Pharmaceutical analysis: titrimetric and instrumental methods

In short

Pharmaceutical analysis is the set of procedures used to identify a drug substance, assay how much of it is present and prove that impurities are within limits. Titrimetry (volumetric analysis) does this by reacting the analyte with a standard solution to a visible or instrument-detected end point; instrumental methods measure a physical property - potential, current, conductance, emission, rotation, heat flow - that varies with concentration. Both are the backbone of pharmacopoeial testing: the Indian Pharmacopoeia 2026 (10th edition, in effect from 1 July 2026), published by the Indian Pharmacopoeia Commission, Ghaziabad, is the legal book of standards under the Drugs and Cosmetics Act, 1940, and most IP assays of inorganic and simple organic drugs are still titrimetric. Universities examine this as Pharmaceutical Analysis I and II (PCI/AICTE B.Pharm curriculum); GPAT, NIPER JEE and drug-inspector exams draw heavily on equivalence factors, indicators and limit tests. Every QC analyst interview at Cipla, Sun Pharma, Dr Reddy's, Zydus, Torrent, Lupin, Aurobindo, Hetero, Mankind, a state FDA lab or a CDSCO/CDL laboratory begins with these questions.

Explained

Fundamentals: standards, concentration and equivalence

• Analysis types: *qualitative* (identity tests, colour reactions, IR/UV identity), *quantitative* (assay, % w/w or % of label claim), *limit tests* (semi-quantitative upper bound on an impurity).
• Primary standard: high purity, stable, non-hygroscopic, high equivalent weight, accurately weighable - potassium hydrogen phthalate (KHP), oxalic acid, potassium dichromate, sodium carbonate (anhydrous), zinc metal, benzoic acid, sodium chloride (for AgNO₃), arsenic trioxide.
• Secondary standard: needs standardisation against a primary standard - NaOH, HCl, H₂SO₄, KMnO₄, Na₂S₂O₃, iodine, EDTA, perchloric acid in glacial acetic acid.
• Concentration units: molarity (mol/L), normality (g-equivalents/L), molality, % w/v, % w/w, ppm, mg/mL. IP expresses volumetric solutions in molarity with a stated *equivalence factor* ("each mL of 0.1 M HCl is equivalent to x mg of…").
• Equivalent weight = molecular weight / n, where n = replaceable H⁺ (acid), OH⁻ (base), electrons transferred (redox) or charge (precipitation/complexation).
• Standardisation and factor: a solution's actual molarity is expressed as nominal molarity × factor; IP permits use of the factor instead of re-adjusting the solution.
• End point vs equivalence point: the equivalence point is stoichiometric; the end point is what is observed. The difference is the titration error, corrected by a blank titration.
• Direct, back (residual) and indirect titration: back titration adds excess reagent and titrates the leftover (ZnO, MgO, light magnesium carbonate); indirect titration converts the analyte to a titratable species (nitrogen by Kjeldahl).

Acid-base (neutralisation) titrimetry

• Theory: strong acid-strong base gives a steep break at pH 7; weak acid-strong base ends alkaline (pH ≈ 8-9); weak base-strong acid ends acidic (pH ≈ 4-5); weak acid-weak base gives no sharp break - titrate potentiometrically or in a non-aqueous medium.
• Indicator choice: the indicator's transition range must lie on the steep part - methyl orange 3.1-4.4 (red→yellow), methyl red 4.2-6.3, bromothymol blue 6.0-7.6, phenolphthalein 8.3-10.0 (colourless→pink), thymolphthalein 9.3-10.5. Mixed indicators (e.g. methyl red + bromocresol green) sharpen a weak break.
• Half-neutralisation: at 50% titration of a weak acid, pH = pKa - the basis of pKa determination by titration curve.
• IP applications: assay of boric acid (after adding glycerol/mannitol to strengthen it), sodium bicarbonate, sodium citrate, ammonium chloride (formaldehyde method), aspirin (after hydrolysis with excess NaOH, back-titrated), magnesium hydroxide, acidity/alkalinity tests, Kjeldahl nitrogen.
• Carbonate interference: NaOH absorbs CO₂, so it is standardised fresh and stored protected from air; carbonate-free NaOH is required for assays with a phenolphthalein end point.

