1.3 Types of analytical methods and their applications
5 min read•august 14, 2024
Analytical chemistry offers a diverse toolkit for investigating matter. From to , these methods help scientists uncover the composition and properties of substances. Each technique has unique strengths and limitations, making them suitable for different applications.
Choosing the right analytical method involves considering factors like , , and cost. Real-world applications span environmental monitoring, clinical diagnostics, and materials characterization. Understanding these methods is crucial for solving complex analytical problems across various fields.
Analytical Method Classification
Spectroscopic Methods
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Based on the interaction of electromagnetic radiation with matter
Involves absorption, emission, or scattering of light
Examples include UV-visible spectroscopy, atomic absorption spectroscopy (), and
Provide information on the electronic structure, molecular vibrations, and elemental composition of analytes
Electrochemical Methods
Involve the measurement of electrical properties to determine analyte concentration or characterize redox reactions
Techniques include , , and
Potentiometry measures the potential difference between two electrodes to determine the concentration of ions in solution
Voltammetry studies the current-potential relationship to investigate redox processes and quantify electroactive species
Conductometry measures the electrical conductivity of a solution to determine the concentration of ionic species
Chromatographic Techniques
Separate and analyze mixtures based on the differential distribution of analytes between a stationary phase and a mobile phase
Examples include (GC), (), and (IC)
Gas chromatography is used for the separation and analysis of volatile compounds
High-performance liquid chromatography is employed for the separation and quantification of non-volatile and thermally labile analytes
Ion chromatography is utilized for the determination of ionic species in aqueous samples
Mass Spectrometry and Thermal Analysis
measures the mass-to-charge ratio of ions to identify and quantify analytes
Often coupled with separation techniques like GC or LC for enhanced specificity
Provides molecular weight and structural information
Thermal analysis methods study the physical and chemical changes in materials as a function of temperature
Examples include (DSC) and (TGA)
DSC measures the heat flow associated with phase transitions and chemical reactions
TGA monitors the mass change of a sample as a function of temperature to study decomposition, oxidation, or dehydration processes
Strengths vs Limitations of Analytical Methods
Sensitivity and Selectivity
Sensitivity refers to the minimum amount of analyte that can be detected or quantified by an analytical method
Techniques like mass spectrometry and fluorescence spectroscopy often have high sensitivity
Some electrochemical methods may have lower sensitivity
Selectivity is the ability to differentiate between the analyte of interest and other components in the sample matrix
Chromatographic techniques and mass spectrometry generally offer high selectivity
Some spectroscopic methods may have lower selectivity due to potential interferences
Speed and Cost Considerations
Speed refers to the time required for sample preparation, analysis, and data processing
Direct spectroscopic measurements can be performed rapidly
Chromatographic separations may require longer analysis times
Cost considerations include the initial investment in instrumentation, maintenance, consumables, and operator training
UV-visible spectroscopy is relatively inexpensive
Mass spectrometry has higher associated costs
The choice of analytical method often involves a trade-off between these factors
The most suitable technique depends on the specific requirements of the application
Selecting Analytical Techniques for Applications
Sample Matrix and Analyte Properties
Sample matrix refers to the components of the sample other than the analyte of interest
The matrix can affect the performance of analytical methods through interferences, suppression, or enhancement of analyte signals
Techniques with high selectivity, such as mass spectrometry or chromatography, are often preferred for complex matrices
Analyte properties, such as volatility, polarity, and molecular weight, influence the choice of analytical method
Gas chromatography is suitable for volatile compounds
Liquid chromatography is used for non-volatile and thermally labile analytes
Desired Information and Sample Preparation
The desired information, such as qualitative identification, quantitative determination, or structural characterization, guides the selection of analytical techniques
Mass spectrometry provides molecular weight and structural information
Spectroscopic methods are often used for quantitative analysis
Sample preparation steps, such as , , or preconcentration, may be required to isolate the analyte from the matrix and improve the performance of the analytical method
(SPE) is commonly used for sample cleanup and analyte enrichment
Derivatization techniques can improve the chromatographic separation or detection sensitivity of certain analytes
Real-world Applications of Analytical Methods
Environmental Monitoring
Gas chromatography-mass spectrometry () is used to detect and quantify persistent organic pollutants (pesticides, polychlorinated biphenyls) in air, water, and soil samples
Ion chromatography is employed to measure inorganic anions (sulfate, nitrate) in precipitation and surface waters
(ICP-MS) is utilized for the determination of trace elements in environmental samples
Atomic absorption spectroscopy (AAS) is used to monitor heavy metal contamination in water and soil
Clinical Diagnostics
, such as (ELISA), are widely used to detect specific antigens or antibodies in biological fluids for the diagnosis of infectious diseases, hormonal disorders, and cancer markers
High-performance liquid chromatography (HPLC) is utilized to measure drug levels in blood or urine for therapeutic drug monitoring and toxicological screening
Gas chromatography-mass spectrometry (GC-MS) is employed for the detection of drugs of abuse and metabolites in forensic toxicology
(PCR) is used for the amplification and detection of specific DNA sequences in genetic testing and infectious disease diagnosis
Materials Characterization and Food Analysis
(XRD) is employed to determine the crystal structure, phase composition, and crystallite size of solid materials (ceramics, polymers, pharmaceuticals)
(SEM) coupled with (EDS) provides information on the surface morphology and elemental composition of materials at the micro and nanoscale
High-performance liquid chromatography (HPLC) is used to detect and quantify food additives, preservatives, and contaminants (mycotoxins, pesticide residues)
Atomic absorption spectroscopy (AAS) is employed to determine the concentration of essential and toxic elements (calcium, iron, lead) in food samples
Gas chromatography-mass spectrometry (GC-MS) is utilized for the analysis of flavor and aroma compounds in food and beverage products