CEN/TC 260 - Fertilizers and liming materials

This document specifies the description of the physical unit in organic, organo-mineral and inorganic fertilizers.

This document specifies the method for taking a sample of solid and liquid forms of organic fertilizers, organo-mineral fertilizers and inorganic fertilizers containing more than 1 % by mass of organic carbon, when in packages, containers or in bulk, to test for levels of controlled pathogens present.

This document specifies methods for the determination of quantity of the following solid and liquid fertilizing products: organic fertilizers, organo-mineral fertilizers, inorganic fertilizers, liming materials and inhibitors in packages, containers or in bulk.
This document is applicable to fertilizing products blends where organic fertilizers, organo-mineral fertilizers, inorganic fertilizers, liming materials and inhibitors are the highest % of the blend by mass or volume, or in the case of liquid form by dry mass. If organic fertilizers, organo-mineral fertilizers, inorganic fertilizers, liming materials and inhibitors are not the highest % of the blend, the European Standard for the highest % of the blend applies. In case a fertilizing product blend is made up of components in equal quantity, the user decides which standard to apply.
This document is not applicable to the quantity determination of: growing media, soil improvers and plant biostimulants.

This document specifies a method for the determination of methylen-urea (MU) oligomers in inorganic fertilizers using high-performance liquid chromatography (HPLC).
The method is applicable to all fertilizers which do not contain interfering organic compounds.
NOTE   By the condensation of urea and formaldehyde, several oligomers are formed, such as methylen-diurea (MDU), dimethylen-triurea (DMTU), trimethylen-tetraurea (TMTU) and higher oligomers. The three molecules named here are the most soluble in water, while the higher compounds are insoluble in hot water, but their nitrogen is available for plants by microbiological decomposition. Also, urea is always a companion of MU-oligomers.

This document specifies a method for the determination of nitrogen content in IBDU (isobutylidenediurea) and CDU (crotonylidenediurea) using high-performance liquid chromatography (HPLC).
The method is applicable to all fertilizers which do not contain interfering organic compounds.

This document specifies a method for the determination of phosphorus in fertilizer extracts.
The method is applicable to all extracts of fertilizers for the determination of the different forms of phosphorus as phosphorus soluble in mineral acids, water-soluble phosphorus, phosphorus soluble in solutions of neutral ammonium citrate, phosphorus soluble in 2 % citric acid and phosphorus soluble in a mass fraction of 2 % formic acid.
The method has only been validated on inorganic fertilizers but can be applicable to all extracted phosphorous if proper extraction methods are used.

This document specifies a method for the determination of total nitrogen in nitrate-free calcium cyanamide.

This document specifies a method for the determination of cyanamide nitrogen in fertilizers. The method is applicable to calcium cyanamide and mixtures of calcium cyanamide with calcium nitrate.

This document specifies a method for the determination of total nitrogen in calcium cyanamide. The method is applicable to calcium cyanamide containing nitrates.

TThis document specifies a complexometric method for the determination of the calcium content and the magnesium content of liming materials.
It is not applicable to products with a mass fraction less than 2 % magnesium or those with a mass fraction more than 1 % P2O5 and is not applicable to silicate liming materials.

This document is applicable to liming materials, which contain oxides, hydroxides, carbonates or silicates of the nutrients calcium (Ca) or magnesium (Mg) and the function of which is to correct soil acidity. It is applicable to fertilizing products, which are classified as PFC 2 or the PFC 2 component in PFC 7 of Regulation (EU) 2019/1009 [3].
NOTE   The methods referred to in this document have not been tested for fertilizing product blends (PFC 7) [3].
This document specifies references to the methods for the determination of the following physical and chemical properties and specific contaminants in liming materials:
-   Determination of the cadmium content;
-   Determination of the chromium VI content;
-   Determination of the mercury content;
-   Determination of the nickel content;
-   Determination of the lead content;
-   Determination of the arsenic content;
-   Determination of the total chromium content;
-   Determination of neutralizing value;
-   Determination of the reactivity;
-   Determination of the grain size/granulometry;
-   Determination of the total CaO content;
-   Determination of the total MgO content.
This document does not specify references to the methods for the determination of the following physical and chemical properties and specific contaminants in liming materials, as they are covered in other European Standards:
-   Determination of the copper and zinc content;
-   Determination of the chloride content;
-   Determination of quantity (indicated by mass or volume);
-   Determination of the phosphonates content.

