CHAPTER 1

REMARKS AND GENERAL DIRECTIONS

I. Success as an Analyst

a. The student must have the ff:i. The ability to follow directions under the supervision of a skilled analystii. A fundamental knowledge of the theory as well as a practical ability in the

application of analytical methodsiii. Must know what reactions are taking place during an analysis and be able

to understand and apply the theory upon which the method is dependentiv. Must acquire skill of technique, patience, neatness, and accuracyv. Must not only use common sense in the laboratory but think throughout

each step of the procedurevi. Analysis is carried out not for the sake of analysis but as a means of

controlling the purity and strength of substances used as medicaments

II. Economy of Time- Best achieved through a preliminary study of the work to be done, followed by a

plan for its prompt execution.

The following ideas or suggestions will save time and increase accuracy1. Keep the desk clean at all times2. Clean all apparatus immediately after using it and put it in the desk3. Label all solutions, filtrates, and precipitates4. Keep two or more operations going at one time5. Utilize all time between operations in making calculations and writing up

experiments.

III. Cleaning Solution- Prepared by dissolving 200 g of Sodium dichromate (Na2Cr2O7) in 100

mL of water and then adding 1500 mL of sulfuric acid slowly with stirring.IV. Wash Bottles

- Usually consist of rubber-stoppered, flat-bottomed flasks of 500- to 1000-

mL capacity fitted with smoothly bent tubes and a jet made flexible by means of a rubber joint.

V. Policeman- A piece of soft rubber tubing fitted to the end of a glass rod.

VI. Reagents- Used in quantitative analysis and must be pure.

- Conform to the requirements of USP&NF, should be used in all assays

which have for their purpose the establishment of the strength or quality of official substances

VII. Purity and Strength Requirements The purity and strength of chemicals and drugs of the USP and of the NF are usually

expressed in terms of PERCENT (%).

CALCULATIONS OF RESULTS AND ERRORS

ERRORS

- Refers to the numerical difference between a measured value and the true value.

MAIN TYPES OF ERRORS

1. Indeterminate errors- Manifest themselves by slight variations in a series of observations made by the

same observer under identical conditions2. Determinate errors

- They recur in a constant manner in each of a series of determinations

*Arise from causes such as:

a. Personal Errors – made by the individual analyst

b. Errors of Method – caused by faulty procedure

c. Apparatus Errors – due to poor construction or calibration

ACCURACY AND PRECISION

Accuracy is used to denote the agreement of an experimental result or the agreement of the mean value of a series of experimental result with the true value, and is usually expressed in terms of error.

i. Absolute Error, the difference between the mean and the true value.ii. Relative Error, found by dividing the absolute error by the true value.

Precision is a measure of reproducibility of data within a series of results. Results within a series which agree closely with one another are said to be precise.

AVERAGE DEVIATION is calculated by finding the differences between individual results and the mean, regardless of sign, adding these differences, and dividing by the number of determinations.

i. Relative average deviation is found by dividing the average deviation by the mean. Expressed in terms of percentage or as parts per thousand.

STANDARD DEVIATION is the preferred measure of precision.

i. Relative standard deviation, also known as the coefficient of variation.

RANGE is the difference between the largest and smallest results in a series of measurements

SIGNIFICANT FIGURES are defined as all certain digits of a measurement plus one doubtful digit.

GENERAL OPERATIONS

Crucibles are made of high-grade porcelains. They withstand high temperature and are suitable for use in the ignition of most drugs and precipitates. Consists of: fused silica, alundum, nickel, and platinum.

GOOCH FILTRATION CRUCIBLE is designed for the separation of precipitates by suction filtration.

-Has a perforated bottom upon which is bedded a mat of asbestos, thus making it possible to collect, wash, dry, and weigh a precipitate in the same crucible.

Evaporation of Liquids, best carried out in porcelain dishes.

- Evaporations should, with few exceptions, be carried out on a water bath to avoid

danger of loss of material due to spattering or bumping and to avoid decomposition.

Transfer of Liquids

- When transferring liquid from one vessel to another, a guide rod should always

be used

Drying and Ignition of Samples and Precipitates

- Many substances are directed to be dried under specified conditions before

analysis to correct for absorbed moisture. - Precipitates frequently must be dried previous to ignition.

CONSTANT WEIGHT

Dried to constant weight means that two consecutive weighings do not differ by more than 0.5 mg/g of substance taken for the determination, the second weighing following an additional hour of drying.

- If the exact weight of an object is desired, the object is heated at the specified

temperature, cooled, and weighed- The object is then reheated, cooled, and again weighed. If the two weights agree

within 0.2 mg, constant weight is said to have been reached.- If the change in wt. is more than 0.2 mg, the process of heating, cooling, and

weighing is repeated until constant weight is obtained.

DESSICATORS

- Are a special form of glass vessel, rendered airtight by means of ground contact

surfaces, used to maintain a dry atmosphere for objects that might be affected by moisture or carbon dioxide. Anhydrous Calcium Chloride, a dehydrating agent charged on the lower compartment of the dessicator.

ANALYTICAL BALANCE

- the single-pan balance maintains a constant weight on the beam at all times, and

the object is weighed by displacing its equivalent weight from the beam.

CHAPTER 3

Principles of Titrimetric (Volumetric) Analysis

Titrimetric methods

- Analytical methods in which the volume of a solution of known concentration

consumed during an analysis is taken as a measure of the active constituents in a sample being analyzed.

a. Analyte or active constituent - chemical substance being analyzedb. Titrant- solution of known concentration; usually added by mean of buret

● Titration- act of adding and measuring the volume of titrant used in the assay

● Indicator- chemical which change color at or very near the point in the titration where equivalent quantities of analyte and tirant have reacted

* Stoichiometric or equivalence point- theoretical point at which equivalent amounts of titrant and analyte have reacted

* End point- a change which is made apparent by use of indicators

* Titration - near the end point or is very close to the equivalence point

* Results in drug assays are expressed as w/w%, w/v% or v/v%

* Titrimetric analysis- uses equivalents for calculations

1 equivalent of acid neutralizes exactly 1 equiv of a base, and vice versa. 1 equiv of oxidizing agent reacts with exactly 1 equiv of a reducing agent, and vice versa.

