Shahim et al. 2019 — FET sensor for multiplexed Cr(III)/Cr(VI) detection in water
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.