⚗️ Selenium in drinking water, groundwater and surface water — hydride generation atomic absorption spectrometry (HGAAS): selenium converted to Se(IV), hydride decomposed thermally, absorbance at 196.0 nm, range 1–10 µg/l (higher after dilution); PN-ISO 9965:2001

Physicochemistry PN-ISO 9965

Overview

WHAT THE STANDARD COVERS. The "Scope" field of the PKN card, in full: "A method is given for determining selenium, including selenium in organic compounds, in drinking water, groundwater and surface water, in the concentration range from 1 microg/l to 10 microg/l. Higher selenium concentrations can be determined after suitable dilution of the water sample. The method consists in AAS measurement of the selenium formed by thermal decomposition of selenium hydride. Under the conditions of this method only Se (IV) forms the hydride quantitatively. To avoid errors in the determination, selenium in other oxidation states has to be converted to Se (IV) before the determination. The absorbance is measured at a wavelength of 196.0 nm" (our translation; no full stop at the end on the card). The description of ISO 9965:1993 in the Standard Norge catalogue says the same. We did not have the text of the standard (8 pages).

STATUS (card as of 13.10.2026). The card of PN-ISO 9965:2001 (Polish version) has neither the heading "Withdrawn" nor a "Withdrawal date" line: publication 13-12-2001, 8 pages, price group D, Health, Environment and Medicine Sector, KT 121 Water Quality — Chemical Testing — Inorganic Substances, "Adopts: ISO 9965:1993 [IDT]", ICS 13.060.50; the card has neither a "Replaces" nor a "Replaced by" field. The PKN search under "PN-ISO 9965" (12.10.2026) returns only this standard. The adopted document is no longer current at its publisher: according to the Standard Norge catalogue (13.10.2026) ISO 9965:1993 (edition 1 of 1 July 1993, ISO/TC 147/SC 2) has the status "Withdrawn" dated 15 July 2014 and the note "Revised by: ISO/TS 17379-2:2013". The PKN search under "17379" (13.10.2026) returns no standard — there is no Polish edition of this technical specification. We do not claim how ISO/TS 17379-2 differs from ISO 9965 — we had the text of neither document.

VALUES IN THE REGULATION. Regulation of the Minister of Health of 22 May 2026 on the quality of water intended for human consumption (Journal of Laws 2026 item 748; status "in force" in the Sejm ELI database, entry into force 24.06.2026, it repealed the 2017 regulation, Journal of Laws 2017 item 2294). Annex 1, part B "Chemical parameters", item 28: selenium — parametric value 20 μg/l, with the note: "A parametric value of 30 μg/l applies to regions where geological conditions may lead to high levels of selenium in groundwater" (our translation). Annex 4, part B: the method must be able to measure concentrations equal to the parametric value with a limit of quantification of 30 % or less of the parametric value (for 20 μg/l — 6 μg/l), and the measurement uncertainty (k = 2) for selenium (item 41) is 40 % of the parametric value. The regulation names no standard for selenium.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server, refreshed on 12.10.2026). Number 9965 appears in 11 records at 11 laboratories; in the current PCA documents (read on 12–13.10.2026; issues from 23.01.2025 — AB 602 — to 29.09.2026 — AB 648) — in 11 rows at the same laboratories, with the same notation. A search of all downloaded PCA documents found no laboratories outside the database copy; no row with the number is set in bold italics (suspension) and no pages are repeated in any document. Notations: "PN-ISO 9965:2001" — 10 laboratories; "PN-EN ISO 9965:2001" — AB 539 (the PKN catalogue has no standard with the EN element under this number). The "Laboratories" tab (search term "PN-ISO 9965") shows 10 laboratories — without AB 539 — checked with the tab query on the labcoda.pl production server on 13.10.2026; the notation "PN-EN ISO 9965" gives 1 there (AB 539).

WHAT THE LABORATORIES TEST (database copy and PCA documents). Test object: water and water intended for human consumption (AB 216, AB 311, AB 435, AB 602, AB 603, AB 618, AB 622, AB 648), water intended for human consumption only (AB 487, AB 539), water, water intended for human consumption and waste water (AB 814). Characteristic: selenium concentration. Technique: hydride generation atomic absorption spectrometry (HGAAS) — all 11. Ranges: (1.0–10) µg/l — AB 622; (1.0–15) µg/l — AB 618; (1.0–20) µg/l — AB 603; (2.0–15) µg/l — AB 311; (2.0–20) µg/l — AB 648; (2.0–30) µg/l — AB 487; (2.0–40) µg/l — AB 602; (2.67–16.00) µg/l — AB 435; (5.0–30.0) µg/l — AB 539; (0.001–0.100) mg/l — AB 216; (0.0010–0.10) mg/l — AB 814.

