Recueil des Méthodes d’analyse des vins et moûts

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Conductivity (Type-IV)

OIV-MA-F1-01 Conductivity

Type IV method

  1. Principle

The electrical conductivity of a column of liquid defined by two parallel platinum electrodes at its ends is measured by incorporating it in one arm of a Wheatstone bridge.

The conductivity varies with temperature and it is therefore expressed at 20°C.

  1. Reagents

 

Use only reagent grade chemicals

2.1.  Purified water for laboratories, with specific conductivity below 2 μS cm-1 at 20°C, for example EN ISO 3696 type II water.

2.2.  Reference solution of potassium chloride.

Dissolve 0.581 g of potassium chloride, KCl previously dried to constant mass at a temperature of 105°C, in demineralised water (2.1). Make up to one litre with demineralised water (2.1). This solution has a conductivity of 1 000 μS cm-1 at 20°C. It should not be kept for more than three months.

A commercial preparation can be used.

  1. Apparatus

3.1.  Conductivity meter enabling measurements of conductivity to be made over a range from 1 to 1 000 microsiemens per cm (μS cm-1).

3.2.  Water bath for bringing the temperature of samples to be analysed to approximately 20°C (20 2°C).

  1. Procedure
    1.   Preparation of the sample to be analysed

Use a solution with a total sugar concentration of 25 0.5 % (m/m) (25° Brix): weigh a mass equal to 2500/P and make up to 100 g with water (2.1),

P = percentage (m/m) of total sugars in the rectified concentrated must.

4.2.  Determination of conductivity

Bring the sample to be analysed to 20°C by immersion in a water bath. Maintain the temperature to within ± 0.1°C.

Rinse the conductivity cell twice with the solution to be examined.

Measure the conductivity and express the result in μS cm-1.

  1. Expression of the Results

The result is expressed in microsiemens per cm (μScm−1) at 20°C to the nearest whole number for the 25% (m/m) (25° Brix) solution of rectified concentrated must.

5.1.  Calculations

If the apparatus does not have temperature compensation, correct the measured conductivity using Table I. If the temperature is below 20°C, add the correction; if the temperature is above 20°C, subtract the correction.

 

  1. Characteristics of the method

Repeatability (r)

  • r = 3 μS/cm

Reproducibility (R)

  • R = 16 μS/cm

Table I

Corrections to be made to the conductivity for temperatures different from 20°C (μS cm−1)

Conductivity

Temperature (°C)

20.2

19.8

20.4

19.6

20.6

19.4

20.8

19.2

21.

19.0

21.2

18.8

21.4
18.6

21.6
18.4

21.8

18.2

22,0(1)

18.0(2)

0

0

0

0

0

0

0

0

0

0

0

50

0

0

1

1

1

1

1

2

2

2

100

0

1

1

2

2

3

3

3

4

4

150

1

1

2

3

3

4

5

5

6

7

200

1

2

3

3

4

5

6

7

8

9

250

1

2

3

4

6

7

8

9

10

11

300

1

3

4

5

7

8

9

11

12

13

350

1

3

5

6

8

9

11

12

14

15

400

2

3

5

7

9

11

12

14

16

18

450

2

3

6

8

10

12

14

16

18

20

500

2

4

7

9

11

13

15

18

20

22

550

2

5

7

10

12

14

17

19

22

24

600

3

5

8

11

13

16

18

21

24

26

(1)Subtract the correction.

(2)Add the correction.