![]() ![]() 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 Procedures under Tests and Assays in 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 Requirements that 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 The diagrams shown below are arranged in alphabetic order by the name of the drug first mentioned, where the diagram is for a procedure for a specific article. Where there is no procedure in this chapter for a particular diagram, reference is to be made to the named monograph.
ANTIBIOTICSHYDROXYLAMINE ASSAY The following procedure is applicable for the assay of those Pharmacopeial antibiotics, such as cephalosporins and penicillins, that possess the beta-lactam structure.
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 480 nm, (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
Hydroxylamine Hydrochloride Solution
Dissolve 20 g of hydroxylamine hydrochloride in 5 mL of polyoxyethylene (23) lauryl ether solution (1 in 1000), and add water to make 1000 mL.
Acetate Buffer
Dissolve 173 g of sodium hydroxide and 20.6 g of sodium acetate in water to make 1000 mL. Dilute 75 mL of this solution with water to 500 mL, and mix.
Ferric Nitrate Solution
Suspend 233 g of ferric nitrate in about 600 mL of water, add 2.8 mL of sulfuric acid, stir until the ferric nitrate is dissolved, add 1 mL of polyoxyethylene (23) lauryl ether, dilute with water to 1000 mL, and mix.
USP Reference Standards
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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 1 mg 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 480 nm, standardize the system until a steady absorbance baseline has been established. Transfer portions of the Standard Preparation and the Assay Preparation to sampler cups, and place in the sampler. Start the sampler, and conduct determinations of the Standard Preparation and the Assay Preparation typically at the rate of 40 per hour, using a ratio of about 2:1 for sample and wash time. Calculate the potency by the formula given in the individual monograph, in which C is the concentration, in mg per mL, of USP Reference Standard in the Standard Preparation; P is the potency, in µg per mg, of the USP Reference Standard; and AU and AS are the absorbances, corrected for the absorbances of the respective blanks, of the solutions from the Assay Preparation and the Standard Preparation, respectively.
ASSAY FOR ASCORBIC ACID The following procedure is applicable for the assay of ascorbic acid in Pharmacopeial multivitamin-minerals combination products (solid and liquid dosage forms) that contain components that interfere in other methods of assay.
Apparatus
Automatic analyzer consisting of (1) a liquid sampler; (2) a proportioning pump; (3) a suitable fluorimeter equipped with a flow cell and filters: primary335 nm, and secondary426 nm; (4) a means of recording fluorimeter readings; and (5) a manifold consisting of the components illustrated in the accompanying pertinent diagram.
Reagents
Extracting Solution
Dissolve 600 g of metaphosphoric acid in 1200 mL of water. Add 400 mL of glacial acetic acid, dilute with water to 2000 mL, and mix.
Dilute Extracting Solution
Dissolve 60 g of metaphosphoric acid in 1200 mL of water. Add 160 mL of glacial acetic acid, dilute with water to 2000 mL, and mix.
Surfactant Solution
Prepare a 30% solution of polyoxyethylene (23) lauryl ether by melting 150 g in a container on a steam bath and slowly adding approximately 250 mL of water with continuous stirring. Cool and dilute with water to make 500 mL.
Wash Solution
Add 1 mL of Surfactant Solution to 3000 mL of Dilute Extracting Solution, and mix.
Carbon Extraction Solution
Dissolve 60 g of metaphosphoric acid in 1200 mL of water. Add 160 mL of glacial acetic acid, and mix. Add 33 g of activated charcoal powder, mix, and dilute with water to 2000 mL. Continually mix the solution at a rate that maintains homogeneity.
Sodium Acetate Solution
Dissolve 500 g of sodium acetate trihydrate in water to make 1000 mL, mix, and filter.
Phenylenediamine Solution
Dissolve 200 mg of o-phenylenediamine dihydrochloride in water to make 1000 mL, and mix. Prepare fresh daily.
USP Reference Standards
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Standard Stock Solution
Dissolve an accurately weighed quantity of USP Ascorbic Acid RS in Dilute Extracting Solution to obtain a solution having a known concentration of about 0.1 mg per mL.
Standard Preparations
Transfer 10.0, 20.0, 30.0, 40.0, and 50.0 mL of Standard Stock Solution to separate 100-mL volumetric flasks, dilute the contents of each flask with Carbon Extracting Solution to volume, mix, and filter to obtain Standard Preparations A, B, C, D, and E having known concentrations of 10 µg, 20 µg, 30 µg, 40 µg, and 50 µg of USP Ascorbic Acid RS per mL, respectively.
