🌿 Digestion of waste with aqua regia (1 volume of 65–70 % nitric acid and 3 volumes of 35–37 % hydrochloric acid) before determination of elements by AAS, ICP-OES and ICP-MS — microwave in closed vessels (at least 8 bar), microwave in semi-open vessels at atmospheric pressure, or heating under a reflux condenser; the result is the aqua regia soluble portion, not the total content, PN-EN 13657

Environment PN-EN 13657

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN 13657:2006 (Polish version), in full (our translation): “Methods of digestion with aqua regia are given. Solutions produced by these methods are suitable for analysis e.g. by atomic absorption spectrometry (FLAAS, HGAAS, CVAAS, GFAAS), inductively coupled plasma emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS)”. We read the text of the standard in the iTeh sample of SIST EN 13657:2004 (text of EN 13657:2002, English): from the title page through the foreword, introduction and Clauses 1–7 to the beginning of 8.2 (Clause 8 — interferences and sources of error). Outside the sample remain the rest of 8.2 and 8.3 (sources of error in closed and semi-open vessels), Clause 9 (blank test and three digestion procedures — amounts of reagents, heating programmes, preparation of the solution for analysis), Clause 10 (test report), Annex A (normative — calibration of microwave power) and Annex B (informative — interlaboratory study and robustness study).

ACCORDING TO THE TEXT OF EN 13657:2002 (to the beginning of 8.2). The standard was prepared by CEN/TC 292 “Characterization of waste” (secretariat NEN); CEN approved it on 19 August 2002. Introduction: the aim is to describe methods for extraction of elements soluble in aqua regia; when the waste is not brought completely into solution, the result is not the total content of the element, and the results cannot be regarded as available for leaching, because digestion with aqua regia is too vigorous to represent natural processes. Scope (1): the solutions are suitable for measurement by, among others, FLAAS, HGAAS, CVAAS, GFAAS, ICP-OES and ICP-MS; aqua regia will not necessarily release all elements completely, but for most environmental applications and waste characterization the results fit the purpose; example elements: Al, Sb, As, B, Ba, Be, Ca, Cd, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Mo, Ni, P, K, Se, Ag, S, Na, Sr, Sn, Te, Ti, Tl, V, Zn. Definitions (3): aqua regia — 1 volume of nitric acid (65–70 % m/m) and 3 volumes of hydrochloric acid (35–37 % m/m); dry residue — after drying at 105 °C ± 5 °C to constant mass. Safety (4): strongly corrosive and partly very toxic reagents, high temperature and pressure; work in a hood; with samples of high organic content explosive intermediates may form; pressurised vessels must not be opened before they have cooled down. Sample (5): the test portion is transferred to the vessel without pre-treatment if it is representative and the effectiveness of digestion is proven; otherwise solid waste is dried or ground below 250 µm and liquid waste homogenised — without changing the concentration of the elements of interest; the mass of the test portion is to be representative and to comply with the manufacturer’s specifications, preferably above 200 mg; in a closed vessel the organic carbon in the portion shall not exceed 100 mg (safety) unless the manufacturer recommends otherwise, and a portion larger than allowed is divided into parts digested separately and combined before analysis. Apparatus (6): closed system — microwave unit with power programmable to within ± 10 W (typically nominal 600–1200 W), calibrated according to Annex A if necessary, with a ventilated cavity safe against vessel explosion; household units are not suitable; vessels with a pressure relief valve, withstanding at least 8 bar, and higher pressures with more than 100 mg organic carbon; semi-open system — unit of typically nominal 200 W or 300 W, vessels working at atmospheric pressure with a reflux condenser, volume at least 50 ml; conventional heating — reaction vessel of at least five times the volume of aqua regia, water-cooled reflux condenser at least 340 mm long, non-return absorption vessel, glass beads 2–3 mm, temperature-controlled heater; balance with an error limit of ± 0.1 mg; for boron determination borosilicate glass must not be used. Reagents (7): analytical grade, water of grade 1 according to EN ISO 3696; hydrochloric acid 35–37 %, nitric acid 65–70 %, diluted nitric acid 0.5 mol/l. Sources of error (8.1): the sample must not be heated before digestion and volatile reaction products must not escape; the container can be a source of error (elemental mercury quickly penetrates polyethylene walls in both directions, glass can contribute B, Na, K, Al); grinding risks contamination and losses of volatile compounds as temperature rises — especially for Hg, As, Pb; a large undissolved part of the sample risks poor repeatability; high acid and solute concentrations in the digest may interfere with the measurement; cleaning vessels with 10 % nitric acid is recommended; the whole portion must be in contact with the acid; some elements may precipitate as insoluble chlorides, fluorides or sulphates — the precipitate can then be analysed separately; filtration must not introduce contaminants.

