Where a sufficiently large number of similar units are to be subjected routinely to the same type of examination,automated methods of analysis may be far more efficient and precise than manual methods.Such automated methods have been found especially useful in testing the content uniformity of tablets and capsules and in facilitating methods requiring precisely controlled experimental conditions.Many manufacturing establishments,as well as the laboratories of regulatory agencies,have found it convenient to utilize automated methods as alternatives to Pharmacopeial methods (see Proceduresunder Tests and Assaysin the General Notices and Requirements).In addition,the detection system and calculation of results for automated methods are often computerized.

Before an automated method for testing an article is adopted as an alternative,it is advisable to ascertain that the results obtained by the automated method are equivalent in accuracy and precision to those obtained by the prescribed Pharmacopeial method,bearing in mind the further principle stated in the General Notices and Requirementsthat “where a difference appears,or in the event of dispute,only the result obtained by the procedure given in this Pharmacopeia is conclusive.”

It is necessary to monitor the performance of the automated analytical system continually by assaying standard preparations of known composition frequently interspersed among the test preparations.Where immiscible solvents are employed in the automated apparatus for rapid extractions,they are often separated for analysis before complete extraction is attained,and the chemical reactions utilized in automated methods rarely are stoichiometric.Both the accuracy and the precision of the determinations depend upon precise adjustment of the equipment,so maintained that all standard and test preparations are exposed to identical physical and chemical manipulations for identical time intervals.Excessive variability in the response of the standard preparations indicates that the analytical system is malfunctioning and that the test results are therefore invalid.However,where automated systems are shown to operate reliably,the precision of the automated method may surpass that of the manual procedure employing the same basic chemistry.

Many of the manual methods given in this Pharmacopeia can be adapted for use in automated equipment incorporating either discrete analyzers or continuous flow systems and operating under a variety of conditions.On the other hand,an analytical scheme devised for a particular automated system may not be readily transposable for use either in a manual procedure or in other types of automated equipment.

The apparatus required for manual methods is,in general,less complicated than the apparatus of automated systems,even those systems used for the direct automated measurement of a single analyte (i.e.,the substance being determined or analyzed for)in a binary mixture.However,because of their versatility,automated systems designed for the rapid determination of a specified substance often can be readily modified by the addition of suitable modules and accessories to permit the determination of one or more additional substances in a dosage form.Such extended systems have been utilized,for example,in the automated analysis of articles containing both estrogens and progestogens.

The accompanying pertinent diagrams represent examples of automated methods.Diagrams for official methods are reproduced here rather than in the individual monographs.The descriptions of the procedural details in these methods exemplify the general approach in automated analysis applicable to dosage forms.It should be noted that the diagrams,with many minutiae,are an indispensable part of the directions for conducting the analysis.

DIAGRAMS

ANTIBIOTICS—HYDROXYLAMINE ASSAY

Apparatus— Automatic analyzer consisting of (1)a liquid sampler,(2)a proportioning pump,(3)suitable spectrophotometers equipped with matched flow cells and analysis capability at 480nm,(4)a means of recording spectrophotometric readings,and/or computer for data retrieval and calculation,and (5)a manifold consisting of the components illustrated in the accompanying pertinent diagram.

Reagents—

USP Reference Standards á11ñ— Use the USP Reference Standard as directed in the individual monograph.

Standard Preparation— Unless otherwise directed in the individual monograph,dissolve an accurately weighed quantity of the USP Reference Standard in water,and quantitatively dilute with water to obtain a solution having a known concentration of about 1mg per mL.

Assay Preparation— Unless otherwise directed in the individual monograph,using the specimen under test,prepare as directed under Standard Preparation.

Procedure— With the sample line pumping water,the other lines pumping their respective reagents,and the spectrophotometer set at 480nm,standardize the system until a steady absorbance baseline has been established.Transfer portions of the Standard Preparationand the Assay Preparationto sampler cups,and place in the sampler.Start the sampler,and conduct determinations of the Standard Preparationand the Assay Preparationtypically at the rate of 40per hour,using a ratio of about 2:1for sample and wash time.Calculate the potency by the formula given in the individual monograph,in which Cis the concentration,in mg per mL,of USP Reference Standard in the Standard Preparation;Pis the potency,in µg per mg,of the USP Reference Standard;and AUand ASare the absorbances,corrected for the absorbances of the respective blanks,of the solutions from the Assay Preparationand the Standard Preparation,respectively.

ASSAY FOR ASCORBIC ACID

Apparatus— Automatic analyzer consisting of (1)a liquid sampler;(2)a proportioning pump;(3)a suitable fluorimeter equipped with a flow cell and filters:primary—335nm,and secondary—426nm;(4)a means of recording fluorimeter readings;and (5)a manifold consisting of the components illustrated in the accompanying pertinent diagram.

