GPAT Pharmaceutical Analysis Syllabus

Compare electron impact (EI) and electrospray ionization (ESI) as ionization methods.

EI is a hard, gas-phase technique giving extensive fragmentation (good for structure, small volatile compounds); ESI is a soft, solution-phase technique giving mainly intact (often multiply charged) molecular ions (good for large, thermolabile biomolecules).

Give two examples each of 'hard' and 'soft' ionization techniques.

Hard: Electron Impact (EI) and Chemical Ionization is borderline; truly hard is EI and Field Ionization. Soft: Electrospray Ionization (ESI) and Matrix-Assisted Laser Desorption/Ionization (MALDI).

What is the principle of polarography?

Polarography measures the current resulting from electrolysis of an analyte at a dropping mercury electrode (DME) as the applied potential is varied, producing a current-voltage curve (polarogram).

Why is the dropping mercury electrode (DME) used in classical polarography?

Its continuously renewed surface gives reproducible results, mercury has a high hydrogen overvoltage (wide cathodic range), and it forms amalgams with many metals.

State the Ilkovic equation and what it relates.

id = 607·n·D^(1/2)·m^(2/3)·t^(1/6)·C, relating the diffusion current (id) to analyte concentration (C); it is the basis for quantitative polarography.

In a polarogram, what is the half-wave potential (E½) and its analytical use?

E½ is the potential at which the current is half the limiting (diffusion) current; it is characteristic of a given species and is used for qualitative identification.

State the Beer-Lambert law and define its terms.

A = ε·b·c, where A is absorbance, ε is the molar absorptivity (L·mol⁻¹·cm⁻¹), b is the path length (cm), and c is the molar concentration.

What is the relationship between absorbance (A) and transmittance (T)?

A = −log₁₀T = log₁₀(1/T) = 2 − log(%T); absorbance is logarithmically related to transmittance.

Name the common electronic transitions in UV-Vis spectroscopy and the lowest-energy one observed.

σ→σ*, n→σ*, π→π*, and n→π*. The n→π* transition is the lowest in energy and longest in wavelength.

Define chromophore and auxochrome in UV-Vis spectroscopy.

A chromophore is an unsaturated functional group that absorbs UV-Vis light (e.g., C=C, C=O); an auxochrome is a saturated group with lone pairs (e.g., -OH, -NH₂) that, when attached to a chromophore, shifts and intensifies absorption.

Define bathochromic and hypsochromic shifts.

Bathochromic (red) shift is a shift to longer wavelength (lower energy); hypsochromic (blue) shift is a shift to shorter wavelength (higher energy).

What is fluorescence, and how does it differ from phosphorescence?

Fluorescence is rapid light emission (10⁻⁹–10⁻⁷ s) from an excited singlet state returning to the ground state; phosphorescence is slower emission (10⁻³–10² s) from a triplet state, persisting after the source is removed.

State Stokes' shift in fluorescence spectroscopy.

Stokes' shift is the difference (longer wavelength) between the emission maximum and the excitation/absorption maximum, caused by energy lost via non-radiative vibrational relaxation before emission.

Why is fluorescence spectroscopy generally more sensitive than UV-Vis absorption spectroscopy?

Fluorescence measures emitted light against a dark background (signal increases from zero), whereas absorption measures a small difference between two large light intensities, making fluorescence intrinsically more sensitive.

Distinguish flame emission spectroscopy from atomic absorption spectroscopy (AAS).

Flame emission (flame photometry) measures light emitted by thermally excited atoms returning to ground state; AAS measures absorption of light by ground-state atoms—emission depends on excited atoms, absorption on the much larger ground-state population.

What is flame photometry primarily used to determine in pharmaceutical analysis?

Quantification of alkali and alkaline earth metals—mainly sodium (Na), potassium (K), calcium (Ca), and lithium (Li)—by measuring characteristic emission intensity.

What is the function of a hollow cathode lamp in atomic absorption spectroscopy?

It serves as the radiation source, emitting the sharp, element-specific line spectrum of the metal being analyzed so that only that element's atoms absorb the light.

What molecular property must change for a vibration to be IR active?

There must be a change in the net dipole moment of the molecule during the vibration; vibrations with no dipole change (e.g., symmetric stretch of homonuclear bonds) are IR inactive.

Give the approximate IR absorption ranges for O-H/N-H stretch, C=O stretch, and the fingerprint region.

O-H/N-H stretch ≈ 3200–3600 cm⁻¹; C=O stretch ≈ 1650–1750 cm⁻¹; fingerprint region ≈ 600–1400 cm⁻¹.

What is the main application of the IR 'fingerprint region' (600–1400 cm⁻¹)?

It provides a complex, compound-specific pattern used to confirm the identity of a substance by matching with a reference spectrum.

What is the principle of differential scanning calorimetry (DSC), a specialized thermal technique?

DSC measures the heat flow (energy difference) into or out of a sample versus a reference as temperature changes, detecting thermal events like melting, crystallization, and glass transitions.

What is the principle of titration in non-aqueous solvents and why is it used?

