Overview
This paper describes the development and characterization of a portable field effect transistor (FET)-based sensor array for simultaneous detection of Cr(III) and Cr(VI) in liquid media, with a detection limit below the US EPA maximum contaminant level (MCL) of 100 ppb (0.1 mg/L) total chromium in drinking water. The sensor uses ion-selective membranes incorporating target-specific ionophores: bis(cyclohexanone)oxaldihydrazone for Cr(III) and quinaldine red for Cr(VI), achieving calibration sensitivities of 99 mV/log[Cr3+] and 71 mV/log[Cr6+] respectively, with detection limits of 10^-11 M. The device is designed for point-of-use water quality monitoring without laboratory infrastructure.
Key numbers
US EPA MCL for total dissolved chromium in drinking water: 100 ppb (10^-6 M). Sensor detection limits: 10^-11 M for both Cr(III) and Cr(VI). Calibration sensitivity: 99 mV/log[Cr3+] (Cr III); 71 mV/log[Cr6+] (Cr VI). pH operating range: 3-8. Response time: ~10 minutes. The US EPA and IARC classify Cr(VI) as a Group I human carcinogen; Cr(III) as Group III. OSHA airborne exposure limit (occupational): 0.5 µg/m3 Cr(VI) as 8-hour TWA.
Methods (brief)
Extended gate FET sensor with ion-selective membrane; gold electrode fabrication by electron beam evaporation; PVC matrix membrane immobilized on gate electrode; drain-source voltage 2 V; gate bias 1 V pulse (100 µs). Tested in phosphate buffer saline and river water spike solutions.
Implications
Certification: methodology-relevant for Cr speciation testing; confirms that Cr(III) and Cr(VI) can be distinguished at very low concentrations without ICP-MS. Relevant context for testing methods pages discussing Cr-VI vs total Cr speciation.
Courses: useful for illustrating low-cost chromium speciation testing approaches and the regulatory distinction between Cr(III) and Cr(VI).
App: not applicable to food-matrix risk estimation.
Wiki pages updated on ingest
Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Change | Description |
|---|---|---|---|
| a8052bb | 2026-08-09 | major | 6 sections added; narrative text revised |