Abstract: A standard reagent kit for analysis of a dialysis fluid includes (1) a vial A filled with an aqueous solution A including an electrolyte component capable of reacting with carbonate ion to form a precipitate, and (2) a vial B filled with an aqueous solution B including at least either one of bicarbonate ion and carbonate ion. At least the vial B is a water-repellent resin vial, and provides a standard reagent for analysis of a dialysis fluid. Precipitation is prevented for a long period of time, a change of a content of bicarbonate ion is controlled, a complicated procedure is not required for preparation thereof, handling thereof is easy, and checking of a dialysis fluid after preparation thereof can be performed easily and accurately at medical treatment site.

Abstract: The present invention provides a stabilized aqueous preparation for injection containing 5-formyl-(6S)-tetrahydrofolic acid or a pharmacologically acceptable salt thereof as an active ingredient and a method of stabilizing 5-formyl-(6S)-tetrahydrofolic acid or a pharmacologically acceptable salt thereof. An aqueous preparation containing 5-formyl-(6S)-tetrahydrofolic acid or a pharmacologically acceptable salt thereof shows extremely excellent preservation stability in the presence of a pH regulator and an antioxidant.