* Equivalent- quantity of a substance that is chemically equivalent to 1.0079 g of Hydrogen ions

* Gram-equivalent weight (GEW) - weight in grams which is chemically equivalent to 1 gram atom of hydrogen ions (1.0079 g). It is the weight of the substance in grams which contains, furnishes, reacts with directly or indirectly, or replaces 1 gram atom of hydrogen ions.

* Gram milliequivalent weight (GmEW) - GEW/1000

* Equivalent- number of GEW in the procedure

* Milliequivalent- number of GmEW involved in the procedure

Normality

- Concentration expressed and is defined as the number of equivalents of solute per liter (equiv/liter) or (meq/liter) of solution

Molarity

- Concentration of a solution in terms of moles per liter

Molality

- Number of solute per 1000g of solvent

Standardization

- Determination of normality and molarity of a solution

a. Primary standard- use of carefully weighed sample of known purityb. Secondary standard- use of another standard solution with known concentration

Standard solution- solution of know molarity or normality

Standard acid solutions used in acidimetry and alkalimetry- HCl used in the titration of compounds that yield a precipitate

- H2SO4 is preferable for hot titrations

Standard alkali solutions - Sodium hydroxide, potassium hydroxide, and barium hydroxide

Titer

- Weight of a substance which is chemically equivalent to 1 ml of a standard solution

Volumetric apparatus

- made to deliver definite volume of liquid, burets ang pipet; made to contain definite volume of liquid, volumetric flasks and graduated cylinders

25 degree Celsius- temperature specified in the USF and NF for volumetric measurements

20 degree Celsius- adopted temperature of national bureau of standard for volumetric apparatus

Milliliter- one thousandth part of a liter; official unit of capacity

Liter- volume occupied by a kilogram of water weighed in a vacuum at 4C

Burets- graduated glass tubes of uniform bore throughout the whole length(mL)

4 types of chemical reactions used in titrimetry

1. Neutralization- acid reacts with a base (product- salt and water)2. Oxidation-reduction3. Precipitation4. Complexation

4 requirements to be met if the reaction is to be used for titrimetric analysis

1. Reaction must proceed to completion; chemical equilibrium constant must be equal or greater than to 108

2. Reaction must proceed to stoichiometric manner3. A suitable end point detecting device must be available4. Direct titration; must be rapid and must have a sharp end point

Indicators

- complex organic compounds used to determine points in neutralization process, to determine hydrogen ion concentration, to indicate a desired change in pH has been effected.

3 theories of change in color of indicators

1. Physicochemical theory- increase in pH causes the appearance of new color, and a decrease in pH causes the disappearance of color or appearance of a different color

2. Organic theory- change in color to a change in molecular structure3. Colloidal theory- change in color depends upon the change in size of the colloidal

particle

Table 3.1 Commonly Used pH indicators

Indicator pH Range Acid BaseMalachite green 0.0 – 2.0 Yellow Green

Methyl yellow 2.9 – 4.0 Red YellowBromophenol Blue 3.0 – 4.6 Yellow Blue

Methyl Orange 3.2 – 4.4 Pink YellowBromocresol green 4.0 – 5.4 Yellow Blue

Methyl Red 4.2 – 6.2 Red YellowBromocresol purple 5.2 – 6.8 Yellow PurpleBromocresol blue 6.0 – 7.6 Yellow Blue

Phenol Red 6.8 – 8.2 Yellow RedCresol Red 7.2 – 8.8 Yellow Red

Thymol Blue 8.0 – 9.2 Yellow BluePhenolphthalein 8.0 – 10.0 Colorless RedThymolphthalein 9.3 – 10. 5 Colorless Blue

Preparation and Standardization

Exercise no.

Title Standard Sample Indicator End point

3.1 Prepare and Standardize 1N

HCL

Anhydrous Sodium

Carbonate- PS

HCl Methyl Red Faint Pink

3.2 1N Sulfuric Acid Sodium Hydroxide- SS

H2SO4 Phenolphthalein Faint Pink

3.3 1N Sodium Hydroxide

Potassium biphthalate-PS

NaOH Phenolphthalein Permanent Pink

Method of analysis (Volumetric)

Analyte Titrant Indicator End point

3.1 – Direct Alkalimetry HCl 1N NaOH Methyl red Faint Pink3.2 -Direct Alkalimetry H2SO4 NaOH Phenolphthalein Faint Pink3.3-Direct Acidimetric NaOH 0.1N H2SO4 Phenolphthalein Permanent Pink

CHAPTER 4

Acidimetric Analysis

Acidimetry

- direct or residual titrimetric analysis of bases using an accurately measured

volume of acid, is supplied in the analytical control of a considerable number of official substances, both inorganic and organic.

Direct Titration

- introduction of a standard acid solution gradually from buret into a solution of the

base being assayed until chemically equivalent amounts of each have reacted as shown by some change in properties (such as color) of the mixture.

Residual Titration/ Back Titration

- used whenever the end point of a direct deviates appreciably from the steriochiometric points for some reason.

- Used when a reaction proceeds slowly or when the substance to be assayed does not give a distinct sharp endpoint with an indicator by direct titration.

Assay of Potassium Sodium Tartrate

- The NF requires that Potassium Sodium Tartrate contain not less than 99%

and not more than 102% of C4H4KNaO- Methyl red- methylene blue is used as the indicator, since the boiling process

rids the solution of any carbon dioxide which may affect the equivalence point of the titration.

