Xylem WTW SenTixSur Flat-Surface pH Electrode

Overview

The Xylem WTW SenTixSur is a specialized flat-surface pH electrode engineered for direct, non-invasive measurement of pH on moist or semi-solid sample surfaces—without requiring sample immersion or dilution. Unlike conventional pH electrodes with spherical or conical glass membranes, the SenTixSur employs a planar pH-sensitive glass membrane mounted flush within a robust polymer housing. This geometry ensures uniform contact pressure and stable electrochemical potential development across heterogeneous, soft, or fragile surfaces such as agar gels, pharmaceutical ointments, cosmetic creams, leather, paper, and biological tissue cultures. Its operation follows the fundamental Nernstian principle: hydrogen ion activity at the glass membrane surface generates a measurable potential difference relative to the internal reference system. The electrode’s low-resistance (<1 GΩ), high-stability glass formulation enables rapid response times and minimal drift—even under intermittent contact or variable hydration conditions.

Key Features

• Flat, impact-resistant pH membrane optimized for reproducible surface contact on soft, uneven, or hydrated substrates
• Referid® polymer-based reference electrolyte system—maintenance-free, leak-proof, and chemically stable over the electrode’s operational lifetime
• Open-ring liquid junction design minimizes clogging and facilitates thorough cleaning between measurements
• High-purity borosilicate glass shaft with integrated temperature sensor (compatible with WTW multi-parameter meters supporting automatic temperature compensation)
• Robust mechanical construction: 12 mm diameter × 120 mm length shaft, rated for repeated use in QC labs, R&D environments, and regulated production settings
• S7 connector interface—designed for seamless integration with WTW handheld meters (e.g., Multi 3630 IDS, pH 3310) and benchtop systems supporting IDS digital communication protocol

Sample Compatibility & Compliance

The SenTixSur is validated for surface pH assessment of materials where conventional immersion electrodes yield unreliable or destructive results. It is routinely applied in ISO 17025-accredited laboratories for quality control of topical formulations (ISO 18842:2019), pharmaceutical dosage forms (USP ), and food-grade packaging substrates. Its design conforms to IEC 61000-6-3 (EMC) and IEC 61000-6-2 (immunity) standards. While not intrinsically certified for hazardous areas, its polymer-filled architecture eliminates electrolyte leakage risks—supporting GLP-compliant documentation workflows where traceability of measurement conditions (e.g., contact time, ambient humidity, surface moisture content) is required per FDA 21 CFR Part 11 Annex 11 guidelines.

Software & Data Management

When paired with WTW’s IDS-enabled instruments (e.g., Multi 3630 IDS), the SenTixSur supports full digital calibration logging, timestamped measurement storage, and user-defined metadata tagging (e.g., sample ID, operator, surface description). Calibration data—including slope, offset, and asymmetry potential—is retained in instrument memory with audit-trail capability. Export options include CSV and PDF reports compatible with LIMS integration. Firmware updates via WTW LabX® software ensure long-term compatibility with evolving regulatory data integrity expectations.

Applications

• Topical product QA/QC: pH mapping of hydrogels, emulsions, and transdermal patches
• Biological surface monitoring: Agar plate surface pH during microbial culture incubation or antibiotic diffusion assays
• Material science: Surface acidity profiling of coated papers, leather tanning intermediates, and polymer films
• Food safety: Non-destructive pH verification of cheese rinds, fermented vegetable surfaces, and edible packaging films
• Environmental testing: pH characterization of wet soil crusts, moss layers, or sediment-water interfaces

FAQ

Can the SenTixSur be used for aqueous solution measurements?
Yes—but it is suboptimal for bulk liquid applications due to slower equilibration and higher susceptibility to air bubble entrapment versus spherical electrodes. For routine solution pH, WTW recommends SenTix 41 or SenTix 950.
Is the Referid® electrolyte compatible with ISO/IEC 17025 calibration requirements?
Yes—the maintenance-free nature of Referid® eliminates variability from refilling errors; calibration stability is verified per ISO 8655-5 and documented using WTW’s accredited calibration certificates.
What cleaning protocols are recommended for the open-ring junction?
Rinse thoroughly with deionized water after each use; for organic residue, soak briefly in 70% ethanol or mild detergent solution, followed by extended DI water rinse and air-drying—never wipe the flat membrane with abrasive materials.
Does the electrode require periodic reconditioning or storage solution?
No—Referid® does not dry out. Store upright at room temperature in ambient air; avoid prolonged exposure to strong acids (pH <1) or fluoride-rich media without post-measurement rinsing.
Is temperature compensation automatic when connected to compatible WTW meters?
Yes—the built-in NTC temperature sensor enables real-time ATC (Automatic Temperature Compensation) per DIN 19265 and ASTM D1293-20 standards.