APPARATUS:
Eppendorfpipettes (100-1000 µl und 1-5 cm³)
Volumetric flasks (100 cm³, 250 cm³)
approx. 10 beakers (10 cm³) + magnetic stir bars
Titration unit with dark glass bottle
Magnetic stirrer
Various bottles to store the reagents

REAGENTS:
EGTA stock solution: 3.8 g EGTA are dissolved in 30 cm³ of 1M NaOH (4 g/100 cm³) and diluted to 100 cm³. This yields a 0.1 M EGTA solution. From this a 10 mM EGTA solution can be made by appropriate dilution.
Borate buffer: 5 g of borax (Na₂B₄O₇*10 H₂O) and 15 g of sodium hydroxide are dissolved in 250 cm³  nanopure water.
Indicator: 40 mg of GHA are dissolved in 100 cm³ ethanol. Should be made fresh each day that titrations are carried out.
Butanol
IAPSO (certificated standard seawater)

TITRATION:
Transfer 0.5 cm³ sample into a 10 cm³ beaker and add 3 cm³ pure water. While stirring, add 0.5 cm³ of GHA solution and 0.5 cm³ of buffer solution. Stir for about 3 min., unless you have quite high calcium values, in which case you must start titrating immediately after adding the buffer (the color tends to fade after 5 or 6 minutes). Add 2 cm³ butanol when the reddish color starts to diminish. When the color becomes even less reddish, stop stirring and wait for the butanol to separate. Examine the color and start stirring again while adding a small amount of the 10 mM EGTA titrant. When red color fails to reappear, the titration is finished.

CALIBRATION:
The calibration is carried out with IAPSO seawater standard which is titrated like the samples. The f-factor is determined as ratio of the theoretical EGTA consumption (0.527 cm³ for IAPSO with 10.55 mM Ca) and the the volume of the EGTA solution consumed during titration of IAPSO (VEGTA).      
                                  

CALCULATION:

or easier for the amounts of sample and concentrations used here:

INTERFERENCES:
High concentrations of H₂S (> 1mM) in the sample have no effect on the measurement. But CaCO₃-precipitations might occur. Therefore, measurements have to be carried out right after sampling.