🌱 Determination of total and water-soluble boron in mineral fertilizers with boron content up to 10 % by spectrophotometry with azomethine-H — yellow complex measured at 410 nm, masking of ions with EDTA, reduction of Fe(III) with ascorbic acid; extracts according to PN-EN 16962 and PN-EN 16964, PN-EN 17041

Physicochemistry PN-EN 17041

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN 17041:2018-07 (Polish version), in full (our translation): “This European Standard specifies a method for the determination of total and water extractable boron in mineral fertilizers containing less than or equal to 10 % boron. The method is not suitable for fertilizers with Fe concentrations more than twenty times higher than the concentration of boron. This method is applicable to water and aqua regia fertilizer extracts obtained according to EN 16962 and/or EN 16964. The method can also be used for the determination of boron in mineral fertilizers containing more than 10 % boron after appropriate dilution of the extracts”. We read the text of the standard in the sample of SIST EN 17041:2018 (the text of EN 17041:2018 without changes) from the cover to 8.3 (preparation of test solutions and blank). We do not have 8.4 (correction solutions), 8.5 (colour development), 8.6 (measurement), Clause 9 (calculation and expression of the result), 10 (test report) or Annex A (verification data — comparison with ICP-AES for water and aqua regia extracts) — we know them only from the table of contents.

ACCORDING TO THE TEXT OF EN 17041:2018 (foreword, introduction, Clauses 1–8.3, table of contents). The standard was prepared by CEN/TC 260 “Fertilizers and liming materials” (secretariat DIN) under a mandate of the European Commission and EFTA (M/335) concerning the modernization of methods of analysis of fertilizers in the framework of Regulation (EC) No 2003/2003. The standard is part of a modular approach and covers only the measurement step — “modular” means that a test standard concerns a specific step in assessing a property and not the whole chain of measurements; extraction is described by PN-EN 16962 (water-soluble micro-nutrients and removal of organic compounds from extracts) and PN-EN 16964 (total micro-nutrients — aqua regia extraction), which have separate entries in the database. Introduction: boron in fertilizers can be determined by ICP-AES (EN 16963); spectrophotometric determination with azomethine-H is more labour-intensive, but reliable and relatively inexpensive, and is an option when ICP-AES is not available; the determination can be influenced by iron, and more attention is needed to the removal of organic matter and to interference from extract colour (organic matter removal — according to EN 16962); warning: tests shall be carried out by suitably trained staff. References (2): EN 1482-2 (sample preparation of fertilizers and liming materials), EN 12944-1 and -2 (vocabulary), EN 16962, EN 16964, EN ISO 3696 (laboratory water). Principle (4): boron reacts with azomethine-H and the yellow complex is determined spectrophotometrically at 410 nm; interfering ions are masked with ethylenediaminetetraacetic acid (EDTA); interference from the intensely coloured Fe(III)-EDTA complex is removed by reduction of Fe(III) to Fe(II). Sampling and preparation (5): sampling is not part of the method (EN 1482-1 recommended); the sample is prepared according to EN 1482-2, the extracts according to EN 16962 and/or EN 16964. Reagents (6): analytical grade, with a boron concentration negligible compared with the lowest concentration in the sample solution — all reagents, including water, are tested for boron; water grade 2 according to EN ISO 3696, free from boron; EDTA buffer: in a 500 ml flask with 300 ml water, 75 g ammonium acetate, 10 g disodium EDTA and 40 ml acetic acid (ρ = 1,11 g/ml), made up to the mark — the pH checked with a glass electrode shall be 4,8 ± 0,1, stored in a plastic bottle; azomethine-H solution: in a 200 ml flask, 10 ml buffer, 400 mg azomethine-H (C17H12NNaO8S2) and 2 g ascorbic acid, made up with water — stable for three days; boron stock solution 100 mg/l: 0,5719 g boric acid in a 1000 ml flask, stored in a plastic bottle at (4–8) °C (commercial solutions may be used; it is considered stable for more than one year, but the manufacturer’s recommendations prevail); nitric acid 14,3 mol/l and diluted 5 mol/l (350 ml acid to 650 ml water). Apparatus (7): important — contact of all solutions with borosilicate glassware must be minimized, plastic or silica ware should be used; glass volumetric flasks may be used for making up to volume, but not for storing extracts and solutions; 100, 200, 500 and 1000 ml flasks, plastic bottles, cuvettes of 10 mm and 20–50 mm, spectrophotometer set to 410 nm with a 10 mm cuvette (for low boron contents a 20–50 mm cuvette with an adapted calibration range), pH meter with glass electrode. Procedure (8.1–8.3): contamination of extracts, blanks and calibration solutions with boron from borosilicate glass and detergents must be avoided; calibration solutions — 0, 1, 2, 3, 4 and 5 ml of stock solution into 100 ml flasks, 10 ml of 5 mol/l nitric acid each, made up with water (0–5 mg/l boron); test solutions — an aliquot of the extract is diluted in one or more steps so that the concentration is within the calibration range, in the final step in a 100 ml flask with 10 ml of 5 mol/l nitric acid (final acid concentration about 0,5 mol/l); aqua regia extracts are diluted at least 5 times to achieve this acid concentration; blank — extracting solution alone, diluted in the same way as the test solution.

