Analytical techniques are the backbone of drug development, quality control and clinical monitoring in the field of pharmacy. Analytical chemistry is essentially the “detective work”. These methods allow pharmacists to identify unknown substances, determine the purity of a drug, and quantify the concentration of active pharmaceutical ingredients (APIs) in various dosage forms. Whether you are working in a manufacturing plant, a research lab, or a hospital, you need to know exactly what is in a medicine and how much of it is there. These analytical techniques are generally classified into four major categories.
Titrimetric (Volumetric) Analysis
This is a classical “wet chemistry” method where the concentration of an unknown solution (analyte) is determined by reacting it with a solution of known concentration (titrant).
Aqueous Acid-Base Titrations
It is used for drugs that are acidic or basic in nature (e.g., Aspirin or Ibuprofen). You neutralize the drug with a base (like Sodium Hydroxide) using an indicator like phenolphthalein to find the “endpoint.”
Non-Aqueous Titration
Many drugs (like Diazepam or Adrenaline) don’t dissolve well in water or are too weakly acidic/basic for water to work. We use solvents like glacial acetic acid.
Redox Titrations
It involves the transfer (gain or loss) of electrons. Common in the analysis of determining the purity of Vitamin C (Ascorbic Acid) tablets using iodine.
Complexometric Titrations
This is the gold standard for testing mineral supplements. This uses chelating agents like EDTA to determine metal ions (e.g., Calcium or Magnesium in antacids).
Precipitation Titrations
Formation of an insoluble precipitate (e.g., Silver Nitrate used to determine chloride content).
Spectroscopic Techniques
Spectroscopy is like giving a molecule a “health check” using light. It measures the interaction between electromagnetic radiation and matter. It is non-destructive and highly sensitive. Depending on the type of light used, we get different information.
UV-Visible Spectroscopy
This is the most common technique used in the labs. It measures the absorption of light in the UV (200–400 nm) and visible (400–800 nm) ranges. Absorbance is directly proportional to concentration. It is primarily used for quantitative analysis i.e. determining how much of a drug is present in a tablet or syrup based on the Beer-Lambert Law.
Infrared (IR) Spectroscopy
Think about IR as a “molecular fingerprint” scanner. It doesn’t tell you how much drug is there; it tells you what the drug is. It measures the vibrations of molecular bonds. It is used almost exclusively for qualitative analysis (identifying what the functional groups are in a drug molecule). Example: Distinguishing between Aspirin and its degradation product, Salicylic Acid. The IR spectrum will show a specific “stretch” for the ester group in Aspirin that disappears if the drug has spoiled.
Nuclear Magnetic Resonance (NMR)
NMR is the ultimate tool for Structure Elucidation. It provides detailed information about the carbon-hydrogen framework of a molecule. If a chemist discovers a new plant extract that might cure a disease, NMR is used to draw the actual map (exact 3D structure) of the molecule’s atoms.
Mass Spectrometry (MS)
It tells about the exact weight and structure of the molecule. It is the ultimate tool for identifying unknown impurities or confirming a newly synthesized drug. It works by Ionization and Fragmentation of the molecule. The ions are separated in a magnetic or electric field based on their mass-to-charge ratio (m/z). It is a destructive method as sample is destroyed in fragmentation process.
Chromatography (Separation Science)
In reality, drugs are rarely pure. They are mixed with binders, colors, and sometimes other drugs. Chromatography separates these complex mixtures into individual components before they are identified or quantified.
Thin Layer Chromatography (TLC)
A quick, inexpensive method used for purity checks and identifying the presence of impurities.
High-Performance Liquid Chromatography (HPLC)
The gold standard in the pharmaceutical industry. A mobile phase (liquid solvent) carries the drug through a stationary phase (column filled with tiny silica beads). Different chemicals move at different speeds. It is used for the separation, identification, and quantification of drugs in complex mixtures. Example: Analyzing a Cold & Flu capsule. The HPLC will separate the Paracetamol, the Caffeine, and the Phenylephrine into three distinct peaks on a graph.
Gas Chromatography (GC)
It is used for volatile substances or to detect residual solvents (impurities) left over from the manufacturing process. Example: Testing for Residual Solvents. When drugs are made, chemicals like ethanol or acetone are used. GC ensures these toxic solvents have been completely removed before the drug reaches the patient.
Electrochemical Methods
These techniques measure the electrical properties of a solution (potential, current, or resistance) to determine the concentration of an analyte.
Potentiometry
It measures the potential difference between electrodes. The most common example is the pH meter, used to ensure the stability of liquid formulations. This is vital for Injectables and Eye Drops, which must be at a specific pH to avoid irritating the patient’s tissues.
Conductometry
It measures the ability of a solution to conduct electricity. It is often used to check the purity of distilled water and Water for Injection (WFI) to ensure no ionic impurities are present.
Summary
| Summary of Analytical techniques | ||
| Techniques | Primary Purpose | Key Application in Pharmacy |
| Titrimetry | Quantitative | Assay of raw materials, “How much API is in this tablet?” |
| UV-Vis | Quantitative | Content uniformity of tablets, “How much API is in this tablet?” |
| IR | Qualitative | Identification of functional groups, “Is this the right drug?” |
| HPLC/GC | Separation/ Quantitative | Stability testing and impurity profiles, “Is the drug contaminated?” |
| NMR | Structural | Drug discovery and characterization |
Pro-Tip for Students
When you are in the lab, always ask yourself: “Am I doing Qualitative or Quantitative analysis?”
- Qualitative = Identity (What is it?)
- Quantitative = Assay (How much is there?)
Understanding this distinction will help you choose the right technique every time.