ALONGSIDE THIS STANDARD. No other document stands in the entries with this standard. Selenium in water is determined by 69 laboratories in the database copy (entries with selenium in the test description or parameters and with water or waste water as the test object, without entries for waste, sediments, soils and eluates); apart from this standard they cite: PN-EN ISO 17294-2 (inductively coupled plasma mass spectrometry) — 32 laboratories, PN-EN ISO 11885 (ICP-OES) — 17, PN-EN ISO 15586 (graphite furnace atomic absorption spectrometry) — 15, in-house procedures — 4. Three laboratories have PN-ISO 9965 next to another of these standards in separate entries: AB 216 (PN-EN ISO 17294-2), AB 622 (PN-EN ISO 11885), AB 814 (PN-EN ISO 15586). The determination of selenium by ICP-OES is described in a separate Knowledge Base entry.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — oxidation state: only Se(IV) forms the hydride quantitatively; selenium in other oxidation states that has not been converted to Se(IV) before the determination does not enter the result, and the result comes out too low although the measurement runs correctly (PKN card). Second — range: the standard covers 1–10 µg/l, while the parametric value of 20 µg/l (30 µg/l in regions with high selenium levels in groundwater) lies above this range — according to the card, samples with concentrations around the parametric value are determined after dilution; the upper limits of the laboratories' ranges are between 10 and 100 µg/l. Third — test object: the card names drinking water, groundwater and surface water; it does not name waste water, which AB 814 has in its scope. Fourth — requirements of the regulation: a limit of quantification of no more than 6 µg/l and an uncertainty of up to 40 % of the parametric value (k = 2) apply to water intended for human consumption assessed under the regulation; the lower limits of the laboratories' ranges are between 1.0 and 5.0 µg/l. Fifth — status: the PKN card bears no withdrawal note, while ISO withdrew the adopted document in 2014.

WHAT WE DO NOT GIVE. We did not have the text of the standard — we do not give how selenium is converted to Se(IV), the reagent forming the hydride, the design of the hydride generation system and of the atomiser, the preparation of calibration solutions, interferences or precision.

Method principle

Before the determination, selenium in other oxidation states is converted to Se(IV), because under the conditions of the method only Se(IV) forms the hydride quantitatively; selenium hydride is decomposed thermally and the selenium formed is measured by atomic absorption spectrometry at a wavelength of 196.0 nm. Range 1–10 µg/l, higher concentrations after diluting the sample (PKN card). WE DO NOT GIVE details of the procedure — we did not have the text of the standard.

Applications

• Drinking water, groundwater and surface water — selenium, including selenium in organic compounds, 1–10 µg/l (PKN card)
• Water intended for human consumption — comparison with the parametric value of 20 µg/l (30 µg/l in regions with high selenium levels in groundwater), Journal of Laws 2026 item 748
• Water and water intended for human consumption — in the current accreditation scopes of 11 laboratories, all with HGAAS; one also for waste water

Key parameters

Standard

Standard number

PN-ISO 9965:2001

Title (PL)

Jakość wody — Oznaczanie selenu — Metoda atomowej spektrometrii absorpcyjnej (technika wodorkowa)

Title (EN)

Water quality — Determination of selenium — Atomic absorption spectrometric method (hydride technique)

Step-by-step procedure

1. Conversion of selenium to Se(IV)

   Selenium in other oxidation states is converted to Se(IV) before the determination (PKN card); WE DO NOT GIVE how. PN-ISO 9965:2001 without a withdrawal note in PKN (13.10.2026).

2. Formation and decomposition of the hydride

   Se(IV) forms the hydride, which is decomposed thermally (PKN card); WE DO NOT GIVE reagents or conditions.

3. Measurement

   Absorbance at 196.0 nm; range 1–10 µg/l, higher concentrations after diluting the sample (PKN card).

4. Result and assessment

   Selenium concentration in µg/l; for water intended for human consumption, comparison with the parametric value of 20 µg/l (Journal of Laws 2026 item 748).

Required equipment and apparatus

Health and safety (OHS)

• Selenium and its compounds — safety rules of a chemical laboratory
• SUBJECT-MATTER NOTE: the result covers only selenium converted to Se(IV); only Se(IV) forms the hydride quantitatively

Frequently asked questions