🌱 Extraction of trace elements from soil with aqua regia — PN-ISO 11466 (withdrawn standard)

Environment PN-ISO 11466

Overview

STATUS — THREE FACTS THAT MUST BE KNOWN TOGETHER (state on 25.09.2026): • the PKN card of PN-ISO 11466:2002 (Polish-language version, publication 18-10-2002, 11 pages, KT 191 Soil Chemistry, implements ISO 11466:1995) has the header "Withdrawn" and the withdrawal date 21-11-2023, but DOES NOT HAVE a "Replaced by" row; • the ISO website gives ISO 11466:1995 as "Withdrawn" (stage 95.99), also without indicating a successor; • the current document on the same subject is PN-EN ISO 54321:2021-07 "Gleba, uzdatnione bioodpady, osady ściekowe oraz odpady — Roztwarzanie frakcji pierwiastków rozpuszczalnych w wodzie królewskiej" [Soil, treated biowaste, sewage sludge and waste — Digestion of aqua regia soluble fractions of elements] (English-language version, publication 02-07-2021, 52 pages, KT 191; implements EN ISO 54321:2021 and ISO 54321:2020; the card has no "Withdrawn" header). We link them on the basis of a comparison of titles and scope, not of a catalogue entry — the catalogue does not link these two standards. The entry on PN-EN 13346 in this database describes a second chain leading to the same standard: from sewage sludge via PN-EN 16174 to PN-EN ISO 54321.

WHAT THE STANDARD DESCRIBED (text of ISO 11466:1995 — in full). Scope (clause 1): aqua regia extraction of trace elements from soil and similar materials, prepared according to ISO 11464, containing less than about 20 % (m/m) of organic carbon determined according to ISO 10694. Materials with a higher organic carbon content require additional nitric acid. The solution is suitable for the determination of trace elements by atomic spectrometry techniques; with a high concentration of dissolved substances, spectral interference and an increased background must be expected. WHAT THE RESULT DOES NOT MEAN (note 1): aqua regia does not completely dissolve most soils, and the extraction efficiency depends on the element and on the matrix. Elements extractable with aqua regia CANNOT be called "total" — nor "bioavailable", because the extraction is too strong to reflect biological processes. An "element content" result after this extraction is therefore the content in the aqua regia extract, not in the soil as a whole.

PROCEDURE (clauses 3, 6 and 7): • about 3 g of a subsample, weighed to the nearest 0.001 g, is moistened with 0.5–1.0 ml of water, and 21 ml of hydrochloric acid c = 12.0 mol/l are added with mixing, followed by 7 ml of nitric acid c = 15.8 mol/l, dropwise if necessary to limit foaming; • the vessel is connected to a reflux condenser and an absorption vessel with 15 ml of nitric acid 0.5 mol/l — the absorption vessel is needed only for the determination of mercury; • the whole is left for 16 h at room temperature (slow oxidation of organic matter), then heated slowly to boiling under the condenser and kept so for 2 h, with the condensation zone lower than 1/3 of the height of the condenser; • the extract is clarified, filtered into a 100 ml volumetric flask and made up with nitric acid; the flask is not filled to the mark until the further method of analysis has been chosen (note 10). The amount of aqua regia is sufficient to oxidise about 0.5 g of organic carbon; with a larger amount, 1 ml of nitric acid is added for every 0.1 g of carbon above 0.5 g, not more than 10 ml at a time (note 8). TO GRIND OR NOT TO GRIND (note 2 and clause 8): usually soil < 2 mm is ground to < 150 µm before extraction; for some soils this does not change the result, but it cannot be said in advance for which. The report MUST state whether ground or unground soil was tested — this is the only requirement for the report apart from identification of the sample and deviations.

