⚗️ Trace Elements in Food — Pressure Digestion of Samples for the Determination of Metals

Food Chemistry PN-EN 13805

Overview

STATUS (as of 02.11.2026). PN-EN 13805:2014-11 — English version with a Polish title (in translation: “Foodstuffs — Determination of trace elements — Pressure digestion”), published on 28.11.2014, implements EN 13805:2014 [IDT]; replaced PN-EN 13805:2003 (the Polish version); the PKN catalogue card has no withdrawal note (read on 02.11.2026). EN 13805:2014 replaced EN 13805:2002; changes according to the foreword: restructuring of some clauses, new subclauses on apparatus with conventional heating, with microwave heating and on the microwave autoclave (5.2.2–5.2.4), a revised subclause on the addition of acid (6.3.2), completely new digestion examples (6.4), a supplemented bibliography and editorial revision of the whole text. The description is based on the preview of EN 13805:2014 (iTeh, SIST EN 13805:2015: clauses 1–5 and 6.1–6.3.3).

SCOPE AND PRINCIPLE (clauses 1 and 3). A method for the pressure digestion of foodstuffs intended for the determination of elements. It has been tested in interlaboratory studies in combination with atomic absorption spectrometry (flame, electrothermal, hydride, cold vapour) and ICP-MS; it can be combined with other techniques, e.g. ICP-OES, voltammetry or atomic fluorescence. The physicochemical digestion is intended to decompose the sample material and give a test solution containing the elements to be determined; it is used when the measurement has been validated in combination with this digestion. The result refers to the total content of the element, depending on the reagents and the measurement procedure used. The sample is homogenized without introducing contamination and then digested with nitric acid (sometimes with other acids added) at high temperature and under pressure in a closed vessel, with conventional or microwave heating. General requirements for the determination of elements in foodstuffs are given in EN 13804 (normative reference).

REAGENTS (clause 4). The trace element content of the reagents and water shall be low enough not to affect the result; nitric and hydrochloric acid of insufficient purity are purified by sub-boiling distillation. Nitric acid — mass fraction of at least 65 %, density about 1.4 g/ml; diluted nitric acid — at least (1 + 9); hydrochloric acid — at least 30 %, about 1.15 g/ml; hydrofluoric acid — at least 40 %, about 1.14 g/ml; hydrogen peroxide — at least 30 %, about 1.11 g/ml.

APPARATUS (clause 5). Everything that comes into contact with the sample is washed with diluted nitric acid and water; vessels can be cleaned with hot acid vapour in an apparatus intended for this purpose. Pressure vessels shall be commercially available and safety-tested, with acid-resistant inserts made of materials with a low risk of contamination, withstand at least 180 °C and have safety devices (e.g. rupture discs, a pressure jacket, power control). With conventional heating, inserts of PTFE, quartz glass, FEP or PFA are used. Microwave systems shall have temperature measurement (internal or external; an infrared sensor only if the manufacturer confirms that the reading corresponds to the temperature of the solution) — without it the system shall not be used; inserts of PTFE, PFA, TFM or quartz. In a microwave autoclave the vessels are closed by a pre-pressure of at least 40 bar. Above 230 °C quartz glass is advantageous; for the determination of mercury and of elements that are readily adsorbed on rough surfaces (e.g. antimony), quartz is recommended. In addition: a heatable ultrasonic bath and a sub-boiling distillation apparatus for acids made of quartz or fluoropolymers.

PROCEDURE (clauses 6.1–6.3.3). Contamination at every stage shall be kept as low as possible; samples are prepared as in a household, and for the determination of chromium and nickel no stainless steel equipment is used. The sample mass is chosen to suit the capacity of the vessel and the permissible pressure increase, without departing from the manufacturer’s data: for carbon-rich samples (fats, carbohydrate-rich products) usually not more than 200 mg of fresh mass (to the nearest 1 mg), with a lower carbon content up to 3 g of fresh mass or 4 ml of liquid; when the mass is changed, the ratio of sample mass to acid volume is kept. 1 ml of water is added to a powder (about 200 mg); none is added to fatty materials. Alcohol is removed from alcohol-containing samples before the acid is added, by gentle heating, e.g. in an ultrasonic bath at 60 °C. Usually 3 ml of nitric acid are sufficient (microwave systems usually require more); 0.5 ml to 1 ml of hydrogen peroxide may be added, which prevents the sample from adhering to the walls, improves mixing and reduces the amount of nitrous gases. The sample shall be covered with acid before the vessel is closed; a pre-reaction at room temperature in an open, loosely covered vessel is recommended (reactive samples — overnight). For the determination of tin, antimony and iron at least 0.5 ml of hydrochloric acid is added — only after the reaction with nitric acid has ended — and the vessel is closed immediately. Foods containing silicates or titanium dioxide may require hydrofluoric acid — then only inserts made of fluoroplastics, because quartz is irreversibly damaged. Digestion takes place at a temperature of at least 180 °C; in microwave systems heating is slow, at reduced power. The required temperature — and thus the degree of decomposition — is set according to the subsequent measurement procedure: a higher temperature gives less residual carbon in the solution and less background interference in ET-AAS and ICP-OES.

