g) Ethylenediamine tetraacetate- Sodium hydroxide solution (1): Dissolve 10 g of
ethylenediaminetetraacetic acid dihydrogen disodium dihydrate specified in JIS K 8107
and 8 g of sodium hydroxide specified in JIS K 8576 in a proper amount of water, add 6
mL - 10 mL of tetraphenylborate solution while mixing according to the volume of
potassium coexisting as impurity after standing to cool and then add water to make 100
mL. After leaving at rest for about 30 minutes while sometimes mixing, filter with Type
3 filter paper