🍎 Determination of fluoride in animal feeding stuffs by ion-selective electrode after hydrochloric acid treatment — 0.5 g of ground sample is stirred for 20 min with 20 ml of 1 mol/l HCl at ambient temperature, 50 ml each of sodium acetate and sodium citrate solutions are added, the pH is set to 5.5 ± 0.1, made up to 200 ml in a plastic flask and, after filtration or centrifugation, the fluoride electrode potential is measured; calibration 0.1–10 mg/l, standard addition from 40 mg/kg, interpolation below 40 mg/kg; the fluoride content corresponds to fluorine in Regulation (EU) No 574/2011, PN-EN 16279

Food chemistry PN-EN 16279

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of SIST EN 16279:2012 (English text of EN 16279:2012): from the title page through the contents, foreword, introduction and Clauses 1–7 to 8.2 (calibration, with the footnote on reading stability) on page 9. Outside the sample remain the rest of the procedure (sample measurement, standard addition), calculation (9), precision (10), test report (11), Annexes A (interlaboratory study), B (flowchart) and C (interpolation reading) and the bibliography.

ACCORDING TO THE TEXT OF EN 16279:2012. The standard was prepared by CEN/TC 327 “Animal feeding stuffs — Methods of sampling and analysis”, whose secretariat is held by NEN, under a mandate from the European Commission and EFTA; CEN approved it on 17.05.2012, and national implementation was due by January 2013 at the latest. According to the introduction, fluorine is one of the most abundant elements in the environment, and animals are exposed to its ionic form — fluoride, which may be present in feeding stuffs; the toxicity of fluoride has been established by EFSA, and its availability depends on the solubility of the compounds — poorly soluble ones are poorly absorbed, while ions from readily soluble ones are almost completely absorbed by passive diffusion in monogastric species; the mild extraction with 1 mol/l hydrochloric acid should reflect the gastric hydrochloric acid concentration of 0.1–0.3 mol/l. Scope (1): an ion-selective electrode (ISE) method after hydrochloric acid treatment for the determination of fluoride in animal feeding stuffs; the fluoride (F-) content corresponds to that of fluorine (F) specified in Commission Regulation (EU) No 574/2011; the standard is strictly based on conventions — e.g. 0.5 g test portion, 20 ml of 1 mol/l HCl, ambient temperature 20–25 °C, 20 min, pH adjusted to 5.5 in the buffered solution before measurement by standard addition; the method was successfully tested in an interlaboratory study at 100–500 mg/kg; if followed strictly, theoretically 40–4000 mg/kg can be analysed within the linear calibration function; only below 40 mg/kg is an interpolation technique required instead of standard addition (Annex C); the quantification limit is 40 mg/kg with standard addition or below 2.5 mg/kg with interpolation. References (2): EN ISO 3696, EN ISO 6498. Principle (3): 0.5 g of sample is treated with 20 ml of 1 mol/l HCl for 20 min at ambient temperature (20–25 °C), and the extracted fluoride is determined with a fluoride-selective electrode; according to a note, the electrode responds linearly within the range given by calibration, so normally the amount of sample is chosen to fit that range, but for reproducibility this procedure as a convention method fixes the ratio of test portion mass to extractant volume for all kinds of feed; a warning on hazardous materials and the user’s responsibility to establish safety practices. Reagents (4): reagents of recognized analytical grade; water of grade 2 according to EN ISO 3696; fluoride (NaF) stock solution 1000 mg/l; hydrochloric acid 37 % (about 1.185 g/ml); perchloric acid 70–72 % (about 1.68 g/ml); glacial acetic acid 99 %; sodium acetate trihydrate 99 %; trisodium citrate dihydrate 99 %; HCl 1 mol/l (83 ml of acid into a 1000 ml flask); sodium acetate 3 mol/l (408 g in 750 ml of water, after cooling pH 7.0 with acetic acid, to 1000 ml); sodium citrate solution (222 g in 250 ml of water, 28 ml of perchloric acid, to 1000 ml); intermediate fluoride solutions 100 mg/l and 10 mg/l in plastic flasks; sodium hydroxide 5 mol/l (according to a note, 1 mol/l may be better for precise pH adjustment). Apparatus (5): usual laboratory apparatus, with plastic rather than glass vessels to avoid reactions of fluoride with silicon from glass in standard and test solutions; grinders to ≤ 0.5 mm and ≤ 0.1 mm; analytical balance 0.1 mg; freeze-drier for liquid feeds; magnetic stirrer with PTFE-coated bar; glass and plastic volumetric flasks, glass and plastic beakers; fluoride-selective electrode (combined possible), combined pH electrode, reference electrode, ion/pH meter accurate to 0.1 mV. Sampling (6): not part of the method — a recommended method is in EN ISO 6497; the laboratory should receive a representative sample not damaged or changed in transport and storage. Preparation of test sample (7): according to EN ISO 6498; grinding without appreciable heating, as quickly as possible to prevent gain or loss of constituents (e.g. water); the whole ground product in a stoppered container, e.g. polypropylene, mixed thoroughly before each weighing; feeds ground as such — laboratory sample (usually 500 g) to ≤ 0.5 mm (e.g. knife mill); liquid feeds — pre-drying at (60 ± 5) °C for at least 16 h to 8–12 % moisture with weighing before and after, or freeze-drying with weighing, then grinding; feed materials — to ≤ 0.1 mm (e.g. ball mill). Extraction (8.1): 0.5 g of sample ground to ≤ 0.5 mm, weighed to 1 mg, into a plastic beaker of about 200 ml; (20.0 ± 0.1) ml of 1 mol/l HCl and stirring for (20 ± 0.25) min at constant speed at 20–25 °C; if the test portion is not completely dissolved, check that the pH after extraction is still ≤ 4 — at pH > 4 the acid may not have been enough to release all fluoride (especially in very alkaline samples), and the report notes the use of a smaller portion or a larger volume of acid; then (50.0 ± 0.1) ml of sodium acetate and (50.0 ± 0.1) ml of sodium citrate, pH exactly 5.5 ± 0.1 (NaOH or HCl), quantitatively into a 200 ml plastic flask and made up with water; with 250 ml flasks — (625 ± 1) mg portion, 25 ml HCl and 62.5 ml of each buffer; filtration through acid-washed gravimetric filter paper into a stoppered plastic flask — this is the solution to be measured; for samples difficult to filter (e.g. bentonites) centrifugation and decanting is preferred. Calibration (8.2): recommended working solutions 0.1, 0.3, 1.0, 3.0 and 10 mg/l (from the 10 and 100 mg/l intermediate solutions, 100 ml plastic flasks), each with 10.0 ml of 1 mol/l HCl, 25.0 ml of acetate and 25.0 ml of citrate, made up with water; the electrodes are connected and stabilized in a low-concentration solution, mV is read in each standard under constant stirring once stable (according to a footnote, a good criterion is a change of not more than 0.1 mV in 30 s), electrodes rinsed and wiped between solutions; the curve — potential in mV against the logarithm of fluoride concentration in mg/l.