Non-aqueous titration

• Why: very weak acids and bases cannot be titrated in water because water levels their strength (levelling effect) and water itself competes; a solvent that is a poorer proton donor/acceptor enhances the break.
• Solvent classes: *protogenic* (acidic - glacial acetic acid), *protophilic* (basic - dimethylformamide, ethylenediamine, pyridine), *amphiprotic* (alcohols, glacial acetic acid), *aprotic/inert* (benzene, chloroform, dioxan - used as diluents).
• Weak bases (alkaloids, amines, their salts): titrated with 0.1 M perchloric acid in glacial acetic acid, standardised against potassium hydrogen phthalate; indicators crystal violet, oracet blue B, quinaldine red, or potentiometric end point.
• Role of mercuric acetate: halide salts (hydrochlorides) would release HCl, which is too weak an acid in acetic acid to be inert but strong enough to blunt the end point; mercuric acetate ties up the halide as undissociated HgX₂, freeing the base for titration. Needed for chlorides/bromides/iodides, not for sulphates or nitrates.
• Weak acids (phenols, sulphonamides, barbiturates, carboxylic acids): titrated with sodium methoxide, lithium methoxide or tetrabutylammonium hydroxide in benzene-methanol or DMF, with thymol blue or azo violet.
• Precautions: solvents must be dry (water is both acid and base here); acetic anhydride is added to remove water from glacial acetic acid; a temperature-correction blank is used because glacial acetic acid has a large coefficient of expansion.

Redox, complexometric and precipitation titrimetry

• Redox principles: oxidation number change, electron balance, electrode potential difference ≥ ~0.3-0.4 V for a usable break; redox indicators (diphenylamine, ferroin, methylene blue), self-indicating KMnO₄, or starch for iodine.
• Permanganometry: 0.02 M KMnO₄ in acid medium (n = 5), standardised with oxalic acid or sodium oxalate; assays hydrogen peroxide, ferrous salts, oxalates. Not used in HCl (chloride is oxidised).
• Dichrometry: 0.0167 M K₂Cr₂O₇ (n = 6) - a primary standard, stable, used with an internal indicator; chromium waste must be handled as hazardous.
• Cerimetry: 0.1 M ceric ammonium sulphate (n = 1), stable in acid, ferroin indicator; assays ferrous sulphate, paracetamol (after hydrolysis).
• Iodimetry vs iodometry: *iodimetry* = direct titration with standard iodine of a reducing analyte (ascorbic acid, sodium thiosulphate, analgin, sodium metabisulphite). *Iodometry* = an oxidising analyte liberates iodine from excess KI, and the liberated iodine is titrated with standard sodium thiosulphate (copper sulphate, chlorinated lime, available chlorine, peroxides).
• Bromometry / bromatometry: KBrO₃ + KBr generates bromine in situ; assays phenol, isoniazid, sulphonamides (with methyl red as a bleached indicator).
• Diazotisation (nitrite) titration: primary aromatic amines (sulphamethoxazole, sulphadiazine, procaine, dapsone precursor amines) titrated with 0.1 M sodium nitrite in cold HCl; end point by starch-iodide paste (blue streak), external indicator, tropaeoline OO/methylene blue, or potentiometry (preferred, IP).
• Complexometric (EDTA) titration: disodium edetate forms 1:1 chelates. pH control is essential (Ca²⁺/Mg²⁺ at pH 10 with ammonia buffer, Bi³⁺ at pH 1-2, Al³⁺ by back titration). Conditional stability constant rises with pH because less EDTA is protonated. Indicators: eriochrome black T, murexide, xylenol orange, calcon. Masking with cyanide/triethanolamine/fluoride; demasking with formaldehyde. Types: direct, back, replacement and alkalimetric titration. Applications: calcium gluconate, magnesium sulphate, zinc oxide, bismuth salts, water hardness, aluminium hydroxide gel.
• Argentometry: *Mohr* (direct, K₂CrO₄ indicator, pH 6.5-9 - red Ag₂CrO₄), *Volhard* (excess AgNO₃ back-titrated with ammonium thiocyanate, ferric ammonium sulphate indicator, acidic; chloroform/nitrobenzene added to coat AgCl), *Fajans* (adsorption indicators - fluorescein, eosin, dichlorofluorescein). Assays sodium chloride, potassium chloride, halide drugs, chlorhexidine.
• Gravimetry (for contrast): precipitate, filter, ignite and weigh - sulphated ash, residue on ignition, loss on drying are the surviving pharmacopoeial gravimetric tests.

