Liquid Chromatography essay

Chromatography is a method of separating mixtures into their respective components (Schroeder 509). In 1903, Mikhail Tswett separated plant pigments by passing it through a glass column percolated with petroleum-ether and calcium carbonate (Fifield and Keally 80). Then, he observed the development of colored zones as the extract permeates into the glass column. Thus, he inferred that the components of the extract were separated into bands of colors due to their different migration rates; he coined than the word “chroma” or “color” to this separation technique (Fifield and Keally 80).

Nowadays, liquid chromatography is utilized in both qualitative and quantitative biochemical and pharmaceutical analyses. Chromatographic analysis is done for quality control and shelf-life determination of industrial products, environmental pollutant analysis and monitoring, identification of illegal and counterfeit drugs, wastewater analysis and pollutant determination, analysis of illegal drugs in biological samples, pesticide detection in agricultural products, and analysis of biological samples (Betts). Chromatographic Process

In the chromatographic process, the mixture components, carried by the mobile phase or eluent, infiltrate the stationary phase column (Fifield and Keally 81). Through a high-pressure pump system, the mixture is directed and forced to flow against the stationary phase at the rate of one to two millimeter per minute (Levin). Then, the mobile phase in which the sample is dissolved, passed through the detector which has low volume cell (Levin). Consequently, the mobile phase causes an interaction between the sample constituents and the stationary phase (Levin).

Thus, controlling this interaction gives different time of retention of various constituents of the sample on the stationary phase (Levin). The separation then is made possible due to the variation in the rate of constituent migration or distribution ratios. As the components move out at the end of the column, the detector sends an electrical signal to the recorder and by means of computer processing system the signal will be displayed as either a graph of time against detector response or a printout of specific component and its concentration in the analyzed sample (Schroeder 515). Liquid Chromatographic System

An efficient mobile phase system must be cautiously decided for it dictates the effective separation of multi-component mixtures (Scott 68). As a rule of thumb, the mobile phase should be selected in such a way that interactions in the mobile phase are minimized as it maximizes the interactions in the stationary phase (Scott 68). In liquid chromatography, the mobiles phase is a substance that can effectively dissolve the sample (Schroeder 519). The technique is an isocratic chromatography when a single solvent like acetonitrile, water, and ethanol was used; the combination of these solvents is also encouraged (Schroeder 519).

On the other hand, solids with fine granular particles like silica gel are employed as stationary phase. As similar with the mobile phase, a single type of stationary phase can be employed for the separation of non-polar compounds (Schroeder 519). Nevertheless, granule modification can be made by reversing the polarity of the gel by means of surface-bonded coatings. The result of this modification is used as column for polar substance separation (Schroeder 519). Even though the stationary phase is solid, moisture can still be present on its granular particles; this also modifies the mobile-stationary phase interactions.

Meanwhile, a 10-25 centimeter column with an internal diameter of 2-4 millimeter is commonly utilized glass column (Schroeder 519). Recently, nano columns were made available but must be employed under much higher pressure for a good elution (Schroeder 519). Normally, a pressure of 30-300 pounds per square inch can cause 1-2 milliliter per minute liquid flow (Schroeder 519).

Works Cited Betts, Tom. “HPLC Instrumentation. ” n. d. Kutztown University of PA. 15 March 2009 <http://faculty. kutztown. edu/betts/html/HPLC. htm#Applications>.

Fifield, F. W. and Keally, D. Principles and Practice of Analytical Chemistry, 5th ed. Oxford: Blackwell Science, 2000. Levin, Shulamit. “Analysis of Ions Using High Performance Liquid Chromatography: Ion-Chromatography. ” 2002. Bioforum. 15 March 2009 <http://www. forumsci. co. il/HPLC/ion_chrm. html>. Schroeder, Patick. “Gas and Liquid Chromatography. ” 30 September 2003. Micromass U. K. Ltd. Back to Basics Manual. 15 March 2009 < http://www. cs. uwm. edu/~cs536/cs536-2/library/gclcbtb. pdf>. Scott, Raymond P. W. “Chrom-Ed Book Series, Liquid