- Methyl red- Methylene blue- Red violet (acid) to dirty blue (transition state) to

green (alkaline)

Assay of Milk of Magnesia

- USP Requirements: Not less than 7% and Not more than 8.5%

Assay of Drug Sample

Exercise No. Title Method of Titration

Chemical Reaction Involved

Method of Analysis

4.1 Sodium Bicarbonate Direct Neutralization Acidimetric4.2 Sodium Hydroxide Direct Neutralization Acidimetric4.3 Sodium Salicylate

TabletsDirect Neutralization Acidimetric

4.4 Zinc Oxide Residual Neutralization Acidimetric4.5 Potassium Sodium

TartrateResidual Neutralization Acidimetric

4.6 Milk of Magnesia Residual Titration

Neutralization Acidimetric

4.7 Methenamine Residual Neutralization Acidimetric4.8 Ammonium Chloride

injectionResidual Neutralization Acidimetric

4.5 Potassium Sodium Tartrate

Residual Neutralization Acidimetric

4.6 Milk of Magnesia Residual Titration

Neutralization Acidimetric

4.7 Methenamine Residual Neutralization Acidimetric4.8 Ammonium Chloride

injectionResidual Neutralization Acidimetric

Analyte Titrant Indicator EndpointSodium Bicarbonate 1N Sulfuric Acid Methyl Orange Faint PinkSodium Bicarbonate 1N Sulfuric Acid Methyl Orange or

PhenolphthaleinPink

Sodium Salicylate 0.1N HCL Bromophenol Blue Pale Green ColorZinc Oxide 1N Sulfuric Acid

1N Sodium Hydroxide

Methyl Orange Yellow (hot)Colorless (cool)

Potassium Sodium Tartrate

0.5 N Sodium Hydroxide

0.5N Sulfuric Acid

Methyl red-methylene blue

Green

Magnesium Hydroxide 1N Sulfuric Acid

1N Sodium Hydroxide

Methyl Red Yellow

Methenamine 1N Sulfuric Acid Methyl Red Disappearance of Violet Color

Ammonium Chloride 0.1 N Sulfuric Acid Methyl Red Red

CHAPTER 5

Alkalimetric Analysis

ALKALIMETRIC ANALYSIS

- As a general principle, it is recommended that the normality of the solution obtained by dissolving the acid sample be approximately the same as that of the titrant.

* Methyl red or phenolphthalein is used as indicators for inorganic acids.

* Phenolphthalein is frequently used as indicator for organic acids; however, thymol blue, bromothymol blue, and thymolphthalein are also employed.

* Potentiometric methods are also used in determining the endpoint.

* Direct titration requires only one standard solution, the standard base, and fewer measurements of volume.

* Residual titration methods are used:

- Whenever direct titrations are not practicable- Applied to official compounds which react too slowly because of poor solubility; otherwise a

heating process is used or precipitation method is used to convert the substance for reaction with the standard base.

-

Assay of Drug Sample

Exercise No. Title Method of Titration

Chemical Reaction Involved

Method of Analysis

5.1 Hydrochloric Acid Direct Neutralization Alkalimetric5.2 Diluted Phosphoric

AcidBlank Neutralization Alkalimetric

5.3 Boric Acid Direct Neutralization Alkalimetric5.4 2-Phenoxyethanol Blank Neutralization Alkalimetric5.5 Tartaric Acid Direct Neutralization Alkalimetric

Analyte Titrant Indicator EndpointHCl 1N Sodium Hydroxide Methyl Red Pink

Diluted Phosphoric Acid 1 N Sodium Hydroxide Thymolphthalein BlueBoric Acid 1 N Sodium Hydroxide Phenolphthalein Pink

2-Phenoxyethanol 1 N Sodium Hydroxide PhenolphthaleinTartaric Acid 1 N Sodium Hydroxide Phenolphthalein

CHAPTER 6

Nonaqueous Titrimetric Analysis

Kjeldahl method – used to determine other organic compounds containing nitrogen

- Moisture is to be avoided in using nonaqueous procedures, since water, being weakly basic, would compete with the weak nitrogen base for the HClO4.

- Moisture content: Less than 0.05%- Greater care in the control of temperature during standardization and analysis

procedures must be considered.

Neutralization

- Neutralization is a reaction between hydrogen ions and hydroxide ions in aqueous solutions of acids and bases

- In dioxane (Neutral solvent), or glacial acetic acid, an acidic solvent, perchloric acid HClO4, is less protophyllic than HCl, and chlorides can be titrated in aqueous solution with standard HCl.

End Points

- Indicators used in neutralization reactions in water are in themselves weak acids or bases which undergo color changes with changes in pH.

- Substances of different acid strength require different indicators to detect the end point of titration

Acidimetry in Nonaqueous Solvents- Weak bases which do not meet this requirement cannot be titrated with accuracy in

aqueous systems because the solvent, water, competes with the basic species in solution for the proton of the titrant.

- To conduct titrations of weak bases, solvent must be changed to eliminate the competing chemical reaction of h20 for the proton

- Titrimetric analysis of a number of weakly basic substances in glacial acetic acid is possible using a standard solution of perchloric acid as the titrant.