Limit tests and general pharmacopoeial tests

• Principle: a comparison, not a measurement - the test solution's turbidity or colour must not exceed that of a standard containing the permitted amount, viewed under identical conditions (Nessler cylinders, equal volumes, same time).
• Chloride: silver nitrate in nitric acid → opalescence compared with a standard NaCl solution.
• Sulphate: barium chloride in presence of dilute HCl, with a trace of barium sulphate seed and alcohol to stabilise turbidity.
• Iron: thioglycollic acid in citrate-buffered ammoniacal medium → pink-purple ferrous thioglycollate.
• Heavy metals: three methods (A/B/C) using hydrogen sulphide or thioacetamide at pH 3.5 → brown lead sulphide, compared with a lead standard (usually 10-20 ppm limits).
• Arsenic: modified Gutzeit apparatus - arsenic reduced to arsine by Zn/HCl (stannous chloride and KI as catalysts), lead acetate paper traps H₂S, arsine stains mercuric chloride paper yellow-brown.
• Others: loss on drying, water by Karl Fischer, sulphated ash, residue on ignition, melting range, pH, refractive index, optical rotation, specific gravity, clarity and colour of solution, particulate matter, sterility and bacterial endotoxin (for parenterals), dissolution and disintegration, uniformity of content and of weight.

Instrumental methods: electroanalytical and physical

• Potentiometry: measures cell potential at near-zero current using an indicator electrode (glass pH, ion-selective, platinum redox, antimony) against a reference (saturated calomel, Ag/AgCl). Nernst equation governs the response; the pH meter is calibrated with two or three buffers (pH 4.00, 6.86/7.00, 9.18). *Potentiometric titration* finds the end point from the inflexion of the E vs V curve or the peak of ΔE/ΔV - the IP end point of choice for coloured, turbid or non-aqueous titrations. Errors: alkaline (sodium) error, acid error, asymmetry potential.
• Conductometry: measures the solution's ability to carry current with an AC bridge and a platinised-platinum cell; the cell constant (l/A) is found with standard KCl. *Conductometric titration* gives V-shaped or break plots; it works for weak acid-weak base, very dilute and coloured solutions, and precipitation titrations. Non-specific - any ion contributes.
• Polarography and voltammetry: current measured at a dropping mercury electrode (DME) as the potential is ramped; the half-wave potential E₁/₂ identifies the species, the diffusion current (Ilkovic equation) measures it. Residual, migration and maximum currents are suppressed with supporting electrolyte and gelatin/Triton X-100; oxygen is purged with nitrogen. Variants: differential pulse polarography, cyclic voltammetry, amperometric titration (two polarised electrodes - the "dead-stop" end point).
• Coulometry: analyte is quantitatively electrolysed and the charge measured; Faraday's laws give the amount with no need for a standard solution. Coulometric Karl Fischer titration (iodine generated in situ) measures water down to a few ppm.
• Karl Fischer titration: water reacts stoichiometrically with iodine, sulphur dioxide, an alcohol (methanol) and a base (imidazole replaced pyridine) - 1 mol I₂ per mol H₂O. Volumetric for 0.1-100% water, coulometric for traces; the reagent is standardised with pure water or sodium tartrate dihydrate (15.66% water) and the water equivalence factor in mg/mL is reported.
• Flame photometry (flame emission): the flame excites alkali and alkaline-earth atoms, which emit at characteristic wavelengths (Na 589 nm, K 766/769 nm, Li 670 nm, Ca 622 nm); used for sodium and potassium in ORS, electrolyte infusions, dialysis fluids and blood. Interferences: spectral, ionisation, self-absorption and radiation; standard-addition and internal-standard (lithium) methods correct them.
• Atomic absorption spectroscopy: a hollow-cathode lamp beam is absorbed by ground-state atoms in a flame or graphite furnace; far more sensitive and selective than flame emission - elemental impurities (ICH Q3D-type limits) in APIs, lead and cadmium in excipients, often now done by ICP-OES/ICP-MS.
• Turbidimetry and nephelometry: turbidimetry measures transmitted light through a suspension, nephelometry the light scattered at 90° (better for very dilute suspensions); applied to sulphate limit tests and antibiotic microbiological assays.
• Polarimetry: measures optical rotation; specific rotation identifies and assays optically active drugs (dextrose, lactose, camphor, ephedrine, quinine) and checks enantiomeric identity. Sodium D line 589.3 nm, temperature and solvent stated.
• Refractometry: refractive index (Abbe refractometer, 25 °C, sodium D line) as an identity and purity test for liquids, oils and syrups.
• Thermal methods: TGA (mass vs temperature - moisture, solvates, decomposition), DSC/DTA (heat flow - melting point, polymorphism, purity by the van't Hoff method, glass transition, excipient compatibility).
• Separation and spectral techniques - HPLC, GC, TLC, UV, IR, NMR and mass spectrometry - are the other half of modern analysis and are covered in their own notes; in practice an API monograph pairs an instrumental identity test with a titrimetric or HPLC assay.

