Sampling Flashcards

Question

Define solubility.

Answer 1

The upper limit of solute that can be dissolved in a given amount of solvent at equilibrium.

Answer 2

Polar solutes tends to dissolve in polar solvents and non-polar solutes tends to dissolve in non-polar solvents.

Answer 3

Normal solvent extraction is separation of a compound from a liquid or solid at room temperature and pressure. Extraction takes place over a duration of hours to days. On the other hand, accelerated solvent extraction is performed at higher temperatures or pressures, to speed up the process (it improves the solvent's abilities to extract compounds in a shorter time period). Extraction takes place within a few minutes.

Answer 4

ASE may be used when there is the extraction of a compounds from complex matrices in a solid. ASE can also just be used for a faster, more efficient extraction than normal solvent extraction (as normal solvent extractions can take from hours to days).

Answer 5

A Soxhlet extraction is a solid-liquid extraction (in which some liquid is extracted from a mixture, to leave a solid). The set up is basically a round bottom flask that sits on a mantle (heat source). In the round bottom flask is the solvent that is used to dissolve ONLY the target molecule in the solid mixture. On top of the round bottom flask is a solvent extractor, held upright using a standing clamp. It is similar to a Liebig condenser in the fact that cool water is fed into the cooling jacket of the Soxhlet extractor to condense any gas that has moved up. The top of the Soxhlet extractor is also open ended like a Liebig condenser. Of course, there will be ports in the Soxhlet extractor to feed cool water in and out from the sink. The difference between a Soxhlet extractor and Liebig condenser is that a Soxhlet extractor is wide enough around the middle to contain a thimble for a sample (another small container). The thimble contains the solid-liquid mixture.

Answer 6

The solvent in the round bottom flask is heated by the mantle, until it evaporates and travels up the Soxhlet extractor, going through the sidearms. When the solvent has reached the top, it reaches the condenser of the Soxhlet extractor where cool water is fed in. The cool water causes the solvent vapours to condense into a liquid, which results in it falling into the thimble containing the solid mixture. When the solvent mixes with the solid-liquid mixture, it causes the target compound to dissolve in the solvent. The solvent then drops back into the round bottom flask, so is 'recycled'. The solvent is continuously run through the extractor as the same amount of solvent is conserved, as it is essentially 'recycled' after it runs through the Soxhlet extractor each time. Overtime, all the soluble components will be extracted into the round bottom flask. The extracted component and the solvent can then be separated by rotary evaporation.

Answer 7

For extraction, the Soxhlet technique relies on repeated solvent contact with the sample to provide a sufficient extraction (continuous solvent contact brought about via continuous heating, evaporation, condensation of the solvent in the Soxhlet extractor). This process can vary from hours to days. On the other hand, ASE sues increased temperature and pressure to speed up the Soxhlet extraction process. So, the solvent is heated above their boiling point, at a higher pressure. The pressure prevents the solvent boiling off due to the high temperatures.

Answer 8

With a Soxhlet extraction: > Much smaller volume of solvent is used. > Extraction takes less time. > Extractions are automated. > Multiple samples can be managed at the same time.

Answer 9

Typically used for analysing tablets, capsules and plant materials.

Answer 10

The sample in the Soxhlet extractor is a solid mixture, but it is said to be a solid-liquid extraction once the solvent passes through the sample.

Answer 11

These solvents are good for forming an organic layer because they are immiscible with water; this means there is a good and distinct separation between the organic phase (so the organic solvent) and the aqueous phase (the water). One would prefer to use one over the other, because some of these (diethyl ether and Ethyl acetate) are highly flammable. Dichloromethane is less flammable than the other two so may be used if the experiment is conducted in an area containing naked flames. Compared to Ethyl acetate, diethyl ether is more volatile, so would evaporate more easily. This would be dangerous as diethyl ether is toxic, especially when breathed in.

Answer 12

> Used for extracting substances from biological fluids, like blood and urine. > used in pharmaceutical products like ointments.

Answer 13

Separating funnel

Answer 14

Prior to the extraction, the sample may have been a solid that was dissolved in the organic layer. If the mixture was a liquid, the organic layer may have just been added to the liquid mixture. If both compounds in the mixture (liquid or solid) have some sort of solubility in the organic layer added, an additional reagent may be added to the mixture to make one compound increasingly more soluble (a common example is an acid-base reaction if one of the compounds in the mixture is a acid or base). This is not necessary if one compound is definitely soluble in the organic layer, and the other compound in the mixture is not. So, the mixture would initially be put in the separating funnel, and then the organic layer would then be added. This can be added by making sure the tap is closer, removing the stopper at the top and using a glass funnel to add the organic solvent. After the organic solvent is added, place the stopper on top and invert the separating funnel and start swirling and shaking the separating funnel to ensure the contents are properly mixed. As one of the compounds are dissolving in the organic layer, a reaction would have had to occur, which could release a gas. So from time to time, after shaking, open the tap at the top to release some gas that is produced. This is to prevent the build of pressure in the funnel that could possible cause the funnel to shatter. After this, close the tap and continue swirling. Repeat this process for around 5 minutes, and when you invert the funnel back around, wait for the two layers (organic and aqueous) to form. Drain the bottom layer (typically the aqueous layer) into a flask by opening the tap.