STATUS (as of 03.10.2026). The PKN search (query “PN-EN 16279”, 03.10.2026) shows two versions of PN-EN 16279:2012 — Polish and English — both “Wprowadza: EN 16279:2012 [IDT]” and without a withdrawal note. In the iTeh catalogue (read on 03.10.2026) EN 16279:2012 has the status “Published”, stage 90.93 (decision to confirm the standard).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 16279 appears in 4 records at 4 laboratories: AB 517, AB 526, AB 545, AB 856. In the current PCA documents (read on 03.10.2026, issues from 31.10.2025 to 17.06.2026) the number appears in 4 rows — one at each; in each of the four documents the number of page markers equals the number of PDF pages, without repetitions; a search of all 1291 PCA documents downloaded from BIP on 03.10.2026 found no laboratories outside the database copy (17 laboratories in the register have no link to a scope document on BIP). Form at all: “PN-EN 16279:2012”. None of these items is suspended. The “Laboratories” tab (query “PN-EN 16279”) shows all 4 laboratories — checked with a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Test object: feeds (AB 517, AB 545), feeds — feed phosphates and mineral mixtures (AB 526), feed materials and compound feeds (AB 856). Characteristic: fluorine content (AB 517, AB 526), fluorine content determined as fluoride (AB 545), fluorine content — fluoride F- (AB 856). Ranges: (8.00–3000.00) mg/kg (AB 517), (10–50000) mg/kg (AB 526), (1.7–2500) mg/kg (AB 545), 5.0–4400 mg/kg (AB 856). Technique: potentiometric method (AB 526, AB 545), with an ion-selective electrode (AB 517, AB 856 — ISE).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. At the convention: 0.5 g per 20 ml of 1 mol/l HCl, 20 min, 20–25 °C — the fixed ratio determines reproducibility and is not adjusted to the concentration (1, 3). At alkaline samples: after extraction the pH must be ≤ 4, otherwise fluoride may not have been released, and a change of portion or acid volume is noted in the report (8.1). At glassware: plastic vessels, because fluoride reacts with silicon from glass (5). At measurement pH: exactly 5.5 ± 0.1 in the acetate–citrate buffer (8.1). At the technique: standard addition from 40 mg/kg, below that interpolation according to Annex C (1). At the range: theoretically 40–4000 mg/kg within the linear function, the interlaboratory study covered 100–500 mg/kg (1) — the upper limits of AB 526 (50 000 mg/kg) and AB 856 (4400 mg/kg) lie above 4000 mg/kg, and the lower limits of all four (1.7–10 mg/kg) below 40 mg/kg, i.e. in the interpolation region. At reading: a stable signal, e.g. a change ≤ 0.1 mV in 30 s (8.2, footnote).

