



Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
Introduction and basic concepts of chromatography. lab manual on how chromatography technique is applied to seprate and identify components.
Typology: Lab Reports
1 / 5
This page cannot be seen from the preview
Don't miss anything!
Chromatography is a technique that is used to separate and to identify components of a mixture. This analytical technique has a wide range of applications in the real world since many substances are mixtures of chemical compounds. In this lab, you will explore two applications of chromatography - identification of an unknown ink sample and the separation of food colorings.
In paper chromatography, the sample mixture is applied to a piece of filter paper, the edge of the paper is immersed in a solvent, and the solvent moves up the paper by capillary action. Components of the mixture are carried along with the solvent up the paper to varying degrees, depending on the compound's preference to be adsorbed onto the paper versus being carried along with the solvent. The paper is composed of cellulose to which polar water molecules are adsorbed, while the solvent is less polar, usually consisting of a mixture of water and an organic liquid. The paper is called the stationary phase while the solvent is referred to as the mobile phase. Performing a chromatographic experiment is basically a three-step process: 1) application of the sample, 2) "developing" the chromatogram by allowing the mobile phase to move up the paper, and 3) calculating Rf values and making conclusions.
In order to obtain a measure of the extent of movement of a component in a paper chromatography experiment, we can calculate an "Rf value" for each separated component in the developed chromatogram. An Rf value is a number that is defined as:
distance traveled by component from application point Rf = ---------------------------------------------------- distance traveled by solvent from application point
The distance traveled by the spot is measured to the MIDDLE of the spot.
Pencil Mark
Solvent Front
A
Forensic chemistry, the profession popularized by TV's "Quincy" is the application of chemical techniques to law. Many samples that are received in a crime laboratory are complex mixtures of chemical compounds and chromatography is often ideal for separating and identifying these components. One example of this is the identification of an unknown ink sample. Suppose the authenticity of a signature or the source of a ransom note is in question. Using paper chromatography, it is often possible to identify the source of the inks that were used and thereby provide strong evidence that can be used in the courtroom
In the second part of the experiment, you will separate a mixture of three food colorings using "reverse-phase" chromatography. In this type of chromatography, the stationary phase is a non-polar material and the mobile phase is relatively polar. You will use a commercial C 18 cartridge, which contains very non-polar 18-carbon long chains as the stationary phase. The mobile phase will be water and/or isopropyl alcohol (IPA).
Using chromatography paper strips
AVOID EXCESSIVE HANDLING OF PAPER
B a s e L in e 1 2 3
II. Separation of Food Colorings
A. Remove the piston and insert the LONG END of the C 18 cartridge snugly into the syringe tip. B. Add 5 mL of IPA, insert the piston, and slowly flush at a flow rate not exceeding 5-10 mL per minute. It is important to not flush liquid through the cartridge more rapidly than 10 mL per minute. Repeat this step with another 5 mL portion of IPA. C. Flush with two 5 mL portions of distilled water. D. Add about 1 mL of the food coloring mixture to the syringe, insert the piston, and push the mixture onto the cartridge. As you push the sample through the cartridge, immediately begin collecting the drops in a test tube. The first color comes off quickly.
solution may be the most concentrated solution needed to remove all of the colors from the cartridge.
E. See what would happen if several of the separated colored solutions were mixed.
F. Make sure the cartridge is clean before returning it.