Measuring Selenium in Water: Methods and Advances

Selenium is both an essential micronutrient and a potential contaminant, with a narrow margin between beneficial and toxic levels. Because its toxicity and bioavailability depend strongly on chemical form—selenite (Se(IV)) being more toxic and less bioavailable than selenate (Se(VI))—accurate detection in water is critical for public health and environmental monitoring.

Atomic Spectrometry

Atomic spectrometry remains the backbone of selenium analysis. Hydride generation atomic fluorescence spectrometry (HG-AFS) is widely used for its high sensitivity and simplicity; it is standardized under ISO/TS 17379-1 and applicable to drinking water, surface water, and groundwater across a wide concentration range. Hydride generation atomic absorption spectrometry (HG-AAS) is another established approach, officially recognized in ASTM D3859 and EPA Method 3114, with a method detection limit around 2 μg/L. Graphite furnace atomic absorption spectrometry (GF-AAS) offers greater sensitivity for low-concentration samples, with linear ranges typically spanning 1 to 50 μg/L.

Inductively Coupled Plasma Mass Spectrometry

ICP-MS delivers exceptional sensitivity and multi-element capability, with detection limits reaching the ng/L level. However, selenium determination by ICP-MS faces two inherent challenges: its high first ionization potential reduces ionization efficiency in argon plasma, and the most abundant isotope (⁸⁰Se) suffers from argon dimer interference. Collision/reaction cell technology has largely overcome these issues, enabling detection limits as low as 5 ng/L for total selenium.

Speciation Analysis

Since total selenium concentration alone cannot reveal toxicity, speciation analysis has become increasingly important. The mainstream approach couples chromatographic separation—typically HPLC or ion chromatography—with element-specific detection such as ICP-MS or AFS. Anion-exchange HPLC coupled to ICP-MS allows simultaneous determination of Se(IV), Se(VI), and organic selenium species in a single run. More recently, HPLC–continuous flow hydride generation–FAAS has been proposed as a cost-effective alternative for inorganic selenium speciation in tap water samples.

Electrochemical and Spectrophotometric Methods

Voltammetry offers a cost-effective complement to spectroscopic techniques. Anodic stripping square wave voltammetry provides selective detection of Se(IV), with detection limits around 0.57 mg/L using unmodified glassy carbon electrodes. Spectrophotometric methods, often based on the reaction of Se(IV) with chromogenic reagents such as 3,3′-diaminobenzidine or iodide–starch systems, remain useful for field screening and resource-limited settings.

Toward Field-Deployable Detection

Recent years have seen growing interest in portable analytical devices for on-site selenium monitoring. Portable chemical vapor generation–point discharge optical emission spectrometers have achieved detection limits of 1.8 μg/L for Se(IV), with precision below 5%. A portable selenium analyzer based on fluorimetric and colorimetric sensing has also been developed, offering a wide detection range and reduced analysis time for field applications.