Выражение встречается в следующем контексте: (все не надо переводить:)

IDENTIFICATION, CONTROL, AND QUANTIFICATION OF RESIDUAL SOLVENTS
NOTE—The organic-free water specified in the following procedures produces no significantly interfering peaks when chromatographed.
Class 1 and Class 2 Residual Solvents
WATER-SOLUBLE ARTICLES
Procedure A—
Class 1 Standard Stock Solution— Transfer 1.0 mL of USP Class 1 Residual Solvents Mixture RS to a 100-mL volumetric flask, add 9 mL of dimethyl sulfoxide, dilute with water to volume, and mix. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 1.0 mL of this solution to a 10-mL volumetric flask, dilute with water to volume, and mix.

Заранее спасибо