Laboratory‎ > ‎Paper Chromatography and Beer’s Law




Chromatography is a method for analyzing complex mixtures (such as ink) by separating them into the chemicals from which they are made. Chromatography is used to separate and identify all sorts of substances. Drugs from narcotics to aspirin can be identified in urine and blood samples, often with the aid of chromatography. The components to be separated are distributed between two phases: a stationary phase bed and a mobile phase which percolates through the stationary bed.

Paper chromatography is one method for testing the purity of compounds and identifying substances. Paper chromatography is a useful technique because it is relatively quick and requires small quantities of material. Separations in paper chromatography involve the same principles as those in thin layer chromatography. In paper chromatography, like thin layer chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate on the stationary phase according to how strongly they adsorb to the stationary phase versus how much they dissolve in the mobile phase.The R f value for each spot should be calculated. R f stands for "ratio of fronts" and is characteristic for any given compound. Hence, known R f values can be compared to those of unknown substances to aid in their identifications.

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