Experiment 4: Extraction and Chromatic Separation of Plant Pigments from Tomato Paste

Topics: Chromatography, Thin layer chromatography, Analytical chemistry Pages: 6 (1883 words) Published: February 4, 2014
Reporter: Instructor: Prof Susana D. Torres Section: 2ChE-C Date Performed: December 17, 2013 Group No.: 8 Date Submitted: January 6, 2014

Experiment 4: Extraction and Chromatic Separation of Plant Pigments from Tomato Paste


In column chromatography a mixture is dissolved in a solvent and poured over a column of solid adsorbent then eluted with the same or a different solvent. This method is often used for preparative purposes; when a relatively large amount of the mixture and the components need to be isolated.

The two main pigments in tomato paste mixture are the yellow-orange β-carotene and the red lycopene. The colors of these pigments are because of the double bonds in their structure. The Lycopene and B-carotene will be separated from tomato paste by using column chromatography. First, the organic layer was separated from the paste by rinsing and drying by addition of sodium sulfate. The remaining solvent was then concentrated by heating before being added to the column in the chromatography. Petroleum ether was used to move the (-carotene down the column where it was desired. The Lycopene was extracted by using a ratio of 90:10 petroleum ether/acetone.


Chromatography is the science which applies laboratory techniques for the separation of mixtures or molecules based on differences in their structure and/or composition. Chromatography may either be preparative (separate the components for advanced uses) or analytical (for relative proportions). It involves a sample (or sample extract) that is dissolved in a mobile phase (which may be in gaseous form, liquid form or is a supercritical fluid). The mobile phase is then forced through an immobile, immiscible stationary phase. The phases are chosen as such that the components of the sample have differing solubilities in each phase. A component which is quite soluble in the stationary phase will take more time to travel through it than a component which is not very soluble in the stationary phase but still very soluble in the mobile phase. Due to these differences in mobilities, the sample components will become separated from each other as they travel through the stationary phase giving us the bands we see from the experiment.

Chromatographic separations can be accomplished by using a variety of apparatus, including compacted silica on glass plates which is also known as thin layer chromatography, volatile gases or also known as gas chromatography, paper for paper chromatography and liquids which incorporate hydrophilic, insoluble molecules for liquid chromatography. Column chromatography is one of the many isolation and purification techniques used widely by chemists to obtain pure samples of chemicals from natural sources or from reactions.

If the compounds to be separated are colored then the separation can be monitored visually; although it is more common that the compounds to be isolated from a column chromatography are colorless (which is not the case for our sample). In that case, several means for monitoring the separation progress have been devised. One of the simplest of these involves the collection of relatively small fractions of the eluent in labeled tubes and the analysis of the component(s) of these fractions thin layer chromatography.

Lycopene is the red pigment found in ripe tomatoes and is a natural antioxidant. Meaning, it helps to fight certain cancers and is a C40-carotenoid made up of eight Isoprene units; making it a tetraterpene. B-Carotene is the yellow pigment of the carrot is an isomer of Lycopene in which the double bonds at C1-C2 and C'1-C'2 are replaced by bonds extending from C1 to C6 and from C'1 to C'6 to form rings, and is also a constituent of the tomato. Each of...

Bibliography: http://en.wikipedia.org/wiki/Chromatography
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