Instrumentation and Spectroscopic Methods – Unit V

Vocabulary flashcards covering key terms, principles, instrumentation and applications of UV–Visible spectroscopy, Beer–Lambert law, Atomic Absorption Spectroscopy, and Flame Emission Spectroscopy from the provided lecture notes.

Instrumental Methods of Analysis

Analytical techniques that use instruments to measure physical properties of analytes, offering speed, sensitivity and selectivity compared with classical wet methods.

Spectroscopy

Branch of instrumental analysis that studies the interaction of electromagnetic radiation with matter to obtain qualitative or quantitative information.

Electrochemistry (as an analytical area)

Instrumental techniques based on measuring electrical properties such as potential, current, charge or resistance to determine analyte concentration.

Chromatography

Separation techniques in which components of a mixture are distributed between stationary and mobile phases for identification or quantification.

Qualitative Analysis

Determination of the identity or nature of chemical species in a sample.

Quantitative Analysis

Determination of the amount or concentration of a substance present in a sample.

Classical (Wet) Chemical Methods

Non-instrumental analytical procedures relying on chemical reactions such as titrations, gravimetry, and color tests.

Electromagnetic Spectrum

Complete range of electromagnetic radiation, from gamma rays to radio waves, characterized by wavelength or frequency.

Absorption Spectroscopy

Technique that measures the amount of light absorbed by ground-state atoms or molecules as a function of wavelength.

Emission Spectroscopy

Technique that measures radiation emitted by excited atoms or molecules returning to lower energy states.

Beer–Lambert Law

Law that describes how light is absorbed by a substance in a solution and how that absorption is related to the concentration of the substance

Transmittance (T)

Fraction of incident light that passes through a sample, T = I/I₀.

Visible region

380 nm - 700 nm

UV region

100nm-380

Molar Absorptivity (ε)

Proportionality constant (M⁻¹ cm⁻¹) in Beer’s law indicating how strongly a species absorbs light at a given wavelength.

Limitations of Beer–Lambert Law

Non-linearity at high concentrations, particle scattering, fluorescence, refractive index changes, non-monochromatic light, stray light, and chemical equilibria shifts.

Single-Beam Spectrophotometer

UV-Vis instrument that measures sample absorbance relative to a blank sequentially with one light path; simpler but less stable.

Double-Beam Spectrophotometer

Instrument that splits light into reference and sample beams simultaneously, compensating for source fluctuations and enabling continuous recording.

Colorimetry

Quantitative analysis based on measurement of solution color intensity, typically using visible filters rather than monochromators.

Monochromator

Optical component (prism or grating) that isolates a narrow band of wavelengths from a broad spectrum.

Cuvette

Sample holder with fixed optical path length (1–5 cm); made of quartz for UV and glass or plastic for visible region.

Photovoltaic Cell

Detector that generates current directly when light strikes a semiconductor–metal junction.

Phototube

Photo-detector in which incident photons cause electron emission from a photosensitive cathode, producing current.

Photoconductive Cell

Detector whose electrical resistance decreases upon light absorption, allowing current flow to be measured.

Signal Processing (Spectroscopy)

Conversion of detector output to readable data via amplification, filtering, and computer-based display or storage.

UV–Visible Spectroscopy

Electronic spectroscopy technique analyzing absorption in the 190–700 nm range due to electronic transitions of valence electrons.

Chromophore

Part of a molecule responsible for light absorption and color; exhibits characteristic λ_max and electronic transitions (π→π, n→π, etc.).

Molar Extinction Coefficient

Synonym for molar absorptivity; slope factor in Beer’s law used to calculate unknown concentrations from absorbance.

Atomic Absorption Spectroscopy (AAS)

Technique measuring absorption of element-specific radiation by ground-state atoms in a flame or furnace for trace metal quantification.

Hollow Cathode Lamp

Element-specific radiation source for AAS consisting of a cathode made of the target metal and an inert gas discharge.

Electrodeless Discharge Lamp

Microwave- or RF-excited sealed lamp producing intense atomic emission without electrodes, used for elements difficult in hollow cathodes.

Flame Emission Spectroscopy (FES)

Technique measuring light emitted by excited atoms in a flame; widely called flame photometry for alkali and alkaline-earth metals.

Nebulizer

Component that converts liquid sample into fine aerosol for introduction into a flame or plasma.

Laminar-Flow Flame Zones

Regions include primary reaction, interconal, secondary reaction, and preheating zones, each with distinct temperatures and chemistry.

Premix Burner

Flame atomizer where fuel, oxidant, and sample aerosol are mixed before reaching the burner tip, giving stable, homogeneous flame.

Total Consumption Burner

Burner that aspirates sample directly into flame with fuel and oxidant separately, allowing high sample throughput but poorer precision.

Trace Metal Analysis

Determination of metals at µg L⁻¹ to mg L⁻¹ levels; AAS is especially powerful for such low-concentration work.

Specificity of AAS

Atoms of one element absorb only their own resonance wavelength, minimizing spectral interferences compared with emission methods.

Flame Photometer

Instrument designed for rapid, routine determination of Na, K, Li, Ca, Ba by measuring their flame emission intensities.

Filter (Flame Photometer)

Optical element selecting the characteristic emission wavelength of the analyte element (e.g., 589 nm for Na).

Photo-Diode Detector

Solid-state detector used in modern flame photometers to convert emitted light into electrical signal.

Calibration Curve

Graph of instrument response versus known analyte concentration used to determine unknown sample concentrations.

Molarity (M)

Concentration unit equal to moles of solute per liter of solution; used in Beer’s law calculations.

Quantitative UV-Vis Applications

Environmental metal assays, clinical protein and cholesterol tests, industrial product quality control, kinetic studies, and pKa determinations.

Stray Light

Unwanted radiation reaching detector outside selected wavelength band, causing baseline errors and limiting Beer-law linearity.

Thermal Gravimetric Analysis (TGA)

Instrumental thermal method measuring mass change of a sample as a function of temperature or time.

Mass Spectrometry

Instrumental technique that measures mass-to-charge ratios of ions to identify and quantify compounds.

Potentiometry

Electrochemical method where electrical potential difference is measured under zero-current conditions to determine ion concentration.

Voltammetry

Electroanalytical techniques measuring current as a function of applied potential to obtain concentration and kinetic information.

Coulometry

Technique determining amount of substance by measuring total charge passed during electrolysis.

Conductometry

Analytical method based on measurement of electrical conductivity of a solution to monitor reaction progress or concentration.

Gravimetry (Instrumental Context)

Mass-based analytical methods, sometimes automated, for determining analyte quantity through precipitation and weighing.

Nebulization

Process of converting liquid sample into aerosol droplets for introduction into atomization sources in AAS or FES.

Atomization

Conversion of sample species into free atoms in the gas phase, essential for atomic spectroscopy.

Excitation (Spectroscopy)

Promotion of electrons or atoms to higher energy states by absorption of energy (thermal or radiative).

Emission Intensity

Strength of light emitted by excited atoms or molecules, proportional to number of excited species in emission spectroscopy.

Ground State Atom

Atom in its lowest electronic energy state, responsible for absorbing characteristic radiation in AAS.