STATUS (as of 03.10.2026). The card of PN-EN 13657:2006 (Polish version, published 06-02-2006, 29 pages, price group N) has no “Withdrawn” header: Health, Environment and Medicine Sector, KT 216 Waste, ICS 13.030.01, “Introduces: EN 13657:2002 [IDT]”, “Replaces: PN-EN 13657:2003 — English version”; the card has no “Replaced by” field. In the PKN catalogue the standard is therefore current alongside PN-EN ISO 54321:2021-07. In the iTeh catalogue (read on 03.10.2026) the Slovenian standard SIST EN 13657:2004, which adopts EN 13657:2002, has the status “Withdrawn” with withdrawal date 03.03.2026 and the field “Replaced By”: SIST EN ISO 54321:2021 “Soil, treated biowaste, sludge and waste — Digestion of aqua regia soluble fractions of elements (ISO 54321:2020)”. This is a reading for the Slovenian standard; we could not read the catalogue page of EN 13657:2002 itself, so we do not give the status of the CEN document. The successor is described in a separate entry “Aqua regia digestion of soil, treated biowaste, sewage sludge and waste before the determination of metals and other elements — heating under reflux (A1), in a heating block (A2) or by microwave in closed vessels at 175 °C (B), PN-EN ISO 54321”.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read on 03.10.2026). The number 13657 appears in 25 records at 8 laboratories: AB 005, AB 054, AB 213, AB 339, AB 550, AB 688, AB 869, AB 1267. In the current PCA documents (read on 03.10.2026, issues from 04.09.2025 to 22.09.2026) the number appears in 25 items of the same 8 laboratories. Forms of notation: “PN-EN 13657:2006” in most items, “PN-EN 13657” without the year at AB 054 (two items) and AB 550. The standard never stands alone — always next to a measurement standard (PN-EN ISO 11885, PN-EN ISO 17294-2, PN-EN ISO 12846, PN-ISO 8288, PN-EN 1233) and it is sometimes cited jointly with other digestion standards: PN-EN 13346:2002 (AB 339), PN-ISO 11466 (AB 213, AB 550), PN-EN 16171 (AB 213), PN-EN 13656 (AB 550, AB 688). The “Laboratories” tab (“PN-EN 13657”) shows the same 8 laboratories — checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Waste with listed codes — content of elements by ICP-OES (AB 005 — two items, with ranges up to 100000 mg/kg; AB 213; AB 688 — oxides and elements in waste and aggregates, e.g. SiO2 (0.10–95.0) %; AB 869; AB 1267 — lead, cadmium, nickel, copper (1.00–100) mg/kg in waste and secondary fuels) or ICP-MS (AB 054, AB 213 — also tellurium (5.0–100) mg/kg). Mercury by CVAAS after aqua regia digestion: AB 213 (building materials, (0.05–25.0) mg/kg) and AB 869 (waste and alternative fuel, (0.10–5.0) mg/kg). Matrices other than waste: soil (AB 213, AB 550), raw materials and building materials as well as plastics and packaging materials (AB 054), hard coal ash (AB 688) and secondary fuels (AB 869, AB 1267, AB 054) — the standard speaks of waste in its scope (1). AB 339 cites it for plant and animal waste, food processing waste, sludges, waste from waste treatment and sewage sludge (FAAS: Cd, Cu, Ni, Pb, Zn, Cr; ICP-OES: P, S, Na, K, Mg, Ca and As, B, Cd, Cr, Cu, Fe, Mo, Mn, Ni, Pb, Zn) — two ICP-OES items are suspended at the laboratory’s request (bold italics) from 27.02.2026 to 18.01.2027. At AB 054 the footnote on suspension of part of the scope from 25.06.2026 concerns other items.

