301ACID-NEUTRALIZING CAPACITY, chemical structure, molecular formula, Reference Standards

á301ñACID-NEUTRALIZING CAPACITY

NOTE— All tests shall be conducted at a temperature of 37±3

Standardization of pH Meter— Standardize a pHmeter using the 0.05m potassium biphthalate and 0.05m potassium tetraoxalate standardizing buffers as described under pHá791ñ.

Magnetic Stirrer— Transfer 100mLof water to a 250-mLbeaker containing a 40-×10-mm magnetic stirring bar that is coated with solid perfluorocarbon and has a spin ring at its center.Adjust the power setting of the magnetic stirrer to produce a stirring rate of 300±30rpm when the stirring bar is centered in the beaker,as determined by a suitable optical tachometer.

Test Preparation—

Powders— Transfer the accurately weighed portion of the substance specified in the individual monograph to a 250-mLbeaker,add 70mLof water,and mix on the Magnetic Stirrerfor 1minute.

Effervescent Solids— Transfer an accurately weighed quantity,equivalent to the minimum labeled dosage,to a 250-mLbeaker,add 10mLof water,and swirl the beaker gently while allowing the reaction to subside.Add another 10mLof water,and swirl gently.Wash the walls of the beaker with 50mLof water,and mix on the Magnetic Stirrerfor 1minute.

Suspensionsand Other Liquids— Shake the container until the contents are uniform,and determine the density.Transfer an accurately weighed quantity of the uniform mixture,equivalent to the minimum labeled dosage,to a 250-mLbeaker,add water to make a total volume of about 70mL,and mix on the Magnetic Stirrerfor 1minute.

Lozenges— Accurately weigh not fewer than 20lozenges,and determine the average weight.Select and weigh 2lozenges,and transfer them to a 250-mLbeaker containing 70mLof water.

Nonchewable Tablets— Weigh not fewer than 20tablets,and determine the average tablet weight.Grind the tablets to a fine powder,mix to obtain a uniform mixture,and transfer an accurately weighed quantity of it,equivalent to the minimum labeled dosage,to a 250-mLbeaker.If wetting is desired,add not more than 5mLof alcohol (neutralized to an apparent pHof 3.5),and mix to wet the specimen thoroughly.Add 70mLof water,and mix on the Magnetic Stirrerfor 1minute.

Chewable Tablets— Prepare as directed for Nonchewable Tablets.

Tablets That Are Required To Be Chewed— Transfer 1Tablet to a 250-mLbeaker,add 50mLof water,and mix on the Magnetic Stirrerfor 1minute.

Capsules— Weigh accurately not fewer than 20capsules.Remove the capsule contents completely,with the aid of a cotton swab if necessary.Accurately weigh the empty capsules,and determine the average weight of the contents per capsule.Mix the combined capsule contents to obtain a uniform mixture,and proceed as directed for Nonchewable Tablets,beginning with “transfer an accurately weighed quantity of it.”

Procedure for Powders,Effervescent Solids,Suspensions and Other Liquids,Lozenges,Nonchewable Tablets,Chewable Tablets,and Capsules— Pipet 30.0mLof 1.0Nhydrochloric acid VSinto the Test Preparationwhile continuing to stir with the Magnetic Stirrer.[NOTE—Where the acid-neutralizing capacity of the specimen under test is greater than 25mEq,use 60.0mLof 1.0Nhydrochloric acid VS.]Stir for 15minutes,accurately timed,after the addition of the acid,begin to titrate immediately,and in a period not to exceed an additional 5minutes,titrate the excess hydrochloric acid with 0.5Nsodium hydroxide VSto attain a stable (for 10to 15seconds)pHof 3.5.Calculate the number of mEq of acid consumed,and express the result in terms of mEq of acid consumed per g of the substance tested.Each mLof 1.0Nhydrochloric acid is equal to 1mEq of acid consumed.

Procedure for Tablets That Are Required To Be Chewed— Pipet 30.0mLof 1.0Nhydrochloric acid VSinto the Test Preparationwhile continuing to stir with the Magnetic Stirrerfor 10minutes,accurately timed,after the addition of the acid.Discontinue stirring briefly,and without delay remove any gum base from the beaker using a long needle.Promptly rinse the needle with 20mLof water,collecting the washing in the beaker,and resume stirring for 5minutes,accurately timed,then begin to titrate immediately,and in a period not to exceed an additional 5minutes,titrate the excess hydrochloric acid with 0.5Nsodium hydroxide VSto attain a stable (for 10to 15seconds)pHof 3.5.Calculate the number of mEq of acid consumed by the Tablet tested.Each mLof 1.0Nhydrochloric acid is equal to 1mEq of acid consumed.