HOW ACCREDITATION SCOPES CITE THE STANDARD. Measurement of 25.09.2026 on the database of PL accreditation scopes (1310 laboratories with entries): 19 entries at 15 laboratories, almost all as "PN-ISO 11466:2002" (17); in addition "PN-ISO 11466" without a year (1) and "PN-EN ISO 11466:2002" (1) — there is no standard with this designation in the catalogue (a search for "11466" returns only PN-ISO 11466:2002). Object: soil (including mineral and organic), in single entries ground and sewage sludge. Methodology: "Zawartość pierwiastków" [element content] (10), "Zawartość metali" [metal content] (5), "Zawartość rtęci" [mercury content] (3), "Zawartość kadmu" [cadmium content] (1). The standard always stands together with a determination technique: ICP-OES, FAAS, CVAAS (mercury), ICP-MS, ETAAS — and the standard for that technique stands next to it in the notation. The extraction alone gives no result; the result comes only from the determination in the extract.

THE KEY OF THE "LABORATORIES" TAB: "PN-ISO 11466" — 14 laboratories and 18 entries, without any foreign entries; it will not show one laboratory (AB 772) with the form "PN-EN ISO 11466:2002".

HOW FAR THE TEXT EXTENDS: ISO 11466:1995 made available by the publisher in full (clauses 1–8, Figures 1–2). Some numbers in the list of apparatus of this text are internally inconsistent (funnel diameter, flask capacity in the list versus the 100 ml flask in the procedure), so we do not copy the list of apparatus dimensions.

Method principle

The soil (usually ground to < 150 µm) is covered with aqua regia — a mixture of 21 ml of concentrated hydrochloric acid and 7 ml of concentrated nitric acid per about 3 g of sample. After 16 h at room temperature the mixture is boiled for 2 h under a reflux condenser; volatile mercury compounds are retained by an absorption vessel with dilute nitric acid. The extract is filtered and diluted with nitric acid, and the elements are determined in it by atomic spectrometry techniques. Aqua regia does not dissolve silicates, so the result is not the total content.

Applications

• Preparation of a soil extract for the determination of metals: cadmium, chromium, copper, nickel, lead, zinc, mercury and other trace elements
• Assessment of contamination of soils and land with trace elements — extract for ICP-OES, ICP-MS, FAAS, ETAAS, CVAAS
• In the accreditation scopes also ground and sewage sludge — outside the scope of this standard; sewage sludge is covered by PN-EN ISO 54321

Key parameters

Standard

Standard number

PN-ISO 11466:2002 (wersja polska; wprowadza ISO 11466:1995 [IDT])

Title (PL)

Jakość gleby — Ekstrakcja pierwiastków śladowych rozpuszczalnych w wodzie królewskiej

Title (EN)

Soil quality — Extraction of trace elements soluble in aqua regia

Step-by-step procedure

1. Preparation of glassware

   Immerse the glassware in warm nitric acid 0.5 mol/l for at least 6 h and rinse with water (clause 5).

2. Sample preparation

   Prepare air-dried soil according to ISO 11464, grind if necessary and sieve through a 150 µm sieve; determine water according to ISO 11465 on part of the subsample (about 20 g).

3. Addition of acids

   About 3 g (± 0.001 g) into a 250 ml vessel, 0.5–1.0 ml of water, 21 ml of HCl 12.0 mol/l, then 7 ml of HNO3 15.8 mol/l — dropwise if necessary.

4. Standing at room temperature

   With the absorption vessel (15 ml of HNO3 0.5 mol/l) and the condenser connected — 16 h.

5. Boiling under reflux

   Slowly to boiling and 2 h of gentle boiling; condensation zone below 1/3 of the height of the condenser. The same procedure for the blank, with anti-bumping granules.

6. Filtration

   Transfer the contents of the absorption vessel through the condenser into the vessel, rinse with 10 ml of HNO3 0.5 mol/l; after settling, decant through the filter into a 100 ml flask, wash the residue with a small amount of HNO3 0.5 mol/l.

7. Determination and report

   Determine the elements in the extract with the chosen technique; state in the report whether the soil was ground.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Digestion with hydrochloric and nitric acid is potentially hazardous — safety glasses or goggles are mandatory (warning of the standard)
• Work in a well-ventilated fume hood; anti-bumping granules or rough glass beads are added to the blanks and test samples
• Gentle boiling without temperature fluctuations — local overheating risks the liquid being ejected
• Nitrogen oxides released during the reaction — do not open the system outside the fume hood

Frequently asked questions