2 , 4-Dinitrophenylhydrazine reagent—Prepare as directed in the Identification test under Glutaral Concentrate.

Procedure— Add 5 mL of Disinfectant Solution to 20 mL of 2, 4-Dinitrophenylhydrazine reagent, mix by swirling, allow to stand for 5 minutes, and proceed as directed for Procedure in the Identification test under Glutaral Concentrate, beginning with “Collect the precipitate on a filter.”

Buffer— Dissolve 2.59 g of monobasic potassium phosphate and 6.77 g of anhydrous dibasic sodium phosphate in 500 mL of water in a 1000-mL volumetric flask, dilute with water to volume, and mix.

Hydroxylamine hydrochloride solution— Prepare a solution of hydroxylamine hydrochloride in Buffer containing 70 µg per mL.

Standard preparation— Transfer an accurately weighed quantity of Glutaral Concentrate, previously assayed as directed in the Assay under Glutaral Concentrate, equivalent to about 2.5 g of glutaraldehyde, to a 100-mL volumetric flask, dilute with water to volume, and mix. Dilute an accurately measured volume of this solution quantitatively and stepwise with water to obtain a solution having a known concentration of about 50 µg per mL.

Standard preparation blank solution— Transfer 10.0 mL of Standard preparation and 10.0 mL of Buffer to a 50-mL volumetric flask, dilute with water to volume, and mix.

Assay preparation— Transfer an accurately weighed portion of Disinfectant Solution, equivalent to about 100 mg of glutaraldehyde, to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a second 100-mL volumetric flask, dilute with water to volume, and mix.

Assay preparation blank solution— Transfer 10.0 mL of Assay preparation and 10.0 mL of Buffer to a 50-mL volumetric flask, dilute with water to volume, and mix.

Reagent blank solution— Transfer 10.0 mL of Buffer and 10.0 mL of Hydroxylamine hydrochloride solution to a 50-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Transfer 10.0 mL each of the Standard preparation and the Assay preparation to separate 50-mL volumetric flasks, to each add 10.0 mL of Hydroxylamine hydrochloride solution, dilute with water to volume, mix, and allow each to stand for 25 minutes. Concomitantly determine the absorbances of both solutions and of the respective blank solutions at the wavelength of maximum absorption at about 238 nm, with a suitable spectrophotometer, using the Reagent blank solution to set the instrument to zero. Calculate the percentage, by weight, of C5H8O2 in the Disinfectant Solution taken by the formula: in which C is the concentration, in µg per mL, of C5H8O2 in the Standard preparation; W is the weight, in g, of Disinfectant Solution taken; AU and AS are the absorbances of the solutions from the Assay preparation and the Standard preparation, respectively; and AUb and ASb are the absorbances of the Assay preparation blank solution and the Standard preparation blank solution, respectively.