CEN/TC 260
Date: 2025-11
prEN 18319:2026
Secretariat: DIN
Fertilizers, liming materials and inhibitors — Determination of the phosphonates content by ion chromatography and conductivity detection (IC-CD)
ICS:
Contents Page
7 Sampling and sample preparation 7
8.1 Preparation of test solution - Water extraction 7
8.2 Preparation of the calibration solutions 8
9 Calculation and expression of the results 10
9.2 Concentration of phosphonates in test sample solutions 10
10.1 Inter-laboratory study 10
Annex B (informative) Results of the inter-laboratory study 14
This document (prEN 18319:2026) has been prepared by Technical Committee CEN/TC 260 “Fertilizers and liming materials”, the secretariat of which is held by DIN.
This document is currently submitted to CEN Enquiry.
This document has been prepared under a Standardization Request addressed to CEN by the European Commission. The Standing Committee of the EFTA States subsequently approves these requests for its Member States.
For the relationship with EU Legislation, see informative Annex ZA, which is an integral part of this document.
This document describes a procedure for the extraction and measurement for the determination of phosphonate (phosphite) in fertilizers, liming materials and inhibitors. It is based on a water extraction of phosphonate (phosphite) followed by ion chromatography with conductivity detection (IC-CD).
The ion chromatography with conductivity detection (IC-CD) method can be used in well-equipped analytical laboratories for the determination of different ions. In the field of fertilizing products, the method is used and standardized for the determination of perchlorates in mineral fertilizers [1] and for the determination of phosphonates in plant biostimulants [2]. The IC-CD method can determine ions simultaneously.
According to Regulation (EU) 2019/1009 [3], phosphonates must not be intentionally added to any EU fertilising product. Unintentional presence of phosphonates must not exceed 0,5 % (mass fraction). The method described in this document was adapted to achieve this requirement and simultaneously to reduce interferences from other co-extracted anions as much as possible.
The definition of phosphonates is not clearly stated in Regulation (EU) 2019/1009 [3] and to avoid any misunderstanding, the results are expressed as a content of phosphorus (P) bound in the form of free water-soluble phosphonates (P-PO3).
1.0 Scope
This document specifies a method for the extraction and determination of phosphonates (P-PO3) in fertilizers, liming materials and inhibitors using ion chromatography and conductivity detection (IC-CD).
This document is applicable to fertilizing product blends, where the blend is a mix of at least two of the following components, fertilizers, liming materials, soil improvers, growing media, inhibitors and plant biostimulants, and where the following category, fertilizers, liming materials and inhibitors, is the highest % in the blend by mass or volume, or in the case of liquid form, by dry mass.
If fertilizers, liming materials and inhibitors is not the highest % in the blend, the European Standard for the highest % of the blend applies. In case a fertilizing product blend is composed of components in equal quantity, the user decides which standard to apply.
NOTE Variations in analytical methods for fertilizing product blends can lead to differing results as some components or matrix interactions can affect the outcome. Validation procedures have shown that developed standard methods are robust and reliable across diverse product compositions, but possible interferences and unexpected results when analysing fertilizing product blends are possible.
2.0 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1482‑2:2024, Fertilizers, liming materials and inhibitors - Sampling and sample preparation - Part 2: General sample preparation provisions
prEN 12944‑1:2026, Fertilizers, liming materials and inhibitors — Vocabulary — Part 1: General terms
prEN 12944‑2:2026, Fertilizers, liming materials and inibitors — Vocabulary — Part 2: Terms relating to fertilizers
EN 12944‑3:2025, Fertilizers, liming materials and inhibitors — Vocabulary — Part 3: Terms relating to liming materials
3.0 Terms and definitions
For the purposes of this document, the terms and definitions given in prEN 12944‑1:2026, prEN 12944‑2:2026, and EN 12944‑3:2025 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org
3.1
phosphonate
salt derived from phosphonic acid (H3PO3)
4.0 Principle
A representative test portion of the sample is extracted with water. Phosphonate in the extract is selectively separated from other compounds using ion chromatography (IC) and determined by a conductivity detection (CD). External calibration is used for quantification of the amount of the phosphonate.
WARNING 1 — Persons using this document should be familiar with usual laboratory practice. This document does not purport to address all of the safety issues, if any, associated with its use. It is the responsibility of the user to establish appropriate health and safety practices and to ensure compliance with any national regulatory conditions.
WARNING 2 — It is absolutely essential that tests conducted according to this document are carried out by suitably trained staff.
5.0 Reagents
All reagents shall be of recognized analytical grade. The concentration of phosphonate in the reagents and water used shall be low enough not to affect the results of the determination.