STATUS (catalogue card as of 03.10.2026). The card of PN-EN 17041:2018-07 (Polish version, published 24-11-2020, 18 pages, price group J) has no “Withdrawn” header: Chemistry Sector, KT 156 Fertilizers, ICS 65.080, “Introduces: EN 17041:2018 [IDT]”. The PKN search engine (query “PN-EN 17041”, 03.10.2026) shows this designation in the English and Polish versions; there are no other editions.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 03.10.2026). The number 17041 appears in 12 records at 8 laboratories: AB 006, AB 180, AB 284, AB 312, AB 317, AB 827, AB 921, AB 1186. In the current scopes on the PCA website (read 03.10.2026, issues from 07.03.2025 to 22.07.2026) all give “PN-EN 17041:2018-07”, usually together with PN-EN 16962:2018-03 or PN-EN 16964:2018-03; AB 284 gives PN-EN 17041 in a separate item, without an extraction standard. The “Laboratories” tab (“PN-EN 17041”) shows 7 laboratories — all except AB 1186, where the designation stands in one value together with the preceding extraction standard; checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA scopes). “Total boron content” (with PN-EN 16964) and “water-soluble boron content” (with PN-EN 16962) in mineral (inorganic) fertilizers, by the spectrophotometric method; ranges from 0,0010 % (AB 006) and 0,005 % to 10,0 %, at AB 180 up to 21,0 %. AB 006 covers with this item also liming fertilizers, liming materials and organo-mineral fertilizers, and determines total boron in the range 10,0–20,0 % according to PN-EN 17042:2018-07 by titration.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Vessels: borosilicate glass and detergents release boron — storing extracts, blanks or standards in glass raises all of them, and a blank with the same error may not reveal it when standards are kept in different vessels than samples (7.1, 8.1). Reagents: every reagent and the water must be tested for boron (6). Iron: fertilizers with iron more than 20 times boron are outside the scope of the method — reduction of Fe(III) to Fe(II) removes the colour of the Fe(III)-EDTA complex only within the scope (1, 4). Colour and organic matter: a coloured extract and organic compounds not removed influence the absorbance at 410 nm — organic matter removal according to EN 16962 (introduction); we do not know the correction solutions of 8.4. Acidity: test solutions and standards shall contain about 0,5 mol/l acid — an aqua regia extract diluted less than 5 times has a different acidity than the standards (8.3). Colour reagent: the azomethine-H solution is stable for three days only (6.3). Range: above 10 % boron the method is applied after dilution (1); a laboratory with PN-EN 17042 for 10–20 % has two methods to choose from. Calculation of the result in mass percent: the concentration in solution is a measurement of this method, while the sample mass and extract volume come from the extraction step according to PN-EN 16962 or PN-EN 16964 — an error made there passes into the result without any trace in the spectrophotometric measurement.

WHAT WE DO NOT GIVE. We do not have 8.4–8.6, Clauses 9–10 or Annex A: the composition of the correction solutions, time and conditions of colour development, the measurement and correction procedure, the calculation formula, the limit of quantification, validation results or the comparison with ICP-AES — so we give none of these values.

Method principle

Boron from the fertilizer extract forms with azomethine-H in an acetate buffer with EDTA (pH 4,8) a yellow complex whose absorbance is measured at 410 nm; EDTA masks interfering ions, and ascorbic acid in the reagent solution reduces Fe(III) to Fe(II), removing the colour of the Fe(III)-EDTA complex; the boron concentration is read from a 0–5 mg/l calibration.

Applications

• Mineral (inorganic) fertilizers — total boron (aqua regia extract, PN-EN 16964) and water-soluble boron (PN-EN 16962); 8 laboratories in PCA scopes
• Fertilizers with boron content above 10 % — after appropriate dilution of the extracts (scope of the standard)
• Laboratories without ICP-AES — an alternative to boron determination according to EN 16963 (introduction)

Key parameters

Standard

Standard number

PN-EN 17041:2018-07

Title (PL)

Nawozy — Oznaczanie boru o zawartości ≤ 10 % metodą spektrometryczną z azometyną-H

Title (EN)

Fertilizers — Determination of boron in concentrations ≤ 10 % using spectrometry with azomethine-H

Step-by-step procedure

1. Extract

   Aqueous extract according to PN-EN 16962 (water-soluble boron) or aqua regia extract according to PN-EN 16964 (total boron); sample prepared according to EN 1482-2. PN-EN 17041:2018-07 current (PKN catalogue card as of 03.10.2026).

2. Reagents

   EDTA buffer of pH 4,8 ± 0,1; azomethine-H solution with ascorbic acid (fresh, up to 3 days); check all reagents and water for boron.

3. Standards

   0–5 mg/l boron: 0, 1, 2, 3, 4 and 5 ml of the 100 mg/l solution into 100 ml flasks with 10 ml HNO3 5 mol/l; store in plastic.

4. Test solutions and blank

   Dilute the extract into the calibration range, in the final step with 10 ml HNO3 5 mol/l per 100 ml (about 0,5 mol/l acid); aqua regia extracts at least 5 times; blank — extracting solution alone diluted in the same way.

5. Colour, measurement, result

   Correction solutions, colour development and measurement at 410 nm according to 8.4–8.6, calculation according to Clause 9 (we do not have the text).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Concentrated nitric acid and aqua regia are strongly corrosive — work in a fume hood, with gloves and safety glasses
• The standard warns that it does not address all hazards and that tests shall be carried out by suitably trained staff (introduction)

Frequently asked questions