Solvents

- Solvents used in acidimetric titrimetry are either neutral or acidic in nature

- Neutral solvents – acetonitrile, alcohols, chloroform, benzene, dioxane, ethyl acetate (aprotic or amphiprotic in nature)

o Used for solvency action primarilyo Do not enhance dissociation

- Acidic solvents – formic, glacial acetic, proprionic acids, acetic anhydride, sulfonyl chloride

o Used for weak bases and their salts

Titrant

- Perchloric Acid – most valuable and widely used titrant in glacial acetic acido Strongest of the known common acids

- Hydrogen Bromide – also used to a limited extent as titrants

Indicators

- Crystal violet, methylrosaniline chloride, quinaldine red, alpha-naphtholbenzein, malachite green

o Indicators for titration of weak bases and their salts- Methyl red, methyl orange, thymol blue

o For stronger bases- Crystal violet – gives visual end point with less than 0.1 ml of titrant at potentiometric end

point

Alkalimtery in Nonaqueous Solvents- Weakly acidic substances can be titrated in an appropriate nonaqeuous solvent with a

sharp end point- Organic compounds involved: acid halides, anhydrides, acids, amino acids, enols such

as barbiturates and xanthenes, imides, phenols, sulfonamides, and organic salts of inorganic acids

- Boric acid – easily titrated using ethylenediamine as solvent

Solvents

- Factors which can be considered in choosing a basic solvent are:o Solubility of the substance to be analyzedo Relative base strength of the solvent

- Strong bases – ethylenediaminem n-butylamine, morpholine- Weak bases – dimethylformamide and pyridine (used for medium-strength acidic

substances- Sulfonamides which contain an n-alkyl substituent possess low acidity; ethylenediamine

would be the solvent of choice for this- N-phenyl or n-pyridyl-substituted sulfonamides; dimethylformamide – preferred solvent- Solvent dimethylformamide + thymol blue – only sulfathiazole will react with sodium

methoxide

Titrants

- Sodium methoxide and lithium methoxideo Bases used for the titration of acidic compounds

- Potassium methoxide – stronger titrant; not used because it may produce a gelatinous reaction product.

- Other base titrants: sodium aminomethoxide(strongest base)o Sodium triphenylmethane: for weakly acidic compounds such as phenols and

pyrroles- Atmospheric moisture and c02 will interfere with metal alcoholate titrations- Blank should not exceed 0.01 ml of titrant per ml of solvent used

Indicators

Potentiometric titration – currently the best way of determining the quivalence point of a given chemical reaction in nonaqueous titrimetry

Azo violet – indicator of choice in the titration of acids of weak or intermediate strength in n-butylamine solvent

Thymol blue – indicator of choice for the determination of intermediate to strong acids in dimethylformamide solvent

Ethylenediamine – solvent for strong acids

In metal alcoholate, azo violet will change in color before thymol blue

O-nitroaniline – for titration of very weak acids

Azo violet/thymol blue endpoint: clear blue color

Other indicators – thymolphthalein and p-hydroxyazobenzene

Preparation and Standardization

Exercise No. TitleStandard

UsedSample Indicator Endpoint

6.10.1N Perchloric

acidPrimary

Potassium Biphthalate

Crystal VioletViolet color will change

to emerald green

6.30.1 N Sodium

MethoxidePrimary Benzoic Acid Thymol blue Blue endpoint

Assay of Drug Sample

Exercise No.

Title

Method of

Titration

Chemical Reaction Involved

Method of

AnalysisAnalyte Titrant

Indicator

Endpoint

6.2 Methacholine Chloride

Blank Titration

Neutralization

Volumetric Analysis

Methacholine Chloride

0.1 N Perchloric

Acid

Crystal Violet

*

6.4 PhenytoinDirect

TitrationNeutralizatio

nVolumetric Analysis

Phenytoin

0.1 N Sodium

Methoxide

Azo Violet

*

CHAPTER 7

Precipitation and Complexation Methods of Analysis

Volumetric Precipitimetry

– Class of reactions is dealt with that require formation of insoluble substances or precipitates to go to sufficient completion to be quantitative in nature.

Determination of Endpoint: (a) Cessation of precipitation or appearance of turbidity (b) Use of internal indicators (c) Instrumental methods – potentiometric, amperometric

Indicators:(a) Ferric ammonium sulfate, ts – thiocyanate reacts with silver or mercuric ions present

to form white precipitate of silver or mercuric thiocyante but as the silver/mercury has precipitated, the thiocyante ion reacts with ferric ammonium sulfate to form red ferric thiocyante. RED COLOR MARKS THE ENDPOINT OF REACTION.

(b) Potassium chromate, ts – forms red precipitate of silver chromate against the background of white silver chloride

(c) Adsorption indicatorsDichlorofluorescein (DCF), Eosin Y TS, Tetrabromophenolphthalein ethyl ester (TEE) – prepare them fresh. They are used in the analyses of halides by direct titration with silver nitrate solution. They are weak organic acids that vary in strength. Endpoint: color of the silver halide precipitate changes abruptly because of adsorbed indicator anions. Best seen in a diffuse light condition.

Direct Titration Method- Silver and mercury can be converted into soluble salts – estimated by direct titration with

standard ammonium thiocyanate solution using ferric ammonium sulfate as indicator. Solution must be acidified with HNO3 to prevent hydrolysis that ferric slats undergo in neutral solution. Chlorides must be absent.

Residual Titration (Volhard) Method- Based on complete precipitation method of insoluble silver salts from nitric acid solution

by addition of excess standard silver nitrate solution to a soluble salt, and determination of amt of silver nitrate solution in excess by residual titration with standard ammonium thiocyanate solution using ferric alum as indicator. Produces slightly soluble silver salts:

chlorides, bromide, iodide, cyanide, thiocyanate, sulfide, phosphate, arsentaes, carbonates

Sodium Tetraphenylboron titration- Na(C6H5)4B, will precipitate organic nitrogen compounds like alkaloids, amines,

quaternanry salts, potassium, ammonium, silver ions- Quaternary compounds will react with bromophenol blue to form blue chloroform soluble

complex, to react with tetraphenylboron to form insoluble compound.

COMPLEXATION METHODS- Quantitative analysis of inorganic pharmaceutical product with metal ions like Al, Bi, Ca,

Mg, Zn- Procedures are time-consuming, since they involve precipitation, filtration, washing,

drying or ignition

Complexation reaction:

Complex – when a metal ion combines with a molecule which can donate electrons. chelate –If the combining molecule contains two or more groups that donate electrons.

