Simple & Fractional Distillations

Separations & Purifications Simple & Fractional Distillations: Distillation is the action of purifying a liquid by a process of heating and cooling (uses mixtures with different boiling points) As you heat the mixture, you’ll see plateaus as phase changes occur When boiling points are too close (such as with water and ethanol), there isn’t a clear separation between the two, and this leads to multiple distillations (such as what happens when you purify alcohol) In order to get around doing it multiple times, you can also do fractional distillation which has the same setup but has a fractional column (that can be filled with stuff like beads) where it will constantly undergo vaporizations and condensations, allowing for multiple distillations to occur at once Extractions: Once the mixture is shaken and allowed to settle down, it will separate out into its individual components (such as with oil and water) Extraction can be done to separate a desired substance when mixed with other (can be done with a separation funnel, stop cock, and a flask) Often times the orange will signify the organic phase (contains uncharged species and/or neutral compounds) and the green with signify the aqueous phase (made up of water and other charged species such as ions) Open/close the stopcock in order to separate the mixtures from one another into the flask You can ionize certain substances in order to bring it into the aqueous phase, or even deionize a substance in order to bring it into the organic phase Remember, mild base/acids cannot interact with mild acids/bases Principles of Chromatography: Chromatography is an analytical technique commonly used for separating a mixture of chemical substances into its individual components Thin Layer Chromatography (TLC) is a qualitative technique to separate mixtures using a polar stationary phase (silica gel) and a nonpolar mobile phase Retention Factor (Rf) is defined as the distance travelled by the individual component divided by the total distance travelled by the solvent (lower the Rf the more polar the substance is) UV Lamps are helpful in seeing compounds that are aromatic (fluoresce) Eluting Power increases with increasing polarity of the solvent Eluent is the fluid entering the column and Eluate is the fluid exiting the column (collected in the flasks) Elution is the process of washing out a compound through a column using a suitable solvent Analyte is the mixture whose individual components have to separated and analyzed Normal-phase is when the stationary phase is polar and mobile phase is nonpolar Reverse-phase is when the stationary phase is nonpolar and the mobile phase is polar Basics of Chromatography: Paper chromatography has paper made of cellulose (polar) and is very similar to TLC (uses a glass plate with silica instead) Size Exchange Chromatography (SEC) has beads with small holes in it, making smaller compounds get stuck and take longer while larger compounds go straight through the column Ion Exchange Chromatography has beads with some charged group on it, where compounds with the same charge will come out of the column and compounds with the opposite charge will bind to the beads Affinity Chromatography where certain substrates will bind to the solid phase and all other will flow straight through (get it to detach by inserting a solvent with higher binding affinity than your substrate of interest) High Performance Liquid Chromatography (HPLC) is basically the same thing as a basic chromatography technique, but you’re working with much smaller quantities and the detector on the machine is more sensitive Gas Chromatography separates substances based on their boiling points Column Chromatography: Make sure to keep the silica wet at all times, because if it dries out it will crack it can cause running/mixing of bands Also, make sure everything you put into the column is flat otherwise it will run weird/slanted, leading to mixtures of the two and the fractions collected won’t be pure samples Differential adsorption is how well a solute adheres to the stationary phase/mobile phase in the column Gas Chromatography: Gas chromatography is important for separating out compounds with different boiling points Insert sample as a liquid where it will be vaporized Joined up with the inert gas which will push the sample into the coiled column (the longer, the better the separation) The first peak is typically the solvent you dissolved the compound in (has a low boiling point typically) and therefore, compounds typically begin to show up on the second peak and on Can also separate things based on size, since smaller particles will get to the detector first This technique is not very definitive and will typically be paired with other techniques Gel Electrophoresis: Gel electrophoresis separates DNA/RNA or protein based on their size The cathode is where the negative charge is located while the anode is where the positive charge is located (will run towards the anode side) The buffer contains ions allowing for current to flow through Agarose gels are typically used for running DNA/RNA (pretty big pores for bigger DNA fragments) Polyacrylamide gels are typically used for running proteins (can also be used for smaller DNA fragments <50 bp long) SDS denatures proteins (disrupts noncovalent interactions) and makes them uniformly negatively charged (allowing separation solely based on size) PAGE is just polyacrylamide gel electrophoresis Resolution of Enantiomers: In order to separate enantiomers, you can use column chromatography using a chiral stationary phase (it will only interact with one of the enantiomer configurations) You can also use gas chromatography where if the stationary phase was chiral, one would stick to the sides of the tubes while the other would race through and get out first