Micronutrients & Trace Elements Analysis - Key Terms (Spectroscopy, Chromatography, MS, and Related Techniques)

Vocabulary-style flashcards covering core concepts across spectroscopy, chromatography, GC, HPLC, MS, and related analytical techniques as presented in the lecture notes.

Spectroscopy

Study of the interaction between matter and electromagnetic radiation, used to detect and quantify food constituents by measuring absorbed or emitted radiation.

Absorption spectroscopy

A type of spectroscopy where radiation is absorbed by the sample; used to estimate components by analyzing transmitted/absorbed light.

Emission spectroscopy

Spectroscopy where radiative energy is released by the sample; limited in food analysis but used for some minerals.

Spectroscopy

The study of how matter interacts with electromagnetic radiation to reveal composition or structure.

UV-Vis spectrophotometry

Spectroscopic technique using ultraviolet and visible light to measure absorbance and infer concentration or identity.

λmax

Wavelength at which a compound shows maximum absorbance; used for identification.

Qualitative analysis (in UV-Vis)

Identification of substances based on characteristic spectra (e.g., λmax and spectral shape).

Quantitative analysis (in UV-Vis)

Determination of concentration from absorbance, often via a calibration curve.

Beer-Lambert Law

A = ε × b × c; relates absorbance to molar absorptivity, path length, and concentration.

Absorbance (A)

Measure of how much light is absorbed by a sample at a given wavelength.

Molar absorptivity (ε)

A constant describing how strongly a species absorbs light at a specific wavelength.

Path length (b)

Distance that light travels through the sample, usually in a cuvette.

Standard curve

Plot of absorbance versus concentration used to determine unknown concentrations.

Blank

Solvent or buffer used to zero the instrument by setting absorbance to zero.

Linear range

Concentration range over which Beer-Lambert Law holds true.

Dilution

Process of reducing sample concentration to fall within the linear range.

Chromatography

Technique to separate mixture components based on differential affinities to stationary and mobile phases.

Mobile phase

The liquid or gas that carries components through the chromatographic system.

Stationary phase

The phase that remains fixed while the mobile phase passes through it.

Retention (in chromatography)

Time or order in which compounds travel through the system; higher mobile-phase affinity elutes faster, higher stationary-phase affinity elutes slower.

Adsorption chromatography

Separation based on adsorption of analytes to active sites on the stationary phase; polarity influences interactions.

Partition chromatography

Separation based on distribution of analytes between a stationary liquid phase and a mobile phase.

Gel Permeation Chromatography (Size Exclusion)

Separation based on molecular size; larger molecules elute first, smaller molecules penetrate pores.

Ion Exchange Chromatography

Separation by reversible charge interactions between analytes and charged sites on the stationary phase; includes cation and anion exchange.

Affinity chromatography

Separation based on specific, reversible interactions between the analyte and a bound ligand on the stationary phase.

Adsorption chromatography

Separation based on adsorption of analytes to the surface of the stationary phase; polarity governs affinity.

Normal-Phase Chromatography

Adsorption-based chromatography using polar stationary phase (e.g., silica) and non-polar mobile phase.

Reversed-Phase Chromatography

Chromatography using non-polar stationary phase (e.g., C18) with polar mobile phase.

Gas Chromatography (GC)

Chromatographic separation of volatile and semi-volatile compounds using a gas as the mobile phase.

Gas-solid chromatography

GC modality where the stationary phase is a solid and the mobile phase is a gas.

Gas-liquid chromatography

GC modality where the stationary phase is a liquid on a solid support and the mobile phase is a gas.

GC instrumentation

Components like carrier gas, injector, column oven, and detector; carrier gases include H2, N2, He.

Split Injection

Small portion of the sample enters the GC column while excess is vented.

Splitless Injection

Entire sample enters the GC column for trace analysis.

On-column Injection

Direct transfer of sample to the GC column; used for thermally sensitive compounds.

GC column types

Packed columns or capillary columns used for separations; temperature programming affects separation.

Temperature programming

Controlled change of column oven temperature to improve separation of wide-boiling-range compounds.

Isothermal programming

Constant temperature operation for narrow-boiling-range separations.

GC detectors

Devices that convert solute interactions into an electrical signal; must be sensitive, stable, linear, and reliable.

FID (Flame Ionization Detector)

GC detector for carbon and hydrogen; destructive detection mechanism.

ECD (Electron Capture Detector)

GC detector that is highly sensitive to halogenated compounds.

TCD (Thermal Conductivity Detector)

Universal GC detector; non-destructive.

Mass Spectrometry (MS) in GC

Detector providing structural information; highly sensitive and selective.

Chromatogram

Plot of detector response versus time; used to identify compounds by retention time and to quantify by peak area or height.

Retention Time (RT)

Time a compound takes to elute from the GC column; used for identification.

Advantages of GC

Good separation, short analysis time, small sample size, robust detection; relies on volatility.

HPLC (High-Performance Liquid Chromatography)

High-pressure liquid chromatography used for separation, identification, purification, and quantitation.

HPLC components

Solvent reservoir, pump, injector, column, detector, recorder; guard column protects the main column.

HPLC detectors

UV/Vis, refractive index (RI), fluorescence (FLR), and mass spectrometry (MS) detectors.

HPLC mobile phases & elution

Mobile phase quality includes purity and compatibility; Normal Phase vs Reversed Phase; isocratic vs gradient elution.

Isocratic elution

Constant mobile phase composition during an HPLC run.

Gradient elution

Changing mobile phase composition during an HPLC run.

HPLC uses

Qualitative: identify components by retention time; Quantitative: measure peak areas with calibration; Preparative: collect and purify components.

HPLC troubleshooting

Calibration with standards; avoid carry-over; blanks for contamination checks; random errors indicate precision issues.

Mass Spectrometry (MS)

Mass-based analytic technique that measures masses of ions by mass-to-charge ratio (m/z) for identification and quantification.

Ionization (MS)

Process of forming gas-phase ions from a sample.

Mass analyzer

Instrument component that separates ions according to m/z.

Mass Spectrum

Graph of ion signals versus m/z showing molecular ion and fragment peaks; base peak is the most intense.

Molecular ion (M+•)

Ion corresponding to the entire molecule after ionization, used to determine molecular weight.

HRMS (High-Resolution MS)

Mass spectrometry with high mass accuracy to determine exact molecular formulas.

Isotopic peaks

Additional peaks in MS spectra due to natural isotopes (e.g., Cl, Br) affecting m/z.

Molecular formula determination in MS

Use precise mass to deduce possible formulas; require matching decimals to confirm.

Uses of Mass Spectrometry

Identification of macro nutrients, quantification of active components, metabolite analysis, contaminants/residues.

Other spectroscopic methods

Colourimetry, infrared (IR), fluorimetry, flame photometry, atomic absorption (AAS), ESR, NMR.