Assay Preparation
For Liquid Preparations
Transfer an accurately measured volume of the liquid preparation, equivalent to 150 mg of ascorbic acid, to a 100-mL volumetric flask. Add 10 mL of Extracting Solution and 6 mL of glacial acetic acid. Dilute with water to volume, and mix. Transfer 2.0 mL of this solution to a 100-mL volumetric flask, dilute with Carbon Extracting Solution to volume, mix, and filter.
For Tablet Preparations
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed quantity of the powder, equivalent to about 250 mg of ascorbic acid, to a 250-mL volumetric flask. Add 25 mL of Extracting Solution, 15 mL of glacial acetic acid, and about 100 mL of water, and swirl to mix. Heat for 15 minutes in a 70
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For Capsule Preparations
Empty the contents, if necessary by cutting open with a sharp blade, of not fewer than 20 Capsules in a suitable container, and mix thoroughly. Transfer a portion of the capsule contents, equivalent to about 250 mg of ascorbic acid, to a 250-mL volumetric flask, and proceed as directed for Tablets above, beginning with Add 25 mL of .
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 the Standard Preparations and the Assay Preparation to sample cups, and place in the sampler. Start the sampler, and conduct determinations of each Standard Preparation and the Assay Preparation at the rate of 40 per hour, using a ratio of about 2:1 for sample and wash time. Derive a standard response line by plotting the respective Standard Preparation concentration (10.0, 20.0, 30.0, 40.0, and 50.0 µg 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 C6H8O6 in the portion of liquids, tablets, or capsule contents taken by the appropriate formula:
For Liquids:
5C/V in which V is the volume, in mL, of liquid preparation taken to prepare the Assay Preparation.
For Tablets or Capsules:
12.5C.
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 420 nm, (5) a means of recording colorimetric readings, and (6) a manifold consisting of the components illustrated in the accompanying pertinent diagram.
Reagents
Acetic Acid Carrier Solution
Transfer 3.0 mL of glacial acetic acid to a 2000-mL volumetric flask containing about 800 mL of water. Add 2 mL of polyoxyethylene (23) lauryl ether, and dilute with water to volume.
Surfactant Solution
Prepare a 30% solution of polyoxyethylene (23) lauryl ether by melting 150 g in a container on a steam bath and slowly adding approximately 250 mL of water with continuous stirring. Cool, and dilute with water to make 500 mL.
Arsenious Acid Solution
Transfer 19.6 g of arsenic trioxide and 14.0 g of sodium hydroxide to a 2000-mL volumetric flask. Add about 150 mL of water, and dissolve with stirring. Dilute with water to a volume of about 800 mL, and add 66 mL of sulfuric acid. Cool to room temperature. Transfer 50.0 g of sodium chloride to the solution, and mix to dissolve. Add 2 mL of Surfactant Solution, dilute with water to volume, mix, and filter.
Ceric Ammonium Sulfate Solution
Transfer 12.65 g of ceric ammonium sulfate to a 1000-mL volumetric flask. Add about 700 mL of water followed by 100 mL of sulfuric acid, swirling to mix. Heat to dissolve, and cool to room temperature. Add 1 mL of Surfactant Solution, dilute with water to volume, mix, and filter.
3% Acetic Acid Solution
Transfer 30 mL of glacial acetic acid to a 1000-mL volumetric flask containing about 300 mL of water. Dilute with water to volume, and mix.
Standard Preparations
Standard Stock Solution
Transfer an accurately weighed quantity of 1.3080 g of potassium iodide, previously dried for 24 hours at 105
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Intermediate Standard Solution
Quantitatively dilute a suitable volume of Standard Stock Solution with water to obtain a solution having an iodide concentration of 1 µg per mL.
Working Standard Preparations
Transfer 2.0, 4.0, 6.0, 8.0, and 10.0 mL of Intermediate Standard Solution to separate 100-mL volumetric flasks. Add 5 mL of 3% Acetic Acid Solution. Dilute the contents of each flask with water to volume, and mix to obtain Standard Preparations A, B, C, D, and E having known iodide concentrations of about 0.02 µg per mL, 0.04 µg per mL, 0.06 µg per mL, 0.08 µg per mL, and 0.1 µg per mL, respectively.