Validation, calibration and the Indian regulatory frame

• ICH Q2(R2) (adopted 2023, with Q14 on analytical procedure development) sets the validation characteristics: specificity, linearity, range, accuracy (recovery, typically 98-102%), precision (repeatability, intermediate precision, reproducibility; RSD limits), detection limit, quantitation limit, robustness; plus system suitability before each run.
• LOD/LOQ are derived from the standard deviation of the response and the slope, or from a signal-to-noise ratio of about 3:1 and 10:1.
• Qualification: DQ, IQ, OQ, PQ of instruments; periodic calibration of balances (NABL-traceable weights), pH meters, pipettes, volumetric glassware (Class A), UV and HPLC systems; ISO/IEC 17025 accreditation through NABL for testing laboratories.
• Indian legal position: the Drugs and Cosmetics Act, 1940 and Rules, 1945 make IP standards enforceable (a drug not of standard quality under the Act's quality provisions attracts action; misbranded, adulterated and spurious drugs are separately defined). CDSCO is the central regulator; the Central Drugs Laboratory, Kolkata and state drug-testing laboratories are the statutory testing bodies. Revised Schedule M (notified 2023, with phased compliance timelines for small manufacturers extended into 2025-26 - check the latest notification) prescribes the quality-control laboratory, instrument, documentation and data-integrity requirements; Schedule L-1 covers approved testing laboratories.
• Data integrity: ALCOA+ principles, audit trails in chromatography data systems, no re-testing without investigation - a standing theme in USFDA and WHO-GMP inspections of Indian plants.
• Where IP is silent, BP, USP-NF, Ph. Eur. or the Japanese Pharmacopoeia may be used; IP takes precedence for drugs marketed in India.

Key points

• Titrimetry - quantitative reaction with a standard solution; cheap, accurate to ~0.1-0.2% for pure substances, but not stability-indicating or specific.
• Primary standard - pure, stable, high equivalent weight; used to standardise secondary solutions such as NaOH and KMnO₄.
• Equivalent weight = M/n, where n is replaceable H⁺/OH⁻, electrons or charge.
• Equivalence factor - the IP statement "each mL of 0.1 M X ≡ y mg of drug"; multiply titre by it to get the drug found.
• Indicator rule - transition range must fall within the steep portion of the titration curve; phenolphthalein for weak acid-strong base, methyl orange for weak base-strong acid.
• Levelling effect - water makes all strong acids equally strong and masks very weak ones; non-aqueous solvents remove it.
• Mercuric acetate - masks halide ions in non-aqueous titration of hydrochloride salts.
• Iodimetry is direct titration with iodine; iodometry titrates iodine liberated by an oxidant, using thiosulphate and starch.
• EDTA titration needs buffered pH; the conditional stability constant rises with pH; EBT and murexide are the common metal indicators.
• Argentometry - Mohr (chromate), Volhard (back titration with thiocyanate), Fajans (adsorption indicator).
• Limit test - visual comparison against a standard, not an assay; identical conditions are essential.
• Gutzeit test - arsenic as arsine staining mercuric chloride paper.
• Potentiometric end point - from the inflexion of E vs V; the fallback for coloured, turbid or non-aqueous systems.
• Karl Fischer - stoichiometric water determination, 1 mol iodine per mol water; volumetric or coulometric.
• Flame photometry measures emission (Na, K, Li, Ca); AAS measures absorption by ground-state atoms and is far more sensitive.
• Polarimetry gives specific rotation; refractometry gives refractive index - both identity/purity tests.
• ICH Q2(R2) validation parameters: specificity, linearity, range, accuracy, precision, LOD, LOQ, robustness.
• IP 2026 (10th edition) is the statutory book of standards in India, published by the IPC, Ghaziabad, under the Drugs and Cosmetics Act, 1940.