It is acid-base titration carried out in non-aqueous media; it is used to analyze very weak acids/bases (whose Ka or Kb is too small to titrate in water) and substances insoluble in water by enhancing their apparent strength.

Which titrant and indicator are commonly used for titrating weak bases in non-aqueous (glacial acetic acid) medium?

Titrant: perchloric acid (HClO₄) in glacial acetic acid; indicator: crystal violet (endpoint can also be detected potentiometrically).

Define a leveling solvent and a differentiating solvent in non-aqueous titrimetry.

A leveling solvent makes all acids (or bases) appear equally strong (e.g., water levels strong acids); a differentiating solvent distinguishes their relative strengths (e.g., glacial acetic acid differentiates strong acids).

On what principle are redox titrations based, and how is the endpoint detected?

They are based on electron-transfer (oxidation-reduction) reactions between titrant and analyte; the endpoint is detected by self-indication, redox indicators, or potentiometrically via a sharp change in electrode potential.

What is iodometry versus iodimetry in redox titration?

Iodimetry is the direct titration of a reducing analyte with a standard iodine (I₂) solution; iodometry is the indirect titration in which an oxidizing analyte liberates iodine from iodide, which is then titrated with standard sodium thiosulfate.

On what principle is precipitation titration based, and name the main argentometric methods.

It is based on formation of a sparingly soluble precipitate between titrant and analyte; argentometric (AgNO₃) methods are Mohr's, Volhard's, and Fajans' methods for halide determination.

Differentiate Mohr's, Volhard's, and Fajans' methods of precipitation titration.

Mohr's: direct titration of chloride/bromide with AgNO₃ using K₂CrO₄ indicator (neutral pH). Volhard's: back-titration of excess Ag⁺ with thiocyanate using ferric (Fe³⁺) indicator (acidic). Fajans': direct titration using an adsorption indicator (e.g., fluorescein).

What is a chelating agent in complexometric titration, and which is most widely used?

A chelating agent forms multiple coordinate bonds to a metal ion, producing a stable ring-structured complex; EDTA (ethylenediaminetetraacetic acid), a hexadentate ligand, is the most widely used.

In complexometric titrations, what is the role of an indicator like Eriochrome Black T?

It is a metal-ion indicator that forms a colored complex with the metal; at the endpoint EDTA strips the metal from the indicator, causing a sharp color change (wine-red to blue for EBT).

On what principle is proton (¹H) NMR spectroscopy based?

Nuclei with spin (e.g., ¹H) placed in a strong magnetic field absorb radiofrequency radiation when resonance occurs, flipping their spin orientation; the absorption depends on the nucleus's electronic environment.

What information does the chemical shift (δ) provide in ¹H NMR?

It indicates the electronic/chemical environment of a proton (degree of shielding/deshielding), helping identify the type of proton; it is measured in ppm relative to TMS (δ = 0).

In ¹H NMR, what do peak (integration) area and spin-spin splitting (multiplicity) reveal?

The integrated peak area is proportional to the number of equivalent protons; spin-spin splitting (n+1 rule) reveals the number of neighboring non-equivalent protons.

Why is tetramethylsilane (TMS) used as the reference standard in ¹H NMR?

TMS is chemically inert, volatile, soluble in organic solvents, gives a single sharp upfield signal (12 equivalent protons), and absorbs at higher field than most organic protons, so it is set as δ = 0.

What is the general principle of chromatographic separation?

Separation of mixture components based on their differential distribution (partition/adsorption) between a stationary phase and a mobile phase, causing components to migrate at different rates.

Differentiate normal-phase and reverse-phase chromatography.

Normal-phase uses a polar stationary phase and non-polar mobile phase (polar compounds elute last); reverse-phase uses a non-polar stationary phase and polar mobile phase (non-polar compounds elute last).

Define retention factor (k) and resolution (Rs) in chromatography.

Retention factor k = (tR − t0)/t0, measuring how long an analyte is retained relative to the unretained (void) time; resolution Rs measures the degree of separation between two adjacent peaks (Rs ≥ 1.5 indicates baseline separation).

What does HETP (height equivalent to a theoretical plate) indicate about column efficiency?

HETP is the column length divided by the number of theoretical plates (N); a smaller HETP means more plates and higher column efficiency (sharper, better-resolved peaks).

What is the principle of gas chromatography (GC) and what types of samples suit it?

GC separates components by partition between a gaseous mobile phase (carrier gas) and a liquid/solid stationary phase in a column; it suits volatile, thermally stable compounds.

What is the principle of potentiometry as an analytical method?

Potentiometry measures the potential (voltage) of an electrochemical cell under near-zero current between an indicator electrode and a reference electrode, relating it to analyte activity via the Nernst equation.

On what principle does conductometric titration work?

It measures changes in the electrical conductivity of a solution during titration; conductivity varies with ion concentration and mobility, and the endpoint is the intersection of two linear conductance segments.

What does the Karl Fischer titration determine and on what reaction is it based?

It determines water (moisture) content; it is based on the stoichiometric reaction of water with iodine and sulfur dioxide in the presence of a base and methanol (consuming one mole of I₂ per mole of water).