Assay Preparation
For Liquid Preparations
Transfer an accurately measured volume of the liquid preparation, equivalent to 16 µg of iodide, to a 200-mL volumetric flask. Add 10 mL of 3% Acetic Acid Solution to dissolve, dilute with deionized water to volume, mix, and filter. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, add 5.0 mL of 3% Acetic Acid Solution, dilute with deionized water to volume, mix, and filter to obtain a solution having an iodide concentration of about 0.08 µg per mL.
For Tablet Preparations
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed quantity of the powder, equivalent to about 250 µg of iodide, to a 250-mL volumetric flask. Add 100 mL of 1 N hydrochloric acid, and mix with the aid of sonication for 30 minutes. Dilute with water to volume, mix, and filter. Transfer 8.0 mL of the filtered solution to a 100-mL volumetric flask, add 5 mL of 3% Acetic Acid Solution, dilute with water to volume, and mix to obtain a solution having an iodide concentration of about 0.08 µg per mL.
For Capsule Preparations
Empty the contents, if necessary by cutting open with a sharp blade, of not fewer than 20 Capsules into a suitable container, and mix thoroughly. Transfer a portion of the capsule contents, equivalent to about 250 µg of iodide, to a 250-mL volumetric flask and proceed as directed for Tablets above, beginning with Add 100 mL of .
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 Preparations and the Assay Preparation to the sampler cups, and place in the sampler. Start the sampler, and conduct determinations of each Standard Preparation and the Assay Preparation at the rate of 30 per hour, using a ratio of about 1:4 for sample and wash time. Derive a standard response line by plotting the respective Standard Preparation concentration (0.02, 0.04, 0.06, 0.08, and 0.10 µg per mL) versus absorbance. [noteThis 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:
For Liquids:
2000C/V in which V is the volume, in mL, of the liquid preparation taken to prepare the Assay Preparation.
For Tablets and Capsules:
3125C.
CONTENT UNIFORMITY OF NITROGLYCERIN TABLETS This is not to be considered as the official method. It is detailed here for further illustration of descriptions of automated methods.
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 545 nm, (5) a means of recording spectrophotometric readings, and (6) a manifold consisting of the components illustrated in the accompanying pertinent diagram.
Reagents
1 Percent Strontium Hydroxide Solution
Dissolve 20.0 g of strontium hydroxide [Sr(OH)2·8H2O] in 1800 mL of carbon dioxide-free water, heating if necessary. Cool to room temperature, dilute with carbon dioxide-free water to 2000 mL, and mix. Allow to stand overnight, and filter. Store the clear solution in tightly closed containers, protected from carbon dioxide.
0.3 Percent Procaine Hydrochloride Solution
Dissolve 3.0 g of procaine hydrochloride in water to make 1000 mL.
0.1 Percent N-(1-Naphthyl)ethylenediamine Dihydrochloride Solution
Dissolve 1.0 g of N-(1-naphthyl)ethylenediamine dihydrochloride in water to make 1000 mL. Prepare fresh each week.
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 30 µg per mL.
Test Preparation
Dissolve 1 Nitroglycerin Tablet in water to obtain a solution having a concentration of about 30 µg of nitroglycerin per mL.
Procedure
With the sample line pumping water, the other lines pumping their respective reagents, and the spectrophotometer set at 545 nm, standardize the system by pumping until a steady absorbance baseline has been established. Transfer portions of the Standard Preparation and the Test Preparation to sampler cups, and place in the sampler. Start the sampler, and conduct determinations of the Standard Preparation and the Test Preparation at a rate of 30 per hour, using a ratio of 1:1 for 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 C3H5N3O9 in the Tablet taken by the formula:
(T / D)C(AU / AS)
in which T is the labeled quantity, in mg, of nitroglycerin in the Tablet; D is 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; C is the concentration, in µg per mL, of nitroglycerin in the Standard Preparation; AU is the absorbance of the Test Preparation; and AS is the average of the absorbances of the two Standard Preparations that bracket the Test Preparation.
Diagram for Automated Drug Release and Content Uniformity Test for Propranolol Hydrochloride and Hydrochlorothiazide Extended-Release Capsules
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USP32NF27 Page 58
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