OHAUS STPURE Glass pH Electrode for Low-Ionic-Strength Water Measurement
| Brand | OHAUS |
|---|---|
| Origin | Shanghai, China |
| Manufacturer Type | Direct Manufacturer |
| Regional Classification | Domestic (China) |
| Model | STPURE |
| Pricing | Available Upon Request |
Overview
The OHAUS STPURE is a specialized glass-body pH electrode engineered for accurate and stable potentiometric measurement in ultra-low ionic strength aqueous solutions—typically below 50 µS/cm conductivity. Unlike standard combination pH electrodes, the STPURE employs a low-resistance, asymmetrically doped glass membrane with an optimized internal reference electrolyte formulation (KCl-saturated gel with Ag/AgCl system) to minimize liquid junction potential drift and stabilize response in near-deionized environments. Its design addresses the fundamental electrochemical challenge of high electrical resistance and slow equilibration encountered when measuring pH in rainwater, distilled water, deionized water, boiler feedwater, and ultrapure process water used in pharmaceutical manufacturing and textile fiber processing. The electrode operates on the Nernst principle, generating a millivolt signal proportional to hydrogen ion activity, with temperature compensation enabled via integrated Pt1000 thermistor.
Key Features
- Glass membrane specifically formulated for low-ionic-strength media—reduces alkali error and improves response time in <100 µS/cm solutions
- Double-junction reference system with ceramic frit and KCl-saturated gel electrolyte to suppress contamination from sample matrix and extend service life
- Integrated Pt1000 temperature sensor compliant with IEC 60751 Class A tolerance (±0.15 °C at 0 °C), enabling precise automatic temperature compensation (ATC)
- Rugged epoxy body with IP67-rated sealing for resistance to mechanical stress and incidental splashes
- Standard BNC connector compatible with all OHAUS ST series benchtop pH meters and third-party analyzers supporting mV input and ATC
- No internal refill port—maintenance-free sealed construction suitable for regulated lab environments requiring traceable calibration history
Sample Compatibility & Compliance
The STPURE electrode is validated for use with non-aggressive, low-conductivity aqueous samples including ASTM D1125 Type IV water, USP Purified Water (PW), and WFI-adjacent streams. It is not intended for use in organic solvents, high-viscosity fluids, or strongly oxidizing/reducing matrices. In pharmaceutical quality control labs, the electrode supports compliance with USP , EP 2.2.3, and JP 2.03 pH measurement guidelines when paired with documented calibration procedures (two-point calibration using NIST-traceable buffers at pH 4.01 and 7.00). Its sealed architecture aligns with GLP documentation requirements by eliminating electrolyte refilling—a common source of procedural variability and audit findings.
Software & Data Management
When connected to OHAUS ST5000 or ST2000 series pH meters, the STPURE enables full data traceability: timestamped calibration records, slope/offset diagnostics, stability thresholds, and user-defined pass/fail criteria per measurement. All data exports comply with CSV and PDF formats suitable for 21 CFR Part 11–aligned systems when deployed with OHAUS LabX Lite software (optional). Audit trail functionality captures operator ID, calibration event type, buffer lot numbers, and environmental temperature—supporting routine QC review and regulatory inspection readiness.
Applications
- Pharmaceutical water system monitoring: PW and WFI loop sampling points where conductivity remains <1.3 µS/cm at 25 °C
- Textile quality assurance: pH testing of rinse baths and final wash effluents to verify neutralization prior to dyeing
- Environmental monitoring: Field and lab-based analysis of precipitation chemistry and surface water acidification studies
- Power generation: Feedwater and condensate pH verification in thermal cycle chemistry control programs
- Research laboratories investigating colloidal stability, hydrolysis kinetics, or surface charge behavior in dilute electrolyte systems
FAQ
Can the STPURE electrode be used with non-OHAUS pH meters?
Yes—it features a universal BNC connector and outputs standard mV signals compatible with any meter supporting asymmetrical pH electrode input and external temperature sensing.
What is the recommended calibration frequency for low-ionic-strength applications?
Daily two-point calibration is advised before first use; additional verification is required after every 5 consecutive measurements or when ambient temperature shifts >3 °C.
Does the STPURE require storage solution?
Yes—store immersed in OHAUS pH 4.01 buffer or dedicated electrode storage solution; never store dry or in deionized water, as this accelerates glass membrane dehydration.
Is the electrode suitable for continuous immersion in ultrapure water loops?
It is designed for intermittent grab-sample measurement—not for permanent online installation. For continuous monitoring, consult OHAUS industrial pH sensor solutions with flow-through housings and auto-cleaning options.