5.1 Water with a specific conductivity not higher than 0,2 mS/m at 25 °C.
5.2 Phosphonate standard stock solution, mass concentration ρ(P-PO3) = 1 000 mg/l is prepared by dissolving sodium phosphite dibasic pentahydrate salt (M = 216,04 g/mol, purity ≥ 98 %). For preparation the phosphonate standard stock solution 0,697 g ± 0,001 g is weighed, transferred to 100 ml volumetric flask, fill with water (5.1) to final volume and mix thoroughly.
5.3 Phosphonate working standard solution, ρ(P-PO3) = 100 mg/l is prepared from a standard stock solution (5.2) by appropriate dilution with water (5.1). Pipette 10 ml of stock solution (5.2) to a 100 ml volumetric flask, fill with water (5.1) to final volume and mix thoroughly.
5.4 Mobile phase, KOH cartridge for ion chromatography (commercially supplied). Concentration of the KOH mobile phase is electrolytically generated in externally supplied water (5.1).
Different mobile phase may be used according to the instructions of the manufacturer of the column.
5.5 Chloride standard, ρ(Cl−) = 1 000 mg/l.
5.6 Nitrate standard, ρ(NO3−) = 1 000 mg/l.
5.7 Solution for checking chromatographic separation, ρ(P-PO3) = 10 mg/l, ρ(Cl−) = 50 mg/l and ρ(NO3−) = 50 mg/l is prepared by pipetting 1 ml of phosphonate standard stock solution (5.2), 5 ml of chloride standard (5.5), 5 ml of nitrate standard (5.6) to 100ml volumetric flask and fill to final volume with water (5.1).
5.8 Sulfuric acid, ρ20(H2SO4) = 1,84 g/ml.
5.9 Sulfuric acid solution, c = 0,56 mol/L, prepared by adding 30 ml of sulfuric acid (5.8) to 800 ml of water in 1 000 ml volumetric flask. Addition is performed slowly with occasional swirling. Volumetric flask is filled to the mark with water (5.1).
6.0 Apparatus
6.1 Common laboratory glassware and plastic.
6.2 Analytical balance, capable of weighing to the nearest ≤ 1 mg.
6.3 Shaker, rotary or horizontal shaker. Shaking shall prevent any settling of the sample during extraction.
6.4 Extraction vessels, capacity 200 ml to 500 ml.
6.5 Centrifuge (optional), for minimum 4 000 min−1 (approx. 2 000 g).
6.6 Single use syringe filters (0,22 µm) or vials with filters, for filtering of test solutions prior to analysis.
6.7 Ion chromatograph, with conductivity detection (IC-CD).
For higher signal/noise a supressed conductivity detector is preferred.
6.8 Chromatographic column for anion exchange, suitable for the selective separation of phosphonates from other anions present in the sample.
It is recommended to use a guard column to prolong the lifetime of the analytical column.
Other columns recommended by a manufacturer may also be used, providing the results are comparable.
7.0 Sampling and sample preparation
Sampling is not part of the method specified in this document. Recommended sampling methods are given in EN 1482‑1 [4] and EN 1482‑3 [5].
It is important that the laboratory receives a sample that is representative of both the product under consideration and the given analysis. The sample should not have been damaged or changed during transport or storage.
Sample preparation shall be carried out in accordance with EN 1482‑2:2024.
8.0 Procedure
8.1 Preparation of test solution - Water extraction
Weigh a sample test portion of approximately 10 g to the nearest milligram into an extraction vessel (6.4) and add (100 ± 1) ml of water (5.1). The tightly closed vessels are then placed in a shaker (6.3) and samples are extracted for (60 ± 5) min. A blank test solution is prepared following the same procedure as for samples.
In the cases that the precipitation is occurred during the sample extraction and/or the final extract is strongly alkaline, only 2 g of sample and 100 ml of sulfuric acid solution (5.9) is preferred for the extraction. This extraction procedure is suitable for e.g.: converter lime, hydrated lime, sample of suspension.
For highly non-homogenous samples it is possible to use a test portion of 25 g and volume of water (5.1) 250 ml. In this case use only extraction vessels of the capacity 500 ml to ensure an effective extraction.
For samples that completely dissolve in water (5.1), dissolution is used instead of extraction.
After extraction the complete extract is carefully transferred to a 200 ml volumetric flask and filled to final volume with water (5.1). Aliquot of extract is then transferred from the volumetric flask to a centrifuge tube and centrifuged for 10 min at 4 000 min−1. The supernatant is then diluted with water (5.1). The optimal dilution is chosen according to the structure of the sample and the dry matter content. One millilitre of diluted extract is finally filtered by a syringe filter (6.6) to a clean vial.
