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DrX Whiz Niraj
Pharmaceutical Analysis: Basics & Standardization
Comprehensive exam notes on Definition, Scope, Techniques of Analysis, Primary & Secondary Standards, and Preparation of Molar/Normal Solutions.
Pharmaceutical Analysis is a branch of chemistry that involves a series of processes for the identification, determination, quantification, and purification of a substance, separation of the components of a solution or mixture, or determination of structure of chemical compounds.
Scope of Pharmaceutical Analysis:
- Quality Control (QC): Ensuring that the raw materials and finished products meet the required standards of purity, safety, and efficacy.
- Quality Assurance (QA): Maintaining the overall quality system during the manufacturing process.
- Diagnosis: Analysis of biological samples (blood, urine) for clinical diagnosis.
- Research & Development (R&D): Discovery of new drugs, their stability testing, and pharmacokinetic studies.
- Regulatory Compliance: Fulfilling the standards set by pharmacopoeias (IP, BP, USP) and regulatory bodies (FDA, CDSCO).
Analytical techniques are broadly classified into Qualitative (What is present?) and Quantitative (How much is present?). Quantitative analysis is further divided into the following techniques:
Concentration is the amount of solute dissolved in a given quantity of solvent or solution.
1. Molarity (M)
Number of moles of solute dissolved per Liter of solution. It changes with temperature.
2. Normality (N)
Number of gram equivalents of solute dissolved per Liter of solution. Very common in titrations.
| Method | Definition / Formula | Temperature Dependence |
|---|---|---|
| Molality (m) | Moles of solute per kg of solvent. | Independent (Because mass doesn't change with temp) |
| Mole Fraction (x) | Ratio of moles of one component to total moles in solution. | Independent |
| % w/w (Weight/Weight) | Grams of solute in 100g of solution. | Independent |
| % w/v (Weight/Volume) | Grams of solute in 100ml of solution. | Dependent |
| ppm (Parts Per Million) | Used for very trace/dilute concentrations. (mg per Liter) | Varies |
In volumetric analysis (titration), a standard solution is one whose exact concentration is known.
Primary Standard
A highly pure chemical compound used to prepare standard solutions directly by weighing.
- Ideal Properties: Should be 100% pure, highly stable, not hygroscopic (doesn't absorb moisture), high equivalent weight.
- Examples: Oxalic acid, Sodium carbonate (Na2CO3), Potassium dichromate (K2Cr2O7).
Secondary Standard
A substance whose exact concentration cannot be prepared directly by weighing. It must be standardized against a primary standard before use.
- Why? They are unstable, impure, or hygroscopic.
- Examples: Sodium hydroxide (NaOH), Hydrochloric acid (HCl), Potassium permanganate (KMnO4).
Below is the summary of standardization procedures for various common laboratory solutions:
| Secondary Standard (To be standardized) | Primary Standard Used | Indicator Used |
|---|---|---|
| 1. Sodium Hydroxide (NaOH) It absorbs CO2 and moisture from air. |
Oxalic Acid (or KHP) | Phenolphthalein |
| 2. Hydrochloric Acid (HCl) & H₂SO₄ | Anhydrous Sodium Carbonate (Na₂CO₃) | Methyl Orange |
| 3. Potassium Permanganate (KMnO₄) | Oxalic Acid (Requires heating to 70°C) |
Self-Indicator (Turns faint pink) |
| 4. Sodium Thiosulphate (Na₂S₂O₃) | Potassium Dichromate (K₂Cr₂O₇) or KIO₃ | Starch Solution (Iodometric titration) |
| 5. Ceric Ammonium Sulphate | Arsenic Trioxide (As₂O₃) | Ferroin Indicator |
Practical Lab Correlation
Why do we heat the solution during KMnO₄ standardization?
The reaction between KMnO₄ and Oxalic acid is extremely slow at room temperature. Heating the conical flask to about 70°C provides the necessary activation energy to start the reaction. Once started, the Mn²⁺ ions formed act as an auto-catalyst to speed up the rest of the reaction.