This document specifies three different methods (Methods A, B and C) for the determination of sulfur present in fertilizer extracts in the form of sulfates. Method A specifies the gravimetric method. Method B specifies the method using inductively coupled plasma optical spectrometry (ICP-OES). Method C specifies the method using ion chromatography (IC).

This document is applicable to organic and organo-mineral fertilizers. It is relevant for fertilizing products which are classified as PFC 1(A) and PFC 1(B) as long as the main function of the EU fertilizing product is classified as PFC 1(A) and PFC1(B) of Regulation (EU) 2019/1009 [2].
This document specifies references to the methods for the:
—   detection of Enterococcaceae;
—   detection of Salmonella spp.;
—   detection of Escherichia coli.

This document specifies a method for the detection and enumeration of Enterococcaceae in fertilizers of the following Product Function Categories (PFCs) of EU fertilizing products, as described in Regulation (EU) 2019/1009 [1]:
•   PFC 1(A): Organic fertilizer;
•   PFC 1(B): Organo-mineral fertilizer;
•   PFC 1(C): Inorganic fertilizer, which contains more than 1 % by mass of organic carbon, other than organic carbon from chelating or complexing agents, nitrification inhibitors, denitrification inhibitors or urease inhibitors, coating agents, urea or calcium cyanamide. The present method was validated on products known as present on the market in April 2021 and conform to Regulation (EU) 2019/1009 [1] that are inorganic fertilizers with more than 1 % of organic carbon such as poultry manure and struvite with low level of organic matter. In case that other products would be developed having other physical and chemical characteristics, it might become necessary to develop different methods to correctly account for pathogens they might contain.
This document specifies a colony-count technique on selective media, Slanetz Bartley agar or Bile Esculin Azide agar, respectively. The method is based on EN ISO 7899 2:2000.

This document specifies references to methods for the determination of the following contaminants: mercury, cadmium, nickel, copper, zinc, arsenic, lead, chromium (VI), biuret, perchlorate and total chromium content in inorganic fertilizers.
This document is applicable to EU fertilizing products classified as PFC 1(C) and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1(C), PFC 2 and PFC 5 as specified in the Regulation (EU) 2019/1009 [3].
An overview of the references to methods for the determination of the specific contaminants is given in Table 1.
NOTE 1   The determination of copper and zinc in inorganic fertilizers as micronutrients is covered by CEN/TS 17754:2022.
NOTE 2   The determination of copper in ammonium nitrate fertilizers of high nitrogen content is covered by CEN/TS 17751:2022.

This document specifies a method for the determination of pH of a solution of ammonium nitrate fertilizers of high nitrogen content.

This document specifies a method for the extraction of phosphorus soluble in neutral ammonium citrate.
The method is applicable to organo-mineral fertilizers.

This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [4]. However, the present method was not validated for blends.
This document specifies a method for the determination of the biuret content by high-performance liquid chromatography (HPLC) with UV detector. The method is applicable to organic and organo-mineral fertilizers containing urea.
Nowadays, there is a method standardized as EN 15479 that allows the determination of biuret in urea by spectrophotometric detection. Organic and organo-mineral fertilizers contain organic matter and other compounds apart from urea that would interfere in a spectrophotometric method. HPLC allows an accurate determination of biuret by separating it from possible interfering compounds [2] [3].