Formulas and examples

Example 1 - standardisation of NaOH with KHP (primary standard). 0.5105 g of potassium hydrogen phthalate (M = 204.22) required 24.8 mL of NaOH.

• Moles KHP = 0.5105 / 204.22 = 2.500 × 10⁻³ mol = 2.500 mmol; the reaction is 1:1.
• Molarity = 2.500 mmol / 24.8 mL = 0.1008 M → factor = 0.1008/0.1 = 1.008.

Example 2 - aqueous acid-base assay of sodium bicarbonate. 1.5000 g dissolved in water and titrated with 0.5 M HCl; titre 35.6 mL. Each mL of 0.5 M HCl ≡ 42.00 mg NaHCO₃ (M = 84.01, n = 1, so 0.5 mmol = 42.005 mg).

• NaHCO₃ found = 35.6 × 42.00 = 1495.2 mg = 1.4952 g.
• % = (1495.2 / 1500.0) × 100 = 99.68% - within the IP limit of 99.0-100.5% (dried basis as specified in the monograph).

Example 3 - non-aqueous titration of ephedrine hydrochloride. 0.2000 g dissolved in glacial acetic acid with mercuric acetate, titrated with 0.1 M perchloric acid to a crystal-violet end point; titre 9.85 mL. Each mL of 0.1 M HClO₄ ≡ 20.17 mg of C₁₀H₁₅NO·HCl (M = 201.69).

• Drug found = 9.85 × 20.17 = 198.67 mg → % = (198.67/200.00) × 100 = 99.34%.
• Without mercuric acetate the liberated chloride would blunt the end point and the result would read low.

Example 4 - complexometric assay of magnesium sulphate. 0.5000 g of MgSO₄·7H₂O (M = 246.47) dissolved in water, buffered to pH 10 with ammonia buffer, titrated with 0.05 M disodium edetate against eriochrome black T; titre 40.3 mL. Each mL ≡ 12.32 mg MgSO₄·7H₂O (0.05 mmol × 246.47 mg/mmol = 12.324 mg).

• Found = 40.3 × 12.32 = 496.5 mg → % = (496.5/500.0) × 100 = 99.30%.

Example 5 - iodimetric assay of ascorbic acid. 0.4000 g dissolved in water with dilute sulphuric acid and titrated with 0.1 M iodine using starch mucilage; titre 22.5 mL. One mol of I₂ oxidises one mol of ascorbic acid (M = 176.13, two electrons), so each mL of 0.1 M iodine ≡ 17.61 mg.

• Found = 22.5 × 17.61 = 396.2 mg → % = (396.2/400.0) × 100 = 99.06%.

Example 6 - Karl Fischer water content. The reagent was standardised with 35.2 mg of purified water, which needed 3.60 mL → F = 35.2/3.60 = 9.78 mg/mL. A 0.5000 g sample of an API then needed 1.25 mL.

• Water = 1.25 × 9.78 = 12.22 mg → % w/w = (12.22/500.0) × 100 = 2.44%. If the monograph limit is "not more than 3.0%", the batch passes.

Example 7 - specific rotation. A 5.00 g/100 mL solution in a 1 dm tube rotates +0.65°.

• [α] = (100 × 0.65)/(1 × 5.00) = +13.0° at the stated temperature and sodium D line.

Where it is used

• QC laboratories of Indian pharma manufacturers (Cipla, Sun, Dr Reddy's, Zydus, Lupin, Torrent, Aurobindo, Hetero, Alkem, Mankind): raw-material and API release by titrimetry, Karl Fischer water, limit tests, loss on drying, sulphated ash.
• Government and regulatory labs: CDL Kolkata, state drug-testing laboratories, CDSCO zonal labs testing survey samples for standard quality; drug inspector and government analyst posts examine exactly this syllabus.
• Formulation and electrolyte products: flame photometry for sodium and potassium in ORS, Ringer's lactate, haemodialysis concentrates; EDTA titration for calcium and magnesium salts and antacid gels.
• Water and utility testing in plants: conductivity and total organic carbon for purified water and water for injection, hardness and chloride by titration in utilities.
• Analytical R&D and method development: validation per ICH Q2(R2)/Q14, transfer of methods to QC, DSC/TGA for polymorph screening and excipient compatibility; CROs and CDMOs in Hyderabad, Ahmedabad, Mumbai and Bengaluru.
• Allied roles: quality assurance and documentation, regulatory affairs (preparing CTD module 3 specifications), NABL-accredited third-party testing laboratories, food and cosmetic testing using the same titrimetric toolkit.

