A: Place 2mLin a 10-mLbeaker,and adjust with 3Nhydrochloric acid to a pHof about 3(pHindicator paper).Add 500mg to 1g of finely powdered sodium chloride,in two portions of about 200mg each initially,and then in smaller portions (about 25mg),stirring after each addition,until a precipitate is formed.Allow to stand at room temperature for 15minutes,and collect the residue by suction filtration:the acetylcysteine so obtained,after being dried as directed in the test for Loss on dryingunder Acetylcysteine,responds to the Identificationtest under Acetylcysteine.

B:Ferro-citrate Solutionand Buffer Solution— Prepare as directed under Epinephrine Assay á391ñ.

Procedure— Place a volume of Inhalation Solution,equivalent to about 0.26mg of isoproterenol hydrochloride,in a test tube with 3mLof 0.1Mmercuric chloride,and mix.Add 100µLof Ferro-citrate Solutionand 1.0mLof Buffer Solution,and mix:the presence of isoproterenol hydrochloride is confirmed by the development of a purple color.

Mobile phase,Internal standard solution,Standard preparation,and Chromatographic system— Proceed as directed in the Assayunder Acetylcysteine.

Assay preparation— Pipet a volume of Inhalation Solution,equivalent to about 1000mg of acetylcysteine,into a 100-mLvolumetric flask,dilute with sodium metabisulfite solution (1in 2000)to volume,and mix.Pipet 10mLof this solution and 10mLof Internal standard solutioninto a 200-mLvolumetric flask,dilute with sodium metabisulfite solution (1in 2000)to volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Acetylcysteine.Calculate the quantity,in mg,of C5H9NO3Sin each mLof the Inhalation Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Acetylcysteine RSin the Standard preparation;Vis the volume,in mL,of Inhalation Solution taken;and RUand RSare the ratios of the peak response of acetylcysteine to that of DL-phenylalanine obtained from the Assay preparationand the Standard preparation,respectively.

Mobile phase— Dissolve 13.6g of monobasic potassium phosphate in 1000mLof water,and pass through a membrane filter having a 0.45-µm porosity.Add 20.0mLof methanol,mix,and degas.

Internal standard solution— Place about 150mg of acetaminophen in a 500-mLvolumetric flask,add 5mLof glacial acetic acid,dilute with water to volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Isoproterenol Hydrochloride RSin 0.05Msodium metabisulfite to obtain a solution having a known concentration of 0.15mg per mL.Transfer 10.0mLof this solution to a 25-mLvolumetric flask,add 10.0mLof Internal standard solution,dilute with 0.2Macetic acid to volume,and mix.

Assay preparation— Transfer an accurately measured volume of Inhalation Solution,equivalent to about 1.5mg of isoproterenol hydrochloride,and 10mLof Internal standard solutionto a 25-mLvolumetric flask,add dilute glacial acetic acid (1in 100)to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 280-nm detector and a 3.9-mm ×40-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.5for isoproterenol hydrochloride and 1.0for acetaminophen;the resolution,R,between isoproterenol hydrochloride and acetaminophen is not less than 6;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of isoproterenol hydrochloride (C11H17NO3·HCl)in each mLof the Inhalation Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Isoproterenol Hydrochloride RSin the Standard preparation;Vis the volume,in mL,of Inhalation Solution taken;and RUand RSare the ratios of the peak responses of isoproterenol hydrochloride to those of acetaminophen obtained from the Assay preparationand the Standard preparation,respectively.