EDTA (H4Y) is a hexadentate that will react with metal ions to form water-soluble, stable complex, chelate compounds.

Ligand-attachment to metal ions. EDTA has MW of 372.24 in 1/20 M solution. Or 18.612 g in 1 L of solution.

* Direct (Monovalent), Residual (Polyvalent), Ferric Chloride Titration (based on reaction of sodium fluoride with ferric chloride to form a reasonably stable complex type of Fef6 3-.

Masking - Determination of metal in presence of another metal. Capable of entering another complexation reaction (adjusting pH of titration medium)

TriethanolamineThioglycolsPotassium cyanideAmmonium fluorideAscorbic acid, citrates and tartrates

Preparation and Standardization

Exercise No.

Title Standard Used

Sample Indicator End point

7.1 0.1 N Silver Nitrate Secondary Silver Nitrate HCl Precipitate7.2 0.1 N Ammonium

ThiocyanateSeconday Ammonium

ThiocyanateFerric ammonium Sulfate

Red-brown color

7.10 0.02 M Sodium Secondary Sodium Potassium Precipitate

tetraphenylboron tetraphenylboron biphthalate7.11 0.05 M Disodium Ethylene

diaminetetraacetatePrimary Calcium

carbonateHydroxynaphthol blue

Blue Color

Assay of Drug Sample

Exercise No.

Title Method of Titration

Chemical Rxn Involved

Method of Analysis

7.3 Phenyl Mercuric Nitrate for Mercury Content

Direct Precipitation Volumetric

7.4 Sodium Lauryl Sulfate for Sodium Chloride Content

Direct Precipitation Volumetric

7.5 Iopanoic Acid Tablets Direct Precipitation Volumetric7.6 Benzyltrimethyammonium chloride Direct Precipitation Volumetric7.7 Sodium Chloride Residual Precipitation Volumetric7.8 Iodine Content in Povidone-Iodine Blank Precipitation Volumetric7.9 Theophylline Residual Precipitation Volumetric

7.12 Determination of the Bismuth Content of Glycobiarsol

Residual Complexation Volumetric

Analyte Titrant Indicator EndpointPhenyl Mercuric Nitrate 0.1 N Ammonium

thiocyanateFerric ammonium sulfate Red Precipitate

Sodium Lauryl Sulfate 0.1 Silver Nitrate Potassium Chromate Red PrecipitateIopanoic Acid 0.05 N Silver Nitrate Tetrabromophenolphthalei

n ethyl esterYellow precipitate

Benzyltrimethylammonium Chloride

Dichlorofluorescein TS

0.1 N Silver nitrate Precipitate

Sodium Chloride Silver Nitrate & 0.1 N Ammonium Thiocyanate

Ferric Ammonium Sulfate Red Precipitate

Povidone-Iodine Silver Nitrate with 0.1 N ammonium

thiocyanate

Ferric ammonium Sulfate Red Precipitate

Theophylline Silver Nitrate and Ammonium Thiocyanate

Ferric ammonium sulfate Red Precipitate

Glycobiarsol Disodium EDTA and 0.025 M zinc sulfate

Dithizone TS, Alcohol, Acetic acid-ammonium

acetate buffer

Clear Rose Pink Color

CHAPTER 8

Oxidation Reduction Methods

- Simplest type of oxidation reduction is the direct combination of elements.

Oxidation reduction that take place in the official assay processes are, for the most part, between electrolytes in aqueous solution. Their quantitative value is based upon the fact that metals, nonmetals, and their ions, under suitable conditions, can be made to undergo a change in the quantity of electric charge associated with them and that in the change there exists a simple relationship between quantity of electricity lost or gained and the weight of the reacting substances.

Faraday’s Law – a change in charge of one is equivalent to the gain or loss of 96500 C of electricity for each formula weight of element or group of elements involved.

Reducing agent – reactant which loses electrons in an oxidation-reduction reaction

Oxidizing agent – reactant containing a constituent atom or atoms which are converted to a lower state of oxidation

* The equivalent weight of a reducing agent is that weight which loses electrons equivalent to 96500 C

* The equivalent weight of an oxidizing agent is that weight which gains electrons equivalent to 1 faraday

Standard Solutions

Oxidizing agents Reducing agentsFerric ammonium sulfate Ferrous ammonium sulfatepotassium permanganate oxalic acidpotassium dichromate potassium arsenitepotassium bromated titanium chloridepotassium iodate sodium thiosulfatepotassium ferricyanideceric sulphate

Iodinebromine

* Nitric acid – does not undergo a single uniform reaction even though conditions are carefully controlled

Permanganate Methods

- Potassium permanganate solution can be standardized easily and retain its concentrations over long periods of time

- Reaction is rapid- Serves as an indicator in titrations where it is used; slight excess of permanganate

imparts distinct pink color

Indirect Titration Methods

- Employed with those compounds that can be converted through chemical reactions to an equivalent amount of oxalate, which in turn can then be quantitatively oxidized by permanganate.

Residual Titration Methods

Two types:

o Titration in which an excess of standard potassium permanganate solution is employed to oxidize a substance, and the amount in excess is determined by reduction with:

Excess standard oxalic acid Excess ferrous ammonium sulfate and back titration with more

standard potassium permanganateo Titration in which an excess of standard oxalic acid solution is added to the

substance and the excess oxalic acid is titrated with standard potassium permanganate

* Advantage of ferric alum over oxalic acid is that no heating is required to initiate reaction of the reducing reagent with the permanganate

* Since permanganate-oxalate reaction is run at elevated temperatures, it is not practical to titrate permanganate directly with a standard oxalate solution.