This document specifies a method for the determination by ion pair chromatography of the iron chelated by each individual ortho(hydroxy)-ortho(hydroxy) isomer of the chelating agents [o,o] EDDHA, [o,o] EDDHMA and by HBED in organo-mineral fertilizers, having an organic matrix based on vegetal residues (cocoa shells, grape residue, soybean residue, ...), algae extract, and animal meal (feather, bones, blood, ...) and containing one or more of these substances, except for [o,o] EDDHMA and HBED mixes.
The method allows the identification and the determination of the total concentration of water soluble iron chelates of these chelating agents. Also, after derivatization with Fe, the soluble amount of the chelating agents can be determined when other micronutrients beside Fe are present in organo-mineral fertilizers containing [o,o] EDDHA, [o,o] EDDHMA or HBED.
This method is applicable to a mass fraction of the metal chelated of at least 0,625 %.
NOTE 1   The substances EDDHA and EDDHMA exist as several different isomeric forms. Positional isomers for the hydroxyl or methyl groups (in ortho, meta, and para positions) as well as stereo isomers (meso and dl-racemic forms) are known. Both meso and dl-racemic forms of the [ortho,ortho] EDDHA and [ortho,ortho]. Since para, meta and ortho methyl positional isomers of the EDDHMA present quite similar stability, they could be grouped: in the method here described the para, meta and ortho methyl positional isomers of the [o,o] EDDHMA are considered together. HBED (N,N'-bis(2-hydroxybenzyl)-ethylenediamine-N,N'-diacetic acid) does not present isomeric forms.
NOTE 2   At present, analytically pure standards only exist for [ortho,ortho] EDDHA, [ortho,ortho] EDDHMA and HBED. All other substances being unavailable as a standard, the influence of their eventual presence in the samples (with respect to the sensitivity and the selectivity of this method) has not been studied.
NOTE 3   The meso and the dl-racemic forms of [o,o] EDDHA and [o,o] EDDHMA can be determined separately by this method.

This document specifies a method for the determination of elements in organic fertilizers and organo-mineral fertilizers digests using inductively coupled plasma-atomic emission spectrometry (ICP-AES).
NOTE   Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) can be used for the measurement if the user proves that the method gives the same results.
This method is applicable to aqua regia digests prepared according to CEN/TS 17768 for the determination of P, K, Ca, Mg, Na, S, B, Co, Cu, Fe, Mn, Mo, Zn, As, Cd, Cr, Ni, Pb by ICP-AES. The method can be used for the determination of other elements, provided the user has verified the applicability.

This document specifies references to the methods for the determination of nitrification inhibitors and urease inhibitors in inorganic fertilizers.
This document is applicable to EU fertilizing products classified as PFC 1(C) and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1(C), PFC 2 and PFC 5 as specified in the Regulation (EU) 2019/1009 [1].

This document specifies a general method for the determination of the micronutrients complexed by complexing agents in organo-mineral fertilizers. The method allows the determination of the total concentration of each complexed micronutrient in complexes after subtraction of the chelated micro-nutrients content, but it does not identify the individual complexing agents.
This procedure concerns EU organo-mineral fertilizing products which contain complexed micro-nutrients covered by Regulation (EU) 2019/1009 [6]. The method is applicable to a mass fraction of the metal complexed of at least 0,07 %, 0,006 % and 0,035 % of Fe, Mn and Zn respectively (see [7]). A lower limit of quantification has not been established for Cu and Co.

This document specifies a method for the determination of the soluble metal that remains in solution at different pHs after the application of a solution of the fertilizer substance containing micronutrient chelates in a tap water solution used as a reference.
The method applies to fertilizing products containing chelated micronutrients.

This document specifies a method for determination of the content of mercury (Hg) in organic fertilizers and organo-mineral fertilizers using (cold) vapour generation apparatus coupled to an atomic absorption spectrophotometer and a method using a direct amalgamation technique. It is applicable to aqua regia digests prepared according to CEN/TS 17768.
NOTE   It is also possible to use other suitable methods for the determination of mercury described in Annex A if users prove that the method gives the same results as the methods described in this standard.

This document specifies a method for the determination of the chloride content in organic fertilizers, organo-mineral fertilizers, inorganic fertilizers and liming materials by potentiometric titration.