Answer 15

Adding water after extracting the aqueous layer, helps to pick up any leftover aqueous solution (that lies within the organic layer) that remains in the separating funnel. We add water, invert and shake the funnel, and drain the aqueous layer. This ensures an efficient extraction.

Answer 16

Like a Soxhlet extraction (solid liquid extraction), there is a round bottom flask that sits on a mantle. Inside the round bottom flask is the organic solvent that evaporates, and travels up an individual tube to the condenser. The condenser causes the solvent vapors to condense and fall into a flask containing the mixture. This flask is independent and separate to the tube mentioned before (tube between round bottom flask and condenser). The solvent vapour have become a liquid, and when it drops into the flask containing the mixture. The additional of the organic solvent allows to immiscible layers to form- an organic and an aqueous layer. The flask has a tube to connect the flask to the round bottom flask (or the tube of the round bottom flask). Through this tube, the organic compound dissolved in the organic solvent both travels and is collected in the round bottom flask. It is continuous because once the solvent (and soluble organic compound) is collected, it is then heated once again to evaporate, condense and fall into the flask. The position of the tube in the flask is dependent on whether the organic layer is more or less dense than the aqueous layer. In most cases, the organic layer is less dense than the aqueous layer, so the tube is found further up the top of the flask.

Answer 17

> Only small volumes of solvents are used (as it is continuously circled through the system). > A high percentage of solute can be extracted. > Extraction can be left unattended for long periods of time (as it an automatic process with the element of heat). > Can extract solids as well as liquids.

Answer 18

So the solute extracted does not continuously run the system again- this way traces of the solute may still remain in the mixture after extraction, making the process less efficient.

Answer 19

SLE is more difficult for extraction from a solid sample. Often have to do multiple extractions from SLE. Can use solvents that are miscible with water, as long as major matrix constituents are not dissolved by solvents. LLE is more easy to extract from a liquid sample. LLE can possibly be done within a single extraction. Immiscible solvents must be used.

Answer 20

In solid-liquid extraction, the initial phase in the state of a solid mixture. A liquid solvent is added to the solid mixture to dissolve the desired compound into the liquid phase. The mixture may be left to sit for some while, shaken or agitation, and after the solid can be separated from the liquid phase via filtration, centrifugation and decantation. So its key principle is dissolving the solid in a liquid solvent, then extracting the solid from it afterwards. In liquid-liquid extraction, the initial phase is in the state of a liquid mixture. A particular solvent is added (that is immiscible in water) to create two layers and dissolve one of the compounds in the liquid mixture. So the key principle is adding a solvent to create soluble partitions between two immiscible solvents.

Answer 21

After a solid is dissolved in a solvent (can be water miscible , or does not have to be water miscible), it is running through solid phase extraction. The mobile phase in this extraction is actually the sample that had just been dissolved, and this moves down a cartilage device (like a syringe) through the solid phase. The solid phase can also be referred to as the stationary phase, and this phase contains an absorbent (an adsorbent is a solid that absorbs gases or dissolved substances) such as silica, polymer and more. The adsorbent forms certain interaction with targeted analytes in solution, so these targeted analytes are retained in the column, while other substances pass through.

Answer 22

Conditioning, sample addition, washing and elution.

Answer 23

Conditioning phase is the process of rinsing the SPE cartridge with a solvent mixture that is similar to the matrix of the sample to be extracted. The nature of the solid phase before conditioning is in a collapsed state, which makes it unable to form necessary bonds with analyte- after conditioning, these interactions are then possible. So, conditioning basically readies the solid phase for when the sample is added (to make sure it effectively retains target analytes).

Answer 24

Sample addition is the process of adding the analyte to the SPE cartridge, then allowing the target molecule to form certain bonds with the solid phase, depending on the target molecules properties. So, this is the retention of the target molecules, while all other molecules are filtered out. Washing in SPE is about washing the cartridge with a solvent (like a weak solvent or buffer) to get rid of any leftover interferents that did not filter out before. Unwanted interfering substances includes salts, proteins and other contaminants.

Answer 25

The target analytes that have retained to the solid phase are now elution (washed out with a solvent) to be extracted (similar to the washing phase, except these analytes are not interferents, but the compounds we want to analyse). Elution is done by adding a strong solvent that will interrupt any interactions between the analytes and solid phase. This elution solvent is important because the right one needs to be chosen. This is because of its strong nature, the elution solvent can still pick up any interferents that remained even after the washing stage.