WHAT WE DO NOT GIVE. We did not read the sample measurement, the performance of standard addition, the calculation formulae, the precision data (10, Annex A) or the interpolation technique (Annex C). We do not give maximum permitted fluorine contents in feed.

Method principle

0.5 g of ground feed is extracted for 20 min with 20 ml of 1 mol/l hydrochloric acid at 20–25 °C; this fixed ratio is a convention of the method. The extract is buffered with sodium acetate and sodium citrate to pH 5.5 ± 0.1, made up to 200 ml in a plastic flask and filtered or centrifuged. Fluoride is measured with an ion-selective electrode against a potential–log concentration curve (0.1–10 mg/l), by standard addition from 40 mg/kg and by interpolation below that.

Applications

• Fluoride in animal feeding stuffs — corresponds to the fluorine content in Commission Regulation (EU) No 574/2011 (1)
• Dry feeds, liquid feeds (after pre-drying or freeze-drying) and feed materials; difficult-to-filter ones, e.g. bentonites — with centrifugation (7, 8.1)
• Feeds, feed phosphates, mineral mixtures, feed materials and compound feeds — items in the accreditation scopes of 4 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN 16279:2012

Title (PL)

Pasze — Oznaczanie zawartości fluorku metodą elektrody jonoselektywnej (ISE) po wcześniejszym traktowaniu kwasem chlorowodorowym

Title (EN)

Animal feeding stuffs — Determination of fluoride content after hydrochloric acid treatment by ion-sensitive electrode method (ISE)

Step-by-step procedure

1. Sample

   EN ISO 6498; grinding to ≤ 0.5 mm (feed materials ≤ 0.1 mm), liquid feeds pre-dried or freeze-dried (7). PN-EN 16279:2012 without a withdrawal note (03.10.2026).

2. Extraction

   0.5 g + 20 ml HCl 1 mol/l, 20 min stirring at 20–25 °C; check pH ≤ 4 (8.1).

3. Buffering

   50 ml each of acetate and citrate, pH 5.5 ± 0.1, to 200 ml, filtration or centrifugation (8.1).

4. Calibration

   Standards 0.1–10 mg/l in the same reagent matrix, mV against log c (8.2).

5. Measurement and result

   Fluoride electrode, standard addition from 40 mg/kg or interpolation below; calculations in Clause 9 (not read).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard may involve hazardous materials and operations — the user establishes safety practices (3, warning)
• Perchloric acid and concentrated hydrochloric acid — work in a fume hood, eye and hand protection

Frequently asked questions