This document specifies the procedure for the digestion of different organic fertilizers and organo-mineral fertilizers with aqua regia to enable a subsequent determination of elements.
The extracts are suitable for analysis using CEN/TS 17770 and CEN/TS 17769.
NOTE   Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) can be used for the measurement if the user proves that the method gives the same results.

This document specifies references to methods for the determination of the following specific parameters in ammonium nitrate fertilizers of high nitrogen content:
-   the nitrogen content as a result of ammonium nitrate;
-   pH of a solution of ammonium nitrate fertilizers of high nitrogen content;
-   the particle size of ammonium nitrate fertilizers of high nitrogen content;
-   the chloride content;
-   the copper content.
This document is applicable to EU fertilizing products classified as PFC 1(C)(I)(a)(i-ii)(A) and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1(C), PFC 2 and PFC 5 and still fulfils the requirements for PFC 1(C)(I)(a)(i-ii)(A) as specified in the Regulation (EU) 2019/1009 [1].

This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [1]. However, the present method was not validated for blends.
This document specifies a colony-count technique at 44 °C on a solid medium containing a chromogenic ingredient for the detection of the enzyme β-glucuronidase. The method is based on ISO 16649-2 [4].
Strains of Escherichia coli which do not grow at 44 °C and, in particular, those that are β-glucuronidase negative, such as Escherichia coli O157, will not be detected. Detected microorganisms are presumptively determined β-glucuronidase-positive Escherichia coli, since some Enterobacteriaceae, in particular Shigella and Salmonella, can also show β-glucuronidase activity at 44 °C.

This document specifies a method for the determination of the copper content in ammonium nitrate fertilizers of high nitrogen content.

This document specifies a method for the determination of the chelated fraction of micronutrients for fertilizers containing one or many micronutrients chelated by EDTA, DTPA, HEEDTA, IDHA or [S,S]-EDDS in fertilizers.
This method is used for inorganic micronutrient fertilizers when micronutrients are chelated only by EDTA, DTPA, HEEDTA, IDHA or [S,S]-EDDS or for mixtures in which EDTA, DTPA, HEEDTA, IDHA or [S,S]-EDDS is one of the chelating agents.
The method is applicable to all inorganic micronutrient fertilizers containing EDTA, DTPA, HEEDTA, IDHA or [S,S]-EDDS as chelating agent for contents > 0,1 % (w/w).
The method is based on ICP or AAS measurement of the concentration of micronutrients according to EN 16963 or EN 16965 after water extraction according to EN 16962 and LC measurement of the chelating agents according to EN 15950, EN 13368-1 and EN 13368-3.

This document specifies the procedure for the extraction of phosphorus in 2 % formic acid (20 g/l), representing the amount of soft natural phosphates.
The method is applicable to organo-mineral fertilizers.

This document specifies references to a method for the determination of the chloride content in organic fertilizers, organo-mineral fertilizers, inorganic fertilizers and liming materials.
This document is applicable to EU fertilizing products classified as PFC 1, PFC 2 and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1, PFC 2 and PFC 5 as specified in the Regulation (EU) 2019/1009 [1].

This document specifies a chromatographic method which allows the identification of heptagluconic acid (HGA) in organo-mineral fertilizers containing heptagluconic acid metal complexes.
NOTE   For the complete names of the chelating agents mentioned in this document, see Annex D.

This document specifies references to methods for the determination of the content of the following specific nutrients in inorganic fertilizers:
-   the total nitrogen content;
-   the ammoniacal nitrogen content;
-   the nitric nitrogen content;
-   the urea nitrogen content;
-   the content of nitrogen from isobutylidenediurea (IBDU) and crotonylidenediurea (CDU);
-   the cyanamide nitrogen content;
-   the methylene-urea nitrogen content (and urea formaldehyde, if applicable);
-   the total phosphorus content;
-   the water-soluble phosphorus content;
-   the neutral ammonium citrate soluble phosphorus content;
-   the water-soluble potassium content;
-   the total magnesium content;
-   the water-soluble magnesium content;
-   the total calcium content;
-   the water-soluble calcium content;
-   the total sulfur content;
-   the water-soluble sulfur content;
-   the total sodium content;
-   the water-soluble sodium content.
This document is applicable to EU fertilizing products classified as PFC 1(C) and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1(C), PFC 2 and PFC 5 as specified in the Regulation (EU) 2019/1009 [1].

