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Chromatographie liquide haute performance: instrumentation
La chromatographie liquide haute performance, ou HPLC, est une technique d'analyse qui sépare des échantillons liquides sous haute pression. Un instru…
Les principaux composants d’un instrument HPLC sont un réservoir de phase mobile, une pompe, un injecteur, une colonne, un détecteur et un système de données.
Le réservoir de phase mobile se compose d’une ou plusieurs bouteilles en verre de stockage de solvant à partir desquelles le solvant est aspiré par des systèmes de pompage.
Dans l’élution par gradient, les solvants sont mélangés avant d’entrer dans la colonne.
Un système d’injection, manuel ou automatique, introduit le mélange d’analytes dans la phase mobile avant qu’il n’entre dans la colonne.
Dans la colonne, les composants de l’analyte sont séparés en fonction de leur interaction avec les phases mobile et stationnaire.
Ensuite, les constituants de l’échantillon séparés se déplacent vers le détecteur, qui génère des signaux caractéristiques.
Ces signaux sont traduits en chromatogramme par un programme assisté par ordinateur, et l’éluant est envoyé dans les déchets.
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Q1: What are the main components of an HPLC instrument?
An HPLC instrument consists of six major components: a mobile phase reservoir for storing solvents, a pump to deliver the mobile phase, an injector to introduce the sample, an analytical column where separation occurs, a detector to identify separated components, and a data system to generate chromatograms. These components work together to separate liquid samples under high pressure.
Q2: How does the pump system work in HPLC?
Modern HPLC instruments use reciprocating piston pumps that create a pulsed mobile phase flow. A pulse damper smooths out these pulses to ensure consistent solvent delivery. The pump draws HPLC-grade solvents from the mobile phase reservoir and delivers them at high pressure into the analytical column, maintaining precise flow rates throughout the separation process.
Q3: What is gradient elution and why is it used in HPLC?
Gradient elution gradually changes the composition of the mobile phase during analysis, enhancing separation of complex mixtures based on their polarity. Gradient controllers maintain consistent solvent flow rates during this process. This technique allows better resolution of compounds with varying chemical properties compared to using a single, constant mobile phase composition.
Q4: How is the sample introduced into the HPLC system?
The sample is introduced using either a manual loop injector or an autoinjector before the mobile phase reaches the column. These injection systems introduce the analyte mixture into the mobile phase stream. Automated systems allow for consistent, reproducible sample introduction, while manual injection provides flexibility for variable sample volumes.
Q5: What role does the analytical column play in HPLC separation?
The analytical column, packed with a stationary phase and maintained at constant temperature by a column oven, is where analyte components separate based on their interactions with both the mobile and stationary phases. Guard columns and scavenger columns may protect the main column from contamination. The separated components then travel to the detector for identification.
Q6: How does the detector convert separated components into usable data?
The detector identifies separated analyte components and generates characteristic signals. A computer-aided program translates these signals into a chromatogram, which displays the separation results. The eluent carrying the separated components either goes into waste or is collected at a fractional collector for further analysis.
Q7: Why is solvent preparation important before HPLC analysis?
HPLC-grade solvents maintain high purity required for accurate analysis. Dissolved gases must be removed using a degasser, such as a vacuum pumping system or sparging with helium, to prevent bubble formation that could disrupt flow and detection. Proper solvent preparation ensures consistent mobile phase delivery and reliable chromatographic results.