12: Chromatographic and Electrophoretic Methods
- Page ID
- 540075
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Drawing from an arsenal of analytical techniques—many of which were the subject of the preceding four chapters—analytical chemists design methods that detect increasingly smaller concentrations of analyte in increasingly more complex matrices. Despite the power of these analytical techniques, they often suffer from a lack of selectivity. For this reason, many analytical procedures include a step to separate the analyte from potential interferents. Although effective, each additional step in an analytical procedure increases the analysis time and the cost of the analysis, and introduces uncertainty. In this chapter we consider two analytical techniques that avoid these limitations by combining the separation and analysis: chromatography and electrophoresis.
- 12.1: General Theory of Separation Effiiciency
- The page explains the process of analytical separation, which aims to isolate an analyte or remove an interferent from a sample matrix. A distinction is made between the chemical or physical properties of these components to achieve separation. Key concepts include the analyte's and interferent's recoveries, defined by specific equations, and the separation factor.
- 12.2: Classifying Separation Techniques
- The document details various analytical separation techniques based on differences in chemical or physical properties between analytes and interferents. It includes methods like filtration, dialysis, and chromatography for size-based separations; centrifugation for mass or density differences; masking for complexation reactions; and techniques such as distillation, sublimation, and recrystallization for changes in physical or chemical states.
- 12.3: Liquid-Liquid Extractions
- The document discusses liquid-liquid extraction as a key method for separating compounds, used in environmental, clinical, and industrial labs. It highlights the importance of this technique in monitoring trihalomethanes in water supplies, often through gas chromatography after extraction with pentane. The text explains the concepts of partition coefficients and distribution ratios, emphasizing their roles in determining extraction efficiency.
- 12.4: Separation Versus Preconcentration
- The page discusses two common analytical issues: interference from matrix components and low analyte concentrations. Separation techniques can address both by isolating the analyte in a new phase and increasing its concentration through preconcentration. An example given is the gas chromatographic analysis for organophosphorous pesticides in water, where analytes are extracted and concentrated 67-fold using solid-phase extraction with ethyl acetate.
- 12.5: Overview of Analytical Separations
- The text discusses methods for separating analytes from interferents, focusing on liquid-liquid extractions and chromatography. Liquid-liquid extractions involve partitioning solutes between two immiscible phases, but face limitations, such as the need for multiple extractions and difficulty separating species with similar distribution ratios. A countercurrent extraction can improve separation efficiency.
- 12.6: General Theory of Column Chromatography
- This page provides a comprehensive overview of column chromatography, focusing on the theoretical concepts and calculations essential for understanding this separation technique. It introduces key concepts like chromatographic resolution, retention time, selectivity, and column efficiency. The content explains how solutes are separated and how to analyze chromatographic data to assess separation quality.
- 12.7: Optimizing Chromatographic Separations
- Now that we have defined the solute retention factor, selectivity, and column efficiency we are able to consider how they affect the resolution of two closely eluting peaks.
- 12.8: Gas Chromatography
- Gas chromatography (GC) is a technique in which a sample, either gas or liquid, is injected into a mobile phase, usually a chemically inert gas like He, Ar, or N2, which carries it through a column. In a packed column, larger samples can be handled, whereas capillary columns allow separation of more complex mixtures. Elution order in gas-liquid chromatography depends on solutes' boiling points and interactions with the stationary phase.
- 12.9: High-Performance Liquid Chromatography
- This page discusses High-Performance Liquid Chromatography (HPLC), a method for separating compounds in a liquid solution. HPLC involves key components: reservoirs for the mobile phase, a pump, an injector, columns (analytical and guard), and detectors. It explains different separation techniques (liquid-solid adsorption, liquid-liquid partitioning, etc.), types of columns (packed and capillary), stationary and mobile phases, and their interactions.
- 12.10: Other Forms of Chromatography
- The text covers various liquid chromatography techniques, focusing on liquid-solid adsorption, ion-exchange, and size-exclusion chromatography. Liquid-solid chromatography involves polar stationary phases and nonpolar solvents for separating compounds, excelling in analyzing isomers. Ion-exchange chromatography uses resin beads with ionic functional groups to separate ions based on their affinity for the exchange sites, utilizing gradient elutions to affect solute retention.
- 12.11: Electrophoresis
- The document provides a comprehensive overview of electrophoresis, focusing notably on capillary electrophoresis (CE). Electrophoresis involves the separation of analytes based on their capacity to move through a conductive medium under an electric field, with cations moving towards the cathode and anions towards the anode.
- 12.12: Problems
- This page presents a comprehensive set of problems in chromatography and capillary zone electrophoresis (CZE). Key topics include calculating theoretical plates, resolving power, chromatographic resolution, retention indices, ion balances, and evaluating chromatographic data for various compounds. Problems engage chemical principles such as pH impact, calibration curves, and the Van Deemter equation.
- 12.13: Additional Resources
- The page provides a comprehensive list of experiments and references related to chromatography and electrophoresis. It categorizes experiments into gas chromatography, high-performance liquid chromatography, ion-exchange chromatography, size-exclusion chromatography, and electrophoresis.
- 12.14: Chapter Summary and Key Terms
- This page highlights the fundamentals of chromatography and electrophoresis, potent analytical techniques used to separate and analyze sample components. It details concepts such as retention factors, column efficiency, and selectivity in chromatographic separations, and how methods like gas chromatography (GC) and high-performance liquid chromatography (HPLC) are applied.