This document specifies references to the methods for the determination of the following specific elements in organic and organo-mineral fertilizers:
—   Determination of the total phosphorus content;
—   Determination of the total potassium content;
—   Determination of the total calcium content;
—   Determination of the total magnesium content;
—   Determination of the total sodium content;
—   Determination of the total sulphur content;
—   Determination of the inorganic arsenic content;
—   Determination of the cadmium content;
—   Determination of the total chromium content;
—   Determination of the total mercury content;
—   Determination of the total nickel content;
—   Determination of the total lead content;
—   Determination of the total copper content;
—   Determination of the total zinc content;
—   Determination of the water-soluble calcium content;
—   Determination of the water-soluble magnesium content;
—   Determination of the water-soluble sodium content;
—   Determination of the water-soluble sulphur content.
This document specifies references to the methods for the determination of the following specific elements in organo-mineral fertilizers:
—   Determination of the water-soluble phosphorus content;
—   Determination of the water-soluble potassium content;
—   Determination of the neutral ammonium citrate soluble phosphorus content
—   Determination of the formic acid soluble phosphorus content;
—   Determination of the total boron content;
—   Determination of the total cobalt content;
—   Determination of the total iron content
—   Determination of the total manganese content
—   Determination of the total molybdenum content;
—   Determination of the water-soluble boron content;
—   Determination of the water-soluble cobalt content;
—   Determination of the water-soluble copper content;
—   Determination of the water-soluble iron content;
—   Determination of the water-soluble manganese content;
—   Determination of the water-soluble molybdenum content;
—   Determination of the water-soluble zinc content.
This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [1]. However, the present method was not validated for blends.

This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [1]. However, the present method was not validated for blends.
This document specifies the procedure for the determination and calculation of the dry matter fraction of organic and organo-mineral fertilizers for which the results of the performed analysis are calculated to the dry matter basis.

This document specifies the references to the methods for the determination of stability of chelating and complexing agents for CMC 1 as specified in the Regulation (EU) 2019/1009. The document specifies references to the methods and requirements for inorganic micronutrient fertilizers in accordance with PFC 1(C)(II) as specified in the Regulation (EU) 2019/1009 [1].
Inorganic micronutrient materials for this purpose are micronutrient chelates or complexes and mixtures of them, in powder or granular form, aqueous or suspension preparations.

This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [5]. However, the present method was not validated for blends.
This document specifies a method for the determination of total organic carbon (TOC) by elemental analysis using dry combustion. The method is applicable to organic and organo-mineral fertilizers containing more than 1 g carbon per kg of dry matter (0,1 %), with the exclusion of organo-mineral fertilizers containing urea-formaldehyde polymers as long as there is no method available to assess carbon in urea-formaldehyde polymers.

This document specifies a method for the determination of particle size of ammonium nitrate fertilizers of high nitrogen content.

This document specifies a method for the determination by ion chromatography of the total amount of each of the individual chelating agents EDTA, HEEDTA, and DTPA in organo-mineral fertilizers, having an organic matrix based on vegetal residues (cocoa shells, grape residue, soybean residue, ...), algae extract, and animal meal (feather, bones, blood, ...) and containing one or more of these substances.
The method allows the identification and the determination of the total water-soluble fraction of each of these chelating agents. It does not allow to distinguish between the free form and the metal bound form of the chelating agents.
This method applies to organo-mineral fertilizers containing chelates of one or more of the following micronutrients: cobalt, copper, iron, manganese, zinc and with a mass fraction of at least 0,1 %.

