11.2
Métodos Cromatográficos: Classificação
As técnicas cromatográficas são classificadas de três maneiras: A classificação é baseada no estado físico das fases estacionária e móvel, em como a f…
Os métodos cromatográficos são classificados com base em vários fatores.
A primeira classificação é baseada nos estados físicos das fases móvel e estacionária.
Por exemplo, na cromatografia gás-líquido, a fase móvel é um gás, enquanto a fase estacionária é um revestimento líquido fino.
Em casos como a 'cromatografia gasosa', em que apenas uma fase é mencionada, a fase dada é a móvel.
A segunda classificação é baseada no equipamento que suporta a fase estacionária, que inclui cromatografia em coluna e plana.
Na cromatografia em coluna, a fase estacionária é embalada em uma coluna ou revestida dentro de um tubo estreito, e a fase móvel passa sob gravidade ou pressão.
Na cromatografia planar, a fase estacionária é imobilizada em uma superfície plana plana e a fase móvel viaja por ação capilar.
A terceira classificação é baseada no mecanismo químico ou físico de separação.
Isso inclui adsorção, partição, troca iônica e cromatografia de exclusão por tamanho.
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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.