WHERE A SEEMINGLY CORRECT RESULT IS EASY. During sample preparation: heating before digestion, grinding with heating or a leaking vessel lower the result for mercury, arsenic and lead without a visible trace (8.1); a polyethylene container changes the content of elemental mercury in both directions, and glass contributes boron, sodium, potassium and aluminium. During digestion: undissolved chlorides, fluorides and sulphates take part of the elements into the precipitate — the solution alone then gives too low a result, and the standard allows separate analysis of the precipitate (8.1). In interpretation: the result is the aqua regia soluble portion — in a report it cannot be called the total content or compared with leachability, because the standard rules out both readings (introduction, 1). For safety and portion mass: more than 100 mg organic carbon in a closed vessel risks rupture of the vessel — that is why the standard requires dividing the portion for organic waste (5.2, 6.1.2). In measurement: the measurement itself is made according to the measurement-technique standards given in the scopes (PN-EN ISO 11885, PN-EN ISO 17294-2, PN-EN ISO 12846) — this entry does not describe them.

WHAT WE DO NOT GIVE. We have not read Clause 9, so we do not give the volume of aqua regia per portion, the power and time programmes in the microwave unit, the time and temperature of heating under reflux or the preparation of the solution for analysis; nor do we give the power calibration (Annex A) or the precision and robustness data (Annex B). We do not give requirements of waste legislation for the results of this digestion — we have not read the texts of the acts for this entry.

Method principle

A portion of waste — if possible without pre-treatment, otherwise after drying or grinding below 250 µm — is covered with aqua regia (1 volume of 65–70 % nitric acid and 3 volumes of 35–37 % hydrochloric acid) and heated in one of three systems: microwave in a closed vessel (at least 8 bar, relief valve), microwave in a semi-open vessel at atmospheric pressure with a reflux condenser, or conventionally under a reflux condenser with an absorption vessel. The digest is measured by AAS, ICP-OES or ICP-MS; the result is the portion of the elements soluble in aqua regia.

Applications

• Waste — digestion before determination of, among others, Al, Sb, As, B, Ba, Be, Ca, Cd, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg, Mo, Ni, P, K, Se, Ag, S, Na, Sr, Sn, Te, Ti, Tl, V, Zn (1)
• Solutions for measurement by FLAAS, HGAAS, CVAAS, GFAAS, ICP-OES and ICP-MS (1)
• Waste, soil, building materials, ashes, secondary fuels, plastics — in the accreditation scopes of 8 laboratories in PCA, always together with a measurement standard

Key parameters

Standard

Standard number

PN-EN 13657:2006

Title (PL)

Charakteryzowanie odpadów — Roztwarzanie do dalszego oznaczania części pierwiastków rozpuszczalnych w wodzie królewskiej

Title (EN)

Characterization of waste — Digestion for subsequent determination of aqua regia soluble portion of elements

Step-by-step procedure

1. Sample preparation

   Without preparation if the portion is representative; otherwise solid waste is dried or ground below 250 µm, liquid waste homogenised; do not heat before digestion. PN-EN 13657:2006 without “Withdrawn” header on the PKN card (card as of 03.10.2026).

2. Portion mass

   Preferably above 200 mg; in a closed vessel at most 100 mg organic carbon — a larger portion is divided and the digests combined before analysis.

3. Digestion

   Aqua regia in one of three systems: microwave in a closed vessel, microwave in a semi-open vessel, heating under reflux. We do not give the amounts of acids and heating programmes (Clause 9).

4. Precipitate and filtration

   Undissolved chlorides, fluorides and sulphates may contain part of the elements — the precipitate can be analysed separately; filtration must not introduce contaminants.

5. Measurement

   According to the standard of the measurement technique (e.g. ICP-OES, ICP-MS, CVAAS); the result is reported as the aqua regia soluble portion.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Strongly corrosive and partly very toxic reagents, high temperature and pressure — work in a hood or in closed force-ventilated equipment (4)
• With samples rich in organic matter strong oxidising reagents may form explosive intermediates; in a closed vessel at most 100 mg organic carbon (4, 5.2)
• Do not open pressurised vessels before they have cooled down; avoid contact with gaseous reaction products (4)

Frequently asked questions