Answer 26

Sample preparation of biological fluids such as plasma, serum and urine.

Answer 27

> Solvents in LLE is limited to ones that are water immiscible (to form two clear layers). > Emulsions can often form. > Relatively large solvents needs to be used. > Multiple extractions may need to occur to increase efficiency and yield of extracted material.

Answer 28

The solid phase sits near the bottom of the SPE cartridge and basically just holds adsorbents. Adsorbents are solids that adorbs (by forming bonds) gases and dissolved substances.

Answer 29

The adsorbent does change with different samples. In order to effectively retain the analyte, the right bonds needs to be formed between solid phase and analyte, and in order for the right bond to be formed, they need to have similar properties (like the like-dissolves-like rule when dissolving substances). For example, you would not use an alkyl adsorbent to retain an analyte like propanol- the right bond would not be formed that would be strong enough to retain propanol; at best we would get London forces formed, which is weak. For propanol, we need an adsorbent that is equally polar, or maybe an adsorbent which propanol can form hydrogen bonds with. Note that the frame work or base of any adsorbent is mostly the same- an oxygen on the walls of the SPE cartridge, that is bonded to a silicon atom. The silicon atom is bonded to two other silicon atoms that runs along the wall of the cartridge. The last bond of silicon is connected to a substituent which can change to change the properties of the adsorbent.

Answer 30

A silica adsorbent involves 3 oxygens bonded to one silicon atom. These oxygens also form a bond with the wall of the SPE cartridge. The last bond of silicon atom goes to a hydroxyl group, which made silica a very polar group. Hence, the analyte it retains will most likely be very polar, where they can form permanent dipoles between one another, or hydrogen bonds.

Answer 31

Dispersive- alkyl groups Pi Pi interactions- phenyl Electrostatic/dipole- Cyano H bonding- Silica

Answer 32

Hydrophobic and hydrophilic interactions.

Answer 33

Normal phase extraction uses a polar adsorbent because the analyte to be extracted is also polar. Polar adsorbents includes silica and alumina. On the other hand, if the analyte to be extracted in non-polar, for more effective interactions and bonds, it would make sense to pick a non-polar adsorbent. Such adsorbents includes C18, C8 (different sized alkyl groups attached to the silicon atom). Most interactions here are hydrophobic. If what keeps the analyte to the solid phase is hydrophobic interactions due to their non-polar nature, it would make sense than polar substances are washed out or filtered out first. However, these types of non-polar adsorbents are not really selective. So the main difference between normal and reversed phase extraction is that normal uses a polar adsorbent and reversed uses a non-polar adsorbent. This is reliant on what type of analyte is being extracted.

Answer 34

Ion exchange SPE uses a charged or partially charged adsorbent (like ions) to retain charged analytes depending on their ionisation states, via electrostatic attractions.

Answer 35

Adsorbents with specific functional groups to extract specific classes of compounds, via conducting specific reactions in the SPE cartridge.

Answer 36

Mixed mode- 2 different phases are simply mixed together in the cartridge. Layered- 2 different phases are stacked on top of one another in the cartridge. Stacked phases- 2 different phases are conducted in different cartridges, but these cartridges are stacked on top of each other.

Answer 37

> Washing steps removes interferents. > Removing interferents gives an increased sensitivity when conducting masses spectrometry. > We can divide the sample up into different fractions (water soluble, soluble in methanol). > Concentrating analyte in sample for analysis to get back a clear and loud reading.

Answer 38

Concentrate and isolate proteins found in the plasma and the blood. If there is an unwanted function or no function at all, we can determine whether it is because there had been a mutation in DNA, by looking at protein structure. Concentrating and isolating proteins from urine. Proteins should not be found in the urine, and by isolating the proteins found in the urine, we can determine what the problem may be (kidney disease, urine infection).

Answer 39

While the factors stated may help with precipitating a protein, these factors can also denature a protein. Precipitating a protein would be meaningless if we cannot analyse it because it has denatured.

Answer 40

For a sample like plasma, we first add a solvent to the solution. This solution can be acetonitrile (quite polar). The idea is the protein cannot interact with the acetonitrile, so precipitates out to form a solid, or a semi-mass of solid. Centrifuging is next, and is basically separating components based on their size, shape and density, by spinning the solution at high speeds. In this case, the precipitated proteins will be at the bottom due to its higher density and the supernatant (liquid lying at the top after centrifuging) would be the plasma. The plasma would then go on to be further analysed.

Answer 41

Green extraction is the design of extraction processes, done in a way to reduce energy consumption, using alternative solvents (that is less damaging to the environment, less toxic and more safe), renewable natural products, while ensuring the whole process is high quality and safe.

Sampling Flashcards

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