Reagents—

USP Reference Standards á11ñ— USP Ascorbic Acid RS.

Standard Stock Solution— Dissolve an accurately weighed quantity of USP Ascorbic Acid RSin Dilute Extracting Solutionto obtain a solution having a known concentration of about 0.1mg per mL.

Standard Preparations— Transfer 10.0,20.0,30.0,40.0,and 50.0mLof Standard Stock Solutionto separate 100-mLvolumetric flasks,dilute the contents of each flask with Carbon Extracting Solutionto volume,mix,and filter to obtain Standard Preparations A,B,C,D,and Ehaving known concentrations of 10µg,20µg,30µg,40µg,and 50µg of USP Ascorbic Acid RSper mL,respectively.

Assay Preparation—

Procedure— With the sample line pumping the Wash Solution,the other lines pumping their respective reagents,and the fluorimeter equipped with proper filters,standardize the system by pumping until a steady baseline has been established.Transfer portions of theStandard Preparationsand the Assay Preparationto sample cups,and place in the sampler.Start the sampler,and conduct determinations of each Standard Preparationand the Assay Preparationat the rate of 40per hour,using a ratio of about 2:1for sample and wash time.Derive a standard response line by plotting the respective Standard Preparationconcentration (10.0,20.0,30.0,40.0,and 50.0µg per mL)versus transmittance.From the measured transmittance and the standard response line,determine the ascorbic acid concentration,C,in µg per mL,of the Assay Preparation.Calculate the quantity,in mg,of C6H8O6in the portion of liquids,tablets,or capsule contents taken by the appropriate formula:

ASSAY FOR IODIDE

Apparatus— Automatic analyzer consisting of (1)a liquid sampler,(2)a proportioning pump,(3)a heating bath,(4)a suitable colorimeter equipped with a 2.0-×50-mm flow cell and analysis capability at 420nm,(5)a means of recording colorimetric readings,and (6)a manifold consisting of the components illustrated in the accompanying pertinent diagram.

Reagents—

Standard Preparations—

Assay Preparation—

Procedure— With the sample line pumping the Acetic Acid Carrier Solution,the other lines pumping their respective reagents,and the colorimeter equipped with 420-nm filters,standardize the system until a steady baseline has been established.Transfer portions of the Standard Preparationsand the Assay Preparationto the sampler cups,and place in the sampler.Start the sampler,and conduct determinations of each Standard Preparationand the Assay Preparationat the rate of 30per hour,using a ratio of about 1:4for sample and wash time.Derive a standard response line by plotting the respective Standard Preparationconcentration (0.02,0.04,0.06,0.08,and 0.10µg per mL)versus absorbance.[NOTE—This is an indirect absorbance relationship:the greater the iodide amount,the less the absorbance.]From the measured transmittance and the standard response line,determine the iodide concentration,C,in µg per mL,of the Assay Preparation.Calculate the quantity,in µg,of iodide in the portion of liquids,tablets,or capsules contents taken by the formula:

CONTENT UNIFORMITY OF NITROGLYCERIN TABLETS

Apparatus— Automatic analyzer consisting of (1)a liquid sampler,(2)a proportioning pump,(3)a heating bath,(4)a suitable spectrophotometer equipped with a 5-mm flow cell and analysis capability at 545nm,(5)a means of recording spectrophotometric readings,and (6)a manifold consisting of the components illustrated in the accompanying pertinent diagram.

Reagents—

Standard Preparation— Dissolve an accurately weighed portion of 10%nitroglycerin-betalactose absorbate,previously standardized,in water,and dilute quantitatively and stepwise with water to obtain a solution having a known concentration of about 30µg per mL.

Test Preparation— Dissolve 1Nitroglycerin Tablet in water to obtain a solution having a concentration of about 30µg of nitroglycerin per mL.

Procedure— With the sample line pumping water,the other lines pumping their respective reagents,and the spectrophotometer set at 545nm,standardize the system by pumping until a steady absorbance baseline has been established.Transfer portions of the Standard Preparationand the Test Preparationto sampler cups,and place in the sampler.Start the sampler,and conduct determinations of the Standard Preparationand the Test Preparationat a rate of 30per hour,using a ratio of 1:1for sample and wash time.First,run two standards,discarding the first value,then continue the run using one standard after each five samples,recording the absorbance values.Calculate the quantity,in mg,of C3H5N3O9in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of nitroglycerin in the Tablet;Dis the concentration,in µg per mL,of nitroglycerin in the solution from the Tablet,based on the labeled quantity per Tablet and the extent of dilution;Cis the concentration,in µg per mL,of nitroglycerin in the Standard Preparation;AUis the absorbance of the Test Preparation;and ASis the average of the absorbances of the two Standard Preparationsthat bracket the Test Preparation.