8.1.1 Preparation of the calibration solutions
Prepare a blank calibration solution and at least three calibration solutions in the linear range of calibration by diluting the phosphonate working standard solution (5.3) with water (5.1). Concentrations of calibration standards 0 mg/l, 0,5 mg/l, 1 mg/l, 2,5 mg/l, 5 mg/l, 10 mg/l, 20 mg/l are recommended. Calibration solutions are prepared according to Table 1. Transfer an aliquot of the calibration solutions to chromatography vials prior to analysis.
NOTE Automated inline calibration techniques can be employed to enhance overall efficiency. Standard techniques are for example inline dilution or partial loop injection. Several calibration levels (0 mg/l to 20 mg/l) are created from a single standard solution, either by diluting the highest standard (inline dilution) or by injection of different volumes of the highest or lowest standard (partial loop injection).
Table 1 — Example of typical calibration solutions preparation
Final concentration of calibration solution | Portion of phosphonate working standard solution | Final volume |
ρ(P-PO3) | ρ(P-PO3) = 100 mg/l |
|
mg/l | ml | ml |
0 | 0 | 100 |
0,5 | 0,5 | 100 |
1 | 1 | 100 |
2,5 | 2,5 | 100 |
5 | 5 | 100 |
10 | 10 | 100 |
20 | 10 | 50 |
NOTE It is possible to calibrate the instrument for higher concentrations of phosphonates if the calibration curve is linear. | ||
8.1.2 Measurement
8.1.3 Instrument conditions
Due to differences between various kinds of instruments, no detailed instructions can be given to operate the specific instrument. The instruction provided by the manufacturer should be followed.
The software of the instrument is used to calibrate the instrument and to calculate concentrations of the phosphonate in the individual test solutions. All test sample solutions, blanks and calibration solutions are measured under the same optimized conditions. An example of the instrument conditions is given in Table 2.
Table 2 — Example settings IC-CD instrumentation
IC-CD settings | |
|---|---|
IC-CD | Dionex™ Integrion™a |
Column and guard column | Dionex™ IonPac ™AS11-HC Analyticala (2 mm × 250 mm) Dionex™ IonPac™ AG11-HC Guarda (2 mm × 50 mm) |
Mobile phase | KOH – eluent generator |
KOH concentrations (mmol/l) | gradual increase of KOH concentration from 10 mmol/l to 45 mmol/l during |
Suppressor | Dionex™ ADRS 600a, 2 mm |
Flow rate (ml⋅min−1) | 0,3 |
Column temperature (°C) | 30 |
Compartment temperature(°C) | 15 |
Conductivity detector temperature (°C) | 35 |
Autosampler temperature (°C) | 15 |
Measurement time (s) | 1 800 |
Injection volume (µl) | 25 |
NOTE Use of a different column and a different mobile phase is possible, providing the results are comparable. | |
a This is an example of suitable and commercially available equipment. This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of this product. Equivalent products may be used if they can be shown to lead to the same results. | |
min equilibration (10 mmol/l) - electrolytically8.1.4 IC-CD measurement
The retention time for the analyte should be approximately twice the retention time corresponding to the void volume of the column, and the nearest peak in the chromatogram should be separated from the analyte peak by at least one full peak width at 10 % of the analyte peak height. It is recommended to verify sufficient separation of the analyte peak using a solution (5.7). Resolution criteria: both sides of the phosphonate peak shall lie on the baseline without any co-elution with the chloride and nitrate peak.
Inject an appropriate volume of the calibration solutions and calibrate the instrument. Then analyse a sequence of blank (the blank value shall not exceed the LOQ of the method), test samples and control samples under the same conditions. The test sample solutions, which give a response outside the calibration range, should be diluted more times appropriately with water (5.1). Check the instrument sensitivity e.g. by analysing one of the calibration solutions throughout the sequence (for example after each five or ten samples). As an analytical control, internal reference samples with known phosphonate concentration shall be analysed in all series of samples. The internal reference samples are to be subjected to all the steps in the method starting from water extraction. If reference samples are not available, spike experiments should be performed to calculate the recovery of the method. It is advisable to check for memory effects, e.g. by the analysis of blank calibration solutions after reference materials.
An example of the chromatographic separation of phosphonates from other interfering ions in a mixture of standards is given in Annex A (informative), Figure A.1.
9.0 Calculation and expression of the results
9.1 Integration of peaks
The retention time of phosphonates is identified by the analysis of the calibration solutions. The phosphonates peak area in the calibration solutions, blanks and test sample solutions is determined.