Ceric Sulfate Titration Methods

- Ceric sulfate in diluted Sulfuric Acid is a strong oxidizing agent and considerably more stable than standard permanganate solutions

- Ceric sulfate combine many of the advantages of permanganate and dichromate:o Solutions are stable even on boilingo React quantitatively with oxalate or arsenite standardo Cerous ion is colorless and does not obscure the indicator end pointo No interemediate products are formed in the reduction of ceric ceriumo High concentrations of chloride ion are not oxidized by ceric salts, so that

ferrous iron can be determined in the presence of chlorideso Ferrous phenanthroline ion is a very satisfactory indicator in titrations with

ceric salts

Orthophenanthroline Test solution

- Dissolves readily in aqueous solutions of ions known as ferroin which have an intensely red color

- Strong oxidizing agents convert the ferrous to a ferric complex which has a slight blue color

- The color change, red to blue, is reversed by reducing agents- Blue oxidized form is very stable to further change by strong oxidizing agents

Assay of ascorbic acid

- Dichlorophenol-indophenol: standard oxidizing agent in determination of ascorbic acid content of ascorbic acid tablets and injection, as well as of the ascorbic acid content in hexavitamin and decavitamin capsules and tablets

- No indicator is necessary

Preparation and Standardization

Exercise No.

Title Standard Used

Sample Indicator Endpoint

8.1 Potassium Permanganate

Primary *Sodium Oxalate

*Permanganate Solution

Pale Pink Color

8.6 of 0.1 N Oxalic Acid

Secondary Oxalic Acid *Permanganate Solution

Pale Pink Color

8.8 0.1 N Ceric Sulfate Arsenic Trioxide

Orthophenanthroline Solution

Pale Blue

Assay of Drug Sample

Exercise No.

Title Method of Titration

Chemical Rxn Involved

Method of Analysis

8.2 Hydrogen Peroxide Solution Direct Redox Volumetric

8.3 Cherry Juice for Malic Acid Indirect Redox Volumetric

8.4 Manganese Dioxide, Precipitated Indirect Redox Volumetric

8.5 Titanium Dioxide Indirect Redox (Reduction)

Volumetric

8.7 Sodium Nitrite Residual Redox (Reduction)

Volumetric

8.9 Ferrous Sulfate Tablets *Residual Redox (Oxidation-Reduction)

Volumetric

Analyte Titrant Indicator Endpoint

Hydrogen Peroxide0.1 N Potassium Permanganate

--

Cherry juice(for malic acid)0.1 N Potassium Permanganate

--

Manganese Dioxide0.1 N Potassium Permanganate

--

Titanium Dioxide0.1 N Potassium Permanganate;

Ferric Ammonium Sulfate

Sodium Nitrite0.1 N Potassium

Permanganate; 0.1 N Oxalic Acid

Ferrous sulfate0.1 N Ceric Sulfate;

Sulfuric Acid Orthophenanthroline Slight blue color

Hydrogen Peroxide 0.1 N Potassium --

Permanganate

Cherry juice(for malic acid)0.1 N Potassium Permanganate

--

CHAPTER 9

Oxidation Reduction: Iodimetric and Iodometric Methods

Ascorbic Acid- Is a fairly strong reducing agent and is determined by simple titration with iodine

solution, which oxidizes the ascorbic acid to dehydroascorbic acid. Iodine is reduced to Iodide.

* Organic arsenical can be determined as trivalent or pentavalent arsenic.

LIBERATION OF IODINE FROM POTASSIUM IODIDE AND TITRATION WITH SODIUM THIOSULFATE

- Substances that are oxidizing agents which cannot be determined by direct titration are assayed indirectly. In this method, an equivalent amt of iodine produced by the oxidation of the iodide ion in an acid medium by the substance is determined by a standard solution of a reducing agent such as sodium thiosulfate.

OXIDATION-REDUCTION WITH 0.1 N BROMINE

- Bromine is employed as an oxidizing agent in place of iodine in assay of aniline, phenol, resorcinol.

Preparation and Standardization

Exercise. No.

Title Standard Used

Sample Indicator Endpoint

9.1 0.1 N Iodine Solution Primary Iodine Solution Starch TS Appearance of Blue Color

9.3 0.1 N Sodium Thiosulfate Primary Sodium Thiosulfate

Starch TS Disappearance of Blue color

9.4 0.1 N Potassium Arsenite Solution

Primary Potassium Arsenite Solution

Starch TS

9.11 0.1 N Bromine, Koppeschaar’s Solution

Primary Bromine Starch TS

9.14 0.05 M Potassium Iodate Primary Potassium Iodate Starch TS9.16 0.1 M Sodium Nitrite

SolutionPrimary Sodium Nitrite Starch TS

Assay of Drug Sample

Exercise No.

Title Method of Titration

Chemical Rxn Involved

Method of Analysis

9.2 Antimony Potassium tartrate Direct Oxidation-Reduction

Volumetric

9.5 Strong Iodine Solution Direct Oxidation-Reduction

Volumetric

9.6 Methionine Blank Oxidation-Reduction

Volumetric

9.7 Selenium Sulfide Blank Oxidation-Reduction

Volumetric

9.8 Sodium Hypochlorite Solution Residual Oxidation-reduction volumetric

9.2 Antimony Potassium tartrate Direct Oxidation-Reduction

Volumetric

9.9 Cupric sulfate blank Oxidation-reduction volumetric9.10 thyroid blank Oxidation-reduction volumetric

9.12 phenol blank Oxidation-reduction volumetric9.13 Ethacrynic acid blank Oxidation-reduction volumetric9.15 Potassium Iodide Direct Oxidation-reduction volumetric

Analyte Titrant Indicator EndpointPotassium tartrate 0.1 N Iodine Starch TS Blue color

Strong Iodine 0.1 N Potassium Arsenite

Starch TS

Methionine Iodine & 0.1 N sodium thiosulfate

Starch TS Disappearance of blue color

Selenium Sulfide 0.05 N Sodium thiosulfate

Starch TS

Sodium hypochlorite Liberated iodine and 0.1 n sodium

thiosulfate

Starch ts

Potassium tartrate 0.1 N Iodine Starch TS Blue colorStrong Iodine 0.1 N Potassium

