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PD ISO TS 17379 — Water Quality Determination of Selenium by Hydride Generation AFS and AAS (Parts 1 & 2)
Water Quality — Determination of Selenium — Part 1: HG-AFS; Part 2: HG-AAS (BSI Published Documents, 2013)
📐 PD ISO/TS 17379 is a BSI Published Document covering the determination of selenium in water. Part 1 uses hydride generation atomic fluorescence spectrometry (HG-AFS) and Part 2 uses hydride generation atomic absorption spectrometry (HG-AAS). Selenium is a trace element of major environmental and health interest: at low levels it is an essential nutrient, but at higher levels it is toxic. Accurate determination of selenium in drinking water, surface water, groundwater and industrial wastewater is therefore essential for water monitoring, environmental assessment and drinking-water safety. The series was prepared by BSI Technical Committee EH/3/2 (physical chemical and biochemical methods) and published in July 2013.
💡 Both methods share the same hydride generation principle: selenium in the sample is converted to gaseous hydrogen selenide (H₂Se) and then detected by atomic fluorescence or atomic absorption. Hydride generation separates the analyte from the matrix and greatly improves sample introduction, giving a highly sensitive means of measuring trace selenium.
1. Scope and General Framework 📌
PD ISO/TS 17379 applies to the determination of selenium in water, particularly at trace levels. Part 1 (HG-AFS) specifies the principle, interferences, reagents and standard solutions, apparatus, sample preparation, procedure, calculation and precision for the determination of selenium by hydride generation atomic fluorescence spectrometry. Part 2 (HG-AAS) specifies the corresponding content for the determination of selenium by hydride generation atomic absorption spectrometry. Part 2 supersedes the withdrawn BS 6068-2.45:1993.
| Part | Reference | Detection Principle | Typical Application |
|---|---|---|---|
| Part 1 | PD ISO/TS 17379-1:2013 | Hydride generation atomic fluorescence spectrometry (HG-AFS) | Trace selenium, low-matrix waters, high sensitivity |
| Part 2 | PD ISO/TS 17379-2:2013 | Hydride generation atomic absorption spectrometry (HG-AAS) | Routine water monitoring, medium concentrations |
⚠️ Selenium exists in several chemical forms (selenite, selenate, organic selenium, etc.). Both methods normally require digestion and pre-reduction to convert the various forms into a hydride-reactive species; otherwise total selenium may be underestimated.
2. Principle 🔧
The common core of both methods is hydride generation. In acid medium, selenium(IV) reacts with sodium borohydride (NaBH₄) or potassium borohydride to produce gaseous hydrogen selenide (H₂Se):
Se(IV) + NaBH₄ + H⁺ → H₂Se↑ + by-products
The H₂Se is carried by an inert gas (e.g. argon) into an atomiser. In HG-AFS, H₂Se is atomised in a hydrogen-argon flame or electrically heated quartz tube; the excited selenium atoms emit characteristic fluorescence whose intensity is proportional to selenium concentration. In HG-AAS, H₂Se is thermally decomposed to atomic selenium and quantified by measuring absorbance at a characteristic line (e.g. 196.0 nm). Both methods use standard curve quantification.
✅ The key advantage of hydride generation is that hydrogen selenide is separated from the liquid matrix, greatly reducing matrix interference while quantitatively delivering most of the selenium to the atomiser in gaseous form — giving high sensitivity and low detection limits.
3. Interferences and their Removal 🔥
In hydride generation atomic spectrometry for selenium, interference mainly comes from coexisting metal ions and volatile hydride-forming elements. Common interfering factors include:
- Transition metal ions: copper, nickel, cobalt and iron react with borohydride or catalyse H₂Se decomposition, reducing generation efficiency.
- Other hydride-forming elements: arsenic, antimony, bismuth and tellurium also form gaseous hydrides, potentially causing spectral interference or matrix effects.
- Oxidising substances and high-salt matrices: high oxidant levels consume the reductant, while high salinity changes reaction kinetics and nebulisation efficiency.
- Acidity control: hydride generation is sensitive to acidity, which must be tightly controlled for stable generation efficiency.
To remove these interferences, the standard specifies reagent purification, masking agents, acidity adjustment, carrier-gas optimisation and matrix matching, and requires spike recovery and precision to be verified during method validation.
4. Reagents, Apparatus and Procedure 🔩
Key reagents include: selenium stock and working standard solutions, sodium (or potassium) borohydride reductant solution, acid (e.g. hydrochloric acid), anti-interference masking agents, and matrix-matched solutions for preparing calibration standards. For apparatus, HG-AFS requires a hydride generation atomic fluorescence spectrometer, while HG-AAS requires a hydride generation atomic absorption spectrometer (or an AAS with a quartz atomiser).
A typical procedure is: sample collection and preservation → digestion/pre-reduction → acidity adjustment → hydride generation → atomisation and detection → quantification against a standard curve → calculation and reporting. The whole procedure should include reagent blanks, duplicate samples and QC samples to ensure reliability.
🚨 Hydrogen selenide (H₂Se) is highly toxic; work in a fume cupboard and ensure exhaust gases are treated before release. Sodium borohydride reacts vigorously with acid — add reductant slowly with cooling to prevent splashing and gas accumulation.
5. Engineering Practice Essentials 🛠️
- 🔍 Method choice: choose HG-AFS for trace selenium in low-matrix waters; use HG-AAS for routine monitoring at moderate concentrations; always assess matrix interference.
- 🔧 Sample preparation: correct digestion and pre-reduction is the prerequisite for total selenium determination; develop procedures for different water matrices.
- 📊 Quality control: include reagent blanks, duplicate samples, calibration curves and certified reference materials (CRM) in each batch, controlling spike recovery within specified ranges.
- 📋 Reporting: report results as selenium mass concentration, stating the detection limit, working range and precision, and noting the sample pre-treatment where relevant.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between HG-AFS and HG-AAS?
A: Both are based on hydride generation; the difference is the detector. HG-AFS measures characteristic fluorescence of selenium atoms — high sensitivity, low background. HG-AAS measures absorbance at a characteristic line — widely available and broadly applicable.
A: Both are based on hydride generation; the difference is the detector. HG-AFS measures characteristic fluorescence of selenium atoms — high sensitivity, low background. HG-AAS measures absorbance at a characteristic line — widely available and broadly applicable.
❓ Q: Why is pre-reduction needed?
A: Selenium in water occurs mainly as Se(IV) and Se(VI), and hydride generation is effective only for Se(IV). Pre-reduction converts Se(VI) to Se(IV) so that total selenium can be measured accurately.
A: Selenium in water occurs mainly as Se(IV) and Se(VI), and hydride generation is effective only for Se(IV). Pre-reduction converts Se(VI) to Se(IV) so that total selenium can be measured accurately.
❓ Q: Which matrices interfere?
A: Transition metals such as copper, nickel, cobalt and iron, and hydride-forming elements such as arsenic, antimony and bismuth can interfere; they are removed by masking, acidity control and matrix matching.
A: Transition metals such as copper, nickel, cobalt and iron, and hydride-forming elements such as arsenic, antimony and bismuth can interfere; they are removed by masking, acidity control and matrix matching.
🔍 Q: Which old standard does Part 2 replace?
A: PD ISO/TS 17379-2:2013 supersedes the withdrawn BS 6068-2.45:1993, the previous method for selenium in water.
A: PD ISO/TS 17379-2:2013 supersedes the withdrawn BS 6068-2.45:1993, the previous method for selenium in water.