol-based solvents.