ArseniteStarch TS

Methionine Iodine & 0.1 N sodium thiosulfate

Starch TS Disappearance of blue color

Cupric sulfate Liberated iodine with 0.1 N sodium

thiosulfate

Starch ts

thyroid 0.1 N sodium thiosulfate

Starch ts

phenol 0.1 N sodium thiosulfate

Starch ts

Ethacrynic acid 0.1 N sodium thiosulfate

Starch ts

Potassium iodide 0.05 M Potassium Iodate

Starch ts

Type of Titration

Titrant Primary Standar

d

Indicator Endpoint

Iodimetry Direct 0.1 N Iodine As2O3 Starch TS Appearance of Blue ColorIodometry Indirect 0.1 N Na2S2O3 K2Cr2O7 Starch TS Disappearance of Blue

Color

CHAPTER 10

Gravimetric Analysis

The Chemical reactions in gravimetric analysis:

a. Reversible Reactions

- Most of the reactions involved in quantitative analysis are of the reversible type.

Three general conditions tend to prevent reversal and lead to completion of a reaction:

(1) The formation of insoluble gas

(2) The formation of a sparingly soluble gas

(3) The formation of very slightly ionized molecules

b. Law of mass action

- the rate of a reaction is proportional to the product of the molecular concentrations of the reacting.

*at a definite temperature the equilibrium constant is a fixed value for any given reaction irrespective of the concentration of the substances present.

c. Solubility product principle

- The product of the concentration of the constituent ions in a saturated solution of a difficulty soluble salt for any given temperature is practically a constant, each concentration

being raised for a power equal to the relative number of ions supplied by bone molecule of the salt upon dissociating.

Table 10. 1Solubility Products of Some Important Salts

Substance Temperature, Celsius

Ions involved Solubility Product

Aluminum Hydroxide 25 Al3+¿¿ + 3OH− 1 x10−33

Barium Carbonate 25 Ba2+¿¿ + CO32−¿¿

8.1 x10−9

Barium Sulfate 25 Ba2+¿¿ + SO42−¿ ¿

1.1 x10−10

Calcium Carbonate 25 C a2+¿ ¿ + CO32−¿¿

8.7 x 10−9

Calcium Oxalate 25 C a2+¿ ¿ + C2O42−¿¿

2.6 x10−9

Calcium Sulfate 25 C a2+¿ ¿ + SO42−¿ ¿

1.9 x10−14

Lead carbonate 18 Pb2+¿¿ + CO32−¿¿

4.0 x 10−8

Lead sulfate 18 Pb2+¿¿ + SO42−¿ ¿

1.1 x10−13

Magnesium Ammonium Phosphate

25 M g2+¿¿ + NH 4+¿¿

+

PO43−¿¿

2.5 x10−11

Magnesium Hydroxide 18 M g2+¿¿ + 2OH−1.5 x10−5

Magnesium Oxalate 18 M g2+¿¿ + C2O42−¿¿

8.8 x10−50

Mercuric sulfide 18 H g2+¿ ¿ + S2−¿¿1 x10−18

Mercurous chloride 25 H g2+¿ ¿ + 2Cl−¿¿1.5 x10−13

Silver bromide 25 A g+¿¿ + Br−¿¿7.7 x10−10

1.5 x10−10

Silver chloride 25 A g+¿¿ + Cl−¿¿

Silver iodide 25 A g+¿¿ +l−¿ ¿1.5 x10−16

Silver thiocyanate 25 A g+¿¿ +SCN−¿¿1.2 x10−12

d. common ion effect

- the equilibrium constant does not change, no matter what the concentration of the reacting substances may be. The relative concentration of the reacting substances may change, but there is no change in the equilibrium constant.

Gravimetric methods:

Gravimetric Analysis, the measurement of the weight of a substance in a sample ot calculation of the weight of a substance in a sample from the weight of a chemically equivalent amount of some other substances, can be accomplished in various ways.

2 ways to accomplish gravimetric analysis:

Physical method - is the separation by extraction of a constituent in a natural stated and weighing of the final product.

Chemical method -is te separation by precipitation or other means of a chemical compound to the analyst and weighing of the final product

General reaction:

A + B = C + D

Example:

NaCl + AgNO3 = AgCl + NaNO3

A chemically equivalent amount of some product can be obtained from a reactant, i.e., the component of the sample being assayed, by one of the various methods:

(1) It may be precipitated from solution

(2) It may be a decomposition product resulting from ignition of a compound

(3) It may be deposited on an electrode by electrolysis etc.

Determination of Chlorine in a Soluble Chloride

The silver chloride which precipitates is collected on a filter, washed, dried and weighed. Other substances that form insoluble silver salts must be absent from the sample.

Determination of Sulfate Ion in a soluble sulfate

The sulfate ion in a soluble sulfate may be determined gravimetrically by precipitation as barium sulfate, the precipitate being collected, dried, ignited weighed

Determination of the phosphate in sodium phosphate solution

The phosphate is precipitated as magnesium ammonium phosphate, washed, dried, ignited to the pyrophosphate, and weighed

Precipitation

Precipitant Product

Determination of Chlorine in a Soluble Chloride

AgNO3 AgCl

Determination of Sulfate Ion in a soluble sulfate

BaCl2 BaSO4

Determination of the phosphate in sodium phosphate solution

H2S HgS

Exercise No.

Title Method of Titration

Chemical Reaction

Method of Analysis

Analyte Titrant Indicator Endpoint

Involved10.1 Sodium Chloride Gravimetric Silver

Nitrate10.2 Sodium Lauryl

SulfatePrecipitation Gravimetric Barium

Chloride TS

10.3 Mercaptomerin Na

Gravimetric

10.4 Sodium Phosphate

Gravimetric Magnesia Mixture

Assay of Drug Sample

CHAPTER 11

Ash and Water Determination

Ash Content- Residue remains after incineration.- Inorganic matter added to the crude drug for the purpose of adulteration.