This document specifies a method for the determination of the soluble metal that remains in solution after the application of a solution of the fertilizer substance containing micronutrient complexes in water and adjusting the pH to 6 and pH 7 for at least one day.
The method applies to fertilizing products containing micronutrient complexes.

This document specifies the method for the determination of free, chelated or complexed micronutrients and chelating and/or complexing agents present in compound inorganic micronutrient fertilizers.
This method applies to compound inorganic micronutrient fertilizers when micronutrients are chelated and/or complexed.
The method is based on the determination of the following specific parameters :
-   the water-soluble micronutrient concentration;
-   the fraction of chelated micronutrients in relation;
-   identification of chelating agents EDTA, DTPA, HEEDTA, IDHA, [S,S]–EDDS, [o,o] EDDHA, [o,o] EDDHMA, [o,p] EDDHA, HBED and EDDHSA;
-   the fraction of complexed micronutrients;
-   identification of complexing agents (lignosulfonates, heptagluconic acid (HGA)).
The method is based on
-   ICP (inductive coupled plasma) or FAAS (flame atomic absorption spectrometry) measurement of the concentration of water-soluble micronutrients according to EN 16963 or EN 16965 after extraction according to EN 16962;
-   LC (liquid chromatography) measurement of the chelating agents according to EN 15950, EN 13368-1, EN 13368-2, EN 13368-3, EN 15451, EN 15452;
and/or complexing agents according to EN 16109 and EN 16847;
-   determination of the concentration of chelated micronutrients by CEN/TS 17786-1 and/or CEN/TS 17786-2;
-   determination of the complexed micronutrients by EN 15962.
To avoid duplication of the analytical methods, CEN/TS 17786-2 describes the determination of micronutrients and the identification and determination of chelating agents.

This document specifies a method for the determination of the chloride content in ammonium nitrate fertilizers of high nitrogen content.

This document specifies a method for the extraction by water for the subsequent determination of elements.
The extracts are suitable for analysis using CEN/TS 17774.
NOTE Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) can be used for the measurement if the user proves that the method gives the same results.
The method is applicable to organic and organo-mineral fertilizers.

This document specifies references to the methods for the:
—   Determination of the total organic carbon content;
—   Determination of the dry matter content.
This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [2].

This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [1]. However, the present method was not validated for blends.
This document specifies a method for the detection of Salmonella spp. in organic, organo-mineral and inorganic fertilizers. The method is based on EN ISO 6579-1 and its validated alternative methods for the detection of Salmonella spp. in food and feeding stuff.
It requires three successive steps: A selective enrichment, an isolation on a chromogenic agar, and if positive a confirmation with a serological test (and if required, a selective media).

This document specifies a method for the determination of boron (B), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) in organic fertilizers and organo-mineral fertilizers extracts using inductively coupled plasma-atomic emission spectrometry (ICP-AES).
NOTE   Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) can be used for the measurement if the user proves that the method gives the same results.
This method is applicable to water extracts prepared according to CEN/TS 17766. The method can be used for the determination of other elements, provided the user has verified the applicability.

This document specifies a reference to the method for the determination of the granulometry.
This document is applicable to solid inorganic macronutrient fertilizers classified as PFC 1(C)(I)(a) and PFC 7 as long as the blend only consists of EU fertilizing products classified as PFC 1(C)(I)(a) and PFC 5 as specified in the Regulation (EU) 2019/1009 [1].

This document specifies a method for extraction, separation, and determination of inorganic arsenic (iAs) in organic or organo-mineral fertilizers using anion-exchange HPLC or IC coupled to ICP-MS.

This document specifies a method for the determination of the chelated iron content and the chelated fraction of iron, in UVCB chelats, EDDHA, EDDHMA, HBED, EDDHSA, in inorganic micronutrient fertilizers by the treatment with a cation exchange resin.
The limit of determination of the chelated iron content highly depends on the specific electrical conductivity of the sample, on the amount of nutrient present, and varies between 0,005 % in simple matrices with high amounts of micronutrient and 0,5 % in more complex cases (see 9.1).