Analytical Techniques & Instrumentation I – Vocabulary

Vocabulary flashcards covering fundamental terms, components, principles, and instrumentation for photometry, spectrophotometry, flame emission photometry, and atomic absorption spectrophotometry as outlined in the Week 4 Clinical Chemistry lecture.

Photometry

Measurement of light intensity (absorbed, transmitted, or scattered) by a sample without wavelength separation.

Spectrophotometry

Analytical method that measures light absorbance at precisely selected wavelengths using a monochromator.

Beer-Lambert Law

Relationship stating absorbance (A) is directly proportional to molar absorptivity (ε), path length (b or l), and concentration (c): A = εbc.

Absorbance (A)

Logarithmic measure of light absorbed by a sample; increases with concentration and path length.

Transmittance (T)

Fraction (%) of incident light that passes through a sample; inversely proportional to absorbance.

Light Source (Spectrophotometer)

Lamp that provides continuous radiation—commonly tungsten-halogen for visible, deuterium for UV.

Tungsten-Halogen Lamp

Incandescent source emitting 340–800 nm; inexpensive, good visible intensity, weak in UV.

Deuterium Arc Lamp

Continuous UV source (190–400 nm) with high stability; essential for UV analyses.

Xenon Flash Lamp

Pulsed broad-spectrum source (190–1000 nm) producing intense flashes with reduced heat.

Light-Emitting Diode (LED)

Solid-state source emitting narrow, fixed wavelengths; energy-efficient, long-lived.

Mercury / Neon Calibration Lamps

Line-source lamps that emit sharp wavelengths used to verify monochromator wavelength accuracy.

Monochromator

Optical device (filter, prism, or grating) that isolates a single wavelength band from polychromatic light.

Colored Glass Filter

Simple monochromator that transmits broad wavelength bands; low cost, limited precision.

Interference Filter

Filter producing nearly monochromatic light via constructive interference; may require accessory filters.

Prism

Wedge-shaped dispersive element that refracts light into a continuous spectrum.

Diffraction Grating

Optical surface with parallel grooves that separates light by diffraction; offers high wavelength resolution.

Cuvette (Sample Cell)

Rectangular container (usually 1 cm path length) that holds the sample solution for measurement.

Photodetector

Device that converts transmitted radiant energy into an electrical signal for readout.

Photocell (Barrier Cell)

Simple, inexpensive photodetector with low sensitivity and fatigue issues.

Phototube

Vacuum tube detector in which incident light releases electrons from a photocathode to an anode.

Photodiode / Phototransistor

Semiconductor photodetectors offering moderate sensitivity across multiple wavelengths.

Photomultiplier Tube (PMT)

Highly sensitive detector that amplifies light signals (~200×) using dynodes; ideal for low light levels.

Single-Beam Spectrophotometer

Instrument that measures absorbance of one beam through the sample; blank measured separately.

Double-Beam Spectrophotometer

Instrument splitting light into sample and reference beams for simultaneous or alternating measurement.

Blank

Cuvette containing reagent (or solvent) only; establishes baseline absorbance for corrections.

Calibrator / Standard

Solution with known analyte concentration used to generate calibration factor or curve.

Quality Control (QC) Sample

Specimen with known values run routinely to verify instrument accuracy and precision.

Stray Light

Unwanted wavelengths reaching the detector; caused by reflections, scratches, or grating artifacts.

Wavelength Accuracy

Degree to which the selected wavelength matches the indicated value; verified with calibration lamps.

Linearity Range

Concentration interval over which Beer-Lambert Law holds and absorbance is proportional to concentration.

Flame Emission Photometry (FEP)

Technique measuring light emitted by excited atoms (Na⁺, K⁺, Li⁺) returning to ground state in a flame.

Atomization (FEP/AAS)

Process of converting sample to free atoms via nebulization and flame or furnace heating.

Flame Photometer

Instrument for FEP containing burner, nebulizer, monochromator (filter), and photodetector.

Atomic Absorption Spectrophotometry (AAS)

Technique quantifying metal ions by measuring light absorbed by ground-state atoms; ~100× more sensitive than FEP.

Hollow Cathode Lamp (HCL)

Element-specific light source for AAS emitting the exact wavelength absorbed by the analyte atoms.

Electrodeless Discharge Lamp (EDL)

Radio-frequency-excited lamp producing intense element-specific emission lines for AAS.

Graphite Furnace AAS

AAS atomizer using electrically heated graphite tubes (up to 3000 °C) for high sensitivity and low sample volume.

Spectral Interference (AAS)

Error from overlapping absorption/emission lines; corrected by narrower slits or background correction.

Chemical Interference (AAS)

Suppression due to stable compounds (e.g., CaPO₄); mitigated with releasing agents like lanthanum.

Ionization Interference (AAS)

Loss of neutral atoms via ionization in hot flames; controlled with ionization suppressors (e.g., K⁺).

Nebulizer

Device that transforms liquid sample into fine aerosol for introduction into a flame or furnace.

Path Length (b or l)

Distance light travels through the sample (typically 1 cm); longer path increases absorbance.

Molar Absorptivity (ε)

Constant defining how strongly a substance absorbs light at a given wavelength; units L·mol⁻¹·cm⁻¹.

Percent Transmittance (%T)

100 × (transmitted intensity / incident intensity); inverse logarithmic relationship with absorbance.