Ash Determination- A basis for judging the identity and cleanliness of a drug and gives information

relative to its adulteration with inorganic matter.

Total Ash- The residue remaining after incineration.- Usually contains carbonates, phosphates, sulfates, chlorides, oxides, etc., of

calcium, magnesium, potassium, sodium, aluminum, iron, and other metallic elements, does not necessarily represent all the inorganic constituents of the drug, since ammonium salts, some alkali iodides and nitrates, etoc., are volatilized or converted to carbonates, etc.

Acid-insoluble Ash- Part of the total ash which is insoluble in diluted hydrochloric acid.

*The diluted hydrochloride acid dissolves the calcium carbonate, alkali chlorides, etc., leaving an acid-insoluble residue that consists almost entirely of silica derived from the soil adhering to the drug.

TemperatureVery dull-red heat 500 to 550˚CDull-red heat 550 to 700˚CBright-red heat 800 to 1000˚C

Yellow-red heat 1000 to 1200˚CWhite heat 1200 1600˚C

Residue on Ignition- The ash content of chemicals is determined by ignition to dull redness in the same

manner as in the determination of the ash content of the crude drug.- It is economically impracticable to make ash determinations on large samples of

expensive chemicals.- Neglible is defined as a quantity not exceeding 500 microgram.

Loss on Ignition- These technique provides a means of determining the percentage of test material

which is volatilized and driven off under the conditions specified.- Substances which have a definite limitations on the amounts of volatile matter they

will lose when heated: USP calamine, magnesium sulfate, titanium dioxide, zinc oxide, NF calcium phosphate, tribasic, kaolin, lime, magnesium hydroxide, magnesium phosphate.

Water Content- To ensure uniformity in the official drugs, it is necessary that the USP and the NF

specify certain water-content limits in the drug monographs.- Water content is generally determined by one of six methods:

Gravimetric, for drugs containing no constituents, other than water, volatile at 105˚C;

Gravimetric, for drugs containing ether-soluble constituents volatile at 105˚C; Azeotropic (Xylene – USP; Toluene – NF); Titrimetric (Karl Fischer); Dew point; Electrolytic hygrometric.

- The water content is also the moisture content of the drug.

Formulas:

% AshContent= Wt of ResidueWt of t he Sample

x 100

% Insoluble Ash=Wt of Residue AfterTreatment of Diluted HClWt of t he Sample

x100

%Residue on Ignition=Wt of Residue After IgnitionWt of t he Sample

x100

% Loss of Ignition=Wt of Chemical Substance−Wt of Residue After IgnitionWtof C hemical Substance

x100

% Sulfated Ash=Wt of Residue after treatment of Conc .H 2SO 4Wt of t he Sample

x 100

Gravimetric Method

%Moisture Content=Wt of SampleBefore Drying−Wt of Sample After DryingWt of the Sample Before Drying

x100

%Moisture Content=Wt of SampleBefore Drying−Wt of Ether Sol . ExtractWt of Sample Before Drying

x 100

Azeotropic Method

%Moisture Content=Vol of Water LayerWt of Sample

x 100

Karl Fischer MethodStandard Solution – Karl Fischer SolutionKarl Fischer Reagent

o Primary Standard – Sodium Tartrateo Secondary Standard – Water-Methanol Solution

%Moisture Content=S (Vol of K .F .Reagent )−F (Water Equivalent Factor)

Wt of the Sample (mg)x100

F=Wtof Primary StandardVol of K . F . Reagent

x 100

CHAPTER 14

Assay of Volatile Oils

Volatile Oils – ethereal oils, essential oils, or essences. They are generally complex products composed of mixtures of compounds of widely variant characteristics:

The most important chemical components of official volatile oils are:

1. Hydrocarbons – occasionally acyclic series, such as heptanes and myrcene but more often isocyclic series.

Ex: pinene, camphene, limonene, bornylene, fenchene, dipentene, sylvestrene, and phellandrene.

2. Alcohols – present in both the free state and in combination with acids as esters

Ex: linalool, geraniol, citronellol, terpineol, borneol, menthol, and santalol

3. Aldehydes – examples are benzaldehyde, cinnamic aldehyde, salicyl aldehye, citral, and citronellal

4. Ketones – examples are camphor, carvone, fenchone, thujone, and menthone

5. Phenols – examples are anethol, eugenol, carvacrol, safrol, chavicol, and thymol

6. Acids – sometimes present In the free state in small quantities

Ex: acetic, propionic, butyric, valeric, benzoic, cinnamic, and hydrocyanic acids.

More often they occur in combinations with alcohols mentioned under 2 as esters, e.g., linalyl acetate, bornyl acetate, and menthyl acetate.

7. Sulfur compounds –allyl isothiocyanate (mustard oil)

Preparation and Standardization

Exercise No.

Title Standard Used Sample Indicator Endpoint

14.1 Alcoholic Potassium Hydroxide

Primary Lead acetate

Phenolphthalein TS

Pale Pink

Assay of Drug Sample

Exercise No.

Title Method of Titration

Chemical Reaction Involved

Method of Analysis

14.2 Peppermint Oil for Total Esters

Blank

14.3 Peppermint Oil for Total Menthol

Blank

14.4 Benzaldehyde Blank14.5 Caraway Oil14.6 Clove Oil14.7 Cinnamon14.8 Peppermint Spirit

Analyte Titrant Indicator EndpointPeppermint Oil 0.5 N HCl Phenolphthalein TS Faint PinkPeppermint Oil 0.5 N Sulfuric Acid Phenolphthalein TSBenzaldehyde 1 N NaOH Bromophenol Light-green

Phenophthalein TSKOH TS