SECOND SOURCE. The FDA method from the Elemental Analysis Manual (EAM 4.7, version 1.3 of April 2025) combines microwave-assisted digestion with nitric acid with ICP-MS determination of, among others, arsenic, cadmium, chromium, lead and mercury in food; it requires a digestion system with temperature control up to at least 200 °C and opens the vessels after cooling below 50 °C.

REGULATIONS. Maximum levels of lead, cadmium, mercury, arsenic and inorganic tin in food are laid down in Regulation (EU) 2023/915 (Annex I, Section 3 “Metals and other elements”), which repealed Regulation (EC) No 1881/2006; the values depend on the type of food.

WHAT WE DO NOT GIVE HERE. The digestion time, cooling and further treatment of the solution, quality control and example digestion programmes (6.3.4–6.4) — these subclauses are not in the preview of the standard. Nor do we give ICP-MS measuring conditions or limits of quantification — the standard does not cover them.

Method principle

A food sample homogenized without contamination is digested with nitric acid — sometimes with hydrogen peroxide, hydrochloric acid or hydrofluoric acid added — in a closed pressure vessel at a temperature of at least 180 °C, with conventional or microwave heating. The organic matter is decomposed and the elements to be determined pass into the test solution.

The solution is analysed by a technique validated together with this digestion — in the interlaboratory study these were flame, electrothermal, hydride and cold-vapour AAS and ICP-MS. The result refers to the total content of the element.

Applications

• Foodstuffs — preparation of a solution for the determination of elements, including metals (clause 1)
• Combination with flame, electrothermal, hydride and cold-vapour AAS and with ICP-MS — tested in interlaboratory studies; ICP-OES, voltammetry, atomic fluorescence — possible (clause 1)
• Determination of tin, antimony and iron — digestion with hydrochloric acid added; foods containing silicates or titanium dioxide — with hydrofluoric acid (6.3.2)
• Checking compliance with the maximum levels of lead, cadmium, mercury, arsenic and tin in Regulation (EU) 2023/915 — after determination by a validated measurement technique

Key parameters

Standard

Standard number

PN-EN 13805:2014-11

Title (PL)

Artykuły żywnościowe — Oznaczanie pierwiastków śladowych — Mineralizacja ciśnieniowa

Title (EN)

Foodstuffs — Determination of trace elements — Pressure digestion

Step-by-step procedure

1. Preparation of the sample

   Homogenization without contamination; for Cr and Ni without stainless steel equipment; in accordance with EN 13804 (6.2).

2. Test portion

   Mass chosen to suit the vessel and the permissible pressure: carbon-rich samples usually up to 200 mg (to the nearest 1 mg), leaner ones up to 3 g or 4 ml; powder with 1 ml of water; alcohol removed at 60 °C (6.3.1).

3. Addition of acid and pre-reaction

   Usually 3 ml of nitric acid, optionally 0.5 ml to 1 ml of H₂O₂; sample completely covered with acid; pre-reaction in an open, loosely covered vessel, for reactive samples overnight (6.3.2).

4. Additions for selected elements

   Sn, Sb, Fe — at least 0.5 ml of HCl after the reaction with nitric acid has ended and immediate closing of the vessel; silicates, TiO₂ — HF only in inserts made of fluoroplastics (6.3.2).

5. Digestion

   At a temperature of at least 180 °C; in a microwave system slow heating at reduced power; the temperature is chosen to suit the measurement procedure (6.3.3).

6. Test solution

   Further treatment and determination according to the standard validated with this digestion (clause 3; details in 6.3.4–6.4 outside the preview).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Perchloric acid shall not be used for pressure digestion, not even in small amounts; digestion of carbon-rich materials (cellulose, carbohydrates, fats, oils) can lead to an explosion (6.1, 6.3.2)
• Alcohol must be evaporated before nitric acid is added — it reacts with it violently after a delay (6.1, 6.3.1)
• A sample not immersed in the acid can locally overheat the vessel in a microwave system, up to its rupture (warning in 6.3.2)
• Beware of nitrous gases; before using the apparatus read the manufacturer’s instructions and safety rules, and when using hydrofluoric acid follow the appropriate safety guidelines (6.1, 6.3.2)

Frequently asked questions