BS EN ISO 23470 pdf download Soil quality — Determination of effective cation exchange capacity (CEC) and exchangeable cations using a hexamminecobalt trichloride solution
This International Standard specifies a method for the getermination of the cation exchange capacity (CEC)and the content of exchangeable cations (Ai3*+， ca 2*, Fe2*，K+，Mg”*，Mn2*，Na+)in soils using ahexamminecobalt trichloride solution as extractant.
NOTE As the pH of a soil suspension in the hexamminecobalt trichloride solution is close to the pH of the suspensionin water, this method is considered to give the effective CEC, i.e. the CEC at the soil pH.
This International Standard is applicable to all types of air-dried soil samples which have been prepared inaccordance with lSO 11464.
References and results of the comparison with other methods (barium chloride, ammonium acetate) are givenin Annex A.
The following referenced documents are indispensable for the application of this document.For datedreferences,only the edition cited applies. For undated references,the latest edition of the referenceddocument (including any amendments) applies.
ISO 11464,Soil quality — Pretreatment of samples for physico-chemical analysis
Cations retained by a soil sample are exchanged with the hexamminecobalt ions of an aqueous solution, withshaking for 60 min ± 5 min at a temperature of 20 °C±2°C.The CEC is obtained by difference between theinitial quantity of hexamminecobalt in solution and the quantity remaining in the extract after the exchangereaction. The measurement of hexamminecobalt concentration in the extract can be performed by directspectrophotometric measurement,or by the determination of total ammonium nitrogen or total cobaltconcentrations.
The quantities of exchanged cations are determined on the same extract using spectrometric methods, suchas inductively coupled plasma atomic emission spectrometry (ICP-AES).
NOTE1 Exchangeable acidity can also be measured in the hexamminecobalt extract.
NOTE2 When exchangeable cations are held in micropores into which ammonium ions but not hexamminecobalt ionscan enter, the CEC and exchangeable cation values determined with this method may be smaller than those determinedby the ammonium acetate method. This has been observed in some soils containing allophane and imogolite, for examplesoils developed on volcanic rocks.
Only reagents of recognized analytical quality shall be used.
4.1 Distilled or demineralized water，exempt from the elements under analysis and having aconductivity of less than 0,5 uS-cm-1.
4.2Hexamminecobalt trichloride [Co(NH3)6Cl3],0,016 6 mol-l—1 solution.
Dissolve, to within a milligram, 4,458 g of hexamminecobalt trichloride in a volumetric flask containing 700 mlof distilled water (4.1). Make up to volume and mix.
NOTE Hexamminecobalt trichloride can be purchased from Sigma-Aldrich or Fluka. 1)4.3Anti-bumping granules (e.g. pumice stone in grain form, glass beads).4.4Boric acid (40 g-l—1 solution).
Dissolve 2,0 g of methyl red and 1,0 g of methylene blue in 1 000 ml of 95° ethanol.4.6Phenolphthalein.
Dissolve 1 g of phenolphthalein in 1 000 ml of 95° ethanol.
4.7Sodium hydroxide solution,33 % (ratio of mass to volume).4.8Sulfuric acid (H2SO4),0,025 mol-l—1 standard volumetric solution.4.9Ammonium sulfate, for analysis.
4.10Stock solutions of Al3+, Ca2+, Fe2+,K+,Mg2+, Mn2+， Na+，1,000 g-—1.
These solutions are supplied with a certified composition from a reputable source and are checked on aregular basis.
Usual laboratory apparatus and glassware, and in particular:
5.1 Analytical balance, the weighing uncertainty range of which will not exceed ±0,1 % of the testportion mass.
5.2Containers for shaking, tightly stoppered, rigid or non-rigid wall, having a volume between 75 ml and100 ml.
5.350 ml distributor, set at ± 0,25 ml of the delivered volume.
5.4 End-over-end shaker,allowing the permanent suspension of the soillextraction solution mixture,