9.1.1 Concentration of phosphonates in test sample solutions
Calculate the concentration of phosphonates in the test sample solutions using the calibration function established by linear regression from the calibration curve.
Calculate the content of phosphonates in the sample, wx as a mass fraction of P-PO3 expressed on dry matter basis, in mg/kg, according to Formula (1):
(1)
where
V is the final volume of extract solution (usually 200 ml), in ml;
ρ is the mass concentration of P-PO3 in the test sample solution, in mg/l;
ρ0 is the mass concentration of P-PO3 in the blank test solution, in mg/l;
m is the mass of the test sample, in g;
wDM is the dry matter content of the test sample expressed as a mass fraction in percent
F is the dilution factor calculated according to Formula (2):
(2)
where
V1,2…n are the volumes of the volumetric flasks, in ml;
Vp1,2…n are the volumes of the pipetted solutions used for an individual diluting step, in ml.
Calculate the content of phosphonates in the sample, wy as a mass fraction of P-PO3, in %; according to Formula (3):
(3)
where
wx is a mass fraction of P-PO3 expressed on dry matter basis, in mg/kg.
10.0 Precision
10.1 Inter-laboratory study
Details of inter-laboratory studies on the precision of the method are summarized in Annex B. Repeatability and reproducibility were calculated according to ISO 5725‑1 [6] and ISO 5725‑3 [7].
It is possible that the values derived from this study are not applicable to concentration ranges and matrices other than those given.
10.1.1 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will in no more than 5 % of the cases be greater than the repeatability limit r given in Table 3.
10.1.2 Reproducibility
The absolute difference between two independent single test results, obtained using the same method on identical test material in different laboratories with different operators using different equipment, will in no more than 5 % of the cases be greater than the reproducibility limit R given in Table 3.
Table 3 — Mean values, repeatability and reproducibility limits of phosphonates
Sample |
| r | R |
mg/kg | mg/kg | mg/kg | |
PO3-S-1 12,5 % N fur hydrolysate, organic fertilizer liquid | 6 900,8 | 356,3 | 828,9 |
PO3-S-2 NPK 7‑6‑6 with guano, organo-mineral fertilizer liquid (blend) | 993,7 | 189,8 | 659,5 |
PO3-S-3 NPK 6‑7‑6, inorganic fertilizer liquid | 4 655,0 | 97,0 | 1 159,9 |
PO3-S-4 Inhibitor of nitrification, inhibitor liquid | 5 870,4 | 313,8 | 1 244,6 |
PO3-S-5 Dolomitic limestone, liming material solid | 3 295,7 | 167,9 | 731,2 |
PO3-S-6 Pellets with N as urea formaldehyde, nutrient polymer solid | 1 511,4 | 66,6 | 260,9 |
11.0 Test report
The test report shall contain at least the following information:
a) all information necessary for the complete identification of the sample;
b) the standard used (including its year of publication);
c) the test method used with reference to this document;
d) the test results obtained;
e) date of sampling and sampling procedure (if known);
f) date when the analysis was performed and finished;
g) all operating details not specified in this document, or regarded as optional, together with details of any deviations from the procedure any incidents occurred or any unusual features observed when performing the method, which might have influenced the test result(s).
Key
X retention time, in min
Y conductivity, in µS
1 chlorides
2 phosphonates
3 nitrates
4 sulfates
5 phosphates
Figure A.1 — Example of chromatographic record of mixture of standards at concentration 10 mg/l
The precision of the method has been determined in the year 2025 in an inter-laboratory study (ILS) with 8 laboratories participating and carried out on 6 samples of organic, organo-mineral, inorganic fertilizers, liming materials, inhibitors and nutrient polymers. Six different sample materials (2 solid and 4 liquid) were included in ILS.
- Statistical results for the determination of phosphonates by ion chromatography with conductivity detection (IC-CD)
Statistical evaluation was carried out using a validated software for ILS based on the mathematical algorithms prescribed by ISO 5725‑3 [7].
The statistical results are given in Table B.1.
