Study Notes on Analytical Chemistry and Chromatography Techniques

Chromatography is used for separating individual components from mixtures, facilitating easier analysis of each component.
Example: Using green Gatorade, which contains two different food dyes, chromatography separates the components so their absorbances can be measured individually.
Process: Solvent runs through a stationary phase (like sand or silica) which allows different colors to emerge at different times.

Thin Layer Chromatography (TLC): A common laboratory technique where a sample is applied to a thin layer of adsorbent material, allowing for the separation of components based on their differing affinities.
Paper Chromatography: An experiential technique often conducted with markers, where water travels up paper, separating different pigments from ink.
Origin of the term 'chromatography' (meaning 'color writing') is due to initial experiments involving chlorophyll.

Extraction: Involves separating compounds based on their solubility in different phases (aqueous vs organic).
Separatory Funnel: Utilized for adding two immiscible liquids, promoting the partitioning of an analyte between the two phases.
- Example: Mixing an aqueous solution with hexane to separate components based on their different levels of solubility.
- Quantitative chemistry assesses the concentration of phases 1 and 2, using partition coefficients to inform how well the components separate.

Transition from batch extraction to continuous chromatography involves maintaining a constant mobile phase moving through a fixed stationary phase.
Stationary phase: Remains fixed, while the mobile phase carries analytes through.
Dynamic equilibrium is maintained where analytes continuously partition between stationary and mobile phases.

Theoretical Plates: The concept arises from the transition from discrete plates to continuous flow in chromatography.
High efficiency is driven by a greater number of theoretical plates, directly impacting separation quality.
Mobile Phase: Can be a liquid (liquid chromatography, LC) or gas (gas chromatography, GC).
Adsorption vs Partitioning: Different physical processes define how analytes engage with stationary and mobile phases; adsorption refers to molecules interacting with the surface of a stationary phase.

Different analytes interact with stationary phases based on conditions (size, polarity).
HPLC (High Performance Liquid Chromatography): A form of liquid chromatography where smaller particles lead to better resolution due to reduced spreading effects during transport through the column.

Retention Time: The time from injection to when the analyte is detected, measured at the peak's center.
Factors affecting retention include:
  - Time delay (dead time)
  - Retention factor, indicating how long an analyte is held back when compared to unretained components.
  - Increasing flow rate can improve separation and reduce dispersion effects.

Resolution is defined by how well peaks separate in a chromatogram and is improved by:
  - Longer retention time between different analytes (greater delta t).
  - Narrower peaks indicating sharp separation.
  - Greater number of theoretical plates and lower plate height enhance resolution efforts.

Bandwidth factor explains peak spreading based on three principles:
  1. Multiple Paths: Analytes take different paths causing separation due to varying path lengths.
  2. Longitudinal Diffusion: Higher concentration diffuses toward lower concentration, causing spreading over time.
  3. Resistance to Mass Transfer: Limits instantaneous interaction between phases.

The Van Deemter equation describes the plate height as a function of mobile phase velocity combined with other scattering factors that influence overall separation quality:
- The terms in this equation quantify contributions from multiple pathways, longitudinal diffusion, and resistance to mass transfer.

Mass spectrometry (MS) is coupled with chromatographic techniques to provide identification of separated analytes based on mass-to-charge ratios.
Quadrupole Systems: Utilize electrical fields to selectively filter ions based on their mass/charge ratios, enhancing analysis post-separation.
Analytes can exhibit different fragmentation patterns, allowing further analysis of structure post-detachment.