11.2
Métodos cromatográficos: clasificación
Las técnicas cromatográficas se clasifican de tres formas: la clasificación se basa en el estado físico de las fases estacionaria y móvil, en cómo se…
Los métodos cromatográficos se clasifican en función de varios factores.
La primera clasificación se basa en los estados físicos de las fases móvil y estacionaria.
Por ejemplo, en la cromatografía gas-líquido, la fase móvil es un gas, mientras que la fase estacionaria es un recubrimiento líquido fino.
En casos como el de la "cromatografía de gases", en el que sólo se menciona una fase, la fase dada es la móvil.
La segunda clasificación se basa en el equipo que soporta la fase estacionaria, que incluye cromatografía en columna y plana.
En la cromatografía en columna, la fase estacionaria se empaqueta en una columna o se recubre dentro de un tubo estrecho, y la fase móvil pasa a través de ella bajo gravedad o presión.
En la cromatografía plana, la fase estacionaria se inmoviliza sobre una superficie plana plana y la fase móvil viaja por acción capilar.
La tercera clasificación se basa en el mecanismo químico o físico de separación.
Estos incluyen adsorción, partición, intercambio iónico y cromatografía de exclusión por tamaño.
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Q1: What are the three main ways chromatographic methods are classified?
Chromatographic methods are classified by the physical states of mobile and stationary phases, the equipment supporting the stationary phase, and the chemical or physical separation mechanism. The first classification distinguishes between gas-liquid and gas-solid chromatography based on phase composition. The second divides methods into column and planar chromatography based on geometry. The third includes adsorption, partition, ion exchange, and size-exclusion chromatography based on separation principles.
Q2: How do column and planar chromatography differ in their physical setup?
In column chromatography, the stationary phase is packed into or coated inside a narrow tube, and the mobile phase passes through under gravity or pressure. In planar chromatography, the stationary phase is immobilized on a flat surface, and the mobile phase travels across it by capillary action. These geometric differences affect how samples move through the system and how separations are achieved.
Q3: What does it mean when a chromatographic technique is named with only one phase?
When a chromatographic method is named with only one phase, such as gas chromatography, the mentioned phase is the mobile phase. The stationary phase is implied but not explicitly stated in the name. This naming convention simplifies terminology while the complete phase composition is understood from the specific technique type.
Q4: How does adsorption chromatography separate solutes from other separation methods?
Adsorption chromatography separates solutes based on their relative adsorption affinities for the solid stationary phase. Unlike partition chromatography, which depends on solubilities in liquid phases, adsorption relies on how strongly solutes bind to the solid surface. This mechanism makes adsorption chromatography effective for separating compounds with different surface interaction strengths.
Q5: What is the principle behind size-exclusion chromatography?
Size-exclusion chromatography separates solutes based on their molecular size and ability to enter pores in the stationary phase. Larger molecules that cannot fit into pores travel shorter path lengths through the column, while smaller molecules that enter pores travel longer paths. This difference in path length creates separation based on molecular dimensions.
Q6: How is the mobile phase typically identified in chromatographic nomenclature?
Chromatographic techniques are named by stating the type of chromatography, followed by the mobile phase, then the stationary phase. For example, in gas-solid chromatography, gas is the mobile phase and solid is the stationary phase. In liquid-liquid chromatography, the first liquid is the mobile phase and the second liquid or liquid-coated solid is the stationary phase.
Q7: How does ion-exchange chromatography achieve separation?
Ion-exchange chromatography separates solutes based on their electrical charge and attraction to the stationary phase. Solutes with different charges interact differently with the charged stationary phase, causing them to elute at different times. This mechanism is particularly useful for separating charged molecules like proteins and nucleic acids.