Table B.1 — Statistical results for the determination of phosphonates in organic, organo-mineral, inorganic fertilizers, liming materials, inhibitors and nutrient polymers
Sample | PO3 S-1 | PO3 S-2 | PO3 S-3 | PO3 S-4 | PO3 S-5 | PO3 S-6 |
L | 8 | 8 | 8 | 8 | 8 | 8 |
LA | 8 | 7 | 7 | 8 | 8 | 7 |
N | 24 | 24 | 24 | 24 | 24 | 24 |
NA | 24 | 21 | 21 | 24 | 24 | 21 |
O | 0,0 | 12,5 | 12,5 | 0,0 | 0,0 | 12,5 |
x̿ | 6900,8 | 993,7 | 4655,0 | 5870,4 | 3295,7 | 1511,4 |
sR | 296,0 | 235,5 | 414,2 | 444,5 | 261,1 | 93,2 |
sr | 127,3 | 67,8 | 34,6 | 112,1 | 60,0 | 23,8 |
sI | 154,2 | 67,8 | 158,1 | 169,0 | 70,8 | 40,3 |
RSDR | 4,3 | 23,7[1] | 8,9 | 7,6 | 7,9 | 6,2 |
RSDr | 1,8 | 6,8 | 0,7 | 1,9 | 1,8 | 1,6 |
R | 828,9 | 659,5 | 1159,9 | 1244,6 | 731,2 | 260,9 |
r | 356,3 | 189,8 | 97,0 | 313,8 | 167,9 | 66,6 |
HorRat | 1,0 | 4,2 | 2,0 | 1,7 | 1,7 | 1,2 |
Key | ||||||
L | Number of participating laboratories; | |||||
LA | Number of laboratories after elimination of outliers; | |||||
N | Number of all analytical values; | |||||
NA | Number of analytical values after rejection of outliers; | |||||
O | Percentage of outliers, in %; | |||||
x̿ | Total mean of results (without outliers), in mg/kg; | |||||
sR | Reproducibility standard deviation, in mg/kg; | |||||
sr | Repeatability standard deviation, in mg/kg; | |||||
sI | Intermediate standard deviation in mg/kg; | |||||
RSDR | Relative reproducibility standard deviation, in %; | |||||
RSDr | Relative repeatability standard deviation, in %; | |||||
R | Reproducibility limit (2,77 sR), in mg/kg; | |||||
r | Repeatability limit (2,77 sr), in mg/kg; | |||||
HorRat | HorRat index. | |||||
(informative)
Relationship of this European Standard and the essential requirements of Regulation (EU) 2019/1009 making available on the market of EU fertilising products aimed to be covered
This European Standard has been prepared under a standardization request M/564 annexed to Commission Implementing Decision C(2020)612, M/564 Amd 1 annexed to Commission Implementing Decision C(2022)47 and M/564 Amd 2 annexed to Commission Implementing Decision C(2023)8288 as regards the EU fertilising products to provide one voluntary means of conforming to essential safety requirements of Regulation (EU) 2019/1009 relating to the making available on the market of EU fertilising products.
Once this standard is cited in the Official Journal of the European Union (OJEU), under Regulation (EU) 2019/1009, compliance with the normative clauses of this standard given in Table ZA.1 confers, within the limits of the scope of this standard, a presumption of conformity with the corresponding essential requirements of that Regulation (EU) 2019/1009, and associated EFTA regulations.
Table ZA.1 — Correspondence between this European Standard and Regulation (EU) 2019/1009
Essential Safety Requirements of Regulation (EU) 2019/1009 | Clause(s)/subclause(s) of this EN | Remarks/Notes |
Determination of the phosphonates content |
|
|
Annex I, Part II, point 6 | 9 | / |
WARNING 1 — Presumption of conformity stays valid only as long as a reference to this European Standard is maintained in the list published in the Official Journal of the European Union. Users of this standard should consult frequently the latest list published in the Official Journal of the European Union.
WARNING 2 — Other Union legislation may be applicable to the product(s) falling within the scope of this standard.
[1] EN 17246, Fertilizers — Determination of perchlorate in mineral fertilizers by ion chromatography and conductivity detection (IC-CD)
[2] EN 17705, Plant biostimulants – Determination of phosphonates
[3] Regulation (EU) 2019/1009 of the European Parliament and of the Council of 5 June 2019 laying down rules on the making available on the market of EU fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC) No 2003/2003. Official Journal of the EU, L 170
[4] EN 1482‑1:2024, Fertilizers, liming materials and inhibitors - Sampling and sample preparation - Part 1: General sampling provisions
[5] EN 1482‑3:2024, Fertilizers, liming materials and inhibitors - Sampling and sample preparation - Part 3: Sampling of static heaps
[6] ISO 5725‑1, Accuracy (trueness and precision) of measurement methods and results - Part 1: General principles and definitions
[7] ISO 5725‑3, Accuracy (trueness and precision) of measurement methods and results - Part 3: Intermediate precision and alternative designs for collaborative studies
At concentrations of P-PO3 <1000 mg/kg, a higher variance of measured values can be expected. Concentrations of P-PO3 <1000 mg/kg are significantly lower than the limit of 0,5 % (5000 mg/kg) given in Regulation (EU) 2019/1009 [3]. ↑