Interview questions

• Q: What makes a substance a good primary standard? A: High purity, chemical stability, non-hygroscopic nature, a high equivalent weight so weighing errors are small, ready solubility and a known stoichiometric reaction.
• Q: Why is non-aqueous titration used for alkaloidal salts? A: Such bases are too weak to give a sharp break in water because of water's levelling effect; in glacial acetic acid their basicity is enhanced and perchloric acid gives a sharp end point.
• Q: Why add mercuric acetate in a non-aqueous titration? A: The halide of a hydrochloride salt would otherwise interfere with the end point; mercuric acetate binds it as undissociated mercuric halide, leaving the free base to be titrated.
• Q: Difference between iodimetry and iodometry? A: Iodimetry titrates a reducing analyte directly with standard iodine; iodometry titrates, with thiosulphate, the iodine that an oxidising analyte liberates from excess potassium iodide.
• Q: Why must pH be controlled in an EDTA titration? A: The conditional stability constant of the metal-EDTA complex depends on how much EDTA is protonated and on competing hydroxide complexation, so each metal has its own optimum buffered pH.
• Q: What is a limit test and how does it differ from an assay? A: A limit test shows only that an impurity does not exceed a stated level by visual comparison with a standard under identical conditions; an assay measures the analyte quantitatively.
• Q: How does the Karl Fischer method determine water? A: Water reacts stoichiometrically with iodine and sulphur dioxide in methanol with a base - one mole of iodine per mole of water - and the end point is detected by excess iodine, usually amperometrically.
• Q: When would you choose a potentiometric end point over an indicator? A: For coloured or turbid solutions, very dilute or weak acid-weak base systems, non-aqueous media, and whenever an objective, recordable end point is needed.
• Q: Flame photometry or AAS - which would you use for sodium in an infusion, and why? A: Flame photometry is sufficient and cheaper because sodium is easily excited and present at high concentration; AAS is reserved for trace metals needing greater sensitivity and selectivity.
• Q: What validation parameters would you report for a titrimetric assay? A: Specificity, accuracy by recovery, repeatability and intermediate precision, linearity and range where applicable, and robustness; LOD and LOQ are not usually required for an assay.
• Q: Why is a blank titration performed? A: To correct for reagent impurities, the indicator's own consumption and the volume needed to produce the visible colour change, so the titration error is removed.
• Q: Your assay result is 101.8% against a limit of 98.0-102.0%. What do you check before releasing? A: The standardisation factor and expiry of the volumetric solution, balance calibration and sample weight, water content/drying basis of the sample, end-point judgement and the blank - then confirm by a repeat determination.

Common mistakes

• Mixing up molarity and normality, or using N₁V₁ = N₂V₂ with molarities when the reaction is not 1:1.
• Ignoring the factor of the volumetric solution, or using its nominal molarity after its stated validity period.
• Forgetting the drying or anhydrous basis - reporting "as is" when the monograph requires the result on dried material.
• Choosing an indicator outside the steep region (phenolphthalein for a weak base-strong acid titration, for instance).
• Omitting mercuric acetate for hydrochloride salts, or titrating in wet glacial acetic acid, in non-aqueous assays.
• Adding starch too early in iodometry (iodine is adsorbed on starch and the end point drags) or running an EDTA titration unbuffered.
• Treating a limit test as quantitative, or comparing solutions in unmatched cylinders, different volumes or different lighting.
• Reporting a result to more significant figures than the burette, balance and method precision justify.

Related topics

Chromatography: HPLC, GC and TLC · Spectroscopy: UV, IR, NMR and mass · Medicinal chemistry: drug classes and SAR · Pharmaceutical quality assurance, GMP and revised Schedule M · Physical pharmaceutics: solubility, pH and stability · Pharmaceutical jurisprudence: Drugs and Cosmetics Act, 1940.