ISO 10390:2021 Soil, treated biowaste and sludge – Determination of pH

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Soil, treated biowaste and sludge – Determination of pH

1 Scope

This document specifies an instrumental method for the routine determination of pH within the range pH 2 to pH 12 using a glass electrode in a 1:5 (volume fraction) suspension of soil, sludge and treated biowaste in either water (pH in H O), in 1 mol/l potassium chloride solution (pH in KCl) or in 0,01 mol/l 2

calcium chloride solution (pH in CaCl ).

2

This document is applicable to all types of air-dried soil and treated biowaste samples.

NOTE For example, pretreated in accordance with ISO 11464 or EN 16179 or EN 15002.

2 Normative references

There are no normative references in this document.

3 Terms a nd definiti ons

No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp

— IEC Electropedia: available at http:// www .electropedia .org/ 4 Principle

A suspension of a test portion is made up in five times its volume with one of the following solutions:

— water;

— a solution of potassium chloride (KCl) in water, c = 1 mol/l;

— a solution of calcium chloride (CaCI ) in water, c = 0,01 mol/l.

2

The pH of the suspension is measured using a pH-meter.

NOTE 1 To make the procedure generally applicable to all types of soil, treated biowaste samples and sludges except liquid sludge, a volume-to-volume shaking ratio is chosen because all test samples can be treated in the same way. If a mass-to-volume ratio were chosen, the weighed amount of test sample would have to be adapted for e.g. soils with a low density, to enable the preparation of the suspension. For the purpose of this document, it is sufficiently accurate to measure the required volume of test portion with a measuring spoon.

NOTE 2 In samples with a high content of charged particles (e.g. organic matter, clay) the suspension effect can modify the potential difference between the electrodes, and thereby have an influence on the recorded pH value. This problem is minimized by gentle stirring of the suspension. For calcareous material, carbon dioxide can be absorbed by the suspension, which makes it difficult to reach an equilibrium value. Other sources of error are associated with materials containing sulfidic minerals or volatile acids.

5 Reagents

Use only reagents of recognized analytical grade.

5.1 Water, with a specific conductivity not higher than 0,2 mS/m at 25 °C.

5.2 Potassium chloride solution, c(KCl) = 1 mol/l

Dissolve 74,5 g of potassium chloride in water (5.1) and dilute to 1 000 ml.

5.3 Calcium chloride solution, c(CaCl ) = 0,01 mol/l

2

Dissolve 1,47 g of calcium chloride dihydrate (CaCl ∙2H O) in water (5.1) and dilute to 1 000 ml.

2 2

5.4 Buffer solutions, for calibration of the pH-meter

Use at least two of the following buffer solutions for calibration. Buffer solutions having a similar or equivalent pH that are commercially available may also be used.

NOTE 1 The buffer solutions 5.4.1, 5.4.2 and 5.4.3 are stable for one month when stored in polyethylene bottles.

NOTE 2 If automated or semi-automated systems are used, buffers recommended by the manufacturer or commercially available buffers can be used.

5.4.1 Buffer solution, pH 4,00 at 20 °C

Dissolve 10,21 g of potassium hydrogen phthalate (C H O K) in water (5.1) and dilute to 1 000 ml.

8 5 4

The potassium hydrogen phthalate shall be dried before use for 2 h at 115 °C ± 5 °C.

5.4.2 Buffer solution, pH 6,88 at 20 °C

Dissolve 3,39 g of potassium dihydrogen phosphate (KH PO ) and 3,53 g of disodium hydrogen 2 4

phosphate (Na HPO ) in water (5.1) and dilute to 1 000 ml.

2 4

The potassium dihydrogen phosphate shall be dried before use for 2 h at 115 °C ± 5 °C.

5.4.3 Buffer solution, pH 9,22 at 20 °C

Dissolve 3,80 g of disodium tetraborate decahydrate (Na B O ·10H O) in water (5.1) and dilute to 2 4 7 2

1 000 ml.

NOTE Disodium tetraborate decahydrate could lose water of crystallization when stored for a long time.

6 Apparatus

6.1 Shaking or mixing machine

6.2 pH-meter, with slope adjustment and temperature control, readable to two decimals.

6.3 Glass electrode and reference electrode, or combined electrode of equivalent performance

In the case of pH values greater than 10, an electrode specifically designed for that range should be used or an additional buffer solution at pH 12 should be used.

NOTE In case of soils, the danger of deterioration of performance caused by breakage or contamination of the electrodes is increased.

6.4 Thermometer or temperature probe, capable of measuring to the nearest 1 °C.

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